Genetic basis and timing of a major mating system shift in Capsella

YesA crucial step in the transition from outcrossing to self-fertilization is the loss of genetic self-incompatibility (SI). In the Brassicaceae, SI involves the interaction of female and male speci-ficity components, encoded by the genesSRKandSCRat the self-incompatibility locus (S-lo-cus). Theory predicts thatS-linked mutations, and especially dominant mutations inSCR, arelikely to contribute to loss of SI. However, few studies have investigated the contribution ofdominant mutations to loss of SI in wild plant species. Here, we investigate the genetic basis of loss of SI in the self-fertilizing crucifer speciesCapsella orientalis, by combining genetic mapping, long-read sequencing of completeS-hap-lotypes, gene expression analyses and controlled crosses. We show that loss of SI inC. orientalisoccurred<2.6 Mya and maps as a dominant trait totheS-locus. We identify a fixed frameshift deletion in the male specificity geneSCRand con-firm loss of male SI specificity. We further identify anS-linked small RNA that is predicted tocause dominance of self-compatibility. Our results agree with predictions on the contribution of dominantS-linked mutations toloss of SI, and thus provide new insights into the molecular basis of mating system transitions.Work at Uppsala Genome Center is funded by 550 RFI / VR and Science for Life Laboratory, Sweden. The SNP&SEQ Platform is supported by 551 the Swedish Research Council and the Knut and Alice Wallenberg Foundation. V.C. 552 acknowledges support by a grant from the European Research Council (NOVEL project, 553 grant #648321). The authors thank the French Ministère de l’Enseignement Supérieur et de la 554 Recherche, the Hauts de France Region and the European Funds for Regional Economical 555 Development for their financial support to this project. This work was supported by a grant 556 from the Swedish Research Council (grant #D0432001) and by a grant from the Science for 557 Life Laboratory, Swedish Biodiversity Program to T.S. The Swedish Biodiversity Program is 558 supported by the Knut and Alice Wallenberg Foundation

Increased diversification rates follow shifts to bisexuality in liverworts

Shifts in sexual systems are one of the key drivers of species diversification. In contrast to angiosperms, unisexuality prevails in bryophytes. Here, we test the hypotheses that bisexuality evolved from an ancestral unisexual condition and is a key innovation in liverworts. We investigate whether shifts in sexual systems influence diversification using hidden state speciation and extinction analysis (HiSSE). This new method compares the effects of the variable of interest to the best-fitting latent variable, yielding robust and conservative tests. We find that the transitions in sexual systems are significantly biased toward unisexuality, even though bisexuality is coupled with increased diversification. Sexual systems are strongly conserved deep within the liverwort tree but become much more labile toward the present. Bisexuality appears to be a key innovation in liverworts. Its effects on diversification are presumably mediated by the interplay of high fertilization rates, massive spore production and long-distance dispersal, which may separately or together have facilitated liverwort speciation, suppressed their extinction, or both. Importantly, shifts in liverwort sexual systems have the opposite effect when compared to angiosperms, leading to contrasting diversification patterns between the two groups. The high prevalence of unisexuality among liverworts suggests, however, a strong selection for sexual dimorphism

Striking autapomorphic evolution in Physotheca J.J.Engel & Gradst. (Marchantiophyta: Lophocoleaceae) blurred its actual relationships with Leptoscyphus Mitt

The taxonomic status and phylogenetic position of the monotypic liverwort genus Physotheca J.J.Engel & Gradst., including P. autoica J.J.Engel & Gradst. endemic to Ecuador, are inferred from phylogenetic analyses of two cpDNA loci. The results indicate that the genus is nested within Leptoscyphus and the new combination, L. autoicus (J.J.Engel & Gradst.) Vanderp. & Gradst., is made. This indicates, along with an increasing body of evidence, that extreme morphological transformations can obscure the phylogenetic signal present in morphological data. © 2012 British Bryological Society

Evolutionary origin of the latitudinal diversity gradient in liverworts

A latitudinal diversity gradient towards the tropics appears as one most recurrent patterns in ecology, but the mechanisms underlying this pattern remain an area of controversy. In angiosperms, the tropical conservatism hypothesis proposes that most groups originated in the tropics and are adapted to a tropical climatic regime, and that relatively few species have evolved physiological adaptations to cold, dry or unpredictable climates. This mechanism is, however, unlikely to apply across land plants, and in particular, to liverworts, a group of about 7500 species, whose ability to withstand cold much better than their tracheophyte counterparts is at odds with the tropical conservatism hypothesis. Molecular dating, diversification rate analyses and ancestral area reconstructions were employed to explore the evolutionary mechanisms that account for the latitudinal diversity gradient in liverworts. As opposed to angiosperms, tropical liverwort genera are not older than their extra-tropical counterparts (median stem age of tropical and extra-tropical liverwort genera of 24.35 ± 39.65 Ma and 39.57 ± 49.07 Ma, respectively), weakening the ‘time for speciation hypothesis’. Models of ancestral area reconstructions with equal migration rates between tropical and extra-tropical regions outperformed models with asymmetrical migration rates in either direction. The symmetry and intensity of migrations between tropical and extra-tropical regions suggested by the lack of resolution in ancestral area reconstructions towards the deepest nodes are at odds with the tropical niche conservatism hypothesis. In turn, tropical genera exhibited significantly higher net diversification rates than extra-tropical ones, suggesting that the observed latitudinal diversity gradient results from either higher extinction rates in extra-tropical lineages or higher speciation rates in the tropics. We discuss a series of experiments to help deciphering the underlying evolutionary mechanisms..P. was funded by the Spanish ‘Ministerio de Economía y Competitividad’ through the Juan de la Cierva Program – Incorporation (IJCI-2014-19691) and Marie Sklodowska-Curie COFUND, Researchers' Night and Individual Fellowships Global (MSCA grant agreement No. 747238, ‘UNISLAND’).Peer Reviewe

No borders during the post-glacial assembly of European bryophytes

info:eu-repo/semantics/publishe

Modeling Species Distributions from Heterogeneous Data for the Biogeographic Regionalization of the European Bryophyte Flora

The definition of biogeographic regions provides a fundamental framework for a range of basic and applied questions in biogeography, evolutionary biology, systematics and conservation. Previous research suggested that environmental forcing results in highly congruent regionalization patterns across taxa, but that the size and number of regions depends on the dispersal ability of the taxa considered. We produced a biogeographic regionalization of European bryophytes and hypothesized that (1) regions defined for bryophytes would differ from those defined for other taxa due to the highly specific eco-physiology of the group and (2) their high dispersal ability would result in the resolution of few, large regions. Species distributions were recorded using 10,000 km2 MGRS pixels. Because of the lack of data across large portions of the area, species distribution models employing macroclimatic variables as predictors were used to determine the potential composition of empty pixels. K-means clustering analyses of the pixels based on their potential species composition were employed to define biogeographic regions. The optimal number of regions was determined by v-fold cross-validation and Moran's I statistic. The spatial congruence of the regions identified from their potential bryophyte assemblages with large-scale vegetation patterns is at odds with our primary hypothesis. This reinforces the notion that post-glacial migration patterns might have been much more similar in bryophytes and vascular plants than previously thought. The substantially lower optimal number of clusters and the absence of nested patterns within the main biogeographic regions, as compared to identical analyses in vascular plants, support our second hypothesis. The modelling approach implemented here is, however, based on many assumptions that are discussed but can only be tested when additional data on species distributions become available, highlighting the substantial importance of developing integrated mapping projects for all taxa in key biogeographically areas of Europe, and the Mediterranean peninsulas in particular. © 2013 Mateo et al

The cosmopolitan moss Bryum argenteum in Antarctica: Recent colonisation or in situ survival?

Since the onset of glaciation following the Oligocene (30–28 Ma), the prevalence of increasingly cold conditions has shaped the evolution of the Antarctic biota. Two hypotheses, postglacial recruitment from extra-regional locations and in situ persistence, have been proposed to explain the biogeography of the contemporary species-poor terrestrial Antarctic biota. Bryophytes, which form a major group of the Antarctic flora, exhibit a strong, inherent ability to survive cold conditions but also have high long-distance dispersal capacities, which are compatible with both hypotheses. Here, we test these hypotheses by means of population genetic and phylogeographic analyses of the cosmopolitan moss Bryum argenteum. We find evidence for at least three independent colonisation events of the species in Antarctica. Ancestral area reconstruction coupled with molecular dating suggests colonisation times of the different Antarctic clades ranging from four million years for the oldest lineage to half a million years for the youngest lineage. This suggests multiple colonisation events of Antarctica by this species during several glacial cycles within the Pleistocene, Pliocene and possibly late Miocene. This is the first study to demonstrate in situ persistence of bryophytes in Antarctica throughout previous glaciations