Correlates of early reproduction and apparent fitness consequences in male Soay sheep

Life history trade-offs are ubiquitous across species and place
constraints on the timing of life history events, including the optimal
age at first reproduction. However, studies on lifetime breeding success
of male mammals are rare due to sex-biased dispersal and the requirement
for genetic paternity inferences. We studied the correlates and apparent
fitness consequences of early-life reproduction among males in a
free-living population of Soay sheep (Ovis aries) on St Kilda, Scotland.
We investigated the factors associated with early breeding success and the
apparent consequences of early success for survival and future
reproduction. We used genetic paternity inferences, population data and
individual morphology measurements collected over 30 years. We found that
individuals born in years with low-density population size had the highest
early-life breeding success, and singletons were more likely to be
successful than twins. Individuals that bred successfully at seven months
were more likely to survive their first winter. For individuals that
survived their first winter, early breeding success was not associated
with later breeding success. Since individual heterogeneity affects
breeding success, we believe that variation in individual quality masks
costs of early reproduction in this population. Our findings provide no
evidence for selection for delayed age at reproduction in male Soay
sheep.