Experts have revealed that shy guys are the best mates, at least among hermit crabs. Findings of a new study revealed that when it comes to hermit crabs, shy males are better mates because they have better quality sperm. It appears that staying hidden in their shell helps improve these timid decapod crustaceans' reproductive capabilities.

For their study published in the journal Proceedings of the Royal Society B on Feb. 11, Mark Briffa from Plymouth University's Marine Biology and Ecology Research Center and colleagues examined the personality of 100 hermit crabs.

The researchers removed each of the crabs from the tank inverting them for five seconds, which caused them to withdraw into their shell, and then returning them back to their tank upright. The boldest of the crabs poked their heads back out of the shell much faster compared with the more timid crabs.

Briffa and colleagues then measured the quality of the sperm of each crabs and found that the more timid ones tend to have better quality sperm. The timid crabs, which were slower to re-emerge from their shells when frightened, had larger spermatophores, which mean they can store more high quality sperm.

The researchers explained that by hiding in their shell when threatened, the crabs could conserve energy that they could use to build up greater sperm reserves. The researchers also said that the timid crabs reduce their odds of losing a shell in a fight, which can increase the amount of stress that they are subjected to. They likewise pointed that the crabs that are less reproductively fit may develop boldness so they can compete with the more fertile albeit shier crabs.

"It appears that in hermit crabs, high-quality individuals that have invested heavily in reproduction, by making large spermatophores, are the most risk averse," Briffa said.

The researchers said that that they did not measure the crabs' metabolic rate but their findings appear to counter the notion that the most productive individuals are the boldest.

"Individual consistency was unrelated to haemocyanin concentration or spermatophore size, but mean startle response duration increased with spermatophore size," the researchers wrote in their study. "Thus, counter to expectations, it was the most risk-averse individuals, rather than the boldest and most risk prone, that were the most productive."

Briffa and colleagues suggested that similar patterns may also be seen in other species, particularly if the most productive individuals were likely to avoid risky behaviors.

Photo: Fred von Lohmann | Flickr