Does habitat fragmentation cause stress in the agile antechinus? A haematological approach
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ORIGINAL PAPER
Does habitat fragmentation cause stress in the agile antechinus? A haematological approach Christopher P. Johnstone • Alan Lill Richard D. Reina
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Received: 16 December 2010 / Revised: 12 June 2011 / Accepted: 16 June 2011 / Published online: 28 June 2011 Ó Springer-Verlag 2011
Abstract Although the vertebrate stress response is essential for survival, frequent or prolonged stress responses can result in chronic physiological stress, which is associated with a suite of conditions that can impair survivorship and reproductive output. Anthropogenic habitat fragmentation and degradation are potential stressors of free-living vertebrates, and in theory could result in chronic stress. To address this issue, we compared haematological indicators of stress and condition in agile antechinus (Antechinus agilis) populations in 30 forest fragments and 30 undisturbed, continuous forest sites (pseudofragments) in south-eastern Australia over 2 years. In peripheral blood, the total leucocyte count was lower and the neutrophil/lymphocyte ratio and percentage of eosinophils in the total leucocyte population was higher in fragment than pseudofragment populations, indicating that fragment populations were probably experiencing higher levels of stress hormone-mediated and/or parasite infectionrelated chronic physiological stress. The total erythrocyte count and haematocrit were higher and mean erythrocyte haemoglobin content was lower in fragment than pseudofragment populations. This suggests that fragment populations showed possible signs of regenerative anaemia, a syndrome associated with elevated hypothalamus–pituitary– adrenal axis mediated stress. However, mean erythrocyte volume was also lower in fragments, and red blood cell distribution width did not differ between the study populations, findings which were not consistent with this diagnosis. Whole blood and mean cell haemoglobin concentrations
Communicated by I.D. Hume. C. P. Johnstone (&) A. Lill R. D. Reina School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia e-mail: [email protected]
were similar in fragment and pseudofragment populations. We suggest that where anthropogenic activity results in habitat fragmentation and degradation, chronic stress could contribute to a decline in agile antechinus populations. The broader implication is that chronic stress could be both symptomatic of, and contributing to, decline of some vertebrate populations in anthropogenically fragmented and degraded habitats. Keywords Antechinus agilis Neutrophil/lymphocyte ratio Physiological stress Repeatability Small mammal
Introduction Habitat fragmentation is associated with changes in the environment that often have negative effects on native vertebrate populations (Fischer and Lindenmayer 2007). These include habitat subdivision, isolation, invasion by generalist competitors or exotic predators and degradation effects (Ewers and Didham 2005; Fischer and Lindenmayer 2007). Evidence from studies on the marsupial carnivore g
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