Cheilanthoid ferns have a worldwide distribution and are found in rocky and seasonally dry habitats. Difficulty in deciphering natural lineages of cheilanthoids has been attributed to morphological convergence associated with adaptation to xeric environments. The goal of this study was to investigate the monophyly of the genus Pellaea by generating a DNA sequence-based cheilanthoid phylogeny. DNA sequences of the chloroplast rps4 gene and rps4-trnS intergenic spacer (IGS) were generated from 105 exemplars; chloroplast trnL-F IGS sequences were also generated from 60 of these samples. Results show that Pellaea sensu Tryon and Tryon is polyphyletic; Pellaea sections Holcochlaena and Ormopteris are distant relatives of sections Pellaea and Platyloma and have closer relationships with Doryopteris. A monophyletic circumscription of ''pellaeoid'' ferns is here defined to include traditional P. sect. Pellaea, P. sect. Platyloma, Astrolepis, and elements of Paragymnopteris and Paraceterach, all of which form a clade sister to Argyrochosma. Several other novel systematic implications of cheilanthoid relationships are also presented. The distribution of base chromosome numbers across the cheilanthoid phylogeny reveals potential synapomorphies of x 5 29 for the pellaeoid clade and x 5 27 for Argyrochosma, and suggests a trend toward reduction in base number during cheilanthoid evolution. Current geographic distribution of cheilanthoid ferns suggests a history of multiple introductions into the Old World from several ancestral New World lineages.

Levels and distribution of genetic variation were analyzed in 15 populations of the homosporous fern Gymnocarpium dryopteris ssp. disjunctum to evaluate the mating system and the genetic structure of this taxon. Estimated rates of intragametophytic selling were 0.000 in all populations, signifying that all sporophytes examined arose via intergametophytic matings. Furthermore, values of F, the fixation index, ranged from –0.171 to 0.038, indicating that all populations approach Hardy‐Weinberg equilibrium. Therefore, not only is intragametophytic selling rare in G. dryopteris ssp. disjunctum, but intergametophytic selling is also uncommon. Factors promoting outcrossing in G. dryopteris ssp. disjunctum include an antheridiogen system, an ontogenetic sequence that favors intergametophytic matings, and high levels of genetic load. Analysis of F‐statistics indicated statistically significant genetic differentiation among populations despite a mean genetic identity of 0.973 and high levels of interpopulational gene flow (Nm = 3.41 to 4.09). These patterns may reflect levels of gene flow that prevent significant interpopulational divergence while permitting slight genetic differentiation among populations.

Social decision-making is commonly explored in the context of adult responder behavior in the ultimatum game. Responder behavior in the game has been proposed to be the consequence of two competing systems that control behavior: an affective system, which promotes an emotional response to unfair offers, and a deliberative system, which instead encourages a rational response to maximize in-game gains. In a secondary analysis of ultimatum game data in children and adolescents (N = 429), the present study demonstrated that trial-level metrics of responder behavior were reflective of a dual systems framework. However, no consistent relationship was found between responder behavior and trait-level measures of emotion regulation. Choice history was found to influence all measures of responder behavior in the game. These results support a dual systems account of social decision-making in children and adolescents and highlight choice repetition bias as an additional factor influencing decision-making within the ultimatum game.

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Although most species of homosporous pteridophytes investigated to date are highly outcrossing, there is little conclusive evidence of the mechanisms promoting intergametophytic matings in natural populations. The hormone antheridiogen, produced by meristematic and usually archegoniate gametophytes, has been implicated as an effective promoter of intergametophytic matings in natural populations. In this study, antheridiogen production and response were analyzed in laboratory‐cultured gametophytes from five outcrossing populations of Gymnocarpium dryopteris ssp. disjunctum. The numbers of antheridia present in gametophytes grown on antheridiogen‐enriched and control nutrient agar were recorded over an 84‐day period; approximately 4200 gametophytes were observed. Contingency table analyses indicated a statistically significant positive response to treatment medium in the majority of cultures analyzed. However, consistently insignificant responses to treatment medium in two gametophyte cultures suggest intrapopulational variation in gametophytic response to antheridiogen. Antheridiogen production and response in gametophytes of G. dryopteris ssp. disjunctum suggest that this antheridiogen system effectively promotes intergametophytic matings in natural populations. The selection pressures under which antheridiogen systems may have evolved are also discussed.