In the absence of sexual prospects, parasitic male worms go spermless

November 10, 2008

When females aren't around, one species of parasitic nematode worm doesn't even bother to make any sperm, reveals a new report in the November 11th issue of Current Biology, a Cell Press publication.

" This is very unusual for a male to need a female to be present before he produces sperm," said Christine Griffin of the National University of Ireland, Maynooth. "We searched the literature but could find no report of this in any other animal. Animals have evolved all sorts of strategies, some quite bizarre, to increase their lifetime reproductive success, but this particular one does not appear to be common." Lifetime reproductive success refers to the number of offspring produced over the course of a lifetime.

Scientists have generally considered sperm production to be cheap relative to the production of eggs in females, she said. But that notion has been challenged of late in animals that must produce a lot of sperm or particularly large sperm. The males of some other species of rodents, fish, and insects, for example, cut back on sperm according to their social circumstances. But they generally don't go without.

The researchers haven't yet shown how this behavior in the parasitic nematodes known as Steinernema longicaudum benefits the males of the species. But, they say, this newly discovered behavior makes some sense in light of the worms' unusual life history.

" Most animals can move around in search of a mate, and so should be ready to make the most of any opportunities that present themselves," Griffin explained. "Like many parasites, Steinernema enter their host insect when they are still juvenile and develop inside. A male that finds himself alone cannot leave the insect to search for a mate." Since only juvenile worms invade insects, those solitary males just have to wait until a young mating prospect joins him and grows up. Under these circumstances, she said, a mating partner can't appear suddenly, leaving the male no reason to be sexually mature.

Griffin's team, which included Lemma Ebssa, now at Rutgers University, made the discovery while studying the reproductive behavior of the nematode. They were surprised to find that it took some time before successful mating occurred between a pair of worms placed together.

"Initially, we thought that perhaps the female was unreceptive and/or immature, as this would be the more normal situation in animals," Griffin said. "However, further experiments showed that it was the male that was unready. We then took a closer look and discovered to our great surprise that the reproductive tract of naive males was smaller than that of males that had been with a female for some time, and it contained no sperm."

The researchers think that the signal from females to mature may be chemical in nature, since lone males matured even when females were placed on the other side of a permeable barrier. (The nematodes don't have eyes with which to see.) The researchers don't yet know whether the pheromones that stimulate male maturity are the same as those that sexually attract him to females.

Source: Cell Press

Explore further: Help scientists research lugworms' sex lives

Related Stories

Help scientists research lugworms' sex lives

September 28, 2016

Love is in the air along our coastlines this autumn and scientists from the University of Portsmouth are asking the public to keep an eye out for signs of passion in the lugworm population.

Cannabinoid receptor activates spermatozoa

August 30, 2016

Biologists from Bochum and Bonn have detected a cannabinoid receptor in spermatozoa. Endogenous cannabinoids that occur in both the male and the female genital tract activate the spermatozoa: they trigger the so-called acrosome ...

Recommended for you

US prepares to cede key role for internet

September 29, 2016

The US government is set to cut the final thread of its oversight of the internet, yielding a largely symbolic but nevertheless significant role over the online address system.

Scientists investigate unidentified radio sources

September 28, 2016

(Phys.org)—A team of researchers led by Andrea Maselli of the Institute of Space Astrophysics and Cosmic Physics of Palermo, Italy, has conducted an observational campaign of a group of unassociated radio sources with NASA's ...

The frontier fields: Where primordial galaxies lurk

September 28, 2016

In the ongoing hunt for the universe's earliest galaxies, NASA's Spitzer Space Telescope has wrapped up its observations for the Frontier Fields project. This ambitious project has combined the power of all three of NASA's ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.