Ultrasonography and hormonal profiles as non-lethal tools to study the reproductive biology of a Patagonian lizard.

Understanding a species' life history requires detailed knowledge of its reproductive biology, which is crucial for developing effective conservation strategies. Reproductive studies in lizards have traditionally involved sacrificing specimens; however, ultrasonography has emerged as a valuable non-lethal approach for assessing reproductive condition and embryonic development in reptiles, though it remains underused in small species such as those of the genus Liolaemus. We determined sexual maturity size, sexual dimorphism, female reproductive cycle, litter size, and reproductive effort using ultrasonography and hormonal profiles in the viviparous lizard Liolaemus attenboroughi. Field observations and ultrasonographic assessments of females were complemented by data from specimens from a herpetological collection and particularly in males, to define size at sexual maturity, based on gonadal histology. Minimum size for sexual maturity (snout-vent length) was 59.42 mm for females and 62.30 mm for males. This species exhibits dimorphism: males have larger heads and limbs, traits associated with territorial defense, fighting, and copulation, whereas females prioritize fecundity by having greater interlimb lengths, which provide more space for embryos. Females exhibited an annual reproductive cycle, with vitellogenesis occurring from late summer to mid-spring, gestation from mid-spring to mid-summer, and births from mid- to late summer. Gravid females in late spring exhibited high concentrations of serum progesterone and estradiol, which declined in non-gravid females by late summer. By combining the study of specimens from a herpetological collection with ultrasonography and hormonal analyses, we characterized the reproductive biology of L. attenboroughi using non-lethal methods as a first step toward investigating reproduction in threatened Patagonian reptiles, thus contributing to their conservation.