Krista A. McCoy

Trophic cascades across ecosystems

Predation can be intense, creating strong direct and indirect effects throughout food webs. In addition, ecologists increasingly recognize that fluxes of organisms across ecosystem boundaries can have major consequences for community dynamics. Species with complex life histories often shift habitats during their life cycles and provide potent conduits coupling ecosystems. Thus, local interactions that affect predator abundance in one ecosystem (for example a larval habitat) may have reverberating effects in another (for example an adult habitat). Here we show that fish indirectly facilitate terrestrial plant reproduction through cascading trophic interactions across ecosystem boundaries. Fish reduce larval dragonfly abundances in ponds, leading to fewer adult dragonflies nearby. Adult dragonflies consume insect pollinators and alter their foraging behaviour. As a result, plants near ponds with fish receive more pollinator visits and are less pollen limited than plants near fish-free ponds. Our results confirm that strong species interactions can reverberate across ecosystems, and emphasize the importance of landscape-level processes in driving local species interactions.

A qualitative meta-analysis reveals consistent effects of atrazine on freshwater fish and amphibians.

Objective The biological effects of the herbicide atrazine on freshwater vertebrates are highly controversial. In an effort to resolve the controversy, we conducted a qualitative meta-analysis on the effects of ecologically relevant atrazine concentrations on amphibian and fish survival, behavior, metamorphic traits, infections, and immune, endocrine, and reproductive systems. Data sources We used published, peer-reviewed research and applied strict quality criteria for inclusion of studies in the meta-analysis. Data synthesis We found little evidence that atrazine consistently caused direct mortality of fish or amphibians, but we found evidence that it can have indirect and sublethal effects. The relationship between atrazine concentration and timing of amphibian metamorphosis was regularly nonmonotonic, indicating that atrazine can both accelerate and delay metamorphosis. Atrazine reduced size at or near metamorphosis in 15 of 17 studies and 14 of 14 species. Atrazine elevated amphibian and fish activity in 12 of 13 studies, reduced antipredator behaviors in 6 of 7 studies, and reduced olfactory abilities for fish but not for amphibians. Atrazine was associated with a reduction in 33 of 43 immune function end points and with an increase in 13 of 16 infection end points. Atrazine altered at least one aspect of gonadal morphology in 7 of 10 studies and consistently affected gonadal function, altering spermatogenesis in 2 of 2 studies and sex hormone concentrations in 6 of 7 studies. Atrazine did not affect vitellogenin in 5 studies and increased aromatase in only 1 of 6 studies. Effects of atrazine on fish and amphibian reproductive success, sex ratios, gene frequencies, populations, and communities remain uncertain. Conclusions Although there is much left to learn about the effects of atrazine, we identified several consistent effects of atrazine that must be weighed against any of its benefits and the costs and benefits of alternatives to atrazine use.

Agriculture Alters Gonadal Form and Function in the Toad Bufo marinus

Background Many agricultural contaminants disrupt endocrine systems of wildlife. However, evidence of endocrine disruption in wild amphibians living in agricultural areas has been controversial. Typically, studies on the effects of pollutants on wildlife attempt to compare polluted with unpolluted sites. Objectives We took a novel approach to address this question by explicitly quantifying the relationship between gonadal abnormalities and habitats characterized by differing degrees of agricultural activity. Methods We quantified the occurrence of gonadal abnormalities and measures of gonadal function in at least 20 giant toads (Bufo marinus) from each of five sites that occur along a gradient of increasing agricultural land use from 0 to 97%. Results The number of abnormalities and frequency of intersex gonads increased with agriculture in a dose-dependent fashion. These gonadal abnormalities were associated with altered gonadal function. Testosterone, but not 17β-estradiol, concentrations were altered and secondary sexual traits were either feminized (increased skin mottling) or demasculinized (reduced forearm width and nuptial pad number) in intersex toads. Based on the end points we examined, female morphology and physiology did not differ across sites. However, males from agricultural areas had hormone concentrations and secondary sexual traits that were intermediate between intersex toads and non-agricultural male toads. Skin coloration at the most agricultural site was not sexually dimorphic; males had female coloration. Conclusions Steroid hormone concentrations and secondary sexual traits correlate with reproductive activity and success, so affected toads likely have reduced reproductive success. These reproductive abnormalities could certainly contribute to amphibian population declines occurring in areas exposed to agricultural contaminants.

Integrator Networks: Illuminating the Black Box Linking Genotype and Phenotype

Emerging concepts in developmental biology, such as facilitated variation and dynamical patterning modules, address a major shortcoming of the Modern Synthesis in Biology: how genotypic variation is transduced into functional yet diverse phenotypic variation. Still, we lack a theory to explain how variation at the cellular and tissue level is coordinated into variation at the whole-organism level, especially as priority of cellular and tissue functions change over an individuals lifetime and are influenced by environmental variation. Here, we propose that interactions among a limited subset of physiological factors that we call, integrators, regulate most phenotypic variation at the organismal level. Integrators are unique among physiological factors in that they have the propensity to coordinate the expression of conserved gene modules of most types of tissues because they participate as nodes in a hierarchical network. In other words, integrator networks impose physiological epistasis, meaning that whole-organism phenotypic responses will be influenced by previous experiences, current environmental conditions, and fitness priorities as encoded by individual integrators. Below, we provide examples of how integrator networks are responsible for both profound and irreversible phenotypic changes (i.e., metamorphosis, sexual differentiation) as well as subtler, transient (e.g., pelage color, seasonal fluctuations in lymphoid and reproductive tissues) variation. The goal of this article is not to describe completely how integrator networks function, but to stimulate discussion about the role of physiology in linking genetic to phenotypic variation. To generate useful data sets for understanding integrator networks and to inform whole-organism physiology generally, we describe several useful tools including vector-field editing, response-surface regression, and experiments of life-table responses. We then close by highlighting some implications of integrator networks for conservation and biomedicine.

Integrating developmental stability analysis and current amphibian monitoring techniques: An experimental evaluation with the salamander Ambystoma maculatum

Many amphibian populations have declined and others are at risk. Developmental stability analysis (DSA) has been proposed as an “early warning system” because it may detect environmental or genetic stress before they lead to population declines. Deviations from perfect symmetry (fluctuating asymmetry or FA) may indicate stress. We experimentally evaluated the efficacy of DSA to detect sublethal acid stress in the salamander Ambystoma maculatum. Our results indicate that traditional fitness correlates, such as size at metamorphosis, were affected by pH stress and revealed pond-specific responses to pH treatments. Fluctuating asymmetry was not correlated with pH stress, suggesting that pH stress did not disrupt aspects of the developmental program that enforce symmetry. Furthermore, FA was altered through preservation, changed through time, and differed in fore and hind limbs. Conclusions about developmental stability depended on whether traits were analyzed separately or with a composite index. Finally, we found that measurement error frequently differed among treatments, such as among pH treatments and between live and preserved groups. In such cases, measurement error must be partitioned out of each FA mean square term in order to make valid comparisons. Any amphibian monitoring program should incorporate a variety of techniques appropriate to the species being investigated and should consider including measures of traditional fitness correlates, which may provide more sensitive indicators of changing levels of environmental stress than does DSA.

Hormonal programming of rat social play behavior: Standardized techniques will aid synthesis and translation to human health

Early social behaviors like juvenile play are important for normal cognitive and social development. Deficits in these behaviors are associated with neurodevelopmental disorders, such as autism. Rat juvenile rough-and-tumble play is a useful behavioral biomarker of neurodevelopment, and is sensitive to chemical factors such as pre and neonatal hormones. Despite a rich body of literature characterizing hormonal programming of rodent juvenile play, the physiological mechanisms that regulate the organization of play behavior are not well characterized. Synthesizing results to understand the role of endocrine signaling in the development of play behavior remains difficult due to methodological inconsistency across studies. In this review, we synthesize what is known about hormonal mechanisms programming play, advocate standardized protocols for investigating rat play, and identify key areas where future research is needed. A synthetic understanding of the relationship between endocrine signaling and behavioral programming will improve our ability to understand the development and onset of neurodevelopmental disorders in humans and ultimately will help prevent these devastating conditions.

Renal pathologies in giant toads (Bufo marinus) vary with land use.

A variety of human land uses involve the release of toxins into the environment. Wildlife live alongside humans across this array of land uses and thus, are exposed to varying chemical milieus. Kidneys are the principle excretory organs for vertebrates and excessive or chronic exposure to exogenous toxins can lead to renal pathology and renal failure. Although studies have linked chemical exposure to specific renal diseases across diverse taxa, none compare renal lesions occurring in wildlife living in different types of human-modified landscapes. We identify lesions characteristic of renal stress, including toxin exposure, in 82 giant toad (Bufo marinus) males living in habitats ranging from suburban to agricultural. In a previous study [McCoy K.A., Bortnick L.J., Campbell C.M., Hamlin H.J., Guillette L.J., Jr., St. Mary C.M. Agriculture Alters Gonadal Form and Function in Bufo marinus. Environ Health Persp; in press.], these individuals were examined for gonadal abnormalities, which were significantly and positively associated with percentage of agriculture at the collection site. Thus, we hypothesized the same association for renal abnormalities. We scored gross anatomical abnormalities and used light microscopy to identify tubular and interstitial lesions that have been associated with toxicant exposure in other organisms, including humans. Renal lesions indicative of tubular disease were observed at one suburban and two agricultural sites, whereas interstitial lesions were most severe at one agricultural site. Although there was no relationship between frequency of renal disease and proportion of agriculture in the collection vicinity, the renal lesions we identify are consistent with toxin exposure and are similar to those found in human drug abusers and patients suffering medication-induced nephropathy. This is the first study to describe renal lesions in a wild amphibian species and investigate the distribution of renal lesions across human altered landscapes. Indentifying the chemicals inducing renal lesions across these landscapes, their toxicological mechanisms, and their implications on wildlife health will help us devise strategies to mitigate the impacts of toxins on humans and animals living in human-modified environments.

A validated protocol to quantify severity of male urogenital feminization using the MOUSE (Mouse objective urethral severity evaluation).

Background:Congenital abnormalities vary in presentation, yet studies using model organisms tend to focus on occurrence rather than severity of the defect. Scoring severity of abnormalities in model systems allows explicit hypothesis testing during basic, translational, and reverse translational studies. We developed and validated a protocol to quantify severity of male urogenital feminization (hypospadias) in the mouse model. Hypospadias is one of the most common birth defects in the world.Methods:To induce genital feminization, pregnant mice were exposed to different concentrations of the antiandrogen vinclozolin. Genitalia were photographed at gestational age 18.5. A dichotomous scoring system to evaluate genital feminization was developed, and validated against histological measurements of urethral length. A training protocol was developed for novice scorers, and criteria were defined to evaluate precision and accuracy of scores.Results:Vinclozolin induced variation in hypospadias severity. Severity scores were tightly correlated with histologically determined urethral length and both techniques showed similar dose–response relationships. Novice observers were trained to precisely and accurately score hypospadias severity.Conclusion:This standardized scoring system advances the mouse as a model to study urogenital development, and will facilitate research on the mechanisms driving genital feminization in males, and aid translational hypospadias research.

Giant toads ( Rhinella marina ) living in agricultural areas have altered spermatogenesis

Across diverse taxa, germ cell development is controlled by an intricate cascade of processes that are tightly controlled by the hypothalamic-pituitary-gonadal axis. Endocrine disturbances, such as those induced by endocrine disrupting chemicals (EDCs) can negatively affect spermatogenesis. Here, we investigate whether spermatogenesis is altered in the giant toad, Rhinella marina, living in agricultural areas where EDCs are used relative to suburban areas. We also ask if reductions in spermatogenesis were associated with developmental gonadal abnormalities (intersex) found in the same frogs. We found that toads in agricultural areas exhibited reduced spermatogenesis relative to non-agricultural animals, and that those reductions were not associated with gross gonadal abnormalities. All toads living in agricultural areas had reduced spermatogenesis relative to those living in non-agricultural areas regardless of whether they had gonadal abnormalities originating during development. Similarities in reproductive dysfunction among diverse taxa living in agricultural areas, including humans, suggest that many vertebrate taxa living in agricultural areas around the globe are likely experiencing some level of reproductive dysfunction.

Organizational effects of the antiandrogen, vinclozolin, on penis development in the mouse†

Abstract Endocrine disrupting chemicals (EDCs) are pollutants found throughout the environment that disrupt normal endocrine processes. In mice, penis development is thought to be most susceptible to EDCs during a critical developmental window occurring on embryonic days (E) 15.5–17.5. However, androgen signaling begins on E13.5 when androgen receptor (AR) protein is found in the genitalia and testosterone is circulating. We hypothesize that disrupting androgen signaling prior to the established critical window sensitizes the penis to future androgen disruption. To test this hypothesis, CD1 dams were exposed to vinclozolin or a corn oil solvent control on E13.5 and E14.5 and AR levels were measured with immunohistochemistry on E14.5. Early antiandrogen exposure reduced AR within nuclei and decreased intensity of AR expression within E14.5 genitalia. To evaluate the influence of antiandrogen exposure before the known critical window of penis development, two groups of pregnant dams (n = 3) were exposed to vinclozolin starting at either E13.5 or E14.5 and continued exposure through E16.5. Histology andM.O.U.S.E. scoring were used to quantify penis abnormalities. To account for differences in total doses mice experienced due to differences in length of dosing time, we compared animals that received the same total doses. Exposure to antiandrogens on E13.5 exacerbated malformations when exposure was continued through sexually dimorphic development. Both exposure time and vinclozolin dose are important for severity of vinclozolin-induced penis abnormalities in mice. This work shows that antiandrogen exposure prior to sensitive periods can exacerbate the effects of later antiandrogen exposure on reproductive development. Summary Sentence Prior to the sensitive window the penis is responsive to antiandrogen exposure, and this early exposure exacerbates antiandrogen-induced penis abnormalities.