Parasite removal increases reproductive success in a social African ground squirrel

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

“…While the per capita litter sex ratio of a more social ground squirrel species may be unaffected by parasitism (Cape ground squirrels: Hillegass et al 2010), the more male-biased sex ratio of insecticide-treated Franklin's ground squirrels in this study is consistent with the original formulation of the Trivers-Willard hypothesis. Kankova et al (2007) likewise provided evidence for a more female-biased litter sex ratio in parasitized laboratory mice as compared to unparasitized controls.…”

“…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).…”

“…analysis of bird species in the family Hirundinidae revealed that social species invested more heavily into immune function. As Franklin's ground squirrels are relatively asocial (Hare 2004) compared to other ground squirrel species in which parasite effects were apparent (Arnold and Lichtenstein 1993;Van Vuren 1996;Neuhaus 2003;Hillegass et al 2010), it is possible that Franklin's ground squirrels have evolved fewer mechanisms for allocating resources to immune function. Thus, any life history trade-offs with immune function, as evidenced by mass gain or reproductive effort, may not be as pronounced.…”

“…Fipronil is classified as a broad-spectrum phenylpyrazole insecticide and is used to control a wide range of insects by blocking chloride channels in the central nervous system (Fipronil Technical Fact Sheet, Merial Limited, Duluth, GA). We administered fipronil to squirrels by spraying 1.5 ml of FRONTLINE™ Spray on the dorsal pelage of squirrels as described by Hillegass et al (2010).…”

“…Inconsistencies in the direction of such biases, however, highlight the complexity of potential trade-offs among body condition, litter size and litter sex ratio in polytocous species. Consideration of litter sex ratio in investigations that affect maternal quality through parasite load manipulation remain rare (Kankova et al 2007;Hillegass et al 2010), yet invariably prove insightful.…”