Comparative reproductive function in cervids: implications for management of farm and zoo populations.
The cervids represent a complex assemblage of taxa characterized by extreme diversity in morphology, physiology, ecology and geographical distribution. Farmed species (for example red deer and fallow deer) are usually the common larger-bodied, gregarious and monotocous species that express marked reproductive seasonality in their temperate environment. Their commercial importance has facilitated considerable research into reproductive physiology and the development of assisted reproductive technologies (ART). In contrast, the remaining species, including many of tropical origin, show wide diversity in reproductive patterns, have generally received little scientific scrutiny, and include a number of endangered taxa that are reliant on ex situ conservation efforts (such as captive breeding) to ensure their survival. Domestication and ex situ management programmes have been associated with widespread translocation of various cervid species around the world, often placing the animals in environments that are not compatible with their evolved reproductive patterns. For example, the summer calving/lactation pattern of red deer, attuned to northern continental climatic patterns, is frequently misaligned with seasonal changes in feed availability in the Australasian pastoral environment. Similarly, seasonal or aseasonal calving patterns of tropical species translocated to temperate regions are usually associated with increased perinatal mortality of calves born in cool seasons. Conversely, temperate species in tropical zones may exhibit aberrant reproductive patterns in the absence of biologically significant photoperiod fluctuations. ARTs, which presently include artificial insemination, embryo transfer and in vitro embryo production, have potential application to the genetic management and population growth of various cervid species. Although application to some farmed cervid species is widespread, these technologies are rarely directly transferable from farmed to endangered species. Even within species, ART protocols developed successfully for one genotype (i.e. subspecies) may be ineffective in another (for example superovulation of red deer and wapiti). Therefore, application to genetic management of endangered species necessitates prior research into their reproductive patterns. This is often difficult because of the rarity of the animals, a lack of suitable handling facilities for the particular species, and the timid nature of the deer. More recently, however, non-invasive reproductive profiling, based on remote collection and monitoring of excreted steroid metabolites, has facilitated such research.