Chapter 24 The Origin of Species

the process by which one species splits into two species

speciation

consists of changes in allele frequency in a population over time

Microevolution

refers to broad patterns of evolutionary change above the species level

Macroevolution

is a group of populations whose members - Have the potential to interbreed in nature - Produce viable, fertile offspring - Do not produce viable, fertile offspring with members of other such groups

species

results when biological barriers impede members of two species from interbreeding and producing viable, fertile offspring

Reproductive isolation

offspring that result from interspecific mating

hybrids

block fertilization from occurring by Impeding different species from attempting to mate - Preventing the successful completion of mating - Hindering fertilization if mating is successful

Prezygotic barriers

biological species concept

Species that breed at different times of the day, in different seasons, or different years cannot mix their gametes - For example, western spotted skunks mate in summer and eastern spotted skunks mate in winter

Temporal Isolation

Courtship rituals and other behaviors unique to a species are effective barriers to mating - For example, many species, including blue-footed boobies, mate only after a unique courtship display

Behavioral Isolation

Two species that occupy different habitats within the same area may encounter each other rarely, if at all - For example, apple maggot flies are isolated from blueberry maggot flies because they feed and lay eggs on different fruits

Habitat Isolation

Mating is attempted, but morphological differences prevent its successful completion - For example, the genital openings of snails in the genus Bradybaena do not align if their shells spiral in opposite directions

Mechanical Isolation

Sperm of one species may not be able to fertilize eggs of another species - For example, surface proteins on the sperm and eggs of different sea urchin species bind poorly to each other, preventing fusion and zygote formation

Gametic Isolation

prevent hybrid zygotes from developing into viable, fertile adults through - Reduced hybrid viability - Reduced hybrid fertility - Hybrid breakdown

Postzygotic barriers

Genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment - For example, the hybrid offspring of different subspecies of salamanders of the genus Ensatina do not usually complete development

Reduced Hybrid Viability

Meiosis may fail to produce normal gametes, resulting in sterility, if the parent species have chromosomes of different number or structure - For example, the hybrid offspring of a male donkey and a female horse, a mule, is robust, but sterile

Reduced Hybrid Fertility

First-generation hybrids are viable and fertile, but offspring in the next generation are feeble or sterile - For example, hybrids between certain strains of cultivated rice are vigorous and fertile, but members of the next generation are small and sterile

Hybrid Breakdown

mating does nor happen in

prezygotic

distinguishes a species by its structural features

morphological species concept

defines a species by its ecological niche, the sum of its interactions with the nonliving and living parts of the environment

ecological species concept

populations are geographically isolated

Allopatric speciation

populations are not geographically isolated

Sympatric speciation

distinguishes a species by its structural features • It applies to sexual and asexual species and does not require information on the extent of gene flow • A disadvantage is that it relies on subjective criteria

morphological species concept

defines a species by its ecological niche, the sum of its interactions with the nonliving and living parts of the environment

ecological species concept

In _________ speciation, gene flow is interrupted when a population is divided into geographically isolated subpopulations

allopatric

In _______ speciation, speciation occurs in populations that live in the same geographic area • Sympatric speciation is less common than allopatric speciation

sympatric

the presence of extra sets of chromosomes

polyploidy

have more than two sets of chromosomes, all derived from a single species

Autopolyploids

have more than two sets of chromosomes, derived from different species

Allopolyploids

is a region in which members of different species mate and produce hybrid offspring

hybrid zone

If hybrids are less fit than the parent species, then strong selection for prezygotic barriers should reduce hybrid production

This process is called reinforcement because it reinforces reproductive barriers • Reinforcement should be stronger for sympatric than allopatric

describes these periods of apparent stasis punctuated by sudden change

Punctuated equilibria