IRFP: Testing Hypotheses Regarding Function and Evolution of Placentotrophy, Using Viviparous Skinks as a Model

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The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four-month research fellowship by Dr. James U. Van Dyke to work with Dr. Michael Thompson at the University of Sydney, in Sydney, Australia. Mechanisms of reproductive allocation are the means by which individual animals provision resources to their offspring. These mechanisms may respond to food web disruption and subsequent resource limitation via alterations of either reproductive output, parental survival, or both. Therefore, understanding mechanisms of reproductive allocation is central to understanding population dynamics within the context of global environmental change. Among amniotes, placentotrophic lizards of the family Scincidae are the only taxa to exhibit intermediacy between complete reliance on yolk (lecithotrophy), and complete reliance on placentation (placentotrophy), for embryonic nutrition. As a result, they have long served as the only available models for studies of evolution of placentation in amniotes. However, only recently has our understanding of the diversity of placental morphology and function progressed to the point that questions regarding the evolution of amniote placentotrophy can be addressed. This research makes two major advances to the understanding of amniote placental function and evolution. First, it provides an analysis of how intermediate reliance on both yolk (lecithotrophy) and placenta (placentotrophy) affect reproductive success during periods of food limitation. Second, it utilizes a novel tracer technique to determine which placental tissues are responsible for providing embryonic nutrition in placentotrophic skinks. Together, the results of this project provide novel insights into the placental function of a species that utilizes both lecithotrophy (yolk) and placentotrophy (placenta), which advances understanding of the evolution of placentotrophy from an ancestral lecithotrophic state in vertebrates. By focusing on reproductive responses to food limitation, this research also provides a template for mechanistically predicting population-level responses to global environmental change. Therefore this research directly links studies of placental function with conservation in the face of global environmental change.