General Biology II: Chapter 24

The Origin of Species

What defines a species?

species have to interbreed with individuals from different species, whatever the offspring is, it has to be fertile

Gene flow between populations does what?

holds species together genetically

Reproductive Isolation

existence of biological factors (barriers) that impede 2 species from producing viable, fertile offspring

Hybrids

offspring of crosses between different species

How can Reproductive Isolation be classified?

pre or post zygotic barrier

Two species look exactly the same, but in two different habitats. What is the reproductive isolation method?

habitat isolation

Prezygotic Barriers

habitat, temporal, behavioral, mechanical, and gametic isolation

Habitat Isolation

2 species encounter each other rarely, or not at all, because they occupy different habitants, even though not isolated by physical barriers

Temporal Isolation

species that breed at different times of the say, different seasons, or different years cannot mix their gametes

Behavioral Isolation

courtship ritual & other behaviors unique to a species are effective barriers to mating

Mechanical Isolation

morphological/anatomical differences prevent successful completion of mating

Gametic Isolation

sperm of 1 species may not be able to fertilize eggs of another species

Postzygotic Barriers

prevent the hybrid zygote from developing into a viable, fertile adult

Reduced Hybrid Viability

genes of the different parent species may interact and impair the hybrid’s development or survival in its environment

Reduced Hybrid Fertility

even if hybrids are vigorous, they may be sterile

What reproductive barrier would create a mule?

reduced hybrid fertility

What is one of the limitations to the Biological Species Concept?

asexual bacteria

The Biological Species Concept cannot apply to what?

fossils

Morphological Species

defines a species by structural features, relies on subjective criteria

Ecological Species

views a species in terms of its ecological niche

Phylogenetic Species

defines a species as the smallest group of individuals on a phylogenetic tree, smallest group of individuals that shares a common ancestor & forms 1 branch on tree of life

Allopatric Speciation

population forms a new species while geographically isolated form parent population, restricts gene flow between populations

Sympatric Speciation

subset of populations form without geographic isolation

Sympathetic Speciation

reproductive barrier isolates a subset of a population without geographic separation from the parent species

Hybrid Zone

a region in which members of different species mate and produce hybrids; can occur in a single band where adjacent species

The best definition of hybrid zone?

area where mating occurs between members of two close species (cousins)

If hybrids don’t become reproductively isolated from their parent species, what outcomes are possible?

reinforcement, fusion, stability

Reinforcement

if hybrids are less fit than the parent species, then strong selection prezygotic barriers should reduce hybrid function

Fusion

reproductive barriers can weaken, and the two parent species may fuse into a single species

Stability

continued formation of hybrids