Speciation = the origin of species Factors that have accelerated speciation: In plants: use of different animal pollinators In animals: modifications in sexual selection Reinforcement

Speciation and its Mechanisms Most animal speciation is visualized as lineage splitting. Y Basic speciation models require separation of gene pools. Darwinian idea: slow accumulation of genetic differences. But there can be large, rapid effects from modest genetic changes (e.g., in developmental pathways). A new species typically originates from only a small segment of an established population. typically messy

Elephants: how many species? Traditional: Loxodonta africana and Elephas maximus But, African elephants are morphologically different Savannah and forest populations Essentially geographically isolated….BSC Phylogenetic species concept applied Sampled: 195 elephants from 21 populations 4 genes sequenced for each of the 195 individuals Genetic distances used to construct a phylogeny Conclusion: two species (L. cyclotis and L. africana)

Galeopsis tetrahit: 2n = 32 Suspected of being an allotetraploid Candidate progenitors: G. pubescens (2n = 16) and G. speciosa (2n = 16) Diploid F 1 hybrids (2n = 16) produced and crossed One rare 3n hybrid produced. Triploid hybrid backcrossed to G. pubescens One rare 4n hybrid produced. The recreation of G. tetrahit, with which it was interfertile. Therefore; an artificially produced species Polyploidization

Evidence of allopatric speciation by vicariance: genetic divergence in refuges mtDNA clades: 3-4 mya H: freshwater refuges formerly separated by salt water barrier

Conservation of climatic niche space: cross predictions of the ranges of two species

Peripatric Speciation by dispersal Representative Hawaiian Drosophila diversity

Sympatric Speciation Flies (Rhagoletis pomonella) (1) Larvae develop in hawthorns (Crataegus) Native to NE U.S. (2) Larvae develop in apples (Pyrus) Apples introduced c. 300 ya H 0 : The flies belong to the same species; there is phenotypic plasticity in use of hosts. H 1 : Speciation has occurred; each species of fly adapted to one host species. Since hawthorns and apples are both within the range of Rhagoletis, this would represent an example of sympatric speciation.

Flies using the two types of fruit cannot be distinguished morphologically (cryptic). But, evidence of lineage splitting: 1. Allele frequency differs for 6 different proteins; therefore can be distinguished genetically. 2. Flies imprint on fruit within which they developed. –Mating takes place on the fruit. –Provides some degree of physical segregation. –Only c. 6% of matings are between mis- imprinted flies.

Plus: flies are diverging because of natural selection Selective agent = timing of fruit ripening. Apples ripen “early.” Larvae in apples –Selected to develop slowly. –Prevents emergence of adults prior to winter. Hawthorns ripen ca. 3 weeks later than apples. Larvae in hawthorn fruit –Selected to develop rapidly. –Enables pupation prior to winter. A few mistakes are made: speciation nearing completion.