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Adaptive differentiation in life history traits despite propensity for hybridization in two sister salamanders
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  • Victor Fitzgerald,
  • Jason Bracken,
  • Alfredo Ascanio,
  • Michael O'Connell,
  • M Strasburg,
  • Joey Zianno,
  • Mason Murphy,
  • Tereza Jezkova
Victor Fitzgerald
Miami University

Corresponding Author:[email protected]

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Jason Bracken
Miami University
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Alfredo Ascanio
Miami University
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Michael O'Connell
Miami University
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M Strasburg
Miami University
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Joey Zianno
Miami University
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Mason Murphy
Bowling Green State University
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Tereza Jezkova
Miami University
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Abstract

Hybridization can have a profound negative effect on population fitness when species exhibit divergence in adaptive traits. The Streamside salamander, Ambystoma barbouri, and the Smallmouth salamander, A. texanum, are closely related species differentiated primarily by breeding habitat and reproduction-related traits, but previous work suggests patterns of hybridization and introgression between them. Here we investigate whether 1) hybridization occurs between the two species in laboratory settings, 2) their divergent reproduction-related traits are retained under a common treatment, and 3) hybrid offspring exhibit similar fitness as their non-hybrid counterparts. We bred conspecific and heterospecific pairs of A. barbouri and A. texanum and raised hybrid and non-hybrid offspring to metamorphosis. Reproduction-related traits such as oviposition location and clutch size remained well differentiated between the two species. Heterospecific pairs hybridized readily, at similar rates to conspecific pairs. The hybrid larvae generally exhibited a maternal effect and, less frequently, intermediate phenotypes with respect to measured traits. Hybrid larvae did not exhibit reduced fitness as measured by survival to metamorphosis. Our results suggest that traits differentiating A. barbouri and A. texanum are likely genetically determined despite the lack of reproductive isolation between them. This suggests that the generally parapatric distribution of the two species, often paired with abrupt transition in traits, might be driven by selection on these traits in local habitats. Further, the maternal effect and consequent lack of intermediate phenotypes observed for several traits likely reduces the negative effect of hybridization in locally adapted populations.