Zachary H. Olson

An eDNA approach to detect eastern hellbenders (Cryptobranchus a. alleganiensis) using samples of water

Abstract Context. Environmental DNA, or eDNA, methods are a novel application of non-invasive genetic sampling in which DNA from organisms is detected via sampling of water or soil, typically for the purposes of determining the presence or absence of an organism. eDNA methods have the potential to revolutionise the study of rare or endangered taxa. Aims. We evaluated the efficacy of eDNA sampling to detect populations of an amphibian of conservation concern, the eastern hellbender (Cryptobranchus a. alleganiensis), indirectly from their aquatic environments. Methods. We developed species-specific primers, validated their specificity and sensitivity, and assessed the utility of our methods in silico and in laboratory trials. In the field, we collected water samples from three sites with known densities of hellbenders, and from one site where hellbenders do not occur. We filtered water samples, extracted DNA from filters, and assayed the extraction products for hellbender DNA by using polymerase chain reaction (PCR) and gel electrophoresis. Key results. Our methods detected hellbenders at densities approaching the lowest of reported natural densities. The low-density site (0.16 hellbenders per 100 m2) yielded two positive amplifications, the medium-density site (0.38 hellbenders per 100 m2) yielded eight positive amplifications, and the high-density site (0.88 hellbenders per 100 m2) yielded 10 positive amplifications. The apparent relationship between density and detection was obfuscated when river discharge was considered. There was no amplification in any negative control. Conclusion. eDNA methods may represent a cost-effective means by which to establish broad-scale patterns of occupancy for hellbenders. Implications. eDNA can be considered a valuable tool for detecting many species that are otherwise difficult to study.

Reducing Baylisascaris procyonis Roundworm Larvae in Raccoon Latrines

Baylisascaris procyonis roundworms, a parasite of raccoons, can infect humans, sometimes fatally. Parasite eggs can remain viable in raccoon latrines for years. To develop a management technique for parasite eggs, we tested anthelmintic baiting. The prevalence of eggs decreased at latrines, and larval infections decreased among intermediate hosts, indicating that baiting is effective.

Spatio-temporal variation in the demographic attributes of a generalist mesopredator

Human land-use practices have dramatically altered the composition and configuration of native habitats throughout many ecosystems. Within heterogeneous landscapes generalist predators often thrive, causing cascading effects on local biological communities, yet there are few data to suggest how attributes of fragmentation influence local population dynamics of these species. We monitored 25 raccoon (Procyon lotor) populations from 2004 to 2009 in a fragmented agricultural landscape to evaluate the influence of local and landscape habitat attributes on spatial and temporal variation in demography. Our results indicate that agricultural ecosystems support increased densities of raccoons relative to many other rural landscapes, but that spatial and temporal variation in demography exists that is driven by non-agricultural habitat attributes rather than the availability of crops. At the landscape scale, both density and population stability were positively associated with the size and contiguity of forest patches, while at the local scale density was positively correlated with plant diversity and the density of tree cavities. In addition, populations occupying forest patches with greater levels of plant diversity and stable water resources exhibited less temporal variability than populations with limited plant species complexity or water availability. The proportion of populations comprised of females was most strongly influenced by the availability of tree cavities and soft mast. Despite the abundance of mesopredators in heterogeneous landscapes, our results indicate that all patches do not contribute equally to the regional abundance and persistence of these species. Thus, a clear understanding of how landscape attributes contribute to variation in demography is critical to the optimization of management strategies.

Use of Rhodamine B to Reveal Patterns of Interspecific Competition and Bait Acceptance in Raccoons

Abstract Passive treatment of raccoons (Procyon lotor) through distribution of vaccine-laden baits recently has emerged as a potential solution to address health and economic conflicts associated with raccoon rabies and may have applications in the management of other pathogens carried by raccoons if frequent bait deployments are used. Consumption of baits by nontarget species reduces the efficiency in which baits can be used to manage wildlife disease, although no study has explicitly evaluated the influence of bait competitor density on the ability to treat raccoons. Our objectives were to use the biomarker Rhodamine B (RB) to 1) evaluate patterns of raccoon bait acceptance as a function of competition with Virginia opossums (Didelphis virginiana), the dominant bait competitor; 2) characterize attributes of opossum bait acceptance to improve efficiency of raccoon treatment; and 3) evaluate the effect of repeated bait exposure on rates of bait acceptance as may be required in the management of wildlife disease issues beyond rabies. Identifying bait consumption by individuals based on the presence of an RB mark in a sample of whiskers, we used logistic regression to model raccoon and opossum bait acceptance as a function of bait availability, previous exposure to baits, demographic attributes, and an index of time spent in the baited area (residency index). For both raccoons and opossums, the best measure of bait availability was the variable number of baits per opossum. The most parsimonious logistic regression model for raccoon bait acceptance included the variables baits per opossum, exposure history, and residency index. The strength of the variable baits per opossum relative to competing measures of bait availability indicated bait consumption by opossums significantly limited the ability to treat raccoons. The most parsimonious model for opossum acceptance was composed of the variables baits per opossum, sex, weight, residency index, baits per opossum × sex, and weight × sex. Patterns of opossum bait acceptance likely were driven by effects of bait availability and sex-dependent differences in movement. Our results call attention to the importance of bait competition in limiting the ability to effectively treat raccoon populations through distribution of baits and suggest managers incorporate information on density of bait competitors, particularly opossums, in allocation of baits.

A Genetic Analysis of the Virginia Opossum Mating System: Evidence of Multiple Paternity in a Highly Fragmented Landscape

Using molecular techniques, we examined patterns of paternity in Virginia opossums occupying a highly fragmented agricultural landscape in northern Indiana. During 2008, we collected tissue from 64 females and their pouch young in 34 forest patches distributed over a 1100-km(2) region. Using genotypes from 10 microsatellite loci, we determined the minimum number of fathers contributing to each litter using GERUD 1.0. Genotyped offspring with known mothers were then analyzed using CERVUS 3.0, incorporating genotypes from 317 males sampled from 2007-2008 to identify potential fathers. Our analyses revealed that promiscuity was common among females, with 26 (41%) litters having > or = 2 sires. Despite the fact that we intensively sampled forest patches for potential fathers, we only were able to identify 13 fathers contributing to 14 litters, with an average Euclidean distance of 18.7 km between father-offspring pairs found in disparate patches (N = 6). Our inability to identify most (85%) fathers of sampled litters, coupled with the extensive distances observed between putative father-offspring pairs, suggests that opossums may not maintain explicit home ranges in highly fragmented landscapes.

Evaluation of experimental genetic management in reintroduced bighorn sheep

Positive demographic responses have been reported in several species where the immigration or supplementation of genetically distinct individuals into wild populations has resulted in a genetic rescue effect. However, rarely have researchers incorporated what could be considerable risk of outbreeding depression into planning for genetic management programs. We assess the genetic effects of an experiment in genetic management involving replicate populations of California bighorn sheep (Ovis canadensis californiana) in Oregon, USA, which previously experienced poor productivity and numerical declines. In the experiment, two declining populations were supplemented with ewes from a more genetically diverse population of California bighorn sheep in Nevada. We incorporated analysis of genetic samples representing both experimental populations prior to supplementation, samples from the supplemented individuals, and samples collected from both experimental populations approximately one generation after supplementation. We used genetic analyses to assess the integration of supplemented and resident populations by identifying interpopulation hybrids. Further, we incorporated demographic simulations to assess the risk of outbreeding depression as a result of the experimental augmentation. Finally, we used data from microsatellites and mitochondrial sequences to determine if genetic management increased genetic diversity in the experimental populations. Our analyses demonstrated the success of genetic management by documenting interpopulation hybrids, identifying no evidence for outbreeding depression as a result of contact between the genetically distinct supplemented and resident populations, and by identifying increased population-level metrics of genetic diversity in postsupplementation populations compared with presupplementation levels.

Survival Estimates for Adult Eastern Hellbenders and Their Utility for Conservation

Abstract The Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) is a large, completely aquatic salamander native to the eastern United States. Hellbender populations have experienced numerical declines and range contractions over a large geographic area, but few demographic data are available to allow biologists to diagnose specific causes of the declines. We estimated survival of Hellbenders in Indiana using radio telemetry. We monitored 21 adult eastern Hellbenders during July 2008–October 2009 and documented three mortalities. Using a known-fate model, we estimated annual survival as 0.804 (±0.089 SE). This estimate is lower than expected for a long-lived species and signals the continued decline of Hellbenders in Indiana. Estimates of survivorship such as this provide baseline data for translocation programs and are useful in parameterizing population models.

Survival of Timber Rattlesnakes (Crotalus horridus): Investigating Individual, Environmental, and Ecological Effects

Abstract:  A major effort in species conservation is the construction of life-history models to better predict, identify, and respond to population changes. Yet demographic studies linking individual, environmental, and ecological factors to survival are rare. We used radio telemetry to monitor 47 adult Timber Rattlesnakes (Crotalus horridus) during five active seasons and four overwinter periods from April 2007–November 2011 in south-central Indiana, USA. The study period serendipitously encompassed an oak (Quercus spp.) mast failure and subsequent 50% decline in prey abundance, allowing us to test hypotheses about ecological effects on survival. We detected 10 mortalities. The causes of mortality during active seasons included predation (n  =  5), human persecution (n  =  2), and vehicle strike (n  =  1). Variation in active season survival was explained best by the interaction of sex and prey availability along with an effect of marking cohort. Seasonal survival estimates ranged from 0.720–0.983 with female survival decreasing by at least 15% the year after prey availability declined. Overwinter survival was high in general (n  =  2 mortalities), with estimates weakly affected by sex (male  =  0.966; female  =  0.990) and decreasing slightly with colder monthly temperatures. Although ecological effects were most powerful in our study, 30% of mortalities were associated with human activities. Focused education and outreach efforts may be useful for improving survival of Timber Rattlesnakes.

Detecting spiny dogfish in grey seal diets

Grey seal (Halichoerus grypus) populations declined dramatically in U.S. waters during the nineteenth and twentieth centuries, but have rebounded in recent decades as a result of legal protection. In the Gulf of Maine, increasing grey seal populations have the potential to impact commercially important groundfish species such as cod and haddock, but the potential also exists for more complex ecological interactions to occur given the recent increase of spiny dogfish (Squalus acanthias), another potential groundfish predator. Specifically, seal predation on dogfish could free groundfish species from additional predation pressure. Little quantitative data exists on intraguild predation rates by grey seals on spiny dogfish, in part because of the limitations of current methods of food habits analysis for grey seals. We report the development, validation, and field testing of a non-invasive genetic method for the detection of spiny dogfish in grey seal diets using DNA collected from seal feces. Our method amplified spiny dogfish DNA from 10 of 10 positive control scats from a captive seal with a known diet, and amplified spiny dogfish DNA from 0 of 10 negative control scats. We field tested the method on 20 scats from wild seals and detected spiny dogfish in two of the samples. All positive amplifications were sequenced to verify the species identify, and all were spiny dogfish. Our method has the potential to provide valuable information about changing predator prey dynamics in the Gulf of Maine and elsewhere.