A Test of the Endogenous and Exogenous Selection Hypotheses for the Maintenance of a Narrow Avian Hybrid Zone

Bronson, C. L.; Grubb, Thomas C.; Braun, Michael

doi:10.1554/0014-3820(2003)057[0630:atotea]2.0.co;2

Cited by 32 publications

(58 citation statements)

References 49 publications

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“…Male sparrows responded more strongly to homotypic than heterotypic song, as measured by proximity to the playback unit and agonistic behaviors (Fig. Response was higher in allopatry than at the edge of the hybrid zone, suggesting that males of either subspecies defend territories against any song sparrow, an important point given that competition between males affects hybridization rates (Bronson et al 2003). This result is consistent with those from numerous other studies of passerines, including the song sparrow (e.g., Searcy et al 1997Searcy et al , 2003.…”

Section: Mate Choice and Agonistic Behaviorsupporting

confidence: 86%

Habitat Selection, Acoustic Adaptation, and the Evolution of Reproductive Isolation

Patten¹,

Rotenberry²,

Zuk³

2004

Evol

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We examined barriers to gene flow in a hybrid zone of two subspecies of the song sparrow (Melospiza melodia). We focused on how mating signals and mate choice changed along an environmental gradient and gathered data on the morphology, genetics, ecology, and behavior across the zone. Melospiza m. heermanni of the Pacific slope of California and M. m. fallax of the Sonoran Desert, each distinct in plumage, meet across a steep environmental gradient in southeastern California. Although both subspecies occur in riparian habitat, their occupied habitat differs structurally, the former subspecies occurring in areas with denser understory and greater vertical heterogeneity. Song elements varied concomitantly, as predicted by the acoustic adaptation hypothesis, with heermanni having lower‐pitched, more widely spaced elements. Females of both subspecies responded more strongly to homotypic than heterotypic song, and addition of subspecific plumage cues increased response if song was homotypic but not if heterotypic. Females thus assess multiple male traits, weighing song more heavily. Males of both subspecies showed significantly greater agonistic response to homotypic song. Microsatellite variation is correlated significantly with plumage variation across the zone and suggests limited gene flow between the taxa. The association of song and plumage with the environment and in turn with assortative mating suggests a means by which reproductive isolation may evolve or be maintained in hybrid zones.

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Section: Mate Choice and Agonistic Behaviorsupporting

confidence: 86%

Habitat Selection, Acoustic Adaptation, and the Evolution of Reproductive Isolation

Patten¹,

Rotenberry²,

Zuk³

2004

Evol

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“…Nonetheless, historical isolation and divergent selection in distinctive, rangewide associations of climate and vegetation likely restricts further expansion and overlap of the two species. Although additional work is needed to test the relative importance of endogenous (geneticbased) and exogenous (environmental-based) selection on B. inornatus and B. ridgwayi in this region (Bronson et al 2003), findings from this study provide important insight into the complex interplay of history, adaptation, and gene flow in influencing distributions and local sympatry of close relatives in recent secondary contact.…”

Section: Secondary Contact Asymmetry Of Gene Flow and Local Adaptatmentioning

confidence: 96%

Barriers to Sympatry Between Avian Sibling Species (Paridae: Baeolophus) in Local Secondary Contact

Cicero¹

2004

Evolution

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Abstract. Range limits and secondary contact zones often occur at ecotones between major associations of habitat and climate. Therefore, understanding processes that limit sympatry between species in such areas provides an important framework for testing biogeographic and evolutionary hypotheses. Theoretical and empirical work has shown that the evolution of species borders is influenced by a complexity of factors, including gene flow from central to peripheral populations and the ability of species to adapt locally to environmental conditions. However, few studies have used bioclimatic models, combined with molecular and morphological data, to predict geographic range limits in the context of gene flow across a secondary contact zone. In this study, I applied these methods to test specific hypotheses about barriers to sympatry between closely related species where they approach and contact each other. Specifically, I examined the importance of historical isolation, local adaptation, and symmetry of gene flow in limiting sympatry and range expansion of ecologically distinct species across environmental gradients. Molecular (mitochondrial DNA, allozymes), morphological, and bioclimatic data were obtained for two avian sibling species (Baeolophus inornatus and B. ridgwayi) that exist in recent, narrow secondary contact in northern California. These species are broadly allopatric and occupy rangewide associations of oak and pinyon-juniper woodlands, respectively, although B. inornatus also inhabits mixed or juniper woodlands locally. Patterns of molecular variation generally were congruent with morphological and bioclimatic data, and support prior evidence for a history of isolation, adaptation, and divergence in distinctive, species-specific vegetation-climate associations. However, molecular and morphological clines fall east of the limit of oaks, and individuals of B. inornatus in this juniper-associated contact zone experience bioclimates that are more similar to B. ridgwayi than to B. inornatus in oak habitat. Thus, B. inornatus is able to adapt and expand locally into the range of its close relative, but not vice versa. These data support the hypothesis that gene flow is asymmetrical where peripheral populations meet at range boundaries. Physiological differences between species may play an important role in influencing these patterns. Empirical studies that highlight the importance of local adaptation and patterns of gene flow in which closely related species contact across ecotones are central to understanding limits on geographic ranges, sympatry, and introgression-a cornerstone of biogeographic and speciation theory.

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“…A survey of the recent animal literature on linkage disequilibrium suggests that, on average, four polymorphic loci (range 2-9 loci) genotyped for ;50 animals per location have been used to detect an LD of ;0.16 (range of significant results 0.02-0.35: see Szymura and Barton 1986, Mallet et al 1990, Bert and Arnold 1995, Duggins et al 1995, Hare and Avise 1996, Planes and Doherty 1997, Lenormand et al 1998, Rawson et al 1999, Bierne et al 2002, 2003, Dasmahapatra et al 2002, Bronson et al 2003, Morgan-Richards and Wallis 2003, Nielsen et al 2003, Rawson et al 2003, Vines et al 2003. A survey of the recent animal literature on linkage disequilibrium suggests that, on average, four polymorphic loci (range 2-9 loci) genotyped for ;50 animals per location have been used to detect an LD of ;0.16 (range of significant results 0.02-0.35: see Szymura and Barton 1986, Mallet et al 1990, Bert and Arnold 1995, Duggins et al 1995, Hare and Avise 1996, Planes and Doherty 1997, Lenormand et al 1998, Rawson et al 1999, Bierne et al 2002, 2003, Dasmahapatra et al 2002, Bronson et al 2003, Morgan-Richards and Wallis 2003, Nielsen et al 2003, Rawson et al 2003, Vines et al 2003.…”

Section: Introductionmentioning

confidence: 99%

The Use of Genetic Clines to Estimate Dispersal Distances of Marine Larvae

Sotka

Palumbi

2006

Ecology

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Many unresolved issues in the ecology and evolution of marine populations center on how far planktonic larvae disperse away from their parents. Genetic tools provide a promising way to define the spatial spread of larvae, yet their accurate interpretation depends on the extent to which genetic loci are under selection. Genetic clines, geographic zones in which genetically differentiated populations interbreed, provide opportunities to explicitly and simultaneously quantify the relative roles of selection and dispersal. Here, we review the theory and analysis of genetic clines and apply these techniques to published studies of multilocus clines in the sea. The geographic width of a stable genetic cline is determined by a balance between the homogenizing effects of dispersal and the diversifying effects of selection. For marine researchers, the power of genetic clines is that, if selection and clinal width are quantified, then the average geographic distances that larvae move can be inferred. Measuring selection or dispersal through laboratory or field-based experimentation is possible, though logistically difficult, for pelagically dispersed organisms. Instead, dispersal may be more robustly quantified from the degree of linkage disequilibrium between two or more loci, because linkage disequilibrium integrates selection across multiple life stages and generations. It is also relatively insensitive to whether exogenous or endogenous selection operates. Even without quantifying linkage disequilibrium, the theory of genetic clines indicates that the average dispersal distance of larvae is a fraction (i.e., generally <35%) of the clinal width. Because cline theory is based on several underlying assumptions, including near-equilibrium between selection and migration, the dispersal distances inferred from empirical data should be of the correct order but may not be precise. Even so, such estimates of larval dispersal are valuable, as they can be utilized to design appropriate scales for future investigations and provide some guidance to conservation efforts.

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A Test of the Endogenous and Exogenous Selection Hypotheses for the Maintenance of a Narrow Avian Hybrid Zone

Cited by 32 publications

References 49 publications

Habitat Selection, Acoustic Adaptation, and the Evolution of Reproductive Isolation

Habitat Selection, Acoustic Adaptation, and the Evolution of Reproductive Isolation

Barriers to Sympatry Between Avian Sibling Species (Paridae: Baeolophus) in Local Secondary Contact

The Use of Genetic Clines to Estimate Dispersal Distances of Marine Larvae

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