Study Guide Test 4

Study Guide Test 4 - BIOLOGY TEST 4 Chapter 25: Speciation...

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BIOLOGY TEST 4 Chapter 25: Speciation Speciation results from genetic isolation (lack of gene flow) and genetic divergence (selection, drift, and mutation proceed independently) Gene flow eliminates genetic differences Criteria for identifying species: biological species concept, morphospecies concept, phylogenetic species concept. o Biological species concept: criterion is reproductive isolation; problems: cannot be evaluated in asexually reproducing species or in fossils; also, geographical constraint Prezygotic: prevents individuals of different species from mating Postzygotic: offspring have low fitness o Morphospecies concept: criterion is differences in size, shape, and other morphological features; widely-accepted; problems: too subjective that disagreements occur o Phylogenetic species concept: based on evolutionary history of populations; both accepted and precise; problems: few population subsets on the tree of life Under this concept, a species is defined as the smallest monophyletic group in a phylogenetic tree Monophyletic group: Ancestral population, all of its descendants, and only those descendants. Subspecies: populations with distinguishing features, but not distinct enough to be separate species; example: seaside sparrows The dusky seaside sparrow was conserved when it was reproductively isolated. It was conserved by mating with a nearby subspecies to form a reintroduced hybrid and save genetic diversity; this was using biological and morphospecies concepts o Actually should have used phylogenetic concept because the subspecies was mated with a subspecies of a different phylogeny; thus, genetic diversity was not preserved. (page 542) Allopatry: speciation that begins with physical isolation: dispersal or vicariance o Dispersal: population colonizes a new habitat and founds a new population o Vicariance: population experiences a barrier that splits the habitats Colonization triggers speciation because (1) the physical separation reduces or eliminates gene flow, (2) genetic drift causes the two populations to diverge rapidly. Natural selection can also act if the new environment is different from the original habitat. o Founder effect if population remains small Vicariance example: Ratites from supercontinent Gondwana (150MYA separated 140MYA) Sympatry: populations live in same geographical area and interbreeding is possible o Example: water snakes with differing colorations in same species; gene flow between the two populations overwhelmed natural selection, preventing speciation. Even though populations are not physically isolated, they may be isolated by preferences for different habitats; example: soapberry bugs o In this case, natural selection can overwhelm gene flow to cause sympatric speciation Mutation (Polyploidy) as a speciation trigger: highly common in plants; the mutation reduces gene flow; 2n and 4n parents produce unstable triploid zygotes
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o Unstable triploid zygotes because homologous chromosomes cannot separate correctly
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Study Guide Test 4 - BIOLOGY TEST 4 Chapter 25: Speciation...

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