Divergence in Bergmann's clines: elevational variation and heritability of body size in a leaf-cutting ant

摘要

The variation in size along elevations has been investigated in various insect species, with contradictory results regarding Bergmann's or James' rules. Positive, negative, or hump-shaped patterns have been commonly found, but the sources of variation are generally unknown, because the contribution of genetic and environmental factors is not usually estimated. Social insects offer the opportunity to study the intraspecific variation and heritability of morphological traits due to the ease of finding family groups in the wild. Thus, we aimed to assess the variation in morphological characters ofAtta cephalotesand to estimate their heritability as an attempt to understand the sources of variation. We sampled 30 soldiers from five nests at six different elevations in Colombia; soldiers were dissected, and ten morphometric characters were measured. Variation was analysed through nested MANOVA and REML analyses, and heritabilities and co-heritabilities were estimated using a full-sib model. We found significant differences between elevations and nests, with larger soldiers occurring at localities in intermediate elevations. Heritabilities varied when they were estimated with all data together or separated by locality, showing low-to-intermediate values, while co-heritabilities were intermediate to high. The nonlinear cline found in this study could be a result of the interactions among the factors generating Bergmann's patterns, such as temperature, the ecology of leaf-cutting ants (management of temperature inside nests) and resource availability. The heritability results imply a genotype-environment interaction, with an overall greater effect of the environment on body size variation inA. cephalotessoldiers.