Mitigating amphibian disease: strategies to maintain wild populations and control chytridiomycosis.

BACKGROUND: Rescuing amphibian diversity is an achievable conservation challenge. Disease mitigation is one essential component of population management. Here we assess existing disease mitigation strategies, some in early experimental stages, which focus on the globally emerging chytrid fungus Batrachochytrium dendrobatidis. We discuss the precedent for each strategy in systems ranging from agriculture to human medicine, and the outlook for each strategy in terms of research needs and long-term potential. RESULTS: We find that the effects of exposure to Batrachochytrium dendrobatidis occur on a spectrum from transient commensal to lethal pathogen. Management priorities are divided between (1) halting pathogen spread and developing survival assurance colonies, and (2) prophylactic or remedial disease treatment. Epidemiological models of chytridiomycosis suggest that mitigation strategies can control disease without eliminating the pathogen. Ecological ethics guide wildlife disease research, but several ethical questions remain for managing disease in the field. CONCLUSIONS: Because sustainable conservation of amphibians in nature is dependent on long-term population persistence and co-evolution with potentially lethal pathogens, we suggest that disease mitigation not focus exclusively on the elimination or containment of the pathogen, or on the captive breeding of amphibian hosts. Rather, successful disease mitigation must be context specific with epidemiologically informed strategies to manage already infected populations by decreasing pathogenicity and host susceptibility. We propose population level treatments based on three steps: first, identify mechanisms of disease suppression; second, parameterize epizootiological models of disease and population dynamics for testing under semi-natural conditions; and third, begin a process of adaptive management in field trials with natural populations.

Antimicrobial peptide defenses in the salamander, Ambystoma tigrinum, against emerging amphibian pathogens.

Skin peptides were collected from living Ambystoma tigrinum larvae and adults and tested against two emerging pathogens, Batrachochytrium dendrobatidis and the Ambystoma tigrinum virus (ATV), as well as bacteria isolated from A. tigrinum. Natural mixtures of skin peptides were found to inhibit growth of B. dendrobatidis, Staphylococcus aureus, and Klebsiella sp., but activity against ATV was unpredictable. Skin peptides collected from salamanders held at three environmentally relevant temperatures differed in activity against B. dendrobatidis. Activity of the A. tigrinum skin peptides was found to be strongly influenced by pH.

Metabolic enzyme activities across an altitudinal gradient: an examination of pikas (genus Ochotona).

Changes in metabolic enzyme activities were examined in three species of pikas that occur over a range of altitudes. Because these closely related mammals live in comparable ecosystems and face similar environmental factors regardless of altitude, modifications of metabolic machinery are probably due to differences in oxygen availability. Citrate synthase (CS), beta-hydroxyacyl CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH) activities were measured in heart, diaphragm, vastus lateralis, gastrocnemius and soleus muscles. Additionally, the activity levels of both M-LDH (skeletal muscle type) and H-LDH (heart type) isozymes were quantified in tissue samples. Pikas from high altitude had greater CS and HOAD activities in heart and diaphragm when compared with pikas from low altitude, while activity levels did not differ in skeletal muscles. The increase in oxidative enzyme activities in tissues with high metabolic demand is thought to enhance oxygen utilization when oxygen availability is low and may reflect greater metabolic demand on heart and diaphragm tissue. Pikas from high altitude were also found to have greater total LDH activities in all tissues examined. High altitude animals had dramatically higher H-LDH activity (2.3-3.8 times greater) while M-LDH activity was more comparable (1.8 times lower to 1.7 times greater) when compared with low altitude animals. High total LDH activity enables pikas to perform short bouts of anaerobic activity, while high levels of H-LDH isozymes may serve to enhance lactate removal and decrease recovery time in animals living at high altitude.