Individual growth and body size variation in the endangered salamander Ambystoma altamirani from the Arroyo los Axolotes, Mexico

Intrinsic and extrinsic factors can influence growth rates in salamanders, including sex, age/size, food availability and environmental temperature. We used a capture-mark-recapture study of a population of the endangered salamander Ambystoma altamirani in a stream in the mountains near Mexico City to examine whether individual growth rates differed between males and females or between the wet and dry seasons. We also compared mean snout-vent length (SVL) in this population between two time periods: 2018–2019 and 2022–2023. Ambystoma altamirani grew faster during the wet season than the dry season, and the difference in growth rate between seasons tended to be greater in males than females. Male A. altamirani grew faster than females. Ambystoma altamirani captured in 2018–2019 were smaller than those captured in 2022–2023. Male A. altamirani were longer than females. Our results suggest that individual growth rates in A. altamirani vary as a function of sex and season. We have also shown that the mean body size of A. altamirani can vary among years and between sexes. Such knowledge may contribute to a better understanding of how stream conditions can influence individual growth rates and population dynamics of these endangered salamanders. Keywords: Ambystomatidae, amphibia, annual variation, snout-vent length, stream