photo: Crotaphytus collaris auriceps near Moab, Utah by Barney Oldfield
Student-Faculty Collaborative Research
Student-Faculty Collaborative Research
Individual Vocal Signatures in Horse "Whinnies"
Long-distance vocalizations in mammals often exhibit sufficient acoustic variability to encode the identity of the caller. The familiar "whinny" vocalization of horses is one such signal. Research student Jillian Campbell and I examined this vocalization for "individual signatures" in a novel manner: by using an acoustic analysis technique known as spectrogram cross-correlation. Jillian recorded whinnies from numerous independently owned adult domestic horses by isolating each horse from its companions and recording it. We required a minimum of ten whinnies with a high signal-to-noise ratio for a horse to be included in the subject pool. Ten subjects met this criterion, and each subject's 10 highest quality whinnies were analyzed. We used "Raven" sound analysis software to conduct the spectrogram cross-correlation analysis, in which two spectrograms "slide" past each other in a stepwise fashion, and the maximum correlation value (= acoustic overlap) for each pair of spectrograms is saved. Results showed that within-subject cross-correlation values were significantly greater than among-subject values for all ten horses. This finding suggests that the individual signatures in whinnies may be sufficiently strong in wild horses to facilitate recognition of herd members that are not within visual range.
Vocal Communication in Domestic Cats
Domestic cats communicate with humans primarily through vocalizations. Research student Gabrielle Farina and I sought to determine the context-specificity of vocalizations in cat/human interactions. Gabielle recorded the vocalizations of ten domestic cats in specified contexts (set up experimentally) and then measured the acoustic structure of their calls with Raven software. Vocalizations were grouped by the following contextual categories: affiliative, contentment, food-related, play, attention seeking, and agonistic. Of 192 calls measured "meows" occurred in all contexts except agonism, but they appeared to differ among contexts in such features as duration, repetition rate, and emphasized frequencies. In contrast, purring was restricted largely to the contentment context, and hissing and growling only occurred in agonistic contexts. This preliminary study raised a number of questions for future research, such as whether apparent differences in meow acoustic structure in different contexts has communicative meaning.
Habitat Light and Damselfly Coloration
Odonates (dragonflies and damselflies) exhibit a range of striking body colorations from shades of violet and blue to green, yellow, orange, and red. These vibrant colors advertise an individual's presence, and play a primary role in species/mate recognition. As natural selection favors visual signals that are readily detectable, and because the ambient light spectrum influences this detectability, we anticipate that the irradiant light in different habitats and at different times of day will favor particular body colors for visibility. Results of previously published research support this "sensory drive" hypothesis of color signal design in damselflies. I worked with research students Meghan Edwards and Amanda Fowler to determine if habitat light had a detectable influence on damselfly coloration in two local lakes: Lake Hollingsworth and Lake Hunter. Damselfly habitat irradiance was gathered using a portable spectrometer wherever damselflies were observed, and damselfly body coloration spectra were gathered under controlled laboratory conditions. Conspicuousness of body color against a vegetation background was compared using 3- and 4-photoreceptor computational visual models of our damselfly species to determine if damselflies were most active at the time of day in which their coloration should be most visible. Although our results were inconclusive, our sample sizes for most species were small. Additional data gathered with future research students will allow us to test the sensory drive hypothesis of damselfly body coloration more robustly in Lakeland lakes.
Brown Anole Limb Growth Plasticity
Cuban brown anoles (Anolis sagrei) exhibit phenotypic plasticity in hindlimb growth: subjects reared on broad substrates develop longer legs than subjects reared on narrow substrates. Under natural conditions this phenomenon probably facilitates more efficient locomotion for capturing prey and escaping predators on native substrates of predominantly differing diameters. Together with research students Chris Bessette, Jen Matey, Brittany Raboin, Ashley Schiffmacher, and Brett Reynolds, Dr. Gabe Langford and I confirmed the results of a previously published study by showing that hatchlings reared on broad perches grew significantly longer hind limbs than those reared on narrow perches. We then housed our experimental subjects in outdoor enclosures and recorded the frequency with which subjects in the two treatment groups perched on broad and narrow dowels.
Population Variation in Green Anole Displays
Green anoles (Anolis carolinensis) in southwest Florida differ genetically, physiologically, and morphologically from populations elsewhere. Research students Lauren Cherry, Brad Bartel, Natasha Mohamed, and I investigated whether display behavior in this population also differs from that seen in other populations. We captured adult males from this "gray-dewlapped" population (as well as local red-dewlapped males), video-recorded their "headbob" displays in the lab, and analyzed those displays in detail. Analyses revealed consistent differences in the durations of several display "units" between gray-dewlapped and red-dewlapped males, confirming that behavioral traits also differ between green anoles from southwest Florida and those located elsewhere.
Polka-Dot Wasp Moth Chemical Ecology
The polka-dot wasp moth (Syntomeida epilais) is an extraordinary day-flying moth with the superficial appearance of a wasp (e.g., wasp wing shape and a bluish refulgence). This moth also mimics wasps when walking and flying. The moth's striking warning color pattern advertises its unpalatability, which arises from its toxic host plant, oleander (Nerium oleander). Research students Nick Brown, Erin Duke, Matt Powers, and Derek Diebert, together with Dr. Gabe Langford (Biology), Dr. An-Phong Le (Chemistry) and myself, used HPLC to determine (1) the impact of larval feeding intensity on production of the defensive compound "oleandrin" (a cardiac glycoside), and (2) the reddish pigments responsible for this moth's bright red abdominal segment and the red wings of its local relative, Empyreuma pugione.
Zebra Heliconian Host Plant Choice
Three groups of research students have contributed to an ongoing project in which I and several colleagues in Biology are investigating a potential relationship between the passion vine (Passiflora sp.) host plant species on which zebra heliconian (Heliconius charithonius) larvae are reared, and the Passiflora species on which such reared adult females choose to lay their eggs. We begin by capturing and maintaining adults in large tents, where wild-caught females lay eggs on a selection of passion vines. Larvae from these eggs are reared to pupation on a host plant species, and the pupae are placed in smaller "choice" tents. Emergent females in these tents mate with males reared on the same host plant species, and then are given a choice of Passiflora species on which to lay their eggs.
Passion Vine Defensive Chemicals
Butterflies in the genus Heliconius use passion vines (Passiflora sp.) as a host plant, and these plants are toxic to most organisms due to their production of cyanogenic glycosides. Research student Ashley Martin worked with Dr. An-Phong Le and myself to determine, using HPLC, whether Passiflora species used as host plants by H. charithonia differed in defensive chemical profiles from one another and from species not used as host plants by H. charithonia. Leaves were gathered for two Passiflora species used as food plants (P. suberosa and P. incense), and one species (unidentified red-flowered species) completely avoided by ovipositing females. Although standards were not available to identify the cardiac glycosides and potentially other noxious compounds via their HPLC retention times, results showed peaks at the same retention times in all three species tested. Notably, the red-flowered species exhibited higher peaks (concentrations) than P. suberosa and P. incense, and in addition exhibited an additional peak between 1.5 and 1.75 seconds not observed in the other two species. We plan to build on the results of this pilot study to further this research in future semesters.
Kangaroo Rat UV Reflectance Patterns
Research students Dan Kostos, Emily Maeda, and Erica Johnson worked with me and graduate student Brandon McDonald (at Cameron University in Lawton, Oklahoma) to investigate ultraviolet reflectance patterns in the fur of kangaroo rats (Dipodomys ordii). We sought to determine whether differences existed in UV reflectance between the sexes, and within-sexes across 8 populations of D. ordii spanning Oklahoma and New Mexico. (1) Adjacent light and dark patches of fur were measured with a spectrometer to calculate brightness contrast, (2) the rod photoreceptor pigment was used to estimate this contrast to the kangaroo rat visual system, and (3) a moonlight spectrum was included into our computational visual model to simulate brightness contrast under nocturnal signaling conditions. No sex differences were found in UV brightness contrast for the two body areas that we measured, and only minor within-sex differences were found among the eight study populations.
Gray Squirrel Alarm Calls
Honors-in-the-major student Jillian Swartz recorded and measured the acoustic structure of gray squirrel (Sciuris carolinensis) alarm calls to determine if different callers could be distinguished by the structure of their calls. She measured six parameters for statistical analysis and also used the spectrogram cross-correlation method in the acoustic analysis program Raven (described above in Jillian Campbell's horse individual vocal signature study). Statistical analyses of "quaa" and "kuk" alarm calls from a dozen squirrels using Discriminant Function Analysis (DFA) indicated that the vast majority of calls could be correctly assigned to the caller based on call acoustic structure. Jillian also conducted pilot work on responses of the squirrels to playbacks of avian and mammalian predator vocalizations, to explore if the squirrels had different escape strategies in response to different predator classes. She presented her research in a presentation at Fiat Lux in April 2011.
Insect Warning Color Pigments
Lex Lister and Alex Jenkins investigated the potential presence of pteridine and carotenoid pigments in the warning coloration of golden rain tree bugs and milkweed bugs. Using several chemical extraction and separation techniques (e.g., 2-D thin-layer chromatography) they determined the pteridine profiles for both insect species, and found that neither used carotenoids in their coloration. Lex and Alex presented a poster on their research at the American Chemical Society Annual Meetings in Salt Lake City, Utah in March 2009.