Ch. 24 Vocab

The Origin of Species

biological species concept

biological species concept

a species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with members of other such groups

reproductive isolation

the existence of biological factors that impede two species from producing viable, fertile offspring

hybrids

offspring that result from mating between different species or from two true-breeding varieties of the same species

prezygotic barriers

block fertilization from occurring by impeding different species from attempting to mate, preventing the successful completion of mating, and hindering fertilization if mating is successful

habitat isolation

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

temporal isolation

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

behavioral isolation

courtship rituals and other unique behaviors to a species are effective mating barriers

mechanical isolation

morphological differences can prevent successful completion of mating

gametic isolation

sperm of one 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 fertility

even if hybrids are vigorous, they may be sterile

reduced hybrid viability

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

hybrid breakdown

some first-generation hybrids are fertile, but when they mate with each other or with either parent species, offspring of the next generation are feeble or sterile

morphological species concept

defines a species by structural features; applies to sexual and asexual species but relies on subjective criteria

ecological species concept

defines a species in terms of its ecological niche; applies to sexual and asexual species and emphasizes the role of disruptive selection

allopatric speciation

gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

peripatric speciation

type of allopatric speciation; a new species is formed from an isolated peripheral population

sympatric speciation

speciation occurs in populations that live in the same geographic area

parapatric speciation

type of sympatric speciation; two species evolve in contiguous, yet spatially segregated habitats; maintain a zone of contact and do not cease the exchange of genes completely

polyploidy

the presence of extra sets of chromosomes due to accidents during cell division; can produce new biological species in sympatry within a single generation

autopolyploid

individual with more than two chromosome sets derived from a single species

allopolyploid

species with multiple sets of chromosomes derived from different species; can successfully mate with each other, but cannot interbreed with either parent species

hybrid zone

region in which members of different species mate and produce hybrids

reinforcement

strengthening of reproductive barriers; when hybrids are less fit than parent species; rate of hybridization decreases

fusion

weakening of reproductive barriers; if hybrids are as fit as parents, there can be substantial gene flow between species; if gene flow is great enough, reproductive barriers weaken, the parent species can fuse into a single species

stability

Continued formation of hybrid individuals; extensive gene flow from outside the hybrid zone can overwhelm selection for increased reproductive isolation inside the hybrid zone

fossil record

includes examples of species that appear suddenly, persist unchanged for some time, and then disappear

punctuated equilibria

in the fossil record, long periods of apparent stasis, in which a species undergoes little or no morphological change, interrupted by relatively brief periods of sudden change

macroevolution

happens on a scale that transcends the boundaries of a single species; evolutionary change above the species level

microevolution

evolutionary change below the species level; change in the allele frequencies in a population over generations

speciation

an evolutionary process in which one species splits into two or more species

species

a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but do not produce viable, fertile offspring with members of other such groups