Adaptation and Speciation SBI 3 U Adaptation Any

Adaptation and Speciation SBI 3 U

Adaptation Any trait that increases an organism’s chance of survival and probability of successful reproduction l A product of natural selection l Organisms become adapted to their environment over a period of time through natural selection l Variations within a species are the raw material upon which natural selection acts l

Types of Adaptations l 1. Structural Adaptation - physical features on an organism – Anatomical - shape and arrangement of features • Ex. Teeth in carnivores, vascular tissue in plants – Mimicry • Enables one species to resemble another species or part of another species – Ex. Fly that resembles a yellow-jacket wasp – Cryptic Colouration • Makes potential prey difficult to spot – Ex. Camouflage

Mimicry – A palatable or harmless species mimics an unpalatable or harmful model (b) Green parrot snake (a) Hawkmoth larva

Cryptic Colouration

Types of Adaptations cont… l 2. Physiological Adaptations – Associated with functions in organisms • • Ex. Enzymes for blood clotting Ex. Proteins in spiders’ silk Ex. Chemical defense in plants Ex. Ability of bacteria to withstand heat

Types of Adaptations cont… l 3. Behavioural Adaptations – How organisms respond to their environment – – Ex. Migration Ex. Courtship displays Ex. Foraging behaviour Ex. Response of plants to light

How Species Form l Scientist must consider the following when distinguishing one species from another: – Physiology – Biochemistry – Behaviour – Genetics

Biological Species Most common definition of species: l - a species consists of a reproductively compatible population l - a population that can interbreed and produce viable and fertile offspring l Note: Not always possible to apply this definition

Forming New Species l Speciation – – formation of a new species from an existing species Macroevolution

l Two general pathways: 1. Transformation - results from accumulated changes over long periods of time such that one species is transformed into another - also called Phyletic Speciation

l 2. Divergent Speciation – One or more species arise from a parent species that continues to exist – Promotes biological diversity • increases number of species

*Support for both concepts suggests that a compromise or a combination of the two models works to produce new species

Barriers to Reproduction l Geographical Barriers – Keeps populations physically separated • Ex. Rivers l Biological Barriers – Keeps species reproductively isolated when their habitats overlap

Biological Barriers l Pre-zygotic Barriers - prevent mating or fertilization l Post-zygotic Barriers - prevent hybrid zygote from developing into a healthy fertile adult

Prezygotic Barriers l l l 1. Habitat Isolation 2. Behavioural Isolation 3. Temporal Isolation 4. Mechanical Isolation 5. Gametic Isolation

Habitat Isolation l Populations live in different habitats or ecological niches. l Ex – mountains vs lowlands.

Behavioral Isolation Mating or courtship behaviors different. l Different sexual attractions operating. l Ex – songs and dances in birds. l

Temporal Isolation Breeding seasons or time of day different. l Ex – flowers open in morning or evening. l

Mechanical Isolation l Structural differences that prevent gamete transfer. l Ex – anthers not positioned to put pollen on a bee, but will put pollen on a bird.

Gametic Isolation l Gametes fail to attract each other and fuse. l Ex – chemical markers on egg and sperm fail to match. – Separates certain closely related species of aquatic snails

Post-Zygotic Barriers l 1. Hybrid Inviability – Hybrid offspring are unlikely to live long • Ex. Hybrid from sheep and goat die in early development l 2. Hybrid Sterility – Offspring of genetically dissimilar parents are likely to be strong but sterile • Ex. Horse + Donkey = Mule

l 3. Hybrid Breakdown – First generation of hybrids are viable and fertile – When hybrids mate the offspring of the next generation are sterile or weak • Ex. Cotton

Types of Speciation l I. Allopatric Speciation - When a population is split into two or more isolated groups by a geographical barrier - Sometimes called geographical speciation - Eventually the groups will become so distinct that interbreeding will be impossible - Isolation does not need to be indefinite, but it does need to be long enough for population to become reproductively incompatible Ex. Glacier, lava flow, ocean levels

Adaptive Radiation l This is a form of allopatric speciation where a common ancestral species diversifies into a variety of differently adapted species l Ex. Darwin’s Finches

Darwin’s Finches

• II. Sympatric Speciation -When populations live in the same geographical area become reproductively isolated -More common in plants than animals -Speciation can occur in 1 generation if genetic change results from parent to offspring Ex. Extra chromosome (called polyploidy) usually in plants which can self pollinate

Convergent vs. Divergent Evolution - a pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly distinct (finches) l Convergent Evolution - similar traits arise because each species has independently adapted to similar environmental conditions, not because they share a common ancestor (ex. birds and bats) l

The Pace of Evolution - 2 Hypotheses l Gradualism – Changes occur slowly and steadily before and after a divergence – Big changes = accumulation of many small changes – Fossil record doesn’t support this hypothesis well – Fossil record shows species appearing suddenly

Punctuated Equilibrium (Gould and Eldredge – 1972) – History consist of long periods stasis (no change) interrupted by periods of divergence – Most species undergo major change when they first diverge from parent species – Fossil records support this theory l