“Intraspecific competition and inbreeding depression: increased competitive effort by inbred males is costly to outbred opponents”

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Jon Richardson and Per T. Smiseth

Increased competitive effort by inbred individuals is costly to outbred opponents in Nicrophorus

Nothing to lose – inbred beetles are better at competing for resources used for breeding

Nicrophorus vespilloides feeding larvae.
(Credit: Per T. Smiseth)

Inbred individuals typically have reduced growth, reproductive success and survival compared to outbred individuals. These negative consequences of inbreeding can be exaggerated when there is intense competition over resources because inbred individuals are often weaker competitors. However, inbred individuals might invest more in competition for resources that can be used for a current breeding attempt, if have a low chance of breeding again in the future.

Researchers from the University of Edinburgh have tested whether inbred individuals increase their competitive effort in burying beetles. This species is native to the UK and breeds on small vertebrate carcasses, which they protect from other intruding beetles. An intruder that succeeds in usurping the resident will kill the resident’s offspring and use the carcass to raise their own brood. The authors set up contests in which an inbred or outbred resident beetle defended a carcass from an inbred or outbred intruder. They found that inbred beetles were more successful at taking over carcasses than outbred intruders and that inbred beetles were more willing to take risks when competing for a carcass. The increased competitive effort of inbred intruders had negative consequences for outbred beetles even when they successfully defended their carcasses, as they produced fewer and smaller offspring than beetles facing either an outbred intruder or no intruder.

This work provides a novel insight on the complex interaction between competition and inbreeding. The results introduce an important twist to the ecology of inbreeding by showing that inbred individuals can increase their reproductive success through increased competitive effort compared to outbred males. Furthermore, this success comes at a cost to outbred individuals interacting with inbred ones. Read the Article