Fancourt Bronwyn A, Nicol Stewart C, Hawkins Clare E, Jones Menna E, Johnson Chris N
School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
Int J Parasitol Parasites Wildl. 2014 May 29;3(2):102-12. doi: 10.1016/j.ijppaw.2014.05.001. eCollection 2014 Aug.
Disease is often considered a key threat to species of conservation significance. For some, it has resulted in localised extinctions and declines in range and abundance. However, for some species, the assertion that a disease poses a significant threat of extinction is based solely on correlative or anecdotal evidence, often inferred from individual clinical case reports. While a species' susceptibility to a disease may be demonstrated in a number of individuals, investigations rarely extend to measuring the impact of disease at the population level and its contribution, if any, to population declines. The eastern quoll (Dasyurus viverrinus) is a medium-sized Australian marsupial carnivore that is undergoing severe and rapid decline in Tasmania, its last refuge. Reasons for the decline are currently not understood. Feral cats (Felis catus) may be undergoing competitive release following the ongoing decline of the Tasmanian devil (Sarcophilus harrisii), with cats suppressing eastern quolls through increased predation, competition, exclusion or exposure to diseases such as toxoplasmosis. To investigate the effects of Toxoplasma gondii infection, eastern quoll populations at four sites were regularly screened for the seroprevalence of T. gondii-specific IgG antibodies. Seroprevalence was approximately five times higher at sites with declining quoll populations, and there was a negative association between seroprevalence and quoll abundance. However, T. gondii infection did not reduce quoll survival or reproduction. Despite a high susceptibility to T. gondii infection, eastern quoll populations do not appear to be limited by the parasite or its resultant disease. Significantly higher seroprevalence is a signal of greater exposure to feral cats at sites where eastern quolls are declining, suggesting that increased predation, competition or exclusion by feral cats may be precipitating population declines.
疾病通常被视为对具有保护意义的物种的关键威胁。对一些物种来说，疾病已导致局部灭绝以及分布范围和数量的减少。然而，对于某些物种而言，认为某种疾病构成重大灭绝威胁的论断仅仅基于相关或轶事性证据，这些证据往往是从个别临床病例报告中推断出来的。虽然可以在许多个体中证明一个物种对某种疾病的易感性，但调查很少扩展到衡量疾病在种群水平上的影响及其对种群数量下降的贡献（如果有的话）。东部袋鼬（Dasyurus viverrinus）是一种中等体型的澳大利亚有袋类食肉动物，在其最后的避难所塔斯马尼亚正经历着严重且迅速的数量下降。数量下降的原因目前尚不清楚。随着袋獾（Sarcophilus harrisii）数量的持续减少，野猫（Felis catus）可能正在经历竞争释放，野猫通过增加捕食、竞争、排斥或传播诸如弓形虫病等疾病来抑制东部袋鼬。为了调查弓形虫感染的影响，对四个地点的东部袋鼬种群定期进行弓形虫特异性IgG抗体血清阳性率筛查。在袋鼬数量下降的地点，血清阳性率大约高出五倍，并且血清阳性率与袋鼬数量之间存在负相关。然而，弓形虫感染并没有降低袋鼬的存活率或繁殖率。尽管东部袋鼬对弓形虫感染高度易感，但该种群似乎并未受到这种寄生虫或其引发疾病的限制。在东部袋鼬数量下降的地点，显著更高的血清阳性率表明接触野猫的机会更多，这表明野猫增加的捕食、竞争或排斥可能正在促使种群数量下降。
