Papers by Ethan Clotfelter
To explore whether selection for testosterone-mediated traits in males might be constrained by co... more To explore whether selection for testosterone-mediated traits in males might be constrained by costs of higher testosterone to females, we examined the effects of experimental elevation of plasma testosterone on physiological, reproductive, and behavioral parameters in a female songbird, the dark-eyed junco (Junco hyemalis). We used subcutaneous implants to elevate testosterone (T) in captive and freeliving female juncos. In captive birds, we measured the effects of high T on body mass, feather molt, and brood patch formation. In the field, we monitored its effects on the timing of egg laying, clutch size, egg size, egg steroid levels, incubation, and nest-defense behavior. Females implanted with testosterone (T-females) had significantly higher circulating levels of testosterone than did control females (Cfemales). Captive T-females had lower body mass, were less likely to develop brood patches, and delayed feather molt relative to Cfemales. Among free-living females, the interval between nest completion and appearance of the first egg was longer for T-females than for C-females and egg yolk concentrations of testosterone were higher, but there were no significant differences in estradiol levels, clutch size, or egg size. Incubation and nest defense behavior were also similar between T-and C-females. Our results suggest that selection on males for higher testosterone might initially lead to a correlated response in females producing changes in body mass and feather molt, both of which could be detrimental. Other possible female responses would be delayed onset of reproduction, which might reduce reproductive success, and higher yolk testosterone, which might have either positive or negative effects on offspring development. We found no reason to expect reduced parental behavior by females as a negative fitness consequence of selection for higher testosterone in males.
Oecologia, 2007
Resource pulses can have cascading eVects on the dynamics of multiple trophic levels. Acorn mast ... more Resource pulses can have cascading eVects on the dynamics of multiple trophic levels. Acorn mast is a pulsed resource in oak-dominated forests that has signiWcant direct eVects on acorn predators and indirect eVects on their predators, prey, and pathogens. We evaluated changes in acorn mast, rodent abundance, raptor abundance, and reproductive success of a ground-nesting songbird over a 24-year period in the southern Appalachian Mountains in an eVort to determine the relationships among the four trophic levels. In particular, we examined the following: acorn mast from red oaks (Quercus rubra) and white oaks (Q. alba), abundance of white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus), population estimates of seven raptor species from three feeding guilds, and nest failure and number of juveniles of dark-eyed juncos (Junco hyemalis). Finally, we recorded seasonal temperature and precipitation to determine the eVects of weather on each trophic level. We found that weather patterns had delayed eVects of up to 3 years on these trophic interactions. Variation in acorn mast, the keystone resource in this community, was explained by weather conditions as far back as 2 years before the mast event. Acorn mast, in turn, was a strongly positive predictor of rodent abundance the following year, whereas spring and summer temperature and raptor abundance negatively aVected rodent abundance. Dark-eyed junco nests were more likely to fail in years in which there were more rodents and raptors. Nest failure rate was a strong predictor of the number of juvenile juncos caught at the end of the summer. Our results improve our understanding of the complex ecological interactions in oak-dominated forests by illustrating the importance of abiotic and biotic factors at diVerent trophic levels.
We investigated the behavioral effects of exposure to waterborne phytoestrogens in male fighting ... more We investigated the behavioral effects of exposure to waterborne phytoestrogens in male fighting fish, Betta splendens. Adult fish were exposed to a range of concentrations of genistein, equol, β-sitosterol, and the positive control 17β-estradiol. The following behaviors were measured: spontaneous swimming activity, latency to respond to a perceived intruder (mirror reflection), intensity of aggressive response toward a perceived intruder, probability of constructing a nest in the presence of a female, and the size of the nest constructed.
We examined the relationship between aggression and cerebral lateralization, as expressed by eye-... more We examined the relationship between aggression and cerebral lateralization, as expressed by eye-use preference in a mirror-response paradigm, in six species of anabantoid fishes in the teleost family Belontiidae. Our objective was to test the hypothesis that frequency-dependent selection should decrease lateralization at the population level in more aggressive species.
While the social interactions of Betta splendens have been studied in the contexts of dominance h... more While the social interactions of Betta splendens have been studied in the contexts of dominance hierarchies, mate choice and communication networks, the social partner preferences of Betta have been largely overlooked. In this study, we presented male and female Betta with a single male, a single female, and a group of three females in dichotomous choice tests in order to better understand basic social interactions in this largely nonsocial species.
MATERIALS AND METHODS We obtained 40-45 mm juvenile minnows from a commercial supplier and allowe... more MATERIALS AND METHODS We obtained 40-45 mm juvenile minnows from a commercial supplier and allowed them to acclimate in 38-L glass aquaria filled with aged tap water for several days before the experiment began. Genistein (mg; Sigma-Aldrich Co.) was dissolved in ethanol (mL) at a 5: 1 ratio (concentration of ethanol far below that at which deleterious effects are observed; L Crawshaw, personal
Abstract Recent advances in the development and availability of genetically modified animals enab... more Abstract Recent advances in the development and availability of genetically modified animals enable researchers to examine the effects of phenotypic characters on social behavior. In fish, shoaling behavior is known to be influenced by characteristics such as body coloration, striping pattern, body shape, and size. GloFish TM are genetically engineered zebrafish (Danio rerio) that express red fluorescent protein (RFP), resulting in on overall red coloration under the dark longitudinal stripes.
Abstract Investment in one life-history stage can have delayed effects on subsequent life-history... more Abstract Investment in one life-history stage can have delayed effects on subsequent life-history stages within a single reproductive bout. We experimentally heated tree swallow (Tachycineta bicolor) nests during incubation to test for effects on parental and nestling conditions. Females incubating in heated boxes maintained higher body condition and fed nestlings at higher rates.
Parents are expected to invest more in young that provide the greatest fitness returns. The cues ... more Parents are expected to invest more in young that provide the greatest fitness returns. The cues that parents use to allocate resources between their offspring have received much recent attention. In birds, parents may use begging intensity, position in the nest or nestling size as cues to provision the most competitive young or those most likely to survive. It may also benefit parents to invest in young differentially by sex or relatedness if the fitness returns of sons and daughters differ or broods are sired by multiple males.
Abstract Carotenoid pigments are responsible for many examples of sexually attractive red, orange... more Abstract Carotenoid pigments are responsible for many examples of sexually attractive red, orange, and yellow coloration in animals and play an important role in antioxidant and immune defenses. Because vertebrates cannot synthesize carotenoids, limited dietary availability may impose a trade-off between maintaining ornamental coloration and health.
Abstract. I examined ecological and behavioural variables influencing the susceptibility of red-w... more Abstract. I examined ecological and behavioural variables influencing the susceptibility of red-winged blackbird, Agelaius phoeniceus, nests to brood parasitism by brown-headed cowbirds, Molothrus ater, in a prairie-nesting population of redwings in southern Wisconsin.
The offspring sex ratio at independence in a colony of Zebra Finches (Taeniopygia guttata) was si... more The offspring sex ratio at independence in a colony of Zebra Finches (Taeniopygia guttata) was significantly male biased. Three possible proximate causes of this bias were examined.(1) The first was that there is a sex-biased laying sequence followed by brood reduction. Males were significantly more likely to hatch from earlier-laid eggs than females, but there was no evidence of increased mortality among late-laid nestlings.(2) The second was that there is sex-biased mortality due to sex-specific growth rates.
Abstract Individual variation in life-history trade-offs can be caused by differences in quality ... more Abstract Individual variation in life-history trade-offs can be caused by differences in quality and age. We tested for individual variation in parental investment in incubating tree swallows (Tacyhcineta bicolor) subjected to a feather-clipping manipulation. Individual quality influenced how females were affected by feather clipping; lower quality clipped females showed a greater reduction in incubation and a greater loss of body condition than higher quality clipped females compared with controls.
To explore whether selection for testosterone-mediated traits in males might be constrained by co... more To explore whether selection for testosterone-mediated traits in males might be constrained by costs of higher testosterone to females, we examined the effects of experimental elevation of plasma testosterone on physiological, reproductive, and behavioral parameters in a female songbird, the dark-eyed junco (Junco hyemalis). We used subcutaneous implants to elevate testosterone (T) in captive and free-living female juncos.
Numerous chemicals are known to interfere with the endocrine systems of animals. These chemicals,... more Numerous chemicals are known to interfere with the endocrine systems of animals. These chemicals, commonly referred to as endocrine-disrupting chemicals (hereafter EDCs), pose a particularly severe threat to animal health. They accumulate in body tissues and are highly persistent in the environment and thus can occur at significant concentrations far from their points of origin. Ecotoxicologists have used a number of animal species to identify physiological and morphological consequences of EDC exposure.
The novel application of a standard technique to assess cell-mediated immune response to phytohae... more The novel application of a standard technique to assess cell-mediated immune response to phytohaemagglutinin (PHA) injected in the caudal peduncle in a small fish (< 2 g) to test the immunosuppressive effect of three phytoestrogens: genistein, equol and β-sitosterol is described. Individual Betta splendens exposed to these oestrogenic chemicals produced weaker inflammatory responses to PHA than did control individuals, suggesting that phytoestrogens are immunosuppressive.
We examined brood parasitism by Brown-headed Cowbirds (Molothrus ater) on a prairie-nesting popul... more We examined brood parasitism by Brown-headed Cowbirds (Molothrus ater) on a prairie-nesting population of Red-winged Blackbirds (Agelaius phoeniceus) from 1984 to 1997 and the extent to which parasitism affected host reproductive success. During this 14-year period, 2-32% of redwing nests were parasitized per year. Two measures of cowbird parasitism, the proportion of nests parasitized and the number of cowbird eggs laid per year, significantly increased over time.
We performed two experiments in which we allowed a male fighting fish, Betta splendens, designate... more We performed two experiments in which we allowed a male fighting fish, Betta splendens, designated a bystander, to observe aggressive contests between pairs of male conspecifics. Another male (naı̈ve male) observed an empty tank or two nonaggressive males, depending on the experiment. Immediately after these observation periods, we allowed the bystander and naı̈ve male to interact in a neutral area.
We examined temporal and spatial nesting aggregations in a prairie-nesting population of Red-wing... more We examined temporal and spatial nesting aggregations in a prairie-nesting population of Red-winged Blackbirds (Agelaius phoeniceus). In particular, we were interested in the effects of aggregated nesting on blackbird nest success and brood parasitism by Brown-headed Cowbirds (Molothrus ater). Most cowbird parasitism occurred early in the breeding season during the peak in Red-winged Blackbird nesting.
Methods We studied Tree Swallows at the University of Wisconsin-Milwaukee Field Station near Sauk... more Methods We studied Tree Swallows at the University of Wisconsin-Milwaukee Field Station near Saukville, WI (43 23% N, 88 01% W) beginning in 1997. That year, we placed a total of 58 nestboxes with aluminum predator guards on two meadows. In 1998, we added an additional 40 nestboxes. We set up grids in which nestboxes were 40 m apart along a row and 28 m on the diagonal between rows.
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Papers by Ethan Clotfelter