Cross-species hybridization and the origin of North African date palms.

Date palm (Phoenix dactylifera L.) is a major fruit crop of arid regions that were domesticated ∼7,000 y ago in the Near or Middle East. This species is cultivated widely in the Middle East and North Africa, and previous population genetic studies have shown genetic differentiation between these regions. We investigated the evolutionary history of P. dactylifera and its wild relatives by resequencing the genomes of date palm varieties and five of its closest relatives. Our results indicate that the North African population has mixed ancestry with components from Middle Eastern P. dactylifera and Phoenix theophrasti, a wild relative endemic to the Eastern Mediterranean. Introgressive hybridization is supported by tests of admixture, reduced subdivision between North African date palm and P. theophrasti, sharing of haplotypes in introgressed regions, and a population model that incorporates gene flow between these populations. Analysis of ancestry proportions indicates that as much as 18% of the genome of North African varieties can be traced to P. theophrasti and a large percentage of loci in this population are segregating for single-nucleotide polymorphisms (SNPs) that are fixed in P. theophrasti and absent from date palm in the Middle East. We present a survey of Phoenix remains in the archaeobotanical record which supports a late arrival of date palm to North Africa. Our results suggest that hybridization with P. theophrasti was of central importance in the diversification history of the cultivated date palm.

Asymmetries of reproductive isolation are reflected in directionalities of hybridization: integrative evidence on the complexity of species boundaries.

The complex nature of species boundaries has been a central topic in evolutionary biology ever since Darwin. Despite numerous separate studies on reproductive isolation and hybridization, their relationship remains underinvestigated. Are the strengths and asymmetries of reproductive barriers reflected in the extent and directionalities of interspecific genetic exchange? We combined field, experimental, and molecular data to quantify strengths and asymmetries of sympatric reproductive barriers and hybridization between florally heteromorphic primroses. We also assessed whether generalist pollinators discriminate between different floral cues and contribute to reproductive isolation, a long-debated topic. Sympatric reproductive isolation is high but incomplete, and most phenotypic intermediates are genetic F1 hybrids, whereas backcrosses are rare, revealing low interspecific gene flow. Species integrity rests on multiple barriers, but ethological isolation is among the strongest, demonstrating that even generalist pollinators crucially contribute to the maintenance of species boundaries. Furthermore, reproductive barriers are weaker for Primula veris and short-styled plants, results corroborated by molecular data. Thus, in florally heteromorphic systems, both species- and morph-dependent asymmetries affect permeability of species boundaries. Our study illustrates how the interactions between complex floral syndromes and pollinators shape species boundaries in unique, previously undescribed ways.

Island plants with newly discovered reproductive traits have higher capacity for uniparental reproduction, supporting Baker's law.

Uniparental reproduction is advantageous when lack of mates limits outcrossing opportunities in plants. Baker's law predicts an enrichment of uniparental reproduction in habitats colonized via long-distance dispersal, such as volcanic islands. To test it, we analyzed reproductive traits at multiple hierarchical levels and compared seed-set after selfing and crossing experiments in both island and mainland populations of Limonium lobatum, a widespread species that Baker assumed to be self-incompatible because it had been described as pollen-stigma dimorphic, i.e., characterized by floral morphs differing in pollen-surface morphology and stigma-papillae shape that are typically self-incompatible. We discovered new types and combinations of pollen and stigma traits hitherto unknown in the literature on pollen-stigma dimorphism and a lack of correspondence between such combinations and pollen compatibility. Contrary to previous reports, we conclude that Limonium lobatum comprises both self-compatible and self-incompatible plants characterized by both known and previously undescribed combinations of reproductive traits. Most importantly, plants with novel combinations are overrepresented on islands, selfed seed-set is higher in islands than the mainland, and insular plants with novel pollen-stigma trait-combinations disproportionally contribute to uniparental reproduction on islands. Our results thus support Baker's law, connecting research on reproductive and island biology.

A taxonomic backbone for the Plumbaginaceae (Caryophyllales).

A taxonomic backbone of the Plumbaginaceae is presented and the current state of knowledge on phylogenetic relationships and taxon limits is reviewed as a basis for the accepted taxon concepts. In total, 4,476 scientific names and designations are treated of which 30 are not in the family Plumbaginaceae. The Plumbaginaceae are subdivided in three tribes with 26 genera and 1,179 accepted species. Two subgenera, 17 sections, two subsections and 187 infraspecific taxa are accepted. At the species and infraspecific level 2,782 synonyms were assigned to accepted taxa, whereas 194 names were excluded from the core checklist (i.e., unplaced taxa, infrageneric subdivisions with still uncertain application, names of verified uncertain application, invalid horticultural names, excluded names from other families, other excluded designations, and unresolved names). The EDIT Platform for Cybertaxonomy was utilized as the tool to compile and manage the names and further taxonomic data under explicit taxon concepts. Secundum references are given in case taxon concepts were taken from the literature, whereas this study serves as reference for newly circumscribed taxa. The family's division into the tribes Aegialitideae, Limonieae, and Plumbagineae departs from earlier two-subfamily classifications, prompted by recent phylogenetic findings that challenge the subfamilial affinity of Aegialitis. The genus Acantholimon was extended to include Gladiolimon, as currently available phylogenetic and morphological data support this merger. In Limonium, all accepted species could be assigned to sections and subsections or the "Mediterranean lineage", respectively, making use of the phylogenetic distribution of their morphological characters and states. A new combination and/or status is proposed for Dyerophytumsocotranum, Limoniumthymoides, Limonium×fraternum, Limonium×rossmaessleri, and Limoniumsect.Jovibarba. Special attention is given to nomenclatural issues, particularly for Staticenomenambiguum to resolve the names under accepted names. The use of artificial groupings like "aggregates", "complexes" and "species groups" in alpha-taxonomic treatments is discussed. The taxonomic backbone will receive continued updates and through the Caryophyllales Taxonomic Expert Network, it contributes the treatment of the Plumbaginaceae for the World Flora Online.

Geo-Climatic Changes and Apomixis as Major Drivers of Diversification in the Mediterranean Sea Lavenders (Limonium Mill.).

The Mediterranean realm, comprising the Mediterranean and Macaronesian regions, has long been recognized as one of the world's biodiversity hotspots, owing to its remarkable species richness and endemism. Several hypotheses on biotic and abiotic drivers of species diversification in the region have been often proposed but rarely tested in an explicit phylogenetic framework. Here, we investigate the impact of both species-intrinsic and -extrinsic factors on diversification in the species-rich, cosmopolitan Limonium, an angiosperm genus with center of diversity in the Mediterranean. First, we infer and time-calibrate the largest Limonium phylogeny to date. We then estimate ancestral ranges and diversification dynamics at both global and regional scales. At the global scale, we test whether the identified shifts in diversification rates are linked to specific geological and/or climatic events in the Mediterranean area and/or asexual reproduction (apomixis). Our results support a late Paleogene origin in the proto-Mediterranean area for Limonium, followed by extensive in situ diversification in the Mediterranean region during the late Miocene, Pliocene, and Pleistocene. We found significant increases of diversification rates in the "Mediterranean lineage" associated with the Messinian Salinity Crisis, onset of Mediterranean climate, Plio-Pleistocene sea-level fluctuations, and apomixis. Additionally, the Euro-Mediterranean area acted as the major source of species dispersals to the surrounding areas. At the regional scale, we infer the biogeographic origins of insular endemics in the oceanic archipelagos of Macaronesia, and test whether woodiness in the Canarian Nobiles clade is a derived trait linked to insular life and a biotic driver of diversification. We find that Limonium species diversity on the Canary Islands and Cape Verde archipelagos is the product of multiple colonization events followed by in situ diversification, and that woodiness of the Canarian endemics is indeed a derived trait but is not associated with a significant shift to higher diversification rates. Our study expands knowledge on how the interaction between abiotic and biotic drivers shape the uneven distribution of species diversity across taxonomic and geographical scales.

Exogenous induction of thermogenesis in Arum concinnatum by salicylic acid.

Arum concinnatum Schott is a highly thermogenic species, with the temperature of the appendix exceeding ~10.9°C above the ambient temperature during thermogenesis, whereas the rates of respiration of the male florets in intact inflorescences peak at 0.92µmol s-1 g-1, which is the highest rate so far measured among the plants. Here, we attempt the ex situ exogenous induction of thermogenesis in whole inflorescences and in separate appendices of the spadix, and explore the thermogenic patterns under controlled laboratory conditions of light and temperature. Mature but unopened inflorescences and appendices showed thermogenic responses when treated with salicylic acid (SA), but not when treated with distilled water (control). With regard to light conditions, the responses revealed only one significant difference for inflorescences, which concerns the higher maximum temperature in the continuous light treatment compared with continuous dark. Along the ambient temperature gradient, at the lowest temperature edge individuals remained stable close to ambient temperature and to control. These findings suggest that, in general, ex situ exogenous induction of thermogenesis can be achieved in whole inflorescences and in separate appendices of spadix of A. concinnatum using SA. This study also indicates that SA acts independently of light conditions, while exogenous induction of thermogenesis takes place within an ambient temperature range.

An expanded molecular phylogeny of Plumbaginaceae, with emphasis on Limonium (sea lavenders): Taxonomic implications and biogeographic considerations.

Plumbaginaceae is characterized by a history of multiple taxonomic rearrangements and lacks a broad molecular phylogenetic framework. Limonium is the most species-rich genus of the family with ca. 600 species and cosmopolitan distribution. Its center of diversity is the Mediterranean region, where ca. 70% of all Limonium species are endemic. In this study, we sample 201 Limonium species covering all described infrageneric entities and spanning its wide geographic range, along with 64 species of other Plumbaginaceae genera, representing 23 out of 29 genera of the family. Additionally, 20 species of the sister family Polygonaceae were used as outgroup. Sequences of three chloroplast (trnL-F, matK, and rbcL) and one nuclear (ITS) loci were used to infer the molecular phylogeny employing maximum likelihood and Bayesian analyses. According to our results, within Plumbaginoideae, Plumbago forms a non-monophyletic assemblage, with Plumbago europaea sister to Plumbagella, while the other Plumbago species form a clade sister to Dyerophytum. Within Limonioideae, Ikonnikovia is nested in Goniolimon, rejecting its former segregation as genus distinct from Goniolimon. Limonium is divided into two major clades: Limonium subg. Pteroclados s.l., including L. sect. Pteroclados and L. anthericoides, and L. subg. Limonium. The latter is divided into three well-supported subclades: the monospecific L. sect. Limoniodendron sister to a clade comprising a mostly non-Mediterranean subclade and a Mediterranean subclade. Our results set the foundation for taxonomic proposals on sections and subsections of Limonium, namely: (a) the newly described L. sect. Tenuiramosum, created to assign L. anthericoides at the sectional rank; (b) the more restricted circumscriptions of L. sect. Limonium (= L. sect. Limonium subsect. Genuinae) and L. sect. Sarcophyllum (for the Sudano-Zambezian/Saharo-Arabian clade); (c) the more expanded circumscription of L. sect. Nephrophyllum (including species of the L. bellidifolium complex); and (d) the new combinations for L. sect. Pruinosum and L. sect. Pteroclados subsect. Odontolepideae and subsect. Nobiles.

Environmental (in)dependence of a hybrid zone: Insights from molecular markers and ecological niche modeling in a hybrid zone of Origanum (Lamiaceae) on the island of Crete.

The role of environment and the relative significance of endogenous versus exogenous selection in shaping hybrid zones have been crucial issues in the studies of hybridization. Recent advances in ecological niche modeling (ENM) offer new methodological tools, especially in combination with the genotyping of individuals in the hybrid zone. Here, we study the hybrid zone between the widely known spices Origanum onites and Origanum vulgare ssp. hirtum in Crete. We analyze the genetic structure of both parental taxa and their hybrid Origanum × intercendens using AFLP markers on 15 sympatric and 12 allopatric populations and employ ecological niche modeling and niche similarity tests to study their niche patterns. We complement these analyses with seed viability measurements. Our study revealed that the hybridizing taxa O. onites and O. vulgare ssp. hirtum and the resulting genotypic classes showed geographical and environmental niche similarities based on the predictions of ENMs and the subsequent similarity tests. The occurrence of the hybrid zone is not directly dependent on environmental factors which favor the fitness of the hybrid compared to the parental taxa, but rather on aspects such as historical factors and management practices, which may contribute to the localization and maintenance of the contact zone between parental species. Our results suggest that if a minimum required niche differentiation between genotypic classes is not achieved, environmental dependence might not have a prominent role on the outcome of the hybridization.