Data from: Evolution of age at primiparity in pinnipeds in the absence of the quality-quantity trade-off in reproduction

Age at primiparity (AP) is a key life history trait which is crucial to
the evolution of life-history strategies. This trait is particularly
interesting in pinnipeds (walrus, eared seals and true seals), which are
monotocous animals. Thus, the commonly observed trade-off between
offspring quality and quantity does not apply to this taxon. Therefore,
comparative studies on the evolution of AP might shed light on other
important evolutionary correlates when litter size is fixed. Using
phylogenetic generalised least squares analyses, we found a strong
negative and robust correlation between relative birth mass (mean pup
birth mass as a proportion of mean adult female mass) and AP. Rather than
trading-off an early start of reproduction with light relative offspring
mass, this result suggests that pinnipeds exhibit either faster (i.e.
higher relative offspring mass leading to shorter lactation length, and
thus shorter inter-birth interval) or slower life histories and that an
early AP and a heavy relative offspring mass co-evolved into a
comparatively fast life history strategy. On the other hand, AP was
positively related to lactation length: a later start of reproduction was
associated with a longer lactation length. Consequently, variation in AP
in pinnipeds seems to be affected by an interplay between costs and
benefits of early reproduction mediated by relative investment into the
single offspring via relative birth mass and lactation length.