Speciation Where do species come from?

Two Basic Patterns of Evolutionary Change Anagenesis Cladogenesis

Definition of a species Biological species A population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but unable to do so with members of other populations

The biological species is based on reproductive isolation Reproductive isolation - the existence of biological factors (=barriers*) the impede two organisms from producing viable, fertile offspring *these barriers are known as reproductive isolating mechanisms or RIM’s

What are these ‘barriers’? 2 kinds: Prezygotic - those that inhibit reproduction before fertilization Postzygotic - those that inhibit reproduction after fertilization

Prezygotic Barriers Habitat Isolation Never meet to breed Water bugs - Trichocorixa Brackish saltmarsh ponds Freshwater ponds Never meet to breed

Prezygotic Barriers Temporal Isolation Western spotted skunk Eastern spotted skunk Area where ranges overlap

Prezygotic Barriers Temporal Isolation Mates in late summer Western spotted skunk Eastern spotted skunk Area where ranges can overlap Mates in late summer Mates in late winter

Prezygotic Barriers Behavioural Isolation Courtship differences Prairie grouse Sage grouse

Prezygotic Barriers Mechanical Isolation - damselflies Mating in Damselflies

Prezygotic Barriers Gametic Isolation -reproduction in sea urchins Red and purple urchins fertilize externally at the same time Gametes are incompatible and won’t fuse

Behavioural Isolation Prezygotic Barriers Summary Habitat Isolation Temporal Isolation Behavioural Isolation Mechanical Isolation Gametic Isolation All prevent production of offspring by acting before fertilization

Postzygotic Barriers - those that inhibit reproduction after fertilization 1. Reduced hybrid viability X E. eschscholtzi E. klauberi Lower viability

Postzygotic Barriers - those that inhibit reproduction after fertilization 1. Reduced hybrid fertility X Horse Donkey Mule - robust but sterile

Postzygotic Barriers - those that inhibit reproduction after fertilization 1. Hybrid Breakdown - hybrid strains of rice Fertile hybrid Fertile hybrid Infertile offspring of the two hybrids

Reduced hybrid viability Reduced hybrid fertility Postzygotic Barriers Summary Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown All prevent production of offspring by acting after fertilization

Postzygotic Barriers Prezygotic Barriers Roughly reflect time Habitat Isolation Temporal Isolation Behavioural Isolation Mechanical Isolation Gametic Isolation Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown Roughly reflect time since species began to differentiate

Summary from your book

Kinds of Speciation Allopatric (= “different country”) Speciation that occurs when the gene flow between populations is interrupted by a geographical barrier

Populations change independently Kinds of Speciation Allopatric - via a vicariance event Geographical separation Original population Populations change independently of one another No interbreeding if barrier is removed

Allopatric - via a vicariance event Kinds of Speciation Allopatric - via a vicariance event A real example - antelope squirrels (Ammophilus) on the edges of the Grand Canyon A. leucurus A. harrisi

Allopatric - Founder effect Kinds of Speciation Allopatric - Founder effect (similar to a bottleneck) - at least one fertilized female invades a new habitat or geographical location Several generations Invasion of new habitat

Allopatric - Founder effect - Hawaiian Drosophila Kinds of Speciation Allopatric - Founder effect - Hawaiian Drosophila Initial invasion (6-8 million years ago)

Allopatric - Founder effect Kinds of Speciation Allopatric - Founder effect Often closely tied with ADAPTIVE RADIATION Adaptive radiation - the evolution of many diversely adapted species from a common ancestor after introduction to new environments

Allopatric - Founder effect Kinds of Speciation Allopatric - Founder effect ADAPTIVE RADIATION - Hawaiian silverswords Tarweed ancestor

Kinds of Speciation 2. Sympatric (= “same country”) Speciation that occurs when there is no geographical barrier to interrupt gene flow between population.

Kinds of Speciation 2. Sympatric (= “same country”) Sympatric speciation occurs most frequently by chromosome changes or through non-random mating.

2. Sympatric (= “same country”) Kinds of Speciation 2. Sympatric (= “same country”) a. Chromosome changes Figure 24.8 in your book

Kinds of Speciation 2. Sympatric (= “same country”) a. Chromosome changes Anemone

Introduction of apples Kinds of Speciation 2. Sympatric (= “same country”) b. Behavioural differences Apple maggot flies -laid eggs on hawthorn Apple maggot flies -lays eggs on hawthorn and apple Introduction of apples 200 years ago Now

2. Sympatric (= “same country”) Kinds of Speciation 2. Sympatric (= “same country”) b. Behavioural differences “apple” flies Females prefer to lay eggs on apples “apple” males prefer “apple” females Females prefer to lay eggs on hawthorn “hawthorn” males prefer “hawthorn” females “hawthorn” flies “hawthorn” flies

Tempo of Speciation How does it occur over time? T I M E

Hybrid Zones Hybrid Zone Range of species A Range of species B

Hybrid Zones

Reinforcement Fusion Stability Gene flow in hybrid zone Divergence and speciation Some barrier to gene flow is established Normal interbreeding populations Reinforcement Fusion Stability

Reinforcement in Hybrid Zones

Fusion in Hybrid Zones Cichlids in Lake Victoria

Speciation Rates Single gene mutant Euhadra – Japanese land snail

Finally, reproductive isolation by a pollinator Mimulus lewisii Mimulus cardinalis

Finally, reproductive isolation by a pollinator Mimulus lewisii yuplewisii gene yupcardinalis gene Mimulus cardinalis

M. lewisii with cardinalis yup gene M. cardinalis Visits by pollinator 68x increase 74x increase M. lewisii M. lewisii with cardinalis yup gene M. cardinalis M. cardinalis with lewisii yup gene