Kristine L. Grayson

Sex-and context-dependent migration in a pond-breeding amphibian

Partial migration, variation in the percentage of a population that completes a migration, can be influenced by the local environment and condition of an individual. We examined the direct and interacting effects of habitat quality and gender on migration decision by manipulating population density and sex ratio in a factorial field experiment using aquatic enclosures. In partially migrating red-spotted newts (Notophthalmus viridescens), we measured the percentage of newts migrating to the terrestrial habitat vs. overwintering as pond residents. Density significantly influenced migration, with 63% of newts migrating from high-density enclosures compared to 39% from low-density enclosures. Newts also migrated earlier from high-density enclosures, but no significant effects of the sex ratio treatment were found. Females migrated earlier than males, and 64% more females developed the migrant phenotype, suggesting important sex-based trade-offs of migration. No differences were found between migrants and residents in initial body size, counter to our prediction that larger individuals would be more likely to remain pond residents. This study demonstrates experimentally that migration can be a plastic response influenced by both local density and gender.

Life history benefits of residency in a partially migrating pond‐breeding amphibian

Species with partial migration, where a portion of a population migrates and the other remains residential, provide the opportunity to evaluate conditions for migration and test mechanisms influencing migratory decisions. We conducted a five-year study of two populations of red-spotted newts (Notophthalmus viridescens), composed of individuals that either remain as residents in the breeding pond over the winter or migrate to the terrestrial habitat. We used multistate mark-recapture methods to (1) test for differences in survival probability between migrants and residents, (2) determine if migrants breed every year or skip opportunities for reproduction, and (3) estimate the frequency of individuals switching migratory tactic. We used estimates of life history parameters from the natural populations in combination with previous experimental work to evaluate processes maintaining partial migration at the population level and to assess mechanisms influencing the decision to migrate. Based on capture-recapture information on over 3000 individuals, we found that newts can switch migratory tactics over their lifetime. We conclude that migrants and residents coexist through conditional asymmetries, with residents having higher fitness and inferior individuals adopting the migrant tactic. We found that newts are more likely to switch from residency to migrating than the reverse and males were more likely to remain as residents. Migration differences between the sexes are likely driven by reproduction benefits of residency for males and high energetic costs of breeding resulting in lower breeding frequencies for females. Environmental conditions also influence partial migration within a population; we found support for density-dependent processes in the pond strongly influencing the probability of migrating. Our work illustrates how migration can be influenced by a complex range of individual and environmental factors and enhances our understanding of the conditions necessary for the evolution and maintenance of partial migration within populations.

Terrestrial Movements and Habitat Use of Juvenile and Emigrating Adult Eastern Red-Spotted Newts, Notophthalmus Viridescens

Abstract The Eastern Red-Spotted Newt (Notophthalmus viridescens) is one of the most widely distributed salamander species in North America. As with many pond-breeding amphibians, little is known about the terrestrial portion of its life cycle. We examined the activities of terrestrial efts and emigrating, postbreeding adults at Mountain Lake Biological Station in Giles County, Virginia, using fluorescent powder tracking. Neither life cycle stage, sex, nor mass affected the distance newts traveled, but emigrating adults traveled in straighter paths than juveniles. Temperature and rainfall affected whether newts emerged from refuge, whereas rainfall and humidity affected the distance traveled of those that emerged. Newts were often found on or close to the surface, using forest debris for cover, and no newts of any stage were observed using subterranean habitat. Our results indicate that newts are wide-ranging and active in the terrestrial habitat postbreeding. We found fluorescent powder tracking to be effective in the field for multiday tracking with some limitations caused by weather and distance. Our results have implications for the conservation of wide-ranging amphibian species, which may travel long distances from wetlands into terrestrial habitat, outside of protective buffer zones.

Behavioral and physiological female responses to male sex ratio bias in a pond-breeding amphibian

IntroductionThe phenomenon of sexual conflict has been well documented, and in populations with biased operational sex ratios the consequences for the rarer sex can be severe. Females are typically a limited resource and males often evolve aggressive mating behaviors, which can improve individual fitness for the male while negatively impacting female condition and fitness. In response, females can adjust their behavior to minimize exposure to aggressive mating tactics or minimize the costs of mating harassment. While male-male competition is common in amphibian mating systems, little is known about the consequences or responses of females. The red-spotted newt (Notophthalmus viridescens) is a common pond-breeding amphibian with a complex, well-studied mating system where males aggressively court females. Breeding populations across much of its range have male-biased sex ratios and we predicted that female newts would have behavioral mechanisms to mitigate mating pressure from males. We conducted four experiments examining the costs and behavioral responses of female N. viridescens exposed to a male-biased environment.ResultsIn field enclosures, we found that female newts exposed to a male-biased environment during the five-month breeding season ended with lower body condition compared to those in a female-biased environment. Shorter-term exposure to a male-biased environment for five weeks caused a decrease in circulating total leukocyte and lymphocyte abundance in blood, which suggests females experienced physiological stress. In behavioral experiments, we found that females were more agitated in the presence of male chemical cues and females in a male-biased environment spent more time in refuge than those in a female-biased environment.ConclusionsOur results indicate that male-biased conditions can incur costs to females of decreased condition and potentially increased risk of infection. However, we found that females can also alter their behavior and microhabitat use under a male-biased sex ratio. Consistent with surveys showing reduced detection probabilities for females, our research suggests that females avoid male encounters using edge and substrate habitat. Our work illustrates the integrated suite of impacts that sexual conflict can have on the structure and ecology of a population.

Performance of Wild and Laboratory-Reared Gypsy Moth (Lepidoptera: Erebidae): A Comparison between Foliage and Artificial Diet

ABSTRACT The effects of long-term mass rearing of laboratory insects on ecologically relevant traits is an important consideration when applying research conclusions to wild populations or developing management strategies. Laboratory strains of the gypsy moth, Lymantria dispar (L.), an invasive forest pest in North America, have been continuously reared since 1967. Selection on these strains has enhanced a variety of traits, resulting in faster development, shorter diapause, and greater fecundity. As in many mass-reared insects, laboratory strains of the gypsy moth are also reared exclusively on artificial diets that lack much of the phytochemical and nutritional complexity associated with natural foliage.We tested for differences in growth and development of wild gypsy moth populations from across the invasive range in comparison to laboratory strains when reared on artificial diet and a preferred foliage host species, northern red oak (Quercus rubra L.). Overall, caterpillars reared on foliage had higher survival and faster development rates, with smaller differences among populations. When reared on artificial diet, laboratory strains had the highest performance as expected. The response from the wild populations was mixed, with two populations performing poorly on artificial diet and another performing nearly as well as the laboratory strains. Performance on diet was enhanced when larvae received cubed portions changed regularly, as opposed to filled cups. Understanding these relationships between food source and population performance is important for informing studies that examine population comparisons using wild and laboratory- reared strains.

The Effects of Fluorescent Tracking Powder on Oxygen Consumption in Salamanders Using Either Cutaneous or Bimodal Respiration

Abstract Fluorescent powder is gaining attention as an effective method for tracking terrestrial amphibian movements, particularly for species that are too small for conventional tracking equipment. The technique requires coating portions of an animal with fluorescent powder, releasing the animal, and following the trail of powder as it is progressively lost during movement. Recent studies have shown that fluorescent powder has no negative effects on survival or growth. However, a substance that coats the skin, a major respiratory organ in most amphibians, may have sublethal effects on performance and consequently behavior. We tested the effect of fluorescent powder application on the respiration of lungless Red-Backed Salamanders, Plethodon cinereus, and lunged terrestrial Red-Spotted Newts, Notophthalmus viridescens. In comparing species with contrasting skin textures and primary modes of respiration, we expected to find P. cinereus, the species relying solely on cutaneous respiration, more sensitive to fluorescent powder. Standard metabolic rate (SMR) and total oxygen consumption for both species were measured before and after application of the powder. We found no significant differences in respiration between control and powdered salamanders. Independent of treatment, SMR was 6–16% higher during the post-treatment trial in both species, and likewise, total oxygen consumed increased by 8–20% in P. cinereus and by 7–10% in N. viridescens. Our results, in combination with other recent work, suggest that fluorescent powder is a safe technique for tracking amphibians.

Variation in growth and developmental responses to supraoptimal temperatures near latitudinal range limits of gypsy moth Lymantria dispar (L.), an expanding invasive species

Variation in thermal performance within and between populations provides the potential for adaptive responses to increasing temperatures associated with climate change. Organisms experiencing temperatures above their optimum on a thermal performance curve exhibit rapid declines in function and these supraoptimal temperatures can be a critical physiological component of range limits. The gypsy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), is one of the best‐documented biological invasions and factors driving its spatial spread are of significant ecological and economic interest. The present study examines gypsy moth sourced from different latitudes across its North American range for sensitivity to high temperature in constant temperature growth chamber experiments. Supraoptimal temperatures result in higher mortality in northern populations compared with populations from the southern range extent (West Virginia and coastal plain of Virginia, U.S.A.). Sublethal effects of high temperature on traits associated with fitness, such as smaller pupal mass, are apparent in northern and West Virginia populations. Overall, the results indicate that populations near the southern limits of the range are less sensitive to high temperatures than northern populations from the established range. However, southern populations are lower performing overall, based on pupal mass and development time, relative to northern populations. This suggests that there may be a trade‐off associated with decreased heat sensitivity in gypsy moth. Understanding how species adapt to thermal limits and possible fitness trade‐offs of heat tolerance represents an important step toward predicting climatically driven changes in species ranges, which is a particularly critical consideration in conservation and invasion ecology.

Detection of pathogenic Batrachochytrium dendrobatidis using water filtration, animal and bait testing

The pathogen Batrachochytrium dendrobatidis (Bd) can be challenging to detect at endangered amphibian reintroduction sites. Pre-release Bd detection can be confounded by imperfect animal sampling and the absence of animals. In Study 1, we used historical Bd-positive sites, to concurrently evaluate water filtrates and mouth bar (tadpoles) or skin swab (caudates) samples for Bd using molecular beacon realtime PCR. In Study 2, during a natural outbreak, we used PCR to detect Bd from zoospore-attracting keratin baits (three avian, three snake species). In Study 1, no captured animals (n=116) exhibited clinical signs, although 10.6% were positive, representing three of seven species sampled. In contrast, 5.4% of water filters (n=56) were Bd-positive. In Study 2, after short incubation times, a single duck down feather tested Bd-positive. In conclusion, Bd was detected in asymptomatic amphibians and water filtrate at two sites, and from water only, at two other sites. With continued refinement, semi-quantitative Bd water filtrate screening could better define zoospore-specific disease risk, allowing better characterization of the free-living phase of the organisms life cycle. Finally, these results suggest wild aquatic birds (e.g., waterfowl) should be systematically explored as a means of Bd spread. Since large numbers of aquatic birds migrate, even low Bd transfer rates could be a significant means for disease dissemination.

Variation in Allee effects: evidence, unknowns, and directions forward

Allee effects, positive effects of population size or density on per-capita fitness, are of broad interest in ecology and conservation due to their importance to the persistence of small populations and to range boundary dynamics. A number of recent studies have highlighted the importance of spatiotemporal variation in Allee effects and the resulting impacts on population dynamics. These advances challenge conventional understanding of Allee effects by reframing them as a dynamic factor affecting populations instead of a static condition. First, we synthesize evidence for variation in Allee effects and highlight potential mechanisms. Second, we emphasize the “Allee slope,” i.e., the magnitude of the positive effect of density on the per-capita growth rate, as a metric for demographic Allee effects. The more commonly used quantitative metric, the Allee threshold, provides only a partial picture of the underlying forces acting on population growth despite its implications for population extinction. Third, we identify remaining unknowns and strategies for addressing them. Outstanding questions about variation in Allee effects fall broadly under three categories: (1) characterizing patterns of natural variability; (2) understanding mechanisms of variation; and (3) implications for populations, including applications to conservation and management. Future insights are best achieved through robust interactions between theory and empiricism, especially through mechanistic models. Understanding spatiotemporal variation in the demographic processes contributing to the dynamics of small populations is a critical step in the advancement of population ecology.

Repeated exposure to fluorescent powder does not affect survival or mass in Eastern red-spotted newts, Notophthalmus viridescens

Research aimed at determining the extent of terrestrial habitat use by amphibians has been impeded by the difficulties associated with relocating and identifying individuals in the field. Recent studies have used fluorescent powder pigments as a method for tracking short-term terrestrial movements of frogs and salamanders. In a laboratory experiment we found no effect of repeated exposure to two different types of fluorescent powder on mass or survival of terrestrial juvenile and adult Eastern red-spotted newts (Notophthalmus viridescens). We provide further evidence that fluorescent powder tracking is safe for use on amphibians and may be an effective tool for studying terrestrial habitat use.