The mites we hate are good helpers for the little beetles

Recently, researchers at the University of Cambridge in the United Kingdom have found that those small beetles that continue to lose in the battle for resources can cooperate with mites to form a mutually beneficial cross-species partnership, thereby gaining a competitive advantage over large beetles. The findings were published in Evolution Letters.

In this study, the researchers looked at the relationship between buried worms and mites that hitchhike on their backs. It turned out that mites were like a warm jacket on the little beetles, and when the beetles moved, the mites made them hot, which made them more competitive against powerful opponents. Although large beetles do not need the help of mites to gain ownership of resources, mites compete with their larvae for food, which reduces the adaptability of large beetles.

Relationships in which both species benefit are known as reciprocal relationships, such as those between pollinating insects and the flowering plants that pollinate them. These relationships are widespread and key to maintaining biodiversity and ecosystem functions, but they are also highly variable. "When the costs of a reciprocal relationship start to outweigh the benefits, they break down." Syuan-Jyun Sun, phD student in the Department of Zoology at the University of Cambridge and first author of the paper, said, "We wanted to know if competition between species is one of the reasons for the diversity of reciprocal relationships. ”

In the race for food or a partner, there are bound to be winners and losers. Researchers at the University of Cambridge wanted to test whether "losers" were more likely to establish reciprocal relationships with other species, thereby gaining a competitive advantage over more powerful rivals. At the same time, for the "winners" who can win the war without any help, this relationship will not bring any benefits and may even become a parasitic relationship.

The researchers tested the idea with experiments with burying worms and mites. Mites are benign passengers on buried worms. Beetles flew around, looking for the carcasses of newly dead critters, such as rats and birds. Both the beetles and the mites on them feed on corpses. However, beetles face fierce competition for ownership of corpses, while smaller beetles tend to lose territory to larger competitors. So since beetles need cadavers to reproduce, how do small beetles reproduce?

"We want to know if mites can help these 'losers' in the battle for corpses," Sun said. In Professor Rebecca Kilner's lab at the University of Cambridge, the researchers put two beetles of comparable size into a battle for the carcass of a rat. One of the beetles carries mites and the other does not. They filmed the battle with infrared thermal imaging and found that the beetles carrying mites were hotter, more aggressive, and therefore more likely to win.

To investigate how this thermal benefit is generated, the researchers built a "gym" for the beetles to work out on a custom treadmill. Beetles either carry mites, substitutes that weigh the same weight as mites, or carry nothing. "We found that overweight causes beetles to generate extra heat when they exercise, and this heat is captured by mites because mites form a thermal insulation layer when they inhabit beetles," Sun said. "These effects are most pronounced in small beetles, which cover a larger surface area than larger beetles. This suggests that mites are more beneficial to small beetles.

To directly test this idea, the researchers again arranged for two beetles to compete for a rat carcass. This time, the two beetles were of different sizes and were then allowed to lay eggs on the carcasses of mice with and without mites. It turned out that small beetles carrying mites were more likely to win the battle for corpses. But mites slightly reduce the reproductive success rate of beetles beetles because they compete with beetle larvae for carrion. However, the huge benefits of obtaining a carcass for reproduction outweigh these small costs. For smaller "loser" beetles, mites are reciprocal because they improve the adaptability of beetles.

For larger beetles, the results of the study were different. They don't need any help to win a corpse, so their connection to mites is of no benefit. To make matters worse, when they breed on cadavers with mites, their health declines. For the larger "winner" beetles, mites reduce their adaptability and do not have a reciprocal relationship with each other, but form an antagonistic relationship.

Editor: Hua Hua Reviewer: Ah Miao Editor-in-Charge: Zhang Meng

Source: Evolution Letters

Issue No. 0014-3820

Original link: https://www.eurekalert.org/pub_releases/2019-03/uoc-mmg030519.php

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