Department of Physics, Chemistry and Biology

Master Thesis

Olfactory discrimination performance and

long-term odor memory in Asian elephants

(Elephas maximus)

Alisa Rizvanovic

LITH-IFM-A-Ex--12/2639--SE

Supervisor: Matthias Laska, Linköpings universitet

Examiner: Mats Amundin, Linköpings universitet

Department of Physics, Chemistry and Biology

Linköpings universitet

SE-581 83 Linköping, Sweden

Rapporttyp Report category

Examensarbete

D-uppsats

Språk/Language

Engelska/English

Titel/Title:

Olfactory discrimination performance and long-term odor memory in Asian elephants (Elephas maximus) Författare/Author:

Alisa Rizvanovic

Sammanfattning/Abstract:

Behavioral evidence suggests that Asian elephants strongly rely on their sense of smell in a variety of contexts including foraging and social communication. Using a food-rewarded two-alternative operant conditioning procedure, three female Asian elephants were tested on their olfactory discrimination ability with 1-aliphatic alcohols, n-aldehydes, 2-ketones, n-carboxylic acids and with a set of twelve enantiomeric odor pairs. When presented with pairs of structurally related aliphatic odorants, the discrimination performance of the elephants increased with decreasing structural similarity of the odorants. Nevertheless, the animals successfully discriminated between all aliphatic odorants even when these only differed by one carbon atom. The elephants were also able to discriminate between all twelve enantiomeric odor pairs tested. Additionally, the elephants showed an excellent long-term odor memory and remembered the reward value of previously learned odor pairs after three weeks and one year of recess. Compared to other species tested previously on the same sets of odorants, the Asian elephants performed at least as good as mice and clearly better than human subjects, South African fur seals, squirrel monkeys, pigtail macaques, and honeybees. Taken together, these results support the notion that the sense of smell may play an important role in regulating the behavior of Asian elephants.

ISBN

LITH-IFM-A-EX—12/2639—SE

__________________________________________________

ISRN

__________________________________________________

Serietitel och serienummer ISSN

Title of series, numbering

Handledare/Supervisor Matthias Laska

Ort/Location: Linköping

Nyckelord/Keyword:

Asian elephant; Elephas maximus; Behavioral testing; Olfactory discrimination; Olfactory memory

Datum/Date

2012-05-25

URL för elektronisk version

Institutionen för fysik, kemi och biologi

Department of Physics, Chemistry and

Biology

Contents

1 Abstract............................................................................................................... 1

2 Introduction ........................................................................................................ 1

3 Material and methods ......................................................................................... 3

3.1 Animals and management ............................................................................ 3

3.2 Odor stimuli.................................................................................................. 3

3.3 Experimental set-up ..................................................................................... 8

3.4 Training and testing procedure .................................................................. 10

3.5 Experimental design ................................................................................... 12

3.6 Statistics ..................................................................................................... 14

4 Results .............................................................................................................. 15

4.1 Experiment 1: Odor discrimination with structurally related aliphatic

odorants ............................................................................................................ 15

4.1.1 Aliphatic 2-ketones .............................................................................. 16

4.1.2 Aliphatic 1-alcohols ............................................................................. 17

4.1.3 Aliphatic n-aldehydes .......................................................................... 18

4.1.4 Aliphatic n-carboxylic acids ................................................................ 19

4.1.5 Comparison between odorant classes .................................................. 20

4.2 Experiment 2: Odor discrimination with enantiomers ............................... 21

4.3 Experiment 3: Long- term odor memory ................................................... 21

5 Discussion ........................................................................................................ 23

5.1 Odor discrimination with structurally related aliphatic odorants .............. 23

5.2 Odor discrimination with enantiomers ....................................................... 25

5.3 Long-term odor memory ............................................................................ 27

5.4 Theoretical explanations for the good odor discrimination in Asian

elephants ........................................................................................................... 28

5.5 Conclusions ................................................................................................ 29

6 Acknowledgements .......................................................................................... 30

7 References ........................................................................................................ 30

1

1 Abstract

Behavioral evidence suggests that Asian elephants strongly rely on their

sense of smell in a variety of contexts including foraging and social

communication. Using a food-rewarded two-alternative operant

conditioning procedure, three female Asian elephants were tested on their

olfactory discrimination ability with 1-aliphatic alcohols, n-aldehydes, 2-

ketones, n-carboxylic acids and with a set of twelve enantiomeric odor

pairs. When presented with pairs of structurally related aliphatic odorants,

the discrimination performance of the elephants increased with decreasing

structural similarity of the odorants. Nevertheless, the animals successfully

discriminated between all aliphatic odorants even when these only differed

by one carbon atom. The elephants were also able to discriminate between

all twelve enantiomeric odor pairs tested. Additionally, the elephants

showed an excellent long-term odor memory and remembered the reward

value of previously learned odor pairs after three weeks and one year of

recess. Compared to other species tested previously on the same sets of

odorants, the Asian elephants performed at least as good as mice and

clearly better than human subjects, South African fur seals, squirrel

monkeys, pigtail macaques, and honeybees. Taken together, these results

support the notion that the sense of smell may play an important role in

regulating the behavior of Asian elephants.

Keyword: Asian elephant; Elephas maximus; Behavioral testing; Olfactory

discrimination; Olfactory memory

2 Introduction

Some authors argue that brain size correlates with cognitive abilities.

However, the few studies so far that assessed cognitive abilities in Asian

elephants (Elephas maximus) showed mixed results depending on the type

of task and the sensory system involved (Cozzi et al., 2001; Hart and Hart

2007; Plotnik et al. 2011).

Behavioral evidence suggests that Asian elephants strongly rely on their

sense of smell in a variety of contexts including foraging and social

communication (Langbauer 2000; Rasmussen 2006; Rasmussen and

Krishnamurthy 2000; Santiapillai and Read, 2010; Scott and Rasmussen

2005; Sukumar 2003; Vidya and Sukumar 2005). The behavior of Asian

elephants has been studied in some detail and suggests that chemical

communication is an important part in their social interactions (Rasmussen

1999; Rasmussen 2006; Rasmussen 1998; Rasmussen and Krishnamurthy

2000; Rasmussen and Schulte 1998; Schulte et el. 2005). In fact, the

2

elephant is one of the few mammal species so far for which a sex

pheromone has been chemically identified and functionally verified

(Rasmussen et al. 1997, 2005). Anatomical evidence of well-developed

olfactory and vomeronasal systems (Göbbel et al. 2004; Johnson and

Rasmussen 2002; Koikegami et al. 1941; Shoshani et al. 2006) as well as

of specialized skin glands (Lamps et al. 2001; Wheeler et al. 1982) further

supports the idea that the sense of smell plays a crucial role in regulating

the behavior of elephants.

Until recently, however, no behavioral test existed which would allow us to

systematically assess the olfactory capabilities in this species. Asian

elephants have successfully been trained in two-choice visual (Rensch

1957); Rensch and Altevogt 1955; Nissani et al. 2005), auditory (Heffner

and Heffner 1982) and tactile (Dehnhardt et al. 1997) discrimination tasks.

A previous study by Arvidsson et al. (2012) developed and successfully

applied an olfactory discrimination paradigm for Asian elephants and

collected first data on learning speed, olfactory memory and olfactory

discrimination performance. The paradigm is based on a food-rewarded

two-alternative operant conditioning procedure. The animals learned to

sniff at two odor ports and were food-rewarded when they performed an

operant response (placing the tip of the trunk at a certain position of the

experimental set-up) upon correctly identifying the rewarded odor. The

study showed that Asian elephants indeed have fast learning abilities and a

good olfactory memory.

Similar operant conditioning procedures to assess olfactory learning

capabilities and olfactory long-term memory have been employed with

other mammals such as squirrel monkeys (Laska and Hudson 1993), spider

monkeys (Laska et al. 2003), pigtail macaques (Hübener and Laska, 2001),

South African fur seals (Laska et al. 2008), mice (Bodyak and Slotnick

1999), rats (Slotnick et al. 1991), and dogs (Lubow et al. 1973). This

allows for direct comparisons of olfactory learning performance and

olfactory long-term memory performance between species.

Using aliphatic odorants and enantiomers that have previously been used

with humans (Laska and Teubner, 1998, 1999; Laska and Hübener 2001),

squirrel monkeys (Laska and Freyer 1997; Laska et al. 1999a,b; Laska et

al. 2005), Pigtail macaques (Laska et al. 2005), South African fur seals

(Laska et al., 2010), mice (Laska and Shepherd, 2007; Laska et al. 2008),

and honeybees (Laska and Galizia, 2001; Laska et al. 1999) in this study

allows for comparisons of olfactory discrimination performance between

species and assessment of the mechanisms underlying between-species

differences and similarities in this basic measure of chemosensory

capabilities.

3

The aims of the present study were to collect data on olfactory

discrimination performance for structurally related odorants in three female

Asian elephants, to collect data on olfactory long-term memory, to assess

odor structure-activity relationships, and to compare them to those of other

species tested previously on the same sets of odorants.

3 Material and methods

3.1 Animals and management

The study was conducted using three adult female Asian elephants

(Elephas maximus) housed at Kolmården Wildlife Park. Saonoi and Bua

were born 1996 and 1997, respectively in Thailand at work camps and have

been housed at the Swedish zoo since 2004. Saba (born 1968) was

transferred to Kolmården Wildlife Park from Zoo Le Pal, France, at the end

of 2007. The animals were kept as a group in two indoor rooms

(approximately 150 m2 and 250 m

2) but were allowed to be in an outdoor

enclosure (750 m2) or an outdoor exhibit (3000 m

2) at least once a day or

for a larger part of the day when the weather was appropriate. The

elephants were fed pellets in the morning and roughage and branches were

provided ad libitum. Environmental enrichment was provided at least once

a day in the form of scattered and hidden fruits and vegetables throughout

the enclosure. During the study no food-deprivation was required. The

elephants were kept in a hands-on system in which the keepers have full

access to the animals and they were therefore trained to follow commands

and perform certain motor patterns upon demands. The experiments

outlined here comply with the Guide for the Care and Use of Laboratory

Animals (National Institutes of Health Publication no. 86-23, revised 1985)

and with current Swedish laws.

3.2 Odor stimuli

For the assessment of odor discrimination with structurally related odorants

two sets of stimuli were used. The first set comprised four aliphatic ketones

(2-butanone, 2-pentanone, 2-hexanone, and 2-heptanone), four aliphatic

alcohols (1-butanol, 1-pentanol, 1-hexanol, and 1-heptanol), four aliphatic

aldehydes (n-butanal, n-pentanal, n-hexanal, n-heptanal), and four aliphatic

carboxylic acids (n-butanoic acid, n-pentanoic acid, n-hexanoic acid, n-

heptanoic acid) (see Figure 1). The second set comprised the enantiomers

of limonene, carvone, dihydrocarvone, dihydrocarveol, limonene oxide,

alpha-pinene, menthol, camphor, beta-citronellol, rose oxide, iso-pulegol

and fenchone (see Figure 2). When introducing new odorants to the

animals, n-amyl acetate and anethole were used by pairing one of these

4

odors with a new odorant. These two odorants were already highly familiar

to the animals and were therefore used as a “standard” task, in which the n-

amyl acetate was used as the rewarded odor and anethole as the

unrewarded odor. For the memory tests, ethyl butyrate was used as the

rewarded odor vs. 2-phenylethanol as the unrewarded odor and n-amyl

acetate was used as the rewarded odor vs. anethole as the unrewarded odor.

All substances were obtained from Sigma-Aldrich (St. Louis, MO) and had

a nominal purity of at least 99 %. They were diluted using near-odorless

diethyl phthalate (Sigma-Aldrich) as the solvent in such a way to provide

clearly detectable stimuli of equal subjective intensity. The concentrations

of the odorants are shown in table 1, 2 and 3.

5

2-ketones 1-alcohols

2-butanone 1-butanol

2-pentanone 1-pentanol

2-hexanone 1-hexanol

2-heptanone 1-heptanol

n-aldehydes n-carboxylic acid

n-butanal n-butanoic acid

n-pentanal n-pentanoic acid

n-hexanal n-hexanoic acid

n-heptanal n-heptanoic acid

Figure 1: The aliphatic odorants used and their molecular structures.

6

Enantiomers

Figure 2: The enantiomers used and their molecular structures modified from Laska (2004) and Laska and Galizia (2001). The black shade in the structures means that it is protruding towards the reader.

7

Table 1: The odorants used for training and long-term odor memory and their concentrations. CAS number is a unique numerical identifier for every chemical.

Odorant CAS number Dilution

n-amyl acetate 628-63-7 1:5 anethole

104-46-1 1:10

ethyl butyrate 105-54-4 1:3 2-phenylethanol 60-12-8 1:3

Table 2: The aliphatic odorants used and their concentrations. Chemical classes are given in italics.

Odorant CAS number Carbon chain length Dilution

1-alcohols

1-butanol 71-36-3 4 1:10

1-pentanol 71-41-0 5 1:10

1-hexanol 111-27-3 6 1:3

1-heptanol 111-70-6 7 1:3

n-aldehydes

n-butanal 123-72-8 4 1:10

n-pentanal 110-62-3 5 1:10

n-hexanal 66-25-1 6 1:10

n-heptanal 111-71-7 7 1:5

2-ketones

2-butanone 78-93-3 4 1:10

2-pentanone 107-87-9 5 1:10 2-hexanone 591-78-6 6 1:3 2-heptanone 110-43-0 7 1:3

n-carboxylic acids n-butanoic acid 67-43-6 4 1:100 n-pentanoic acid 109-52-4 5 1:100 n-hexanoic acid 142-62-1 6 1:100 n-heptanoic acid 111-14-8 7 1:20

8

Table 3: The enantiomers used and their concentrations.

Odorant CAS number Dilution

(S)-(+)-carvone 2244-16-8 1:3

(R)-(–)-carvone

6485-40-1 1:3

(R)-(+)-limonene 5989-27-5 1:3

(S)-(–)-limonene

5989-54-8 1:3

(+)-fenchone 4695-62-9 1:3

(–)-fenchone

7787-20-4 1:3

(+)-dihydrocarvone 5524-05-0 1:2

(–)-dihydrocarvone

7764-50-3 1:2

(+)-dihydrocarveol 22567-21-1 1:2

(–)-dihydrocarveol

20549-47-7 1:2

(R)-(+)-beta-citronellol 1117-61-9 1:3

(S)-(–)-beta-citronellol

7540-51-4 1:3

(1R)-(+)-camphor 464-49-3 1:10

(1S)-(–)-camphor

464-48-2 1:10

(+)-rose oxide 16409-43-1 1:3

(–)-rose oxide

5258-11-7 1:3

(+)-limonene oxide 1195-92-2 1:3

(–)-limonene oxide

42477-94-1 1:3

(+)-iso-pulegol 104870-56-6 1:5

(–)-iso-pulegol

89-79-2 1:5

(1S,2R,5S)-(+)-menthol 15356-60-2 1:10

(1R,2S,5R)-(–)-menthol

2216-51-5 1:10

(+)-alpha-pinene 7785-70-8 1:5

(–)-alpha-pinene 7785-26-4 1:5

3.3 Experimental set-up

To present the odorants two high density polyethylene (HDPE) boxes with

removable lids (Rubbermaid Cooling Bags, 35 cm high x 35 cm wide x 20

cm deep) were used. The tight fitting lid of each container was equipped

with a ventilator (6 cm in diameter) powered by a lead accumulator (Clas

Ohlson, power: 12V, 1.3Ah). The ventilator provided an ingoing airflow of

approximately 0.58 m3 min

-1. A total of 130 holes of 3 mm diameter were

placed in intervals of even distance to form a filled circle with a diameter

9

of 7.5 cm. These holes were drilled in an exact pattern in the middle of one

of the front sides of each odor box, serving as an outlet for the airflow

provided by the ventilator.

For the presentation of the odorant, a circular filter paper of 9 cm diameter

(Grycksbo Pappersbruk AB) was placed into an open Petri dish and 1 ml of

the odorant was pipetted onto it and put in an odor box. After each session

the odor boxes were cleansed with warm water and perfume-free detergent.

The testing was carried out in the indoor quarters, in a separate room in

which the animals could be trained individually. The experimenter was

situated in a hayloft on the second floor where an opening in the wall was

fitted with a service door (106 cm high x 90 cm wide x 5 cm deep) made of

steel (see Figure 3). This door was modified to hold a window (45 cm high

and 75 cm wide) in its upper part which was covered with a steel grid (with

a mesh width of 4 x 4 cm). This grid separated the experimenter from the

animals while allowing the experimenter to observe and interact with the

animals and to present the food-reward. The grid also served as a barrier

that kept the elephants from reaching and grabbing the odor boxes. The

location of the door allowed the experimenter to observe the animals while

the animals had a very limited opportunity to see the experimenter.

The service door was located approximately 3 meters above the ground of

the test room and it was divided by a vertical bar in the middle into a left

and a right section. Each section contained an odor port (a round opening

with a diameter of 21 cm) at the lower half part of the door. Above the odor

ports was the rectangular grid-covered window through which the reward

could be given to the animals. A wooden platform inside the

experimenter’s room ensured that the odor boxes were placed with their

outlets congruent with the odor ports of the experimental set-up.

10

Figure 3: The experimental set-up from the experimenter’s side. The odor boxes were manually placed in front of the test grid with its odor ports at each test trial, then removed after the reward was given, to be randomly shifted for the next trial. The experimenter was separated from the elephant by a service door covered with a grid but was still able to present the odorants and the reward.

3.4 Training and testing procedure

The training and testing took place between the 6th

of September 2011 and

the 3th of February 2012. All training and testing was carried out in the

indoor quarters, in a room which the animals could be separated. The

elephant to be tested was brought individually, in a predetermined and

fixed order (with some exceptions), into the test room by the keepers. Once

the elephant was brought into the test room, the keepers locked the door

and left the room. The animals had no visual contact with each other during

testing but were within auditory range.

The sessions took place five days a week twice a day (with some

exceptions). The time of day varied from 8.00 am to 15:00 pm. During

each session 30 trials were completed. Each animal participated in a total

number of 168 sessions.

11

Each session started with the removal of a wooden board covering the

experimenter’s side of the experimental set-up. This made the animals

voluntarily approach the set-up. Each trial started with the experimenter

presenting the odor boxes with their outlets facing the odor ports. After a

verbal command – the loudly spoken word “now” – the elephants were

allowed to sample the odor ports and to indicate their decision by putting

the tip of their trunk onto the grid above the corresponding odor port (see

Figure 4). As the animals were not restrained they could always explore the

set-up with their trunks but any exploring of the set-up before the verbal

command was ignored. Only decisions made after the odor boxes were in

place and the command had been given were considered as valid decisions.

The rewarded and unrewarded odorants were presented in an order that was

pseudo- randomized either to the right or to the left. However, the same

side for the odorants was not used more than three times in a row. Since

one session had 30 trials, left side was the correct decision in 15/30 trials

and the right side was the correct decision in the other 15/30 trials. The

decision (correct or incorrect) of the animals was recorded after each trial.

Correct decisions were rewarded with a bridge (a whistle) followed by a

food-reward (a carrot). When an animal made an incorrect decision, the

odor boxes were simply removed and no reward was given.

When the elephants had completed the 30 trials comprising a session, the

end of the session was signalled by a verbal command – the loudly spoken

words “now you’re done” - followed by a few carrots being distributed

through the grid into the room. This made the animals move away from the

experimental set-up and the wooden board was again placed to cover the

inside of the set-up. The elephant was then led out from the test room by

the keepers.

12

Figure 4: The experimental set-up. The picture on the left shows an elephant exploring one of the two round odor ports, and the picture on the right shows an elephant performing the operant response, that is, placing the tip of its trunk onto one of the two rectangular grids to obtain a food reward. The vertical bar in the middle serves as a divider to make the animal’s choice behavior unequivocal.

3.5 Experimental design

A total of 3 experiments were conducted (see table 4). Experiment 1 was

conducted to assess the ability of the animals to discriminate between

aliphatic odors that are structurally related to each other (only differ in

carbon chain length). Experiment 2 was conducted to assess the ability of

the animals to discriminate between enantiomeric odor pairs which are

structurally identical except for chirality. Finally, Experiment 3 was

conducted to evaluate the long-term odor memory of the animals for a

given odor combination after a recess in training for three weeks and one

year.

13

Table 4: Experimental design. The table shows the different odor combinations used. Chemical classes are given in italics.

Experiment Rewarded odor Unrewarded odor

1. Odor discrimination with structurally related odorants

1-alcohols C7 vs. C4 C7 vs. C5 C7 vs. C6

1-heptanol 1-heptanol 1-heptanol

vs. vs. vs.

1-butanol 1-pentanol 1-hexanol

n-aldehydes C7 vs. C4 C7 vs. C5 C7 vs. C6

n-heptanal n-heptanal n-heptanal

vs. vs. vs.

n-butanal n-pentanal n-hexanal

2-ketones C7 vs. C4 C7 vs. C5 C7 vs. C6

2-heptanone 2-heptanone 2-heptanone

vs. vs. vs.

2-butanone 2-pentanone 2-hexanone

n-carboxylic acids C7 vs. C4 C7 vs. C5 C7 vs. C6

n-heptanoic acid n-heptanoic acid n-heptanoic acid

vs. vs. vs.

n-butanoic acid n-pentanoic acid n-hexanoic acid

2. Odor discrimination with enantiomers

(R)-(–)-carvone

vs.

(S)-(+)-carvone

(R)-(+)-limonene vs. (S)-(–)-limonene (+)-fenchone vs. (–)-fenchone (+)-dihydrocarvone vs. (–)-dihydrocarvone (+)-dihydrocarveol vs. (–)-dihydrocarveol (S)-(–)-beta-citronellol vs. (R)-(+)-beta-citronellol (1S)-(–)-camphor vs. (1R)-(+)-camphor (+)-rose oxide vs. (–)-rose oxide (+)-limonene oxide vs. (–)-limonene oxide (–)-iso-pulegol vs. (+)-iso-pulegol (1S,2R,5S)-(+)-menthol vs. (1R,2S,5R)-(–)-menthol (+)-alpha-pinene vs. (–)-alpha-pinene

3. Odor memory Three week recess

n-amyl acetate

vs.

anethole

One year recess ethyl butyrate vs. 2-phenylethanol

14

Experiment 1 was performed to assess the discrimination ability of the

animals with structurally related odorants. One of the odorants (with 7

carbons, from here on named C7) from each of the four chemical classes

was chosen as the rewarded odor and during the initial phase the animals

were allowed to become familiar with this rewarded odor. This was done

by using anethole as the unrewarded odor for 2-4 days (4-8 sessions). Once

familiarized with the rewarded odor the anethole was exchanged for one of

the other odorants of the same chemical class and each of the critical

stimulus combinations (C7 vs. C6, C7 vs. C5, and C7 vs. C4) was

presented for two consecutive sessions. The animals were assigned to

different treatments to avoid a possible order effect. One elephant was

assigned C4 as the first unrewarded odor, followed by C5 and C6 as the

second and third unrewarded odor while the second elephant was assigned

C6 as the first unrewarded odor (followed by C4 and C5). Thus the third

elephant was assigned C5 as the first unrewarded odor (followed by C6 and

C4). Between the different test combinations, up to two sessions with

anethole as the unrewarded odor was implemented if needed in order to

boost the animal’s confidence and to refresh its memory for the reward

value of the rewarded odor.

Experiment 2 was conducted to assess the discrimination ability of the

animals with enantiomers (that is, pairs of odorants that are mirror images

of each other). With each of the enantiomeric odor pairs one of the forms,

(+) or (-), was chosen as the rewarded odor and in an initial phase each

animal was allowed to become familiar with its rewarded odor by using

anethole as the already familiar unrewarded odor. Then, each rewarded

odor of a given enantiomeric odor pair was tested for two sessions against

its other form.

Experiment 3 was performed to assess the long-term odor memory of the

animals by using odor pairs that the animals have learned in a previous

study. The elephants were presented with these pairs of stimuli for two

sessions each after three weeks of recess for the n-amyl acetate vs. anethole

and one year recess for ethyl butyrate vs. 2-phenylethanol.

3.6 Statistics

In the method described here, the animal had two options: (1) to correctly

respond to the positive stimulus (hit), and (2) to falsely respond to the

negative stimulus (false alarm). The percentage of correct decisions was

used as the measure of performance.

15

In all tasks, the criterion of individual performance was set at either 70%

hits in one session of 30 decisions (corresponding to p < 0.05, two-tailed

binomial test), or at 80% hits in one session (corresponding to p < 0.01,

two-tailed binomial test). The rationale for choosing these criteria is that

the same criteria have been used in previous studies on olfactory learning

and discrimination performance with other species that data is being

compared to. First session was used when analyzing only one session and

first and second session was used when analyzing the combined sessions.

Correlations between discrimination performance and structural similarity

of odorants in terms of differences in carbon chain length were evaluated

using the Spearman rank correlation coefficient. Comparisons of

performance across individuals were made using the Mann-Whitney U-test

for independent samples.

4 Results

4.1 Experiment 1: Odor discrimination with structurally related

aliphatic odorants

The three elephants were presented with aliphatic ketones, aliphatic

alcohols and aliphatic aldehydes. Two elephants were presented with

aliphatic carboxylic acids (Saba did not participate in this task). Each group

of odorants allowed for three combinations that were tested with each

elephant (see table 4). The rewarded odors in this experiment were always

kept constant while the unrewarded odors were altered.

16

4.1.1 Aliphatic 2-ketones

Figure 5 shows the performance of the elephants in discriminating between

aliphatic 2-ketones. The left panel shows the elephants’ performance in the

first session and the right panel shows their performance in the first and

second sessions combined. The rewarded odor, 2-heptanone (C7) was

structurally most similar to 2-hexanone (C6), and differed from the

unrewarded odor by only one carbon atom, ΔC1. 2-heptanone (C7) was

least structurally similar to 2-butanone (C4), and differed from the

unrewarded odor by three carbon atoms, ΔC3. All three elephants

performed above criterion level (70%) in both the first session alone and in

the two sessions combined. A positive correlation between discrimination

performance and structural similarity of the odorants in terms of

differences in carbon chain length was found both for the first session alone

(r=+0.58, p=0.099) and a significant positive correlation for the two

sessions combined (r=+0.72, p=0.043).

Figure 5: Olfactory discrimination performance of the three elephants Saba (diamond), Saonoi (square), and Bua (triangle) with 2-ketones. Each data point represents the percentage of correct decisions from a total of 30 decisions (first session, left panel) or from a total of 60 decisions (first and second session combined, right panel). ΔC1 corresponds to the discrimination of 2-ketones which differ by only one carbon atom, and ΔC2 and ΔC3 to the discrimination of 2-ketones which differ by two and three carbon atoms, respectively. The horizontal dotted lines represent chance level (at 50%) and the criterion level (at 70%, two-tailed binomial test, p<0.05)

17

4.1.2 Aliphatic 1-alcohols

Figure 6 shows the performance of the elephants in discriminating between

aliphatic1-alcohols. The left panel shows the elephants’ performance in the

first session and the right panel shows their performance in the first and

second sessions combined. The rewarded odor, 2-heptanone (C7) was

structurally most similar to 2-hexanone (C6), and differed from the

unrewarded odor by only one carbon atom, ΔC1. 2-heptanone (C7) was

least structurally similar to 2-butanone (C4), and differed from the

unrewarded odor by three carbon atoms, ΔC3. All three elephants

performed above criterion level (70%) in both the first session alone and in

the two sessions combined. A positive correlation between discrimination

performance and structural similarity of the odorants in terms of

differences in carbon chain length was found both for the first session alone

(r=+0.35, p=0.320) and for the two sessions combined (r=+0.35, p=0.322).

Figure 6: Olfactory discrimination performance of the three elephants Saba (diamond), Saonoi (square), and Bua (triangle) with 1-alcohols. Each data point represents the percentage of correct decisions from a total of 30 decisions (first session, left panel) or from a total of 60 decisions (first and second session combined, right panel). ΔC1 corresponds to the discrimination of 1-alcohols which differ by only one carbon atom, and ΔC2 and ΔC3 to the discrimination of 1-alcohols which differ by two and three carbon atoms, respectively. The horizontal dotted lines represent chance level (at 50%) and the criterion level (at 70%, two-tailed binomial test, p<0.05).

18

4.1.3 Aliphatic n-aldehydes

Figure 7 shows the performance of the elephants in discriminating between

aliphatic n-aldehydes. The left panel shows the elephants’ performance in

the first session and the right panel shows their performance in the first and

second sessions combined. The rewarded odor, n-heptanal (C7) was

structurally most similar to n-hexanal (C6), and differed from the

unrewarded odor by only one carbon atom, ΔC1. N-heptanal (C7) was least

structurally similar to n-butanal (C4), and differed from the unrewarded

odor by three carbon atoms, ΔC3. All three elephants performed above

criterion level (70%) in both the first session alone and in the two sessions

combined. A positive correlation between discrimination performance and

structural similarity of the odorants in terms of differences in carbon chain

length was found both for the first session alone (r=+0.29, p=0.412) and for

the two sessions combined (r=+0.29, p=0.412).

Figure 7: Olfactory discrimination performance of the three elephants Saba (diamond), Saonoi (square), and Bua (triangle) with n-aldehydes. Each data point represents the percentage of correct decisions from a total of 30 decisions (first session, left panel) or from a total of 60 decisions (first and second session combined, right panel). ΔC1 corresponds to the discrimination of n-aldehydes which differ by only one carbon atom, and ΔC2 and ΔC3 to the discrimination of n-aldehydes which differ by two and three carbon atoms, respectively. The horizontal dotted lines represent chance level (at 50%) and the criterion level (at 70%, two-tailed binomial test, p<0.05).

19

4.1.4 Aliphatic n-carboxylic acids

Figure 8 shows the performance of the two elephants in discriminating

between aliphatic n-carboxylic acids. Saba did not participate in this task.

The left panel shows the elephants’ performance in the first session and the

right panel shows their performance in the first and second sessions

combined. The rewarded odor, n-heptanoic acid (C7) was structurally most

similar to n-hexanoic acid (C6), and differed from the unrewarded odor by

only one carbon atom, ΔC1. N-heptanoic acid (C7) was least structurally

similar to n-butanoic acid (C4), and differed from the unrewarded odor by

three carbon atoms, ΔC3. Both elephants performed above criterion level

(70%) in both the first session alone and in the two sessions combined. A

positive correlation between discrimination performance and structural

similarity of the odorants in terms of differences in carbon chain length was

found both for the first session alone (r=+0.37, p=0.409) and significant

positive correlation for the two sessions combined (r=+0.89, p=0.047).

Figure 8: Olfactory discrimination performance of the two elephants Saonoi (square), and Bua (triangle) with n-carboxylic acids. Each data point represents the percentage of correct decisions from a total of 30 decisions (first session, left panel) or from a total of 60 decisions (first and second session combined, right panel). ΔC1 corresponds to the discrimination of n-carboxylic acids which differ by only one carbon atom, and ΔC2 and ΔC3 to the discrimination of n-carboxylic acids which differ by two and three carbon atoms, respectively. The horizontal dotted lines represent chance level (at 50%) and criterion level (at 70%, two-tailed binomial test, p<0.05).

20

4.1.5 Comparison between odorant classes

In all eight cases for which a correlation between discrimination

performance and structural similarity of the odorants was calculated, this

correlation was positive. In two out of eight cases the correlation was

statistically significant. Saonoi scored a higher percentage of correct

discriminations with odors which differed by three carbons (C7 vs. C4)

than with odors which differed by only one carbon (C7 vs. C6) in all eight

cases. Similarly, Bua scored a higher percentage of correct discriminations

with odors which differed by three carbons (C7 vs. C4) than with odors

which differed by only one carbon (C7 vs. C6) in six out of eight cases. For

the remaining two cases Bua had equally good results for C7 vs. C4 and C7

vs. C6 that is 100% correct decisions on both. Saba scored a higher

percentage of correct discriminations with odors which differed by three

carbons (C7 vs. C4) than with odors which differed by only one carbon (C7

vs. C6) in three out of six cases. In the remaining cases she had better

results on C7 vs. C6 than C7 vs. C4. This may be due to a so-called “order

effect” since Saba always started with the odor combination in the critical

tests which supposedly was the “easiest” combination and then improved in

performance in the subsequent tasks. A comparison of performance across

individuals showed a significant difference between Saba and Saonoi

(p=0.0003) with Saonoi performing better than Saba. The comparison of

performance across individuals also showed significant differences

between Saba and Bua (p=0.0001) with Bua performing better than Saba.

No significant difference in performance was found between Bua and

Saonoi (P=0.8555).

21

4.2 Experiment 2: Odor discrimination with enantiomers

Figure 9 shows the performance of the elephants in discriminating between

enantiomeric odor pairs. All three elephants performed above criterion

level (70%) in all 12 discrimination tasks and thus were clearly able to

discriminate between all enantiomeric odor pairs presented. This was true

not only when the data of the two sessions performed per odor pair were

combined (as depicted in figure 9), but also for the first of two sessions

alone, suggesting a fast learning of the discrimination tasks.

A comparison of performance across individuals showed a significant

difference between Saba and Saonoi (p=0.0001) with Saonoi performing

better than Saba. The comparison of performance across individuals also

showed significant differences between Saba and Bua (p=0.0001) with Bua

performing better than Saba. No significant difference in performance was

found between Bua and Saonoi (p=0.3183).

Figure 9: Olfactory discrimination performance of the three elephants Saba (diamond), Saonoi (square), and Bua (triangle) with enantiomers. Each data point represents the percentage of correct decisions from a total of 60 trials (first and second session combined). The black vertical lines separate the data points for the different enantiomers. The horizontal dotted lines represent chance level (at 50%) and the criterion level (at 70%, two-tailed binomial test, p<0.05).

4.3 Experiment 3: Long- term odor memory

The three elephants were tested on their long- term odor memory by using

two different odor combinations that they had learned previously (see

Figure 10). The testing was carried out after a period of recess. For n-amyl

22

acetate vs. anethole the period that had passed was three weeks and for

ethyl butyrate vs. 2-phenylethanol it was one year.

All three animals performed at least as good in the two sessions after the

three-week recess compared to the two last sessions with n-amyl acetate vs.

anethole before the recess. On the very first 10 decisions after the recess all

three elephants scored 10 out of 10 correct decisions. Similarly, all three

animals performed at least as good in the two sessions after the 1-year

recess compared to the two last sessions with ethyl butyrate vs. 2-

phenylethanol before the recess. Here, too, on the very first 10 decisions

after the recess all three elephants scored 10 out of 10 correct decisions.

This clearly demonstrates that the animals did not quickly re-learn the

reward values of the rewarded and the unrewarded odor, but that they

indeed remembered them over these periods of time.

Figure 10: Long-term odor memory performance of the three elephants Saba (diamond) Saonoi (square) and Bua (triangle). The figure shows the performance of the animals in the two last sessions before the recess in testing, followed by the performance in the first two sessions after three weeks and one year of recess, respectively, for the given odor combination. The black vertical line separates the two tasks. The horizontal dotted lines represent chance level (at 50%) and the criterion level (at 70%, two-tailed binomial test, p<0.05).

23

5 Discussion

5.1 Odor discrimination with structurally related aliphatic odorants

The results of the present study show that Asian elephants are able to

discriminate between structurally related aliphatic ketones, alcohols,

aldehydes and carboxylic acids. Further, the results show a positive

correlation between discrimination performance and structural similarity of

the odorants in terms of differences in carbon chain length.

The same odorants have previously been tested with humans (Laska and

Teubner, 1998, 1999; Laska and Hübener 2001), squirrel monkeys (Laska

et al. 1999a), South African fur seals (Laska et al., 2010), mice (Laska et

al. 2007; Laska et al. 2008), and honeybees (Laska et al. 1999). This

allows for direct comparisons of olfactory discrimination performance

between species.

Humans have well-developed olfactory discrimination ability when it

comes to aliphatic alcohols, aldehydes, ketones and carboxylic acids. The

human subjects succeeded in discriminating between all odor pairs that

were also tested with the elephants (Laska and Teubner 1998; Laska and

Teubner 1999; Laska and Hübener 2001). Similar to the elephants, a

positive correlation between human discrimination performance and

structural similarity of the odorants in terms of differences in carbon chain

length was found. This means that the human subjects indeed had more

difficulties to discriminate odor pairs that differed by only one carbon atom

than those that differed by two or three carbon atoms (Laska and Teubner

1999).

Squirrel monkeys have been tested with aliphatic alcohols, aldehydes,

ketones and carboxylic acids in previous studies (Laska and Teubner 1998;

Laska et al. 1999a). The squirrel monkeys managed to discriminate above

chance level between all odor pairs tested for the aliphatic alcohols,

aldehydes, ketones and carboxylic acids, which were also tested with the

elephants. With all four classes that were tested, a significantly positive

correlation was found between discrimination performance and structural

similarity of the odorants in terms of differences in carbon chain length.

South African fur seals have been tested with aliphatic alcohols, aldehydes,

ketones and carboxylic acids in a previous study (Laska et al., 2010). The

South African fur seals were able to discriminate between all odor pairs

tested for aliphatic alcohols, aldehydes, ketones and carboxylic acids that

were also tested with the elephants, suggesting that South African fur seals

have a well-developed ability to discriminate between structurally related

aliphatic odorants. There was no statistically significant correlation

24

between discrimination performance and structural similarity of the

odorants in terms of differences in carbon chain length. Only a

nonsignificant trend was observed towards a positive correlation with the

alcohols.

CD-1 mice have been tested with aliphatic alcohols, aldehydes, ketones and

carboxylic acids (Laska et al. 2007; Laska et al. 2008). All mice managed

to significantly discriminate between all odor pairs tested. A significant

positive correlation was found between discrimination performance and

structural similarity of the odorants in terms of differences in carbon chain

length in aliphatic ketones but not with alcohols, carboxylic acids and

aldehydes (Laska et al. 2008) which is not the same as for the Asian

elephant. In the study only addressing aldehydes (Laska et al. 2007) a

significant positive correlation was found between discrimination

performance and structural similarity of the odorants in terms of

differences in carbon chain length. These two studies suggest that CD-1

mice have well-developed discrimination ability for aliphatic odorants.

Honeybees have been tested with aliphatic alcohols, aldehydes and ketones

in a previous study (Laska et al. 1999). The results show that there is a

significant positive correlation between discrimination performance and

structural similarity of the odorants in terms of differences in carbon chain

length with all three classes tested. The odor pairs that differed by only one

carbon atom were significantly more difficult to discriminate than odor

pairs that differed by two or three carbon atoms which is in agreement with

the Asian elephants.

When comparing the Asian elephants with other species tested previously

on the same aliphatic odor pairs, the results show that Asian elephants are

at least as good at discriminating aliphatic alcohols, aldehydes, ketones and

carboxylic acids as other animals. This is not surprising since they strongly

rely on their sense of smell (Greenwood et al., 2005; Langbauer 2000;

Rasmussen 2006; Rasmussen and Krishnamurthy 2000; Scott and

Rasmussen 2005; Schulte and Rasmussen 1999; Sukumar 2003). All

aliphatic odorants tested here are found in nature and are likely to be a part

of the Asian elephant’s chemical environment. Some of the aldehydes,

ketones, alcohols or carboxylic acids have also been reported in the

temporal gland secretions of male elephants in musth and in the urine of

females (Rasmussen et al. 1990; Rasmussen, et al. 1997; Rasmussen, 1998;

Rasmussen and Krishnamurthy 2001; Rasmussen and Wittemyer 2002;

Rasmussen et al. 2005).

25

5.2 Odor discrimination with enantiomers

The results of the present study show that Asian elephants are able to

discriminate between all enantiomeric odor pairs tested.

The same odorants have previously been tested with humans (Laska and

Teubner 1999), squirrel monkeys (Laska et al. 1999b; Laska et al. 2005),

pigtail macaques (Laska et al. 2005), South African fur seals (Kim 2012),

mice (Laska and Shepherd 2007), honeybees (Laska and Galizia 2001;

Laska et al. 1999) and SD/LE rats (Linster et al. 2001; Rubin and Katz

2001). This allows for direct comparisons of olfactory discrimination

performance between species.

Table 5 shows an across-species comparison of discrimination performance

with enantiomers. Table 5: Across-species comparison of discrimination performance with enantiomers. The “+”-symbol stands for a species being able to discriminate between the enantiomeric pair, the “-“-symbol stands for a species not being able to discriminate between the enantiomeric pair and the empty space means that the enantiomeric pair was not tested with this species. The numbers in brackets show how many out of the total number of animals tested with each species succeeded in discriminating between the given enantiomers.

Asian elephant

South African fur seal

CD-1 mice

Human subjects

Squirrel monkeys

Pigtail macaques

Honey bees

SD/LE rats

limonene +

(3/3)

-

(0/3)

+

(8/8)

+

(18/20)

+

(6/6)

+

(3/3)

+

(6/6)

+

(11/11)

carvone +

(3/3)

+

(3/4)

+

(8/8)

+

(17/20)

+

(5/6)

+

(3/3)

+

(5/6)

+

(6/6)

dihydrocarvone +

(3/3)

+

(3/4)

+

(8/8)

+

(16/20)

+

(4/4)

+

(3/3)

dihydrocarveol +

(3/3)

+

(4/4)

+

(8/8)

+

(18/20)

+

(4/4)

+

(3/3)

isopulegol +

(3/3)

-

(1/3)

+

(8/8)

-

(3/20)

-

(0/4)

+

(3/3)

limonene oxide +

(3/3)

+

(3/3)

+

(8/8)

-

(4/20)

-

(0/4)

-

(0/3)

camphor +

(3/3)

-

(1/4)

+

(8/8)

-

(4/20)

-

(0/6) -

(1/6)

fenchone +

(3/3)

+

(4/4)

+

(8/8)

-

(5/20)

+

(5/6) -

(0/6)

+

(6/6)

rose oxide +

(3/3)

-

(0/4)

+

(7/8)

-

(2/20)

-

(0/6) -

(0/6)

menthol +

(3/3)

+

(3/3)

+

(8/8)

-

(5/20)

-

(3/6) +

(6/6)

beta-citronellol +

(3/3)

-

(2/4)

+

(8/8)

-

(8/20)

-

(3/6) +

(6/6)

alpha-pinene +

(3/3)

+

(3/3) +

(18/20)

+

(6/6) +

(6/6)

26

The Asian elephants were able to discriminate all enantiomeric pairs tested

(12/12) which is as good as the CD-1 mice, who also managed to

discriminate all enantiomeric pairs tested for this species (11/11).

The South African fur seal managed to discriminate seven out of twelve

enantiomeric pairs showing that they are not as capable of discriminating

enantiomers as the Asian elephants and mice. The SD/LE rats managed to

discriminate all three enantiomeric pairs tested with this species which

suggests well-developed olfactory discrimination ability. Human subjects

discriminated five out of twelve enantiomeric pairs while squirrel monkeys

discriminated six out of twelve enantiomeric pairs. These two species are

able to discriminate the same enantiomeric pairs except fenchone. The

results for humans and squirrel monkeys demonstrate a very similar pattern

of discrimination performance. This is not surprising since these two

species are phylogenetically closely related and are likely to share many

molecular odor receptors (Rouquier et al. 2000). Pigtail macaques

discriminated five out of six enantiomeric pairs also showing a high degree

of similarity of discrimination performance to humans and squirrel

monkeys. Honeybees discriminated five out of eight enantiomeric pairs.

Several insect pheromones are single enantiomers making it important for

insects to be able to discriminate between certain enantiomers (Laska and

Galizia 2001).

Asian elephants and CD-1 mice are able to discriminate all enantiomeric

odor pairs tested here. This supports the idea that these animals strongly

rely on their sense of smell and thus have a highly evolved olfaction

system.

Elephants use their trunk to be able to detect both enantiomeric forms of

the pheromone frontalin. A study showed that Asian elephants release the

(+)- and the (-)-form of frontalin in a specific ratio that depends on the

elephant’s stage in musth and its age (Greenwood et al. 2005). The

reactions to frontalin from both male and female conspecifics were

different depending on its ratio, proposing that Asian elephants are able to

detect molecular chirality and use it for social communication.

Several of the enantiomeric pairs tested here such as carvone, limonene and

alpha-pinene are found in a variety of food plants (König et al. 1990;

Mosandl et al 1990) which may explain why a plant eating species as the

elephant is able to recognize and discriminate them. Enantiomers such as

rose oxide, for which only one of the two forms has been found in nature,

in contrast, are almost never found in essential oils (König et al. 1990;

Mosandl et al 1990). This is also shown by the discrimination performance

where several species had difficulties discriminating it.

27

5.3 Long-term odor memory

The results of the present study show that Asian elephants can remember

the reward value of odorants after recesses of three weeks and one year.

The Asian elephants showed no sign of forgetting, supporting the idea that

they do have a very good long-term memory for odors. Arvidsson et al

(2012) was the first to test the long-term odor memory in Asian elephants

with two-, four-, eight- and 16 week recesses in which the animals showed

a remarkably good long-term memory.

Other species such as spider monkeys (Laska et al. 2003), squirrel monkey

(Laska and Hudson 1993), pigtailed macaques (Hübener and Laska 1998;

Hübener and Laska 2001) and South African fur seals (Laska et al. 2008)

have also been shown to have a good long-term odor memory although

only recesses up to 15 weeks were tested.

Elephants are able to recognize members of their family by taking a sample

of the urine and transfer it from the trunk tip to the vomeronasal organ,

which is located at the roof of the mouth (Rasmussen and Munger, 1996).

This allows the elephant to evaluate and detect the chemical signals in the

urine. Since elephants are long-lived it is near at hand to assume that they

should also have a good long-term memory to be able to survive in nature.

They have to travel over long distances and should benefit from

remembering details of the environment, e. g. water and food resources

(Hart and Hart 2007; Hart et al. 2008) but they should also be able to

recognize individuals from the social group. There are even suggestions

that individuals can recognize their own mother by the smell of her urine

even if they have been separated from her up to 27 years (Bates et al.

2008b).

There are only a few studies that have tested the long-term memory in

elephants with other senses (Irie and Hasegawa 2009). Elephants

demonstrated a good long-term memory in visual discrimination tasks with

symbols, after one year of recess (Rensch, 1957). Markowitz et al (1975)

retested a captive Asian elephant in a visual discrimination task after eight

years of recess and the animal showed very good memory. She needed only

six minutes to reach the criterion of making 20 correct decisions in a row,

with only two errors made, showing that she did not have any problems

remembering what she had learned many years ago. Auditory memory of

elephants has been shown by McComb et al. (2000) to be very good.

Members of a family group of wild African elephants were able to

recognize the calls of group members that had been absent for two to

twelve years. The elephants responded in the same way when hearing the

calls from these absent members as for the present group members. The

family group showed no such response to sounds from unknown elephants

28

or from unrelated family groups. This finding suggests that elephants do

have an outstanding long-term auditory memory.

The results of the long-term odor memory tests in this present study

support the notion that elephants do have an excellent long-term memory.

5.4 Theoretical explanations for the good odor discrimination in Asian

elephants

Asian elephants have been shown to have very good olfactory

discrimination ability for both aliphatic odorants and enantiomeric odor

pairs. There are three different theoretical explanations for this.

The first explanation involves the functional genes coding for olfactory

receptors. Some authors suggest that the higher the number of functional

genes one has for olfactory receptors, the better one can distinguish

between different odorants. Humans, for example, have around 390

functional genes coding for olfactory receptors (Glusman et al. 2001).

Squirrel monkeys have about 900, rats about 1200, mice about 1000 and

pigtail macaques have around 700 (Rouquier et al. 2000; Gilad et al. 2004;

Godfrey et al. 2004) functional genes. Studies have indicated that the

number of receptor types may correlate with discrimination performance

(Laska and Shepherd 2007). Honeybees have been shown to have only 160

(Robertson and Wanner 2006) although they also were able to distinguish

between aliphatic aldehydes, alcohols, ketones and some enantiomers

(Laska and Galizia 2001; Laska et al. 1999). This suggests that the number

of functional genes may not be the only factor important for discrimination

performance. For the Asian elephant the number of functional genes for

olfactory receptors has yet not been determined. However, the African

elephant has recently been shown to have around 1500 functional genes

coding for olfactory receptors (Suwa et al. 2011) which is more than in the

mouse, honeybee, human and squirrel monkey. Since phylogenetically

closely related species usually have a similar number of functional genes

for olfactory receptors (Nei et al. 2008) this suggests that the Asian

elephant may also have a similarly high number of functional olfactory

receptor genes.

The second theoretical explanation for very good olfactory discrimination

ability is that it may correlate with the size of the olfactory brain or

olfactory bulbs.

Humans, squirrel monkeys and pigtail macaques differ in the relative size

of their olfactory structures of the brain. Squirrel monkeys have the largest

29

relative size of the olfactory bulbs followed by pigtail macaques and

humans (Stephan et al. 1988).

A recent study found that the olfactory bulbs of the African elephant have

an unusual feature in that their glomerular layer is composed of two to four

layers of glomeruli while the typical olfactory bulbs from mammals have

one to two layers of glomeruli. This suggests an unusually high

connectivity between the secondary neurons such as tufted and mitral cells

and the olfactory receptors (Ngweny et al. 2011).

The third theoretical explanation for very good olfactory discrimination

ability has to do with the behavioral relevance of the sense of smell. It is

near at hand to assume that species that rely to a high degree on their sense

of smell should also have a very good sense of smell. Humans, for

example, do not rely on their sense of smell as much as, for example, Asian

elephants. For the Asian elephant a well-developed sense of smell is

important in foraging, but is also used in a social context. Chemical

communication has been studied in elephants and is considered as a vital

mechanism in regulating the behavior of elephants (Rasmussen 1998;

Rasmussen 1999; Rasmussen and Krishnamurthy 2000). The complex

society of the Asian elephant requires a well-functioning communication

system to be able to identify potential mates and to be able to keep group

cohesion. This is all done by chemical signals and vocalization (Langbauer

2000, Sukumar 2003). The Asian elephant releases chemical signals

through secretions from different glands but also in urine and breath

(Rasmussen and Krishnamurthy 2000) and these are processed by the

vomeronasal and olfactory systems by other individuals. The signals are

important in recognizing individuals but they also tell the receiver about the

social status of the emitter (Schulte and Rasmussen 1999; Greenwood et al.

2005).

5.5 Conclusions

The present study shows that these three Asian elephants are able to

discriminate between all structurally related aliphatic odorants and all

enantiomeric odor pairs tested. The discrimination performance of the

elephants concerning structurally related aliphatic odorants increased with

decreasing structural similarity of the odorants. The Asian elephants are at

least as good, or better, at discriminating among aliphatic odorants and

among enantiomeric odor pairs as other species. The long-term odor

memory of the Asian elephant was shown to be outstanding as the animals

successfully remembered the reward value of a previously learned odor

30

pair after one year of recess. The next logical step would be to assess the

olfactory sensitivity in the Asian elephant.

6 Acknowledgements

I would like to thank my supervisor, Professor Matthias Laska for great

help and support throughout this thesis project. I would also like to thank

the elephant caretakers, Stefan Aspegren, Andreas Levestam, Tommy

Karlsson, Stefan Mattson and Erik Andersson at Kolmården Wildlife Park

for the invaluable help that made this work possible.

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