Cenozoic history of the tropical marine biodiversity hotspot.

The region with the highest marine biodiversity on our planet is known as the Coral Triangle or Indo-Australian Archipelago (IAA)1,2. Its enormous biodiversity has long attracted the interest of biologists; however, the detailed evolutionary history of the IAA biodiversity hotspot remains poorly understood3. Here we present a high-resolution reconstruction of the Cenozoic diversity history of the IAA by inferring speciation-extinction dynamics using a comprehensive fossil dataset. We found that the IAA has exhibited a unidirectional diversification trend since about 25 million years ago, following a roughly logistic increase until a diversity plateau beginning about 2.6 million years ago. The growth of diversity was primarily controlled by diversity dependency and habitat size, and also facilitated by the alleviation of thermal stress after 13.9 million years ago. Distinct net diversification peaks were recorded at about 25, 20, 16, 12 and 5 million years ago, which were probably related to major tectonic events in addition to climate transitions. Key biogeographic processes had far-reaching effects on the IAA diversity as shown by the long-term waning of the Tethyan descendants versus the waxing of cosmopolitan and IAA taxa. Finally, it seems that the absence of major extinctions and the Cenozoic cooling have been essential in making the IAA the richest marine biodiversity hotspot on Earth.

Deciphering deterministic factors of predation pressures in deep time.

Predation pressure occurs as a result of predation frequency and prey vulnerability. Although quantifying these factors individually is essential to precisely understand predation effects on evolution, they have been generally less accessible. Here, using a modified form of Poisson function, we quantified the frequencies and vulnerabilities, as well as the resulting predation pressures, concerning the shell drillers versus prey interactions from the Eocene and Miocene periods. Our analysis quantitatively revealed that low-spired shells tend to show increased vulnerability except for two planispiral species that exhibit an unexpectedly low vulnerability. We then identified septal structures within the two species that resemble those in nautiloids and ammonoids but which provided a defensive role against the predators, enhancing the mean lifetime by approximately 20%. The current approach enables us to quantitatively trace how predation frequency and prey vulnerability have interacted, been transformed spatio-temporally, and been a driving force of evolution at geological time scales.

A new species of false spider crab of the genus Elamena H. Milne Edwards, 1837 (Crustacea: Decapoda: Brachyura: Hymenosomatidae), from Davao Gulf, Philippines.

A new species of hymenosomatid crab of the genus Elamena H. Milne Edwards, 1837, is described from the island of Samal, in the Davao Gulf, Mindanao, southern Philippines. Elamena samalensis sp. nov. belongs to the Elamena truncata species-group and is most similar to E. simplidenta Ng & Chuang, 1996, in the general form of the carapace and in the presence of only one subdistal tooth on the ambulatory dactyli. It can be distinguished from this species, however, by its more projecting rostrum, relatively longer and more slender ambulatory legs, and by the pointed apex of the female pleotelson.

Permanent El Niño during the Pliocene warm period not supported by coral evidence.

The El Niño/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3-5 million years ago) may have existed in a permanent El Niño state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean. This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change, ENSO variability--and related global climate teleconnections-could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial. Here we show that permanent El Niño conditions did not exist during the PWP. Our spectral analysis of the δ(18)O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, δ(18)O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ(18)O events in the fossil corals closely resemble the decreases in δ(18)O seen in the live coral during El Niño events. Prior research advocating a permanent El Niño state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.

Color polymorphism and historical biogeography in the Japanese patellogastropod limpet Cellana nigrolineata (Reeve) (Patellogastropoda: Nacellidae).

Cellana nigrolineata is amongst the most common and largest patellogastropod limpets in Japan, and has two color morphs. Analyses of anatomical and morphological characters, shell structure, and mitochondrial COI data (658bp) of these color morphs suggested that they represent intraspecific genetic variation. Molecular analysis demonstrated that the species can be subdivided into three genetically distinct groups: (Clade 1) Honshu, Shikoku to Eastern Kyushu, (Clade 2) Western Kyushu and (Clade 3) Southern Kyushu. Clade 1 and Clade 2 + 3 are distributed on the coastlines adjacent to two warm-water currents, the Kuroshio and Tsushima Currents, respectively. The southern population (Clade 3) is currently isolated by inhospitable sandy shores. The subdivision of these groups likely dates from the glacial period of Plio-Pleistocene time.

A 5000-year fossil record of larval shell morphology of submarine cave microshells.

A 5000-year fossil series of minute submarine cave bivalves was studied using morphometric and evolutionary analyses. The obtained results indicate that the shapes of larval shells of studied species were labile, whereas the size of the larval shell was stable in each species studied. This result is different than that previously reported in most other studies in which size change is more common than shape change. This unique evolutionary pattern of these bivalves might be attributed to their refugial lifestyle.

Major adaptive radiation in neritopsine gastropods estimated from 28S rRNA sequences and fossil records.

A well-supported phylogeny of the Neritopsina, a gastropod superorder archaic in origin, radiated ecologically and diverse in morphology, is reconstructed based on partial 28S rRNA sequences. The result (Neritopsidae (Hydrocenidae (Helicinidae + Neritiliidae) (Neritidae + Phenacolepadidae))) is highly congruent with the fossil records and the character distribution of reproductive tracts in extant taxa. We suggest that the Neritopsina originated in subtidal shallow waters, invaded the land and became fully terrestrial at least three times in different clades, by the extinct Dawsonellidae in the Late Palaeozoic and by the Helicinidae and Hydrocenidae in the Mesozoic. Invasion of fresh- and brackish waters is prevalent among the Neritopsina as the Jurassic and freshwater ancestory is most probable for helicinids. The Phenacolepadidae, a group exclusively inhabiting dysoxic environments, colonized deep-sea hydrothermal vents and seeps in the Late Cretaceous or Early Cenozoic. Submarine caves have served as refuges for the archaic Neritopsidae since the Early to Middle Cenozoic, and the marine neritopsine slug Titiscania represents a highly specialized but relatively recent offshoot of this family. The Neritiliidae is another clade to be found utilizing submarine caves as shelter by the Oligocene; once adapted to the completely dark environment, but some neritiliids have immigrated to surface freshwater habitats.

A new species of Thetispelecaris (Crustacea: Peracarida) from submarine cave on Grand Cayman Island.

A new species of the peracaridan order Bochusacea, Thetispelecaris yurikago, is described from a submarine cave on Grand Cayman Island, the Caribbean Sea. The new species is the fourth species of the order and family, and the second of the genus. Recent studies have strongly suggested a close phylogenetic affinity between cave-dwelling and deep-sea taxa in the Bochusacea as recognized in other cavernicolous/deep-sea crustaceans such as amphipods and copepods. The morphology of the gut and female reproductive system is observed for the first time in the Bochusacea: the stomach is complex with structures such as ridges, processes, spinules, and hairs in the lumen; paired gonopores are located near the base of the fifth pereiopods on the sternite.