It's survival of the fittest in nature, and an alien-looking ground mite demonstrates how the most promiscuous males fight and sometimes even cannibalise other males to 'win' greater access to females.
Flinders University researchers have found that these tiny mites (Rhizoglyphus echinopus), which can breed to pest levels and damage bulb crops including onions and garlic, can regulate their aggression to target and eat rivals which are not related to them.
"We know male competition influences long-term population growth and understanding levels of aggression in populations can help to understand their strengths and weaknesses if conservation or control measures are required," says evolutionary biologist Dr Bruno Buzatto, senior author of a new journal article about these microscopic bulb mites, barely visible at less than 0.5mm on average.
For example, separate studies have previously found some arthropods such as Colorado potato beetles, forked fungus beetles, praying mantises and wolf spiders do not exhibit kin discrimination and display equal levels of aggression regardless of relatedness.
"With these mites, we were able to examine levels of fighter aggression towards their own brothers versus unrelated males, and when females were present," says Dr Buzatto, who leads the Behaviour and Ecology of Terrestrial Arthropods (BETA) Lab in the College of Science and Engineering.
"Male fighters can quickly kill their rivals and are more likely to do so if their rivals are unrelated genetically.
"Like some insects and spiders, this study noted less aggression towards kin and higher mortality among mites not related to fighter males - and more intensity in fighter aggression when females are present."
Researchers say the study helps to fully understand the impact of kinship on aggression within the context of mate competition, especially when aggression evolved as part of a reproductive tactic.
The article, 'Mate competition and relatedness among males mediate the evolution of lethal fights in bulb mites' (2025) by Incheol Shin, Sebastian Hayden and Bruno A Buzatto has been published in the journal Evolution (Oxford Academic). DOI: 10.1093/evolut/qpaf094. https://doi.org/10.1093/evolut/qpaf094
