octopus gender differences

[michaelg]

This comes from Science Vol 298, pg 531.

 

If a sparrow tried to mate with a fighter jet, that would fairly describe the kamikaze sex lives of males of a bizarre seafaring octopus. Australian and British scientists have discovered that among the rarely encountered blanket octopus (Tremoctopus violaceus), females outweigh males by up to 40,000 times.

 

 

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Male (right) is small enough to fit in eye of female (left).

 

CREDITS (LEFT TO RIGHT): P. WIRTZ; D. PAUL

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Zoologist Mark Norman of Museum Victoria in Melbourne and his colleagues had what they say is scientists' first-ever encounter with a live male blanket octopus, photographing and collecting one during night dives in deep water off the northern Great Barrier Reef. The adult male is about the size of a jellybean, weighing about a quarter-gram--making it about the size of the pupil in a female's eye.

 

Blanket octopuses are pelagic, never touching the sea floor. It's hard for males to find females in the open ocean, says Norman, and pelagic males seem to devote all their resources to sex. He suggests one reason the males miniaturized was to cut down on development time and beat competitors to the punch. Females grow large to produce as many eggs as possible so at least a few will survive in the vast deep. Males give females their all when it comes to mating, says Norman. When a male uses his special reproductive arm, the sperm-loaded limb breaks off and crawls into the female's gill cavity, and the males usually die. Scientists have found females containing multiple still-living arms from males in them--evidence of male competition, Norman says.

 

"The extreme nature of the size dimorphism is staggering," says cephalopod specialist John Forsythe of the University of Texas Marine Biomedical Institute in Galveston. More extreme examples can be found among several barnacle species, but there the male lives on the female and is basically "reduced to a sperm generator," Norman says. The scientists will describe their findings in the December New Zealand Journal of Marine and Freshwater Research.