World Turtle Day is celebrated on 23 May every year since its inception in 2000. The American Tortoise Rescue sponsors this day of awareness to bring attention to one of the world’s oldest reptiles, and encourage humans to help in the conservation and protection of these grand animals. In honour of these grandiose creatures, we have compiled a reading list of biology titles and articles that have helped to further research into the conservation biology of all chelonians.
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By Rebecca Cramp
In recent decades, the extraordinarily rapid disappearance of frogs, toads, and salamanders has grabbed the attention of both the scientific community and concerned citizens the world over. Although the causes of some of these losses remain unresolved, the novel disease chytridiomycosis caused by the skin-based fungus Batrachochytrium dendrobatidis (Bd), has been identified as the causative agent in many of the declines and extinctions worldwide. Bd is now regarded as being responsible for the greatest disease-driven loss of vertebrate biodiversity in recorded history. Like other entirely cutaneous microbes, interactions with the skin of its host determine how and under what conditions the fungus can induce disease.
The skin plays an important role in immune defence. In the first instance, skin acts as a physical barrier against microbes and pathogens. It also produces anti-microbial skin secretions and supports a large microbial community made up of good (commensal), bad (pathogenic) and indifferent (neither good nor bad; having no discernable effect) microbes. Like most animals, the outer skin layer of amphibians is shed (sloughed) on a regular basis—as often as daily to every couple of weeks. However, unlike mammals, amphibians shed (and often eat) the entire outer skin layer in one piece. Therefore, anything adhering to or within that outer layer would be lost from the body every time the animal sloughs it skin. As such, regular sloughing could play a role in regulating the abundance and persistence of microbes (including Bd) at the body’s surface. To date, however, the potential for regular skin sloughing to serve as an immune defense strategy in amphibians has been largely overlooked.
A green tree frog. Photo by Ed Meyer.
To test the hypothesis that sloughing in plays a role in the management of cutaneous microbe abundance, we investigated changes in the number of cultivable cutaneous bacteria on the ventral and dorsal body surfaces of the Green tree frog (Litoria caerulea) with sloughing. Effects of temperature on sloughing periodicity were also investigated in order to determine how the efficacy of sloughing in regulating microbial infection might vary with climate and season. Our study showed that sloughing massively reduced the overall abundance of bacteria, in some cases by as much as 100%. In addition, temperature had a marked effect on sloughing periodicity, with animals in cooler temperatures having a much longer time between sloughs compared with animals at held higher temperatures.
Most importantly however, we found that the extended time between sloughs in animals in the cold treatments allowed skin microbe numbers to increase to levels in excess of those seen in animals in the warm treatment. These data suggest that for pathogens that like relatively cooler conditions (like Bd), the effect of temperature on host sloughing frequency may allow pathogen numbers to build up to such a degree that fatal disease occurs.
What does it all mean, though? Firstly, the epidemiology of skin based diseases like Bd could be in part attributed to the effects of temperature on host sloughing periodicity particularly when disease outbreaks occur in cool habitats and/or at cooler times of year. Secondly, differences between species in the frequency of sloughing could influence pathogen establishment and go some way to explaining why some amphibian species are more resistant to cutaneous pathogens than others. Thirdly, the ability of commensal (good) bacteria to protect against pathogens may be reduced in frog species which slough frequently as commensal bacteria would also be lost from the skin with sloughing, unless they are able to recolonise the skin rapidly.
Understanding the role the skin plays as the first bastion of defense against external pathogens is vitally important as the rate of emergence of both novel and pre-existing infectious diseases is predicted to skyrocket in the future as a result of anthropogenic climate change.
Dr Rebecca Cramp is a Research Officer at The University of Queensland in the laboratory of Professor Craig Franklin. Rebecca has diverse research interests and is currently working on several projects including a study of disease susceptibility in frogs, the control of ion regulation in acid-tolerant amphibian larvae and the effects of environmental stressors on immune function in amphibian larvae. She is a co-author of the paper ‘First line of defence: the role of sloughing in the regulation of cutaneous microbes in frogs‘, which appears in the journal Conservation Physiology.
Conservation Physiology is an online only, fully open access journal published on behalf of the Society for Experimental Biology. Biodiversity across the globe faces a growing number of threats associated with human activities. Conservation Physiology publishes research on all taxa (microbes, plants and animals) focused on understanding and predicting how organisms, populations, ecosystems and natural resources respond to environmental change and stressors. Physiology is considered in the broadest possible terms to include functional and mechanistic responses at all scales.
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Image credit: A green tree frog. Photo by Ed Meyer. Do not reproduce without permission.
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By Mark van Kleunen
Conservation physiology was first identified as an emerging discipline in a landmark paper by Wikelski and Cooke, published in Trends in Ecology and Evolution in 2006. They defined it as “the study of physiological responses of organisms to human alteration of the environment that might cause or contribute to population decline”. Although the case studies and examples presented by Wikelski and Cooke focused on wild animals, they indicated already that conservation physiology should be applicable to all taxa. With the launch of the journal Conservation Physiology – one year ago – this taxonomic inclusiveness was made more explicit, and the definition was broadened to “an integrative scientific discipline applying physiological concepts, tools and knowledge to characterizing biological diversity and its ecological implications; understanding and predicting how organisms, populations and ecosystems respond to environmental change and stressors; and solving conservation problems across the broad range of taxa (i.e. including microbes, plants and animals)”.
Although the definition of conservation physiology, and also the journal with the same name, covers in principle all taxa, plants (and also microbes, and among animals the invertebrates) are still clearly underrepresented. Of the 32 papers that were published in the journal in 2013, only three (9%) focussed on plants. This underrepresentation of plants, however, appears to be a general trend in conservation science, as the journal Conservation Biology had only ten out of 93 contributed papers (11%) focussing on plants in 2013. The journal Biological Conservation did a bit better with 59 out of 309 regular papers (19%) focussing on plants in 2013. Given the importance of plants as primary producers, which are indispensable for all other organisms, and the fact that 10,065 of the 21,286 species (47%) assessed by the IUCN Red List as globally threatened are plants, they clearly deserve more attention in the field of conservation physiology, and conservation science in general.
Conservation science has many important, frequently intertwined, sub-disciplines, including among others conservation policy, conservation genetics and conservation physiology. The strength of physiology, and thus of conservation physiology, is that it focusses on the mechanisms underlying patterns by identifying cause-and-effect relationships, preferably through experimentation. Physiology is directly related to the functioning and function of plants. This means that physiological knowledge is imperative for understanding the habitat requirements of endangered native plants and of potentially invasive exotic plants, and the ecological impacts of invasive exotic plants and migrating native plants. An accessory advantage of working with plants is that they lend themselves extremely well for experimental studies, as they are sessile, can easily be marked, and frequently can be grown in large numbers under greenhouse or garden conditions. Plants are thus ideal objects for conservation physiological studies.
Given that plants are underrepresented, a logical question is what kind of plant studies fall under the umbrella of conservation physiology. The three reviews on plants that were published in Conservation Physiology in 2013 do a great job in setting the scene. Hans Lambers and colleagues reviewed the research on phosphorus-sensitive plants in a global biodiversity hotspot. Many of these species are threatened by the introduced pathogen Phytophthora cinnamomi and by eutrophication; the latter partly due to large-scale application of phosphite-containing fungicides (biostats) that are used to fight the pathogen. This illustrates how one conservation measure may cause undesired side effects. Physiological understanding of how phosphite functions could help to develop alternative fungicides with less negative side effects. Fiona Hay and Robin Probert reviewed recent research on seed conservation of wild plant species. They clearly make the case that if we want to preserve genetic material of wild plant species in ex-situ seed banks for conservation purposes, physiological research is imperative for developing optimal storage, germination and growth conditions. Last but not least, Jennifer Funk reviewed research on physiological characteristics of exotic plant species invading low-resource environments. Prevention of invasions and mitigation of the impacts of invasions requires physiological research that resolves the question whether exotic species manage to invade low-resource environments through enhanced resource acquisition, resource conservation or both. These three reviews thus illustrate already three important plant-related topics in conservation physiology: causes of threat of native plants, ex-situ conservation, and invasive exotic plants.
An important topic that hasn´t been covered yet in the journal Conservation Physiology is how plants will respond to climate change. As physiology underlies the fundamental niche of a species, physiological studies can inform predictive models on potential responses of plants to climate change. Related topics are how endangered and invasive plant species will respond to increased CO2 levels, and how their vulnerability to diseases may change under novel climatic conditions. Furthermore, as we seem to miserably fail in reducing greenhouse-gas emissions, it becomes also more likely that governments will start to implement climate engineering methods to reduce incoming solar radiation or atmospheric CO2 levels. Undesired ecological side effects of these methods will raise novel conservation issues for which physiological knowledge will be imperative. Other topics that haven’t been covered yet are physiological responses of plants to pollution, and how endangered species that are difficult to propagate from seeds could be multiplied using tissue culture or other techniques. Obviously, the list of potential topics that I have mentioned here is far from exhaustive, but I hope it illustrates that many of the plant-related topics on which many of us work already or will work in the future fit within the discipline of conservation physiology.
Mark van Kleunen is a Professor of Ecology at the University of Konstanz. His research focusses on invasiveness of exotic plants, plant responses to global change and life-history evolution. This blog post is an adapted version of his editorial ‘Conservation Physiology of Plants‘ in the journal Conservation Physiology.
Conservation Physiology is an online only, fully open access journal published on behalf of the Society for Experimental Biology. Biodiversity across the globe faces a growing number of threats associated with human activities. Conservation Physiology publishes research on all taxa (microbes, plants and animals) focused on understanding and predicting how organisms, populations, ecosystems and natural resources respond to environmental change and stressors. Physiology is considered in the broadest possible terms to include functional and mechanistic responses at all scales.
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Image credit: California wildflowers. By Rennett Stowe. CC-BY-2.0 via Wikimedia Commons
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