Dr. Rachel M. Bowden
Office – SLB 244, Lab – SLB 245, Phone: 438-3834, Email: rmbowde@ilstu.edu
Maternal Resource Provisioning of Offspring
I investigate the influences of maternally derived resources, primarily sex steroids, on offspring development in turtles with temperature-dependent sex determination (TSD). Typically, sex can be predicted by incubation temperature in species with TSD, but we currently have a limited understanding of how temperature regulates sex at a mechanistic level. Further, under experimental conditions it is possible to override the effects of incubation temperature by exogenous administration of steroids, suggesting a key role for steroids (and possibly their receptors) in this process. Studies in my lab focus on understanding the importance of maternal steroids, present in the yolk at oviposition, in the processes of sex determination and differentiation.
Ontogeny of sex steroid receptor development
Elevated estradiol levels in yolk at oviposition have been linked to higher proportions of female offspring under controlled laboratory conditions, but this does not establish a causal link between the early presence of steroids and sex determination. In order for these early steroids to effect sex determination, the embryo must either possess the relevant receptors sufficiently early in development or the embryo must have a means of sequestering these steroids for later action. My lab is currently investigating when, during embryogenesis, do steroid receptors develop and where they are located within the developing embryo.
Influence of glucocorticoids and sex steroids on the development of immunity
Steroid hormones are known to influence the functioning of the vertebrate immune system. Androgens and glucocorticoids are generally regarded as having immunosuppressive effects while estrogens are typically immunostimulatory. During folliuclogenesis females transfer both steroids and immunoglobulins along with energetic components to their eggs. These immunoglobulins confer passive humoral immunity on the offspring during the early stages of immune system development. My lab is examining the interplay between steroids, incubation temperature, and immunity in embryonic and juvenile turtles.
The study system: Emydid turtles
We primarily work with two widely distributed turtle species, the red-eared slider (Trachemys scripta) and the painted turtle (Chrysemys picta, pictured here), both of which possess temperature-dependent sex determination. Much is known about the ecology and life history of these intensively studied species, and whenever possible, we attempt to integrate both laboratory and field studies to investigate the functional relevance of laboratory findings in nature.