Systematics and the Origin of Species On Ernst Mayr's 100th Anniversary (2005) / Chapter Skim
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Part II--DISCERNING RECENT DIVERGENCE: 6 Speciation in Birds: Genes, Geography, and Sexual Selection--SCOTT V. EDWARDS, SARAH B. KINGAN, JENNIFER D. CALKINS, CHRISTOPHER N. BALAKRISHNAN, W. BRYAN JENNINGS, WILLIE J. SWANSON, AND MICHAEL D. SORENSON
Part II--DISCERNING RECENT DIVERGENCE: 6 Speciation in Birds: Genes, Geography, and Sexual Selection--SCOTT V. EDWARDS, SARAH B. KINGAN, JENNIFER D. CALKINS, CHRISTOPHER N. BALAKRISHNAN, W. BRYAN JENNINGS, WILLIE J. SWANSON, AND MICHAEL D. SORENSON
Pages 91-119
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From page 91... ...
, which outlines how present-day studies on speciation in birds are gaining the genetic and theoretical sophistication that had formerly only been associated with the model Drosophila systems. Topics such as the role of sexual selection and the frequency of sympatric speciation are now being addressed genetically in a number of avian systems.
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From page 92... ...
shows that the history has not been this straightforward and that host switches by wasps, and possibly species hybridization by figs, have created partly independent phylogenetic histories of figs and wasps. In Mayr's world view, new species arise under allopatry, and, after that, as divergence accrues, the geographic ranges of related species may later come to overlap.
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(2004) Using nuclear haplotypes with microsatellites to study gene flow between recently separated Cichlid species.
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The re cent completion of a draft sequence of the chicken genome, and an abundance of single nucleotide polymorphisms on the auto somes and sex chromosomes, will dramatically accelerate re search on the molecular mechanisms of avian speciation over the next few years. The challenge for ornithologists is now to inform well studied examples of speciation in nature with in creased molecular resolution -- to clone speciation genes if they *
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This renaissance, spearheaded largely by recent reviews by Price (Irwin and Price, 1999; Price, 1998, 2002; Price and Bouvier, 2002) , builds in part on the ancient tradition of avian husbandry and domestication, and in part on theoretical models suggesting a role for diverse behavioral factors in bird speciation, including sexual selection, sexual imprinting, learning, reinforcement, and genetic incompatibilities.
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. Now, a draft of the complete chicken genome and >2.8 million chicken SNPs have been determined roughly 60 years after Mayr's landmark book (International Chicken Genome Sequencing Consortium, 2004; International Chicken Polymorphism Map Consortium, 2004)
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It is not surprising that a number of workers have advocated the use of mtDNA in species delimitation, given its rapid attainment of reciprocal monophyly (relative to nuclear genes) and frequent ability to diagnose populations (Moore, 1994; Moritz, 1994, 2002; Wiens and Penkrot, 2002)
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Nonetheless, these data, the first substantial sampling of multiple gene trees for an avian species, suggest that species arising rapidly or having ancestors with large effective population sizes will not satisfy the concordant genealogies criterion even though they are reasonable species under the BSC or morphological PSC. For avian species, finding any nuclear gene that has achieved reciprocal monophyly, whether by
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(a) Frequency distribution of all three possible gene trees encountered in a survey of nuclear DNA sequence variation among three species of Australian grassfinches (Poephila)
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Nuclear gene trees will not provide enough phylogenetic resolution to satisfy avian systematists. Furthermore, the high levels of recombination detected in the first surveys of avian SNP variation appear prohibitive for standard phylogenetic analysis (Edwards and Dillon, 2004; International Chicken Polymorphism Map Consortium, 2004)
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From page 102... ...
Thus, divergence in characters involved in mate choice, such as song, plumage, and behavioral displays, likely play a central role in avian speciation. The role of song is particularly interesting given the multiple factors influencing vocal evolution and the potential for rapid change through learning and cultural evolution.
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. A well known example of reproductive character displacement involves the Ficedula flycatchers in which a sexually selected male plumage trait shows greater divergence in sympatry
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. Song learning and sexual imprinting explain the recent diversification of brood parasitic indigobirds (genus Vidua)
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Sex Chromosomes and Avian Speciation The architects of the Modern Synthesis laid the foundation for a body of work that has resulted in two "rules" of speciation that directly implicate sex chromosomes: Haldane's rule and the large X(Z) -effect (Coyne and Orr, 1989)
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sterility before heterogametic (female) inviability in birds may reflect a general trend, regardless of sex-chromosome system, of the rapid evolution of male reproductive genes via sexual selection, resulting in high divergence between species at these loci (Wu and Davis, 1993)
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107 a or parent whereas novel provides a of their also hosts, nest from but their the of in species isolated lay songs the females indigobird of mimic reproductively Rarely, cohesion therefore indigobirds parasitize. are genetic Male they and and host nests colonized.
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From page 108... ...
Additionally, the domain of such sexually selected genes needs to be determined: Do they include sexually selected traits such as plumage and song that are not directly involved in the physical production of gametes? Because males and females of many bird species exhibit correlated evolution of plumage and other sexually selected traits, the specific expression patterns of genes related to both reproduction and morphology need to be investigated to determine how such traits will influence Haldane's rule.
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. The avian Z chromosome is expected to have a higher neutral mutation rate than the autosomes because it passes through the male germ line twice as often as the female germ line, whereas avian autosomes spend equal time in both germ lines.
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The positive feedback loop is enhanced when the linkage group occurs on a sex chromosome for two reasons. First, if as assumed in the model crossing over does not occur between sex chromosomes in the heterogametic sex, hitchhiking is enhanced.
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CRYPTIC MATE CHOICE AND CONFLICT: A ROLE FOR REPRODUCTIVE PROTEINS IN AVIAN SPECIATION? Birds provide an abundance of examples of intense sexual selection through cryptic female choice and sperm competition (Birkhead and Møller, 1992)
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. The recent comparison of predicted genes in chicken genome with the human genome supports the pattern of divergence found in reproductive proteins across taxa (International Chicken Genome Sequencing Consortium, 2004)
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. Combining evolutionary data on reproductive proteins with predictions of sperm competition and mate choice from behavioral studies, as has been attempted with the SEM2 locus in primates (Dorus et al., 2004)
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. Linking of these genetic analyses with predictions from theory and application to natural populations will make for exciting times to come in avian speciation studies.
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(2000) Rapid evolution of reproductive barriers driven by sexual conflict.
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14, 446452. International Chicken Genome Sequencing Consortium.
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(1998) Song learning in brood parasitic indigobirds Vidua chalybeata: Song mimicry of the host species.
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(2000) Does bill size polymorphism affect courtship song characteristics in the African finch Pyrenestes ostrinus?
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(2001b) Positive Darwinian selection drives the evolution of several female reproductive proteins in mammals.
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