Meeting Abstract
Major aspects of embryonic development, such as the rate and timing of development, and maternal-fetal interactions can be critical features of early-life fitness and may impact population trends. Development is known to be affected by a combination of factors such as photoperiod, temperature, humidity, and reproductive mode. How environmental and phylogenetic factors interact to regulate development in the wild, however, can be challenging information to obtain. Information on development in wild squamate reptiles is particularly limited, due to the secretive habits of many in this clade. Nevertheless, the repeated evolution of viviparity and consequent diversity of reproductive mode make squamates a particularly valuable subject of study. We used field-portable ultrasonography to investigate embryonic development in two sympatric species of garter snake, Thamnophis sirtalis and T. elegans living in meadows in the Sierra Nevada mountains. Both species are viviparous, primarily lecithotrophic, occupy similar ecological niches and experience the same annual environmental conditions. We found that T. sirtalis embryos were more developmentally advanced than T.elegans embryos during June of three consecutive years. We also found that eggs increased in volume more substantially across developmental stages in T. elegans than in T. sirtalis, indicating differences in the degree to which embryos received additional maternal provisioning via placental transfer. These findings demonstrate interspecific differences in developmental phenology within the same environmental context, and deepen our understanding of differences in maternal-fetal interactions even in closely-related viviparous species.
