Mating system and brain size in bats

Abstract

The contribution of sexual selection to brain evolution has been little investigated. Through comparative analyses of bats, we show that multiple mating by males, in the absence of multiple mating by females, has no evolutionary impact on relative brain dimension. In contrast, bat species with promiscuous females have relatively smaller brains than do species with females exhibiting mate fidelity. This pattern may be a consequence of the demonstrated negative evolutionary relationship between investment in testes and investment in brains, both metabolically expensive tissues. These results have implications for understanding the correlated evolution of brains, behaviour and extravagant sexually selected traits.

Figure 1

Mean residual ln brain mass (a–c) and testis mass (d–f) for bat species relative to the occurrence of female promiscuity (a,d), their mating system (b,e; MG, monogamy; PG, polygyny; PGN, polygynandry), and their roosting association (c,f; SM–SF, single male, single female; SM–MF, single male, multi female; MM–MF, multi male, multi female). Residuals were generated from regression of ln brain mass or ln testis mass on ln body mass, with regressions performed separately by family as partial phylogenetic control. These data are for illustrative purposes only; all conclusions from discrete analyses are based on ANCOVAs (table 1). Relationships for residual ln neocortex volume (not shown) are qualitatively similar to those illustrated for total brain mass. Error bars equal one s.e.m. Number of species indicated at base of columns.