No one would be mad enough to run a marathon without any training, but that is essentially what Christmas Island red crabs do every year. They spend months hunkered down, relatively inactive, in inland burrows waiting for the monsoon to come and as soon as the rains hit they're off, marching across the island for up to 12 h a day to the beaches where they mate and reproduce. So how do they pull off this remarkable athletic feat with virtually no training? Having been fascinated by the physiology of these extraordinary crustaceans for much of his career, Steve Morris, from the University of Bristol, knew that the crabs must make major changes to their muscle composition over a very short time to switch from muscle suited to anaerobic short-term sprinting (while inland) to aerobic high endurance muscle to sustain their coastal march. Curious to find out what modifications the crabs make, Morris teamed up with Ute Postel, Fiona Thompson, Gary Barker and Mark Viney to find out which genes are expressed most in the legs of crabs before and after embarking on their long haul hike (p. 1740).

Travelling to Christmas Island just before the monsoon broke, Morris and Postel collected leg muscles from crabs while they were migrating and returned 6 months later to collect muscles from the animals during the dry season. Back in the UK, Postel isolated the mRNA (the code molecule that is transcribed from genes and then translated to make protein) from the muscles to see if there were differences between the genes that were transcribed during the monsoon migration and those transcribed when the crabs were inactive during the dry season.

After months building a library from the mRNA molecules from both tissues and analysing the expression levels of many genes, the team could see that there were dramatic differences between the migrating and inactive crabs' muscles. Not surprisingly the majority of the genes expressed in the muscles coded for muscle proteins, such as actin, which forms part of the muscle's contractile unit, and troponin and tropomyosin, which regulate muscular contraction. And, when the team took a closer look at the versions of genes that were expressed, they could see that the immobile dry season crabs' muscles were tuned to short anaerobic sprints while the muscles of crabs that migrated during the monsoon were aerobic, extremely resistant to fatigue and ideal for the crab's arduous odyssey.

The team also found that mRNA transcripts of genes that code for proteins involved in muscle reconstruction were more abundant in the migrating crabs' legs and say ‘their comparative up-regulation is consistent with remodelling of leg muscle for migration in the wet season’. So the crabs' muscles undergo a dramatic change as the monsoon sets in, ready for their migration to the coast. Tragically, Morris did not live to see this work published as he was knocked off his bike on the way into the lab on the morning of 11 August 2009 and died later from his injuries. ‘The accident that killed Steve was on the day that the referees' comments came back; he never saw them,’ remembers Viney. ‘Steve was a traditional physiologist and this was the first time that he had done a study at the molecular level. It was a brave new departure for him and this paper is the first manifestation of this new direction of his research,’ says Viney. Reflecting on the impact of Morris's death on his friends and colleagues Viney says, ‘Steve never let anything stop him and we took that spirit on to get this paper out’.

Migration-related changes in gene expression in leg muscle of the Christmas Island red crab Gecarcoidea natalis: seasonal preparation for long-distance walking
J. Exp. Biol.