4.1: Speciation

speciation

evolutionary process by which new species arise through reproductive isolation - causes evolutionary lineage to split into 2+ lineages

allopatric speciation

ancestral population is divided by a physical barrier which prevents gene flow

example of allopatric

2 populations of the same squirrel species was separated by the formation of the grand canyon = evolved into 2 distinct species

sympatric speciation

ancestral population is divided without geographic barriers with populations diverging through ecological specialisation, natural selection or sexual selection - occurs within same geographic location

example of sympatric speciation

Howea palms had different soil preferences leading to temporal reproductive isolation due to different flowering times

species

group of organisms that interbreed and produce fertile offspring. Also shares similar characteristics that stem from sims in DNA

reproductive isolation

a state in which 2 groups of organisms are prevented from interbreeding and producing viable offspring, often due allopatric and sympatric barriers

prezygotic isolation

when barriers to reproduction act before the formation of a zygote, preventing fertilization from occurring.

examples of prezygotic isolation

• geographic isolation

• mechanical iso - physical differences in reproductive organs

• behavioural iso - differences in behaviour esp mating rituals prevent interbreeding between closely related species

• mating time differences

• ecological differences

postzygotic isolation

when barriers to reproduction act after the union of gametes

• when fertilised egg/offspring is inviable

hybrids

offspring resulting from the mating of two different species, often with reduced viability or fertility - e.g. of postzygotic

does allopatric or sympatric have stronger reproductive isolation given same divergence times

sympatric has stronger reproductive isolation bc face stronger selection to avoid hybridisation and competition, reinforcing isolating mechanisms, whereas allopatric species are already separated by geography and thus experience weaker pressure for such reinforcement.

How does mutation, genetic drift and selection promote speciation?

by introducing genetic variations. Mutation introduces new variations, genetic drift alters allele frequencies randomly, and selection favours advantageous traits, potentially leading to reproductive isolation and the formation of new species.