Males still necessary, even in asexually reproducing species

Chuck Bednar for redOrbit.com – @BednarChuck

Despite evolutionary adaptations that have allowed female members of some fish, reptile, and amphibian species to reproduce by cloning themselves, a new study published online recently in The Science of Nature shows that males still play an important role in reproduction.

Researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) discovered that even in species capable of perpetuate offspring through cloning, fertilization is still very much required to ensure the survival of the maximum number of healthy offspring, thus indicating that males have not become obsolete just yet.

The mystery of the Little Fire Ant

In harsh environments, some species are able to increase their numbers more quickly when females don’t have to take the time to find a suitable mate. Experts believe that this ability may have first arisen independently in creatures either due to conflict between the species or to keep the species alive when worthy males are difficult to find.

Many of these species are now almost exclusively female, and the researchers from the OIST Ecology and Evolution Unit set out to analyze how the transition from sexual reproduction to asexual, clonal reproduction evolved by studying a species known as the Little Fire Ant.

The Little Fire Ant is a creature in which some populations reproduce sexually and others do so clonally, yet there are still male members in both types of populations. As in other types of ants, male Little Fire Ants fertilize queens to produce a worker class that is sterile and accepts genetic contributions from both parents.

The offspring of the reproductive classes differ, however. As the study authors explain, fertile males hatch with no genetic contribution from the queen laying the egg, while new queens hatch without any genetic contributions from the father. What remained unclear was why male Little Fire Ants continued to exist when queens can clonally produce both workers and queens.

Reproductive systems enhanced by sexual stimulus

To solve the mystery, the OIST team studied colonies from that reproduced both sexually and clonally, and found that inseminated queens had close to a 100 percent success rate in terms of how many of their eggs hatched. However, in queens that reproduced clonally, most of the eggs did not make it beyond the early stages of embryo development.

Furthermore, mating was found to stimulate queens to lay eggs faster than not mating. The results suggest that in the case of this species, the battle of the sexes theory is unlikely, as mating with males allows queens to produce a greater number of healthy offspring that is possible through cloning. Furthermore, having sex made the queens more fit, as evidenced by the higher success rates of egg laying and hatching, and is beneficial to the colony.

While the mechanisms through which evolution keeps sex from being eliminated completely is still unknown, the study authors said that it is clear that even in species that can bypass the need to have sex to reproduce, there seems to be some evolutionary constraint causing the females to anticipate the sexual stimulus. Their reproductive systems do not perform as well without it, the OIST researchers concluded.

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