Adaptation – describes any trait that enhances an organisms fitness or increases its chance of survival.

While adaptations are products of natural selection, variations within a species are the raw material upon which natural selection acts.

Exaptation – an adaptation that evolved for one function that could also be used for another purpose.

Limbs on a lungfish

1. Structural (anatomical) Adaptations – these may include external or internal changes within an individual, or even mimicry and cryptic colors can be considered physical.

2. Physiological adaptations – changes within the function of the organism.• Enzymes• Chemical defenses

3. Behavioral adaptations – how an organism responds to the environment.• Migration• courtship

Is evolution perfect????????

WHAT IS SPECIATION?• The formation of a species (a reproductively

compatible population , ie. a population that can interbreed and produce viable offspring)

There are two pathways that lead to new species: transformation vs. divergence pg 708

• For species to remain distinct, they must remain reproductively isolated, or prevent breeding between closely related species lines.

GEOGRAPHIC BARRIERS or ISOLATIONGEOGRAPHIC BARRIERS or ISOLATION REPRODUCTIVE (Biological ) BARRIERS or ISOLATIONREPRODUCTIVE (Biological ) BARRIERS or ISOLATION

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

http://evolution.berkeley.edu/evolibrary/home.php

Nature has frequently provided geographical barriers that prevent individuals from interbreeding.

Given sufficient time and generations new species may emerge.

Even when individuals live in the same region factors may exist that prevent interbreeding:• Pre-zygotic Barriers – impede the mating

process or prevent the egg from becoming fertilized

• Post-zygotic Barriers – if sperm from one species is capable of fertilizing the egg of another species. There are mechanisms to prevent this hybrid individual from developing.

Behavioural Isolation – a species may have special signals or rituals that is species specific.• Eg. Songs of birds, pheromones etc…

Habitat Isolation – two species can live the same region but occupy different habitats.• Eg. Garter snake lives near water where

most other snakes prefers open areas.

Temporal Isolation- species may be isolated due to the time or season they are active or are reproductively viable.

Mechanical Isolation- related species may attempt to mate but are anatomically incompatible.

Gametic Isolation – even if gametes from different species do meet, rarely will a zygote form.• Sperm from one species can not survive in

the female reproductive tract of another species.

Hybrid Inviability – development of the hybrid zygote is stopped at some stage during embryonic development.

Hybrid Sterility – when two different species can mate but the offspring is sterile. • Horse + Donkey = Mule (sterile)

Hybrid Breakdown – when first generation hybrids are viable and fertile but if these hybrids are mated, the next generation are sterile or weak.

The biological definition of a species does not work in all instances… (discuss)

Other models include:• Morphological species concept (physical or

phenotype characteristics)• Cohesion species concept• Ecological species concept• Evolutionary species concept