Search for: All records

The potential emergence of Batrachochytrium salamandrivorans (Bsal) in North America threatens salamander diversity and ecosystem functioning, thus an understanding of mechanisms influencing host survival during infection is key to predict future impacts. Previous studies indicate that temperature plays a role in regulating infection dynamics, in that access to a thermal gradient provides the means to prevent infections. Phenotypic flexibility is a likely mechanism, as temperature can enhance (or suppress) host functional capacity in both lunged and lungless salamanders. However, we know very little about how hosts are using thermal environments to achieve effective immune gene expression during Bsal infection. Through a series of experiments, we aim to 1) reveal if interspecific differences in disease susceptibility and functional responses are exacerbated by thermal environments, 2) determine if hosts can minimize the metabolic costs of infections by selecting optimal environments, and 3) project susceptibility risk across the landscape using information about species’ thermal preferences. We discuss our plans to evaluate immune gene expression, metabolic rates and thermoregulation relating to infection with Bsal and access to different thermal environments in plethodontid salamanders from Florida. Additionally, to develop models to predict infection susceptibility, we are seeking collaborations in compiling data on thermal preferences and thermal limits across plethodontid salamander species. 

Comparative analyses in biology rely on the quality of available data. Methodological differences among studies may introduce variation in results that obscure patterns. In the field of eco-immunology, functional immune assays such as antimicrobial capacity assays are widely used for among-species applications. Sample storage time and animal handling time can influence assay results in some species, but how sample holding time prior to freezing influences assay results is unknown. Sample holding time can vary widely in field studies on wild animals, prompting the need to understand the implications of such variation on assay results. We investigated the hypothesis that sample holding time prior to freezing influences assay results in six species (Leiocephalus carinatus, Iguana iguana, Loxodonta africana, Ceratotherium simum, Columba livia, and Buteo swainsoni) by comparing antibacterial capacity of serum with varying processing times prior to snap-freezing. Blood was collected once from each individual and aliquots were placed on ice and assigned different holding times (0, 30, 60, 180, and 240 min), after which each sample was centrifuged, then serum was separated and snap-frozen on dry ice and stored at −80ºC for 60 days prior to assaying. For each aliquot, we conducted antibacterial capacity assays with serial dilutions of serum inoculated with E. coli and extracted the dilution at 50% antibacterial capacity for analysis. We found a decrease in antibacterial capacity with increased holding time in one of the six species tested (B. swainsoni), driven in part by complete loss of antibacterial capacity in some individuals at the 240-min time point. While the majority of species’ antibacterial capacity were not affected, our results demonstrate the need to conduct pilot assays spanning the anticipated variation in sample holding times to develop appropriate field protocols.

 

Ontogenetic shifts in venom occur in many snakes but establishing their nature as gradual or discrete processes required additional study. We profiled shifts in venom expression from the neonate to adult sizes of two rattlesnake species, the eastern diamondback and the timber rattlesnake. We used serial sampling and venom chromatographic profiling to test if ontogenetic change occurs gradually or discretely. We found evidence for gradual shifts in overall venom composition in six of eight snakes, which sometimes spanned more than two years. Most chromatographic peaks shift gradually, but one quarter shift in a discrete fashion. Analysis of published diet data showed gradual shifts in overall diet composition across the range of body sizes attained by our eight study animals, while the shifts in abundance of different prey classes varied in form from gradual to discrete. Testosterone concentrations were correlated with the change in venom protein composition, but the relationship is not strong enough to suggest causation. Venom research employing simple juvenile versus adult size thresholds may be failing to account for continuous variation in venom composition lifespan. Our results imply that venom shifts represent adaptive matches to dietary shifts and highlight venom for studies of alternative gene regulatory mechanisms.