The effects of intra- and interspecific competitions on personality and individual plasticity in two sympatric brown frogs

We studied how individuals modify their behavior in response to inter- and intraspecific competitors and how these changes affected the pattern of variation between populations and species. As study models, we used tadpoles of two brown frogs, Rana latastei and R. dalmatina. Since R. latastei is always sympatric to R. dalmatina, whereas R. dalmatina is sympatric to R. latastei only in the periphery of its range, we predicted a stronger response to heterospecifics in R. latastei than in R. dalmatina and, within each species, in syntopic than in allotopic populations. To test these predictions, we raised tadpoles, from either syntopic or allotopic populations, in either syntopy or allotopy and repeatedly tested them in open field trials in the presence of a caged conspecific, a caged heterospecific, or an empty cage. As predicted, we found that, on average, R. latastei tadpoles modified their behavior across treatments more than R. dalmatina tadpoles and individuals from the syntopic population changed more than their conspecifics from the allotopic population. In both species, the pattern of variation at the individual level mirrored that at the population and species levels providing no evidence for an individual-by-environment interaction (I x E). Besides these differences, however, individuals of the two species also showed unpredicted and context-independent behavioral differences, suggesting that there might be more to interspecific behavioral variation than the effect of selection by heterospecific competitors.Significance statementDoes the distribution range of a species influence the evolution of plastic behaviors to heterospecific competitors? And how do differences in plasticity affect animal personality? To answer these questions, we raised tadpoles of two brown frog species, Rana dalmatina and R. latastei, and studied how the amount and the type of their swimming varied with the presence of the other species. R. latastei, whose small distribution range fully overlaps with that of R. dalmatina, plastically responds to it, whereas R. dalmatina, which is sympatric to R. latastei only in the periphery of its broader range, does not. These interspecific differences mirrored those among individuals: tadpoles of both species show repeatable behaviors, but only those of R. latastei plastically changed their behavior with the presence of the other species; however, neither R. latastei nor R. dalmatina show among-individual variation in plasticity.