Comparative Phylogeography of North American Atlantic Salt Marsh Communities

Identifying differential population structure within metacommunities is key toward describing the mechanisms that maintain biodiversity in natural systems. At both local and regional scales on the North American Atlantic coast, we assessed phylogeographic and genetic diversity patterns of six common salt marsh invertebrates using equivalent sampling schemes and sequence data from the same mitochondrial locus. In general, our results suggest little genetic structure across four previously sampled biogeographic regions and a slight increase in genetic diversity from northern to southern areas; however, two of the species (Geukensia demissa and Uca pugilator) exhibited significant differentiation between the northernmost populations and other regions, consistent with a number of previous studies. Although the minimal genetic structure recovered in this community is consistent with expectations based on the larval life history of the species examined, confirmation of this result suggests that latitudinal shifts in ecological interactions in salt marsh systems are environmentally driven, rather than due to heritable adaptation.     

Genetical Processes of Evolution on High Oceanic Islands

The Hawaiian Drosophila project has been in progress for 20 years. Recently, emphasis has been placed on studies of genetic variability in natural populations. The data generated are of extraordinary interest for understanding the genetic basis of evolution. The findings are relevant not only to islands forms but also to species in continental ecosystems. Chromosomal, electrophoretic and morphometric studies of specimens from local populations (demes) of island species have shown them generally to be as rich in genetic variability as demes of widespread continental species. The main difference between continntal and insular species is that the latter have smaller total population sizes insular species have fewer demes. On high volcanic islands, the most striking mode of speciation is through one or a few inter-island or inter-volcano founders. The case of Drosophila silvestris from the island of Hawaii is presented. Enforced isolation appears to foster genetic divergence. An unexpected results is that the founder effect does not drasticaly reduce genetic variablity. Rather, it appears to induce a shift in the polygenic heterozygous balances that underlie the genetics of quantitative characters, especially those dealing with mating behavior.In view of these findings, the well-known exuberance of novel adaptations and species observed on isolated oceanic islands is understandable.     

Population Genetic Structure of the New Zealand Estuarine Clam <Emphasis Type="Italic">Austrovenus stutchburyi</Emphasis> (Bivalvia: Veneridae) Reveals Population Subdivision and Partial Congruence with Biogeographic Boundaries

We examined the population genetic structure of the New Zealand endemic clam, Austrovenus stutchburyi, to determine (1) whether populations of this estuarine taxon are genetically subdivided and (2) if the locations of genetic boundaries were congruent with known biogeographic break points. We obtained sequences of the mitochondrial gene cytochrome c oxidase I for 372 A. stutchburyi from 29 New Zealand estuaries and conducted analyses to identify population genetic structure. We detected a pattern of genetic isolation by distance and identified six A. stutchburyi subpopulations, a greater number of subpopulations than reported for much of New Zealand’s open coast benthos. Although these data indicate that long distance dispersal may be less frequent in estuarine than in open coast taxa, partial congruence between genetic and biogeographic boundaries suggests that historical events and natural selection may also contribute to the observed population genetic structure.     

Ostracods as tsunami tracers in Holocene sequences

This review analyses the ostracod record in Holocene tsunami deposits, using an overview of the 2004 Indian Ocean tsunami impact on its recent populations and the associated tsunamigenic deposits, together with results from numerous investigations of other Holocene sequences. Different features such as the variability of the local assemblages, population density, species diversity, age population structure (e.g., percentages of adults and juvenile stages) or taphonomical signatures suggest that these microorganisms may be included amongst the most promising tracers of these high-energy events in marshes, lakes, lagoons or shallow marine areas.     

Morphological and genetic variation among shortnose sturgeonAcipenser brevirostrum from adjacent and distant rivers

Shortnose sturgeon,Acipenser brevirostrum, is a small, endangered species which occurs in 19 estuary systems along the east coast of North America. These populations are considered as separate entities by the U. S. National Marine Fisheries Service although evidence of morphologic or genetic differentiation among populations has not been documented. The purpose of this study was to compare morphological and genetic atributes among shortnose sturgeon collected from the Kennebec and Androscoggin Rivers, Maine, and the Hudson River, New York. Six morphometric and five meristic characteristics were quantified. Multivariate and univariate analyses of covariance and variance were used to assess differences among populations. Our analyses provided evidence for distinct populations in the Androscoggin and Kennebec Rivers, but character differentiation was greater between fish from these two locations and the Hudson River. Analysis of morphometric characters indicated significant differences in fish shape among the three rivers, with Hudson River sturgeon differing from the Maine rivers for the characters of head length, snout length, and mouth width. Significant differences were observed for meristic characters, but pairwise comparisons did not reflect a clear pattern of variability. Sequencing of a portion of the mitochondrial DNA control region revealed 15 haplotypes among 73 total specimens from the three rivers. Shortnose sturgeon from the Kennebec and Androscoggin Rivers were different from each other (p=0.0260); both differed significantly (p<0.0001) from the Hudson River collection. Gene flow was estimated at approximately 7 female migrants per generation between the two Maine populations and about 1 per generation between each of the Maine populations and the Hudson River population. Such strong stock structuring among presumably recently established post-Pleistocene (<10,000 yr) populations suggests that this species occurs in highly discrete units. Morphological and genetic variation observed in this study combined with current knowledge of life history attributes of shortnose sturgeon indicate that conservative management decisions are necessary until the patterns and extent of differentiation among populations species-wide can be investigated further.     

A pseudo-genetic algorithm suited to compositional data

Genetic algorithms can solve least-squares problems where local minima may trap more traditional methods. Although genetic algorithms are applicable to compositional as well as noncompositional data, the standard implementation treats compositional data awkwardly. A need to decode, renormalize, then reincode the fitted parameters to regain a composition is not only computationally costly, but may thwart convergence. A modification to the genetic algorithm, described here, adapts the tools of reproduction, crossover, and mutation to compositional data. The modification consists of replacing crossover with a linear mixture of two parents and replacing mutation with a linear mixture of one of the members of the breeding population and a randomly generated individual. By using continuously evolving populations, rather than discrete generations, reproduction is no longer required. As a test of this new approach, a mixture of four Gaussian functions with given means and variances are deconvolved to recover their mixing proportions.     

Winter Flounder Larval Genetic Population Structure in Narragansett Bay,RI: Recruitment to Juvenile Young-of-the-Year

The genetic population structure of winter flounder larvae was examined in Narragansett Bay, RI. Winter flounder larvae collected from 20 stations within Narragansett Bay and one station outside of the Bay were analyzed for six microsatellite loci. When analyzed by geographic collection sites, there were 16 distinct genetic populations of winter flounder larvae (R _ST values from 0.1 to 0.6). The presence of distinct genetic populations was supported by assignment of individual larvae to populations by Bayesian analysis. Bayesian analysis resulted in 14 distinct genetic populations that overlapped with the geographically distributed populations (R _ST values from 0.1 to 0.6). Young-of-the-year juveniles collected in the same year as the larvae were also analyzed at the same six microsatellite loci. Juveniles were assigned to larvae populations by both a Bayesian approach and a neural network approach. Juveniles collected from within Narragansett Bay were found to arise from geographically adjacent Narragansett Bay winter flounder larval populations (>99%), suggesting no widespread movement of juveniles away from spawning grounds. These results are discussed in the context of winter flounder population biology in Narragansett Bay, RI.     

Response of macrobenthic communities to restoration efforts in a New England estuary

Changes in macrobenthic communities were studied over a 3.5 yr period following restoration activities in Alewife Cove, a small estuary located in southeastern Connecticut, U.S. Development around this estuary had resulted in reduced freshwater and tidal inflows, loss of critical habitats such as salt marshes, and eutrophication. Early in 1988 the lower reach of the estuary was dredged to increase tidal flushing and enhance environmental quality. Following dredging, tidal range within the Cove increased from 52 to 83 cm. Due to erosion within the Cove's lower channel and sediment migration into the Cove, tidal flows and ranges approached pre-dredge levels by 1991. Despite these changes, the percentage of silt/clay in the surface sediments in the middle and upper basins of the Cove declined by 30–45% over the study period. Changes in infaunal community structure in the lower reach following dredging were not great, primarily comprising shifts in the relative abundances of species typical of sandier versus muddier sediments. Directional changes in community structure were most evident in the middle and upper basins, away from the dredged area. Infaunal species richness increased significantly, with many species previously found only in the sand habitats of the lower reach establishing populations in the middle and upper basins. There was a significant decrease in the summer abundances of the pollution indicator polychaeteCapitella capitata throughout much of the middle and upper basins. Restoration efforts in Alewife Cove centering on altered bydrology resulted in selected positive changes. Increases in tidal flow altered environmental conditons in the middle and upper basins where shifts in infaunal community structure indicated decreases in organic loading of sediments over 2–3 yr. Continued changes in the physical dynamics of the lower reach reduced tidal flow, arresting the positive ecological changes that were beginning to occur. This type of restoration approach of small estuaries can have positive results, but there may be a lag in the ecological response of the system. Macrobenthic communities, in particular summer abundance patterns of selected species, provided an integrated assessment of ecological changes in the Cove.     

Morphological,demographic and genetic traces of Upper Palaeolithic human impact on limpet assemblages in North Iberia

Human activities have an impact on extant biotic communities, and may have had just as important an impact in the past. We assess human impact on limpet assemblages during the Upper Palaeolithic in Asturias (north‐west Spain). The intensely exploited genus Patella exhibited a marked size decrease and a change in species assemblage composition, substituting the larger species P. vulgata for the smaller P. depressa. The present Patella assemblages in the upper tidal level exhibit the same pattern as those of the Epipalaeolithic (approx. 12 000 to 6000 years before the present). Although climate change may have contributed to such species replacement, spatial differences between close areas with different densities of Palaeolithic human settlements indicate unequivocal human impact. Present Patella species sampled from the region exhibit genetic signatures of past bottlenecks in mitochondrial DNA, which also indicate recent demographic expansion, suggesting that old impacts have been sufficiently important to leave genetic traces in current populations. Copyright © 2011 John Wiley & Sons, Ltd.     

Environmental determination of shoot height in populations of the cordgrassSpartina maritima

Spartina species tend to exhibit a range of phenotypes, often with short and tall growth forms. Such differences have been attributed variously to environmentally induced phenotypic plasticity and genetic diferentiation between populations. This work examines the basis of height variation inSpartina maritima (Curtis) Fernald at Odiel salt marshes, southwest Spain. Populations from sites with lower sediment redox potentials tended to have significantly taller shoots. Thirty-four natural populations with an 8-fold range of shoot height were transplanted to a common environment on an unvegetated, intertidal plain and shoot height was measured annually for 3 yr. There was a striking convergence in height across populations after transplantation and the change in height in each year of a population was linearly related to its initial height. Most populations grew taller after transplantation, suggesting environmental limitation in their natural habitats. Populations that were originally tall tended to become shorter. The change in shoot height was negatively related to the difference in surface sediment redox potential between their natural sites and the common transplant site. Hypoxic sediments may stimulate stem growth, resulting in improved photosynthetic gas exchange and internal aeration of roots and rhizomes. Although height variation inS. maritima appears mainly to be a result of phenotypic plasticity, a genetic component cannot be ruled out. This study emphasizes the importance of long-term studies, preferably longer than turnover time of shoot populations. The highly plastic growth form ofS. maritima allows it to colonize a wide range of habitats in environmentally heterogeneous salt marshes.     

Evaluating Adaptive Processes for Conservation and Management of Estuarine and Coastal Resources

This special feature: Genetic Structure and Adaptation in Coastal Ecosystems emphasizes the importance of research focused on population genetic structure and evolutionary change for understanding estuarine and coastal communities. Many studies have examined the effect of environmental gradients on community-level patterns in estuarine habitats; however, relatively little is known about the role of genetically based adaptation (the heritable response to these environmental gradients) in these organisms. This special feature presents 11 studies that use a variety of approaches including ecophysiology, ecological genetics, molecular markers, and patterns of gene expression occurring within these populations. These studies provide examples of the role of genetic diversity and adaptation across a diversity of estuarine and coastal environments, and highlight the temporal and spatial scales at which adaptation impinges upon management. This collection of papers is especially timely, given the increasing importance of understanding and predicting the response to global climate change in order to effectively manage these communities.     

Vegetation history of the penultimate glacial period (Marine isotope stage 6) at Ioannina,north‐west Greece

The vegetational history of the penultimate glacial period, Marine Isotope Stage (MIS) 6 (c. 185–135 ka), has remained relatively unexplored. Here we present a new record from the Ioannina basin, north‐west Greece, which constitutes the highest‐resolution terrestrial pollen record for this interval produced to date. It shows that the vegetation history of MIS 6 in this region can be divided into two parts: an early period (185–155 ka) with pronounced oscillations in tree population extent, and a later period (155–135 ka) with much smaller tree populations and subdued oscillations. This pattern is analogous to the MIS 3/MIS 2 division during the last glacial in the same sequence, although the early part of MIS 6 had larger Pinus populations and fewer temperate trees relative to the equivalent interval in MIS 3. This implies cooler and wetter conditions, which is somewhat counterintuitive given the high summer insolation during MIS 6e, but is in line with other palaeoclimatic evidence from the Mediterranean. Comparison with North Atlantic records suggests that despite the absence of pronounced iceberg discharges during MIS 6, North Atlantic millennial‐scale variability had a significant downstream impact on tree populations in north‐west Greece. Copyright © 2011 John Wiley & Sons, Ltd.     

Interannual and long-term variation in the nearshore fish community of the mesohaline Hudson River estuary

The detection of long-term shifts in species composition and spatial structuring of aquatic communities may be obscured by high levels of interannual variation. Estuarine fish communities are likely to exhibit high levels of variation owing to the influence of riverine forcing and the importance of anadromous and transient species, whose abundances may not be locally controlled. We describe patterns of interannual variation and long-term shifts in the nearshore fish community of the mesohaline Hudson River estuary based on 21 yr of beach seine sampling conducted annually between late August and mid November. Of the 60 species encountered, the most abundant were Atlantic silversides (Menidia menidia), striped bass (Morone saxatilis), white perch (Morone americana), American shad (Alosa sapidissima), and blueback herring (Alosa aestivalis). Relationships between annual community composition and seasonal flow and temperature regimes were examined with canonical correspondence analysis. Annual variation was most closely correlated with river flows in the 3-mo period preceding fish sampling, indicating a persistent effect of environmental conditions on community structure. Despite significant interannual variation in composition, longer-term trends in community structure were observed. These included declines in catch rates of freshwater and estuarine species and a dramatic increase in the catch of Atlantic silversides, an annual marine species. Associated with these changes were declines in community diversity and increased compositional variation. These results indicate that analyses of temporal changes in community structure need to account for the multiple time scales under which forcing factors and community composition vary.     

Indian monsoon variability during the last 46 kyr: isotopic records of planktic foraminifera from southwestern Bay of Bengal

The Indian monsoon carries large amounts of freshwater to the northern Indian Ocean and modulates the upper ocean structure in terms of upwelling and productivity. Freshwater-induced stratification in the upper ocean of the Bay of Bengal is linked to the changes in the Indian monsoon. In this study, we test the usefulness of δ¹⁸O and δ¹³C variability records for Globigerina bulloides and Orbulina universa to infer Indian monsoon variability from a sediment core retrieved from the southwestern Bay of Bengal encompassing the last 46 kyr record. Results show that the northeast monsoon was dominant during the Last Glacial Maximum. Remarkable signatures are observed in the δ¹⁸O and δ¹³C records during the Marine Isotope Stage (MIS) 3 to MIS-1. Our study suggests that Indian monsoon variability is controlled by a complex of factors such as solar insolation, North Atlantic climatic shifts, and coupled ocean–atmospheric variability during the last 46 kyr.     

Quantification of turbate microstructures through a subglacial till: dimensions and characteristics

Despite extensive study and debate regarding the significance of turbate (also known as ‘rotational’) microstructures in glacially deformed sediments, characteristics regarding the dimensions of these features remain unresolved. This study presents the first explicitly quantitative measurement and analysis of turbate microstructure dimensions, and their relation to till texture through thin section analysis. Samples were taken from coarse‐resolution horizontal and vertical transects of a macroscopically homogenous subglacial till, with subset areas of each thin section (30 mm²) analysed. The frequency and apparent a‐axes and b‐axes of both coreless and cored turbate structures (and their corestones) were measured, and simple univariate statistical methods used to establish the (in‐)variability of these dimensions through the till profile. Summarizing findings, (i) the dimensions of both cored and coreless turbate populations display log‐normal distributions when all measurements are analysed together, although not all individual sample populations possess these same distributions; (ii) turbate dimension populations are inconsistent within a sample block, precluding evaluation of turbate variability through a profile from single thin sections; (iii) analysis of turbate morphology and variability provisionally indicate that the three‐dimensional structure of turbates are likely to be cylindrical or flared, while weak relationships are also observed amongst till texture, turbate dimensions and frequency.     

The upper Cenomanian (Cretaceous) ammonite Neolobites vibrayeanus () in the Middle East: taxonomic and palaeoecologic remarks

In the Middle East and Africa, the Cenomanian ammonite genus Neolobites occurs, partly in great abundance, in shallow marine shelf settings. The genus includes several species but it has remained uncertain to what extent these species reflect biospecies, chronospecies or morphological variants. Based on material from Jordan and Egypt, the morphological variation of Neolobites vibrayeanus is described and discussed. From the several species of Neolobites described in the literature, only N. vibrayeanus, N. fourtaui and N. peroni appear to deserve specific separation. Sedimentological and lithological data, notably the common occurrence in strata that were possibly deposited above storm wave base, suggest that Neolobites was able to inhabit shallow marine settings. In these settings, it seems to form a distinct assemblage with the nautiloid Angulithes. Although N. vibrayeanus shows morphological variability between distinct populations, local N. vibrayeanus assemblages seem to develop morphologically stable populations that show only a little morphological overlap with those of other areas. This may be the reason for the earlier taxonomic splitting. The occurrence in habitats in which other stratigraphically significant ammonites are often missing may be the reason for the previous poor dating of Neolobites assemblages.     

Partial Migration Across Populations of White Perch (<Emphasis Type="Italic">Morone americana</Emphasis>): A Flexible Life History Strategy in a Variable Estuarine Environment

We evaluated the prevalence of partial migration, coexisting resident and migratory life history types, within six white perch (Morone americana) populations in sub-estuaries (Upper Bay, and Potomac, Choptank, Nanticoke, James, and York Rivers) of the Chesapeake Bay. Otolith stable isotope (δ¹⁸O) values were used to resolve fish habitat use along an estuarine salinity gradient and define resident or migratory behavior. The majority of adults within Upper Bay and Potomac River populations were resident, whereas individuals from the Choptank, Nanticoke, James, and York Rivers were predominantly migratory. Beyond population differences, large interannual variability in life history types was observed, likely due to differences in estuarine conditions that influence growth rate of individuals (e.g., temperature, zooplankton density). Because we observed partial migration in all study populations, we suggest that this trait is characteristic of this species, permitting plastic responses to variation in the estuarine environment.     

Distinguishing breeding populations of mallards (Anas platyrhynchos) using trace elements

The knowledge of connectivity among breeding and overwintering populations of migratory bird species is critical for the conservation of their habitats. Conventional field work for the tracking of migratory birds involving bird banding often yields poor results due to low recovery rates, or is expensive when satellite tracking methods are used. Intrinsic tools such as genetic markers, stable isotopes, strontium isotopes and trace elements have been successfully used for tracing origins and/or migratory pathways of bird populations. We studied elemental signatures in the tail feathers to group breeding populations and an overwintering population of Mallards (Anas platyrhynchos). Tail feathers from five locations in Canada and the U.S. were analyzed using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). We used 18 elements to discriminate between Mallard populations. Linear discriminant analysis on a selected set of elements demonstrated that 93% of the Mallards could be accurately located back to their predicted locations. Mallard feathers from Arkansas (an important overwintering area), grouped together with any combination of elements as predictors. We predicted the breeding locations of overwintering Mallards from Arkansas. Our results confirm that the LA-ICP-MS technique shows high potential to estimate the origin of migratory animals.     

Quantitative Analysis of Flabellophyton from the Ediacaran Lantian Biota,South China: Application of Geometric Morphometrics in Precambrian Fossil Research

As a more efficient quantitative method for morphological analysis, geometric morphometrics is applied to the flabellate fossils Flabellophyton including Flabellophyton lantianensis and Flabellophyton strigata from Neoproterozoic Ediacaran Lantian biota, South China. Both traditional morphometric analysis (including diverging angle, length, and width distribution) and geometric morphometric analysis [including superposition of normalized area analysis, non-metric multidimensional scaling (n-MDS), Bray-Curtis similarity cluster analysis (CLUSTER) and analysis of similarities (ANOSIM)] were performed. The results indicate there are great interspecific morphological differences between F. lantianensis and F. strigata, in addition to some intraspecific variations within each species. Here we preliminarily suggest that the previously defined Flabellophyton should be subdivided into 2 genera at least: one marked by the dark transverse striated structure, and the other without. This recharacterization and reclassification work still needs further careful observation and comprehensive analysis with large number of flabellate fossils combining morphology, structure, population, and community-ecology study.     

Evaluating salt marsh restoration in Delaware Bay: Analysis of Fish response at former salt hay farms

In a continuing effort to monitor the fish response to marsh restoration (resumed tidal flow, creation of creeks), we compared qualitative and quantitative data on species richness, abundance, assemblage structure and growth between pre-restoration and post-restoration conditions at two former salt hay farms relative to a reference marsh in the mesohaline portion of Delaware Bay. The most extensive comparison, during April–November 1998, sampled fish populations in large marsh creeks with otter trawls and in small marsh creeks with weirs. Species richness and abundance increased dramatically after restoration. Subsequent comparisons indicated that fish size, assemblage structure, and growth of one of the dominant species,Micropogonias undulatus, was similar between reference and restored marshes 1 and 2 yr post-restoration. Total fish abundance and abundance of the dominant species was greater, often by an order of magnitude, in one of the older restored sites (2 yr post-restoration), while the other restored site (1 yr post-restoration) had values similar to the reference marsh. The success of the restoration at the time of this study suggests that return of the tidal flow and increased marsh area and edge in intertidal and subtidal creeks relative to the former salt hay farms contributed to the quick response of resident and transient young-of-the-year fishes.