Meeting Abstract

90.6  Friday, Jan. 6  Ectoparasites as a determinant of host litter size PATTERSON, Jesse; Univ. of Calgary

Life-history theory states that offspring number and offspring size trade-off with each other, as dictated by the energetic environment of the breeder. Mammalian mothers adjust the size of their litters before birth and also during lactation in accordance with their ability to successfully wean offspring. In the present study, I investigated the role of ectoparasites as a possible determinant of litter sizes in a population of free-ranging North American red squirrels (Tamiasciurus hudsonicus). I hypothesized that if ectoparasites were experimentally removed from their hosts shortly after mating (approx. 30 days before birth) that mothers would have more energy to invest in their offspring during pregnancy and could invest that energy into producing more offspring. The results of the current study support this hypothesis as it was found that mothers immunized against ectoparasites at mating produced significantly more offspring at birth when compared to non-immunized controls. No litter size effect was found between mothers only immunized at birth and non-immunized controls, suggesting that the presence of parasites and the energetic environment of the mother during gestation may determine the size of the litter she gives birth to. These results indicate that ectoparasites impose strong costs on the reproductive success and life-history strategies of female red squirrels.