Genetic analysis of sensitivity to ethanol-induced depression of motor activity and impairment of swimming in rats

Phenotypic integration and independence: Hormones, performance, and response to environmental change

Hormones coordinate the co-expression of behavioral, physiological, and morphological traits, giving rise to correlations among traits and organisms whose parts work well together. This article considers the implications of these hormonal correlations with respect to the evolution of hormone-mediated traits. Such traits can evolve owing to changes in hormone secretion, hormonal affinity for carrier proteins, rates of degradation and conversion, and interaction with target tissues to name a few. Critically, however, we know very little about whether these changes occur independently or in tandem, and thus whether hormones promote the evolution of tight phenotypic integration or readily allow the parts of the phenotype to evolve independently. For example, when selection favors a change in expression of hormonally mediated characters, is that alteration likely to come about through changes in hormone secretion (signal strength), changes in response to a fixed level of secretion (sensitivity of target tissues), or both? At one extreme, if the phenotype is tightly integrated and only the signal responds via selection's action on one or more hormonally mediated traits, adaptive modification may be constrained by past selection for phenotypic integration. Alternatively, response to selection may be facilitated if multivariate selection favors new combinations that can be easily achieved by a change in signal strength. On the other hand, if individual target tissues readily "unplug" from a hormone signal in response to selection, then the phenotype may be seen as a loose confederation that responds on a trait-by-trait basis, easily allowing adaptive modification, although perhaps more slowly than if signal variation were the primary mode of evolutionary response. Studies reviewed here and questions for future research address the relative importance of integration and independence by comparing sexes, individuals, and populations. Most attention is devoted to the hormone testosterone (T) and a songbird species, the dark-eyed junco (Junco hyemalis).

The relationship between ethanol-induced locomotor activation and narcosis in long-sleep and short-sleep mice

Mice selectively bred for marked response to hypnotic doses of ethanol (long-sleep, LS) respond to subhypnotic doses of ethanol (ETOH) with less stimulation of locomotor activity than their short-sleep (SS) counterparts. This assessment was made by comparing ETOH-induced alterations in locomotor activity to an untreated baseline within individual subjects, and to a saline-treated control group. A correlational study, using the same method in F2 generation hybrids of the LS and SS lines, produced a negative correlation (-.36) between locomotor stimulant effects of a subhypnotic dose of ETOH and length of loss of the righting reflex following a hypnotic dose. This relationship also appeared in a factor analysis of baseline locomotor activity, ETOH-stimulated activity, and depressant response variables. The genetic selection for LS and SS mice appears to have differentiated loci that influence more than one type of behavioral response to ETOH, an example of pleiotropism.