title: Reproductive effort and costs of reproduction in female European ground squirrels.
abstract: Reproductive effort, factors affecting reproductive output and costs of reproduction were studied in primiparous yearling compared to multiparous older female European ground squirrels (Spermophilus citellus). Yearling females weaned smaller litters than older ones. Litter size increased with posthibernation body mass at the expense of slightly lighter young for yearling but not for older mothers. In older females, on the other hand, emergence body mass influenced offspring mass, whereas litter size was affected by oestrus date. High reproductive effort entailed reproductive costs in terms of reduced subsequent fecundity but not subsequent survival for both yearling and older females. The production of large litters and long duration of lactation delayed subsequent oestrus, which, in turn, correlated negatively with litter size. During the second half of lactation, oestradiol levels were significantly elevated, indicating the initiation of follicular maturation processes. Oestradiol levels during that time correlated negatively with current, but positively with subsequent litter size. We therefore assume that inhibitory effects of lactation on gonadal development may mediate the negative relationship between reproductive effort and subsequent reproductive timing in adults. This effect is absent in yearlings because they are reproducing for the first time. Reproductive output in yearlings was influenced by interactions between structural growth and puberty.
authors.affiliation: Research Institute of Wildlife Ecology, University of Veterinary Medicine of Vienna, Savoyenstrasse 1, A-1160 Wien, Austria e-mail: susanne.huber@vu-wien.ac.at, , , , , , AT.
authors.forename: Susanne
authors.initials: S
authors.lastname: Huber
authors.affiliation: Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Wien, Austria, , , , , , AT.
authors.forename: Eva
authors.initials: E
authors.lastname: Millesi
authors.affiliation: Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Wien, Austria, , , , , , AT.
authors.forename: Manfred
authors.initials: M
authors.lastname: Walzl
authors.affiliation: Institute of Zoology, University of Vienna, Althanstrasse 14, A-1090 Wien, Austria, , , , , , AT.
authors.forename: John
authors.initials: J
authors.lastname: Dittami
authors.forename: Walter
authors.initials: W
authors.lastname: Arnold
keywords: Female; Gonad development; Key words Ground squirrel; Lactation; Reproduction