Basic considerations on seasonal breeding in mammals including their testing by comparing natural habitats and zoos

Abstract

Seasonal reproduction is common in mammals. Whereas specific conditions triggering a seasonal response can only be identified in controlled experiments, large-scale comparisons of reproduction in natural habitats and zoos can advance knowledge for taxa unavailable for experimentation. We outline how such a comparison can identify species whose seasonal physiology is linked to photoperiodic triggers, and those whose perceived seasonality in the wild is the consequence of fluctuating resources without a photoperiodic trigger. This concept groups species into those that do not change their aseasonal pattern between natural habitats and zoos because they are not constrained by resources in the wild, those that do not change a seasonal pattern between natural habitats and zoos because they are triggered by photoperiod irrespective of resources, and those that change from a more seasonal pattern in the natural habitat to an aseasonal pattern in zoos because the zoo environment alleviates resource limitations experienced in the wild. We explain how detailed comparisons of mating season timing in both environments can provide clues whether a specific daylength or a specific number of days after an equinox or solstice is the likely phototrigger for a taxon. We outline relationships between life history strategies and seasonality, with special focus on relative shortening of gestation periods in more seasonal mammals. Irrespective of whether such shortening results from the adaptive value of fitting a reproductive cycle within one seasonal cycle (minimizing ‘lost opportunity’), or from benefits deriving from separating birth and mating (to optimize resource use, or to reduce infanticide), reproductive seasonality may emerge as a relevant driver of life history acceleration. Comparisons of data from natural habitats and zoos will facilitate testing some of the resulting hypotheses.

Mammalian intestinal allometry, phylogeny, trophic level and climate

“…On the one hand, it has been proposed for small mammals that increased plasticity in the digestive tract is linked to high-latitude habitats, so that more intestinal tissue can be made available when required [53]; on the other hand, our findings might indicate that a long small intestine itself is an adaptive feature for life at high latitudes. Given that seasonal environments have been linked to an increase in the pace of life [78], increased intestinal capacity might thus facilitate intense resource processing during periods of resource limitation.…”

Non-Invasive Determination of Annual Fecal Cortisol, Androstenedione, and Testosterone Variations in a Herd of Male Asian Elephants (Elephas maximus) and Their Relation to Some Climatic Variables

“…In wild animals, differences in reproductive rates between seasons may be due to food availability and animal health. However, if similar seasonal reproduction is observed in zoo animals despite the constant provision of resources in captivity, then we must consider that the reproduction of the species is triggered by an additional signal other than the availability of food [ 22 ]. Our results show that high temperatures and low humidity levels might act as non-photoperiodic triggers of androgen production in male Asian elephants.…”

“…However, there is a paucity of data regarding the influence of climatic variables on endocrine regulation in male elephants. The influence of seasonality on the reproduction of mammals is a topic of interest [ 22 , 23 , 24 , 25 , 26 , 27 ]. The breeding season of elephants is not easily defined, however.…”

Seasonal Patterns of Oestrus and Reproduction in Street Dogs of Indian Cities

“…Photoperiod provides a predictable cue to adjust breeding efforts to coincide with peak food availabilities, typically associated with annual rainfall fluctuations in tropical regions (25). While the majority of reproductive seasonality is thought to be controlled by photoperiod, a more basal condition-dependent control-such that reproductive effort is moderated by energy balance-ensures reproductive failure in circumstances of energy deficit (18,21,26), whether linked to seasonal fluctuation or otherwise. Additionally, other seasonal cues may act to trigger seasonal reproductive dynamics independent of or in addition to photoperiod, particularly in regions of lesser correlation between food availability and day length, such as arid and equatorial environments (27).…”