Genetics of adaptive radiation in Hawaiian species of Tetramolopium (Asteraceae). III. Evolutionary genetics of sex expression

The explosive radiation of Cheirolophus (Asteraceae, Cardueae) in Macaronesia

Background

Considered a biodiversity hotspot, the Canary Islands have been the key subjects of numerous evolutionary studies concerning a large variety of organisms. The genus Cheirolophus (Asteraceae) represents one of the largest plant radiations in the Canarian archipelago. In contrast, only a few species occur in the Mediterranean region, the putative ancestral area of the genus. Here, our main aim was to reconstruct the phylogenetic and biogeographic history of Cheirolophus with special focus on explaining the origin of the large Canarian radiation.

Results

We found significant incongruence in phylogenetic relationships between nuclear and plastid markers. Each dataset provided resolution at different levels in Cheirolophus: the nuclear markers resolved the backbone of the phylogeny while the plastid data provided better resolution within the Canarian clade. The origin of Cheirolophus was dated in the Mid-Late Miocene, followed by rapid diversification into the three main Mediterranean lineages and the Macaronesian clade. A decrease in diversification rates was inferred at the end of the Miocene, with a new increase in the Late Pliocene concurrent with the onset of the Mediterranean climate. Diversification within the Macaronesian clade started in the Early-Mid Pleistocene, with unusually high speciation rates giving rise to the extant insular diversity.

Conclusions

Climate-driven diversification likely explains the early evolutionary history of Cheirolophus in the Mediterranean region. It appears that the exceptionally high diversification rate in the Canarian clade was mainly driven by allopatric speciation (including intra- and interisland diversification). Several intrinsic (e.g. breeding system, polyploid origin, seed dispersal syndrome) and extrinsic (e.g. fragmented landscape, isolated habitats, climatic and geological changes) factors probably contributed to the progressive differentiation of populations resulting in numerous microendemisms. Finally, hybridization events and emerging ecological adaptation may have also reinforced the diversification process.

The genus Artemisia (Asteraceae: Anthemideae) at a continental crossroads: molecular insights into migrations, disjunctions, and reticulations among Old and New World species from a Beringian perspective

Artemisia is the largest genus (ca. 350-500+ spp.) in the tribe Anthemideae and is composed of ecologically, morphologically, and chemically diverse species that are found primarily throughout the Northern Hemisphere. Two major centers of diversity for the genus are located in Eurasia and western North America, but phytogeographic links connecting these two regions are observed all across the North Pacific Rim and adjacent areas in the Arctic, including many islands and archipelagos. Previous phylogenetic studies have helped to clarify major lineages and identify likely sister relationships, but many questions remain unanswered regarding the relationships and migration history of New and Old World species. Here we investigate the phylogenetics of Artemisia within a biogeographic context centered in the Beringian Region and offer new hypotheses concerning species relationships, migration history, and the likely role of reticulate evolution in the genus. Our sampling included many new taxa and emphasized multiple accessions of widespread species, species from proposed refugia, and species with disjunct/vicariant distributions. The ITS phylogeny contained 173 accessions (94 new and 79 from GenBank) and indicated that Artemisia is paraphyletic by the exclusion of several small Asian genera and the North American genus Sphaeromeria. Following a survey of thirteen chloroplast loci, phylogenies based on two plastid markers (psbA-trnH and rpl32-trnL spacers) were constructed with a reduced data set, and though largely consistent with the ITS topology, revealed several cases of possible introgression among New World and Beringian species. Our analysis reveals that North American Artemisia species have multiple origins, and that western North America has served as a source for some colonizing elements in eastern Asia and South America.

Mapping unexplored genomes II: genetic architecture of species differences in the woody Sonchus alliance (Asteraceae) in the Macaronesian Islands

Despite numerous, well-documented evolutionary histories of plant groups which underwent rapid radiation in various oceanic archipelagos, very little is known about the genetic basis of species differences and adaptive radiation. This paper represents the first such study in the Macaronesian Islands using non-model endemic plants, the woody Sonchus alliance. Here I inferred the genetic basis of species differences between two Canary Island endemics, the herbaceous perennial, shade tolerant Lactucosonchus webbii and the woody, coastal desert perennial Sonchus radicatus by quantitative trait locus (QTL) mapping using AFLP markers. A total of 23 QTL (7.3-23.8% PVE; phenotypic variance explained) for 11 morphological traits were found, one for flowering time (31% PVE), and five QTL (7-10.7% PVE) for two physiological traits (intrinsic water use efficiency and stomatal conductance). Interpreted cautiously, these results suggest that major morphological and some physiological differences between the two species are controlled by numerous genes with small to moderate effect. This implies that major morphological changes in island plants can be more complex than suggested by other studies, such as in Tetramolopium in the Hawaiian Islands. The genetic basis of arborescence on islands, one of the most spectacular convergent features of plants across different lineages and archipelagos, is also discussed.

Phylogenetic analysis of sexual systems in Inuleae (Asteraceae)

From an ancestor with bisexual flowers, plants with unisexual flowers, or even unisexual individuals have evolved in different lineages of angiosperms. The Asteraceae tribe Inuleae includes hermaphroditic, monoecious, dioecious, and gynomonoecious species. Gynomonoecy, the sexual system in which female and bisexual flowers occur on the same plant, is prevalent in the Asteraceae. We inferred one large gene phylogeny (ndhF) and two supertrees to investigate whether gynomonoecy was a stage in the evolution from hermaphroditism to monoecy. We identified transitions in sexual system evolution using the stochastic character mapping method. From gynomonoecious ancestors, both hermaphroditic and monoecious descendants have evolved. Gynomonoecy was not restricted to a stage in the evolution toward monoecy because the number of transitions and the rate of change from monoecy to gynomonoecy were much higher than the opposite. We also investigated one hypothesized association among female flowers and the development of a petaloid ray as an explanation of gynomonoecy maintenance in Asteraceae. We found that peripheral female flowers and petaloid rays were phylogenetically correlated. However, empirical evidence shows that a causal relationship between these traits is not clear.

Genetic relationships and variation in reproductive strategies in four closely related bromeliads adapted to neotropical 'inselbergs': Alcantarea glaziouana, A. regina, A. geniculata and A. imperialis (Bromeliaceae)

BACKGROUND AND AIMS

Bromeliads (Bromeliaceae) adapted to rock outcrops or 'inselbergs' in neotropical rain forests have been identified as suitable plant models for studying population divergence and speciation during continental plant radiations. Little is known about genetic relationships and variation in reproductive strategies within and among inselberg-adapted species, yet knowledge of these parameters is important for understanding divergence processes and for conservation planning.

METHODS

Nuclear microsatellites were used to assess the role of clonal reproduction, estimate genetic diversity and explore genetic relationships and variation in reproductive strategies for a total of 15 populations of four closely related Alcantarea inselberg species in south-eastern Brazil: A. glaziouana, A. regina, A. geniculata and A. imperialis.

KEY RESULTS

Clonal propagation is frequent in coastal populations of A. glaziouana and A. regina, but absent in the high-altitude species A. geniculata and A. imperialis. Considerable variation in clonal diversity, gene diversity (H(e)), allelic richness, and Wright's inbreeding coefficient (F(IS)) exists within and between species of Alcantarea. A Bayesian analysis of coastal inselberg species indicated pronounced genetic structure. A neighbor-joining analysis grouped populations of each species together with moderate bootstrap support, except for the high altitude species A. imperialis.

CONCLUSIONS

The coastal inselberg species A. glaziouana and A. regina tend to propagate asexually via vegetative clonal growth, and both reproductive strategies and breeding systems vary greatly between populations and species of Alcantarea. The microsatellite data indicate a history of hybridization and reticulation involving the high-altitude species A. geniculata and A. imperialis in areas of co-occurrence. The results highlight the need to understand similarities and differences in reproductive strategies both within and between related species for conservation planning and as a basis for understanding evolutionary processes in tropical radiations.

Molecular phylogenetics of the Macaronesian-endemic genus Bystropogon (Lamiaceae): palaeo-islands, ecological shifts and interisland colonizations

Abstract A molecular phylogenetic study of Bystropogon L'Her. (Lamiaceae) is presented. We performed a cladistic analysis of nucleotide sequences of the internal transcribed spacers (ITS), of the nuclear ribosomal DNA, and of the trnL gene and trnL-trnF intergenic spacer of the chloroplast DNA. Bystropogon odoratissimus is the only species endemic to the Canary Islands that occurs in the three palaeo-islands of Tenerife. This species is not part of an early diverging lineage of Bystropogon and we suggest that it has a recent origin. This phylogenetic pattern is followed by most of the species endemic to the palaeo-islands of Tenerife. The two sections currently recognized in Bystropogon form two monophyletic groups. Taxa belonging to the section Bystropogon clade show interisland colonization limited to the Canary Islands with ecological shifts among three ecological zones. Taxa from the section Canariense clade show interisland colonization both within the Canary Islands and between the Canary Islands and Madeira. Speciation events within this clade are mostly limited to the laurel forest. The genus has followed a colonization route from the Canaries towards Madeira. This route has also been followed by at least five other plant genera with species endemic to Macaronesia. Major incongruences were found between the current infrasectional classification and the molecular phylogeny, because the varieties of Bystropogon origanifolius and Bystropogon canariensis do not form two monophyletic groups. The widespread B. origanifolius appears as progenitor of the other species in section Bystropogon with a more restricted distribution.

Molecular phylogeny of Subtribe Artemisiinae (Asteraceae), including Artemisia and its allied and segregate genera

BACKGROUND

Subtribe Artemisiinae of Tribe Anthemideae (Asteraceae) is composed of 18 largely Asian genera that include the sagebrushes and mugworts. The subtribe includes the large cosmopolitan, wind-pollinated genus Artemisia, as well as several smaller genera and Seriphidium, that altogether comprise the Artemisia-group. Circumscription and taxonomic boundaries of Artemisia and the placements of these small segregate genera is currently unresolved.

RESULTS

We constructed a molecular phylogeny for the subtribe using the internal transcribed spacers (ITS) of nuclear ribosomal DNA analyzed with parsimony, likelihood, and Bayesian criteria. The resulting tree is comprised of three major clades that correspond to the radiate genera (e.g., Arctanthemum and Dendranthema), and two clades of Artemisia species. All three clades have allied and segregate genera embedded within each.

CONCLUSIONS

The data support a broad concept of Artemisia s.l. that includes Neopallasia, Crossostephium, Filifolium, Seriphidium, and Sphaeromeria. However, the phylogeny excludes Elachanthemum, Kaschgaria, and Stilnolepis from the Artemisia-group. Additionally, the monophyly of the four subgenera of Artemisia is also not supported, with the exception of subg. Dracunculus. Homogamous, discoid capitula appear to have arisen in parallel four to seven times, with the loss of ray florets. Thus capitular morphology is not a reliable taxonomic character, which traditionally has been one of the defining characters.