EvolutionGenetically-controlled changes in physiology, anatomy and behaviour over time

Microevolution: evolutionary changes within a speciesMacroevolution: evolutionary changes within larger

taxonomic units

Speciation: the development of two or more (cladogenesis) genetically differentiable species from

a single common ancestor

Not all evolutionary changes result inspeciation

Physiology, anatomy and behaviour of species are controlled by genes

Genes consist of molecules of deoxyribonucleic acid (DNA)

Components of DNA:

Sugars and phosphates, joined by nitrogenous compounds

Physical structure known sinceThe 1940’s (Francis Crick and James Watson)

Nucleic Acids

A nucleic acid is a complex, high-molecular-weight, biochemical macromolecule composed of nucleotide chains that convey genetic information.

Chromosomes Genes are arranged into paired, thread-like structures calledchromosomes within the cells of an organism

The locus is the pointat which a particulargene is found on thechromosome

Human beings have46 chromosomes,arranged into 23pairs

Cells with completesets of pairs are calleddiploid, while spermcells are haploid(1/2 of each pair)

THOUSANDS OF GENESON EACH CHROMOSOME

Polymorphism

The specific chemical form of a gene at an individual locus cause variation in the appearance of an organism

Different gene forms that exist at a given locus are called alleles

Heterozygosity:

Different forms of an allele at a locus(a measure of genetic diversity)

Implications for sexual reproduction

The genes themselves do not change or blend during reproduction

If chromosomes and loci of the male and female do notmatch perfectly, reproduction cannot occur (prevents interbreeding)

Offspring will resemble parents because genes must match ateach locus, but the offspring will differ from both parents in traits for which there was more than one allele

GenomeThe complete range of genes present in a speciesThere are over 25,000 different genes in the human genome.

Phenotypic variations

Differences in physiology, anatomy or behaviour of differentspecies or different individuals of the same species

Phenotypic differences may result from genetic differences(genotypic variation), but this is not necessarily true – relates tonature vs. nurture arguments

Phenotype may differ betweenorganisms of the same genotype because of environmental differencesor between organisms in the same environment due to genotype.

EpigeneticsEnvironment can affect gene expression

Natural SelectionTraits that provide an advantage for reproduction are selected for, whereas disadvantaged traits are selected against.

Allopatric speciationThe formation of new species by geographic isolation

Theory heavily favoured by Charles Darwin

Honeycreepers, Hawaii

Sympatric speciationThe development of new species within the same area

No physical barriers, so how does it happen?

Distinct reproductive timing:Ex: Different flowering times of plants adapted to distinctconditions or mating duringday vs. night (insects)

Distinct courtship rituals

Genetic diversity of cichlids isvery high in African lakes, dueto sympatric speciation

Source: Gotelli (2007)

Population Bottleneck

If the population of aspecies decreases toa very small size andthen recovers, thenan extended period oflow genetic diversityensues

Do cheaters never prosper?

Pangaea250 million years BP

Supercontinent had split ~ 200 MY BP

Laurasia North America, Asia and Europe

Gondwana Antarctica, Australia, South America, Africa and India

Vicariance or Dispersal ?Vicariance theory suggests that ancestors of existing lineages drifting with the repositioned land masses: slow speciation

Nothofagus pumilio and Nothofagus betuloides

Torres del Paine, Patagonia, Argentina

Nothofagus fusca

South Island, New Zealand

80 MYA: Both part of GondwanaBUT…

Recent DNA analyses

Nothofagus spp. of New Zealand and Australiaare more closely-related to each other than to those of South America

This proves that dispersal was involved in Australia and New Zealand, but the differences between those of New Zealandand South America are consistent with vicariance

Important considerations•DNA analysis holds promise for the investigating questions oflong-range dispersal vs. vicariance when used in combinationwith modern observation and the fossil record •Fossil record does not necessarily capture the first appearance of a species•Extinctions and reinvasions can occur, resulting in the appearance of a continous presence in the fossil record

Analogous evolution of phenotypically-similar life-forms of different taxa in similar climates

CactaceaeNorth American deserts

EuphorbiaceaeSouthern African deserts

I. PLANTS

ConvergentEvolution

(A form of homoplasy)

Similar niches can bepredictably occupiedby phylogenetically-distinct, but phenotypically similarorganisms when great distances

II. ANIMALS

• Palaeozoogeographic event in which North and South America became bridged after

150 million years of isolation

• Land and freshwater fauna

crossed the volcanic Isthmus

of Panama

• North-south climatic asymmetry

delayed and limited the success

of some of these interactions

Great American Interchange

The Influence of Geographic Barriers

Distinct marine biota

Similar marine biota

http://client.blueskybroadcast.com/AIBS/8485/index.asp?vAD=MTIxMw==&vUS=LTk5&vMP=MA==&vHT=bGl2ZS5ibHVlc2t5YnJvYWRjYXN0LmNvbS8=&vPing=VHJ1ZQ==&vPICQ=MA==