Ectoparasites and fitness of female Columbian ground squirrels

Abstract

Parasites play an important role in the evolution of host traits via natural selection, coevolution and sexually selected ornaments used in mate choice. These evolutionary scenarios assume fitness costs for hosts. To test this assumption, we conducted an ectoparasite removal experiment in free-living Columbian ground squirrels ( Urocittelus columbianus ) in four populations over three years. Adult females were randomly chosen to be either experimentally treated with anti-parasite treatments (spot-on solution and flea powder, N = 61) or a sham treatment (control, N = 44). We expected that experimental females would show better body condition, increased reproductive success and enhanced survival. Contrary to our expectations, body mass was not significantly different between treatments at mating, birth of litter or weaning of young. Further, neither number nor size of young at weaning differed significantly between the two treatments. Survival to the next spring for adult females and juveniles was not significantly different between experimental and control treatments. Finally, annual fitness was not affected by the treatments. We concluded that females and their offspring were able compensate for the presence of ectoparasites, suggesting little or no fitness costs of parasites for females in the different colonies and during the years of our experiments.

The sociality–health–fitness nexus: synthesis, conclusions and future directions

“…[30,31]), and ectoparasites are known to transmit infectious agents, such as the Lyme disease spirochete [32], which may negatively impact fitness. Why did Raveh et al [8] fail to find support for their predictions in these ground squirrels? The answer may have to do with the other ecological conditions faced by these squirrels, and their ability to mount effective immune and physiological defences to the ectoparasites under different conditions.…”

“…Notable here is the experimental fieldwork by Raveh et al [8], which examined the fitness consequences of ectoparasitism in Columbian ground squirrels. Based on theory and previous research [28], the authors expected to find that ectoparasitism had fitness costs for the squirrels, yet newer data and analyses suggested otherwise [29].…”

“…Some papers in this theme issue provide examples of the mechanisms that underlie predicted interactions, such as the effects of dominance rank, sex and stress on hormone production [6], their effects on immune function and parasitism [7], and the role of the sympathetic nervous system in mediating effects of social instability on immune function [5]. Other papers in this issue have investigated the fitness consequences of sociality and parasitism, for example in Columbian ground squirrels [8]. The papers also take a wide range of approaches, including broad-scale comparative and meta-analysis [3,7,9], long-term field research on food availability, stress and population density [10], social networks and disease spread in wild animals [4], and experimental studies of behaviour in captive primates [5].…”

“…The specific future directions that we consider involve additional studies of the fitness consequences of parasitism [8]; a greater understanding of behavioural and physiological responses to infectious disease, especially including their effects on individual health and spread of infectious diseases in populations [2,17]; and emerging links between sociality, the microbiome and health.…”

Costs of Franklin’s ground squirrel (Poliocitellusfranklinii) ectoparasitism reveal adaptive sex allocation

“…As noted above, however, sample sizes were small (n = 7), and thus trends must be interpreted cautiously. Among sciurid species studied D r a f t to date, female body mass is sometimes influenced by parasitism (Van Vuren 1996;Neuhaus 2003;Scantlebury et al 2010), though not always (Hillegass et al 2010;Raveh et al 2015).…”