In celebration of the first 20 theoutershores posts, I made this fishy Word Cloud from tagxedo.com. The size of words is an index of how frequently they are used in my posts. Surfperch is the biggest word; that’s no surprise. Another relatively big word is color. I think about color a lot. Evolutionary biologists think that visual systems evolve in response to colors that are important in major life events such as finding food or choosing a mate, or both.
In An Abundance of Orange I illustrated the striking similarity between the color of spots we find on the anal fin of some silver surfperch and the color of eggs in the Pacific mole crab, a major food source for surfperch. The orange color, in both cases, is a carotenoid pigment whose source, among vertebrates, is strictly dietary. It is not synthesized like some other pigments.
Thus, if a surfperch is going to have an orange spot, it’s got to eat something orange. Why would a surfperch have an orange spot? Let’s explore that question. Surfperch have big eyes, diurnal habits and internal fertilization. When we see that orange spot on the anal fin, which in male surfperch is modified into the intromittant organ, we can’t help but think the orange spot plays a role in the mating system. Maybe males that are best at finding mole crabs have a good supply of carotenoids and advertise it by showing off a big orange spot. Could it be that females, already visually attuned to orange for hunting mole crabs and other crustacean prey favor males that are able to show off a big orange spot? Why not? Helen Rodd and her colleagues study a system that might be similar to what I’ve described, only in freshwater guppies. Female guppies have an inherent preference for orange and they like males that display orange spots. She has written a couple of really interesting papers on carotenoids, diet and mate choice. If you are interested in this kind of thing, check out what her lab is working on.
I decided to present colored lures to fish in the wild to see if any preferences showed up. With variable orange spots on the anal fin and and a diet rich in crustaceans it is tempting to hypothesize that I would find a preference for orange. With a lot of help from Helen Rodd and a bunch of other people, I was able to design a simple field preference test. I threw bait and colored lures (shown above) into the surf and then recorded takes by various surf-dwelling species. I think this is the first time anyone has tried something like this in the wild. I recorded 51 takes by silver surfperch and I show the results below.
The take rate was lowest on bait and highest for a two lures, one a flecked brown colored lure called pumpkinseed; the other, straight orange. You can see all the lures in the photo above (what you don’t see is bait which is not shown – that’s just a chunk of sand shrimp). Statistically, there is a high probability that the differences I observed did not occur by chance alone. Takes of bait were under-represented and pumpkinseed and orange were over-represented compared to what we would expect if takes occur independent of color. It looks like color matters in my experiment.
I had takes from 58 staghorn sculpins while conducting this experiment, so in my next post I’ll show those results. Staghorns and silvers are two very different fishes. I’ve introduced some important staghorn characteristics in previous posts, A Camoflaged Big-mouth on Summer Shores and Camo Rules! Can you make a prediction about their lure color choices?