Sperm Physiological Differences Between Two Altitudinal Populations of the Lizard Sceloporus grammicus Under Contrasting Thermal Environments

Temperature is one of the most important parameters affecting reproduction in ecto-therms. Therefore, some lizards have modified certain behavioral strategies to optimize their thermoregulation. This includes shifting their distribution area toward higher altitudinal gradients to achieve optimal temperatures. This article focuses on comparing the sperm physiology of two populations of Sceloporus grammicus from contrasting envi-ronments in the Sierra del Ajusco, Mexico. Ten organisms from each of the two different populations of Sceloporus grammicus (2250 and 3500 m of elevation) were collected. Morphological data, organ dissection, and spermatozoa were obtained from the three re-gions of the epididymis to determine sperm parameters. The population at 2250 m pre-sented a higher gonadosomatic index (GSI) compared to the population at 3500 m, the opposite case occurred in the case of epididymosomatic index (EI). The percentage of cy-toplasmic droplet (CD) was higher in male gametes of the lower population at the epi-didymal corpus and cauda level. DNA compaction was greater than 40% for both popula-tions. Four distribution patterns of intracellular calcium ([Ca2+]i) were determined in both populations. S. grammicus presents physiological adaptations depending on the ambient temperature and the distribution of sperm’s intracellular Ca2+ responds to the body tem-perature presented by the lizard.