Evol Ecol Res 11: 1099-1109 (2009)     Full PDF if your library subscribes.

Cryptic divergence: countergradient variation in the wood frog

Nisha F. Ligon1 and David K. Skelly1,2

1Department of Ecology and Evolutionary Biology and  2School of Forestry and Environmental Sciences, Yale University, New Haven, Connecticut, USA

Correspondence: N.F. Ligon, Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06511, USA.
e-mail: nisha.ligon@gmail.com


Questions: Do wood frog (Rana sylvatica) populations show evidence of cryptic variation, wherein inherited variation is masked by environmental effects? Have these populations diverged in larval traits across a gradient of canopy cover? How do trends in larval traits differ when observed in the field versus in a common garden experiment?

Hypothesis: Due to strong selection in their cooler environment, wood frogs from heavily shaded wetlands will grow and develop more slowly in the field but more quickly in a common garden experiment, compared with their counterparts from sunnier wetlands.

Methods: We monitored growth and development of wood frog larvae from six wetlands of varying canopy cover. We studied populations in the natal wetlands and individuals raised in incubators from embryos through metamorphosis.

Conclusions: Observations of natural populations revealed no evidence of strong trends in phenotype. However, when raised in a common environment, larvae from more shaded natal wetlands grew and developed faster, and were larger at any given stage. This is evidence for cryptic divergence wherein the lack of an observed phenotypic trend masks the underlying inherited variation.

Keywords: amphibian, countergradient variation, cryptic, divergence, light, microgeography, phenotypic variation, temperature.

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