Chapter 24

Page 1

Origin of species

Speciation - The process by which one species splits into two or more species

Reproductive Isolation - existence of biological factors that impede two species from producing offspring

Hybrids - offspring that result from mating between different species

Prezygotic barriers: Impeding different species from attempting to mate.

Preventing successful mating

Habitat Isolation: Potential mates do not meet

Two species encounter rarely/not at all becuz diff habitats

Temporal isolation: Potential mates breed at different times

Diff times of day, seasons, years

Behavioral isolation: mating signals different between species

Mechanical isolation: copulation attempted but no sperm transferred

Gamete isolation: Sperm can only bind to conspecific egg

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

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

Hybrid breakdown: Some first-gen hybrids are fertile but mate and have sterile children

Steps in speciation process:

1. Decrease gene flow

2. Genetic differences accumulate between separate populations(natural and sexual select)

3. Reproductive isolation often evolves

Allopatric Speciation - gene flow interrupted/reduced when a population is divided into geographically isolated subpopulations

Isolated:

Natural selection favors local adaptations

Sexual selection changes female mating preferences

Adaptive radiation: Ancestral colonist, due to different niches

Sympatric Speciation - in populations that live in the same geographic area

Polyploidy - no prior isolation/change in chromosome #, crops

Sexual selection

Habitat differentiation - appearance of new ecological niches