Download Chapter 24 Notes Speciation - process by which one species splits

Chapter 24 Notes
Speciation - process by which one species splits into two or more species
● allopatric speciation - gene flow is interrupted when a population is divided into
geographically isolated subpopulations (with geographic isolation)
○ 1: isolation; 2: mutations, natural selection, genetic drift, etc.
●
sympatric speciation - speciation occurs in populations that live in the same geographic
area
○
Polyploidy - accident during cell division that results in an extra set of
chromosomes and may create a new species
■ autopolyploid - individual that has more than two chromosome sets that
are all derived from a single species
■
allopolyploid - hybrid offspring (may not be fertile, but may be able to
reproduce asexually)
○
Habitat differentiation - genetic factors enable a subpopulation to exploit a habitat
or resource not used by the parent population
○
Sexual selection - choosiness of one sex for their mates
Species ● *(biological) group of populations whose members have the potential to interbreed in
nature and produce fertile offspring--but can’t with members of other groups
●
(morphological) characterizes a species by body shape and other structural features
○ applicable to sexual and asexual organisms
○
subjective criteria - some disagreements on features
●
(ecological) characterizes species by their niche
●
(phylogenetic) smallest group of individuals with a common ancestor, forming one
branch on the tree of life
Reproductive isolation - existence of biological factors that impede members of two species
● Prezygotic barriers - block fertilization from occurring (preventing mating attempts,
preventing mating completion, or hindering fertilization)
●
Postzygotic barriers - barriers that hinder development after a zygote is formed
(developmental errors, infertile offspring, etc.)
Hybrid - offspring that result from interspecific mating (mule)
Hybrid zone - a region in which members of different species meet and mate, producing at least
some offspring of mixed ancestry.
●
Reinforcement - process that involves reinforcing reproductive barriers. (Female pied
and collared flycatchers mating with males from allopatric opposite species.)
●
Fusion - reversal of speciation process in which two species contact one another in
a hybrid zone, but there are no reproductive barriers; gene flow may occur and the
two gene pools become increasingly alike. (Polluted waters in Lake Victoria made it
impossible for females to distinguish between species causing interspecies mating and
gene flow.)
●
Stability - a state of a hybrid zone in which hybrids continue to be produced.
○ Hybrid zone narrowness - Bombina hybrid zone narrowness allows high levels
of gene flow throughout the whole zone and overwhelms selection for increased
reproductive isolation in the zone.
○
Offspring higher fitness - Allonemobius hybrids have a higher fitness than their
parents and mate with each other and the parents, the parents’ undergo a fusion
of gene pools. (This is not common.)
Punctuated equilibria - periods of apparent stasis punctuated by sudden change. (Stephen Jay
Gould) This occurs because of rapid morphological change in a species in a “short” period of
time--short enough that the strata are not distinguishable from each other.