Madagascar sheds new light on the molecular systematics and biogeography of grammitid ferns: New unexpected lineages and numerous long-distance dispersal events

'Out of Africa' origin of the pantropical staghorn fern genus Platycerium (Polypodiaceae) supported by plastid phylogenomics and biogeographical analysis

BACKGROUND AND AIMS

The staghorn fern genus Platycerium is one of the most commonly grown ornamental ferns, and it evolved to occupy a typical pantropical intercontinental disjunction. However, species-level relationships in the genus have not been well resolved, and the spatiotemporal evolutionary history of the genus also needs to be explored.

METHODS

Plastomes of all the 18 Platycerium species were newly sequenced. Using plastome data, we reconstructed the phylogenetic relationships among Polypodiaceae members with a focus on Platycerium species, and further conducted molecular dating and biogeographical analyses of the genus.

KEY RESULTS

The present analyses yielded a robustly supported phylogenetic hypothesis of Platycerium. Molecular dating results showed that Platycerium split from its sister genus Hovenkampia ~35.2 million years ago (Ma) near the Eocene-Oligocene boundary and began to diverge ~26.3 Ma during the late Oligocene, while multiple speciation events within Platycerium occurred during the middle to late Miocene. Biogeographical analysis suggested that Platycerium originated in tropical Africa and then dispersed eastward to southeast Asia-Australasia and westward to neotropical areas.

CONCLUSIONS

Our analyses using a plastid phylogenomic approach improved our understanding of the species-level relationships within Platycerium. The global climate changes of both the Late Oligocene Warming and the cooling following the mid-Miocene Climate Optimum may have promoted the speciation of Platycerium, and transoceanic long-distance dispersal is the most plausible explanation for the pantropical distribution of the genus today. Our study investigating the biogeographical history of Platycerium provides a case study not only for the formation of the pantropical intercontinental disjunction of this fern genus but also the 'out of Africa' origin of plant lineages.

Five long-distance dispersals shaped the major intercontinental disjunctions in Tectariaceae s.l. (Polypodiales, Polypodiopsida)

Intercontinental disjunct distributions can arise either from vicariance, from long-distance dispersal, or through extinction of an ancestral population with a broader distribution. Tectariaceae s.l., a clade of ferns in Polypodiales with ca. 300 species mainly distributed in the tropics and subtropics, provide an excellent opportunity to investigate global distribution patterns. Here, we assembled a dataset of eight plastid markers and one nuclear marker of 636 (92% increase of the earlier largest sampling) accessions representing ca. 210 species of all eight genera in Tectariaceae s.l. (Arthropteridaceae, Pteridryaceae, and Tectariaceae s.s.) and 35 species of other families of eupolypods Ⅰ. A new phylogeny is reconstructed to study the biogeography and trait-associated diversification. Our major results include: (1) a distinct lineage of Tectaria sister to the rest of the American Tectaria is identified; (2) Tectariaceae s.l., and the three families: Arthropteridaceae (Arthropteris), Pteridryaceae (Draconopteris, Malaifilix, Polydictyum, Pteridrys), and Tectariaceae s.s. (Hypoderris, Tectaria, and Triplophyllum), might have all originated in late Cretaceous; (3) only five intercontinental dispersals occurred in Pteridryaceae and Tectariaceae s.s. giving rise to their current intercontinental disjunction; (4) we provide the second evidence in ferns that a long-distance dispersal between Malesia and Americas during the Paleocene to Eocene led to the establishment/origin of a new genus (Draconopteris); and (5) diversification rate of each state of leaf dissection is different, and the lowest is in the simple-leaved taxa.

Out of Madagascar, repeatedly: The phylogenetics and biogeography of Dombeyoideae (Malvaceae s.l.)

Dispersals have been shown to be critical to the evolution of the long isolated but megadiverse flora of Madagascar and the surrounding islands of the western Indian Ocean, but we are just beginning to understand the directionality of these dispersals. With more than half of its species occurring in the western Indian Ocean region (WIOR), the paleotropical subfamily Dombeyoideae provides a particularly useful case study through which to better understand the biogeography of the WIOR, and yet its biogeography is poorly understood. Here we sampled six molecular markers from all 20 genera in the Dombeyoideae to reconstruct the most complete phylogeny to date for the subfamily. From this, divergence times, calibrated with three fossils (two dombeyoid, one malvoid), and ancestral range estimations were hypothesized. Biogeographic stochastic mapping (BSM) analyses on the maximum clade credibility tree were completed and compared to BSM analyses on 1,000 trees randomly sampled from the posterior distribution of trees resulting from the dating analysis. We found the Dombeyoideae crown node diverged ca. 53 million years ago out of a broad ancestral range involving all three major areas of its distribution: Madagascar, Africa, and Asia. The majority of diversification and dispersals in the subfamily occurred within the last ca. 10 million years, mostly from the Pliocene onwards. There were roughly five dispersals from Madagascar to Africa (and only one in reverse), at least six from Madagascar to surrounding islands of the WIOR (Mascarenes and Comoros), and one dispersal from Madagascar to Asia (and ca. 1 in reverse). Other long-distance dispersals included one from Africa to St. Helena and one from Africa to Australasia, both from within the most widespread clade, the Cheirolaena & allies clade, and one dispersal from Asia to Africa. Critically, the Dombeyoideae provide strong evidence for considering the island of Madagascar as a source for the colonization of continents, as well as the surrounding islands of the WIOR. Furthermore, narrow sympatry was a key process in the evolution of the subfamily, particularly in Madagascar and the Mascarenes.

Splitting one species into 22: an unusual tripling of molecular, morphological, and geographical differentiation in the fern family Didymochlaenaceae (Polypodiales)

The pantropical fern genus Didymochlaena (Didymochlaenaceae) has long been considered to contain one species only. Recent studies have resolved this genus/family as either sister to the rest of eupolypods I or as the second branching lineage of eupolypods I, and have shown that this genus is not monospecific, but the exact species diversity is unknown. In this study, a new phylogeny is reconstructed based on an expanded taxon sampling and six molecular markers. Our major results include: (i) Didymochlaena is moderately or weakly supported as sister to the rest of eupolypods I, highlighting the difficulty in resolving the relationships of this important fern lineage in the polypods; (ii) species in Didymochlaena are resolved into a New World clade and an Old World clade, and the latter further into an African clade and an Asian-Pacific clade; (iii) an unusual tripling of molecular, morphological and geographical differentiation in Didymochlaena is detected, suggesting single vicariance or dispersal events in individual regions and no evidence for reversals at all, followed by allopatric speciation at more or less homogeneous rates; (iv) evolution of 18 morphological characters is inferred and two morphological synapomorphies defining the family are recognized-the elliptical sori and fewer than 10 sori per pinnule, the latter never having been suggested before; (v) based on morphological and molecular variation, 22 species in the genus are recognized contrasting with earlier estimates of between one and a few; and (vi) our biogeographical analysis suggests an origin for Didymochlaena in the latest Jurassic-earliest Cretaceous and the initial diversification of the extant lineages in the Miocene-all but one species diverged from their sisters within the last 27 Myr, in most cases associated with allopatric speciation owing to geologic and climatic events, or dispersal.

Morphological and molecular evidence reject conspecificity of Malagasy and Mascarene Parablechnum (Polypodiopsida, Blechnaceae)

Under the current treatment of the Blechnaceae, only one species of the fern genus Parablechnum is recognised in the western Indian Ocean, often referred to as P.marginatum. Two varieties are currently recognised within it: a type variety present in the Mascarene Islands of Réunion and Mauritius and P.marginatumvar.humbertii in Madagascar. Recent molecular evidence suggested that these two varieties are not closely related, questioning their conspecific status. To collect further evidence to support a taxonomic decision, we performed a morphological study based on 57 herbarium specimens comparing traits from general morphology, cross section of the fertile pinnae, sporangia and spores. As a result, Malagasy specimens can be distinguished morphologically from the Mascarene ones by pinna apex and pinna section, the presence of sporangiasters and spore ornamentation. Additionally, spore size analyses resulted in statistically significant differences between both varieties. Our results, aligned with the available phylogenetic data, support that these two taxa should be recognised as separate species and, hence, we propose the necessary new combination and provide full descriptions.

Biogeography and eye size evolution of the ogre-faced spiders

Net-casting spiders (Deinopidae) comprise a charismatic family with an enigmatic evolutionary history. There are 67 described species of deinopids, placed among three genera, Deinopis, Menneus, and Asianopis, that are distributed globally throughout the tropics and subtropics. Deinopis and Asianopis, the ogre-faced spiders, are best known for their giant light-capturing posterior median eyes (PME), whereas Menneus does not have enlarged PMEs. Molecular phylogenetic studies have revealed discordance between morphology and molecular data. We employed a character-rich ultra-conserved element (UCE) dataset and a taxon-rich cytochrome-oxidase I (COI) dataset to reconstruct a genus-level phylogeny of Deinopidae, aiming to investigate the group's historical biogeography, and examine PME size evolution. Although the phylogenetic results support the monophyly of Menneus and the single reduction of PME size in deinopids, these data also show that Deinopis is not monophyletic. Consequently, we formally transfer 24 Deinopis species to Asianopis; the transfers comprise all of the African, Australian, South Pacific, and a subset of Central American and Mexican species. Following the divergence of Eastern and Western deinopids in the Cretaceous, Deinopis/Asianopis dispersed from Africa, through Asia and into Australia with its biogeographic history reflecting separation of Western Gondwana as well as long-distance dispersal events.

Global Diversification of Anelosimus Spiders Driven by Long-Distance Overwater Dispersal and Neogene Climate Oscillations

Vicariance and dispersal events, combined with intricate global climatic history, have left an imprint on the spatiotemporal distribution and diversity of many organisms. Anelosimus cobweb spiders (Theridiidae), are organisms ranging in behavior from solitary to highly social, with a cosmopolitan distribution in temperate to tropical areas. Their evolutionary history and the discontinuous distribution of species richness suggest that 1) long-distance overwater dispersal and 2) climate change during the Neogene (23-2.6 Ma), may be major factors in explaining their distribution and diversification. Here, we test these hypotheses, and explicitly test if global Miocene/Pliocene climatic cooling in the last 8 Ma affected Anelosimus radiation in parallel in South America and Madagascar. To do so, we investigate the phylogeny and spatiotemporal biogeography of Anelosimus through a culmination of a 20-year comprehensive global sampling at the species level (69 species, including 84% of the known 75 species worldwide, represented by 268 individuals) using nucleotide data from seven loci (5.5 kb). Our results strongly support the monophyly of Anelosimus with an Oligocene ($\sim $30 Ma) South American origin. Major clades on other continents originate via multiple, long-distance dispersal events, of solitary or subsocial-but not social-lineages, from the Americas. These intercontinental dispersals were to Africa, Madagascar (twice), and SE Asia/Australasia. The early diversification of Anelosimus spiders coincides with a sudden thermal increase in the late Oligocene ($\sim $27-25 Ma), though no causal connection can be made. Our results, however, strongly support the hypothesis that global Neogene climatic cooling in the last 8 Ma drove Anelosimus radiation in parallel in South America and Madagascar, offering a rare empirical evidence for diversification of a socially diverse group driven by an interplay between long-distance dispersal and global Neogene climatic changes. [Cobweb spiders; diversification; global biogeography; long-distance dispersal; molecular phylogenetics; neogene climate changes; sociality; vicariance.].

Razafimandimbison, Janssens S. Four new endemic genera of Rubiaceae (Pavetteae) from Madagascar represent multiple radiations into drylands

The taxonomic positions and phylogenetic relationships of six Pavetteae species endemic to Madagascar were tested with a phylogenetic study of the Afro-Madagascan representatives of the tribe Pavetteae based on sequence data from six markers rps16, trnT-F, petD, accD-psa1, PI and ITS. The six species were resolved into four well-supported and morphologically distinct clades which we here formally recognise at generic level. The new genera are the monospecific Exallosperma and Pseudocoptosperma, each with a single species, and Helictosperma and Tulearia, each with two species. Each genus is characterised by one or more autapomorphies or by a unique combination of plesiomorphic characters. Mostly, the distinguishing characters are found in fruit and seed; Exallosperma differs from all other Pavetteae genera by the fruit consisting of two stony pyrenes, each with a single laterally flattened seed with irregularly distributed ridges on the surface; Helictosperma is unique by its single spherical seed rolled-in on itself in the shape of a giant pill-millipede. Pseudocoptosperma is characterised by the combination of three ovules pendulous from a small placenta and triangular stipules with a strongly developed awn, whereas Tulearia is characterised by robust sericeous flowers, small leaves, uni- or pauciflorous inflorescences and fruits with two pyrenes, each with a single ruminate seed. The four new genera show marked adaptations to the dry habitats in which they grow. They represent multiple radiations into drylands and highlight the importance of the dry forest and scrub vegetation in western, southern and northern Madagascar for plant biodiversity. The description of the four new genera shows that the tribe Pavetteae exhibits the same pattern as many plant groups in Madagascar, which are characterised by a high proportion of endemic genera comprising a single or a few species. In the four new genera, five new species are described and one new combination is made: Exallosperma longiflora De Block; Helictosperma malacophylla (Drake) De Block, Helictosperma poissoniana De Block, Pseudocoptosperma menabense Capuron ex De Block; Tulearia capsaintemariensis De Block and Tulearia splendida De Block.