It is sometimes necessary for men wanting to attract the opposite sex to come out of their shell. Yet it seems that by often choosing the bolder males, women may be missing out on the best possible mate. Researchers have found that the shyest males actually have the most to offer a potential lover - at least in the world of hermit crabs. Hermit crabs, like the ones above, borrow the shells from other creatures to keep them safe and new research has shown that those crabs that stay in their shells more often tend to be a better mate for female crabs . Professor Mark Briffa, a marine animal behaviour researcher at Plymouth University, and his colleagues have found that the most timid crabs tend to more high quality sperm - making them a better option for females looking for a mate. This, they say, is because the crabs that spend more time hiding from the world inside their shells, also have invested the most resources in becoming reproductively fit. Males of a species of hairy chested crab, which has been given a nickname David Hasselhoff, spend their lives largely separate from the females, according to new research. In a study looking at the private life of the deep-sea crab known as the 'Hoff' have found that the males and females spend separate lives at volcanic vents 1.5 miles deep near Antarctica. This, according to the British research, is because of the conflicting demands of feeding and raising young among the sexes. In 2010, a British expedition revealed a 'lost world' of deep-sea animals including the crab named after the Baywatch star thriving on the ocean floor near Antarctica. Using a deep-diving remotely operated vehicle (ROV) to examine the distribution, size and sex of these crabs at the vents, Dr Leigh Marsh and colleagues from the University of Southampton have now pieced together their private lives. The researchers found that large male Hoff crabs live highest on the mineral spires of the deep-sea vents, closest to the hot fluids that jet from them. Smaller males tend to mingle with the females at the base of the mineral spires. It is an unusual approach in the animal kingdom, where the boldest, bravest and strongest usually win the right to mate. Indeed, in many species males have to prove their physical fitness with bold and dramatic displays - like in peacocks and birds of paradise - and even mortal combat in some cases. Writing in the journal Proceedings of the Royal Society B, Professor Briffa and his colleagues said: 'It appears that in hermit crabs, high-quality individuals that have invested heavily in reproduction, by making large spermatophores, are the most risk averse. 'Although we did not measure metabolic rate, a key process for the pace of life syndrome, this result seems counter to the idea that the most productive individuals should also be the boldest.' The researchers examined the 'personality' of 100 hermit crabs collected from Mount Batten and Hannafore Point in Plymouth. They did this by testing the 'startle response' of each crab by removing it from its tank, inverting the crab for five seconds, which caused it to withdraw into its shell, and then returning it back into the tank upright. The boldest crabs would then poke their heads back out of their shells far faster than the more timid crabs. On average most crabs emerged within 16 seconds. The researchers then measured the levels of a protein called haemocyanin, which is responsible for carrying oxygen around the crabs bodies. They found crabs that stayed in their shells longer after being startled tended to have higher levels of this protein. Hermit crabs, like the one pictured above, hide in their shells when startled, but it also helps them become better mates . This is because when inside their shell, the crabs are unable to access the oxygen rich sea water around them and so higher levels of this protein helps use the oxygen already in their bodies more efficiently. Next the researchers examined the crustacean's gonads and measured the size of the tube shaped bundles of sperm there, called spermatophores. Again they found in the timid crabs, those that were slower to reemerge from their shells after being frightened, had larger spermatophores and so more high quality sperm stored. As they grow, hermit crabs like the one above, 'upgrade' their shells by seeking out larger ones as finding the right home can offer them protection from danger but also give them a way of growing better stores of sperm . Professor Briffa and his colleagues said that hiding in the shell when threatened may allow the crabs to conserve their energy for building up greater sperm reserves. It also reduces the risk of losing a shell in a fight with another crab, something that can increase the amount of stress a crab is exposed to. They said that in hermit crabs less reproductively fit individuals may develop boldness to help them compete with the shier more fertile crabs. They said: 'Low-quality males may emerge more quickly in an attempt to maximize their chance of mating, or because they need to return more quickly to foraging, or through a combination of these causes.'
Biologists at Plymouth University studied how crabs reacted when startled . They found shyer crabs had larger packets of sperm than the bolder ones . It contrasts with many species where bold displays tend to attract mates . Males in other species must prove their fitness by fighting or showing off . Scientists say hiding allows crabs to invest more energy in making sperm .