PHYLOGENY AND BIOGEOGRAPHY OF THE ATLANTIC AND EASTERN PACIFIC HYPSELODORIS STIMPSON, 1855 (NUDIBRANCHIA, CHROMODORIDIDAE) WITH THE DESCRIPTION OF A NEW SPECIES FROM THE CARIBBEAN SEA

A new species, based on two specimens from Guana Island, BritishVirgin Islands, is described. The new species agrees with thegenus Hypselodoris in having a high body profile, a large vestibulargland and mantle glands. It differs from other members of thegenus in the Atlantic Ocean by having a reddish background bodycolour. In addition, dorsal colour patterns such as a broadcentral white line with lateral extensions and the lack of yellowlines or spots further differentiate this species. The radularformula of 52x41.0.41 and a smaller seminal receptacle are alsodistinctive. The phylogenetic relationships of 34 species andsubspecies of Hypselodoris from the eastern Pacific and Atlanticare examined using morphological characters. With the exceptionof the new species, these are characterized by a dark blue backgroundbody colour. The phylogenetic analysis of the data matrix resultedin eight most-parsimonious trees. The resulting consensus treeshows that eastern Pacific and Atlantic species of Hypselodorisconstitute a monophyletic group that is basally split into twosister clades. One clade contains the eastern Pacific speciesand most of the Caribbean species, whereas the other clade containsthe eastern Atlantic species. The new species is the sisterto the rest of the Caribbean species, which also form a monophyleticgroup. This phylogenetic hypothesis suggests that two consecutivevicariant events have affected the biogeography of Hypselodoris:(1) the closure of communication between the tropical Indo-Pacificregion and the Atlantic and eastern Pacific, completed withthe formation of the East Pacific Barrier; and (2) the riseof the Panama isthmus. (Received 19 December 2003; accepted 12 October 2005)     

The distribution of radiolarian assemblages in the modern and ice-age Pacific

Data on radiolarian abundances from several recent regional studies of the Pacific have been combined with new data from the temperate and tropical area to provide an ocean-wide view of radiolarian distributions. A Q-mode factor analysis of these data identified seven factors which have their areas of dominance in the following regions: tropics, western Pacific, subarctic, Antarctic, transitional zone, temperate regions, and the eastern central water masses. The distributions of these factors tended to follow those of surface water masses and major ocean currents. A more detailed analysis of the temperate and tropical region better delineated the complex flow and counter flow in this area. The relationship between the distribution of modern radiolarian assemblages and the surface circulation of the Pacific can be used to deduce the nature of oceanographic changes which occurred in the past. The modern radiolarian distributions are compared with those mapped at the 18, 000 B.P. level and reveal two major differences in the ice-age Pacific. The Tropical Factor, restricted primarily to the eastern half of the ocean in modern times, ranged across the entire ocean at 18, 000 B.P. and extended into the area of the western boundary currents. The Subarctic Factor, now found mainly in the western subarctic, expanded to the east and south at 18, 000 B.P. and had strong similarities to an assemblage found in the subantarctic area. The expansion of these two dominant assemblages was at the expense of the Western Pacific, Temperate, and Transitional Factors. These differences in the 18, 000 B.P. distributions are thought to be caused by an increase in the influence of arctic air masses in the North Pacific and by a general increase in the wind-driven zonal flow.     

Radiolarian biogeography in surface sediments of the eastern Indian Ocean

We analyzed recurrent groups of Radiolaria in 74 core top samples from a transect through the eastern Indian Ocean in order to supplement our previous results from the western Indian Ocean (Johnson and Nigrini, 1980). We now identify six distinct recurrent groups and nine radiolarian assemblages in the combined data set of 120 samples; this extended sample coverage has led to several re-interpretations of the oceanographic significance of the radiolarian distribution patterns. Assemblage boundaries closely reflect the presence of major oceanographic fronts and surface currents including the South Equatorial Divergence, Subtropical Gyre, Subtropical Convergence, and Antarctic Convergence. At least four major aspects of the assemblages in the eastern transect are notably different from those in the western transect, leading to a marked east-west asymmetry in faunal distribution patterns across the Indian Ocean. The assemblage formerly associated with strong upwelling near the Arabian Peninsula is present throughout the Bay of Bengal as well, and is interpreted to reflect high salinity and low oxygen in the subsurface waters of the Indian Ocean north of the Equator. A new assemblage has been identified associated with the westward-flowing Pacific water into the eastern Indian Ocean in low latitudes, and may be a potential stratigraphic and paleoclimatic marker for times of low sea level when this westward near-surface flow was shut off (i.e., glacial maxima). An extensive region in the core of the subtropical gyre between 25°S and 35°S is relatively barren of Radiolaria, yet is marked by a characteristic assemblage distributed asymmetrically, perhaps reflecting the lack of a strong boundary current off the west coast of Australia. Assemblage boundaries in the vicinity of the eastward circumpolar flow are not strictly zonal, and may indicate significant deviations from the mean eastward flow as a necessary condition for conservation of potential vorticity when the flow encounters topographic irregularities.     

PHYLOGENY OF THE GENUS ROSTANGA (NUDIBRANCHIA), WITH DESCRIPTIONS OF THREE NEW SPECIES FROM SOUTH AFRICA

Rostanga elandsia sp. nov., Rostanga aureamala sp. nov. andRostanga phepha sp. nov. are characterized by having the radulawith slender innermost lateral teeth, which lack denticles onthe inner side of the cusp and have a single denticle on theouter side. The outermost lateral teeth of these three speciesare elongate, but shorter than in other species of the genus.In addition, R. aureamala is the only species of the genus withrachidian teeth and R. phepha is unique within the genus Rostanga byvirtue of its white coloration with dark spots. A phylogenetic analysis shows that the three new species fromSouth Africa and Rostanga setidens (Odhner, 1939) are the sistergroup of the rest of the genus. The species from Japan and MarshallIslands (North Pacific Ocean) are basal in the sister cladecontaining the other species of Rostanga Bergh, 1879. The tropicalIndo-Pacific species of Rostanga are not monophyletic. The Atlanticand Eastern Pacific species form a monophyletic, derived clade,being the sister group of Rostanga australis Rudman & Avern,1989, which has a narrow range restricted to south eastern Australia.The widespread Indo-Pacific species Rostanga bifurcata Rudman& Avern, 1989, is the sister group of Rostanga dentacus Rudman& Avern, 1989, also widesprad in the tropical western Pacific. This phylogeny suggest s a viariant origin of the Sourth African, Atlantic-EasternPacific, and probably North Pacific species, whereas in thetropical Indo-Pacific most sister speceis are sympatric. (Received 16 May 1999; accepted 31 July 2000)     

Revised radiolarian zonation of the Upper Cretaceous Izumi inter-arc basin (SW Japan)

The radiolarian zonation of the Izumi Group is revised for an integrated biostratigraphy across the Campanian/Maastrichtian boundary, together with the ammonite occurrence, fission track and magnetostratigraphic calibration of the acidic tuff key beds. The significance of direct correlation in the same sections, between macro- and micro-fossils (i.e. between relatively near-shore nektonic and turbiditic planktonic-fauna) is discussed in relation to the litho- and bio-facies of the Izumi group. Late Cretaceous paleoceanographic changes inferred from the studied radiolarian fauna represent a regional marker event for the chronostratigraphic correlation of continental shelf to turbidite deep-sea sequences, which accumulated on a mid latitudinal margin facing towards the NW paleo-Pacific. The proposed Campanian/Maastrichtian boundary is at the limit between Pachydiscus awajiensis and Nostoceras hetonaiense ammonite zones. This boundary corresponds to the radiolarian last occurrence of Amphipyndax pseudoconulus (= A. enesseffi), Archaeodictyomitra sliteri, Dictyomitra formosa, D. koslovae and Rhopalosyringium magnificum at the top of the Myllocercion acineton Assemblage Zone (uppermost Campanian), and the first occurrence of Clathrocyclas gravis and Dorcadospyris sp. A, at the base of the Maastrichtian C. gravis Assemblage Zone. The new data settle partly a chronostratigraphic discrepancy between radiolarian and ammonite zonations in the Izumi Group, which was pointed out previously by Ishida et al. (2010).     

Evolution of Eastern Pacific Warm Pool and upwelling processes since the middle Miocene based on analysis of radiolarian assemblages: Response to Indonesian and Central American Seaways

A quantitative radiolarian study at Ocean Drilling Program Site 1241 in the eastern tropical Pacific enables us to reconstruct paleoceanographic changes that occurred since the latest middle Miocene. Today, this site is located just under the Eastern Pacific Warm Pool (EPWP). Based on the abundance variations of radiolarian characteristic species which are indicators of upwelling and thermocline changes, it is suggested that three notable changes occurred at 10.6, 9.8, and 4.2 Ma in the region. Four distinct periods of oceanographic conditions bounded by these notable changes were characterized on the basis of the following: (1) stratified seawater (12.0 to 10.6 Ma); (2) a shallowing of the thermocline and an increasing of upwelling (10.6 to 9.8 Ma); (3) significant inflow of warm water to the eastern tropical Pacific caused by an intensified Northern Equatorial Countercurrent (NECC), resulting in the formation of EPWP (9.8 to 4.2 Ma); and (4) the reduction of the EPWP and the NECC, and an increase in upwelling (4.2 to 0 Ma). The timing of these paleoceanographic events indicated the strong relations with the opening and closing of the Indonesian and Central American (Panama) Seaways. The reduction of the EPWP (this study) and the deepening of the thermocline in western Pacific at about 4.2 Ma (Cannariato and Ravelo, 1997; Chaisson and Ravelo, 2000) indicated a change from a state resembling El Niño in the late Miocene and the early Pliocene time to a state resembling La Niña by the late Pliocene.     

The vertical distribution of Radiolaria in the waters surrounding Japan

Geographic and vertical distribution patterns of living Radiolaria are closely related to the characters of the water column. We studied living Radiolaria in samples collected at closely spaced depth intervals in the waters surrounding Japan in order to understand their vertical distribution and its controlling factors. Such information is needed to reconstruct past vertical water mass structure. The Japanese Islands are surrounded by the marginal Japan Sea and the North Pacific Ocean, and from approximately 46° N to 26° N. They thus extend across a large latitudinal range and are exposed to a similarly wide range of environmental conditions, inducing the warm Kuroshio, Tsushima, and Tsugaru Currents and the cold Oyashio Current.We performed plankton tows (mesh size 63 mm) from late May to early June 2002 at eight sites, sampling the upper 200 m of the water column, at seven depth intervals.We recognized five radiolarian assemblages: the Upper Surface Assemblage (0–40 m), the Lower Surface Assemblage (40–80 m), the Surface Assemblage (0–80 m), the Subsurface Assemblage (80–200 m), and the Lower Surface–Subsurface Assemblage (40–200 m) groups. Pseudodictyophimus gracilipes and Tetrapyle octacantha (juvenile) show “tropical submergence”, i.e. they live at the surface in high latitudes and at greater depth in low latitudes. Four taxa live at specific temperature and salinity: Acrosphaera spinosa, Larcopyle butschlii, Challengeron diodon, and Stichocorys seriata. Four taxa are associated with characteristic temperatures: Neosemantis distephanus, Arachnocorys umbellifura, Antarctissa sp. 1, and Saccospyris conithorax.     

The distribution of the dinoflagellate Ceratium in relation to environmental factors along 28N in the eastern North Pacific

The distribution of the species of the dinoulagellate Ceratiumare related to the oceanographic conditions observed in January1983 across the eastern North Pacific central gyre, the CaliforniaCurrent and the transition zone between them. A change in dominanceoccurs in the central gyre not accompanied by Concomitant changesin the observed physical or chemical features.Ceratium ‘recognized’the edge of the California Current although it seems unaffectedin its abundance and species structure by a major warm temperatureanomaly.     

Equatorial Pacific sea surface temperatures, faunal patterns, and carbonate burial during the Pliocene

A high-resolution record of radiolarian faunal abundances from the eastern equatorial Pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical Pacific climate processes during the Pliocene. These data provide a means to evaluate the sensitivity of the equatorial Pacific to the onset of Northern Hemisphere glaciation around 2.8−2.5 Ma, to the closure of the Isthmus of Panama around 4.4−3.2 Ma, and to orogeny-related weathering changes before 4.0 Ma. Radiolarian faunal assemblages and sea surface temperature (SST) estimates indicate a gradual cooling from early to late Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation. Records of carbonate and noncarbonate mass accumulation show a long term decrease from the Miocene/Pliocene boundary to the upper Pliocene. Greater carbonate burial in the early Pliocene relative to the late Pliocene parallels a gradual cooling from early to late Pliocene, and may reflect changes related to Isthmus closure or widespread orogeny. No significant time domain changes are seen in the eastern equatorial Pacific that could be related to the onset of Northern Hemisphere glaciation.Evolutive spectral analyses of these equatorial Pacific climate parameters indicate that variance in SST and seasonality commonly concentrate at frequencies not linearly related to orbital variations. Furthermore, cross spectral comparisons with a high resolution benthic δ¹⁸O record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the Pliocene. Given the high degree of chronostratigraphic control in these records, these results suggest that Milankovitch-band surface ocean processes as well as carbonate burial in the equatorial Pacific are decoupled from high latitude climate processes during the Pliocene.     

Distribution of holoplanktonic typhloscolecids (Annelida-Polychaeta) in the eastern tropical Pacific Ocean

The distribution and composition of the holoplanktonic speciesof the family Typhloscolecidae are reported from 579 samplesobtained over an extensive area in the eastern tropical PacificOcean. The EASTROPAC Oceanographic Program collected the samplesin twelve cruises during five periods made between January–September1967 and January–April 1968. The 2105 specimens identifiedbelonged to three genera and four species. Typhloscolex muelleriand Sagitella kowalewski were dominant together, accountingfor 57–59% of the relative abundance and 36–49%of the occurrence. Travisiopsis dubia is recorded for the firsttime from the eastern tropical Pacific, and Travisiopsis lanceolatais reported in almost the same locality as its first recordin the surveyed region.     

Shell characters and taxonomy of Latirus and related fasciolariid groups

The neogastropod family Fasciolariidae contains a complex ofgenera related to Latirus Montfort, 1810, many of which havetraits unusual for the family. In a taxonomic revision of someof these genera, based on shell characters, we restrict Latirusto a mainly Indo-West Pacific group of Pliocene to Recent species,which closely resemble the middle Miocene to Recent pantropicalgenus Hemipolygona Rovereto, 1899. Hemipolygona stenomphalus(Habe & Kosuge, 1966) is synonymized with H. recurvirostris(Schubert & Wagner, 1829). Lathyropsis Oostingh, 1939, basedon a small Pliocene species from Indonesia, is here tentativelysubsumed under Polygona Schumacher, 1817. The latter genus,ranging from the late Oligocene to Recent, occurs mainly inthe New World and eastern Atlantic, and contains at least twospecies groups centered on P. infundibulum Schumacher, 1817(type of genus) and P. angulatus (Röding, 1798). Taxa assignedby many authors to Latirulus Cossmann, 1889, are here reassignedto the new genus Turrilatirus (type species: Voluta turritaGmelin, 1791), from the Pliocene to Recent of the Indo-WestPacific. Latirulus is restricted to Eocene species. We assignvarious early Miocene to Recent species from the western Atlanticand eastern Pacific to the new genus Pustulatirus (type species:Latirus mediamericanus, Hertlein & Strong, 1951a). Taxaformerly assigned to Latirus but here removed from Fasciolariidaeinclude Latirus ewekoroensis Adegoke, 1977; the Eocene RusculaCasey, 1904; Lathyrus granifer and L. compactilis, both of Martin,1931; Latirus kirbyi Clark, 1938; Latirus tortilis var. nanafaliusHarris, 1899; and Latirus quercotillaensis Olsson, 1931. (Received 6 September 2005; accepted 29 May 2006)     

DESCRIPTION OF A NEW GENUS AND SPECIES BELONGING TO THE FAMILY PHYLLIDIIDAE (NUDIBRANCHIA: DORIDOIDEA)

A new genus of phyllidiid nudibranch, Reticulidia, is described.Distinguishing features are the reticulate pattern of smoothridges on the dorsum and the radially arranged, glandular discswhich make up the pharyngeal bulb. Additional features of theforegut are described and compared with other genera. The importanceof the alimentary system for the separation of genera withinthe Phyllidiidae is supported and its validity reinforced bythis new genus. One species, Reticulidia halgerda, is describedas new and differentiated from a second, sympatric species.Reticulidia is presently known from the eastern Indian Ocean,South China Sea and western Pacific Ocean. ^*Present address: Australian Biological and Environmental Survey,Australian National Parks and Wildlife Service. GPO Box 1383,Canberra. ACT 2601. Australia. (Received 15 August 1989; accepted 8 January 1990)     

Radiolaria as a reflection of environmental conditions in the eastern and southern sectors of the Indian Ocean: A new statistical approach

Cluster analysis and species abundance plots of radiolarian abundance counts from core tops from the eastern Indian Ocean between 12° S and 31° S, and the southern Indian Ocean between 31° S and 62.5° S, demonstrate the existence of environmentally-related provinces supporting distinct taxa assemblages. These provinces are closely associated with currents in the eastern sector of the Indian Ocean and with fronts in the southern sector.The radiolarian assemblages correlate strongly with salinity-normalised total alkalinity (NTA) at the sea-surface, with temperature, salinity, and density from the sea-surface to 300 m, and with dissolved oxygen and nitrate and phosphate concentrations from the sea-surface to 100 m. Palaeo-reconstructions of these parameters at the sea-surface have been made for six Last Glacial Maximum (LGM) samples from five eastern Indian Ocean cores. The LGM sea-surface temperature estimates are comparable with those based on planktonic foraminiferal counts of the same samples obtained by other researchers. The reconstructions show that, since the LGM, density increased markedly along the Western Australian coast south of 20° S but changed little further from the Western Australian coast. By contrast, phosphate concentrations were marginally lower than modern values along the Western Australian coast south of 20° S but more than twice modern values in the other LGM samples.The utility of various regression and calibration techniques is discussed. It is concluded that, probably due to the effects of differences in radiolarian habitat, ocean currents, and/or environmental gradients, only one method, weighted averaging — partial least squares, is reliable in a study area of this size and complexity. If other methods are to be used, the study area must be partitioned into at least two separate regions with the major split between the eastern and southern sectors of the Indian Ocean.     

Biostratigraphy and paleoceanographic significance of Paleocene radiolarians from offshore eastern New Zealand

A 100-m-thick Paleocene sequence of mainly pelagic sediments at ODP Site 1121, on the eastern flanks of the Campbell Plateau, contains few to common radiolarians of relatively low diversity in the lower 40 m (Early to early Late Paleocene) and abundant, diverse radiolarian assemblages in the upper 60 m (mid-Late Paleocene). The 150 taxa recorded from the entire Paleocene interval are thought to under-represent the actual species diversity by at least one half as many morphotypes have not been differentiated below the level of genus. Assemblages in the lower 40 m are similar to those described from onland New Zealand and DSDP Site 208 (northern Lord Howe Rise); they are correlated with South Pacific radiolarian zones RP4 and RP5. Assemblages in the upper 60 m differ from other known Late Paleocene assemblages in the great abundance of plagiacanthids and cycladophorids. Similarities are noted with later Cenozoic cool-water assemblages. This upper interval is correlated with South Pacific zone RP6, as revised herein, based on comparison with faunas from Site 208 and Marlborough, New Zealand. The interval is also correlated with the upper part of North Atlantic zone RP6 (RP6b–c) based on the presence of Aspis velutochlamydosaurus, Plectodiscus circularis and Pterocodon poculum. Other species, such as Buryella tetradica and Buryella pentadica, are valuable for local correlation but exhibit considerable diachroneity between the Pacific, Indian and Atlantic Oceans. An age model for the Paleocene interval at Site 1121, based on well-constrained nannofossil and radiolarian datums, indicates that the rate of compacted sediment accumulation doubles from 15 to 30 mm/ka at the RP5/RP6 zonal boundary. In large part this is due to a sudden and pronounced increase in accumulation rates for all siliceous fossils; radiolarians and larger diatoms increase from <100 to >10 000 specimens/cm²/ka. This apparent increase in biosiliceous productivity is age-equivalent to a mid-Paleocene cooling event (57–59 Ma) identified from global stable isotope records that is associated with the heaviest δ¹³C values for the entire Cenozoic.     

Trans‐Pacific and trans‐Arctic pathways of the intertidal macroalga Fucus distichus L. reveal multiple glacial refugia and colonizations from the North Pacific to the North Atlantic

Aim We examined the phylogeography of the cold‐temperate macroalgal species Fucus distichus L., a key foundation species in rocky intertidal shores and the only Fucus species to occur naturally in both the North Pacific and the North Atlantic. Location North Pacific and North Atlantic oceans (42° to 77° N). Methods We genotyped individuals from 23 populations for a mitochondrial DNA (mtDNA) intergenic spacer (IGS) (n = 608) and the cytochrome c oxidase subunit I (COI) region (n = 276), as well as for six nuclear microsatellite loci (n = 592). Phylogeographic structure and connectivity were assessed using population genetic and phylogenetic network analyses. Results IGS mtDNA haplotype diversity was highest in the North Pacific, and divergence between Pacific haplotypes was much older than that of the single cluster of Atlantic haplotypes. Two ancestral Pacific IGS/COI clusters led to a widespread Atlantic cluster. High mtDNA and microsatellite diversities were observed in Prince William Sound, Alaska, 11 years after severe disturbance by the 1989 Exxon Valdez oil spill. Main conclusions At least two colonizations occurred from the older North Pacific populations to the North Atlantic between the opening of the Bering Strait and the onset of the Last Glacial Maximum. One colonization event was from the Japanese Archipelago/eastern Aleutians, and a second was from the Alaskan mainland around the Gulf of Alaska. Japanese populations probably arose from a single recolonization event from the eastern Aleutian Islands before the North Pacific–North Atlantic colonization. In the North Atlantic, the Last Glacial Maximum forced the species into at least two known glacial refugia: the Nova Scotia/Newfoundland (Canada) region and Andøya (northern Norway). The presence of two private haplotypes in the central Atlantic suggests the possibility of colonization from other refugia that are now too warm to support F. distichus. With the continuing decline in Arctic ice cover as a result of global climate change, renewed contact between North Pacific and North Atlantic populations of Fucus species is expected.     

Sea-surface temperature changes in the North Pacific during the Late Miocene

Twenty-seven radiolarian species and species groups are identified and used in this study. Their stratigraphic ranges span from Late Miocene to modern times and they appear to have distributions which have changed little over this interval of time. Census data for these 27 taxa in surface sediment samples are used to define six assemblages (Q-mode factors). The distribution of these assemblages are similar to modern water-mass distributions and can be statistically related to modern sea-surface temperatures.Census data on these same 27 taxa have been collected in the Upper Miocene intervals of six Pacific sites. These faunal data are described in terms of the modern radiolarian assemblages; and based on the multiple regression equations relating the modern assemblages to modern temperatures, estimates of Late Miocene temperatures are made. The estimated temperatures indicate that there is an overall cooling trend in the later part of the Miocene (magnetic Chron 8 to Chron 5), punctuated by several distinct cooling events. In August the low-latitude sites appear to be slightly cooler, and the mid-latitude sites warmer than in modern times. In February both the low- and mid-latitude sites appear to be warmer than modern temperatures at the same locations. The relatively warm temperatures near the base of the interval studied may be associated with the passage of warm tropical Atlantic waters into the eastern Pacific via the Isthmus of Panama. The general cooling trend seen in these records is thought to be associated with the gradual closure of these straits and the increased influence of the high southern latitudes.     

The first-stage zoeas of Carpilius convexus (Forskal, 1775) and Carpilius maculatus (Linnaeus, 1758) (Crustacea: Decapoda: Brachyura: Xanthoidea: Carpiliidae): an example of heterochrony

The first-stage zoeas of Carpilius convexus (Forskål,1775) and Carpilius maculatus (Linnaeus, 1758) are describedand fully illustrated. Both these Indo-West Pacific speciesexhibited a unique xanthoidean character for the basis of thesecond maxilliped, which possesses five (arranged 1,1,1,2) setaeinstead of the expected four (arranged 1,1,1,1). A comparisonwith the zoeal stages of Carpilius corallinus (Herbst, 1783)as reported by Laughlin et al. (Laughlin et al., 1983) revealedmarked differences including the possession of carapace lateralspines (v. absent in C. convexus only), the subterminal setationof the distal maxillule endopod segment with two subterminalsetae (versus one subterminal seta in Indo-West Pacific species),the terminal setation of the distal maxillule endopod segmentwith four setae (versus three setae in C. convexus only), twolateral spines on the telson (versus three in Indo-West Pacificspecies) and the number of zoeal stages. The first-stage zoeasof the two Indo-West Pacific species appear to have hatchedin a more advanced state of development than those of C. corallinus,and the expression of a number of characters has been accelerated(early onset). In fact, the zoeal stages of both Indo-West Pacificspecies and carpiliid species appear to be abbreviated becausethe first zoeas are considered to be equivalent to the third-stagezoeas of C. corallinus.     

Late Quaternary history of atmospheric and oceanic circulation in the eastern equatorial Pacific

Four radiolarian assemblages have been defined in recent seafloor sediments of the equatorial Pacific Ocean. The distribution of these assemblages corresponds to the modern pattern of oceanic circulation and water mass structure in this region: the eastern Pacific shallow permanent thermocline and the Equatorial Undercurrent; Peru Current upwelling and the oxygen minimum; the subtropical water mass; warm western tropical water and the North Equatorial Countercurrent. In twelve cores chosen to transect the region both longitudinally and latitudinally, the distribution of these four assemblages has been reconstructed for six time-intervals during the last 127,000 years: 18,000 B.P. (glacial Stage 2); 36,000 B.P. and 52,000 B.P. (interstadial Stage 3); 65,000 B.P. (glacial Stage 4); 82,000 B.P. and 120,000 B.P. (interglacial Stage 5). Atmospheric and oceanic circulation changes through time have been inferred from the reconstructed microfossil assemblage distributions. Changes in assemblage distributions indicate that variations in intensity, direction and mean position of the tradewinds caused marked changes in the oceanic circulation patterns through the last glacial cycle.Near the end of interglacial Stage 5, the disappearance of the North Equatorial Countercurrent from the eastern Pacific suggests that the mean position of the tradewinds was shifted to the south approximately 5° of latitude relative to the modern position, so that the Northeast trades prevented the flow of the North Equatorial Countercurrent into the eastern Pacific. Near the end of interstadial Stage 3, a change in wind direction occurred from predominantly zonal winds, which enhance equatorial divergence and surfacing of the Equatorial Undercurrent, to more meridional winds, which enhance coastal upwelling associated with the Peru Current.In the tropical Pacific Ocean, late Quaternary changes in atmospheric and oceanic circulation are linked with times of continental ice sheet growth in the Northern Hemisphere (i.e., the interglacial-to-glacial transitions across oxygen isotope stage boundaries $\text{5}\text{4}$ and $\text{3}\text{2}$). The major changes in circulation seem to occur a few thousand years in advance of the glacial episodes, at or near periods of ice sheet growth. This relationship indicates that changes in atmospheric circulation in the tropics led and influenced the development of conditions suitable for polar and continental ice sheet growth in the Northern Hemisphere.     

ALLOZYME COMPARISON OF LITTORINA SPECIES FROM THE NORTHWESTERN PACIFIC

Three unknown Littorina species were revealed by allozyme studyof snails from the northwestern Pacific. One of them was foundin Kasatka Bay (Pacific coast of Iturup Island, south KurileIslands) together with L. sitkana, which it resembled in anatomicalfeatures, but the genetic distance between these species wasD=0.622. The second one was found in Tauiskaya Inlet (northernpart of Okhotsk Sea) and was again similar to L. sitkana inmorphological and anatomical features, but D=1.160. The thirdspecies was found in Egvekinot Inlet (Anadyrskiy Gulf, BeringSea) in sympatry with L. natica, to which was close genetically(D=0.256) although it differed in shell shape. (Received 4 April 2005; accepted 26 August 2005)     

Adaptive evolution of sperm bindin tracks egg incompatibility in neotropical sea urchins of the genus Echinometra

Bindin is a gamete recognition protein known to control species-specificsperm-egg adhesion and membrane fusion in sea urchins. Previousanalyses have shown that diversifying selection on bindin aminoacid sequence is found when gametically incompatible speciesare compared, but not when species are compatible. The presentstudy analyzes bindin polymorphism and divergence in the threeclosely related species of Echinometra in Central America: E.lucunter and E. viridis from the Caribbean, and E. vanbruntifrom the eastern Pacific. The eggs of E. lucunter have evolveda strong block to fertilization by sperm of its neotropicalcongeners, whereas those of the other two species have not.As in the Indo-West Pacific (IWP) Echinometra, the neotropicalspecies show high intraspecific bindin polymorphism in the samegene regions as in the IWP species. Maximum likelihood analysisshows that many of the polymorphic codon sites are under mildpositive selection. Of the fixed amino acid replacements, mosthave accumulated along the bindin lineage of E. lucunter. Weanalyzed the data with maximum likelihood models of variationin positive selection across lineages and codon sites, and withmodels that consider sites and lineages simultaneously. Ourresults show that positive selection is concentrated along theE. lucunter bindin lineage, and that codon sites with aminoacid replacements fixed in this species show by far the highestsignal of positive selection. Lineage-specific positive selectionparalleling egg incompatibility provides support that adaptiveevolution of sperm proteins acts to maintain recognition ofbindin by changing egg receptors. Because both egg incompatibilityand bindin divergence are greater between allopatric speciesthan between sympatric species, the hypothesis of selectionagainst hybridization (reinforcement) cannot explain why adaptiveevolution has been confined to a single lineage in the AmericanEchinometra. Instead, processes acting to varying degrees withinspecies (e.g., sperm competition, sexual selection, and sexualconflict) are more promising explanations for lineage-specificpositive selection on bindin.