Manipulative mothers and selective forces: the effects of reproduction on thermoregulation in reptiles

In many taxa of squamate reptiles, thermal conditions during incubation affect fitness-relevant phenotypic traits of the offspring. Therefore, a gravid female can enhance the fitness of her offspring by selecting appropriate thermal regimes. The maternal manipulation hypothesis (MMH) attributes phylogenetic shifts in a broad array of maternal traits (such as nest-site selection, prolonged uterine retention of eggs, and shivering thermogenesis) to selective advantages driven by embryonic developmental plasticity: mothers enhance the viability of their offspring by providing "better" incubation conditions. In Herpetologica 68:147-159, Schwarzkopf and Andrews (2012) pointed out an alternative possibility: that reproduction-induced shifts in maternal thermoregulatory tactics have evolved because they enhance maternal, not offspring, fitness. Although possible on logical grounds, this alternative hypothesis is inconsistent with available evidence on squamate biology, especially with the diversity of thermoregulatory modifications induced by reproduction. Most reproduction-associated shifts in maternal thermoregulation likely reflect benefits to offspring (as posited by the MMH), or are nonadaptive consequences of ecological shifts that are enforced by reproduction.