Body condition, skin bacterial communities and disease status: insights from the first release trial of the limosa harlequin frog, Atelopus limosus.

Many endangered amphibian species survive in captive breeding facilities, but there have been few attempts to reintroduce captive-born individuals to rebuild wild populations. We conducted a soft-release trial of limosa harlequin frogs, Atelopus limosus, which are highly susceptible to the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), to understand changes associated with the transition from captivity to the wild. Specifically, we assessed changes in body condition, skin-associated bacterial communities and disease status after release. Frogs were housed individually in field mesocosms and monitored for 27 days. Body condition did not significantly change in the mesocosms, and was similar to, or higher than, that of wild conspecifics at day 27. The skin bacteria of captive-born frogs, based on 16S rRNA gene amplicons, became similar to that of wild conspecifics after 27 days in mesocosms. Prevalence of Bd in wild conspecifics was 13-27%, and 15% of the A. limosus in mesocosms became infected with Bd, but no mortality of infected frogs was observed. We conclude that mesocosms are suitable for systematically and repeatedly monitoring amphibians during release trials, and that body condition, the skin microbiome, and Bd status can all change within one month of placement of captive-born individuals back into the wild.

Skin bacterial communities of neotropical treefrogs vary with local environmental conditions at the time of sampling.

The amphibian skin microbiome has been the focus of recent studies aiming to better understand the role of these microbial symbionts in host defense against disease. However, host-associated microbial communities are complex and dynamic, and changes in their composition and structure can influence their function. Understanding temporal variation of bacterial communities on amphibian skin is critical for establishing baselines from which to improve the development of mitigation techniques based on probiotic therapy and provides long-term host protection in a changing environment. Here, we investigated whether microbial communities on amphibian skin change over time at a single site. To examine this, we collected skin swabs from two pond-breeding species of treefrogs, Agalychnis callidryas and Dendropsophus ebraccatus, over 4 years at a single lowland tropical pond in Panamá. Relative abundance of operational taxonomic units (OTUs) based on 16S rRNA gene amplicon sequencing was used to determine bacterial community diversity on the skin of both treefrog species. We found significant variation in bacterial community structure across long and short-term time scales. Skin bacterial communities differed across years on both species and between seasons and sampling days only in D. ebraccatus. Importantly, bacterial community structures across days were as variable as year level comparisons. The differences in bacterial community were driven primarily by differences in relative abundance of key OTUs and explained by rainfall at the time of sampling. These findings suggest that skin-associated microbiomes are highly variable across time, and that for tropical lowland sites, rainfall is a good predictor of variability. However, more research is necessary to elucidate the significance of temporal variation in bacterial skin communities and their maintenance for amphibian conservation efforts.

Graphene nanoplatelet-reinforced silicone for the valvular prosthesis application.

Newly developed elastomer heart valves have been shown to better re-create the flow physics of native heart valves, resulting in preferable hemodynamic responses. This emergence has been motivated in part by the recent introduction of percutaneous valve approaches in the clinic. Unfortunately, elastomers such as silicone are prone to structural failure, which drastically limits their applicability the development of a valve prosthesis. To produce a mechanically more robust silicone substrate, we reinforced it with graphene nanoplatelets (GNPs). The nanoplatelets were introduced into a two-part silicone mixture and allowed to cure. Cytotoxicity and hemocompatibility tests revealed that the incorporation of GNPs did not adversely affect cell proliferation or augment adhesion of platelets on the surface of the composite materials. Static mechanical characterization by loading in the tensile direction subsequently showed no observable effect when graphene was utilized. However, cyclic tensile testing (0.05 Hz) demonstrated that silicone samples containing 250 mg graphene/L of uncured silicone significantly improved (p<0.05) material fatigue properties compared with silicone-only controls. This finding suggests that for the silicone-graphene composite, static loads were principally transferred onto the matrix. On the other hand, in cyclic loading conditions, the GNPs were recruited effectively to delay failure of the bulk material. We conclude that application of GNPs to extend silicone durability is useful and warrants further evaluation at the trileaflet valve configuration.

Evaluating group housing strategies for the ex-situ conservation of harlequin frogs (Atelopus spp.) using behavioral and physiological indicators.

We have established ex situ assurance colonies of two endangered Panamanian harlequin frogs, Atelopus certus and Atelopus glyphus, but observed that males fought with each other when housed as a group. Housing frogs individually eliminated this problem, but created space constraints. To evaluate the potential stress effects from aggressive interactions when grouping frogs, we housed male frogs in replicated groups of one, two, and eight. We measured aggressive behavioral interactions and fecal glucocorticoid metabolite (GC) concentrations as indicators of stress in each tank. In both small and large groups, frogs initially interacted aggressively, but aggressive interactions and fecal GCs declined significantly after the first 2 weeks of being housed together, reaching the lowest levels by week 4. We conclude that aggressive interactions in same-sex groups of captive Atelopus may initially cause stress, but the frogs become habituated within a few weeks and they can safely be housed in same-sex groups for longer periods of time.