Erratum: Revisiting the Dioecy-Polyploidy Association: Alternate Pathways and Research Opportunities

The evolutionary transition from hermaphroditism (combined sexes) to dioecy (separate sexes) is associated with whole genome duplication (polyploidy) in several flowering plant genera. Moreover, there is evidence for transitions in the opposite direction, i.e. a loss of dioecy with an increase in ploidy. Here, we review evidence for these associations, synthesize previous ideas on the mechanism underlying the patterns and explore alternative pathways. Specifically, we examine potential ecological and genetic mechanisms, differentiated by whether ploidy or gender (functional sex expression of the plant) changes are the primary cause and whether the effect is direct or indirect. An analysis of 22 genera variable for both ploidy and gender indicates that gender monomorphism (hermaphroditism, monoecy) is more common among diploid than polyploid species, whereas gender dimorphism (dioecy, gynodioecy, subdioecy) is more frequent among polyploid species. The transition from diploid hermaphroditic to polyploid gender-dimorphic taxa may arise directly through changes in gender as a result of genome duplication through genomic rearrangements or homeologous recombination, or changes in gender may result in increased unreduced gamete production leading to polyploid formation. Alternatively, the transition may occur through the indirect effects of genome duplication on mating system and inbreeding depression, which favor selection for unisexuality, or habitat shifts associated with unisexuality may simultaneously cause increased unreduced gamete production. Novel mechanisms for transitions in the opposite direction (from dioecy to hermaphroditism with increase in ploidy) include disruption of genetic sex determination and the benefits of reproductive assurance. We highlight key questions requiring further attention and promising approaches for answering them and better clarifying the genesis of sexual system polyploidy associations. See also the sister article focusing on animals by Wertheim et al. in this themed issue

Distribution and environmental correlates of fungal infection and host tree health in the endangered American chestnut in Canada

Restoration of plants endangered by introduced pathogens relies in part on the ability to predict geographic variation in the incidence of disease and its impact on tree health. Environmental factors can influence plant-pathogen interactions but large scale, multifactorial analyses of environmental determinants are often lacking. Here we use a multi-year survey of the endangered American chestnut in southern Canada and geospatial data on climatic, edaphic, and landscape characteristics to test for spatial heterogeneity in, and environmental associations with, blight occurrence (current incidence of chestnut blight, infection of healthy individuals over 13 years) and tree health (presence of healing/healed cankers, tree mortality). We detected geographic hotspots for all measures of blight occurrence and tree health, suggesting tree-pathogen interactions are moderated by local conditions. Individual measures of blight occurrence were correlated with nine climatic, edaphic and landscape variables and were consistently related to precipitation, surficial geology and elevation. Measures of tree health were consistently affected by mean annual temperature, and individually correlated with five climatic and landscape variables but no edaphic variables. Overall, environmental variables explained 9–22% of variation in blight and tree health, reflecting the complex processes underlying host -pathogen interactions in a system in which blight persists throughout the range. Nevertheless, environmental correlates are sufficient to guide further research on mechanisms of tolerance and aid conservation priorities and action in this species

Esterase polymorphism in remanant populations of Aspidosperma polyneuron Müll.Arg. (Apocynaceae) Polimorfismo de esterases em populações remanescentes de Aspidosperma polyneuron Müll.Arg. (Apocynaceae)

The population genetic structure of the endangered tree species Aspidosperma polyneuron Mull.Arg. (Apocynaceae) was reported based on analysis of esterase polymorphism in two remanant populations. Allelic variation was detected at three isoesterase loci (Est-3, Est-9, and Est-10). The proportion of polymorphic loci for both populations was 30% and deviation from Hardy-Weinberg equilibrium was observed for the Est-3 locus observed in the northern population. Segregation distortion and the lower level of observed and expected heterozygosity in this population were attributed to founder genotype. The high genetic identity values for northern and northwestern populations are in accordance with the low levels of interpopulation genetic divergence demonstrated by the F(ST) (0.03) value. The F(IS) value (0.23) indicated moderate levels of inbreeding. A. polyneuron can be indicated as an example of endangered species suggesting high genetic variation in contrast to the low genetic variation reported for endangered species. The esterase isozymes may be a good genetic marker for studies of natural A. polyneuron populations.<br>A análise do polimorfismo de isozimas esterases foi usada para reportar a estrutura genética de duas populações remanecentes da espécie de árvore em extinção Aspidosperma polyneuron Müll.Arg. (Apocynaceae). Variação alélica foi detectada em três locos de isoesterases (Est-3, Est-9, e Est-10). A proporção de locos polimórficos de ambas as populações foi de 30%, sendo observado um desvio do equilíbrio de Hardy-Weinberg no loco Est-3 na população da região norte do Estado do Paraná. Uma distorção na segregação e um mais baixo nível de heterozigosidade observada e esperada nesta população foram atribuídos ao efeito do genótipo fundador. Os valores altos de identidade genética das populações do norte e noroeste do Estado estão de acordo com o baixo nível de divergência genética interpopulacional demonstrado pelo valor de F(ST) (0,03). O valor de F(IS) (0,23) indicou moderado nível de endocruzamentos. A. polyneuron pode ser indicada como um exemplo de espécie em extinção apresentando variação genética alta, contrastando com a variação genética baixa reportada sobre espécies em extinção. As isozimas esterases podem ser um bom marcador genético em estudos de populações naturais de A. polyneuron