Outnumbered and on others' turf, misfitssometimes thrive31 May 2017

Two male sticklebacks of the same age -- one from astream (top) and one from a lake (bottom) -- are eachhighly adapted to their own local environment. Accordingto Bolnick, apart from a dramatic difference in size, thefish also differ in immune traits, body shape, armor todefend against predators, and "basically anything wecan think to measure." Credit: Daniel Bolnick/U. of Texasat Austin

It's hard being a misfit: say, a Yankees fan in aroom full of Red Sox fans or a vegetarian at abarbecue joint. Evolutionary biologists have longassumed that's pretty much how things work innature too. Animals that wander into alienenvironments, surrounded by better-adaptedlocals, will struggle. But a team of researchers fromThe University of Texas at Austin was surprised tofind that sometimes, misfits can thrive among theirmuch more numerous native cousins.

"One hundred years of evolutionary theory is builtaround the idea that immigrants from onepopulation dropped into another population of thesame species don't do well," says Daniel Bolnick, aprofessor of integrative biology and the primaryinvestigator on the study published today in the

journal Nature. "Such immigrants are usually rare,and we have found that sometimes their rarityprovides a competitive edge."

Bolnick and his team studied a small fish called athree-spined stickleback that lives in the lakes andstreams of Vancouver, British Columbia. Theystudied two populations of the same species: onegroup that lives in a lake and another group in anadjacent stream.

Evolutionary theory suggests that taking the fishthat are adapted to the lake environment andplacing them into the stream would put them at acompetitive disadvantage compared with theresidents. In the dog-eat-dog world of naturalselection, outsiders are often poorly adapted to anew environment and less likely to survive or passon their genes. In the case of the sticklebacks,that's because the lake-adapted fish have differentphysical traits from their stream-adaptedcousins—such as their overall size, immune traits,body shape and defenses against predators—thatallow them to fare better back home but notnecessarily in other environments.

Yet when the researchers did a series ofexperiments placing varying numbers of fish fromone habitat into the other habitat with local fish,they found the transplants fared surprisingly well.Monitoring the fish in underwater cages over time,the researchers observed that survival had less todo with where a fish was from, and more to do withwhether they were the common or rare type withintheir cage. In either habitat, when stream fish werein the minority, they survived better than when theywere in the majority, for instance.

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Bolnick and his team study a small fish called a three-spined stickleback that lives in the lakes and streams ofVancouver, British Columbia. This photo: Comida Lakeand its outlet stream. Credit: Thor Veen

The scientists found that immigrants could fly underthe radar in the face of some threats, which helpedthem beat the odds.

"You come in and you eat something nobody elsearound you eats, so you aren't competing for food,"Bolnick says. "The local parasites don't know whatto do with you because you have an unfamiliarimmune system. So you're better off than theresidents."

Bolnick notes that being less adapted to theenvironment also has some negative effects onimmigrants, just as theory predicts, but their studyshows that in some instances the benefits of raritycan outweigh the drawbacks of being in anunfamiliar environment.

"We found newcomers in the population pass ontheir genes more often than residents, and theycontribute more to the next generation," Bolnicksays.

The team found that this effect gives migrants anoutsized impact on the genetics of their adoptedpopulation. This slows the pace of evolutionarydivergence—the rate at which each of the two

populations might pick up new traits that make itdiffer more from the other.

When Bolnick and his team transplanted small numbersof fish from one habitat (either lake or stream) tounderwater cages in the other habitat, they found thetransplants fared surprisingly well. Credit: DanielBolnick/U. of Texas at Austin

Bolnick says this work could have implications forthe protection and restoration of endangeredspecies. For example, coral reefs are in declinearound the world, but attempts to transplant coralsfrom one location to another to restore reefs so farhave met only limited success.

"My advice to someone doing any restoration workis that they can't just consider how well matchedimmigrants are to the local habitat," Bolnick pointsout. "They also need to consider how the immigrants' rarity affects their survival andreproduction."

In a separate paper published on May 22 in thejournal Nature Ecology & Evolution, Bolnick and hiscolleagues made findings that also apply to speciesrestoration. They found that stickleback adapt moreclosely to their environments than previouslythought. So even fish from two streams that looksimilar might have different traits. That's becauseno two streams are exactly the same. There aresubtle differences in water depth, flow rates, foodsources and the presence of pathogens and

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predators.

"Just because the streams look similar to us, on thesurface, doesn't mean that they areinterchangeable," says Bolnick. "Every stream isecologically unique. And so every streampopulation's adaptations must be similarly unique."

More information: Daniel I. Bolnick et al,Frequency dependence limits divergent evolutionby favouring rare immigrants over residents, Nature(2017). DOI: 10.1038/nature22351

Yoel E. Stuart et al. Contrasting effects ofenvironment and genetics generate a continuum ofparallel evolution, Nature Ecology & Evolution(2017). DOI: 10.1038/s41559-017-0158

Provided by University of Texas at AustinAPA citation: Outnumbered and on others' turf, misfits sometimes thrive (2017, May 31) retrieved 23June 2018 from https://phys.org/news/2017-05-outnumbered-turf-misfits.html

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