Current health status of the Adélie penguin (Pygoscelis adeliae) on Ross Island, Antarctica: a seabird in an extreme environment, and an evaluation of its resilience to disease threats

Abstract

Antarctica is the most isolated of all the continents, separated from the other major landmasses by vast expanses of oceans. Due to its position at the southern geographic pole of our planet, its other attributes consist of a list of extremes - the coldest, windiest, driest, and highest in terms of both latitude and elevation. As such, its animal life has evolved in isolation for at least 30 million years when the Drake Passage opened up, relinquishing Antarctica’s handhold to South America and thus the rest of the world. This isolation and the extreme environment have most likely buffered Antarctic megafauna against the continuous assault of the infectious disease agents commonly affecting wildlife in other parts of the globe and might have also had a profound effect on the evolution of the immune systems of these animals. In light of a changing climate and increased human activity in the Antarctic Treaty area, there is a need to determine if this isolation might have placed Antarctic species at risk in terms of their ability to respond to infectious disease agents. This research seeks to answer several questions relating to the ability of one of the avian species found in the Antarctic, the Adélie penguin (Pygoscelis adeliae Hombron & Jacquinot, 1841) on Ross Island, to be able to respond to infectious disease agent exposure in the future. The first issue I addressed involved identifying the drivers of infectious diseases on a global scale and then seeking to determine which of those would be relevant within the Antarctic Treaty area. For human and animal populations worldwide, the drivers of disease emergence have been described generally as (human) population expansion, increased travel and trade, escalation in livestock production, antibiotic abuse, habitat fragmentation and degradation, and climate change (Daszak et al 2001; Murray & Daszak 2013). My synthesis of the literature revealed that of the drivers of disease in wildlife worldwide, those most likely to affect the health of Antarctic wildlife were: pollution (related to habitat degradation), interconnectivity (through means of migratory fauna and increased human travel), and the physical and biological effects of climate change. I next sought to determine the nature and extent of infectious diseases affecting penguin species and which ones might have an impact on the Adélie penguins on Ross Island. My review of the literature showed that penguin species are exposed to and affected by a variety of microbial agents, though only viruses and bacteria are dealt with in this thesis. The most common of those investigated were avian influenza A, Newcastle disease, and infectious bursal disease. These three, plus West Nile disease, then became the focus of my multi-year serological study, that found no antibodies to avian influenza A or West Nile viruses in the three-year study period. On the other hand, there were low-titre positive results for antibodies to Newcastle disease virus (in one year only) and infectious bursal disease virus (all three years). I conclude that there is an apparent transience in these viral diseases but their ecology is not known and additional work would be required to determine if these agents are indeed present on Ross Island. To further address the question of the Adélie penguin’s ability to respond to infectious agents, I employed a variety of methods ranging from ‘old school’ laboratory techniques to cutting-edge next-generation sequencing. Two of the tools commonly used to gain insight into the health status of an individual in human and veterinary medicine are the manual leukocyte (or white blood cell) differential and the hematocrit; I established reference intervals for each of these. I also developed a novel molecular method incorporating real-time polymerase chain reaction (RT-PCR) for determining the sex of Adélie penguins. The output of the RT-PCR shows that males unambiguously produce a single peak and females produce a double peak, consistent with other traditional, but tedious and time-consuming, molecular methods used to determine the sex of birds. This method was used to ascertain the sex of all individuals whose samples were used for white blood cell differentials and hematocrits. No statistically significant differences in the values of either test were found between the sexes. These two tests can now be used without having to know the sex of individuals, as the normal ranges would apply to either sex. I used PCR and Sanger sequencing for characterization of Toll-like receptors (TLRs), a key component of the vertebrate innate immune system responsible for initiating a cascade of host immune responses to pathogens. Sequences of six of the ten known avian TLRs were produced. Analysis of the sequences of a small set of four geographically wide-ranging Adélie penguin populations (n = 3/population) demonstrated a high degree of heterogeneity (relative to the findings of the few other studies on avian TLRs). This is important for Adélie penguins, as this would suggest that these birds have the immunological capacity to respond to novel microorganisms. An observation of a previously unreported feather loss condition in Adélie penguins on Ross Island prompted an initial investigation into possible causes. I used metagenomic analysis combined with scanning electron microscopy and white blood cell differentials for pathogen discovery in an attempt to identify the cause of this abnormal feather loss condition. While no definitive cause emerged from somewhat limited samples, further studies into this abnormal occurrence should be conducted as this might represent an emerging disease. Finally, I discuss the overall findings of the chapters in this thesis, limitations of this research, and give some suggestions for future research. The results presented in the chapters that follow can be used as a benchmark for future comparisons and some of the methods described in this thesis can be employed in research, not only for the Adélie penguin, but also for other penguin species found elsewhere.