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Young beetles engage in sibling rivalry when competing for parental attention

Tom Houslay/University of Cambridge/PA Wire

By Nilima Marshall
Sibling rivalry is not just commonplace in human families.

A new study suggests young beetles compete with each other as well, especially when it comes to receiving care from their parents.

A team of researchers, led by Darren Rebar, from Emporia State University in Kansas in the US, studied 22 generations of the common sexton beetle (Nicrophorus vespilloides) to find out more about family interactions within the species.

Also known as "burying beetles", these insects are seen as "the undertakers of the animal world" as they bury dead and decaying animals, such as mice and small birds, and feed on their corpses.

Parental caregiving can vary among sexton beetle populations, with some parents continuing to tend to their young until they reach the larvae stage, while others leave shortly after laying eggs.

In two of the experiments, the authors separated the parents from their brood to examine their behaviour.

The found young beetle siblings which were cared for by their parents were more competitive towards each other, while those which received no care appeared to be more co-operative.

But the researchers also noted that when parents stopped providing care for their offspring, the rival siblings started co-operating with each other.

Writing in the journal Proceedings of the National Academy of Sciences, the authors noted: "Rapid evolutionary switching between sibling rivalry and sibling co-operation is possible because siblings induce greater levels of rivalry (or co-operation) in each other.

"This generates positive evolutionary feedback, rapidly locking larvae into evolving greater levels of competition (or co-operation) in the presence (or absence) of parental care."

The researchers then created mixed broods so that they contained equal numbers of co-operative and competitive larvae.

They found that once most of the offspring in a brood started to express co-operative or competitive behaviour, it induced greater levels of co-operation or competition, respectively, within the rest of the group.

The researchers said both parental strategies, be it caring for their offspring or leaving them to fend for themselves, can "increase an individual's genetic fitness".

The authors wrote: "In natural populations of burying beetles, it is likely that the supply of care fluctuates greatly from one generation to the next, maintaining a mixture of co-operative and competitive larvae and so preventing any evolutionary runaway to purely competitive or purely co-operative broods."

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