Comment on “Insulative capacity of the integument of the dugong (Dugong dugon): thermal conductivity, conductance and resistance measured by in vitro heat flux”

Communicated by U. Sommer. This article presents original research to investigate the relationship between integumentary composition and predictive thermal capacity. The authors suggest that cold stress syndrome (CSS) is unlikely to occur in dugongs, a claim that is at odds with a recent study from our group where we described the local appearance of mortality cases consistent with this syndrome. Horgan et al. (2014) made two statements, in particular, which disregarded a diagnosis following observations by specialist veterinary pathologists, yet without, to our knowledge, accessing the material themselves and instead quoting ‘unpublished data’ to support their conclusions. Further, and importantly, Horgan et al. (2014) ignore the pathological changes we described in other organ systems, which were consistent with changes noted during CSS in manatees and led to our diagnosis. Cold stress syndrome is an incompletely understood but clearly very complicated, multisystemic entity that has been described as affecting Florida manatees chronically exposed to cold water (Bossart et al. 2002). Florida and south-east Queensland (QLD) are very similar in climate, species composition and marine environment. In 2013, our group published an article comparing the lesions described in manatees with those we were seeing in many of the dugongs presenting to our post-mortem room during the colder months of the year in Queensland. This description was combined with presentation of supporting environmental data (Owen et al. 2013). Horgan, Booth, Nichols and Lanyon have made statements contradicting our argument in their article, namely: “with no credible pathological evidence of CSS (cf. Owen et al. 2013)” and “Skin lesions suggested as characteristic of cold stress and reported for dugongs by Owen et al. (2013) are grossly and histologically different to those reported for the Florida manatee, are found in dugongs throughout the tropics (Woolford and Lanyon unpublished data) and are also found in dugongs in cooler waters outside the winter period (the latter point also reported by Owen et al. 2013). Each of these factors casts serious doubt as to these skin characteristics being thermally related”. These statements are not based on sound scientific principles. In the former instance, this statement has been made without offering any supporting or qualifying evidence and is therefore an unsubstantiated opinion. The dugong samples used for Owen et al. (2013) were assessed and compared by experienced pathologists and experts in marine population health, one of whom (MF) is in the unique position of having first-hand experience with disease in both manatees in Florida and dugongs in southeast QLD. Data and the resulting interpretations in this article were also deemed as credible by multiple reviewers. The qualifying evidence in support of the second unsubstantiated statement by Horgan et al. (2014) is that dugongs do not exhibit cold stress at 15 °C, which has been linked to Bossart et al. (2002, 2004) studies on manatees. Neither of these articles have any reference to dugongs, raising question as to where this information was derived. Further, the evidence offered by Horgan et al. (2014) in this statement is logically questionable in the way it concludes dugongs cannot get cold stress and is insufficient, based on unpublished data and misleading for other studies into this syndrome. It is inadequate to suggest that skin lesions in the two species are different without supportive data and a reasonable scientific basis. A major concern of this rebuttal of our work is that the authors are hinging their scientific arguments by making a statement about lesions in cases they have not seen (grossly or histologically) and are then using this unfounded opinion to dismiss peer-reviewed scientific data. In addition, the precise nature of these “differences” identified by the authors needs to be described in order for their significance to be determined by the reader. Even without this information, we are sceptical that diagnostically significant differences exist as skin has a very stereotypical and non-specific range of responses to any chronic injury. Chronic lesions that are essentially indistinguishable, particularly on gross examination, can be produced by a wide array of triggers. For this reason, even though the authors have noted similar lesions in “dugongs throughout the tropics”, these lesions could have a completely different cause to those reported in our study. Also, it is diagnostically dangerous to assume that an animal in one region requires the same conditions (in this case, the same low-temperature trigger point) as an animal in another region to express the clinical signs of a disease. We do not understand the influences of geography and species differences on precipitating environmental conditions, and it is important that researchers keep an open mind and report without bias. Finally, the authors’ suggestion that these lesions are seen in dugongs throughout the tropics is misleading given dugongs’ vast range and the nature of response to syndromes. The dugong’s range spans estimated tropical and subtropical coastal and island waters of some 40 countries encompassing approximately 860,000 km2 (Marsh et al. 2012) and would require a range of trigger points unique to each locale to manifest skin lesions. Even if the authors have noted these lesions in their study sites, they cannot extrapolate to all dugong habitat and aetiologies to draw their presented conclusions. This article highlights how misleading it can be to examine one lesion in isolation rather than the animal as a whole and to make generalizations on syndromes without solid evidence, particularly in species where response to disease is not well documented or understood. Cold stress syndrome is also obviously a complicated disease, and a multifactorial aetiology is likely, given that some animals in a particular environment can be affected while others are not. Expecting a direct cause-and-effect relationship with water temperature risks oversimplifying the syndrome and will encourage future researchers to overlook data that could be vital to increase our understanding. A holistic and multidisciplinary approach is required in order for us to progress our understanding of this entity. We hope researchers in this field are not swayed or discouraged by the opinion presented in Horgan, Booth, Nichols and Lanyon’s recent article and rather view the data presented as a potential piece in the CSS puzzle that requires a collegial effort to solve.