When you think of romantic animals, cockroaches may not be top of your list; I suspect they would struggle to even make the top 10. Despite these human preconceptions, the presence of many baby cockroaches worldwide suggests that male cockroaches have something special up their ‘sleeves’ to get the ladies going. Before getting down and dirty, a frisky male must first get past his competitors, all raring to fight for valuable female attention.
This competition is what Dr Kate Durrant, here at the University of Nottingham, has been exploring to increase our understanding of the lengths that males in the natural world go to in order to impress their dates.
When it comes to the fighting style of the Hissing cockroach, think majestic stags locking antlers and facing off…but on a slightly smaller scale. Males that are successful in fights can gain a higher ranking, hold territory and find themselves preferentially chosen by females. Small horns on the front of the male allow them to beat off competitors, but appear to carry costs in other, arguably important, areas.
“If a male loses the genetic lottery and finds himself with small horns as he approaches adulthood he may invest more into producing enough sperm”
Researchers measured male horn length along with testicle size in two Hissing cockroach species and found that males with large horns were *ahem* lacking in the other area. This suggests a trade-off, with males either gaining more mates through fighting ability or through producing more sperm (with the bigger testicles) to compete with other males after mating. ‘Strength in numbers’ certainly applies here, with increased sperm production being linked to a greater paternity share, compared to other males that the female may have mated with.
While features of testicular size may be genetically fixed, there could also be an aspect of ‘choice’ made by the males as they mature. Some insects can change the size of body parts during their final moult, such as butterflies growing larger front wings if their hind ones are damaged.
Dr Kate Durrant suggests that the same system could be occurring with these cockroaches’ sexy characteristics. If a male loses the genetic lottery and finds himself with small horns as he approaches adulthood he may invest more into producing enough sperm to make the most of any encounters he does manage to sneak past the fighting males.
While perhaps they are often overlooked in favour of more photogenic species, cockroaches are a remarkable group to study, with some varied and multifaceted social behaviours. Exploratory research into such complex insect society, as is undertaken at the University of Nottingham’s Life Sciences department, can provide invaluable insights into the development of ‘higher’ societies such as our own, and specifically in the case of sexual selection.
However far removed you think cockroach mating competition is from the ‘mate search’ of the Crisis dancefloor, it really does suggest that, pretty universally, size does matter.
Ella Deutsch
Image courtesy of Nasrullah Taha on Flikr
To find out more about the cockroach research going on at the University of Nottingham, have a look at the scientific article in Nature
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