• 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 maximusBut, African elephants are morphologically differentSavannah and forest populationsEssentially geographically isolated….BSCPhylogenetic species concept applied Sampled: 195 elephants from 21 populations4 genes sequenced for each of the 195 individualsGenetic distances used to construct a phylogenyConclusion: two species (L. cyclotis and L. africana)

Galeopsis tetrahit: 2n = 32 Suspected of being an allotetraploidCandidate progenitors: G. pubescens (2n = 16) and G. speciosa (2n = 16)Diploid F1 hybrids (2n = 16) produced and crossedOne 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 Speciationby dispersal

Representative HawaiianDrosophila 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• H0: The flies belong to the same species; there is

phenotypic plasticity in use of hosts.• H1: 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.