Diversity of S-alleles and mate availability in 3 populations of self-incompatible wild pear (Pyrus pyraster).

Small populations of self-incompatible plants may be expected to be threatened by the limitation of compatible mating partners (i.e., S-Allee effect). However, few empirical studies have explicitly tested the hypothesis of mate limitation in small populations of self-incompatible plants. To do so, we studied wild pear (Pyrus pyraster), which possesses a gametophytic self-incompatibility system. We determined the S-genotypes in complete samplings of all adult trees from 3 populations using a PCR-RFLP approach. We identified a total of 26 different S-alleles, homologous to S-alleles of other woody Rosaceae. The functionality of S-alleles and their Mendelian inheritance were verified in artificial pollination experiments and investigations of pollen tube growth. The smallest population (N = 8) harbored 9 different S-alleles and showed a mate availability of 92.9%, whereas the 2 larger populations harbored 18 and 25 S-alleles and exhibited mate availabilities of 98.4% and 99.2%, respectively. Therefore, we conclude that even small populations of gametophytic self-incompatible plants may exhibit high diversity at the S-locus and are not immediately threatened owing to reduced mate availability.

Evolutionary dynamics of mating system shifts in Arabidopsis lyrata.

Outcrossing is the prevalent mode of reproduction in plants and animals despite its substantial costs, while selfing and mixed mating occur at much lower frequency. Comparative research on plants has demonstrated the lability of self-incompatibility, but there is little information about the transition on a within-species level from self-incompatibility to predominant selfing. We studied variation in mating system among 18 populations of Arabidopsis lyrata within a phylogenetic context to shed light on the evolution of selfing. Realized and potential mating systems were assessed by genetic analysis with microsatellite markers and hand-self-pollinations on 30 plants from each population. The fraction of self-incompatible plants in a population was highly correlated with the outcrossing rate, showing that the spread of self-compatibility is accompanied by or soon followed by an increase in the rate of selfing. The four predominantly selfing populations (outcrossing rates <0.25) fell into more than one phylogenetic cluster, suggesting that the transition to selfing occurred more than once independently. Hence, A. lyrata offers an opportunity for the comparative analysis of outcrossing as a predominant mode of reproduction in plants and of the causes of the shift to selfing.

Intoxication and self-orientations during alcohol use: an empirical assessment of the relationship and of its determinants among employed men and women.

Analysis of data from a survey of employed adults in Detroit indicates that frequency of intoxication is associated with a masculine self-orientation among men and a feminine self-orientation among women during alcohol use. The study calls attention to the importance of fathers' drinking, life events, social class relations and a generalized alienation from self, work and society for understanding frequency of intoxication and masculine and feminine orientations during alcohol use. A path analysis suggests that the men and women who become intoxicated may regain a sense of self and relationships to others that they do not have in sober everyday life. Implications for future research on heavy drinking and self-orientations during alcohol use are discussed.