The reproductive performance of roe deer in relation to environmental and genetic factors

Abstract

This thesis investigates the influences of density-dependent and density independent factors on the reproductive performance of roe deer (Capreolus capreolus) in Britain. Studies were based on fifteen wild populations, in Forestry Commission commercial plantations and on Ministry of Defence training areas. Extensive data were available for each site from cull records covering between 5 and 21 years, and included the number of embryos present and eviscerated body weight for each female shot, totalling more than five thousand deer. For the nine Forestry Commission sites, which form the core of the study, the ovaries and the lower jaw bone were also collected from each animal. The age of each of these animals was assessed by tooth sectioning.

Reproductive performance was assessed in terms of age at first breeding, percentage ovulation (corpora lutea present in the ovaries), average number of succesfully fertilised ovulations per ovulating doe (as number of corpora lutea), percentage pregnancy (embryos present) and average number of embryos per pregnant doe. Precocious reproductive activity among kids rarely resulted in successful pregnancy, while the majority of yearlings did conceive, but generally produced smaller litter sizes than older does. A uniform level of reproductive performance was observed among all animals over two years old within a single population.

Generally, little significant variation in reproductive performance between years within a site was detected. However, at the two sites with the longest span of data available (21 and 12 years) some significant variation between years in potential litter size was observed; this variation was entirely explained by correlated variation in maternal body weight. A sequence of increasing reproductive cost was suggested as one male, one female, two females, two males, according to the average body weight of the mother. Between populations, reproductive performance was highly variable (although adult ovulation always approached 100% ). Percentage pregnancy, average number of corpora lutea, and average number of foetuses were all highly correlated with maternal body weight, but this relationship was insufficient to explain the very highly significant differences between populations in reproductive performance.(DX176326)

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