Thomas S. Risch

Reproductive and resource benefits to large female body size in a mammal with female-biased sexual size dimorphism

Factors underlying the evolution of female-biased sexual size dimorphism in mammals are poorly understood. In an effort to better understand these factors we tested whether larger female southern flying squirrels, Glaucomys volans, gained reproductive advantages (larger litters or more male mates) and direct resource benefits, such as larger home ranges or access to more food (i.e. mast-producing trees). As dimorphism can vary with age in precocial breeding species, we compared females during their first reproduction and during a subsequent breeding attempt. Females were not significantly larger or heavier than males at first reproduction, but became about 7% heavier and 22% larger than males at subsequent breeding. Larger females produced larger litters and had home ranges containing a greater proportion of upland hardwood trees. Female body size was not associated with either multiple male mating or home range size, but females with larger home ranges had higher indexes of body condition. Females in precocial breeding flying squirrels initiate reproduction before sexual size dimorphism is evident, and thus, may be allocating resources to both reproduction and growth simultaneously, or delaying growth entirely. Larger females produce more pups and have access to more food resources. Thus, selection for increased female size may partly explain how female-biased sexual size dimorphism is maintained in this species.

TRAP HEIGHT AND CAPTURE SUCCESS OF ARBOREAL SMALL MAMMALS : EVIDENCE FROM SOUTHERN FLYING SQUIRRELS (GLAUCOMYS VOLANS)

Studies of small mammals often use live traps, but the effect of different trapping heights on capture effectiveness of arboreal mammals has not been directly addressed. We compared the capture success of three trap heights ({open_quotes}low{close_quotes} = 2m, {open_quotes}medium{close_quotes} = 4.5-5m, and {open_quotes}high{close_quotes} high = 8-8.5 m) in capturing arboreal mammals. Southern flying squirrels (Glaucomys volans) constituted 86% of the captures. Low traps captured approximately half as many squirrels (15) as either medium (30) or high traps (28), and individual squirrels were recaptured at a single trap height more often than expected based on chance. Traps at the three heights exhibited significantly heterogeneity in initially capturing individual flying squirrels (i.e., previously unmarked squirrels). The hypothesis that trap height does not affect capture success of southern flying squirrels in southern forests during the summer is rejected. The general importance of trap height in studies of mammalian community ecology and conservation is discussed. 32 refs., 4 tabs.

The Use of Nest Boxes to Sample Arboreal Vertebrates

Abstract Tree cavities are rarely incorporated into surveys of forest ecosystem biodiversity, due to difficultly in their systematic sampling. We examined the feasibility of using southern flying squirrel (Glaucomys volans Thomas) nest boxes for monitoring arboreal vertebrates at 11 sites within the Savannah River Site, SC. We recorded 3130 vertebrates of 11 species (3 mammals, 3 birds, 5 reptiles) using nest boxes for nesting, roosting, and foraging. G. volans represented the majority of these with 3019 individuals, but flying squirrel occupancy did not affect occupancy of boxes by other species. Upland hardwood forests had the most species that used boxes; however, due to uneven sampling, nest boxes placed in dense-canopy plantations detected the most species per box. We conclude that nest boxes are a useful means of surveying for cavity-dwelling species. We recommend a protocol that uses different size nest boxes at varying heights to accurately survey a traditionally under-sampled component of forest ecosystems, those species using tree cavities.

Isolation and identification of an extracellular subtilisin-like serine protease secreted by the bat pathogen Pseudogymnoascus destructans.

White nose syndrome (WNS) is a cutaneous fungal disease of bats. WNS is responsible for unprecedented mortalities in North American cave bat populations. There have been few descriptions of enzyme activities that may function in WNS host/pathogen interactions, while no study has isolated and described secreted proteases. To address the hypothesis that Pseudogymnoascus destructans secretes extracellular proteases that function in wing necrosis during WNS infection, the object of this study was to culture P. destructans on various media, then isolate and structurally identify those proteases accumulated stably in the culture medium. We found a single dominant protease activity on minimal nutrient broth enriched with protein substrates, which was strongly inhibited by phenylmethylsulfonyl fluoride. This P. destructans serine protease (PdSP1) was isolated by preparative isoelectric focusing and concanavalin A lectin affinity chromatography. PdSP1 showed a molecular weight 27,900 (estimated by SDS-PAGE), broad pH optimum 6-8, and temperature optimum 60°C. Structural characterization of PdSP1 by MALDI-TOF MS, Orbitrap MS/MS, and Edman amino-terminal peptide sequencing matched it directly to a hypothetical protein accession from the sequenced P. destructans genome that is further identified as a MEROPS family S8A subtilisin-like serine peptidase. Two additional isoforms, PdSP2 and PdSP3, were identified in the P. destructans genome with 90% and 53% homology, respectively. P. destructans S8A serine proteases showed closer sequence conservation to P. pannorum and plant pathogenic fungi than to human pathogenic dermatophytes. Peptide-specific polyclonal antibodies developed from the PdSP1 sequence detected the protein in western blots. These subtilisin-like serine proteases are candidates for further functional studies in WNS host-pathogen interaction.

Sebaceous Lipid Profiling of Bat Integumentary Tissues: Quantitative Analysis of Free Fatty Acids, Monoacylglycerides, Squalene, and Sterols

White‐nose syndrome (WNS) is a fungal disease caused by Pseudogymnoascus destructans and is devastating North American bat populations. Sebaceous lipids secreted from host integumentary tissues are implicated in the initial attachment and recognition of host tissues by pathogenic fungi. We are interested in determining if ratios of lipid classes in sebum can be used as biomarkers to diagnose severity of fungal infection in bats. To first establish lipid compositions in bats, we isolated secreted and integral lipid fractions from the hair and wing tissues of three species: big brown bats (Eptesicus fuscus), Eastern red bats (Lasiurus borealis), and evening bats (Nycticeius humeralis). Sterols, FFAs, MAGs, and squalene were derivatized as trimethylsilyl esters, separated by gas chromatography, and identified by mass spectrometry. Ratios of sterol to squalene in different tissues were determined, and cholesterol as a disease biomarker was assessed. Free sterol was the dominant lipid class of bat integument. Squalene/sterol ratio is highest in wing sebum. Secreted wing lipid contained higher proportions of saturated FFAs and MAGs than integral wing or secreted hair lipid. These compounds are targets for investigating responses of P. destructans to specific host lipid compounds and as biomarkers to diagnose WNS.

Keeping Tabs: Are Redundant Marking Systems Needed for Rodents?

Abstract We use survival analysis to compare failure of passive integrated transponder (PIT) tags and loss of metal ear tags in 2,277 southern flying squirrels (Glaucomys volans), 124 house mice (Mus musculus), 112 hispid cotton rats (Sigmodon hispidus), and 374 deer (Peromyscus maniculatus) and cotton mice (P. gossypinus). With the exception of cotton rats, failure rates between ear and PIT tags differed by species. Flying squirrels exhibited the highest proportional loss of both tag types and lost ear tags more readily than PIT tags failed. The opposite was true for cotton rats and deer and cotton mice. Most PIT tags appeared to fail shortly after implantation (≤3 days), except for flying squirrels and, to a lesser extent, cotton rats. Ear tags exhibited a consistent rate of loss in flying squirrels. Body mass did not influence failure of PIT tags; however, flying squirrel body mass was associated with increased loss of ear tags. For flying squirrels PIT tag failure increased with the number of times an individual had already received a PIT tag that failed. We provide recommendations for using PIT and ear tags in marking rodents based on species-specific patterns and suggest the combined use of external and internal markers to obtain the most reliable estimates of population parameters.

Live Trap for Pocket Gophers

Abstract We presented a new trap for pocket gophers and compared its effectiveness with the Baker and Williams live trap. Our box trap readily captured juveniles ≥44 g and adults ≤294 g. We had ≤50% capture success. In general, capture success was similar to the Baker and Williams live trap. However, analyses suggested that our trap was superior in some aspects, e.g., capture of heavier pocket gophers and males. Our trap was user friendly and could be employed to equally capture all portions of a population of pocket gophers.

Profiling the Triacylglyceride Contents in Bat Integumentary Lipids by Preparative Thin Layer Chromatography and MALDI-TOF Mass Spectrometry

The mammalian integument includes sebaceous glands that secrete an oily material onto the skin surface. Sebum production is part of the innate immune system that is protective against pathogenic microbes. Abnormal sebum production and chemical composition are also a clinical symptom of specific skin diseases. Sebum contains a complex mixture of lipids, including triacylglycerides, which is species-specific. The broad chemical properties exhibited by diverse lipid classes hinder the specific determination of sebum composition. Analytical techniques for lipids typically require chemical derivatizations that are labor-intensive and increase sample preparation costs. This paper describes how to extract lipids from mammalian integument, separate broad lipid classes by thin-layer chromatography, and profile the triacylglyceride contents using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This robust method enables a direct determination of the triacylglyceride profiles among species and individuals, and it can be readily applied to any taxonomic group of mammals.

Distribution and Habitat Attributes of an Endemic Subspecies of Pocket Gopher

Abstract Ozark pocket gophers, Geomys bursarius ozarkensis, are endemic to Izard County, Arkansas with a distribution of ∼2300 km2. Limited data exists on this subspecies; thus, we collected vegetation and soil habitat data within the current range. Pocket gophers were present in 11 named soil types with loamy sand being the most common texture. No statistical significance was found between pocket gopher density and several soil parameters. We documented pocket gophers predominantly occurring in grazing land, hay fields and lawns. Twenty-one families of vegetation were recorded from samples collected from pocket gopher habitat.

Habitat Associations of Bottomland Bats, With Focus on Rafinesque's Big-Eared Bat and Southeastern Myotis

ABSTRACT Bottomland forests in the eastern United States are used by bat populations for both roosting and foraging. To quantify habitat characteristics important to bat presence in the Mississippi River alluvial valley, we measured forest habitat variables and related them to bat captures obtained in six management areas located near Jonesboro, Arkansas. Forest measurements included species composition, stem count, canopy height, basal area, canopy coverage and percent vegetative ground coverage for trees found in 120 0.03-ha circular plots from 12 bat capture sites. Principal component analysis was conducted on habitat data, and compared to bat captures by use of multiple regression analysis. Interaction effects due to the nested structure of the sampling design were measured with mixed linear models. We found significant correlations between total bat captures, composed of all captures for eight species and forests of high stem count and vegetative ground cover. Mixed model analysis revealed that Rafinesques big-eared bats (Corynorhinus rafinesquii) were more likely to be captured at dry corridor sites than corridors over water, where as regression analysis revealed a significant (P  =  0.016) relationship between southeastern myotis and percent oaks.