Hotspot swells and the lifespan of volcanic ocean islands

Volcanic ocean islands generally form on swells-seafloor that is shallower than expected for its age over areas hundreds to more than a thousand kilometers wide-and ultimately subside to form atolls and guyots (flat-topped seamounts). The mechanisms of island drowning remain enigmatic, however, and the subaerial lifespan of volcanic islands varies widely. We examine swell bathymetry and island drowning at 14 hotspots and find a correspondence between island lifespan and residence time atop swell bathymetry, implying that islands drown as tectonic plate motion transports them past mantle sources of swell uplift. This correspondence argues strongly for dynamic uplift of the lithosphere at ocean hotspots. Our results also explain global variations in island lifespan, which influence island topography, biodiversity, and climate.

Deconstructing an infamous extinction crisis: Survival of Partula species on Moorea and Tahiti

Eleven of eighteen Society Island Partula species endemic to the Windward Island subgroup (Moorea and Tahiti) have been extirpated by an ill-advised biological control program. The conservation status of this critically endangered tree snail radiation is of considerable import, but is clouded by taxonomic uncertainty due to the extensive lack of congruence among species designations, diagnostic morphologies, and molecular markers. Using a combination of museum, captive, and remnant wild snails, we obtained the first high-resolution nuclear genomic perspective of the evolutionary relationships and survival of fourteen Windward Island Partula species, totaling 93 specimens. We analyzed ~1,607-28,194 nuclear genomic loci collected with the double digest restriction-site associated sequencing method. Results from phylogenomic trees, species estimation, and population assignment tests yielded monophyly of the Windward Island subgroup. Within this group, two well-supported clades encompassing five species complexes were recovered. Clade 1 was restricted to Tahiti and contained two species complexes: "P. affinis" (three species) and "P. otaheitana" (five species). Clade 2 occurred on Moorea and on Tahiti and consisted of three species complexes: one Tahitian, "P. clara/P. hyalina"; the other two, "P. taeniata" (three species) and "P. suturalis" (six species), Moorean. Our genomic results largely corroborated previous mitochondrial DNA survival estimates for Moorea and Tahiti, with all five species complexes having members surviving in captivity and/or as remnant wild populations, although the details vary in each case. Continued, proactive conservation and management may yet ensure a phylogenetically representative survival of the fabled Partula species of Moorea and Tahiti.

Phylogeny of the central-western Pacific subgenus Inseliellum (Diptera: Simuliidae)

Subgenus-level groups of western and central Pacific Simuliidae are briefly assessed using phylogenetic principles. Inseliellum and Nevermannia (ruficorne-group) are established as sister taxa. Detailed morphological analysis of 32 species of Inseliellum shows that the Micronesian Simulium trukense is the basal lineage. Austral and Cook islands species, plus those of the Marquesas Islands, form the next basal clade. Simulium malardei is the sister taxon of all other Society Islands species, including Simulium adamsoni from the Marquesas Islands. There are three clades: the tahitiense-group, which is weakly supported, the castaneum-group, which is moderately well supported, and the oviceps-group, which is strongly supported. One of two most parsimonious phylogenies that is in agreement with independent cytological information is presented. Habitat preference and larval behaviour are optimized on this phylogeny, providing information about evolutionary trends. Brief comments are made regarding geological development of the habitats of larvae of some species.

A taxonomic revision of the Pacific black fly subgenus Inseliellum (Diptera: Simuliidae)

The simuliid subgenus Inseliellum is revised and additional diagnostic characters are provided. This taxon, found in Guam, Truk, Cook, Austral, Marquesas, and Society islands, now comprises 40 species. Sixteen new species are described: S. bogusium, S. clibanarium, S. concludium, S. connae, S. dojeycorium, S. dussertorum, S. evenhuisi, S. fossatiae, S. jnabsium, S. lonckei, S. maraaense, S. middlemissae, S. proctorae, S. pufauense, S. rurutuense, and S. shannonae. Additional descriptions are given for most other species. A key to the larvae of Society Islands species is given. Brief comments are made concerning relationships within Inseliellum, larval habitats, and biology.