Phylogenomics and morphology of Celmisiinae (Asteraceae: Astereae): Taxonomic and evolutionary implications

The tribe Astereae (Asteraceae) includes 36 subtribes and 252 genera, and is distributed worldwide in temperate and tropical regions. One of the subtribes, Celmisiinae Saldivia, has been recently circumscribed to include six genera and ca. 160 species, and is restricted to eastern Australia, New Zealand, and New Guinea. The species show an impressive range of growth habit, from small herbs and ericoid subshrubs to medium-sized trees. They live in a wide range of habitats and are often dominant in subalpine and alpine vegetation. Despite the well-supported circumscription of Celmisiinae, uncertainties have remained about their internal relationships and classification at genus and species levels. This study exploited recent advances in high-throughput sequencing to build a robust multi-gene phylogeny for the subtribe Celmisiinae. The target enrichment Angiosperms353 bait set and the hybpiper-nf and paragone-nf pipelines were used to retrieve, infer, and assemble orthologous loci from 75 taxa representing all the main putative clades within the subtribe. Because of the diploidised ploidy level in Celmisiinae, as well as missing data in the assemblies, uncertainty remains surrounding the inference of orthology detection. However, based on a variety of gene-family sets, coalescent and concatenation-based phylogenetic reconstructions recovered similar topologies. Paralogy and missing data in the gene-families caused some problems, but the estimated phylogenies were well-supported and well-resolved. The phylogenomic evidence supported Celmisiinae and three main clades: the Pleurophyllum clade (Pleurophyllum, Macrolearia and Damnamenia), mostly in the New Zealand Subantarctic Islands, Celmisia of mainland New Zealand and Australia, and Shawia (including 'Olearia pro parte' and Pachystegia) of New Zealand, Australia and New Guinea. The results presented here add to the accumulating support for the Angiosperms353 bait set as an efficient method for documenting plant diversity.

Biogeographic-tectonic calibration of 14 nodes in a butterfly timetree

The butterfly subtribe Coenonymphina (Nymphalidae: Satyrinae) comprises four main clades found, respectively, in (1) the Solomon Islands, (2) Australasia, (3) NW South America and (4) Laurasia, with a phylogeny: 1 (2 (3 + 4)). In assessing biogeographic evolution in the group we rejected the conversion of fossil-calibrated clade ages to likely maximum clade ages by the imposition of arbitrary priors. Instead, we used biogeographic-tectonic calibration, with fossil-calibrated ages accepted as minima. Previous studies have used this approach to date single nodes (phylogenetic-biogeographic breaks) in a group, but we extended the methodology to date multiple nodes. Within the Coenonymphina as a whole, 14 nodes coincide spatially with ten major tectonic events. In addition, the phylogenetic sequence of these nodes conforms to the chronological sequence of the tectonic events, consistent with a vicariance origin of the clades. Dating of the spatially coincident tectonic features provides a timescale for the vicariance events. The tectonic events are: pre-drift intracontinental rifting between India and Australia (150 Ma); seafloor spreading at the margins of the growing Pacific plate, and between North and South America (140 Ma); magmatism flare-up along the SW Pacific Whitsunday Volcanic Province-Median Batholith (130 Ma); a change from extension in the Clarence basin, eastern Australia, to uplift of the Great Dividing Range (114 Ma); Pamir Mountains uplift, foreland basin dynamics and high eustatic sea-levels leading to marine transgression of the proto-Paratethys Ocean eastward to Central Asia and Xinjiang (100 Ma); predrift rifting and seafloor spreading west of New Caledonia (100-50 Ma); sinistral strike-slip displacement along the proto-Alpine fault, New Zealand (100-80 Ma); thrust faulting in the Longmen Shan and foreland basin dynamics around the Sichuan Basin (85 Ma); pre-drift rifting in the Coral Sea basin (85 Ma); and dextral displacement on the Alpine fault (20 Ma).

The Galápagos Islands: biogeographic patterns and geology

In the traditional biogeographic model, the Galápagos Islands appeared a few million years ago in a sea where no other islands existed and were colonized from areas outside the region. However, recent work has shown that the Galápagos hotspot is 139 million years old (Early Cretaceous), and so groups are likely to have survived at the hotspot by dispersal of populations onto new islands from older ones. This process of metapopulation dynamics means that species can persist indefinitely in an oceanic region, as long as new islands are being produced. Metapopulations can also undergo vicariance into two metapopulations, for example at active island arcs that are rifted by transform faults. We reviewed the geographic relationships of Galápagos groups and found 10 biogeographic patterns that are shared by at least two groups. Each of the patterns coincides spatially with a major tectonic structure; these structures include: the East Pacific Rise; west Pacific and American subduction zones; large igneous plateaus in the Pacific; Alisitos terrane (Baja California), Guerrero terrane (western Mexico); rifting of North and South America; formation of the Caribbean Plateau by the Galápagos hotspot, and its eastward movement; accretion of Galápagos hotspot tracks; Andean uplift; and displacement on the Romeral fault system. All these geological features were active in the Cretaceous, suggesting that geological change at that time caused vicariance in widespread ancestors. The present distributions are explicable if ancestors survived as metapopulations occupying both the Galápagos hotspot and other regions before differentiating, more or less in situ.

Recent advances in New Caledonian biogeography

The biota of New Caledonia is one of the most unusual in the world. It displays high diversity and endemism, many peculiar absences, and far-flung biogeographic affinities. For example, New Caledonia is the only place on Earth with both main clades of flowering plants - the endemic Amborella and 'all the rest', and it also has the highest concentration of diversity in conifers. The discovery of Amborella's phylogenetic position led to a surge of interest in New Caledonian biogeography, and new studies are appearing at a rapid rate. This paper reviews work on the topic (mainly molecular studies) published since 2013. One current debate is focused on whether any biota survived the marine transgressions of the Paleocene and Eocene. Total submersion would imply that the entire fauna was derived by long-distance dispersal from continental areas since the Eocene, but only if no other islands (now submerged) were emergent. A review of the literature suggests there is little actual evidence in geology for complete submersion. An alternative explanation for New Caledonia's diversity is that the archipelago acted as a refugium, and that the biota avoided the extinctions that occurred in Australia. However, this is contradicted by the many groups that are anomalously absent or depauperate in New Caledonia, although represented there by a sister group. The anomalous absences, together with the unusual levels of endemism, can both be explained by vicariance at breaks in and around New Caledonia. New Caledonia has always been situated at or near a plate boundary, and its complex geological history includes the addition of new terranes (by accretion), orogeny, and rifting. New Caledonia comprises 'basement' terranes that were part of Gondwana, as well as island arc and forearc terranes that accreted to the basement after it separated from Gondwana. The regional tectonic history helps explain the regional biogeography, as well as distribution patterns within New Caledonia. These include endemics on the basement terranes (for example, the basal angiosperm, Amborella), disjunctions at the West Caledonian fault zone, and great biotic differences between Grande Terre and the Loyalty Islands.

Metapopulation vicariance explains old endemics on young volcanic islands

Terrestrial plants and animals on oceanic islands occupy zones of volcanism found at intraplate localities and along island arcs at subduction zones. The organisms often survive as metapopulations, or populations of separate sub-populations connected by dispersal. Although the individual islands and their local subpopulations are ephemeral and unstable, the ecosystem dynamism enables metapopulations to persist in a region, more or less in situ, for periods of up to tens of millions of years. As well as surviving on systems of young volcanic islands, metapopulations can also evolve there; tectonic changes can break up widespread insular metapopulations and produce endemics restricted to fewer islands or even a single island. These processes explain the presence of old endemic clades on young islands, which is often reported in molecular clock studies, and the many distribution patterns in island life that are spatially correlated with tectonic features. Metapopulations can be ruptured by sea floor subsidence, and this occurs with volcanic loading in zones of active volcanism and with sea floor cooling following its production at mid-ocean ridges. Metapopulation vicariance will also result if an active zone of volcanism is rifted apart. This can be caused by the migration of an arc (by slab rollback) away from a continent or from another subduction zone, by the offset of an arc at transform faults and by sea floor spreading at mid-ocean ridges. These mechanisms are illustrated with examples from islands in the Caribbean and the Pacific. Endemism on oceanic islands has usually been attributed to chance, long-distance dispersal, but the processes discussed here will generate endemism on young volcanic islands by vicariance.