Scientists have found a rare species of arachnid in New Zealand that is home to three different types of males. Recent insights into the species are forcing rethinking of animal mating systems and the development of reproductive strategies.
First a short review. We have known since 2020 that male harvestmen (Forsteropsalis pureora) – or papa-longlegs, as you may know them better – look alike and have similar genes, there seemed to be three different types.
At the top of the hierarchy is the large alpha male, who has short but strong, pincer-like jaws that he uses to pin down the competition in a fight for territory or a mate.
Next is the beta male, which has longer and thinner pincers. And last but not least is the gamma male, which is seven times smaller than the other two.
Gamma males not only look different from the rest, they also act differently.
Instead of fighting over females like their larger counterparts, researchers found that these smaller, weaponless males have all but given up fighting.
Their survival tactic is to sneak around and look for undefended females to breed with.
The rare pecking order is known as trimorphism and was first discovered in animals by researchers in 2009.
Now researchers at the University of Auckland – many of whom conducted the 2020 study – believe they have discovered why trimorphism develops in harvestmen, in particular.
According to the new study, a male harvestman who loses a leg in his youth and voluntarily “drops” it to avoid a hungry predator is unable to regrow the lost limb and is 45 times more likely to grow smaller and weaker than his colleagues.
“Perhaps that’s because they don’t get enough food for their development because their hunting is hampered,” posits evolutionary ecologist Erin Powell.
“Perhaps it makes no sense to invest in large combat weapons if they are already at a disadvantage in combat. Therefore, arachnids’ resources can be invested in other things, such as testicle size, sperm count, or aerobic husbandry.” Make sure they make the most of the mating opportunities presented to them.
The latter possibility is particularly intriguing as it suggests that male harvestmen may permanently “lay down their arms” and adopt a new lifestyle that does not rely on competition. So egEven when males have fewer legs to stand on, they can still find opportunities to reproduce.
If that is the case, then Charles Darwin’s theory of sexual selection, which places great emphasis on sexual ornaments and weapons, may not be complete; There might be other ways to snag a mate in nature.
In fact, the same male dung beetles that Darwin used to support his theory of sexual selection over a century ago also turned out to be trimorphic. This means that not all male dung beetles possess large mandibles for fighting other males or for courting females.
While trimorphism may be a result of different genetics producing different male roles in a society, in the case of dung beetles and harvestmen the phenomenon appears to have less to do with how animals are born and more to do with how they are raised.
What happens in their youth seems to dictate how they develop sexually.
More research is needed to find out what differentiates alpha and beta males.
“With their ridiculously high armament and extreme male size disparity, New Zealand harvestmen are both charming and enigmatic,” says Powell.
“We still have a lot to learn about their fascinating biology, and they can teach us a lot about the evolution of mating systems in different animal taxa.”
The study was published in behavioral ecology.