Death by coitus

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by Alice
Publish date
14 April 2014
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The other week I attended Isabella Rossellini’s comic and educational monologue Green Porno, a fascinating lecture on the sexual escapades of the natural world. It really got me thinking about the various and bizarre methods of animal reproduction that I've encountered since commencing my role at the Discovery Centre. We see an intriguing array of specimens brought in to be identified and in some cases even added to the collection. Many of these animals would be well-deserving of a feature episode on Isabella’s show, but none have captivated my attention more than our recent acquisition of a male phascogale. 

Phascolgales belong to the same group of marsupials as the Tasmanian Devil and the quolls. But unlike their relatives they have managed to keep a very low profile. Considering that male phascogales live fast, die young, and have such a frantic sex life that it kills them, I was really surprised that the first time I became aware of this genus was through the arrival of a neatly wrapped frozen specimen.

  Mount of Phascogale tapoatafa, Brush-tailed Phascogale  Mount of Brush-tailed Phascogale
Image: Benjamin Healley
Source: Copyright Museum Victoria 2003
 

Phascogales are among a rare breed of mammals that practice suicidal reproduction, or semelparity, where one or both sexes die after a single episode of mating. This strategy is seen in some invertebrate and plant species, but is extremely rare in mammals, only occurring in a few marsupials native to Australia, South America and Papua New Guinea. In Australia the male Phascogale, Antechinus, Dasykaluta and Parantechinus are the only mammals where the males literally mate themselves to death.

Mating season for these dasyurid marsupials lasts only a few short weeks, during which promiscuous females and anxious males copulate for hours at a time (Antechinus have been known to go at it for up to 14 hours!). During this concentrated period of breeding the males’ levels of testosterone and stress hormones become so extreme that even their muscles start to break down to help fuel the act. The intensity of prolonged mating causes the males' bodily functions such as their immune system to shut down, exposing their exhausted bodies to infection, internal bleeding and disease shortly after. The males will not even get to see the fruits of their labour, as they all die before their young are born.

Phascogale tapoatafa: Brush-tailed Phascogale Brush-tailed Phascogale from J. Gould's Mammals of Australia, 1863, vol 1, pl 31
Image: Artist: John Gould; Lithographer: H.C. Richter
Source: Out of Copyright
 

So why do you think male phascogales have been programmed to pursue such a life ending labour of love?

The answer lies in their sperm. For phascogales sexual selection occurs after copulating, where the sperm compete inside the female for fertilisation. Rather than fighting to gain access to mate with a female, males need to put all of their energy into fertilising as many females with as much sperm as possible. This also explains the lengthy duration of the mating spree – the more time one male spends mating with a female, the less opportunity other males have at gaining access to her. Combine this with the promiscuous frenzy of their breeding period and many females may nurture offspring from multiple fathers. 

I can only imagine the field day that Isabella would have illuminating the fascinating science behind the phascogale's reproductive biology. A glimpse at any of her online videos will give you an idea.

Links:

Diana O. Fisher, Christopher R. Dickman, Menna E. Jones, and Simon P. Blomberg (2013) Sperm competition drives the evolution of suicidal reproduction in mammals Proceedings of the National Academy of Sciences, published ahead of print 7 October 2013: doi:10.1073/pnas.1310691110

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