Adaptation and Adaptation and SpeciationSpeciation

SBI 3U

AdaptationAdaptation

Any trait that increases an organism’s chance of survival and probability of successful reproduction

A product of natural selection Organisms become adapted to their

environment over a period of time through natural selection

Variations within a species are the raw material upon which natural selection acts

Types of AdaptationsTypes of Adaptations

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

MimicryMimicry

– A palatable

or harmless

species

mimics an unpalatable

or harmful

model

(a) Hawkmoth larva

(b) Green parrot snake

Cryptic ColourationCryptic Colouration

Types of Adaptations cont…Types of Adaptations cont…

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…Types of Adaptations cont…

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 FormHow Species Form

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

Biological SpeciesBiological Species

Most common definition of species: - a species consists of a

reproductively compatible population - a population that can interbreed

and produce viable and fertile offspring

Note: Not always possible to apply this definition

Forming New SpeciesForming New Species

Speciation– formation of a new species from an

existing species – Macroevolution

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

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 ReproductionBarriers to Reproduction

Geographical Barriers– Keeps populations physically separated• Ex. Rivers

Biological Barriers– Keeps species reproductively isolated

when their habitats overlap

Biological BarriersBiological Barriers

Pre-zygotic Barriers - prevent mating or fertilization

Post-zygotic Barriers - prevent hybrid zygote from developing into a healthy fertile adult

Prezygotic Barriers Prezygotic Barriers

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

Habitat IsolationHabitat Isolation

Populations live in different habitats or ecological niches.

Ex – mountains vs lowlands.

Behavioral IsolationBehavioral Isolation

Mating or courtship behaviors different.

Different sexual attractions operating.

Ex – songs and dances in birds.

Temporal IsolationTemporal Isolation

Breeding seasons or time of day different.

Ex – flowers open in morning or evening.

Mechanical IsolationMechanical Isolation

Structural differences that prevent gamete transfer.

Ex – anthers not positioned to put pollen on a bee, but will put pollen on a bird.

Gametic IsolationGametic Isolation

Gametes fail to attract each other and fuse.

Ex – chemical markers on egg and sperm fail to match.– Separates certain closely related

species of aquatic snails

Post-Zygotic BarriersPost-Zygotic Barriers

1. Hybrid Inviability– Hybrid offspring are unlikely to live long• Ex. Hybrid from sheep and goat die in early

development

2. Hybrid Sterility– Offspring of genetically dissimilar

parents are likely to be strong but sterile• Ex. Horse + Donkey = Mule

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 SpeciationTypes of Speciation

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 RadiationAdaptive Radiation

This is a form of allopatric speciation where a common ancestral species diversifies into a variety of differently adapted species

Ex. Darwin’s Finches

DarwinDarwin’’s Finchess 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 Convergent vs. Divergent EvolutionEvolution

Divergent Evolution - a pattern of evolution in which species that were once similar to an ancestral species diverge, or become increasingly distinct (finches)

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)

The Pace of Evolution - 2 HypothesesThe Pace of Evolution - 2 Hypotheses

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