Something Fishy about Threat Displays: Breathing Handicaps Amplified by Gill-Cover Ornaments?
Yoni Brandt & Rich Granquist (Department of Biology, IU)
ABSTRACT Zahavi's handicap principle suggests that display reliability is maintained by the cost of display production. Recent experiments with lizards are consistent with the notion that threat displays are costly because the laterally compressed display posture interferes with respiration, resulting in decreased locomotor performance. Fishes are an additional taxon in which threat displays are likely to interfere with respiration and reduce locomotor performance. Among fishes, threat displays are often performed with an open mouth, lowered mouth-floor and raised gill-covers (operculi). Breathing is driven by coordinated movements of the mouth, mouth floor and operculi, drawing water through the buccal cavity, over the gills and out of the opercular cavity. Hence threat displays are expected to interrupt water flow over the gills, thereby reducing ventilation. Here we review the literature relating fish energetics, locomotor performance and aggressive interactions to examine the plausibility of the hypothesis that threat displays in fishes function as breathing handicaps. Next, we hypothesize that ornaments on the gill-covers function as amplifiers of the threat displays, predicting a consistent relationship between the use of opercular displays and the presence of opercular ornaments. We propose to examine the relationship between opercular ornaments and opercular displays using a comparative approach, starting with cichlid fishes.
Behavior Modification in Male Threespine Stickleback as a Result of Rival Presence
Teresa Dzieweczynski (Department of Biology, IU)
Communal nesters like the threespine stickleback have ample opportunity to observe and interact with other individuals in the population. This has both advantages and disadvantages. For example, communal nesting exposes females to many males simultaneously and can, thus, influence mate choice. However, a male must deal with neighboring males that witness and attempt to disrupt his courtship. Threespine stickleback from Long Island are anadromous and have a breeding season that lasts only a few weeks, thus, losing a courtship opportunity would be highly disadvantageous. Social learning allows an individual to gain about its environment from other individuals. A variety of fish species have been found to learn foraging routes from other individuals in a population and this ability may function in other contexts. The effects of social environment on behavior are often ignored, especially in fish. When communication is studied in animals, it is usually the signaler-receiver interaction, a dyadic relationship, that is examined. Communication in nature, however, often occurs through networks of many individuals that interact and compete for the receiver's attention. I propose to examine whether male stickleback modify their behavior and manipulate the context in which it is performed. For example is where and when males choose to court a female based on his social environment. In other words, is a male capable of adjusting his courtship behavior if another male is present. I will also determine whether the presence of an audience affects the type and/or frequency of behavior that is performed by the male.
The Ethological Basis of Female Preference for Male Sailfin and Body Size in Sailfin Mollies, Poecilia latipinna
Dave MacLaren (Department of Biology, IU)
I tested mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in (1) sailfin size, (2) body size, and (3) sailfin:body size ratio while holding each dummy's overall lateral projection area (LPA) constant. Females responded to the dummies much as they do to live conspecifics and spent more time near dummies of greater sailfin or greater body size. The preference function for sailfin LPA was similar to that for body size, but there was no directional selection for either trait when LPA was held constant. Nor did females prefer any particular dummy across treatments. These findings suggest that body size and sailfin size may exploit the same underlying female preference for increased LPA and that the sailfin may be a metabolically cheap way for males to exploit this sensory bias and appear larger to prospective mates.
Birthing Biparentally: What Spiny Mouse Parents May Give Their Perinates
Jill Menge (Department of Psychology, IU)
Most studies of perinatal experiences and mammalian development have used the Norway rat. These studies are constrained, however, by the Norway rat's ontogeny and parental system. Norway rat offspring are born highly immature and males typically do not provide parental care. Thus, the Norway rat is not a useful species for assessing the father as a source of sensory stimulation to a precocial perinate. Nevertheless, there are mammalian species in which the male contributes to offspring care and the newborns are born precocious. We selected the spiny (Acomys cahirinus), a species is known for the precocity of the offspring and its biparental activities. We identified and quantified behaviors of dams and sires that may contribute to the sensory experience of the perinatal spiny mouse during late gestation, labor, and delivery.
An Efficient Code for Auditory Space in Non-Specialized Birds and Mammals
Brian Nelson (Department of Biology, IU)
Jeffress (1948) suggested that animals may use labeled lines to code for auditory space and considerable support for this model has since been obtained in numerous studies of the barn owl (Tyto alba). The barn owl is a sound localization specialist and, as a result, it remains unclear whether results obtained in studies with the barn owl can be generalized to mammals or non-specialized birds. I describe behavior associated with sound localization in a small passerine bird, the eastern towhee (Pipilo erythrophthalmus), and argue that labeled lines are unlikely to code for auditory space in this species. As an alternative, I present a computational model in which azimuth is coded efficiently across 3 broadly tuned channels. I compare this 3 channel model with 2 channel models proposed previously for mammals and argue that efficient coding of direction is likely to be requisite for localization over distance in natural habitat.
Effects of Parasite Density on Within-Host Parasite Growth Rate
Erik Osnas (Department of Biology, IU)
Virulence theory predicts that growth rate (virulence) of parasites should increase when there are multiple competing parasite genotypes within a host. I tested this prediction by studying parasite infection and growth rate in two populations of the freshwater prosobranch snail, Potamopyrgus antipodarum, in relation to dose of a digenetic trematode, Microphallus spp. I found that infection level increased with dose to high levels in the sympatric host-parasite population (~85%) but not in the allopatric host-parasite population (~15%). I also found that parasite growth rate was inversely related to parasite dose for both populations. This could be due to changes in the internal host environment. Evidence that these snails mount an immune response to trematode parasites is presented. These results have implications for the evolution of virulence, mechanisms of host-parasite compatibility, and regulation of parasite populations in this system.
The Effects of Exogenous Testosterone on Male Incubation in Blue-headed Vireos (Vireo solitarius)
Brandi Van Roo (Department of Biology, IU)
Natural variation in circulating testosterone (T) is thought to play a proximate role in inter- and intra-specific variation in paternal care in birds. In previous studies, experimental manipulation of T in males has reduced rates of feeding young in several species. Fewer studies have experimentally tested the effects of testosterone on male incubation behavior, particularly in a genetically monogamous passerine in which biparental care is likely to be essential to breeding success. Blue-headed vireo males were given subcutaneous implants filled with testosterone (n=13), flutamide (F, an androgen-receptor antagonist, n=13), or left empty (C, n=9). Testosterone treatment significantly reduced care and increased song relative to the other treatment groups, whereas treatment with flutamide resulted in trends opposite to T but not statistically different from the control group. Specifically, the proportion of total observed incubation time performed by males decreased from 0.54 to 0.48 to 0.34 for F, C, and T treatments, respectively. The average period of time that the nest was left unattended during incubation increased from 0.6 to 2.1 to 7.6 minutes for F, C, and T treatments, respectively. Consistent with previous studies, treatment of males with T significantly reduced rates of feeding offspring relative to F and C treatments. During both the incubation and the nestling stages, males treated with T spent more time singing and sang more phrases per minute than males in the F and C treatments. These results demonstrate that male incubation in the strictly monogamous blue-headed vireo is a plastic behavior that is sensitive circulating levels of testosterone.