University of California, Davis

Category: plasticity

Stickleback camouflage

This week, the Wainwright blog returns to a topic of perennial interest, the threespine stickleback. I will discuss a recent paper from the Schluter lab at UBC on color plasticity and background matching in stickleback.

To set the stage, it’s important to realize that from a stickleback’s perspective, “bird” is a four-letter word. Predation by diving birds like grebes and coots is commonplace in many freshwater stickleback populations. Unlike predatory dragonfly larva, which detect prey by vision and by water movement, diving birds generally detect their prey by sight alone. In other words, if you’re a freshwater stickleback, it’s very important that the top of your body blends in with your surroundings.

This stickleback didn't get the memo. (http://www.lifeontheslea.co.uk )

In this paper, Jason Clarke and Dolph Schluter tried to assay background matching capability between limnetic and benthic sticklebacks in Paxton Lake, British Columbia. First, they used a spectrometer to record the background color in the limnetic and benthic habitats. The open-water limnetic habitat was a bluish color, but the benthic habitat, which has more aquatic vegetation, tended to be more greenish. Additionally, the benthic habitat showed much more variation in color than the limnetic habitat.

After checking the background color, the authors painted two sets of cups, one designed to look like the limnetic background, and one designed to look like the benthic background. Then they put benthic and limnetic sticklebacks on each background, let them adjust their color for 15 minutes, photographed each fish, then measured how well each fish matched its background. They also did the same experiment again, but this time taking pictures every 20 seconds.

What did they find? Limnetic fish and benthic fish were equally good at matching the blue limnetic background, but limnetic fish were not as good at matching the green benthic background as benthics were. The time trial experiment helped to clear up what was going on: benthics rapidly adapted their colors to match the background, but limnetics were doing something different. Limnetic fish were cycling through different colors instead of fixing a particular color. Limnetics were more variable in color when viewed with a benthic background, but even on their “home turf” in the limnetic background, they still showed variation in color, but to a lesser degree.

The authors suggest that the patterns of color chance exhibited by benthics and limnetics are probably adaptive. Their spectrometer data indicates that the benthic habitat is more variable in color, and their background experiments show that benthics are better at rapidly changing their colors to match the background. The limnetic habitat, on the other hand, is much more uniform, so there would be little incentive for limnetics to evolve rapid color matching. However, limnetics may be adapting to their light environment in an entirely different way:  the  “flickering” exhibited by limnetics could be an adaptation to fluctuating light intensity in open water.

After reading this paper, I’m particularly curious what the color-matching abilities of the ancestral marine sticklebacks are like. If they resemble the limnetic, then this color matching ability will be another interesting benthic stickleback adaptation. It will be cool to see if it is possible to discern the genetic basis for this shift in plasticity.

Clark JM, Schluter D. Colour plasticity and background matching in a threespine stickleback species pair. Biological Journal of the Linnean Society. DOI: 10.1111/j.1095-8312.2011.01623.x

Stickleblog: Plastic stickleback

ResearchBlogging.orgWhen I was an undergraduate at UNC, I worked in the Pfennig lab on spadefoot toads, which exhibit a striking form of polyphenism. Polyphenism occurs when one genotype can produce multiple phenotypes in response to environmental conditions. As it turns out, stickleback have polyphenic traits too!

Matthew Wund
in Susan Foster’s lab at Clark University published a paper in American Naturalist this past year that deals with an especially interesting form of plasticity called the “flexible stem” hypothesis. The idea is that polyphenism in an ancestral species may influence the pattern of diversification in its descendant lineages.

Stickleback are a great system for testing this idea, because freshwater sticklebacks have repeatedly diverged into “benthic” and “limnetic” forms when the ancestral marine form colonized freshwater habitats at the end of the last glaciation period.

Matthew and the Foster lab collected stickleback from a marine population, a freshwater limnetic population, and a freshwater benthic population, and bred them in the lab. They then took the young sticklebacks and fed them either limnetic food(small swimming crustaceans) or benthic food(bottom-dwelling insect larva).

Interestingly, the head morphology of marine fish changed; fish fed a benthic diet developed a head that looked like a benthic freshwater fish, and marine fish fed a limnetic diet developed a limnetic-like head.

The ancestral marine fish exhibit a polyphenism that resembles the descendent freshwater populations, which suggests that this ancestral polyphenism may be important in governing how a lineage diversifies.

Wund, M., Baker, J., Clancy, B., Golub, J., & Foster, S. (2008). A Test of the “Flexible Stem” Model of Evolution: Ancestral Plasticity, Genetic Accommodation, and Morphological Divergence in the Threespine Stickleback Radiation The American Naturalist, 172 (4), 449-462 DOI: 10.1086/590966

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