Alison McCombe Roark

Compensatory responses to food restriction in juvenile green turtles (Chelonia mydas).

The purpose of this study was to assess the compensatory responses to food restriction and subsequent increased food availability in juvenile green turtles (Chelonia mydas). Turtles were fed an ad libitum ration for 12 weeks (AL), a restricted ration for 12 weeks (R), or a restricted ration for 5 weeks and an ad libitum ration for 7 weeks (R-AL). Analysis of covariance was used to test the relationships between (1) growth and body size, (2) intake and body size, and (3) growth and intake for each of the three treatment groups. Body composition of turtles in each group was also evaluated at the beginning of the study and after weeks 5 and 12. After the switch to ad libitum feeding, R-AL turtles consumed comparable amounts of food and grew faster than AL turtles on a size-adjusted basis, but mean body sizes did not converge, although the overlap in their size ranges increased with time. The R-AL turtles also converted food to growth more efficiently and allocated proportionally more nutrients to protein accretion, thereby restoring body composition (except mineral content) to AL levels by the end of the study. Thus, accelerated size-specific growth without hyperphagia restored body condition but not size. These results indicate that (1) intake in juvenile green turtles is maximal when food is readily available and cannot be increased to compensate for a previous period of food limitation, (2) growth rates of ad libitum-fed turtles are only mildly plastic in response to past nutritional history, and (3) priority rules for nutrient allocation favor the attainment of an optimal condition rather than an optimal size. Nutritional setbacks experienced during the vulnerable juvenile stage could therefore have long-lasting consequences for wild turtles in terms of size-specific mortality risk, but these risks may be mitigated by the potential benefits of maintaining sufficient body stores.

Metabolic rate depression is induced by caloric restriction and correlates with rate of development and lifespan in a parthenogenetic insect

Caloric restriction (CR) extends lifespan in most animals, but the mechanisms underlying this phenomenon are the subject of much debate. We investigated the association between longevity and resting metabolic rate (RMR) in Indian stick insects (Carausius morosus) by (i) determining the appropriate scaling coefficient for calculating mass-corrected RMR of insects throughout development, (ii) quantifying the response of RMR to diet history, and (iii) correlating RMR in multiple life-history stages with adult and total lifespan. Over a range of body sizes, whole-body RMR (measured as oxygen consumption rate) scaled linearly with body mass. Mass-specific RMR decreased in response to CR, particularly when food was restricted during juvenile stages. With one exception, RMR of insects in different life-history stages matched current feeding level and was not substantially affected by intake history. Total lifespan was affected by intake, with insects that experienced CR early in development living longer than insects that were fed ad libitum. Although CR was associated with extended total lifespan and decreased RMR, it was also associated with shortened adult lifespan. Thus, we found limited evidence that decreased RMR plays a causative role in determining longevity. Instead, CR and decreased RMR were associated with slower progression through pre-reproductive life-history stages.

Gene–environment interactions: The potential role of contaminants in somatic growth and the development of the reproductive system of the American alligator

Developing organisms interpret and integrate environmental signals to produce adaptive phenotypes that are prospectively suited for probable demands in later life. This plasticity can be disrupted when embryos are impacted by exogenous contaminants, such as environmental pollutants, producing potentially deleterious and long-lasting mismatches between phenotype and the future environment. We investigated the ability for in ovo environmental contaminant exposure to alter the growth trajectory and ovarian function of alligators at five months after hatching. Alligators collected as eggs from polluted Lake Apopka, FL, hatched with smaller body masses but grew faster during the first five months after hatching, as compared to reference-site alligators. Further, ovaries from Lake Apopka alligators displayed lower basal expression levels of inhibin beta A mRNA as well as decreased responsiveness of aromatase and follistatin mRNA expression levels to treatment with follicle stimulating hormone. We posit that these differences predispose these animals to increased risks of disease and reproductive dysfunction at adulthood.

Group-Advantaged Training of Research (GATOR): A Metamorphosis of Mentorship

We describe Group-Advantaged Training of Research (GATOR), a yearlong structured program at the University of Florida that guided graduate student mentors and their undergraduate mentees through the mentored research process. Using the national Survey of Undergraduate Research Experiences for an academic year, we found that outcomes for our mentees were similar to those for other programs. We also used an internal survey, combined with qualitative observations, to develop a road map of the mentoring process, which we call the “Metamorphosis of Mentorship.” This model provides tangible steps on the road to becoming a scientist, incorporates reasons mentees stall in research, and suggests ways to overcome mentoring challenges and prevent attrition. The structure and outcomes of this program will be useful to researchers and administrators working to engage undergraduates in scientific research, particularly at large universities where undergraduates are often mentored by graduate students.

Endogenous and exogenous estrogens during embryonic development affect timing of hatch and growth in the American alligator (Alligator mississippiensis)

Prenatal exposure to estrogenic endocrine disrupting chemicals (EDCs) can affect length of gestation and body mass and size of offspring. However, the dose, timing, and duration of exposure as well as sex and strain of the experimental animals determine the direction and magnitude of these effects. In this study, we examined the effects of a one-time embryonic exposure to either 17 β-estradiol (E2) or bisphenol A (BPA) on rate of development and growth in American alligators (Alligator mississippiensis). Our results indicate that BPA and E2-treated alligators hatched approximately 1.4 days earlier than vehicle-treated (control) alligators, suggesting that estrogenic chemicals hasten hatching in these animals. We assessed growth rates, growth allometry, and body condition for 21 weeks after hatching and found that BPA-treated alligators grew more quickly shortly after hatching but more slowly thereafter compared to control alligators. Conversely, E2-treated alligators grew more slowly shortly after hatching but more quickly thereafter compared to control alligators. As a result of differences in growth rate, BPA-treated alligators were heavier, longer, and fatter than control alligators at age 5 weeks but were similar in size and leaner than control alligators at age 21 weeks. Biochemical analytes were examined at the end of the 21-week study to assess overall metabolic condition. We found that E2-treated alligators had significantly higher circulating plasma concentrations of cholesterol and triglycerides than control alligators while BPA-treated alligators had blood profiles comparable to control alligators. Our results provide important insights into the effects of exogenous estrogens on morphology and metabolism in an oviparous, semi-aquatic reptile.

Bridging developmental boundaries: lifelong dietary patterns modulate life histories in a parthenogenetic insect

Determining the effects of lifelong intake patterns on performance is challenging for many species, primarily because of methodological constraints. Here, we used a parthenogenetic insect (Carausius morosus) to determine the effects of limited and unlimited food availability across multiple life-history stages. Using a parthenogen allowed us to quantify intake by juvenile and adult females and to evaluate the morphological, physiological, and life-history responses to intake, all without the confounding influences of pair-housing, mating, and male behavior. In our study, growth rate prior to reproductive maturity was positively correlated with both adult and reproductive lifespans but negatively correlated with total lifespan. Food limitation had opposing effects on lifespan depending on when it was imposed, as it protracted development in juveniles but hastened death in adults. Food limitation also constrained reproduction regardless of when food was limited, although decreased fecundity was especially pronounced in individuals that were food-limited as late juveniles and adults. Additional carry-over effects of juvenile food limitation included smaller adult size and decreased body condition at the adult molt, but these effects were largely mitigated in insects that were switched to ad libitum feeding as late juveniles. Our data provide little support for the existence of a trade-off between longevity and fecundity, perhaps because these functions were fueled by different nutrient pools. However, insects that experienced a switch to the limited diet at reproductive maturity seem to have fueled egg production by drawing down body stores, thus providing some evidence for a life-history trade-off. Our results provide important insights into the effects of food limitation and indicate that performance is modulated by intake both within and across life-history stages.

Reproductive and developmental effects of tributyltin, bisphenol A, and 17 β-estradiol in pale anemones (Aiptasia pallida)

The effects of exposure to estrogenic endocrine-disrupting chemicals in most clades of marine invertebrates are unknown. The purpose of this study was to determine if exposure to 3 such chemicals modulates asexual reproduction and development in pale anemones (Aiptasia pallida). Anemones (n = 18 in each group) were exposed for 21 days to one of 8 treatments: seawater alone, seawater containing vehicle, or seawater containing a low (environmentally relevant) or high dose of tributyltin (TBT), bisphenol A (BPA), or 17 β-estradiol (E2) dissolved in vehicle. The number of asexually generated pedal lacerates produced by each anemone and the number of days required for each lacerate to develop a stomodeum and tentacles were recorded. At the end of the study, parent anemones were homogenized, and total protein content (as a proxy for body size) was quantified by Bradford assay. The roles of chemical treatment and parent anemone size in determining lacerate production were evaluated with binomial-Poisson hurdle models, and their roles in determining development rate were evaluated with generalized linear models. Application of model selection criteria suggested that exposure to E2 (at 45 ng/L) but not to TBT or BPA was associated with increased pedal lacerate production. Neither low nor high doses of any chemical tested affected the number of days required for lacerates to develop into juveniles. Although cnidarians are not thought to express genes homologous to vertebrate estrogen receptors, evidence from this and other studies suggests that estrogens, at least at high doses, are bioactive in these basal metazoans.