Interactions between the environment and maternal and embryonic physiology can have critical ramifications for early-life phenotypes and survival in a range of species. A major component of the environment-maternal-embryonic nexus is the regulation of embryonic heart rate, which can have important ramifications for developmental phenology, but remains relatively unexplored in viviparous reptiles. The goal of this study was to test for a relationship between embryonic heart rate and maternal body temperature in two species of viviparous garter snakes. The embryonic heart rates of Thamnophis elegans and T. sirtalis were assessed using a field-portable ultrasound. For both T. elegans and T. sirtalis, embryonic heart rate was strongly correlated to maternal temperature. Interestingly, there was also a strong correlation between embryonic and maternal heart rate that was most likely mediated by a common response to maternal body temperature, in spite of the effects of handling during ultrasound on maternal heart rate. Furthermore, embryos at earlier developmental stages had lower heart rates. To our knowledge, this study is the first to explore embryonic heart rate in viviparous reptiles, providing a foundation for future work using ultrasonography to test ecological and evolutionary hypotheses related to developmental dynamics in free-ranging viviparous species.

环境与母体和胚胎生理学之间的相互作用可能对一系列物种的早期生命表型和存活产生关键影响。环境-母体-胚胎关系的一个主要组成部分是胚胎心率的调节，这可能对发育物候学产生重要影响，但在胎生爬行动物中仍然相对未探索。这项研究的目的是测试两种胎生吊袜带蛇的胚胎心率与母体体温之间的关系。使用现场便携式超声评估Thamnophis elegans和T. sirtalis的胚胎心率。对于T. elegans和T. sirtalis，胚胎心率与母体温度密切相关。有趣的是，胚胎和母体心率之间也有很强的相关性，这很可能是由对母体体温的共同反应介导的，尽管超声处理对母体心率有影响。此外，处于早期发育阶段的胚胎心率较低。据我们所知，这项研究是第一个探索胎生爬行动物胚胎心率的研究，为未来使用超声检查与自由放养胎生物种发育动力学相关的生态和进化假设的工作奠定了基础。