Conrad Hailey, Pollock Nicholas B, John-Alder Henry
Department of Ecology, Evolution, and Natural Resources Rutgers University New Brunswick New Jersey USA.
Present address: Department of Biological Sciences Virginia Polytechnic Institute and State University Blacksburg Virginia USA.
Ecol Evol. 2023 Oct 11;13(10):e10590. doi: 10.1002/ece3.10590. eCollection 2023 Oct.
Parasitism is nearly ubiquitous in animals and is frequently associated with fitness costs in host organisms, including reduced growth, foraging, and reproduction. In many species, males tend to be more heavily parasitized than females and thus may bear greater costs of parasitism. is a female-larger, sexually size dimorphic lizard species that is heavily parasitized by chigger mites (). In particular, the intensity of mite parasitism is higher in male than in female juveniles during the period of time when sex differences in growth rate lead to the development of sexual size dimorphism (SSD). Sex-biased differences in fitness costs of parasitism have been documented in other species. We investigated whether there are growth costs of mite ectoparasitism, at a time coinciding with sex differences in growth rate and the onset of SSD. If there are sex-biased growth costs of parasitism, then this could suggest a contribution to the development of SSD in . We measured growth and mite loads in two cohorts of unmanipulated, field-active yearlings by conducting descriptive mark-recapture studies during the activity seasons of 2016 and 2019. Yearling males had consistently higher mid-summer mite loads and consistently lower growth rates than females. However, we found that growth rate and body condition were independent of mite load in both sexes. Furthermore, growth rates mite loads were higher in 2019 than in 2016. Our findings suggest that juveniles of are highly tolerant of chigger mites and that any costs imposed by mites may be at the expense of functions other than growth. We conclude that sex-biased mite ectoparasitism does not contribute to sex differences in growth rate and, therefore, does not contribute to the development of SSD.
寄生现象在动物界几乎无处不在，并且常常与宿主生物的适应性代价相关联，包括生长、觅食和繁殖能力的降低。在许多物种中，雄性往往比雌性更容易受到寄生虫感染，因此可能承受更大的寄生代价。鬃狮蜥是一种雌性体型大于雄性、具有两性异形特征的蜥蜴物种，受到恙螨的严重寄生。特别是在生长速率的性别差异导致两性异形发育的时期，雄性幼体的螨虫寄生强度高于雌性幼体。在其他物种中也有关于寄生适应性代价的性别差异的记录。我们调查了在与生长速率的性别差异以及两性异形开始同时出现的时期，恙螨外寄生是否存在生长代价。如果存在寄生的性别偏向生长代价，那么这可能表明其对鬃狮蜥两性异形的发展有一定作用。我们在2016年和2019年的活动季节通过进行描述性标记重捕研究，测量了两组未受操控、活跃于野外的一岁蜥蜴的生长情况和螨虫负载量。一岁雄性蜥蜴的仲夏螨虫负载量始终高于雌性，生长速率始终低于雌性。然而，我们发现两性的生长速率和身体状况均与螨虫负载量无关。此外，2019年的生长速率和螨虫负载量高于2016年。我们的研究结果表明，鬃狮蜥幼体对恙螨具有高度耐受性，并且螨虫造成的任何代价可能是以生长以外的其他功能为代价的。我们得出结论，性别偏向的恙螨外寄生对生长速率的性别差异没有影响，因此对两性异形的发展也没有影响。
