Geographic variation in the advertisement calls of Hyla eximia and its possible explanations.

Ruth E Rodríguez-Tejeda,Constantino Macías Garcia,María Guadalupe Méndez-Cárdenas,Valentina Islas-Villanueva

doi:10.7717/peerj.420

Ruth E Rodríguez-Tejeda, Constantino Macías Garcia + Show 2 more

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https://doi.org/10.7717/peerj.420

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Abstract

Populations of species occupying large geographic ranges are often phenotypically diverse as a consequence of variation in selective pressures and drift. This applies to attributes involved in mate choice, particularly when both geographic range and breeding biology overlap between related species. This condition may lead to interference of mating signals, which would in turn promote reproductive character displacement (RCD). We investigated whether variation in the advertisement call of the mountain treefrog (Hyla eximia) is linked to geographic distribution with respect to major Mexican river basins (Panuco, Lerma, Balsas and Magdalena), or to coexistence with its sister (the canyon treefrog, Hyla arenicolor) or another related species (the dwarf treefrog, Tlalocohyla smithii). We also evaluated whether call divergence across the main river basins could be linked to genetic structure. We found that the multidimensional acoustic space of calls from two basins where H. eximia currently interacts with T. smithii, was different from the acoustic space of calls from H. eximia elsewhere. Individuals from these two basins were also distinguishable from the rest by both the phylogeny inferred from mitochondrial sequences, and the genetic structure inferred from nuclear markers. The discordant divergence of H. eximia advertisement calls in the two separate basins where its geographic range overlaps that of T. smithii can be interpreted as the result of two independent events of RCD, presumably as a consequence of acoustic interference in the breeding choruses, although more data are required to evaluate this possibility.

Highlights

Populations of species occupying large geographic ranges are likely to experience different selective pressures (West-Eberhard, 1983; Panhuis et al, 2001; Coyne & Orr, 2004) which, together with drift (Wiens, 2004), may result in phenotypic and genotypic differences between populations (e.g., Avise, 2000; Laugen et al, 2003; Amezquita et al, 2009)
A comprehensive study of call variation across the whole geographic range of the Canyon treefrog revealed that such differences are not large enough to promote speciation, a degree of assortative mating preferences was evident over large geographic scales (Klymus & Gerhardt, 2012), and at least some of that variation may be linked to introgression with species in the H. eximia group
An attribute often involved in mate recognition in these treefrogs (e.g., Klymus & Gerhardt, 2012), was not different between populations, the authors suggested that call variation in H. wrightorum is unlikely to promote mating isolation ( we note that differences in dominant frequency may be due to local adaptation to facilitate transmission (Littlejohn, 1970) and could lead to assortative mating)

Summary

INTRODUCTION

Populations of species occupying large geographic ranges are likely to experience different selective pressures (West-Eberhard, 1983; Panhuis et al, 2001; Coyne & Orr, 2004) which, together with drift (Wiens, 2004), may result in phenotypic and genotypic differences between populations (e.g., Avise, 2000; Laugen et al, 2003; Amezquita et al, 2009). Other modalities (e.g., visual; Hartmann et al, 2005; Reynolds & Fitzpatrick, 2007; Taylor et al, 2008) are sometimes involved, it is common in anurans that species recognition and female preference depend on a single acoustic signal; the advertisement call Wells, 1977; Cocroft & Ryan, 1995; Wells & Schwartz, 2007 This is produced by males, typically during the mating season. We describe the variation of the advertisement calls of H. eximia across a substantial part of its geographic range, and explore whether this variation is linked to genetic structure (based on mitochondrial and nuclear DNA sequences), geography (i.e., hydrographic basins) and/or range overlaps with its sister species, the canyon treefrog (H. arenicolor), and a related species, the Mexican dwarf treefrog (Tlalocohyla smithii)

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