Improving Natural History Research with Image Analysis: The Relationship Between Skin Color, Sex, Size and Stage in Adult Red-Spotted Newts

Natural history researchers are increasingly using digital cameras and computer software to measure their study animals. Adult Red-spotted Newts (Notophthalmus viridescens viridescens) are known to display a range of skin colors, from brown to green, but it has not been possible to quantify this variation until the advent of image analysis technology. We used an image analysis approach to compare skin color between sexes, across a range of sizes, and between aquatic and post-breeding (emigrating to the terrestrial habitat) stage adult newts. From 232 individuals (53% male, 47% female) we documented a wide but subtle range of skin colors, measured as the average hue value of all pixels in digital images of each newt body. We found that terrestrial post-breeding individuals were browner than aquatic individuals, consistent with the morphological adaptations of emigrating individuals for the terrestrial habitat. However, we also discovered that males were statistically greener than females but this effect depended on their stage. We suggest this difference may represent different degrees of adaptation for the terrestrial habitat between the sexes. Finally, we used image analysis to obtain measures of body length comparable to traditional snout-vent length and a measure of total body surface area, which provided a better correlation with newt mass than did body length and therefore could potentially serve as an alternative to mass or body condition. We suggest that image analysis methodology offers great promise for future questions relating to size and color in amphibians and provides researchers with an improved way to study aspects of the natural history of amphibians

\u3ci\u3eAmbystoma maculatum\u3c/i\u3e (Spotted Salamander) Occurrence

Natural History Notes: Ambystoma maculatum is a wide ranging mole salamander found from Nova Scotia and southern Ontario through Georgia and eastern Texas (Conant and Collins 1998)

Spots of Adult Male Red-Spotted Newts are Redder and Brighter than in Females: Evidence for a Role in Mate Selection?

As aquatic adults, eastern red-spotted newts (Notophthalmus v. viridescens) are generally green with two rows of dorsal spots, which vary in number between individuals and range in colour from orange to red. The function of these spots is unknown, but it is possible that they serve as sexual ornamentations and we examined this hypothesis by testing for sexual dimorphism in spot characteristics. We used an image analysis approach that has been used previously with this and other amphibian species to compare the number, size and colour – redness (hue score) and brightness – of spots in 100 male and 100 female aquatic adult newts captured during the breeding season in Virginia. While we found no apparent sex-related differences in the numbers of spots, and only a minor difference in spot sizes, we discovered that adult male red-spotted newts had significantly redder and more brightly coloured dorsal spots than did females. We also found that spot brightness is positively associated with body size. As male red-spotted newts entice females to mate in part with a highly visual display (the “hula dance”), the sexual dimorphism in spot colour we found could be associated with this display. Our results, taken together with current knowledge on the carotenoid pigments behind the red spot colour, suggest a role for spot coloration in the mating system of N. v. viridescens that should be examined further and considered in other studies of mate choice. In a more general sense, this discovery also leads us to question if this phenomenon is present in other amphibian species previously thought to be “monomorphic”

Glow Sticks as Effective Bait for Capturing Aquatic Amphibians in Funnel Traps

Funnel traps of various designs have been used to capture adults and larvae of aquatic amphibians (e.g., Buech and Egeland 2002; Richter 1995). Most studies use unbaited funnel traps to capture amphibians while others have used shrimp or salmon eggs (Adams et al. 1997). Light traps and light sticks are commonly used in studies of fish, particularly larvae (Doherty 1987; Marchetti et al. 2004), but have not been widely used to capture amphibians. Glow sticks have been mentioned briefly in the literature as a means to increase capture rates of aquatic amphibians (Smith and Rettig 1996), but no studies have estimated their effectiveness. In this study we compared the capture success of unbaited funnel traps and funnel traps baited with glow sticks

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

Survival, Breeding Frequency, and Migratory Orientation in the Jefferson Salamander, \u3ci\u3eAmbystoma Jeffersonianum\u3c/i\u3e

Accurate estimates of demographic parameters, such as survival and breeding frequency, are necessary for the conservation and management of animal populations. Additionally, life-history data are required for gaining an empirical understanding of the ecology of natural populations. We monitored a population of Jefferson Salamanders (Ambystoma jeffersonianum) breeding in a permanent mountain-top pond at the southern limit of this species’ geographic range in Virginia over four years. We used closed multistate mark-recapture models with Pollock\u27s robust design to estimate the demographic parameters of this population. Additionally, we used point-of-capture data to compare the orientation of migrations into and out of the pond within and among years. Our model selection results support consistent annual adult survival across years with higher estimates for males compared to females. Our estimates of the probability of breeding in sequential years were high for both sexes during the four years of our study. Our model rankings and capture probability estimates indicate that females had a higher probability of detection when entering the breeding pond, likely reflecting differences between the sexes in arrival time to the pond. We found directionality in some, but not all, annual migrations, despite indications of individual fidelity in orientation across years. Our study provides the first estimates of breeding probability and assessment of migratory orientation patterns for A. jeffersonianum and contributes to the understanding of the reproductive ecology and natural history of pond-breeding amphibians

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

A Threat to New Zealand\u27s Tuatara Heats Up

No matter how many times we head to one of New Zealand\u27s offshore islands, the feelings are always a mix of sheer awe at the beauty and biodiversity preserved in these special refuges and lingering nerves. Did we remember all the gear? Do we have enough food and water in case we get stuck? Can the helicopter land on the side of a cliff in these winds? These epic journeys are in pursuit of a lone remnant of the reptile evolutionary tree, with a unique ecology that has big implications under climate change

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

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, Notophtholmus 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

Spatiotemporal Variability in Allee Effects of Invading Gypsy Moth Populations

The Allee threshold, the critical population density separating growth from decline in populations experiencing strong Allee effects, can vary over space and time but few empirical studies have examined this variation. A lack of geographically extensive, long-term studies on low density population dynamics makes studying variability in Allee effects difficult. We used North American gypsy moth population data from 1996-2016 to quantify Allee thresholds in 11 regions of the invasion front. Allee thresholds spanned a continuum from being undetectable due to strong population growth at all densities, to being unmeasurable because populations declined across all densities. The lag-1 temporal autocorrelation in Allee thresholds tended to be negative and spatial synchrony in Allee thresholds extended no further than adjacent regions. This work furthers understanding of spatiotemporal variation in Allee effects using extensive empirical data at the range edge of an invasive insect