Friday, July 12, 2013

Squid family planning

ResearchBlogging.orgFemale southern bottletail squid may be able to influence the paternity and quality of their offspring by eating the sperm of males. This behaviour is likely to be the result of the conflict that arises between males and females because of their competing evolutionary interests in reproduction. Both sexes use a variety of tactics to manipulate the outcome of mating into their favour. In southern bottletail squid, Sepiadarium austrinum, males use aggression to coerce females into copulations that they might otherwise avoid. 

A new paper from Ben Wegener, Devi Stuart-Fox, Mark Norman and Bob Wong shows that males don’t have it all their own way. Mating occurs head-to-head and is initiated by the male who lunges at the female and grasps her in his tentacles. The male then transfers packets of sperm, called spermatophores, to the female by sticking them into a cavity just below her mouth where they can survive for up to three weeks. But, the spermatophores often have shorter lives because the females will remove and eat them, sometimes before the male has finished copulating with her.

The authors also determined how females were using the nutrients gained from eating the spermatophores. They fed a group of spermatophore-depleted males on a diet laced with a radioactive marker, which was incorporated into new spermatophores as they produced them. Once the females had eaten the radiolabeled spermatophores it was possible to find where the nutrients were being used by assaying for the marker in tissue samples. 

Levels of the marker were elevated in a number of tissues, including the eggs and reproductive glands. Females, therefore, benefit from consuming spermatophores by gaining some additional nutrition that can be allocated to producing offspring. It’s also possible that spermatophore consumption is a form of cryptic female choice, where the spermatophores of low quality males are eaten preferentially. But, this remains to be demonstrated.

This story is also published on the Australasian Evolution Society website in the Research Highlights section.

Reference
Wegener, B. J., Stuart-Fox, D., Norman, M. D., & Wong, B. B. M. (2013). Spermatophore consumption in a cephalopod Biology Letters, 9 (4) DOI: 10.1098/rsbl.2013.0192

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