Chapter 24 Flashcards
Speciation
the process by which one species splits into two species
Macroevolution
refers to broad patterns of evolutionary change above the species level
Microevolution
consists of changes in allele frequency in a population over time
Biological Species Concept
have the potential to interbreed in nature, produce viable, fertile offspring, and do not produce viable, fertile offspring with members of other such groups
Prezygotic Reproductive Barriers
impeding different species from attempting to mate, preventing the successful completion of mating, hindering fertilization if mating is successful
Habitat Isolation
two species that occupy different habitats within the same area may encounter each other rarely, if at all
Example-Apple maggot flies are isolated from blueberry maggot flies because they feed and lay eggs on different fruits
Temporal Isolation
species that breed at different times of the day, in different seasons, or different years cannot mix their gametes
Example-Western spotted skunks mate in summer and eastern spotted skunks mate in winter
Behavioral Isolation
courtship rituals and other behaviors unique to a species are effective barriers to mating
Example-Many species including blue-footed boobies mate only after a unique courtship display
Mechanical Isolation
mating is attempted, but morphological differences prevent its successful completion
Example-The genital openings in snails in the genus Bradybaena do not align if their shells spiral in opposite directions
Gametic Isolation
Sperm of one species may not be able to fertilize eggs of another species
Example-Surface proteins on the sperm and eggs of different sea urchin species bind poorly to each other, preventing fusion and zygote formation
Post Zygotic Reproductive Barriers
prevent hybrid zygotes from developing into viable, fertile adults
Reduced Hybrid Viability
genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment
Example-The hybrid offspring of different subspecies of salamanders of the genus Ensatina do not usually complete development
Reduced Hybrid Fertility
Meiosis may fail to produce normal gametes, resulting in sterility, if the parent species have chromosomes of different number or structure
Example-The hybrid offspring of a male donkey and a female horse, a mule, is robust, but sterile
Hybrid Breakdown
First generation hybrids are viable and fertile, but offspring in the next generation are feeble and sterile
Example-Hybrids between certain strains of cultivated rice are vigorous and fertile, but members of the next generation are small and sterile
Limitations of Biological Species Concept
The number of species to which the biological species concept can be usefully applied is limited
The biological species concept emphasizes absence of gene flow, but gene flow occurs between many morphologically and ecologically distinct species
