Clonality, local population structure and gametophyte sex ratios in cryptic species of the Sphagnum magellanicum complex.

BACKGROUND AND AIMS: Sphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300-500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites. METHODS: Four hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex. KEY RESULTS: All four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males. CONCLUSIONS: These four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases.

The influence of group discussion on performance judgments: rating accuracy, contrast effects, and halo.

The authors investigated the effect of group discussion, such as may occur formally in panel interview scenarios, assessment centers, or 360-degree feedback situations, on judgments of performance. Research on group polarization suggests that the effect of group discussion combined with raters' preexisting impressions of ratees or interviewees should result in an extremitization of impressions. Thus, the authors hypothesized that group discussion would (a) make ratings less accurate, (b) polarize impressions that were already good or poor as reflected by greater contrast effects, and (c) increase positive halo. Results indicated that group discussion resulted in less accurate ratings and greater contrast effects. Additional analyses suggested that group discussion increased positive halo. The authors discuss implications for research on group or panel judgments.

The validity of physical aggression in predicting adolescent academic performance.

BACKGROUND: Aggression has a long history in academic research as both a criterion and a predictor variable and it is well documented that aggression is related to a variety of poor academic outcomes such as: lowered academic performance, absenteeism and lower graduation rates. However, recent research has implicated physical aggression as being predictive of lower academic performance. AIMS: The purpose of this study was to examine the role of the 'Big Five' personality traits of agreeableness, openness to experience, conscientiousness, neuroticism and extraversion and physical aggression in predicting the grade point averages (GPA) of adolescent students and to investigate whether or not there were differences in these relationships between male and female students. SAMPLE: A sample of 992 students in grades 9 to 12 from a high school in south-eastern USA as part of a larger study examining the students' preparation for entry into the workforce. METHOD: The study was correlational in nature: students completed a personality inventory developed by the second author with the GPA information supplied by the school. RESULTS: Results indicated that physical aggression accounts for 16% of variance in GPA and it adds 7% to the prediction of GPA beyond the Big Five. The Big Five traits added only 1.5% to the prediction of GPA after controlling for physical aggression. Interestingly, a significantly larger amount of variance in GPA was predicted by physical aggression for females than for males. CONCLUSIONS: Aggression accounts for significantly more variance in the GPA of females than for males, even when controlling for the Big Five personality factors. Future research should examine the differences in the expression of aggression in males and females, as well as how this is affecting interactions between peers and between students and their teachers.

Psychological reactance: examination across age, ethnicity, and gender.

Psychological reactance is a motivational state aroused when real or perceived personal freedoms are threatened, reduced, or eliminated. Although psychological reactance theory has existed for almost 40 years, there is still dissent over some of its most basic characteristics. Research on age and ethnicity is scant, and research on gender has not produced a clear pattern of results. We attempted to clarify the relationships of these variables to psychological reactance. A total of 3,499 undergraduates completed the Therapeutic Reactance Scale and a brief demographic questionnaire. We found a curvilinear relationship between age and reactance, with older and younger participants exhibiting higher reactance than the middle age group. African Americans, Asians, and Hispanics exhibited higher total, behavioral, and verbal reactance than Caucasians and Native Americans. Men produced higher total, behavioral, and verbal reactance scores than women. We discuss the implications of these findings and make suggestions for further research.