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New Zealand Arachnid Species Exhibits Rare Trimorphism In Male Members

Study reveals environmental factors influence development of alpha, beta, and gamma males with varying body sizes and weaponry.

This arachnid species has three different types of male.

Male members of one type of harvestman have three different possible forms which they can develop into.

The strange New Zealand-based creature is now believed to take their differing forms depending on environmental factors.

A new study shows the ‘trimorphic’ arachnids may become fearsome alpha or beta males with huge jaws which account for up to half of their overall body weight.

Or the creepy crawlies could become sneaky gamma males seven times smaller with their resources focused on reproduction – to ensure they take advantage of the few mating opportunities they get.

Scientists now believe which form the male body takes could now depend on their interactions with predators, with some harvestmen shedding legs to escape the clutches of larger animals that they will never regrow.

Arachnids, which also include mites, scorpions and spiders differ from insects in that they have four pairs of legs and no antennae.

Researchers from the University of Auckland studied the cave-dwelling creature to evaluate why males develop such vastly different bodies and weaponry.

A beta male harvestman with prey. A new study shows the ‘trimorphic’ arachnids may become fearsome alpha or beta males with huge jaws which account for up to half of their overall body weight. PHOTO BY ERIN POWELL/SWNS

Female huntsmen are all of one type, but males are of three – each with their own unique body size, shape and tools.

Alpha and beta males use their giant, protruding jaws to compete with each other over females.

However, gamma males grow up to seven times smaller than their fearsome male counterparts and, instead of fighting, are said to search out undefended females to ‘sneakily’ mate with.

Now research from Dr. Erin Powell has revealed telling clues as to why some males fall to the bottom of the hierarchy.

Huntsmen have the ability to shed legs in order to escape predators – much like lizards are able to self-detach their own tails.

But where lizards are able to regrow their lost tail, huntsmen are unable to regain their lost legs.

Visible scars on the creatures indicate whether they lost their legs as a juvenile or an adult.

Dr. Powell’s research shows that males who lost at least one leg during their development were 45 times more likely to grow up to be the smaller, weaker gamma males.

But the study, published in the journal Behavioral Ecology, found that gamma males instead focus their development elsewhere after giving up on becoming an alpha or beta.

Dr. Powell, who is now a research scientist for the Florida Department of Agriculture and Consumer Services, explained: “Perhaps gamma males grow smaller because they can’t get enough food for their development because their hunting is impeded.

“Or maybe there’s no point in investing in big fighting weapons when they’re already disadvantaged when it comes to fighting.

“So, the arachnids’ resources may be invested in other things, such as testes size, sperm count, or aerobic poise, to ensure they make the most of the mating opportunities they get.”

Dr. Powell added that adopting this strategy is perhaps more advisable than trying and failing to compete with larger, more fearsome alpha and beta males in dangerous male-on-male contests.

Trimorphism is exceptionally rare in the animal kingdom and, so far, researchers have come to believe that a combination of genetics and nutrition may drive so much variation within a single species.

Dr. Powell’s Ph.D. study, however, showed that environmental factors, like encounters with predators, may be more important than previously thought in determining the final adult form of males.

However, it remains a mystery as to why alpha and beta huntsmen both evolve with big bodies and weaponry of differing shapes.

Dr. Powell presumes that each may have its own advantages during battles with other males, with one providing more power but the other affording a longer reach in scuffles of limbs and claws.

“With their ridiculous towering weaponry and extreme male size variation, New Zealand harvestmen are both charming and puzzling.”

“We still have much to learn about their fascinating biology and they have much to teach us about the evolution of mating systems across animal taxa,” said Dr. Powell.

Produced in association with SWNS Talker

Edited by Saba Fatima and Asad Ali

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