Research Interests
My research interests fall under the broad category of behavioral ecology. More specifically, I am interested in mating systems, sexual selection and sex allocation, as well as the extreme life-history adaptations of marine birds. In 2004, I completed my M.S. in Biology at Bucknell University in the lab of Dr. Donald C. Dearborn. My master's research involved offspring sex ratios and the influence of three factors (age, body condition, and food availability) on adaptive sex allocation in great frigatebirds (Fregata minor) breeding in the northwest Hawaiian Islands. As part of this project, I collaborated with Dr. Mark Haussmann and Dr. Carol Vleck from Iowa St. University on a telomere-based technique for estimating ages of individual frigatebirds in wild populations.

Sex Allocation: Modern sex-allocation theory predicts that if ecological or social conditions differentially influence the fitness benefits gained from producing male or female offspring, parents should correspondingly adjust their production of sons and daughters to maximize their fitness. Theoretical and empirical research supports the theory, though the empirical data have centered around organisms where a clearly defined mechanism of adjustment exists, such as in haplodiploid insects. Sex-ratio studies conducted on organisms with chromosomal sex determination are especially intriguing because they underscore the complex tradeoffs between evolutionary adaptation and genetic constraint. Chromosomal sex determination would seemingly constrain the evolution of adaptive manipulation of offspring sex ratios in many vertebrates. Although the mechanisms for circumventing any constraints set by chromosomal sex determination remain unclear, increasing evidence now suggests that some vertebrates, including birds, are capable of adjusting their offspring sex ratio.

Telomere Aging: Telomeres are protein-DNA complexes that cap the ends of linear eukaryotic chromosomes. By nature of the linear DNA replication process, DNA polymerase is unable to complete the replication of the 3' end. Therefore, during each replication cycle of a cell, some telomeric repeats are left as single stranded ends that are eventually lost to breakage or degradation. Telomere restriction fragments (TRFs) have been shown to serve as a fairly reliable marker for age in several bird species, though the rate of TRF shortening has been directly related to the lifespan of each species. Obtaining information about individual age and age structure for a population of wild animals is often not possible due to the time and expense involved in long-term mark-recapture studies, particularly for long-lived species. If the ages of some, but not all, individuals of a given population were known, it should be possible to calibrate the rate of TRF shortening for that population and then make age estimates of other population members for which there is no known history.
Dissertation Research
I have continued exploring various aspects of great frigatebird breeding biology in the northwest Hawaiian Island as part of my dissertation research at the University of Miami. I have focused on several issues having to do with sexual selection and the evolution of female mating preferences and male ornaments.
1) Carotenoids and throat pouch coloration: Carotenoid pigments are a common source of red, orange, and yellow coloration in birds. The potential role that carotenoids play in both color signaling and immunocompetence suggests a mechanism by which carotenoid-based colors could provide honest information about individual quality. Male great frigatebirds display a bright red inflated gular pouch as part of their elaborate courtship display. I first set out to investigate the basis of this coloration.

In collaboration with Dr. Kevin McGraw, I determined that great frigatebird plasma contained three carotenoid pigments in dilute concentrations, tunaxanthin, zeaxanthin, and astaxanthin, with astaxanthin accounting for nearly 85% of the carotenoids present.  Astaxanthin concentration in throat pouch tissue was extremely high compared to the total carotenoid concentrations found in blood plasma, and to my knowledge was the highest reported concentration of carotenoids in any bird tissue.  Because these concentrations are so high, it is likely that astaxanthin contributes substantially to the red color of these ornaments. The spectral reflectance curves also suggest an additional role for hemoglobin in the production of color in this ornament.

2) Throat pouch coloration: I am continuing to investigate correlations between carotenoids, immune system strength, reflectance spectra of display pouches, and mating success in male great frigatebirds.

3) Vocal performance: Vocal performance, defined as the tradeoff between frequency bandwidth and repetition rate of a warble, may provide information about a male’s muscular coordination and respiratory capacity, attributes that may be correlated with other tasks involving endurance and concise movements.  Male great frigatebirds produce a rapid warble vocalization as a component of their elaborate courtship display. Vocalizations produced by males during the breeding season may convey honest information for females about male quality.  In addition, peak frequency of a call may transmit information about male body size.  What I discovered was that body condition was a significant predictor of vocal performance and that gular pouch size (but not body size) was a significant predictor of peak frequency, with larger pouches associated with lower peak frequencies.  However, neither peak frequency nor vocal performance was a significant predictor of pairing success in my study population.

4) MHC genes and mate choice: MHC (major histocompatibility complex) genes influence immunological self/non-self recognition, and play a critical role in disease resistance. It has been postulated that these genes may also play an important role in mate choice and kin recognition. MHC-dependent mating preferences may have evolved as a mechanism for inbreeding avoidance, as well as for enhancement of offspring fitness through heterozygosity of MHC genes. Hypotheses relating to both “good genes” and “optimal compatibility” with respect to MHC and a chosen mate have been proposed. Currently, there is some evidence for MHC-influenced mating in mammals and fish, though very little evidence exists for birds. Great frigatebirds may provide a good opportunity for exploring the role of MHC in mate choice, as males exhibit exaggerated secondary sexual traits which may correlate with particular MHC genotypes, and thus convey indirect benefits through “good genes” that could influence female mate choice.

See this work featured in the Cornell Blog of Ornithology, Round Robin!