Genetic evidence for the occurrence of a cryptic species with the littoral nemerteans Lineus ruber and L. viridis (Nemertea: Anopla)

Lineus ruber and L. viridis are common intertidal heteronemerteans found on the coasts of northern Europe and the east coast of North America. The two species resemble each other morphologically and were synonymised for many years prior to being separated on the basis of larval development. In this study, specimens of L. ruber and L. viridis were collected from sites along the west and southwest coast of Britain, northern France and the east coast of North America. The external morphology and allele frequencies of isozymes of the two species were compared from all sites. The external morphology of L. ruber and L. viridis was similar but they could generally be separated by colour. Allele frequencies for up to 13 enzyme loci between sympatric populations of L. ruber and L. viridis indicated that these two species are genetically very different (Nei's genetic identity=0.090 to 0.083). Allele-frequency data also indicated the presence of a third genetic type occurring sympatrically with populations of both L. ruber and L. viridis on the coasts of Britain and France but not on the coast of North America. Fixed differences in allele frequencies between populations of the third genetic type and sympatric populations of L. ruber and L. viridis were observed across multiple loci. Genetic identity between the third genetic type and sympatric populations of L. ruber and L. viridis were extremely low (Nei's genetic identity =<0.078). Such large genetic differences between populations indicate a barrier to gene flow and reproductive isolation. The aberrant type, which exhibits sufficient morphological variation to prevent individuals being distinguished from those of both L. ruber and L. viridis, therefore represents a separate species. The low genetic identities found in intrageneric comparisons of species found in this study have been found in other studies on nemerteans. They may indicate systematic problems within these groups or other phenomena such as morphological stasis.     

Enzymatic and morphological criteria for distinguishing between Cardium edule and C. glaucum of the Portuguese coast

Cardium edule L. and C. glaucum Bruguière are two sibling species of cockles commonly found in littoral systems along the Portuguese coast, where they sometimes occur as mixed populations. The problem of morphological separation of these two cockle species has not been completely solved. Indeed, the distinctive morphological criterion proposed by Brock after identifying the specimens by means of electrophoretic patterns of hepatopancreatic malate dehydrogenase was not effective when applied to Portuguese Cardium spp. The object of the present study was to establish morphological discrimination criteria for distinguishing Portuguese C. edule and C. glaucum on the basis of initial identification of individuals through the enzymatic criterion established by Brock. Cockles were collected from 1988 to 1991 at 16 estuarine and lagoonal systems along the Portuguese coast. Hepatopancreatic extracts were submitted to horizontal starch gel electrophoresis following Brock's procedure. The malate dehydrogenase patterns obtained were identical to those found by Brock. Clear interspecific differences in the leucine aminopeptidase and esterase isozyme systems were also detected. The morphological study of the shells involved 7 morphometric and 9 qualitative and semiquantitative characters. Canonical variate analysis of the morphometric characters showed that these could not be used for identification purposes. However, a clear separation between the two species was obtained by a principal-component analysis of qualitative and semiquantitative characters. The characters mainly useful for distinguishing between the two species were valve profile, shape of ventral valve junction, type of calcareous scales and shell colour.     

Surf-zone fish assemblages in south-western Australia: do adjacent nearshore habitats and the warm Leeuwin Current influence the characteristics of the fish fauna?

Nearshore fish faunas from 32 sites along 1500 km coastline of temperate south-western Australia were sampled by seine net between 1991 and 1992 to examine the species composition in sandy surf zones along this region, and to determine whether it is influenced by adjacent nearshore habitats and the warm southward flowing Leeuwin Current. Although the ichthyofauna was diverse, with 95 species from 47 families recorded, it was numerically dominated by only a few species. Species of Atherinidae, Mugilidae, Tetraodontidae, Clupeidae and Pomatomidae, such as Atherinomorus ogilbyi, Leptatherina presbyteroides, Mugil cephalus, Aldrichetta forsteri, Torquigener pleurogramma, Hyperlophus vittatus, Spratelloides robustus and Pomatomus saltatrix, were often common to these surf zones. When the species composition of the surf zones was compared with that found in adjacent nearshore habitats, 38 and 42% of the species were shared with reefs and seagrass beds, respectively, and 22% were present in all three habitats. Classification and ordination demonstrated that the faunal composition on the west coast was distinct from that on the south coast, and within each of these regions there were discrete assemblages. There was a marked decline in the number of species on the south coast, with 20 to 66 species reported from the six west-coast assemblages and 11 to 16 species collected from the four south-coast assemblages. A high proportion of resident species was found in the surf zones on both coasts; however, there was a smaller contribution of transient species on the south coast than on the west coast. This decline in transient species was associated with the absence of tropical species on the latter coast. Benthic invertevores were dominant on both coasts, while trophic diversity decreased and the proportion of zooplanktivores increased on the south coast. These differences in the characteristics of the fish fauna between the two coasts can be related to the presence of seagrass beds and limestone patch reef adjacent to sandy surf-zone areas on the west coast which provide more microhabitats for fish. The presence of inshore limestone reefs along the west coast moderates wave energy, producing more sheltered and temporally stable surf zones. The lower number of species on the south coast can also be attributed to the reduced influence of the Leeuwin Current. This southward flowing current acts as a mechanism for the dispersal of tropical species which display no regular association with the surf zones on the lower west coast.     

Fine-scale chemical fingerprinting of an open coast crustacean for the assessment of population connectivity

Chemical fingerprinting techniques recently have been used to track larval dispersal of estuarine species that bear calcified structures, but the applicability of this important approach may be limited on the open coast where chemical signatures may be less distinctive and for the many species that do not retain calcified structures throughout development. Externally brooded embryos of the porcelain crab, Petrolisthes cinctipes, and inductively coupled plasma mass spectrometry were used to determine whether fine-scale variation in trace-elemental composition occurred along an open coast. Embryos were collected from 16 sites from 37.8° to 39.5° north latitude along the Pacific Coast of California, USA during late January and early February 2003. Discriminant function analysis revealed that collection sites, many separated by only a few kilometers along an open coast, could be differentiated with an overall accuracy of 73%, and combining the sites into three regions increased the accuracy to 88%. Thus, distinctive elemental signatures can be detected in open coast species even at a fine scale raising the possibility that larval tags can be developed for many more species than previously thought possible.     

Lack of population structure in the fiddler crab Uca annulipes along an East African latitudinal gradient: genetic and morphometric evidence

Phylogeographic patterns in Uca annulipes sampled from 30 locations across an East African latitudinal gradient were investigated using mitochondrial DNA cytochrome oxidase I sequences and analysed together with patterns of morphometric differentiation. Four hundred and four specimens along the east African coast were sampled, and 18 haplotypes were encountered. Haplotype and nucleotide diversity values were very low and the phylogenetic analysis did not reveal any clear phylogeographic structure. Furthermore, the analysis of molecular variance and pairwise Φ _ST values showed no significant spatial population differentiation. Mismatch analyses and tests of neutrality supported the hypothesis that this species has undergone a fairly recent demographic expansion. Our results, therefore, failed to demonstrate significant geographical structure in the pattern of genetic variation, indicating that populations of U. annulipes are capable of extensive gene flow among mangroves along the coast. The genetic structure of this species could be panmictic due to a high amount of gene flow along the geographical gradient in study during the planktonic larval phase, when larvae are carried along stream by the dominant currents. Moreover, the morphometric analysis performed did not reveal differences of shape differentiation according to a geographical pattern, although significant differences among the sampling areas were found.     

Oculina patagonica: a non-lessepsian scleractinian coral invading the Mediterranean Sea

The scleractinian coral Oculina patagonica De Angelis is a new immigrant from the Southwest Atlantic to the Mediterranean Sea, having established itself only recently along the Israeli coast. This species is the only scleractinian coral reported to have invaded a new region. In order to understand the swift establishment of this species along the Israeli coast, from 1994 to 1999 we studied its distribution, abundance, reproduction, recruitment, survival, and the effect of bleaching events on its population abundance. In addition, population studies of O. patagonica were performed at several localities along the eastern and western Mediterranean coasts. Highest abundance was recorded along the Spanish coast, reaching 30lj colonies per 10 m line transect in shallow water. Second in abundance was the Israeli coast, with a maximum of 10DŽ colonies per transect. O. patagonica was rare along the coast of Italy, and absent along the Mediterranean coast of France. During the study, both mortality and recruitment along the Israeli coast were very low. In contrast, recruitment along the Spanish coast was very high. Reproduction of the species was studied using gonadal histology. O. patagonica is gonochoric. Female gonads were first observed in May and male gonads in July, both reaching maturity in late August and early September. Naturally occurring azooxanthellate colonies of O. patagonica inhabiting small dark caves developed gonads and spawned in parallel to zooxanthellate colonies exposed to light. No gonads were found in zooxanthellate colonies that underwent bleaching during the reproduction season. The high incidence of bleaching events along the Israeli coast observed throughout the years of this study may explain the low recruitment of new colonies during the same period. In view of its current recruitment patterns, we expect further expansion of O. patagonica in range and abundance in the western Mediterranean, but very small expansion of the population in the eastern Mediterranean, due to repetitive annual bleaching events.     

Worms without borders: genetic diversity patterns in four Brazilian <Emphasis Type="Italic">Ototyphlonemertes</Emphasis> species (Nemertea,Hoplonemertea)

Understanding the evolutionary processes from recent demographic history is especially difficult for interstitial organisms due to their poorly known natural history. In this study, the genetic variation and population history of the four Ototyphlonemertes (Diesing in Sitz ber Math Nat Kl Akad Wiss Wien 46:413–416, 1863) species were evaluated from samples collected along the Brazilian coast (between 27°31′S and 13°00′W) in 2006. The mitochondrial region cytochrome c oxidase subunit 3 (COX3) is analyzed to assess the genetic variation of these dioecious species. Although these species have a sympatric distribution along the coast, our data suggest that their levels of differentiation and their demographic histories differ sharply. There is strong evidence of gene flow among demes in O. erneba and O. evelinae, and their level of structuring is much lower than for the other two species. Indeed, the COX3 fragment reveals cryptic lineages in O. lactea and O. parmula. The results seem to contradict the high genetic structuring and low intrapopulational variability expected with the ecological constriction and habitat discontinuity faced by these organisms, meaning that there might be gene flow among populations or their dispersal capability has been underestimated.     

Mitochondrial control region sequence analyses indicate dispersal from the US East Coast as the source of the invasive Indo-Pacific lionfish Pterois volitans in the Bahamas

Lionfish are popular aquarium fish from the Indo-Pacific that have invaded the western Atlantic. Two species, Pterois volitans and P. miles, were well established along the United States east coast before the first lionfish were reported from the Bahamas in 2004, where they quickly dispersed throughout the archipelago by 2007. The source of the Bahamian lionfish invasion has been in question because of the hypothesized low connectivity between Florida and Bahamas reef species as well as the temporal lag in their arrival in the Bahamas. Mitochondrial control region haplotypes (680 bp) were determined and analyzed for lionfish specimens from the Bahamas, North Carolina, and two sites within their native range (Indonesia and the Philippines). Exact tests, pairwise F _st and AMOVA analyses all showed no significant differentiation between the Bahamas and North Carolina specimens. The similarity between the Bahamas and North Carolina lionfish was also reflected in a minimum spanning network and neighbor-joining distance tree generated from the data. Sequence analyses also revealed the presence of only Pterois volitans, as no P. miles were detected in the Bahamian sample. These results indicate that the source of the Bahamian lionfish is egg and larval dispersal from the United States east coast population, and support previous models of reef fish dispersal that suggest a low level of connectivity between the Bahamas and east coast of Florida.     

Genetic evidence of the presence of two species of Crassostrea (Bivalvia: Ostreidae) on the coast of Brazil

 Although oysters are commercially very important in Brazil, there is still much dispute about the number of Crassostrea species occurring on the Brazilian coast. The dispute is centered around C. brasiliana, considered by some authors to be a junior synonym of C. rhizophorae. In this paper we compared, by allozyme electrophoresis, sympatric and allopatric populations of the two putative species. Of the 17 loci analysed, five were diagnostic for the two species in sympatry (gene identity = 0.46 to 0.47), clearly demonstrating that they are distinct biological species. Heterozygosity (h) levels were high for both species (h = 0.24 to 0.28), and no heterozygote deficiencies were observed in any population (local inbreeding, F _IS  = 0.141; P > 0.70). Levels of population structure in C. rhizophorae along 1300 km of coast were very low (population inbreeding, F _ST  = 0.026; P > 0.15), indicating that the planktonic, planktotrophic larvae of these species are capable of long-range dispersal. Received: 14 January 1999 / Accepted: 8 December 1999     

Spatial and temporal variation in distribution and protein ubiquitination for <Emphasis Type="Italic">Mytilus</Emphasis> congeners in the California hybrid zone

Along the west coast of North America, the invasive mussel Mytilus galloprovincialis and a native congener M. trossulus overlap in range and compete for habitat in an extensive hybrid zone along central California. The two species have been shown to exhibit differential abiotic tolerances in laboratory studies, yet little is known about how such tolerances affect spatial and temporal patterns of geographic distribution, particularly in areas of competition. We examined distributions of the two congeners and their hybrids in neighboring intertidal and subtidal habitats in Bodega Bay, CA over 2 years, and compared shell length and seasonal ubiquitin (Ub) conjugates to estimate protein turnover and physiological stress for the species at each site. The two species were spatially segregated, with M. galloprovincialis dominating the subtidal habitat, and M. trossulus constituting a majority of the intertidal mussel population. Hybrid individuals appeared in low numbers at both sites. For each habitat, there was no statistical difference between shell lengths of M. galloprovincialis and hybrids but M. trossulus mussels were statistically smaller than the other two. In regards to physiological performance, ubiquitin conjugate values showed different seasonal cycles for the two species, suggesting different periods of peak environmental stress. The highest levels of Ub-conjugated proteins were observed in winter for M. galloprovincialis and in summer for M. trossulus, consistent with the respective range edges for their distributions since Bodega Bay is near the northern range edge of the invader and the southern edge of the native species. These findings suggest that future assessments of Mytilus populations along the California coast may need to consider vertical distributions and seasonal cycles as part of monitoring and research activities.     

Biodiversity in the ecosystem of the Portuguese continental shelf: distributional ecology and the role of benthic amphipods

The biodiversity and distributional ecology of amphipod crustaceans were analysed from benthic surveys in 1985 and 1986 along the coast of Portugal, from the Tagus canyon to the coast of Minho, in order to determine their role in the ecosystem of the Portuguese continental self. In samples obtained from different types of substrate between 18 and 545 m, we identified 113 species belonging to 51 genera of 24 families. Seventeen of these species were new records for the Portuguese coast. The relative frequencies and number of individuals of all species were analysed. The genus Ampelisca clearly dominated the group of the most frequent and abundant species, which also exhibited a large range of vertical distribution. Most of the 113 species were found only down to 150 m depth, corresponding roughly to the lower limit of the continental shelf. Fifteen species exhibited clear bathyal traits, being consistently found deeper than 100 m, especially in the Tagus canyon and the upper zone of the continental slope. The most frequent and abundant species were found predominatly or in large numbers in medium to fine sand bottoms. This type of substrate also contained the highest number of species. The granulometric structure of the habitat could constitute the most important factor controlling both biodiversity and development of large amphipod populations, since oxygen level, water exchange, number of available shelters, and probably the quantity and quality of nutritional resources all vary as a function of substrate texture. Because of their dominance in both frequency and abundance, several Ampelisca species may constitute an important food source for many secondary consumers of the shelf sediments, especially for demersal fishes.     

Population genetics of Crassostrea ariakensis in Asia inferred from microsatellite markers

Crassostrea ariakensis is an important aquacultured oyster species in Asia, its native region. During the past decade, consideration was given to introducing C. ariakensis into Chesapeake Bay, in the United States, to help revive the declining native oyster industry and bolster the local ecosystem. Little is known about the ecology and biology of this species in Asia due to confusion with nomenclature and difficulty in accurately identifying the species of wild populations in their natural environment. Even less research has been done on the population genetics of native populations of C. ariakensis in Asia. We examined the magnitude and pattern of genetic differentiation among 10 wild populations of C. ariakensis from its confirmed distribution range using eight polymorphic microsatellite markers. Results showed a small but significant global θ _ST (0.018), indicating genetic heterogeneity among populations. Eight genetically distinct populations were further distinguished based on population pairwise θ _ST comparisons, including one in Japan, four in China, and three populations along the coast of South Korea. A significant positive association was detected between genetic and geographic distances among populations, suggesting a genetic pattern of isolation by distance. This research represents a novel observation on wild genetic population structuring in a coastal bivalve species along the coast of the northwest Pacific.     

Seasonal patterns in size and abundance of <Emphasis Type="Italic">Phyllorhiza punctata</Emphasis>: an invasive scyphomedusa in coastal Georgia (USA)

Phyllorhiza punctata, commonly called the Australian white spotted jellyfish, invaded the Caribbean in the 1960s, becoming established there and subsequently in the United States in the northern Gulf of Mexico (by 2000) and eastern Florida (2001). With the prevailing Loop Current flowing clockwise around the Gulf of Mexico and joining the Gulf Stream along eastern Florida, potential transport of P. punctata along the eastern seaboard of the USA could be facilitated. P. punctata medusae were collected in small numbers along the entire Georgia coast during May–November in 2007 and 2008. Medusa bell diameters increased both years from ca. 10 cm in May to ca. 33 cm in autumn. Specimens lacked zooxanthellae, as reported for medusae in the northern Gulf of Mexico and Florida. It is possible that the P. punctata medusae observed were transported from established populations to the south; however, whether or not this species is established along the Georgia coast has yet to be determined.     

Multiple trans-Arctic passages in the red alga Phycodrys rubens: evidence from nuclear rDNA ITS sequences

In order to investigate how episodes of geological and climatic change have influenced the distribution and evolutionary diversification of Arctic to cold temperate-North Atlantic seaweed species, intraspecific genetic variation was analyzed among isolates of the sublittoral, benthic red alga Phycodrys rubens (collected between June 1992 and January 1994). Rooted phylogenetic analyses of nuclear ribosomal DNA internal transcribed spacer (ITS) sequences and the plastid encoded Rubisco spacer sequences suggest that P. rubens invaded the North Atlantic from the Pacific shortly after the opening of the Bering Strait (3 to 3.5 million years ago), colonizing both the western and eastern Atlantic coasts. Based on these data we further hypothesize that P. rubens survived along the European coasts during the more recent Pleistocene glaciations, while becoming locally extinct along the North American Atlantic coasts. Following retraction of the last ice sheet, the western Atlantic coast was colonized a second time from the Pacific. The presence of two distinct genetic types (based on ITS and Rubisco sequences) along the European coasts is postulated to be a result of isolation and subsequent differentiation. This is likely because ice-free areas are known to have existed in northern Scotland and Norway during the last glaciation. The presence of an East Atlantic genetic type along the West Atlantic coast is believed to be a recent introduction (caused by human activity) of P. rubens to Newfoundland.     

Die verbreitung der uferwanzen (Heteroptera: Saldidae) im brackigen und marinen litoral der nordamerikanischen pazifikküste

Shore bugs (Heteroptera: Saldidae) were collected during summer 1973 along the Pacific Coast of North America between the arctic and the subtropical regions. The field studies were aimed at determining the species-specific upper and lower limits of distribution in the littoral, and the distribution range of these species in estuaries. The saldids inhabiting the littoral zones can be divided into two groups: those species which live mainly along the coast (coastal species), and those which live mainly inland (inland species). Species found in the supralittoral occur at inland localities as well, and thus can either tolerate limnetic-oligohaline conditions (Salda littoralis, S. provancheri, Saldula coxalis) or are confined to habitats along salt lakes (Pentacora signoreti). Inhabitants of the eulittoral can either occur in the supralittoral and inland localities as well and are holeuryhaline (Saldula palustris, S. pallipes), or have disconnected inland populations (S. nigrita), or they live exclusively in the intertidal zones. In the subarctic, coastal species are distributed from the intertidal zones to inland limnetic habitats. The increasing aridity of southern climatic zones may act as a limiting factor confining the distribution of coastal species to the coast. On the other hand, the distribution of inland species may be influenced by competition with the coastal forms.

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Mit dankenswerter Unterstützung der Deutschen Forschungsgemeinschaft.     

Invasion by the marine gastropod<Emphasis Type="Italic"> Ocinebrellus inornatus</Emphasis> in France. III. Comparison of biological traits with the resident species<Emphasis Type="Italic"> Ocenebra erinacea</Emphasis>

Invasive species impacts on native species and communities have been widely recognised for decades and may involve important economical losses. In this study, we examined two marine muricid gastropods: an invader, Ocinebrellus inornatus, and a resident, Ocenebra erinacea. Both species co-occur on French Atlantic coasts and probably have economical impacts on oyster farming areas of the Charente-Maritime region of France. In previous studies, we investigated the introduction source and the expansion patterns of O. inornatus, using molecular markers. However, these studies are not sufficient to fully understand the expansion dynamics of the exotics. The present framework is devoted to comparing life-history traits between the introduced and resident species. Our results first showed that O. inornatus has more favourable traits, such as a better mean growth rate and a higher reproductive effort, in comparison with O. erinacea. These traits may explain the invader establishment and, partly, its spread along the coast of France. Secondly, the resident species drilled a higher rate of oysters than the invader. Finally, the establishment of O. inornatus in France does not seem to be at the expense of O. erinacea because: (1) resources are not limiting in oyster farming areas and (2) there does not appear to be competition by interference between the species.Communicated by O. Kinne, Oldendorf/Luhe     

Cryptobenthic fishes of the “Ciclopi Islands” marine reserve (central Mediterranean Sea): assemblage composition,structure and relations with habitat features

The fish assemblage of the Ciclopi Islands marine reserve, which is located along the eastern coast of Sicily (Central Mediterranean), was unknown until our study provided insight into the cryptobenthic fish assemblage inhabiting this integral reserve zone. Visual census surveys were periodically conducted along the littoral rocky shores of Lachea, the largest island of the Ciclopi archipelago. The fish assemblage, which comprised 20 species belonging to Blenniidae, Gobiidae, Tripterygiidae, Scorpaenidae and Gobiesocidae, was dominated by Scorpaena maderensis and Trypterigion delaisi. Species richness (S) did not show significant differences between the northern, eastern, southern and western island coasts, whereas both species diversity (H) and evenness (J) were significantly higher on the western coast than on the northern coast. The effect of the island coast on fish density was not significant with regard to the whole assemblage or to single species, except for S. maderensis and T. delaisi. The pattern of variation of assemblage parameters was mainly positively correlated with microhabitat variables, especially substratum composition and type of cover. The best predictors of fish total density were bottom slope, rugosity and substratum composition. Variations in relative species density were specified by a different combination of macro- and microhabitat variables. The density pattern of S. maderensis showed a positive relationship with depth. In T. delaisi, the influence of slope was interrelated to that of exposure to waves. This species preferentially inhabited flat habitat, sheltered from the open sea and covered by small boulders, but also more-exposed rockwalls. The population densities of Tripterygion melanurus and Lipophrys trigloides were negatively affected by depth, thus reflecting their preference for the upper infralittoral. T. melanurus was associated with a more complex habitat (stones and boulders), whereas L. trigloides was mainly censused on a narrow strip of solid rock between the waterline and 1 m depth.Communicated by R. Cattaneo-Vietti, Genova     

High levels of genetic subdivision in peripherally isolated populations of the atherinid fish Craterocephalus capreoli in the Houtman Abrolhos Islands,Western Australia

The atherinid fish Craterocephalus capreoli Rendahl is abundant in the Houtman Abrolhos Islands, 70 km off the Western Australia coast and 250 km south of the southern limit of the range of the species along the mainland. Electrophoretic examination of 7 allozyme loci at 17 sites in the Houtman Abrolhos revealed a substantially lower level of polymorphism than found in an earlier study of the species in its mainland distribution, with many of the uncommon alleles and some common ones missing. There is a very high degree of genetic subdivision among the populations in the Houtman Abrolhos, measured by a mean F _ST of 0.437 over a distance of 35 km. This F _ST (standardized variance in allelic frequencies) is six times that found previously among populations along the mainland coast over distances up to 850 km. The subdivision of populations in the Houtman Abrolhos is similar within one island group on a scale up to 12 km, and between two groups that are separated by 15 km of deep water. Significant differences in allelic frequencies were found between populations from the open shore and enclosed lagoons less than 800 m apart, but the overall levels of subdivision were similar for the two types of environment. Previous work had shown high levels of genetic subdivision in the Houtman Abrolhos for a gastropod with direct development. The results for C. capreoli demonstrate that the archipelago favours subdivision even for a species with potentially much greater mobility and different life history.     

Riverine and marine ecotypes of <Emphasis Type="Italic">Sotalia</Emphasis> dolphins are different species

The current taxonomic status of Sotalia species is uncertain. The genus once comprised five species, but in the twentieth century they were grouped into two (riverine Sotalia fluviatilis and marine Sotalia guianensis) that later were further lumped into a single species (S. fluviatilis), with marine and riverine ecotypes. This uncertainty hampers the assessment of potential impacts on populations and the design of effective conservation measures. We used mitochondrial DNA control region and cytochrome b sequence data to investigate the specific status of S. fluviatilis ecotypes and their population structure along the Brazilian coast. Nested-clade (NCA), phylogenetic analyses and analysis of molecular variance of control region sequences showed that marine and riverine ecotypes form very divergent monophyletic groups (2.5% sequence divergence; 75% of total molecular variance found between them), which have been evolving independently since an old allopatric fragmentation event. This result is also corroborated by cytochrome b sequence data, for which marine and riverine specimens are fixed for haplotypes that differ by 28 (out of 1,140) nucleotides. According to various species definition methods, we conclude that marine and riverine Sotalia are different species. Based on priority criteria, we recommend the revalidation of Sotalia guianensis (Van Bénéden 1864) for the marine animals, while riverine dolphins should retain the species name Sotalia fluviatilis (Gervais 1853), thus becoming the first exclusively riverine delphinid. The populations of S. guianensis show a strong subdivision (Φ_ST=0.628) along the Brazilian coast, with at least three evolutionarily significant units: north, northeastern and south/southeastern.     

Geographic variation,niche breadth and genetic differentiation at different geographic scales in the mussels Mytilus californianus and M. edulis

Genetic differentiation was investigated in the marine mussels Mytilus californianus Conrad and M. edulis Linn. from the west coast of North America. In allopatry with M. californianus, M. edulis occurs throughout the intertidal zone; however, in microgeographic sympatry its ecological range is restricted to above the M. californianus mussel bed and to patches of substratum opened by natural disturbances within the bed. Over the same geographic scale, the broader-niched M. edulis shows greater among-locality genetic difference and greater levels of polymorphism than M. californianus at two enzyme loci. Genetic differentiation on a geographic basis was investigated in M. californianus at a single rock (on a scale of meters), on an island (on a scale of kilometers), throughout a strait (on a scale of 10² kilometers), and along the west coast of North America (on a scale of 10³ km). Differentiation was minimal over the west coast, and could be explained by microhabitat differences in a local area. The minimal differentiation in west coast mussels relative to strong geographic differentiation of M. edulis on the east coast of North America may be related to the steeper latitudinal thermal gradient on the east coast. Local ecologically related microgeographic variation can result in biased and misleading estimates of genetic heterogeneity but microgeographic variation at enzyme loci may not be due to selection at the loci investigated or may even be due to the breeding structure of the mussel populations, as suggested by Tracey et al. (1975).