Speciation and diversity on tropical rocky shores: a global phylogeny of snails of the genus Echinolittorina

A phylogenetic approach to the origin and maintenance of species diversity ideally requires the sampling of all species within a clade, confirmation that they are evolutionarily distinct entities, and knowledge of their geographical distributions. In the marine tropics such studies have mostly been of fish and reef-associated organisms, usually with high dispersal. In contrast, snails of the genus Echinolittorina (Littorinidae) are restricted to rocky shores, have a four-week pelagic development (and recorded dispersal up to 1400 km), and show different evolutionary patterns. We present a complete molecular phylogeny of Echinolittorina, derived from Bayesian analysis of sequences from nuclear 28S rRNA and mitochondrial 12S rRNA and COI genes (nodal support indicated by posterior probabilities, maximum likelihood, and neighbor-joining bootstrap). This consists of 59 evolutionarily significant units (ESUs), including all 50 known taxonomic species. The 26 ESUs found in the Indo-West Pacific region form a single clade, whereas the eastern Pacific and Atlantic species are basal. The earliest fossil occurred in the Tethys during the middle Eocene and we suggest that the Indo-West Pacific clade has been isolated since closure of the Tethyan seaway in the early Miocene. The geographical distributions of all species (based on more than 3700 locality records) appear to be circumscribed by barriers of low temperature, unsuitable sedimentary habitat, stretches of open water exceeding about 1400 km, and differences in oceanographic conditions on the continuum between oceanic and continental. The geographical ranges of sister species show little or no overlap, indicating that the speciation mode is predominantly allopatric. Furthermore, range expansion following speciation appears to have been limited, because a high degree of allopatry is maintained through three to five branching points of the phylogeny. This may be explained by infrequent long-distance colonization, habitat specialization on the oceanic/continental gradient, and perhaps by interspecific competition. In the eastern Pacific plus Atlantic we identify five cases of divergence on either side of the Isthmus of Panama, but our estimates of their ages pre-date the emergence of the Isthmus. There are three examples of sister relationships between species in the western Atlantic and eastern Atlantic, all resulting from dispersal to the east. Within the Indo-West Pacific, we find no geographical pattern of speciation events; narrowly endemic species of recent origin are present in both peripheral and central parts of the region. Evidence from estimated divergence times of sister species, and from a plot of the number of lineages over time, suggest that there has been no acceleration of diversification during the glacio-eustatic cycles of the Plio-Pleistocene. In comparison with reefal organisms, species of Echinolittorina on rocky shores may be less susceptible to extinction or isolation during sea-level fluctuations. The species richness of Echinolittorina in the classical biogeographic provinces conforms to the common pattern of highest diversity (11 species) in the central "East Indies Triangle" of the Indo-West Pacific, with a subsidiary focus in the eastern Pacific and western Atlantic, and lowest diversity in the eastern Atlantic. The diversity focus in the East Indies Triangle is produced by a mosaic of restricted allopatric species and overlap of a few widespread ones, and is the result of habitat specialization rather than historical vicariance. This study emphasizes the plurality of biogeographic histories and speciation patterns in the marine tropics.     

Extinction and replacement in the Indo-West Pacific Ocean

Aim To provide evidence suggesting the existence of a dynamic system of extinction and replacement. Location The Indo-West Pacific Ocean. Methods Utilization of species distribution patterns produced by detailed systematic works. Results The distribution patterns appear to suggest a sequence of events that is consistent with the centre of origin hypothesis. The East Indies centre is considered to operate according to the centrifugal speciation model. Main conclusions Disjunct patterns appear to have originated in the East Indies and spread out from there. In cases where the vacated area is occupied by a sibling species, competitive (sympatric) speciation may have occurred. Over time the extinction pattern will gradually extend outward until it is played out among small populations far from their centre of origin     

The marine East Indies: diversity and speciation

Aim To discuss the impact of new diversity information and to utilize recent findings on modes of speciation in order to clarify the evolutionary significance of the East Indies Triangle. Location The Indo‐Pacific Ocean. Methods Analysis of information on species diversity, distribution patterns and speciation for comparative purposes. Results Information from a broad‐scale survey of Indo‐Pacific fishes has provided strong support for the theory that the East Indies Triangle has been operating as a centre of origin. It has become apparent that more than two‐thirds of the reef fishes inhabiting the Indo‐Pacific are represented in the Triangle. An astounding total of 1111 species, more than are known from the entire tropical Atlantic, were reported from one locality on the small Indonesian island of Flores. New information on speciation modes indicates that the several unique characteristics of the East Indian fauna are probably due to the predominance of competitive (sympatric) speciation. Main conclusions It is proposed that, within the East Indies, the high species diversity, the production of dominant species, and the presence of newly formed species, are due to natural selection being involved in reproductive isolation, the first step in the sympatric speciation process. In contrast, speciation in the peripheral areas is predominately allopatric. Species formed by allopatry are the direct result of barriers to gene flow. In this case, reproductive isolation may be seen as a physical process that does not involve natural selection. Allopatric species formation often takes millions of years, while the sympatric process is generally much faster. Following species formation, dispersal from the East Indies appears to take place according to the centrifugal hypothesis.     

Antitropicality of Pacific Fishes: Molecular Insights

Twenty-one molecular genetic studies of thirteen antitropical Pacific fishes are herein reviewed. High dispersal potentials and Plio-Pleistocene transequatorial divergence are suggested for approximately half of the taxa studied, consistent with movement across the tropics during glacial periods. Divergences within two fish groups were mid-Miocene in age, corresponding to a period suggested for vicariant isolation associated with equatorial warming, but high dispersal potentials complicate the interpretation of biogeographic history. Only one study suggested transequatorial divergence older than 20 million years. There is a greater proportion of Pleistocene transequatorial divergences in the East Pacific than the West Pacific, consistent with the suggestion that conditions in the East Pacific are more amenable to the formation of antitropical distributions. Multiple transequatorial divergences have been observed within at least two groups, and instances of cryptic speciation have been identified twice. Areas for future research concern taxa that differ from the majority studied to date with respect to latitudinal distribution, bathymetry, evolutionary age, and dispersal potential. Molecular characters have demonstrated utility for the study of antitropical fishes, but with limitations.     

Copepods associated with reef corals: a comparison between the Atlantic and the Pacific

Endoparasitic copepods are very numerous in Indo-West Pacific corals. In West Indian corals they were thought to be absent, but recent studies have shown that a varied endoparasitic copepod fauna exists as well. Striking is the taxonomic composition of the coral-inhabiting copepods:In the Indo-West Pacific Lichomolgidae and Xarifiidae are the dominant families, both are absent in the West Indies. On the other hand, Corallovexiidae and Asterocheridae dominate in the West Indies; the former family is absent and the latter is apparently rare and not very diversified in the Indo-West Pacific.     

The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris splendida, C. aspersa and Hypselodoris placida colour groups

Eleven species of Chromodoris, two species of Hypselodoris, three species of Mexichromis and one species of Noumea are described from the Indo-West Pacific, of which four species of Chromodoris and one of Mexichromis are new species. All species have a colour pattern dominated by red, purple or black spots. All previously described species with similar colour patterns, from both the Indo-West Pacific and other regions, are discussed.     

On the affinities of three fossil ocypodid crabs and their relevance to the time and place of origin of the genus Macrophthalmus (Crustacea: Brachyura)

All the species of Macrophthalmus described from fossil material belong to the still extant subgenus Venitus. M. vindobonensis and M. aquensis , the two earliest known species of the genus, are closely related to the extant M. latreillei , while M. guamensis is conspecific with M. leptophthalmus.
Doubt is cast on Remy's (1952) theory of the late Tertiary migration of Macrophthalmus from the Mediterranean, its suggested place of origin, to the Indo-West Pacific, its present distributional range. Instead it is proposed that Macrophthalmus arose in the Indo-West Pacific during the late Eocene-Oligocene, and extended its range into the Mediterranean during the early-middle Miocene. The Mediterranean species became isolated during the late Miocene by a land bridge, and probably became extinct following the elevation of their brackish habitat during the late Miocene-Pliocene.     

The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris aureomarginata, C. verrieri and C. fide lis colour groups

Nineteen species of chromodorid nudibranchs are described including three new species of Chromodoris , two of Glossodoris and one each of Noumea, Cadlina and Thorunna from the Indo-West Pacific. The colour of all species is white with either a single yellow or gold band at the edge of the mantle or a double band of red and yellow, or orange and red or purple. All previously described species with similar colour patterns, from both the Indo-West Pacific and other regions are discussed.     

COINCIDENT BIOGEOGRAPHIC PATTERNS: INDO-WEST PACIFIC OCEAN

The majority of tropical marine families demonstrate their greatest concentration of species within the relatively small East Indies Triangle. In every direction, the species diversity decreases with distance from the East Indies. Other patterns suggest that the East Indies is where the average generic age is youngest, where some historical routes of dispersal originate, where the most apomorphic species occur, where genetic diversity is the greatest, and where extinctions are likely to originate. These coincident patterns provide support for the hypothesis that the East Indies has been operating as a center of evolutionary radiation. The driving force for this dynamic system is apparently the predominance of successful speciation involving relatively large populations with higher genetic diversity. This mechanism fits the centrifugal speciation model that was proposed more than 50 years ago.     

Trochus kotschyi, the first Indian Ocean record of the genus Osilinus (Mollusca: Gastropoda: Trochidae)

The species Trochus kotschyi Philippi, 1849, and Priotrochus obscurus (Wood, 1828) have been much confused in the past. Consistent differences between these taxa in respect of shell morphology, external anatomy and radular and opercular form are demonstrated. The distribution of T. kotschyi and the extent to which it and P. obscurus are sympatric are discussed. T. korschyi is referred to the genus Osilinus Philippi, 1847, a new combination and the first record of the genus from the Indo-West Pacific. The species is thought to be a pre-Miocene relict reflecting a mid-Tethyan origin of the genus. A note on the type species designation of Osilinus is provided.     

Genetic evidence on the demography of speciation in allopatric dolphin species

Under a neutral model, the stochastic lineage sorting that leads to gene monophyly proceeds slowly in large populations. Therefore, in many recent species with large population size, the genome will have mixed support for monophyly unless historical bottlenecks have accelerated coalescence. We use genealogical patterns in mitochondrial DNA and in introns of four nuclear loci to test for historical bottlenecks during the speciation and divergence of two temperate Lagenorhynchus dolphin species isolated by tropical Pacific waters (an antitropical distribution). Despite distinct morphologies, foraging behaviors, and mitochondrial DNAs, these dolphin species are polyphyletic at all four nuclear loci. The abundance of shared polymorphisms between these sister taxa is most consistent with the maintenance of large effective population sizes (5.09 x 10(4) to 10.9 x 10(4)) during 0.74-1.05 million years of divergence. A variety of population size histories are possible, however. We used gene tree coalescent probabilities to explore the rejection region for historical bottlenecks of different intensity given best estimates of effective population size under a strict isolation model of divergence. In L. obliquidens the data are incompatible with a colonization propagule of an effective size of 10 or fewer individuals. Although the ability to reject less extreme historical bottlenecks will require data from additional loci, the intermixed genealogical patterns observed between these dolphin sister species are highly probable only under an extended history of large population size. If similar demographic histories are inferred for other marine antitropical taxa, a parsimonious model for the Pleistocene origin of these distributions would not involve rare breaches of a constant dispersal barrier by small colonization propagules. Instead, a history of large population size in L. obliquidens and L. obscurus contributes to growing biological and environmental evidence that the equatorial barrier became permeable during glacial/interglacial cycles, leading to vicariant isolation of antitropical populations.     

Morphological and genetic differentiation of the acorn barnacle Tetraclita squamosa (Crustacea, Cirripedia) in East Asia and description of a new species of Tetraclita

The common intertidal barnacle Tetraclita squamosa occurs in two morphologically and genetically distinct forms in East Asia. The north-western Pacific form (Japan, Okinawa and Taiwan) has green parietes and the tergo-scutal flaps are black without any patterns. The south China form (Xiamen, Hong Kong) also has green parietes but the tergo-scutal flaps are black with two white spots on the tergal and scutal margin. Compared to the NW Pacific form, the south China form has a beaked tergum, a sharper tergal spur and cirrus I lacks serrulate type setae that have four rows of setules. The two forms differ by 15–16% in COI divergence, which is comparable to values for other congeneric barnacle species. The 12S rRNA and ITS1 sequences are also distinct between the two forms. Our results support the conclusion that the two forms are genetically differentiated species. We describe the NW Pacific form as a new species, Tetraclita pacifica . We are treating the other species as Tetraclita squamosa based on the fact that Pilsbry, in 1916, redescribed T. squamosa squamosa using samples collected from south China and the Philippines. Further studies are needed to confirm the identity and geographical distribution of the 'widely distributed' T. squamosa in the Indo-West Pacific.     

A phylogenetic test of multiple proposals for the origins of the East Indies coral reef biota

Aim  We analysed data on Indo-Pacific coral reef taxa to test four mechanisms proposed for the origins of the biodiversity centre in the East Indies Triangle: (1) the centre of origin hypothesis, (2) the centre of accumulation hypothesis, (3) the centre of overlap hypothesis, and (4) the bioaccumulation hypothesis.
Location  The Indian and western Pacific oceans.
Methods  The data set consisted of eight clades of fishes, four of corals and one of molluscs, consisting of a total of 95 species, with 72 informative nodes, in 29 areas. We used phylogenetic analysis for comparing trees (PACT) to reconstruct reticulate area relationships.
Results  An analysis using PACT produced very little congruence between area relationships among the histories of the taxa examined. Only two sets of two taxa each showed substantial congruence; several other taxa showed partial congruence.
Main conclusions  Despite numerous 'explanatory' claims for the incredible biodiversity of the marine macrofauna of the East Indies Triangle, the patterns obtained here did not accord with any of the hypotheses proposed. It is possible that, with the addition of more taxa, additional patterns would emerge. Much more systematic work within the East Indies is required to resolve this problem.     

TRACING BACK THE ORIGIN OF THE INDO-PACIFIC MOLLUSC FAUNA: BASAL TRIDACNINAE FROM THE OLIGOCENE AND MIOCENE OF THE SULTANATE OF OMAN

Abstract:  Two new tridacnine species are described from the Chattian and Aquitanian of the Arabian Peninsula. For these, the new names Omanidacna eos gen. et sp. nov. and Tridacna evae sp. nov. are erected. Omanidacna is interpreted as an Oligocene ancestor of Hippopus , being the oldest record of this tridacnine lineage. The Aquitanian Tridacna evae is the first occurrence of the genus Tridacna . These Arabian taxa imply that the modern tridacnine lineages are rooted in the Palaeogene and early Neogene of the East African-Arabian Province, although their Eocene ancestors, such as Byssocardium , are Western Tethyan taxa. During the Neogene they successfully settled the Indo-Polynesian Province and became typical elements of the entire Indo-West Pacific Region. The tridacnines are thus an example of a successive transformation and gradual eastward dispersal of an originally Tethyan element contributing to late Neogene diversity in the Indo-West Pacific.     

Global phylogeography of the ridley sea turtles (Lepidochelys spp.) as inferred from mitochondrial DNA sequences

The Kemp's ridley sea turtle (Lepidochelys kempi) is restricted to the warm temperate zone of the North Atlantic Ocean, whereas the olive ridley turtle (L. olivacea) is globally distributed in warm-temperate and tropical seas, including nesting colonies in the North Atlantic that nearly overlap the range of L. kempi. To explain this lopsided distribution, Pritchard (1969) proposed a scenario in which an ancestral taxon was divided into Atlantic and Pacific forms (L. kempi and L. olivacea, respectively) by the Central American land bridge. According to this model, the olive ridley subsequently occupied the Pacific and Indian Oceans and recently colonized the Atlantic Ocean via southern Africa. To assess this biogeographic model, a 470 bp sequence of the mtDNA control region was compared among 89 ridley turtles, including the sole L. kempi nesting population and 7 nesting locations across the range of L. olivacea. These data confirm a fundamental partition between L. olivacea and L. kempi (p=0.052-0.069), shallow separations within L. olivacea (p=0.002-0.031), and strong geographic partitioning of mtDNA lineages. The most divergent L. olivacea haplotype is observed in the Indo-West Pacific region, as are the central haplotypes in a parsimony network, implicating this region as the source of the most recent radiation of olive ridley lineages. The most common olive ridley haplotype in Atlantic samples is distinguished from an Indo-West Pacific haplotype by a single nucleotide substitution, and East Pacific samples are distingushed from the same haplotype by two nucleotide substitutions. These shallow separations are consistent with the recent invasion of the Atlantic postulated by Pritchard (1969), and indicate that the East Pacific nesting colonies were also recently colonized from the Indo-West Pacific region. Molecular clock estimates place these invasions within the last 300,000 years. This revised version was published online in July 2006 with corrections to the Cover Date.     

中国第四纪冰期与陆生脊椎动物残留分布

在第四纪冰期中 ,中国东部地区是否发生过冰川 ,长期存在争议。中国东部地区冰川说的创始人李四光教授在提出该学说时 ,从古生物方面未得到冰期生物群的证据。现存生物种的地理残留现象可反映地质历史时期的气候变化。本文作者依据中国陆生脊椎动物的北方残留、热带 -亚热带残留、温带湿润带残留等现象 ,推断 :(1)在冰期的冷期中喜暖动物南迁时 ,中国东部地区是一避难地 ;(2 )在中国东部地区未见有典型冰川残留种的存在 ;(3)一些湿润种的间断残留分布与中国北方黄土及干旱气候的发展有密切的关系。此结论似不支持中国东部冰川说     

Molecular phylogeny of the antitropical genus Pseudolabrus (Perciformes: Labridae): evidence for a Southern Hemisphere origin

The genus Pseudolabrus comprises 11 species of marine nearshore fishes which are antitropically distributed: two species occur in East Asia, the remaining nine species being distributed in the Southern Hemisphere, mainly in the temperate Pacific. The distributions of their closely allied genera, collectively called "pseudolabrines" are, however, restricted to the Australia-New Zealand region. The molecular phylogeny of six of the 11 Pseudolabrus species from both Hemispheres and four of the five other pseudolabrine genera was reconstructed from nucleotide sequence data from mitochondrial DNA 12S rRNA, tRNAVal, and 16S rRNA genes. Both parsimony and Bayesian analyses were performed. Results are not consistent with a previous phylogenetic hypothesis based on osteological data, particularly in the relationship between Pseudolabrus and Notolabrus, indicating a probable need for reviewing the status of Notolabrus (or the delimitations of both Pseudolabrus and Notolabrus). The two Northern Hemisphere species of Pseudolabrus were monophyletic and nested deep into the clade of the Southern Hemisphere pseudolabrines, which indicates that both pseudolabrines and Pseudolabrus originated in the Southern Hemisphere. A dispersal rather than vicariance explanation for the antitropical distribution of Pseudolabrus is more parsimonious given the number of dispersal events, extinctions, and evolutionary adaptations required under the phylogeny. Based on molecular clock calibrations, the transequatorial divergence was suggested to be early to mid Pliocene at the earliest.     

The evolution of marine insects: phylogenetic, ecological and geographical aspects of species diversity in marine water striders

No other group of insects have been more successful in colonizing marine habitats than water striders and their allies (Heteroptera, Gerromorpha). More than 10% of the 1700 species of gerromorphan bugs are marine. Water striders have colonized the marine environment at least 14 times. The fossil records suggest that marine habitats were invaded by members of the families Veliidae and Gerridae earlier than 20-30 and 45 million years before present, respectively. Estuaries and mangrove swamps are undoubtedly the ancestral type of habitat, but water striders have diversified further in marine habitats including the surface of the open ocean (sea skaters. Halobates). Except for being obligatorily flightless, marine water striders are structurally very similar to their non-marine relatives. Physiological and behavioral rather than morphological specializations are likely to have been key innovations in the transition from limnic to marine habitats. The oldest and most species-rich clades originated in the Indo-West Pacific region. There are 3.5 times as many species of marine water striders in the Indo-West Pacific region than in the Atlantic/Caribbean/East Pacific region. This "diversity anomaly" is explained historically by region-specific differences in the origin and proliferation of clades, in paleoclimate and paleogeography, and in the propensity for dispersal between regions.     

Oceanic barriers as indicated by scombrid fishes and their parasites

Four genera of scombrid fishes (26 species) and their copepod (32 species) and monogenean ectoparasites (25 species) were used to test the hypothesis that the East Pacific Barrier is responsible for the most pronounced break in the circum-tropical warm water fauna of the continental shelves, and not the New World Barrier. Analysis at the species level showed that there is a primary centre of diversity in the West Pacific, and a secondary centre in the West Atlantic. The former, almost entirely, shares its species of the largely coastal Scomberomorus and Grammatorcynus and their parasites with seas located to the west. Only four parasites (all copepods) are shared by the East and West Pacific, and they are circum-tropical. In contrast, the West Pacific shares species of the more pelagic Scomber and their parasites with seas both to the east and west, although at the genus level, only two circum-tropical monogenean genera are shared by the E and W Pacific. We conclude that the East Pacific Barrier has been a 100% or almost 100% effective barrier to dispersal of species of Scomberomorus, Grammatorcynus and their parasites, whereas for species of Scomber and their parasites, the East Pacific has been a less effective barrier.     

Migratory routes of red‐necked phalaropes Phalaropus lobatus breeding in southern Chukotka revealed by geolocators

The migration routes of red‐necked phalaropes breeding around the Bering Sea are poorly known, despite the fact that the Bering Sea could mark the boundary between the East Palearctic populations that winter in the Pacific Ocean around the East Indies and the West Nearctic populations that winter in the Pacific Ocean off the coast of South America. Geolocator data retrieved from two male phalaropes tagged in southern Chukotka, Far Eastern Russia, confirm that birds breeding in this region belong to the East Palearctic population and winter in the East Indies, suggesting that the division line with the West Nearctic population is farther to the east. The routes taken by the two phalaropes were almost entirely pelagic, totaling around 18 000–20 000 km round‐trip, with the birds continuously on the move during migration, rather than resident in any particular stopover site, contrary to most other migratory shorebirds.