Being or becoming a specialist: can ontogenetic shifts in prey preference affect the development of complex phenotypes in Brazilian lanceheads?

Abstract Feeding specialization in organisms with indeterminate growth often leads to size-structured populations characterized by ontogenetic shifts in prey preferences (OSPPs). These shifts drive phenotypic changes that enhance feeding performance for specific prey. In snakes, OSPP is widely common, with juveniles typically consuming small ectotherms and transitioning to larger and potentially more dangerous endothermic prey as they grow. These transitions impose selective pressures on skull structure that are likely to influence cranial development in gape-limited predators, such as snakes. We examined skull ontogeny in pitvipers of the genus Bothrops, comparing species born as endotherm specialists [early-stage endotherm specialists (ESEnS)] with those that become endotherm specialists later through OSPPs [late-stage endotherm specialists (LSEnS)]. Using linear and geometric morphometric data, we analysed skull shape relative to body size through ontogenetic allometric trajectories (OATs). We hypothesized that ESEnS undergo slower, more gradual, and stable morphological changes throughout ontogeny, without abrupt shifts in OAT slopes, whereas LSEnS exhibit faster morphological changes, with shifts in OAT slopes coinciding with the onset of endothermic prey consumption. Our findings supported these predictions, revealing slower cranial morphological changes in ESEnS and rapid alterations in gnathic bones (key determinants of gape size) in LSEnS. These accelerations coincided with their dietary transition, supporting the hypothesis that divergent feeding strategies drive differential cranial development in Bothrops.