Evolutionary Ecology of Freshwater Turtles

This long-term study explores the evolution of life history traits(e.g. reproductive traits such as mating system, migratory behavior,sex determination, demography) and the footprint that those traits leave on the genetic makeup of populations(e.g. genetic differentiation, gene flow) to understand the ecological and evolutionary significance of trait variation, and to provide information important for the conservation of reptiles, particularly turtles. The project consists of several phases that investigate complementary ecological and evolutionary modules related to this main goal. Those modules are: population genetics, paternity analyses, gene expression during sex differentiation, and molecular evolution of genes and chromosomes

Not All Antibodies Are Created Equal: Factors That Influence Antibody Mediated Rejection.

Consistent with Dr. Paul Terasaki's "humoral theory of rejection" numerous studies have shown that HLA antibodies can cause acute and chronic antibody mediated rejection (AMR) and decreased graft survival. New evidence also supports a role for antibodies to non-HLA antigens in AMR and allograft injury. Despite the remarkable efforts by leaders in the field who pioneered single antigen bead technology for detection of donor specific antibodies, a considerable amount of work is still needed to better define the antibody attributes that are associated with AMR pathology. This review highlights what is currently known about the clinical context of pre and posttransplant antibodies, antibody characteristics that influence AMR, and the paths after donor specific antibody production (no rejection, subclinical rejection, and clinical dysfunction with AMR)

Nest-site philopatry and the evolution of temperature-dependent sex determination

Despite intensive research, there is no clear empirical evidence to explain the evolution and persistence of temperature-dependent sex determination in reptiles. A recent hypothesis presented by Reinhold proposes that natal homing could lead directly to the evolution of temperature-dependent sex determination. According to his hypothesis, daughters are produced in rare high-quality sites (associated with higher survival rates) to which they return and use to nest, thus deriving higher fitness than sons for whom the quality of the natal patch does not affect their reproductive output if they survive to maturity. We performed an initial empirical evaluation of several assumptions and predictions of this hypothesis as applied to painted turtles (Chrysemys picta), using data from five consecutive nesting seasons, on a major nesting beach. Females were somewhat philopatric to microgeographic sites and to vegetation cover types within the nesting beach, consistent with one of the assumptions of Reinhold’s hypothesis. The variables we examined that influence hatchling fitness (predation, hatching success and sex ratio) were not stable at microgeographic nesting sites or at vegetation cover types. Predation was repeatable within females, whereas hatching success and sex ratio were not. Contrary to Reinhold’s hypothesis, females did not nest more frequently in open sites (which tend to produce more females) than in patches with more vegetation (which tend to produce more males). Furthermore, preferred nest sites (as measured by nest density) did not produce predominantly females. However, nests with higher hatching success tended to produce slightly more females (although the magnitude of this effect was very small). Therefore, Reinhold’s hypothesis is not applicable to C. picta at the level studied – that is, within a nesting beach over a 5 year period – because most of the essential conditions were not met by our data

Sex-Biased Expression of Sex-Differentiating Genes FOXL2 and FGF9 in American Alligators, Alligator mississippiensis

Across amniotes, sex-determining mechanisms exhibit great variation yet the genes that govern sexual differentiation are largely conserved. Studies of evolution of sex-determining and sex- differentiating genes require an exhaustive characterization of functions of those genes such as FOXL2 and FGF9. FOXL2 is associated with ovarian development and FGF9 is known to play a role in testicular organogenesis in mammals and other amniotes. As a step toward characterization of the evolutionary history of sexual development, we measured expression of FOXL2 and FGF9 across three developmental stages and eight juvenile tissue types in male and female American alligators, Alligator mississippiensis. We report surprisingly high expression of FOXL2 before the stage of embryonic development when sex is determined in response to temperature and sustained and variable expression of FGF9 in juvenile male but not female tissue types. Novel characterization of gene expression in reptiles with temperature-dependent sex determination such as American alligators may inform the evolution of sex-determining and sex-differentiating gene networks as they suggest alternative functions from which the genes may have been exapted. Future functional profiling of sex-differentiating genes should similarly follow other genes and other species to enable a broad comparison across sex-determining mechanisms.Organismic and Evolutionary Biolog

The Lesser Known Challenge of Climate Change: Thermal Variance and Sex-Reversal in Vertebrates with Temperature-Dependent Sex Determination

Climate change is expected to disrupt biological systems. Particularly susceptible are species with temperature-dependent sex determination (TSD), as in many reptiles. While the potentially devastating effect of rising mean temperatures on sex ratios in TSD species is appreciated, the consequences of increased thermal variance predicted to accompany climate change remain obscure. Surprisingly, no study has tested if the effect of thermal variance around high-temperatures (which are particularly relevant given climate change predictions) has the same or opposite effects as around lower temperatures. Here we show that sex ratios of the painted turtle (Chrysemys picta) were reversed as fluctuations increased around low and high unisexual mean-temperatures. Unexpectedly, the developmental and sexual responses around female-producing temperatures were decoupled in a more complex manner than around male-producing values. Our novel observations are not fully explained by existing ecological models of development and sex determination, and provide strong evidence that thermal fluctuations are critical for shaping the biological outcomes of climate change

Sex-specific Aging in Animals: Perspective and Future Directions

Sex differences in aging occur in many animal species, and they include sex differences in lifespan, in the onset and progression of age-associated decline, and in physiological and molecular markers of aging. Sex differences in aging vary greatly across the animal kingdom. For example, there are species with longer-lived females, species where males live longer, and species lacking sex differences in lifespan. The underlying causes of sex differences in aging remain mostly unknown. Currently, we do not understand the molecular drivers of sex differences in aging, or whether they are related to the accepted hallmarks or pillars of aging or linked to other well-characterized processes. In particular, understanding the role of sex-determination mechanisms and sex differences in aging is relatively understudied. Here, we take a comparative, interdisciplinary approach to explore various hypotheses about how sex differences in aging arise. We discuss genomic, morphological, and environmental differences between the sexes and how these relate to sex differences in aging. Finally, we present some suggestions for future research in this area and provide recommendations for promising experimental designs

Sex-specific aging in animals: Perspective and future directions

Sex differences in aging occur in many animal species, and they include sex differences in lifespan, in the onset and progression of age‐associated decline, and in physiological and molecular markers of aging. Sex differences in aging vary greatly across the animal kingdom. For example, there are species with longer‐lived females, species where males live longer, and species lacking sex differences in lifespan. The underlying causes of sex differences in aging remain mostly unknown. Currently, we do not understand the molecular drivers of sex differences in aging, or whether they are related to the accepted hallmarks or pillars of aging or linked to other well‐characterized processes. In particular, understanding the role of sex‐determination mechanisms and sex differences in aging is relatively understudied. Here, we take a comparative, interdisciplinary approach to explore various hypotheses about how sex differences in aging arise. We discuss genomic, morphological, and environmental differences between the sexes and how these relate to sex differences in aging. Finally, we present some suggestions for future research in this area and provide recommendations for promising experimental designs

Sensitization in transplantation: Assessment of risk (STAR) 2019 Working Group Meeting Report.

The purpose of the STAR 2019 Working Group was to build on findings from the initial STAR report to further clarify the expectations, limitations, perceptions, and utility of alloimmune assays that are currently in use or in development for risk assessment in the setting of organ transplantation. The goal was to determine the precision and clinical feasibility/utility of such assays in evaluating both memory and primary alloimmune risks. The process included a critical review of biologically driven, state-of-the-art, clinical diagnostics literature by experts in the field and an open public forum in a face-to-face meeting to promote broader engagement of the American Society of Transplantation and American Society of Histocompatibility and Immunogenetics membership. This report summarizes the literature review and the workshop discussions. Specifically, it highlights (1) available assays to evaluate the attributes of HLA antibodies and their utility both as clinical diagnostics and as research tools to evaluate the effector mechanisms driving rejection; (2) potential assays to assess the presence of alloimmune T and B cell memory; and (3) progress in the development of HLA molecular mismatch computational scores as a potential prognostic biomarker for primary alloimmunity and its application in research trial design