Jack of all trades fish are better equipped to make the transition from water to land, but a new survey of blennies, a diverse group of small fish, suggests specialization helps species stay there.
Blennies are found all over the globe in marine, brackish and freshwater habitats. Most of the nearly 900 species live along the coasts, and though the majority of blennies spend their days fully submerged, a sizable percentage spend much of their lives out of the water.
Some species, often called rock hoppers, hang out in intertidal zones, in tidal pools where temperatures and water levels fluctuate rapidly. Others are completely adapted to life on the sand, in the splash zones where they get wet only periodically to help them breathe.
"The blennies are a very exciting group to study, from both an ecological and evolutionary standpoint," Terry Ord, study co-author and evolutionary ecologist, told UPI in an email.
"They allow the unique opportunity to see how habitat transitions occur in nature, and also the evolutionary causes and consequences of those transitions," said Ord, who is director of research at the University of New South Wales' School of Biological, Earth and Environmental Science.
While studying blennies in Mauritius, an African island in the Indian Ocean, Ord got to talking with Peter Hundt, a fish ecologist and postdoctoral researcher at the University of Minnesota. The two scientists had amassed a large amount of data on blennies.
"We decided to combine our interests and use our respective data to see how diet might be related to fish leaving water for a life on land," Ord said. "Peter had detailed information on diet and teeth morphology, while I had lots of data on behavior and frequency of different species emerging from water for brief or extended periods on land."
When the two scientists subjected their data sets to a series of complex evolutionary statistical models, they found a strong link between dietary and behavioral flexibility and transitional success.
In other words, blennies that were generalists were more likely to have made the transition from water to semi-aquatic or terrestrial lifestyles.
However, the statistical analysis — published Wednesday in the journal Functional Ecology — suggests unique conditions found on land have forced transitional species to specialize.
On land, blennies are blessed with an abundance of detritus. Aquatic blennies eat detritus, too, but underwater, there are a variety of food resources.
"There's an advantage for aquatic blennies to being a generalist because it allows them to switch back and forth depending on what's immediately available at the time," Ord said.
"On land, there's a single, but ample source of detritus on the rocks in the splash zone, so blennies have shifted to feeding on that resource and effectively only that resource," Ord said. "To acquire that food even better than before, natural selection has adapted their tooth morphology in a very unique way to allow them to more efficiently scrape the rocks, or essentially graze over the rocks for detritus, which also includes algae stuck to the rocks."
Diet and tooth morphology aren't the only characteristics that change when blennies make the switch from water to land, and in future studies, Ord hopes to investigate how the transition impacts other aspects of the species' behavior, ecology and morphology
"For example, these fishes are really agile out of the water, and I suspect they've adapted their body shape to allow them to hop about the rocks so freely," he said. "Which in turn implies that land blennies might not be able to go back to water because they're not only specialized in their diets, but also their morphology and this makes them terrible swimmers."
