Evolution__3rd_Edition

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Full Contents xv
14.2 A newly evolving species could theoretically have an allopatric,
parapatric, or sympatric geographic relation with its ancestor 382
14.3 Reproductive isolation can evolve as a by-product of divergence
in allopatric populations 383
14.3.1 Laboratory experiments illustrate how separately evolving
populations of a species tend incidentally to evolve
reproductive isolation 384
14.3.2 Prezygotic isolation evolves because it is genetically correlated
with the characters undergoing divergence 386
14.3.3 Reproductive isolation is often observed when members of
geographically distant populations are crossed 387
14.3.4 Speciation as a by-product of divergence is well documented 389
14.4 The Dobzhansky–Muller theory of postzygotic isolation 389
14.4.1 The Dobzhansky–Muller theory is a genetic theory of
postzygotic isolation, explaining it by interactions among
many gene loci 389
14.4.2 The Dobzhansky–Muller theory is supported by extensive
genetic evidence 391
14.4.3 The Dobzhansky–Muller theory has broad biological
plausibility 392
14.4.4 The Dobzhansky–Muller theory solves a general problem
of “valley crossing” during speciation 394
14.4.5 Postzygotic isolation may have ecological as well as genetic
causes 395
14.4.6 Postzygotic isolation usually follows Haldane’s rule 396
14.5 An interim conclusion: two solid generalizations about speciation 399
14.6 Reinforcement 399
14.6.1 Reproductive isolation may be reinforced by natural selection 399
14.6.2 Preconditions for reinforcement may be short lived 401
14.6.3 Empirical tests of reinforcement are inconclusive or fail to
support the theory 402
14.7 Some plant species have originated by hybridization 405
14.8 Speciation may occur in non-allopatric populations, either
parapatrically or sympatrically 408
14.9 Parapatric speciation 409
14.9.1 Parapatric speciation begins with the evolution of a
stepped cline 409
14.9.2 Evidence for the theory of parapatric speciation is
relatively weak 411
14.10 Sympatric speciation 411
14.10.1 Sympatric speciation is theoretically possible 411
14.10.2 Phytophagous insects may split sympatrically by host shifts 412
14.10.3 Phylogenies can be used to test whether speciation has been
sympatric or allopatric 413
14.11 The influence of sexual selection in speciation is one current trend
in research 413