Geographical subdivision,demographic history and gene flow in two sympatric species of intertidal snails, <Emphasis Type="Italic">Nerita scabricosta</Emphasis> and <Emphasis Type="Italic">Nerita funiculata</Emphasis>, from the tropical eastern Pacific

The patchy distribution of rocky intertidal communities in the tropical eastern Pacific (TEP) may impose severe constraints on the genetic connectivity among populations of marine invertebrates associated with this habitat. In this study, we analyzed a portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene in two sympatric species of marine snails, Nerita scabricosta and Nerita funiculata, common inhabitants of the rocky intertidal from the Gulf of California (Sea of Cortez) and outer Pacific coast of the southern Baja California (Baja) peninsula to northern South America, to assess genetic connectivity among populations of each species. One of our aims was to determine whether the morphological, behavioral, and ecological differences observed among populations of both species throughout their range in the TEP corresponded to population genetic differences. In addition, we were interested in elucidating the demographic history of both species. We found no evidence of genetic structure throughout the Gulf of California and outer coast of the Baja peninsula region for either species. Comparisons between Gulf of California/Baja and Panama populations, however, showed significant genetic differentiation for N. scabricosta, but not for N. funiculata. The genetic differences between Mexican and Panamanian populations of N. scabricosta were consistent with previously reported ecological and behavioral differences for this species between these two distant regions. However, previously reported size differences between northern and central/southern Gulf of California individuals of N. scabricosta do not correspond with our findings of genetic connectivity among these populations. Results from neutrality tests (Tajima’s D and Fu’s F _S), the mismatch distribution, and Bayesian skyline analyses suggested that both species have experienced dramatic population expansions dating to the Pleistocene.     

Lactate formation in Callianassa californiensis and Upogebia pugettensis (Crustacea: Thalassinidea)

The ability to accumulate lactate as a result of laboratory exposure to anoxia was examined in 2 species of mud-dwelling shrimp, the ghost shrimp Callianassa californiensis and the mud shrimp Upogebia pugettensis. Hemolymph lactate accumulated to a much greater degree in the mud shrimp, even though the overall levels of lactate dehydrogenase activity were similar in tissues of the two species. Carbohydrate reserves, estimated as glycogen, were not significantly depleted in muscle or midgut gland of either species as a result of anoxic stress. The results are discussed in relation to possible metabolic strategies employed to cope with the hypoxic environment of these crustaceans.     

Population genetic structure of North American <Emphasis Type="Italic">Ophiactis</Emphasis> spp. brittle stars possessing hemoglobin

With the discovery of previously unreported populations of hemoglobin-possessing Ophiactis from the Texas coast in the Gulf of Mexico, an investigation into its population structure, including populations of O. simplex from the Pacific coast of California and O. rubropoda from the Atlantic coast of Florida, was undertaken using DNA sequence data from the mitochondrial COI gene. The reconstructed haplotype network suggests that California populations contain the ancestral source of mtDNA variation, and there is no evidence of recent introductions into Texas. Population genetic analyses reveal the California, Florida, and Texas Ophiactis populations to each be significantly differentiated from one another. Sequence divergence among the three areas is shallower than would be predicted given biogeographic history. Texas and Florida populations are equally genetically diverged from California populations as they are to one another, despite the greater potential for gene flow between these areas. The genetic distinctiveness of the Texas populations and the concordance of this pattern with phylogeographic patterns in other brittle star systems indicate an isolated and independent evolutionary history and we hypothesize that the three geographic regions included in this study each serve as hypotheses of population-level lineages that remain to be tested with independent sources of data.     

Regional differentiation and post-glacial expansion of the Atlantic silverside, <Emphasis Type="Italic">Menidia menidia,</Emphasis> an annual fish with high dispersal potential

The coastal marine environment of the Northwest Atlantic contains strong environmental gradients that create distinct marine biogeographic provinces by limiting dispersal, recruitment, and survival. This region has also been subjected to numerous Pleistocene glacial cycles, resulting in repeated extirpations and recolonizations in northern populations of marine organisms. In this study, we examined patterns of genetic structure and historical demography in the Atlantic silverside, Menidia menidia, an annual marine fish with high dispersal potential but with well-documented patterns of clinal phenotypic adaptation along the environmental gradients of the Northwest Atlantic. Contrary to previous studies indicating genetic homogeneity that should preclude regional adaptation, results demonstrate subtle but significant (F _ST = 0.07; P < 0.0001) genetic structure among three phylogeographic regions that partially correspond with biogeographic provinces, suggesting regional limits to gene flow. Tests for non-equilibrium population dynamics and latitudinal patterns in genetic diversity indicate northward population expansion from a single southern refugium following the last glacial maximum, suggesting that phylogeographic and phenotypic patterns have relatively recent origins. The recovery of phylogeographic structure and the partial correspondence of these regions to recognized biogeographic provinces suggest that the environmental gradients that shape biogeographic patterns in the Northwest Atlantic may also limit gene flow in M. menidia, creating phylogeographic structure and contributing to the creation of latitudinal phenotypic clines in this species.     

Genetic structure of leopard shark (<Emphasis Type="Italic">Triakis semifasciata</Emphasis>) populations in California waters

The leopard shark (Triakis semifasciata) is an important predator in coastal marine ecosystems of California, targeted by recreational and commercial fishermen and of specific interest in fisheries management. From October 2003 to August 2006, 169 leopard sharks were collected from the coast of California (between 40.750°N and 32.678°N) and analyzed for mitochondrial and nuclear genetic structure. Analyses of mtDNA control region sequences revealed relatively low levels of genetic variation (five haplotypes, average pairwise divergence π = 0.0067). In contrast, leopard sharks were highly polymorphic for inter simple sequence repeats (ISSRs), which characterize a broad range of the nuclear genome. The null hypothesis of panmixia in California waters was rejected for both genetic markers, and ISSRs displayed a statistically significant pattern of isolation by distance (IBD) across the species range (P = 0.002). A variety of analyses showed that divergence is most pronounced in the northernmost population of Humboldt Bay. Natal philopatry in T. semifasciata was tested using Siegel-Tukey tests on data partitioned by breeding site status, and sex-specific philopatry was tested by comparing IBD plots between sexes. Although there was some evidence for natal philopatry in leopard sharks (P = 0.038), and population divergence may be related to the proximity of breeding sites (P = 0.064), we found no support for sex-specific philopatry. In addition to identifying a novel set of highly variable genetic markers for use in shark population studies, these results may be used to better inform management decisions for leopard sharks in California.     

Historical demography and contemporary spatial genetic structure of an estuarine crab in the northeast Pacific (<Emphasis Type="Italic">Hemigrapsus oregonensis</Emphasis>)

Discrete estuary subpopulations of the mud crab Hemigrapsus oregonensis (Dana, 1851) are connected via larval dispersal. Sequence variation at the mtDNA COI locus was examined in eight populations sampled in 2001–2002 from central California through northern Oregon in the northeast Pacific (36.6–45.8°N) to infer patterns of dispersal and historical connectivity in the region. Strong evidence for persistence since the mid-Pleistocene, with no range truncation resulting from southward shifting temperature isoclines, was provided by a phylogeographic pattern of haplotypes of an older clade distributed throughout the sampled range. A recently derived clade became widespread only north of Cape Blanco after the last glacial maximum. Its clear pattern of restriction to the northern area, in the absence of similarly restricted southern clades, suggests that contemporary dispersal around Cape Blanco is rare (population F _ST = 0.192). Low pairwise differentiation within Oregon and within central California, as well as contrasts between northern and southern groups in the shape of the pairwise mismatch distribution, nucleotide diversity, and Tajima’s D suggest that these regions reflect different demographic histories. Potential mechanisms explaining this latitudinal break include contemporary coastal circulation patterns, selection, and ancient patterns of larval dispersal in the California Current.     

Sympatry and allopatry in the deeply divergent mitochondrial DNA clades of the estuarine pulmonate gastropod genus <Emphasis Type="Italic">Phallomedusa</Emphasis> (Mollusca,Gastropoda)

DNA sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene were collected from estuarine snails in the genus Phallomedusa to examine the effects of estuarine isolation on population structure and gene flow. Three clades were recovered, one corresponding to Phallomedusa austrina and two others with the morphology of Phallomedusa solida. The haplotype diversity in all three clades indicated recent population expansion. Phallomedusa austrina was restricted to the west of a previous land bridge in the Bass Strait between mainland Australia and Tasmania, and P. solida to its east and to northern Tasmania. Phylogeographic analysis of P. austrina and P. solida shows strong geographic separation of species, but no local genetic structure indicative of regional or estuarine isolation. The clades of P. solida exhibit substantial genetic divergence and were sympatric across their entire distribution in eastern Tasmania and mainland Australia. Such a situation, which has not previously been observed in phylogeographic studies of southeast Australia, suggests that P. solida has had a complex refugial history during periods of environmental challenge.     

Phylogeography of the pipefish, <Emphasis Type="Italic">Urocampus carinirostris</Emphasis>, suggests secondary intergradation of ancient lineages

We assayed the pattern of mitochondrial DNA evolution in the live bearing, seagrass specialist pipefish, Urocampus carinirostris, in eastern Australia. These life history attributes were predicted to result in strong phylogeographic structure in U. carinirostris. Phylogenetic analysis of cytochrome b sequences detected two monophyletic mtDNA clades that differed by 8.69% sequence divergence - a large level of intraspecific divergence for a marine fish. The geographical distribution of clades was non-random and resembled clinal secondary intergradation over a 130-km stretch of coastline. Contrary to phylogeographic predictions, this large phylogeographic break does not occur across a traditionally recognised biogeographic boundary. Analyses of historical demography suggested that individuals belonging to the most widespread clade underwent a population expansion from a small refuge population during the Pleistocene.     

Regional extinction of a conspicuous dorid nudibranch (Mollusca: Gastropoda) in California

Felimare californiensis (=Hypselodoris californiensis) was once common throughout the Southern California Bight (SCB) and California Channel Islands. This well-known shallow-water nudibranch, which specializes on dysideid sponges, has persisted for decades in Mexico, but in California disappeared from its entire range by 1984. Since reappearing in 2003, it has been found only at Santa Catalina Island, plus sightings of single individuals in 2011 at Santa Cruz Island and San Diego. The decline of F. californiensis in California was documented using published historical records, museum collections, unpublished field accounts, and images posted online. The loss of this emblematic species is unique among Californian nudibranchs, including (1) its congener Felimare porterae (=Mexichromis porterae), with which it appears to overlap in diet, and (2) opisthobranch species with similar historical geographic ranges and mode of development. The decline in F. californiensis is not predicted by warming trends and climate variation over the past 40 years, including the strong El Niño events of 1983 and 1998. Coastal pollution from the large human population in southern California may have impacted Dysidea amblia, the primary reported prey of F. californiensis. Historical overcollecting of the nudibranch and habitat loss through the development of major ports likely also contributed to its decline. Sightings since 2003 are consistent with a nascent recovery, as elements of water quality have improved in the SCB in recent decades.     

Molecular population structure of the kuruma shrimp <Emphasis Type="Italic">Penaeus</Emphasis><Emphasis Type="Italic"> japonicus</Emphasis> species complex in western Pacific

In a previous study on the kuruma shrimp Penaeus japonicus from the South China Sea, we detected high genetic divergence between two morphologically similar varieties (I and II) with distinct color banding patterns on the carapace, indicating the occurrence of cryptic species. In the present study, we clarify the geographical distribution of the two varieties in the western Pacific by investigating the genetic differentiation of the shrimp from ten localities. Two Mediterranean populations are also included for comparison. Based on the mitochondrial DNA sequence data, the shrimps are separated into two distinct clades representing the two varieties. Variety I comprises populations from Japan and China (including Taiwan), while variety II consists of populations from Southeast Asia (Vietnam, Singapore and the Philippines), Australia and the Mediterranean. Population differentiation is evident in variety II, as supported by restriction profiles of two mitochondrial markers and analysis of two microsatellite loci. The Australian population is genetically diverged from the others, whereas the Southeast Asian and Mediterranean populations show a close genetic relationship. Variety I does not occur in these three localities, while a small proportion of variety II is found along the northern coast of the South China Sea and Taiwan, which constitute the sympatric zone of the two varieties. The present study reveals high genetic diversity of P. japonicus. Further studies on the genetic structure of this species complex, particularly the populations in the Indian Ocean and Mediterranean, are needed not only to understand the evolutionary history of the shrimp, but also to improve the knowledge-based fishery management and aquaculture development programs of this important biological resource.     

Phylogeography and demographic history of <Emphasis Type="Italic">Atherina presbyter</Emphasis> (Pisces: Atherinidae) in the North-eastern Atlantic based on mitochondrial DNA

A fragment of the mitochondrial control region was used to assess phylogeographic patterns and historical demography of the sand-smelt Atherina presbyter in the North-eastern Atlantic, covering its geographical range. A striking result is the highly marked differentiation between the Canary Islands population and western European ones. A genetic structure among European populations of A. presbyter was revealed, with a pattern of isolation-by-distance or a gradient effect at a scale of hundreds kilometres, an uncommon pattern likely related to the biological and life-history traits of the sand-smelt. The northern European populations present a much lower genetic diversity when compared to southern populations, which is consistent with a recent colonization from southern populations. The results showed signs of Pleistocene signatures, with the population age estimates for the European populations being clearly older than the Last Glacial Maximum (18,000 years bp). Nevertheless, paleotemperature reconstructions show that the sand-smelt could not have inhabited the western European shores during the last glacial phase. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Structure and function of the stomachless digestive system in three related species of New World silverside fishes (Atherinopsidae) representing herbivory, omnivory, and carnivory

We explored possible diet-related specializations in the digestive tract of stomachless fishes by summarizing the diets, verifying the absence of a stomach, and comparing gut lengths, microvilli surface areas, and activities of five digestive enzymes in four taxa of silversides from southern California coastal waters. For the comparisons, we examined these gut features in Atherinops affinis from both estuarine and kelp-forest habitats, and Atherinopsis californiensis and Leuresthes tenuis from open coastal habitats. A. affinis was found to be primarily herbivorous in estuaries and carnivorous in kelp forests, whereas As. californiensis was shown to be somewhat omnivorous but mainly carnivorous, and L. tenuis strictly carnivorous. Estuarine A. affinis exhibited the longest gut, largest microvilli surface area, and highest amylase and maltase activities, all arguably reflecting responses to an algal diet. In contrast, kelp-forest A. affinis displayed the highest trypsin activity and generally similar microvilli surface areas and aminopeptidase, amylase, and maltase activities to the two other carnivorous taxa. All four taxa showed similar lipase activities that compared closely with published values for other fishes. Taken together, our results reveal striking differences in gut structure and function among the four taxa, but especially between the estuarine and kelp-forest populations of A. affinis. Further studies are required to assess the roles of genetic variation and phenotypic plasticity in explaining the differences in these herbivorous and carnivorous taxa.     

Phylogeography of two species of <Emphasis Type="Italic">Lysidice</Emphasis> (Polychaeta,Eunicidae) associated to the seagrass <Emphasis Type="Italic">Posidonia oceanica</Emphasis> in the Mediterranean Sea

The aim of this work was to define the phylogeographic patterns of the two species of polychaete Eunicidae, Lysidice ninetta Audouin and Milne Edwards and Lysidice collaris Grube, both associated as sheath borers to the Mediterranean seagrass Posidonia oceanica, and with reference to their different origin and their actual geographic distribution. L. ninetta is distributed in the Atlantic and in the Mediterranean Sea while L. collaris is a tropical species, whose introduction into the Mediterranean Sea through the Suez Canal (lessepsian migrant) has been hypothesized in recent years. The two species have been often confused in the past, although they appear morphologically distinct. They share the same microhabitat (Posidonia sheaths) and they co-exist along a broad bathymetric range (1–30 m). Several populations for both taxa were sampled all along the coast of the Mediterranean basin. A variable no coding region of nuclear DNA (rDNA, ITS1) and a portion of a more conservative coding region of mitochondrial DNA (sub-unit one of citochrome oxidase, COI) were used as molecular markers. Both markers confirmed the separation between the two species. Low intraspecific polymorphism was present in L. collaris, together with absence of phylogeographic structure. In L. ninetta, instead, the presence of intraspecific cryptic lineages, sympatric in some sites, was recorded. Clustering of single populations in the two main clades was not always consistent between markers. The mitochondrial COI region showed more resolution at the given spatial scale. Our results suggest that Lysidice collaris could be recently introduced into the Mediterranean Sea from one or more separate events. On the other hand, for L. ninetta one could presume a re-colonization of the Mediterranean basin from the Atlantics, after the Messinian crisis (dry-out of the Mediterranean Sea, 5.5 my) with the subsequent separation of intraspecific lineages. The phylogeographic patterns of both Lysidice spp. are disjoined with respect to that of the host plant, P. oceanica. The obtained results suggest that environmental constraints and evolutionary history of these polychaetes and their host plant act in different ways to determine their actual genetic spatial structure.     

A tropical/subtropical biogeographic disjunction in southeastern Africa separates two Evolutionarily Significant Units of an estuarine prawn

Recent phylogeographic research has indicated that biodiversity in the sea may be considerably greater than previously thought. However, the majority of phylogeographic studies on marine invertebrates have exclusively used a single locus (mitochondrial DNA), and it is questionable whether the phylogroups identified can be considered distinct species. We tested whether the mtDNA phylogroups of the southern African sandprawn Callianassa kraussi Stebbing (Decapoda: Thalassinidea) are also recovered using nuclear sequence data. Four mtDNA phylogroups were recovered that were each associated with one of South Africa’s four major biogeographic provinces. Three of these were poorly differentiated, but the fourth (tropical) group was highly distinct. The nuclear phylogeny recovered two major clades, one present in the tropical region and the other in the remainder of South Africa. Congruence between mitochondrial and nuclear DNA indicates that the species comprises two Evolutionarily Significant Units sensu Moritz (1994). In conjunction with physiological data from C. kraussi and morphological, ecological and physiological data from other species, this result supports the notion that at least some of the mtDNA phylogroups of coastal invertebrates whose distributions are limited by biogeographic disjunctions can indeed be considered to be cryptic species.     

Genetic analysis of sympatric morphotypes of common dolphins (genus Delphinus)

Sympatric populations of two forms of the common dolphin, currently recognized collectively as Delphinus delphis Linnaeus, occur in several areas of the world's oceans. A molecular genetic study was initiated to determine whether these forms are genetically distinct in the Northeast Pacific. We compared mitochondrial DNA sequences from the control region and cytochrome b gene between specimens of the long-beaked and the short-beaked morphotypes collected between 1986 and 1989 off the coast of southern California. Additional short-beaked specimens collected from the eastern tropical Pacific (in 1978 and 1982) and the Black Sea (in 1989) were also compared. There were no shared mitochondrial DNA haplotypes between the two morphotypes, and both gene regions exhibited frequency and fixed nucleotide substitutions between the two morphotypes. This genetic differentiation, coupled with unique morphological characters of the short-beaked and long-beaked morphotypes determined in a parallel study, indicate that although sympatric, these populations of common dolphin are reproductively isolated from one another and may represent separate species.     

Phylogeographic structure of <Emphasis Type="Italic">Octopus vulgaris</Emphasis> in South Africa revisited: identification of a second lineage near Durban harbour

In a previous study that investigated genetic structure of Octopus vulgaris along the South African coast by sequencing the mitochondrial cytochrome oxidase III gene (COIII), all sequences generated were identical. Such a finding is unusual, because mitochondrial DNA mutates quickly, and several marine invertebrates present in southern Africa show considerable genetic variation and structure. We reanalysed the samples using two different mitochondrial markers, namely cytochrome oxidase I (COI) and the large ribosomal subunit (16S rRNA). Sequences of both these markers showed variation. The conclusion of the previous study, that South Africa’s O. vulgaris population is characterised by a lack of genetic structure along the coast, is rejected. Some specimens from Durban (southeast Africa) were genetically more different from those found in the remainder of the country than were specimens from other regions (Tristan da Cunha and Senegal). We suggest that the lineage in Durban may have been recently introduced.     

New insights on population genetic structure of <Emphasis Type="Italic">Delphinus delphis</Emphasis> from the northeast Atlantic and phylogenetic relationships within the genus inferred from two mitochondrial markers

The taxonomic status of common dolphins (Delphinus sp.) remains controversial despite the increased number of studies focusing on its populations. Two species are presently recognized, Delphinus delphis and D. capensis. Apart from a phylogeographic study of the genus Delphinus, genetic studies focusing specifically in the northeast (NE) Atlantic remain scarce. Following ecological and morphological evidence for the existence of different common dolphin morphotypes in the Portuguese coast, we examined the population structure of D. delphis from the NE Atlantic by comparing DNA sequences from two mitochondrial regions (control region and cytochrome b gene). Additionally, we compared the sequences obtained with existing sequences of D. delphis from the Azores, Black Sea, Canary Islands, Pacific Ocean, D. capensis and also two closely related delphinid species (Stenella coeruleoalba and Tursiops truncatus). In the analysis of the NE Atlantic populations, we found evidence for the existence of some level of genetic differentiation. In the broader phylogenetic analysis, D. delphis and D. capensis did not show reciprocal monophyly and we found a group of highly divergent individuals. We discuss the possibility for the existence of two divergent lineages that have evolved independently, a separate subspecies or events of introgressive hybridization. These findings could have important implications on a taxonomic level, although further investigation based on a larger geographical scale and on nuclear loci information will certainly elucidate the origin of these highly divergent individuals.     

The cockle <Emphasis Type="Italic">Cerastoderma edule</Emphasis> at Northeast Atlantic shores: genetic signatures of glacial refugia

The cockle Cerastoderma (Cardium) edule (L.) ranges from NW Africa to northern Scandinavia. Abundance in shallow coastal sediment is often high, and it attracts commercial harvest. In this study, a complex genetic pattern has been revealed by mitochondrial DNA in 383 individuals from 19 sampling sites. Parsimony network analysis of 79 haplotypes identified two dominant central haplotypes separated by low divergence. One is characteristic for a homogenous southwestern group of populations from Africa to the British Isles. The other is characteristic for a heterogeneous northern group with a deviant Arctic population. At the entrance of the Baltic Sea, a mixture zone of the dominant haplotypes was found. The estimated population expansion time for the northern haplotype group predates that of the southwestern one, suggesting northern glacial refugia and a subsequent southern expansion of C. edule populations.     

Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales

Many studies have examined latitudinal differences in reproduction of marine invertebrates, but few have measured variation at small to intermediate scales (kilometres to hundreds of kilometres), which may confound comparisons across broader geographic regions. Here, we examined variation in the reproductive biology of a little-studied species of burrowing ghost shrimp (Trypaea australiensis) at spatial scales ranging from km (between sites within estuaries) to 100s of km (among estuaries), over a 2-year period in south-eastern Australia. Sex ratios of populations were consistently biased towards females through time and space. Although reproduction started in summer months across all spatial scales, there was a pattern of earlier spawning from southern to northern estuaries. Integration of results from previous studies of T. australiensis supported a similar pattern of earlier breeding from high to low latitudes. Fecundity of shrimp increased linearly with female size, but the relationship varied inconsistently across the different spatial scales. Similarly, sizes at maturity varied from small to intermediate scales and observed patterns were not consistent with general predictions e.g. shrimp were smaller and ovigerous at smaller sizes at sites in the southern-most estuary, compared to estuaries further north. We found no differences in the sizes of embryos across the different spatial scales, but confirm that T. australiensis employs a strategy of high fecundity and small embryo size compared to other thalassinidean shrimp. Our results suggest that factors at smaller scales (e.g. food availability) may be important in affecting reproductive dynamics of T. australiensis, but further research is needed in testing hypotheses about patterns observed here. A lack of similar studies on other marine organisms remains an impediment to understanding life-history strategies and the sustainable management and conservation of populations.     

Phylogeography of California and Galápagos sea lions and population structure within the California sea lion

We investigate the phylogeography of California (Zalophus californianus) and Galápagos (Z. wollebaeki) sea lions and describe within-population structure for the California sea lion based on mitochondrial DNA. Fifty control-region haplotypes were found, 41 from Z. californianus and 9 from Z. wollebaeki, with three fixed differences between the two species. Ranked population boundaries along the range of Z. californianus were defined based on the Monmonier Maximum Difference Algorithm, resulting in five genetically distinct populations, two in the Pacific Ocean and three inside the Gulf of California. A Minimum Spanning Network showed a strong phylogeographic signal with two well-defined clusters, Z. californianus and Z. wollebaeki, separated by six base-pair differences, supporting the existence of two genetically distinct species with an estimated divergence time of ~0.8 Ma. Results are discussed in the context of the historical geologic and paleoceanographic events of the last 1 Ma in the eastern Pacific.