Objective: Speciation Do Now: Why is this population of horses considered to be the same species?

Speciation, the origin of new species Remember: Microevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level

Microevolution A change in allele frequency from generation to generation in a population What is an allele?

Fig. 23-1

The Biological Species Concept The biological species concept states that a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations

Reproductive Barriers A biological feature of the organism themselves that prevents species from interbreeding (even if they are closely related!) What could prevent different species from breeding? Not made for each other:(

Why can’t we mate? Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring

Prezygotic barriers block fertilization from occurring by: –Impeding different species from attempting to mate –Preventing the successful completion of mating –Hindering fertilization if mating is successful

Habitat isolation: Two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers

Temporal isolation: Species that breed at different times of the day, different seasons, or different years cannot mix their gametes

Behavioral isolation: Courtship rituals and other behaviors unique to a species are effective barriers

Fig. 24-4g (e) Courtship ritual of blue- footed boobies

Mechanical isolation: Morphological differences can prevent successful mating

Gametic isolation: Sperm of one species may not be able to fertilize eggs of another species

Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult: –Reduced hybrid viability –Reduced hybrid fertility –Hybrid breakdown

Reduced hybrid viability: Genes of the different parent species may interact and impair the hybrid’s development

Reduced hybrid fertility: Even if hybrids are vigorous, they may be sterile

Prezygotic Barriers:  Hybrid Sterility: offspring are sterile (ex: mule, liger)

Fig. 24-4m (i) Donkey

Fig. 24-4n ( j) Horse

Fig. 24-4o (k) Mule (sterile hybrid)

Geographic Isolation Can lead to speciation when a population gets separated, each group can follow its own evolutionary course

What may cause speciation? Speciation can occur in two ways: –Allopatric speciation –Sympatric speciation

Fig (a) Allopatric speciation (b) Sympatric speciation

Allopatric (“Other Country”) Speciation In allopatric speciatio occurs when a population is divided into geographically isolated subpopulations

Fig A. harrisi A. leucurus

Evidence of Allopatric Speciation Regions with many geographic barriers typically have more species than do regions with fewer barriers

Fig Mantellinae (Madagascar only): 100 species Rhacophorinae (India/Southeast Asia): 310 species Other Indian/ Southeast Asian frogs Millions of years ago (mya) mya65 mya 56 mya India Madagascar

Sympatric (“Same Country”) Speciation Does not require geographic distance to reduce gene flow Possibly the result of a small group inhabiting a new niche

Sexual Selection Sexual selection can drive sympatric speciation Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

Adaptive Radiation The emergence of numerous species from a common ancestor introduced to new and diverse environments and exploit different niches (ex: Darwin’s finches)

Speciation by Polyploidy Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division (chromosmes in a cell can become doubled) - Makes it very difficult for individual to reproduce, but in plants its no so much of a problem!

Fig n = 64n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue. 2n2n Gametes produced are diploid.. 4n4n Offspring with tetraploid karyotypes may be viable and fertile.

Polyploidy is much more common in plants than in animals Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

Allopatric and Sympatric Speciation: A Review In allopatric speciation, geographic isolation restricts gene flow between populations Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations Even if contact is restored between populations, interbreeding is prevented

In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species Sympatric speciation can result from polyploidy, natural selection, or sexual selection

Patterns in the Fossil Record The fossil record includes examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear punctuated equilibrium is used to describe periods of apparent stasis (no change) punctuated by (followed by) sudden change The punctuated equilibrium model contrasts with a model of gradual change in a species’ existence

Fig (a) Punctuated pattern (b) Gradual pattern Time

Speciation Rates The punctuated pattern in the fossil record and evidence from lab studies suggests that speciation can be rapid The interval between speciation events can range from 4,000 years (some cichlids) to 40,000,000 years (some beetles), with an average of 6,500,000 years

From Speciation to Macroevolution Macroevolution is the cumulative effect of many speciation and extinction events

Fig. 24-UN2 Ancestral species: Triticum monococcum (2n = 14) AABB Wild Triticum (2n = 14) Product: AA BB DD T. aestivum (bread wheat) (2n = 42) Wild T. tauschii (2n = 14) DD