Postnatal growth of skull linear measurements of Cape Hare Lepus capensis in northern China: an analysis in an adaptive context

304 skulls of Cape hare (Lepus capensis) were collected from two climatically distinct localities in northern China. With eye lens weight as a continuous age variable, postnatal growth patterns of 25 cranial linear measurements in relation to sex, growth season and region were analysed to understand the morphological basis of life history adaptation. In almost all the skull measurements, no significant differences were found between either sex or growth seasons. Principal component analysis revealed that facial elements accounted for the greatest proportion of skull morphological variation. Von Bertalanffy function was applied to describe growth trajectories of the skull elements. Based on this model, the growth rates of skull elements and the age at which they reached a certain proportion (95%) of asymptotes were compared. The results showed that skull growth exhibited an allometric pattern, with neural components attaining their final size more rapidly (at about 2–3 months old in tympanic bulla and 4–6 months old in others) than did the facial, which continued to grow well into postnatal life (at 6–10 months old). The earlier establishment of neurocranial morphology was associated with a fully developed central nervous system, which may play a key role in improving the survival of animals during the early phase of life. There was a regional difference in developmental rate of the hare skull. For all the skull parameters, northern hares had a more rapid rate of cranial growth compared to the southern, i.e. skull elements of juveniles from northern population were relatively larger at comparable ages and achieved adult size 0.5–4.0 months earlier than those from the south. In adult hares, however, no significant regional differences in any of the skull parameters were present. Adaptive explanations for the regional difference in ontogenetic pattern of skull morphology include age-specific thermoregulation constraint, season-related food availability and age-dependent predation pressure. Based on the findings of this study, it is suggested that the postnatal growing period represents a crucial time of life, and that improvement of survivorship when young by growth adaptation forms an important aspect of the hare's life history strategies.