Dispersal, philopatry and intergroup relatedness: fine-scale genetic structure in the white-breasted thrasher, Ramphocinclus brachyurus.

Dispersal is a fundamental process influencing evolution, social behaviour, and the long-term persistence of populations. We use both observational and genetic data to investigate dispersal, kin-clustering and intergroup relatedness in the white-breasted thrasher, Ramphocinclus brachyurus, a cooperatively breeding bird that is globally endangered. Mark-resighting data suggested sex-biased dispersal, with females dispersing over greater distances while males remained philopatric. Accordingly, spatial autocorrelation analysis showed highly significant fine-scale genetic structure among males, but not among females. This fine-scale genetic structuring of the male population resulted in very high levels of relatedness between dominant males at neighbouring nests, similar to that seen within cooperative groups in many species where kin selection is cited as a cause of cooperation. By implication, between-group as well as within-group cooperation may be important, potentially creating a feedback loop in which short-distance dispersal by males leads to the formation of male kin clusters that in turn facilitate nepotistic interactions and favour further local recruitment. The strength of spatial autocorrelation, as measured by the autocorrelation coefficient, r, was approximately two to three times greater than that reported in previous studies of animals. Relatively short dispersal distances by both males and females may have a negative impact on the white-breasted thrasher's ability to colonize new areas, and may influence the long-term persistence of isolated populations. This should be taken into account when designating protected areas or selecting sites for habitat restoration.

The therapeutic effect of toothbrushing on naturally occurring gingivitis.

A majority of previous toothbrushing studies have examined proposed virtues of particular brushing techniques or the relative cleaning ability of various toothbrushes. A smaller number were concerned with their role in prevention of gingivitis. Whether toothbrushing could be therapeutic in naturally occurring gingivitis was tested in 40 teenagers aged 12 to 14 years. Groups from two public schools were examined for gingivitis and plaque. Students from both groups were given a soft multi-tufted toothbrush and nonfluoridated toothpaste to be used daily. Students at one school were given a single intensive oral hygiene session. All students were reexamined 42 days later and given a thorough prophylaxis. Final readings were obtained 84 days after baseline and the results analyzed statistically. Sign test analysis disclosed a significant (P less than .01) improvement in plaque and gingivitis scores for both groups. Wilcoxon tests of patient means revealed a significant improvement in plaque scores, whereas gingivitis means were more variable. Chi square analysis between groups showed that the groups receiving oral hygiene instructions had significantly better (P less than .01) plaque and gingivitis scores at session 2. Gingivitis differences were generally significant at session 3. Toothbrushing has a therapeutic effect on naturally occurring gingivitis, enhanced by oral hygiene instruction.