Natal philopatry varies with larval condition in salamanders

Abstract

An individual’s physiological condition early in ontogeny often regulates natal dispersal and philopatry decisions; however, increased condition promotes dispersal in some organisms and philopatry in others. These disparate findings likely arise from interactions among an individual’s early life stage physiological condition, its likelihood of surviving a dispersal event (i.e., dispersal capacity), and its motivation to leave its natal site (i.e., dispersal propensity). Due to the broad importance of reproductive site selection to population structure and dynamics, studies disentangling these various phenotype-dependent effects are critical. We evaluated the relationships between two aspects of larval physiological condition and natal philopatry in Arizona tiger salamanders (Ambystoma tigrinum nebulosum) in an isolated pond system. In this population, geographic distance between ponds is small, adult survivorship is very high, and thus the likelihood of a successful breeding event should mediate reproductive site selection as opposed to the likelihood of surviving the dispersal event. We found that natal philopatry increased with an estimate of long-term body condition in males, but there was no relationship in females. However, natal philopatry decreased with an estimate of short-term body condition. We also found that an individual’s natal pond had effects on philopatry that influenced both sexes and were independent of the pond’s direct effects on body condition. Together, these findings strongly support the importance of an individual’s early developmental experience in the natal environment to its reproductive behaviors across its lifespan, and further highlight the value of considering how phenotype-dependent dispersal mechanisms may vary between the sexes. Previous research has not discerned a generalizable relationship between larval physiological condition and natal philopatry, likely because of the complex interaction between an individual’s ability (dispersal capacity) and its motivation (dispersal propensity) to reproduce in its natal habitat. Using a salamander population with small inter-pond distances and high adult survival, we isolated the effects of two aspects of physiological condition on dispersal propensity. We found that increased long-term larval physiological condition was associated with natal philopatry in male, but not female, tiger salamanders, as well as differences in philopatry based on natal pond. In contrast, short-term larval physiological condition was negatively associated with philopatry. Our findings suggest an important, long-lasting role of the natal environment on reproductive site selection, and further implicate that the conditions experienced in early development can strongly affect reproductive behaviors across the life cycle.