Habitat-specific differences in feeding morphology of fire salamander larvae (Salamandra salamandra)

Abstract Amphibians exploit a variety of aquatic habitats for breeding, with local environmental factors shaping physiology, behavior, and morphology. Ponds and streams are representatives of contrasting environments. Due to the low ecological stability, reduced oxygen levels, and limited food availability, higher predation pressure and intra- and interspecific competition, ponds represent a less favorable habitat. Consequently, pond-dwelling larvae are expected to exhibit morphological traits that improve food intake and assimilation. Here, we demonstrate intraspecific morphological variation in early fire salamander larvae from a single population, where offspring are deposited in both pond and stream habitats. Contrary to expectations, larvae from streams exhibited significantly more vomerine and palatine teeth, shorter gill rakers and reduced inter-raker distances. These features may confer advantages in prey suction, handling, and retaining smaller prey items within the oral cavity. However, the observed variation in head shape, with pond-dwelling larvae having wider heads, aligns with the characteristic typically associated with cannibalism in food-poor environments. The gut length did not differ between the two types. Our results suggest habitat-driven intraspecific adaptations in feeding morphology in fire salamander larvae. While many previous studies did not focus on feeding morphology, our findings shed light on hidden or overlooked trait variation between pond- and stream-dwelling individuals. This could accelerate future studies by investigating the underlying causes and effects of these traits on feeding behavior. Such studies may improve our understanding of how environmental changes drive morphological adaptations and influence amphibian survival.