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Spatial and temporal patterns of phenotypic variation in a Neotropical frog

Authors

  • J. M. Robertson,

    Corresponding author
    1. Department of Ecology and Evolutionary Biology, A406b Corson Hall, Cornell University, Ithaca, NY 14850, USA
      *J. M. Robertson, Department of Ecology and Evolutionary Biology, A406b Corson Hall, Cornell University, Ithaca, NY 14850, USA. E-mail: jmr79@cornell.edu
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  • A. D. Robertson

    1. EDORSS, Department of Systems Engineering, Morgan Hill, CA 95037, USA
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*J. M. Robertson, Department of Ecology and Evolutionary Biology, A406b Corson Hall, Cornell University, Ithaca, NY 14850, USA. E-mail: jmr79@cornell.edu

Abstract

Aim  Studies of the spatial and temporal patterns of phenotypic diversity help to elucidate the fine-scale evolutionary and ecological mechanisms underlying geographical differentiation. The red-eyed tree frog, Agalychnis callidryas, is a widespread Neotropical frog that exhibits a broad range of polymorphism of coloration and flank-stripe pattern. The goal of this study was two-fold: first, to investigate the stability of polymorphisms over a 38-year period; and second, to evaluate biogeographical hypotheses of diversification between lower Central American populations through quantification of phenotypic diversity on a fine geographical scale.

Location  This study was conducted at 12 sites across four biogeographical regions in Costa Rica and Panama.

Methods  We quantified colour, categorized flank-stripe pattern from digital photos taken during field sampling, and measured body size for each individual. We compared the regional frequency of each flank-stripe pattern in 2005 with the frequency distribution from a previous study of the same sites in 1967 using logistic regression analyses. We determined the geographical signal of leg coloration by employing linear discriminant function analyses to generate a classification matrix based on covariance similarities, and by comparison of the average hue values within and between regions.

Results  We found a temporal shift in the frequency of flank-stripe patterns in three of four regions over 38 years. Based on measures of leg coloration, the frequency distribution of flank-stripe patterns and body size, we conclude that A. callidryas populations are easily distinguishable at a regional scale.

Main conclusions Agalychnis callidryas exhibits regional differentiation in all phenotypic traits measured in this study, supporting the role of three major biogeographical barriers to gene exchange. We found evidence of a putative contact zone between polytypic regions in Costa Rica. In addition, we report temporal instability of the relative frequency of stripe patterns located on the flanks. The ecological and evolutionary mechanisms that may underlie this variation include sexual selection and avoidance of predators.

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