Biomedical subjects

Ethan D Clotfelter

Publications and source records attributed to Ethan D Clotfelter.

3 recordsLinked to original sources

PubMed2006

Cerebral lateralization and its relationship to phylogeny and aggression in anabantoid fishes.

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. The mean laterality index did not differ significantly among the six species, nor did any of the species differ from zero, which suggests that populations of these fishes are neither left- nor right-eye biased. In spite of species differences in aggressive behavior, there was no relationship between population-level laterality and aggression as we had originally predicted. The degree of individual lateralization did differ significantly among some species. A phylogenetic generalized least squares (PGLS) analysis showed that these species differences were not due to phylogenetic distance. Individual laterality was also unrelated to aggression. Fishes in the genus Betta were the most individually lateralized, but varied in the intensity of aggressive behavior they displayed toward the mirrors. Taxa such as paradise fish (Macropodus opercularis and Pseudosphromenus dayi) were intermediate in eye-use preferences and gourami (Trichogaster trichopterus) displayed little cerebral lateralization. We also used the PGLS method to reconstruct ancestral values for individual lateralization in this group of fishes, from which we conclude that the ancestral condition was one of low variance in eye-use preference.

Aggression↗

PubMed2006

Behavioral changes in fish exposed to phytoestrogens.

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, beta-sitosterol, and the positive control 17beta-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 found few changes in spontaneous swimming activity, the latency to respond to the mirror, and nest size, and modest changes in the probability of constructing a nest. There were significant decreases, however, in the intensity of aggressive behavior toward the mirror following exposure to several concentrations, including environmentally relevant ones, of 17beta-estradiol, genistein, and equol. This suggests that phytoestrogen contamination has the potential to significantly affect the behavior of free-living fishes.

Aggression↗

PubMed2004

Consequences of elevating plasma testosterone in females of a socially monogamous songbird: evidence of constraints on male evolution?

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. 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 (C-females). Captive T-females had lower body mass, were less likely to develop brood patches, and delayed feather molt relative to C-females. 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.

Animals↗