title: Paroxetine exposure skews litter sex ratios in mice suggesting a Trivers-Willard process.
abstract: While conducting a toxicity assessment of the antidepressant paroxetine (Paxil®), in wild-derived mice (Mus musculus), we observed that exposed dams (P0) produced female biased litters (32:68 M:F). Though numerous experimental manipulations have induced sex ratio bias in mice, none have assessed the fitness of the offspring from these litters relative to controls. Here, we retrospectively analyze experimentally derived fitness data gathered for the purpose of toxicological assessment in light of 2 leading hypothesis (Trivers-Willard hypothesis [TWH] and cost of reproduction hypothesis [CRH]), seeking to test if this facultative sex ratio adjustment fits into an adaptive framework. Control F1males were heavier than F1females, but no differences in mass were detected between exposed F1males and females, suggesting that exposed dams did not save energy by producing fewer males, despite producing 29.2% lighter litters relative to controls. F1offspring of both treatments were released into seminatural enclosures where fitness was quantified. In enclosures, the relative reproductive success of F1-exposed males (compared with controls) was reduced by ~20% compared with the relative reproductive success of F1-exposed females. Thus, exposed dams increased their fitness by adjusting litters toward females who were less negatively affected by the exposure than males. Collectively, these data provide less support that the observed sex ratio bias results in energetic savings (CRH), and more support for the TWH because fitness was increased by biasing litters toward female offspring. These mammalian data are unique in their ability to support the TWH through the use of relevant fitness data.
authors.affiliation: Department of Biology, University of Utah , 257 South 1400 East, Salt Lake City, UT 84112 , USA.
authors.forename: Shannon Marie
authors.initials: SM
authors.lastname: Gaukler
authors.affiliation: Department of Biology, University of Utah , 257 South 1400 East, Salt Lake City, UT 84112 , USA.
authors.forename: James Steven
authors.initials: JS
authors.lastname: Ruff
authors.affiliation: Department of Biology, University of Utah , 257 South 1400 East, Salt Lake City, UT 84112 , USA.
authors.forename: Wayne K
authors.initials: WK
authors.lastname: Potts
keywords: SSRI.; adaptive sex allocation; cost of reproduction hypothesis; fitness assay; paroxetine