Applying the tools of ecological immunology to conservation: a test case in the Galapagos sea lion

Abstract

Infectious disease threatens biodiversity and human health on a global scale, and disease emergence may become more common as humans further encroach on habitats and modify environments. To accurately assess the risk of disease emergence in free‐ranging populations of vertebrates, we require an understanding of the dynamics of immunity in the wild. We applied techniques from the emergent discipline of ecological immunology to describe immune activity and dynamics in the endangered Galapagos sea lion Zalophus wollebaeki, which is threatened simultaneously by disease from domestic animals and fluctuations in food supply driven by unpredictable environmental variation. We compared immune activity from shortly after birth until 2 years of age between two Galapagos sea lion colonies: one heavily influenced by humans and the other on an uninhabited island, using a generalized linear model framework. Controlling for development, immune activity was higher in the human‐impacted colony, as assessed with both humoural and cellular immune components and cumulative and snapshot measures of immune activity. We discuss the possibility that sea lions in the human‐impacted colony are under greater immunostimulatory pressure than those in the comparison colony, which could have implications for individual fitness, colony stability and the risk of disease emergence. The study demonstrates the utility of a generalized and widely applicable approach to quantifying immune activity in wild vertebrates, as it highlights important aspects of the system for targeted analysis and further study.

Population Abundance of the Endangered Galapagos Sea Lion Zalophus wollebaeki in the Southeastern Galapagos Archipelago

“…These strategies include management to reduce the contact of humans and domestic dogs with sea lions, health studies in rookeries exposed and not exposed to human disturbances [52,53], the establishment of annual population monitoring in the entire archipelago, and the standardization of count methods. However, strategies for improving the quality of the marine and terrestrial habitats of sea lions have not been fully implemented.…”

Experimental infection dynamics: using immunosuppression andin vivoparasite tracking to understand host resistance in an amphibian-trematode system

“…Understanding variation in disease susceptibility in non-model systems has become a growing priority (Pedersen and Babayan, 2011), particularly in systems where infectious disease represents a conservation threat. For instance, a recent study of cellular and humoral immune activity in endangered Zalophus wollebaeki (Galapagos sea lions) from two colonies revealed that animals in a human-impacted colony suffered greater immune-stimulatory pressure, which could increase the likelihood of disease emergence (Brock et al, 2013).…”

Immune Activity, Body Condition and Human-Associated Environmental Impacts in a Wild Marine Mammal

“…We have previously measured variation in 12 immune-related physiological measures during the first two years of life in the Galapagos sea lion [38], and discussed its significance in the conceptual framework of ecological immunology [8]–[10]. We found that Galapagos sea lions from the human-impacted colony on San Cristobal had relatively higher levels of immune activity – quantified using cell-mediated and humoral immune components, and snapshot and cumulative measures – than sea lions from a colony on the uninhabited island of Santa Fe [38]. In this study we used three of the previously described immune measures: total immunoglobulin G (IgG) concentration, the in vivo inflammation response to phytohemagglutinin (PHA), and total leukocyte concentration.…”

“…In this study we used three of the previously described immune measures: total immunoglobulin G (IgG) concentration, the in vivo inflammation response to phytohemagglutinin (PHA), and total leukocyte concentration. To aid the interpretation of this immune variation we took repeated measurements of known individuals from two age classes [38]: pups (3 months or younger) and juveniles (6 months or older). In pups, in which the involution of the thymus is unlikely to have taken place [39], increases in IgG and total leukocyte concentrations are likely to be driven by the establishment of protective baseline levels in response to the post-natal antigenic environment [40].…”