Evolution Genetically-controlled changes in physiology, anatomy and behaviour over time Microevolution: evolutionary changes within a species Macroevolution: 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 in speciation

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 since The 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 called chromosomes within the cells of an organism The locus is the point at which a particular gene is found on the chromosome Human beings have 46 chromosomes, arranged into 23 pairs Cells with complete sets of pairs are called diploid, while sperm cells are haploid (1/2 of each pair) THOUSANDS OF GENES ON 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 not match perfectly, reproduction cannot occur (prevents interbreeding) Offspring will resemble parents because genes must match at each locus, but the offspring will differ from both parents in traits for which there was more than one allele Genome The complete range of genes present in a species There are over 25,000 different genes in the human genome.

Phenotypic variations Differences in physiology, anatomy or behaviour of different species or different individuals of the same species Phenotypic differences may result from genetic differences (genotypic variation), but this is not necessarily true – relates to nature vs. nurture arguments Phenotype may differ between organisms of the same genotype because of environmental differences or between organisms in the same environment due to genotype. Epigenetics Environment can affect gene expression

Natural Selection Traits that provide an advantage for reproduction are selected for, whereas disadvantaged traits are selected against. Allopatric speciation The formation of new species by geographic isolation Theory heavily favoured by Charles Darwin Honeycreepers, Hawaii

Sympatric speciation The 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 distinct conditions or mating during day vs. night (insects) Distinct courtship rituals Genetic diversity of cichlids is very high in African lakes, due to sympatric speciation

Source: Gotelli (2007) Population Bottleneck If the population of a species decreases to a very small size and then recovers, then an extended period of low genetic diversity ensues Do cheaters never prosper?

Pangaea 250 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 Gondwana BUT…

Recent DNA analyses Nothofagus spp. of New Zealand and Australia are 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 Zealand and South America are consistent with vicariance Important considerations DNA analysis holds promise for the investigating questions of long-range dispersal vs. vicariance when used in combination with 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 Cactaceae North American deserts Euphorbiaceae Southern African deserts I. PLANTS

Convergent Evolution (A form of homoplasy) Similar niches can be predictably occupied by phylogenetically- distinct, but phenotypically similar organisms when great distances II. ANIMALS

Great American Interchange 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