Rebecca E. Koch
The University of Tulsa
MATE CHOICE AND THE EVOLUTION OF ORNAMENTATION
My research is shaped by my background in behavioral research, specifically in the sexually selected displays of birds. To reach a fundamental understanding of such emergent characteristics of complex animals, many of my studies are of the mechanisms that underlie the production of traits--including, most recently, mitochondrial bioenergetics. By better understanding the genetic and physiological underpinnings of such displays, we can better explain the role of such displays in maintaining species boundaries and, ultimately, shaping speciation processes themselves.
CAROTENOID-BASED COLORATION IN BIRDS
My Ph.D. research focused on testing the best-accepted hypothesis for why the expression of particular colored ornaments in birds (those formed by carotenoid pigments) often correlates with aspects of physiological quality. The “resource trade-off hypothesis” proposes that individuals face a costly trade-off between retaining carotenoid pigments for internal benefit (they have antioxidant properties) versus “spending” them as ornamental colorants (see this review). To test this hypothesis, I examined measurements of oxidative and immune health in a novel system with carotenoid knock-down mutations: white and yellow canaries. I found that carotenoid-deficient white canaries (left, bottom) performed indistinguishably from carotenoid-rich yellow canaries (left, top) on a suite of physiological measurements (results here), presenting a major empirical challenge to the longstanding hypothesis.
Such a dramatic null result demands explanation and further testing, so my current research explores new hypotheses that have the potential to link display trait expression to the quality of internal physiological processes without invoking resource trade-offs (see here and here). Mitochondrial presents a surprising, yet promising series of mechanistic explanations for variation in display behaviours. These mitochondrial function hypotheses have been well received but have not been definitively tested--yet.
Plasma isolated from whole blood in capillary tubes from yellow (top) and white (bottom). The colour indicates the presence and absence, respectively, of circulating carotenoid pigments.
COMING SOON: Updates from the Toomey Lab!
DOES MITOCHONDRIAL PERFORMANCE SHAPE DISPLAY QUALITY?
Biomedical research has established clear mechanistic links between many processes related to sexually selected mating displays and mitochondrial function--both in cellular respiration and in signalling.
Sometimes, these relationships are indirect. For example, mitochondria lie at the hub of a multitude of signaling pathways for innate immune system development and function such that high-functioning mitochondria are necessary for effective immune defense. In turn, the expression of many mating displays has been found to correlate with measurements of immune system performance. Logically, then, displays that indicate immune system functionality may also indicate mitochondrial functionality.
Excitingly, some types of mating displays may have more direct connections to mitochondrial activity. The two we best understand to date are red carotenoid-based ornaments--see a recent study by my Ph.D. advisor's lab here--and cognitively complex displays, such as song (proposed here).
A recent system I studied, the fruit fly, provides an outstanding opportunity to test this latter relationship in a controlled way not yet possible in vertebrate systems like songbirds. During courtship, male fruit flies "sing" by vibrating their wings in stereotyped rhythms that have been found to influence female mating decisions. I recently discovered that one of the mitochondrial haplotypes I study appears to impair competitive mating success in males, and I wonder if the songs of these males may be altered.
I used a 16-channel fruit fly song recording apparatus to detect and quantify fly song sounds, focusing on the speed of "pulses" (inter-pulse interval). I used this apparatus to test how varying mitochondrial genotype affects song performance. Data from this study is currently being analyzed!