Speciation

Agenda Definition of a Species and Speciation Reproductive barriers between species Different forms of Speciation Adaptive radiation Convergent Evolution Co-evolution Rates of speciation

What is a Species A species is a population or group of populations whose members have the ability to breed with one another in nature and produce fertile offspring. Hybrids can also exist, however they produce offspring with reduced or no capabilities of producing fertile offspring. Only occur in species close in evolutionary history

Hybrids – Tigon (Tiger – Lion)

Grolar/Pizzly Bear (Grizzly – Polar)

Mule (Horse – Donkey)

Exceptions To the Species Definition Fossils: Cannot be assessed on whether extinct species were able to breed with other species Organisms that reproduce asexually Binary Fission

Speciation The production of a new species is referred to as speciation. A new species only occurs when two species can no longer breed with one another. This means that each species must be reproductively isolated from one another This means that two species may look exactly alike but if their reproductive system is different, then they are two distinct species.

Example: Western/Eastern Spotted Skunk

Reproductive Barriers Between Species

Reproductive Barriers Reproductive barriers are barriers that exist preventing species from breeding with one another. Often facilitates evolution There are several types of reproductive barriers: Geographic Isolation Habitat Isolation Other barriers

Geographic Isolation Geographical isolation occurs when a population of species becomes geographically isolated. The same species will have two populations separated by a geographical barrier (e.g. river, mountain, canyon) While separated, one of the individual populations may change allele frequencies. I.e. undergo speciation Both species will be unable to breed

Habitat Isolation Habitat isolation occurs when similar species adapt to different habitats in the same general location. E.g. Two similar species of garter snake (land and water habitat)

Other Reproductive Barriers Temporal Isolation: Species have different breeding seasons (e.g. Eastern/Western spotted skunks) Behavioural Isolation: Species have different mating behaviours (courtships) (e.g. Blue footed booby) Mechanical isolation: Incompatible reproductive structures

Other Reproductive Barriers Gametic Isolation: Sperm and eggs from different species do not recognize one another Hybrid inviability: Hybrid offspring does not live a full expected life Hybrid infertility: Hybrid offspring matures into adulthood but cannot reproduce (e.g. horse + donkey = mule)

Different forms of speciation

Adaptive Radiation Occurs when a small population(s) migrates to a new island This population may undergo evolutionary change (new gene pool) Some of these individuals may then migrate to another island in the chain where they may undergo an evolutionary change This process, known as adaptive radiation, may repeat itself

Adaptive Radiation And the Galapagos Islands The Galapagos islands have a diverse and unique amount of species due to adaptive radiation Adaptive radiation explains why there are various Galapagos finches on the different islands.

Convergent Evolution In convergent evolution, distantly related species that live in similar environments develop similar adaptations. Recall the Rhea, Emu, and Ostrich

Co-evolution Co-evolution is the process in which one species evolves in response to the evolutionary changes of another species Occurs most often in predator-prey relations E.g. The preys will evolve ways of avoiding the predator and the predator will evolve ways of capturing the prey

Co-evolution – Zebra and Lion The zebra is constantly evolving to become quicker, more camouflaged, more agile, a good sense of smell and sight. The lion will likewise evolve to become quicker, more agile, more stealthy, and also possess a strong sense of smell and sight.

Co-Evolution – Garder Snakes And Poisonous newt Newts are heavily preyed upon by garder snakes Newts evolved to be poisonous in order to reduce attacks by garder snakes. Meanwhile, garder snakes co-evolved to be resistant to newt toxins

Co-evolution - Mimicry In mimicry, one species (“the mimic”), resembles another species (“the model”), in order to gain a survival advantage. E.g. The hoverfly (“the mimic”) and the wasp (“the model) Wasp has a poisonous sting while hoverfly does not

Mimicry E.g. 2 - Monarch and Viceroy

Mimicry (Video)

Rates of Speciation Darwin proposed the gradualism model Species diverge and accumulate small changes over time creating two distinct species Niles Eldredge and Stephen Gould developed the punctuated equilibrium model to explain species development. Species diverge in spurts of relatively rapid evolutionary change