Hormones are one avenue in which the sexes can express competely different phenotypes despite sharing almost an entire genome. However, testosterone’s effects on behaviors utilized in complex interactions require some testing. In collaboration with Dr. Robert Cox and Tyler Wittman, I asked if testosterone affected the correlation between visual signal traits and expression of aggressive behaviors.
Anolis sagrei, the brown anole, are known for their exaggerated dewlaps that they flare out as an aggressive display towards potential competitions. Brown anoles are sexually dimorphic for this trait, where males have large and brightly colored dewlaps while female dewlaps are small and dull. Previous research showed that testosterone enables the development of larger dewlaps in both sexes, so we set out to ask if these morphological differences are correlated with behavioral differences in expression of aggression. Overall, testosterone affected morphology in both sexes, but only affects behavior in males. Testosterone increased the size of dewlaps in both sexes, but only increased aggression in males.
The ecology of color: how color affects visual behaviors in aquatic habitats in a sexually dimorphic species (Lucania goodei) and their major predator (Micropterus salmoides) – Fuller lab – University of Illinois at Urbana Champaign
We all know largemouth bass as the popular recreational fish species, but who knew that their ecology was just as important as their economic value?! Largemouth bass are an important top predator for many fish and invertebrate species in lake and stream habitats across the United States. Their predatory behavior is visually driven, making their vision an important area of study. During my Master’s, I modeled color vision in bass and tested the assumptions of those models using behavioral assays. Overall, the model determined that bass should have difficulty distinguishing bright yellow from white and blue from green. Behavioral tests confirmed that bass have difficulty distinguishing bright yellow from white, but they could readily distinguish blue from green. However, bass did have difficulty distinguishing between blue and black. Bass may have difficulty perceiving bright yellow against light background and deep blue against dark backgrounds providing a potential avenue for prey to camoflague themselves from bass predator while also maintaining vibrant mating displays.
The most interesting and unintended result from my bass color vision study was the bass were most responsive to red coloration. Red may serve as an ecologically important color – likely related to prey coloration.
Bluefin killifish are small, colorful topminnows native to Florida swamps and springs. These fish make an intriguing study system because their bright anal fin coloration is contradictory to what we might expect from a largemouth bass prey species! Bluefin killifish males are polymorphic for anal fin coloration, where males can have either red, yellow, or blue anal fin (see image below). But why do males have such vibrant displays? Sexual selection may be the answer to that question.
One prediction put forth by sensory drive is that the evolution of color signals will depend on the visual physiology of the perceivers and the condition under which the signals are displayed. Bluefin killifish have 5 photoreceptors and excellent perception of blue, red and yellow color. Moreover, mating and competition displays occur in close range. Bluefin killifish may optimize mating opportunities and minimize predation by performing their courting and competition displays in close range to females against lighting environments that do not translate those colors effeciently to far away predators.
Most fascinating is that the proportion of male color morphs differs between tannin-stained swamp habitats and clear spring habitats. Blue color morphs are highly abundant in tannin-stained swamp habitats while red and yellow color morphs are more abundant in spring habitats. What is the cause of this variation?!
Blue color is highly contrasted by the tannin-stained water of swamps, while yellow and red colors are highly contrasted in clear spring water. If sexual selection favors highly contrasting male fin displays, one would predict that the more overt display within a given lighting environment is beneficial for both male competition and female choice. Blue-finned males should win competitions and be preferred by females in tannin-stained swamp water while red and yellow-finned males should win competitions and be preferred by females in clear spring water. My study partially supported these predictions. Blue males were more likely to emerge as winners of male competition in tannin-stained water over clear water, but there was little evidence of female preference for any color morph in either lighting environment. The maintenance of blue coloration in swamps is likely perpetuated in part by the outcomes of male competition.