Is a low metabolic rate responsible for the bizarre mating behaviour of Tasmanian echidnas?

Stewart C Nicol, Gemma E. Morrow and Rachel L. Harris

Juvenile Tasmanian echidna. Photo credit: Jenny Sprent
Juvenile Tasmanian echidna. Photo credit: Jenny Sprent

Egg-laying mammals are found only in Australia and New Guinea, but the most common of these, the short-beaked echidna, occurs throughout Australia and parts of New Guinea. In Tasmania echidnas hibernate, but the timing of hibernation is quite surprising. Males enter hibernation in late summer and emerge in late autumn and search for females, and groups of up to four males attempt to mate with individual females.

We analysed data from an 18-year field study to try to understand this behaviour. Because echidnas have a very low metabolic rate, they have a long lactation period and the best time for mating is about mid-July as it allows young to be weaned in January. After January food availability decreases and the young may not be able to be able to find enough food to fatten up and survive the winter. If they mate too early, females will need to forage for food to support lactation when food is scarce and the weather is cold. As in other seasonal breeders echidna testes shrink after the mating season, but their low metabolic rate means that for males to regrow their testes for the next mating season takes 2-3 months, and so, uniquely among hibernators, echidna testes regrow before hibernation. Females do not breed every year, and only produce a single young, so competition between males for females has led to early emergence and mating, with the males in best condition emerging and mating earliest. Because early mating presents a problem for females they re-enter hibernation while pregnant, suspending development of the egg. This female strategy is frequently thwarted by males that disturb her hibernation and mate with her although she is already pregnant.

Similar competition between groups of males for females is seen in some armadillos, which fill a similar ecological niche, but because they have higher metabolic rates and the young grow more quickly they do not need to mate in mid-winter.

Read the paper in full here.

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