![]() ![]() However, indirect evidence for seasonality of breeding have been suggested, especially in free-ranging dogs. Is the availability of resources the only cause of increased reproductive activities during the wet season in the tropical regions? More importantly, how does rainfall trigger reproductive activity in the tropics?ĭogs ( Canis lupus familiaris) are the first species to have been domesticated, and though most canids are known to be seasonal breeders domestic dogs are known to breed continuously, with no clear mating season. The most accepted hypothesis to explain seasonality of reproduction in the tropics pertains to the maximum availability of resources during the wet season. Though seasonality of reproduction is well understood in temperate species, especially with respect to shift in day length, the mechanism of seasonality in tropical animals is open to exploration. The fact that seasonal breeders can become continuous breeders in resource abundant conditions like domestication and in zoos also lends support to this hypothesis. This idea is substantiated by observations on many species like giraffes (Giraffa camelopardalis), African elephants (Loxodonta africana), gazelles, rhesus macaques ( Macaca mulatta) and wolves ( Canis lupus). Lactation is the most energetically costly phase in the reproductive cycle of female mammals it is thus beneficial to the female to match this phase with a period of resource abundance, so that she has access to food supply to replenish her lost reserves of energy. Why do animals in the tropics display seasonality of reproduction? It has been suggested that seasonal breeders are able to maximize fitness in individuals by synchronizing energetically demanding periods of the breeding cycle with periods of maximum food availability or quality, by giving birth just before or during the peak in resource availability. The width of the peak of birth seasonality can be extremely variable, and is often dependent on multiple environmental as well as biological factors. Temperate species are more sensitive to changes in day length and temperature, while tropical species are more affected by rainfall patterns. In fact, it has been shown, at least in the case of primates, that the effects of climate and latitude on birth seasonality are mediated via the availability of resources. Seasonality of reproduction can be strongly influenced by abiotic factors like variations of day length, temperature and humidity, which in turn can affect resource availability. Animals living in seasonally harsh climates tend to display sharply delineated, short breeding seasons, while those that live in relatively non-varying environments display little or no seasonality of reproduction. This can be observed in animals, both in terms of the onset of reproductive maturity for young individuals, as well as reproductively active phases for the population in an annual scale. Seasonality of reproduction is observed in mammals across all latitudes and has even been suggested in the archetypal example of continuously breeding species, Homo sapiens. Seasonal breeders successfully mate only during a particular time of the year, typically giving birth to offspring at a time which is ideal for the survival of the young. ![]() Most species of mammals exhibit some degree of reproductive synchrony, so that breeding occurs during optimal conditions. A shower leads to increased humidity and reduced temperature of the air, leading to intensification of pheromone signals that trigger a sexual response in the dogs. In the urban environment, dogs are exposed to a lot of olfactory noise, which can dilute the signal present in sex pheromones of the females in heat. While male dogs can mate round the year, females come into estrous seasonally. We speculate that this strong correlation is an effect of chemistry, rather than biology. There are two clear mating seasons, of which the primary mating season coincides with the monsoon (rainy season) and the secondary mating season coincides with the nor’westerlies in this part of India. We carried out an extensive study to identify the mating seasons of free-ranging dogs, and observed a strong correlation between both the incidence and frequency of mating related behaviours of dogs, and precipitation levels. Interestingly, in India, free-ranging dogs seem to mate, and not whelp, when it rains-an observation that cannot be explained by the resource abundance hypothesis. In many tropical species offspring are born during the season of high precipitation, which also coincides with high resource availability. While such seasonality is easy to understand in temperate species exposed to extreme climates, it is more difficult to explain in the tropics. Seasonality of reproduction is observed in many species of organisms, across taxa, and is influenced by both biotic and abiotic factors.
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