Niche partitioning and the storage effect facilitate coexistence in an amphibian community.

Virtually all natural community assemblages are dominated by a handful of common species. Dominant species can exert negative impacts on biodiversity through competitive exclusion, and thus there is a strong incentive to understand imbalances in community composition, changes in dominance hierarchies through time, and mechanisms of coexistence. Pond-breeding amphibians that utilize ephemeral wetlands provide an excellent opportunity to evaluate theoretical predictions of community composition in stochastic environments. One of the most striking features of pond-breeding amphibians is the marked stochastic fluctuations in abundance across years. Given strong theoretical and empirical links between evenness and biomass, one would expect community evenness to change from year to year. Moreover, if different species exhibit different boom-and-bust reproductive cycles, then a storage effect may help to explain why one species does not outcompete all others. Here, we explore the interplay between biotic and abiotic conditions in shaping amphibian communities at two ephemeral wetlands on Eglin Air Force Base, Florida. We document consistent community composition over 6 years of monitoring, resulting from a lack of species turnover and similar responses of all community members to environmental conditions. The similar dynamics of species argues against a storage effect as the sole mechanism for coexistence and instead points to niche partitioning as a more important factor. In support of this conclusion, we show that the degree of synchrony in breeding migrations only correlates with environmental conditions within species, not between species. The lack of pattern seen between species implies that individuals are somewhat constrained in the timing of breeding migrations, perhaps owing in part to competition with other community members. We hope that our work reinvigorates interest in amphibian communities and highlights ephemeral wetlands as model systems to study community dynamics in stochastic environments.

Forecasting the flooding dynamics of flatwoods salamander breeding wetlands under future climate change scenarios.

Ephemeral wetlands are globally important systems that are regulated by regular cycles of wetting and drying, which are primarily controlled by responses to relatively short-term weather events (e.g., precipitation and evapotranspiration). Climate change is predicted to have significant effects on many ephemeral wetland systems and the organisms that depend on them through altered filling or drying dates that impact hydroperiod. To examine the potential effects of climate change on pine flatwoods wetlands in the southeastern United States, we created statistical models describing wetland hydrologic regime using an approximately 8-year history of water level monitoring and a variety of climate data inputs. We then assessed how hydrology may change in the future by projecting models forward (2025-2100) under six future climate scenarios (three climate models each with two emission scenarios). We used the model results to assess future breeding conditions for the imperiled Reticulated Flatwoods Salamander (Ambystoma bishopi), which breeds in many of the study wetlands. We found that models generally fit the data well and had good predictability across both training and testing data. Across all models and climate scenarios, there was substantial variation in the predicted suitability for flatwoods salamander reproduction. However, wetlands with longer hydroperiods tended to have fewer model iterations that predicted at least five consecutive years of reproductive failure (an important metric for population persistence). Understanding potential future risk to flatwoods salamander populations can be used to guide conservation and management actions for this imperiled species.

Corrigendum: Gender Differences in Grant Submissions across Science and Engineering Fields at the NSF.

[This corrects the article DOI: 10.1093/biosci/biaa072.].

Gender Differences in Grant Submissions across Science and Engineering Fields at the NSF.

There has been great growth in women's participation in the US academic doctoral workforce, but underrepresentation remains in all science and engineering fields, especially at high academic ranks. We obtained estimates of the numbers of professorial women and men in fields likely to seek funding from the National Science Foundation and aligned those numbers with each of six research directorates to investigate temporal trends in submission patterns. We found that women are as likely to be funded as men, but the percentage of women submitting proposals was less than expected in every field but engineering. Women are as likely as men to be employed at the most research active institutions, but women are less likely than men to self-report research as their primary work activity in almost all fields but engineering. This work imbalance ultimately limits the diversity of basic science research ideas in science and engineering.

A demographic approach to understanding the effects of climate on population growth.

Amphibian life history traits are affected by temperature and precipitation. Yet, connecting these relationships to population growth, especially for multiple populations within a species, is lacking and precludes our understanding of amphibian population dynamics and distributions. Therefore, we constructed integral projection models for five populations along an elevational gradient to determine how climate and season affect population growth of a terrestrial salamander Plethodon montanus and the importance of demographic vital rates to population growth under varying climate scenarios. We found that population growth was typically higher at the highest elevation compared to the lower elevations, whereas varying inactive season conditions, represented by the late fall, winter and early spring, produced a greater variation in population growth than varying active season conditions (late spring, summer, and early fall). Furthermore, survival and growth were consistently more important, as measured by elasticity, compared to fecundity, and large females had the greatest elasticity compared to all other body sizes. Our results suggest that changing inactive season conditions, especially those that would affect the survival of large individuals, may have the greatest impact on population growth. We recommend future experimental studies focus on the inactive season to better elucidate the mechanisms by which these conditions can affect survival.

Social and endocrine correlates of immune function in meerkats: implications for the immunocompetence handicap hypothesis.

Social status can mediate effects on the immune system, with profound consequences for individual health; nevertheless, most investigators of status-related disparities in free-ranging animals have used faecal parasite burdens to proxy immune function in the males of male-dominant species. We instead use direct measures of innate immune function (complement and natural antibodies) to examine status-related immunocompetence in both sexes of a female-dominant species. The meerkat is a unique model for such a study because it is a cooperatively breeding species in which status-related differences are extreme, evident in reproductive skew, morphology, behaviour, communication and physiology, including that dominant females naturally express the greatest total androgen (androstenedione plus testosterone) concentrations. We found that, relative to subordinates, dominant animals had reduced serum bacteria-killing abilities; also, relative to subordinate females, dominant females had reduced haemolytic complement activities. Irrespective of an individual's sex or social status, androstenedione concentrations (but not body condition, age or reproductive activity) negatively predicted concurrent immunocompetence. Thus, dominant meerkats of both sexes are immunocompromised. Moreover, in female meerkats, androstenedione perhaps acting directly or via local conversion, may exert a double-edged effect of promoting dominance and reproductive success at the cost of increased parasitism and reduced immune function. Given the prominent signalling of dominance in female meerkats, these findings may relate to the immunocompetence handicap hypothesis (ICHH); however, our data would suggest that the endocrine mechanism underlying the ICHH need not be mediated solely by testosterone and might explain trade-offs in females, as well as in males.

Shifts in frog size and phenology: Testing predictions of climate change on a widespread anuran using data from prior to rapid climate warming.

Changes in body size and breeding phenology have been identified as two major ecological consequences of climate change, yet it remains unclear whether climate acts directly or indirectly on these variables. To better understand the relationship between climate and ecological changes, it is necessary to determine environmental predictors of both size and phenology using data from prior to the onset of rapid climate warming, and then to examine spatially explicit changes in climate, size, and phenology, not just general spatial and temporal trends. We used 100 years of natural history collection data for the wood frog, Lithobates sylvaticus with a range >9 million km2, and spatially explicit environmental data to determine the best predictors of size and phenology prior to rapid climate warming (1901-1960). We then tested how closely size and phenology changes predicted by those environmental variables reflected actual changes from 1961 to 2000. Size, phenology, and climate all changed as expected (smaller, earlier, and warmer, respectively) at broad spatial scales across the entire study range. However, while spatially explicit changes in climate variables accurately predicted changes in phenology, they did not accurately predict size changes during recent climate change (1961-2000), contrary to expectations from numerous recent studies. Our results suggest that changes in climate are directly linked to observed phenological shifts. However, the mechanisms driving observed body size changes are yet to be determined, given the less straightforward relationship between size and climate factors examined in this study. We recommend that caution be used in "space-for-time" studies where measures of a species' traits at lower latitudes or elevations are considered representative of those under future projected climate conditions. Future studies should aim to determine mechanisms driving trends in phenology and body size, as well as the impact of climate on population density, which may influence body size.

Unexpected rarity of the pathogen Batrachochytrium dendrobatidis in Appalachian Plethodon Salamanders: 1957-2011.

Widespread population declines in terrestrial Plethodon salamanders occurred by the 1980s throughout the Appalachian Mountains, the center of global salamander diversity, with no evident recovery. We tested the hypothesis that the historic introduction and spread of the pathogenic fungus Batrachochytrium dendrobatidis (Bd) into the eastern US was followed by Plethodon population declines. We expected to detect elevated prevalence of Bd prior to population declines as observed for Central American plethodontids. We tested 1,498 Plethodon salamanders of 12 species (892 museum specimens, 606 wild individuals) for the presence of Bd, and tested 94 of those for Batrachochytrium salamandrivorans (Bs) and for ranavirus. Field samples were collected in 2011 from 48 field sites across a 767 km transect. Historic samples from museum specimens were collected at five sites with the greatest number and longest duration of collection (1957-987), four of which were sampled in the field in 2011. None of the museum specimens were positive for Bd, but four P. cinereus from field surveys were positive. The overall Bd prevalence from 1957-2011 for 12 Plethodon species sampled across a 757 km transect was 0.2% (95% CI 0.1-0.7%). All 94 samples were negative for Bs and ranavirus. We conclude that known amphibian pathogens are unlikely causes for declines in these Plethodon populations. Furthermore, these exceptionally low levels of Bd, in a region known to harbor Bd, may indicate that Plethodon specific traits limit Bd infection.

Widespread rapid reductions in body size of adult salamanders in response to climate change.

Reduction in body size is a major response to climate change, yet evidence in globally imperiled amphibians is lacking. Shifts in average population body size could indicate either plasticity in the growth response to changing climates through changes in allocation and energetics, or through selection for decreased size where energy is limiting. We compared historic and contemporary size measurements in 15 Plethodon species from 102 populations (9450 individuals) and found that six species exhibited significant reductions in body size over 55 years. Biophysical models, accounting for actual changes in moisture and air temperature over that period, showed a 7.1-7.9% increase in metabolic expenditure at three latitudes but showed no change in annual duration of activity. Reduced size was greatest at southern latitudes in regions experiencing the greatest drying and warming. Our results are consistent with a plastic response of body size to climate change through reductions in body size as mediated through increased metabolism. These rapid reductions in body size over the past few decades have significance for the susceptibility of amphibians to environmental change, and relevance for whether adaptation can keep pace with climate change in the future.

Short-term treadmill running in the rat: what kind of stressor is it?

The use of short-term (1-5 days) treadmill running is becoming increasingly common as a model to study physiological adaptations following the exercise. Although the beneficial effects of acute exercise seem clear, a paucity of data exist describing potential markers of stress in response to forced running. We subjected male and female Sprague-Dawley rats to 0, 1, 2, 5, or 10 days of treadmill running. Twenty-four to 32 h after the last bout of exercise animals were killed and examined for training-induced changes in several physiological variables. No effect of skeletal citrate synthase activity was observed in the male animals after any duration, and only at 10 days of running did females show a significant increase in citrate synthase. Myocardial heat shock protein 72 (HSP72) content was higher in male rats than female rats, and exercise led to increased HSP72 in both sexes, although the time course was different between males and females. Animals displayed several markers of systemic stress in response to the treadmill running, and this was done in a sex-dependent manner. Serum corticosterone was significantly elevated in both sexes 24 h after exercise in three of four exercise groups. Corticosterone-binding globulin was higher in females, and decreased after running in female rats. Body and spleen weights decreased in males (but not females) in response to the exercise training, and running did not alter adrenal gland weights in either sex. These data indicate that in response to short-term treadmill running both male and female rats show signs of systemic stress, but that the pattern of changes occurs in a sex-specific manner.

Susceptibility of the heart to ischaemia-reperfusion injury and exercise-induced cardioprotection are sex-dependent in the rat.

The cardioprotective effects of short-term exercise against myocardial ischaemia-reperfusion injury in male and female rats were examined. We subjected male and female rats to 0 (Sed; n = 8 males and 8 females), 1 (1 day; n = 10 males and 8 females), or 5 (5 day; n = 6 males and 6 females) days of treadmill running. Langendorff-perfused hearts underwent 1 h of regional ischaemia and 2 h of reperfusion, and infarct size (expressed as a percentage of the zone at risk; ZAR), left ventricular pressure development, and coronary flow were measured for each heart. Preischaemic pressure development and coronary flow did not differ between the sexes nor were they influenced by exercise. Sed females had significantly smaller infarct sizes (25 +/- 3%) than Sed male hearts (37 +/- 3%; P < 0.001). Short-term running significantly reduced infarct size following 1 day (27 +/- 3%; P < 0.05) and 5 days (30 +/- 4%; P < 0.10) of exercise in males. One day of running did not reduce infarct size in females (19 +/- 3%; P = NS), but 5 day females did show a significant reduction in infarct size (13 +/- 2%; P < 0.05). There was no relationship between postischaemic coronary vascular hyperaemia and infarct size across sexes or exercise training groups. Hearts from Sed females exhibited significantly higher manganese superoxide dismutase (MnSOD) protein expression than hearts from Sed males, but short-term exercise (neither 1 nor 5 days) did not alter MnSOD protein in either sex. Increased sarcolemmal ATP-sensitive K(+) (K(ATP)) channel subunit protein expression (SUR2A and/or K(ir)6.2) correlated closely with sex-dependent and exercise-acquired protection against myocardial infarction. These data indicate that: (1) sex-dependent and exercise-induced differences in the susceptibility of the heart to ischaemia-reperfusion injury are not associated with improved coronary flow or postischaemic hyperaemia; (2) increased MnSOD protein expression is not necessary for exercise-induced protection from infarction; and (3) one possible mechanism for sex-dependent and exercise-mediated reductions in infarct size involves an increased protein expression of cardiac sarcolemmal K(ATP) channels.