72.5 Friday, Jan. 6 Adaptive hormone-mediated maternal effects in red squirrels DANTZER, B*; BOONSTRA, R; BOUTIN, S; HUMPHRIES, M.M.; PALME, R; MCADAM, A.G.; Michigan State University; University of Toronto at Scarborough; University of Alberta; McGill University; University of Veterinary Medicine; University of Guelph firstname.lastname@example.org
Red squirrels (Tamiasciurus hudsonicus) in the Canadian Yukon live in a variable environment in which fluctuations in population density driven by pulses of their major food source generate density-dependent selection on offspring phenotype. Population density during pregnancy is positively associated with the strength of directional selection on offspring postnatal growth rates. We conducted a multiyear study (2007-2011) to test the hypothesis that the hormonal responses of breeding female squirrels to variation in population density are associated with adaptive modifications in offspring growth rates. We found that pregnant and lactating squirrels experiencing heightened population density had significantly higher fecal cortisol (FCM) and androgen (FAM) metabolite concentrations. Heightened FCM and FAM during pregnancy and lactation were associated with significantly higher offspring growth rates. When population density was experimentally elevated using long-term food supplementation or playbacks of territorial vocalizations, pregnant and/or lactating squirrels also had significantly higher FCM and FAM. Offspring growth rates were significantly higher on the high density food-supplementation study area compare to lower density control study areas. Similarly, females experiencing experimentally heightened perceived density (playbacks) produced offspring that grew significantly faster than those exposed to control playbacks but at a similar rate to those produced by females on the high density food-supplemented study areas. These data suggest that the endocrine responses of female red squirrels to variation in population density influences offspring postnatal growth rates in a direction that is adaptive.