Evolution of an instinct under long-term divergent selection for geotaxis in domesticated populations of Drosophila melanogaster

Long-term divergent selection for geotaxis in lines of Drosophila melanogaster (the fruit fly) is described. After 26 years (600+ generations) of intermittent selection, the mean geotactic scores now remain stable upon relaxed selection, a result suggesting that evolutionary changes have occurred in these lines. Because the stability is not due to genetic fixation (homozygosity) of the lines, it must be due to either close linkage of genes associated with geotaxis (which would not result in enduring change) or the development of new coadapted gene complexes utilizing genes associated with extreme geotaxis expression (which should result in enduring change). Better evidence for the latter hypothesis is obtained from the low, than from the high, line. The notions of coadaptation and genetic homeostasis are considered, as well as the prospective use of the geotaxis lines to study such concepts experimentally. The geotactic behavior expressed in each line is defined as "instinctive": It increases reproductive success and is characteristic of a population.     

Dispositional and explanatory style optimism as potential moderators of the relationship between hopelessness and suicidal ideation

To test the hypothesis that higher levels of optimism reduce the association between hopelessness and suicidal ideation, 284 college students completed self-report measures of optimism and Beck scales for hopelessness, suicidal ideation, and depression. A statistically significant interaction between hopelessness and one measure of optimism was obtained, consistent with the hypothesis that optimism moderates the relationship between hopelessness and suicidal ideation. Hopelessness is not inevitably associated with suicidal ideation. Optimism may be an important moderator of the association. The development of treatments to enhance optimism may complement standard treatments to reduce suicidality that target depression and hopelessness.     

The haptic oblique effect in the perception of rod orientation by blind adults

The haptic perception of vertical, horizontal, +45° oblique, and +135° oblique orientations was studied in completely blind adults. The purpose was to determine whether the variations of the gravitational cues provided by the arm-hand system during scanning would affect the manifestation of the oblique effect (lower performance in oblique orientations than in vertical-horizontal ones) as they did in blindfolded sighted people (Gentaz & Hatwell, 1996). In blindfolded sighted adults, the oblique effect was reduced or absent when the magnitude of gravitational cues was decreased. If visual experience participated in the haptic oblique effect, we should observe no oblique effect in early blind subjects in the conditions of manual exploration where late blind and blindfolded sighted manifest this effect. The magnitude of gravitational cues was therefore varied by changing gravity constraints, whereas the variability of these cues was varied by changing the plane in which the task was performed: horizontal (low variability) and frontal (high variability). Early and late blind adults were asked to explore haptically a rod and then to reproduce its orientation ipsilateraUy in one of two exploratory conditions in each plane. In the horizontal plane, the oblique effect was absent, whatever the gravity constraints, in both groups (early and late blind subjects). In the frontal plane, the oblique effect was present, whatever the gravity constraints, in both groups. Taken together, these results showed that, in blind people, the variability of gravitational cues played a role in the haptic oblique effect; no effect of previous visual experience was observed.