The evolution of sweet taste perception in hummingbirds · Hummingbirds respond to T1R1/T1R3...

The evolution of

sweet taste perception

in hummingbirds

Maude W. Baldwin and Yasuka Toda

Evolution of Sensory Systems

Max Planck Research Group

Max Planck for Ornithology, Seewiesen Germany

Parallel Sensory Universes

Photo: Rudi Gunawan/ Smithsonianmag.com

D. McCafferty, www.flir.com

Chemosensory receptors

vary in number

Nei, Niimura and Nozawa, Nature Reviews Genetics 2008

Multimodal taste buds

Yarmolinsky, Zuker and Ryba. Cell 139 (2009)

Five taste modalities

Salty

Na+Cl-

Sour

H+

Bitter

caffeine

nicotine

Sweet

sucrose

saccharin

Umami

glutamate

Ion channels

T2Rs T1Rs

G-protein coupled receptors

T1R3T1R1 T1R2T1R3

The T1R family mediates

and savory and sweet tastes

Umami Sweet

T1R1 = umami

T1R2 = sweet

T1R3 = shared

T1R1

T1Rs loss linked to diet

T1R1 = umami

T1R2 = sweet

T1R3 = shared

T1R2 T1R2

Bird diet diversity

nectarivory

T1R2 loss in birds

T1R

3}

}

T1R

1

T1R2

T1R1 = umami

T1R2 = sweet

T1R3 = shared

1.T1R2 is lost in birds

2. T1R2 is required for sweet perception

3. How do nectar-feeding birds detect sweet?

Wild

Anna’s hummingbirds, Calypte anna

Captive

Ruby-throated hummingbirds, Archilochus colubris

lon

g b

outs

p

er

min

ute

0.5

bou

t le

ng

th,

se

co

nd

s

0

3.5

00

no

rma

lized

tim

e d

rin

kin

g

0.04

Erythritol

2.15 M

Sucrose

333 mM

test stimuli sucrose

Erythritol

2.15 M

Sucrose

333 mM

Water Erythritol

2.15 M

Sucrose

333 mM

Aspartame

3 mM

Water Aspartame

3 mM

*** *** *** ** ***

*** ***

Asp

art

am

e 1

5 m

M

Ace

su

lfa

me

K 5

0 m

M

Cycla

ma

te 3

0 m

M

Su

cra

lose

10

mM

Ery

thri

tol 2.1

5 M

So

rbito

l 1.5

6 M

0

Glu

co

se

Fru

cto

se

Su

cro

se

Su

cro

se

Wa

ter

bout le

ngth

, s

0

A

B

Figure 4

3

0

3 3

Aspartame

3 mM

Water

******

******

mean bout length, seconds(± SE)

Erythritol preference in

captivity

Rapid discrimination

0 2 4 6 8 10

Aspartame

Erythritol

Sucrose

Water

drinking bout time (seconds)

Bo

ut

tim

e, s

human sweeteners

10/27 7/55 10/44 6/43 5/8 37/ 8 16/46 19 70 17

JI HGFEDCBA

2

1

0

3

50

water sucrose

lick n

um

ber

upo

n fir

st e

nco

un

ter

carbohydrates

sugar alcohols

0Sucrose

WaterTime

If T1R2 is lost in birds, what

functions as the sweet receptor?

Hypothesis 1: T1R3 acts as the sweet taste receptor by

forming a homodimer

Hypothesis 2: T1R1 and T1R3 are no longer merely

functioning as the umami taste receptor but have acquired the

ability to detect carbohydrates

Hypothesis 3: Hummingbirds detect carbohydrates via a non-

T1R-mediated methodT1R1 = umami

T1R2 = sweet

T1R3 = shared

T1R3 T1R2 T1R3 T1R3

Cloning bird T1Rs

T1R3

T1R1

EXON 3

T1R1

T1R3

T1R1

T1R3

T1R1 = umami

T1R2 = sweet

T1R3 = shared

Chicken T1R cloning

NNNNNNNNNNNNNNNNNNNNNNNNNNNN

T1R3

T1R1

EXON 3 EXON 61 21 4 5

EXON 3

EXON 3 EXON 621 4 5

T1R1 = umami

T1R2 = sweet

T1R3 = shared

Functional assays of cloned

T1Rs in tissue culture

Gα

IP3

PLCβ2

Agonist

coelenteramidecoelenterazine

mitochondria

mt-clytin II

Ca2++

2O

Ca2++

T1R function in mammals

UmamiSweet

Hummmingbird T1Rs respond

differently

Recepto

r A

ctivity

Umami Umami Umami Sweet+Umami

T1R1/T1R3 dose response

AlanineSerine Proline

Sucrose FructoseGlucose

T1R3 Venus Fly Trap Chimeras

A

putative ligand-

binding pocket

to transmembrane domain

C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity

Receptor 1 Receptor 2 Receptor 3 Receptor 4

4

TMExtracellular (Venus Fly Trap) 7-Transmembrane

1

2

3

HummingbirdChicken

1

4

2

Buffer Alanine Sucrose Sucralose0

8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8R

ece

pto

r A

ctivity

important residues

for sweet response

Venus Fly Trap Domain Venus Fly Trap DomainTM TM

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

pto

r A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

pto

r A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

19 key residues identified

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8R

ece

pto

r A

ctivity

important residues

for sweet response

Venus Fly Trap DomainTM TM

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

A

putative ligand-

binding pocket


C

B

D

1 10 1000

4

Sucrose

Re

ce

ptor A

ctivity


4


1

2

3

HummingbirdChicken

1

4

2


8


8


8


8

Re

ce

pto

r A

ctivity

important residues

for sweet response

Recepto

r A

ctivity

Venus Fly Trap Domain Venus Fly Trap Domain

Preferred solutions elicit long bouts

Hummingbirds respond to

T1R1/T1R3 agonists

T1R1/T1R3 agonists

Wild

Anna’s hummingbirds, Calypte anna

Cycla

mate

7/55

Acesu

lfa

me K

10/44

Su

cra

lose

6/43

Ery

thrito

l

37/8S

orb

ito

l16/46

Asp

art

am

e

10/27

bo

ut

len

gth

, se

co

nd

s

3

0

Glu

co

se

Fru

cto

se

Sucro

se

19 70 17

3

Captive

Ruby throated hummingbirds, Archilochus colubris

Water Aspartame Erythritol Sucrose

0.5

lon

g b

ou

ts

pe

r m

inu

te

0.04

Water Aspartame Erythritol Sucrose

norm

aliz

ed t

ime

drin

kin

g

0

bou

t le

ngth

, seco

nds

Water

3 test stimuli sucrose

Sucrose

Evolution of a novel vertebrate

sweet receptor

• T1R2 was lost early in birds, perhaps in

carnivorous dinosaurian ancestors

• Hummingbird carbohydrate detection

occurs via widespread mutation of

T1R1/T1R3

• Recognition properties of T1R1/T1R3

instruct hummingbird taste behavior in

the wild

……. yet nectar-feeders

regained sweet perception

T1R1 = umami

T1R2 = sweet

T1R3 = shared

AcknowledgementsYasuka Toda, Yoshiro Ishimaru

Tomoya Nakagita, Takumi Misaka and Keiko Abe

Evolution of Sensory Systems Research Group

Glenn Cockburn

Daniel Mendez Aranda

Julia Cramer

Qiaoyi Liang

Meng-Ching Ko

Collaborators

Scott Edwards, Simon Sin, Tim Sackton (Harvard)

Kirk Klasing (UC Davis)

Mary O’Connell (Leeds)

Concord Field Station (Harvard), Lytle field station (BYU)

Sungbo Cho and Eugeni Roura (University of Queensland)

Pablo Oteiza (Harvard, Max Planck for Ornithology)

Tom Smith, Brenda Larison (UCLA)

Bill Buttemer, Alejandro Rico-Guevara (Deakin University, Australia)

Tissue collection: Wildlife Care Lindsey Wildlife Hospital, Holly Ernest (UC Davis), Michelle Hawkins

(UC Davis), Pedro Ramirez and Ivo Ros (CFS Harvard) (OEB), Flavia Termignoni (UNAM)

Funding: NSF DDIG, Putnam (OEB), Sigma Xi, SICB, Frank Chapman (AMNH), MBB (Mind, Brain

and Behavior, Harvard), OEB student research grants, Blake-Nuttall Ornithological Club

The evolution of sweet taste perception in hummingbirds · Hummingbirds respond to T1R1/T1R3...

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