SREL Reprint #2897




Asymmetric reproductive isolation among polymorphic salamanders

Howard H.Whiteman1,2 and Raymond D. Semlitsch2,3

1Department of Biological Sciences, Murray State University, Murray, KY 42071 USA
2Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802 USA
3Division of Biological Sciences, University of Missouri, Columbia, MO 65211 USA

Abstract: The study of reproductive isolation (RI) as a prerequisite to sympatric speciation has been limited by a focus on species that have already experienced isolation. However, a complete understanding of speciation depends on observing taxa before they complete the speciation process. We estimated RI in field populations of the polyphenic mole salamander, Ambystoma talpoideum, by capturing paedomorphic (aquatic) and metamorphic (terrestrial) adults during the breeding season from two natural populations. We found evidence for asymmetric RI between morphs, such that paedomorphic males and metamorphic females had functionally zero RI, whereas metamorphic males and paedomorphic females had substantial RI. Evidence suggests that ecological factors such as the abundance of each morph, timing of rainfall, and water depth of the breeding habitat play a large role in the production of these asymmetries. Spatial aspects of RI had a greater relative impact on overall isolation than temporal differences, in part because metamorphic adults were often captured in shallower water than paedomorphic adults. However, morph separation varied across populations and year, suggesting that environmental heterogeneity likely plays a large role in the potential for RI, particularly between metamorphic males and paedomorphic females. In addition, body-size variation and behavioural differences could also influence the RI estimates presented here. Although facultative paedomorphosis appears to have played a large role in macroevolutionary change via allopatric speciation in some taxa, our results suggest that there is little potential for sympatric speciation in the future within these populations. However, asymmetric RI creates the opportunity for fitness differences between morphs and sexes that would directly affect the maintenance of this polymorphism. Our results suggest that further studies on this and other polyphenisms may provide valuable insight into the evolution of RI and the role of environmental heterogeneity in the production and maintenance of biological diversity.

Keywords: body size, breeding phenology, environmental heterogeneity, facultative paedomorphosis, fitness, polyphenism, reproductive behaviour, sympatric speciation

SREL Reprint #2897

Whiteman, H. H. and R. D. Semlitsch 2005. Asymmetric reproductive isolation among polymorphic salamanders. Biological Journal of the Linnean Society 86:265-281.

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