Size-based variation in intertissue comparisons of stable carbon and nitrogen isotopic signatures of bull sharks (Carcharhinus leucas) and tiger sharks (Galeocerdo cuvier)

Stable isotopes are important tools for understanding the trophic roles of elasmobranchs. However, whether different tissues provide consistent stable isotope values within an individual are largely unknown. To address this, the relationships among carbon and nitrogen isotope values were quantified for blood, muscle, and fin from juvenile bull sharks (Carcharhinus leucas) and blood and fin from large tiger sharks (Galeocerdo cuvier) collected in two different ecosystems. We also investigated the relationship between shark size and the magnitude of differences in isotopic values between tissues. Isotope values were significantly positively correlated for all paired tissue comparisons, but R2 values were much higher for δ13C than for δ15N. Paired differences between isotopic values of tissues were relatively small but varied significantly with shark total length, suggesting that shark size can be an important factor influencing the magnitude of differences in isotope values of different tissues. For studies of juvenile sharks, care should be taken in using slow turnover tissues like muscle and fin, because they may retain a maternal signature for an extended time. Although correlations were relatively strong, results suggest that correction factors should be generated for the desired study species and may only allow coarse-scale comparisons between studies using different tissue types

Contrasting patterns of individual specialization and trophic coupling in two marine apex predators

1. Apex predators are often assumed to be dietary generalists and, by feeding on prey from multiple basal nutrient sources, serve to couple discrete food webs. But there is increasing evidence that individual level dietary specialization may be common in many species, and this has not been investigated for many marine apex predators. 2. Because of their position at or near the top of many marine food webs, and the possibility that they can affect populations of their prey and induce trophic cascades, it is important to understand patterns of dietary specialization in shark populations. 3. Stable isotope values from body tissues with different turnover rates were used to quantify patterns of individual specialization in two species of ‘generalist’ sharks (bull sharks, Carcharhinus leucas, and tiger sharks, Galeocerdo cuvier). 4. Despite wide population-level isotopic niche breadths in both species, isotopic values of individual tiger sharks varied across tissues with different turnover rates. The population niche breadth was explained mostly by variation within individuals suggesting tiger sharks are true generalists. In contrast, isotope values of individual bull sharks were stable through time and their wide population level niche breadth was explained by variation among specialist individuals. 5. Relative resource abundance and spatial variation in food-predation risk tradeoffs may explain the differences in patterns of specialization between shark species. 6. The differences in individual dietary specialization between tiger sharks and bull sharks results in different functional roles in coupling or compartmentalizing distinct food webs. 7. Individual specialization may be an important feature of trophic dynamics of highly mobile marine top predators and should be explicitly considered in studies of marine food webs and the ecological role of top predators

Provision of ecosystem services by human-made structures in a highly impacted estuary

Water filtration is one of the most important ecosystem services provided by sessile organisms in coastal ecosystems. As a consequence of increased coastal development, human-made shoreline structures (e.g., docks and bulkheads) are now common, providing extensive surface area for colonization by filter feeders. We estimate that in a highly urbanized sub-tropical estuary, water filtration capacity supported by filter feeding assemblages on dock pilings accounts for 11.7 million liters of water h−1, or ~30% of the filtration provided by all natural oyster reef throughout the estuary. Assemblage composition, and thus filtration capacity, varied as a function of piling type, suggesting that the choice of building material has critical implications for ecosystem function. A more thorough depiction of the function of coastal ecosystems necessitates quantification of the extensive ecosystem services associated with human-made structures

Shared and unique features of predator-associated morphological divergence in three livebearing fishes

Divergent natural selection (fitness trade-offs) between environments often drives intraspecific diversification. When multiple species face a common environmental gradient their patterns of divergence might exhibit both shared and unique elements. We investigated shared and unique elements of diversification for three species of livebearing fishes (Poeciliidae) across a predator gradient (piscivorous fish vs. no piscivorous fish). All species (Gambuia affinis from the United States, G. hubbsi from the Bahamas and P. reticulata from Trinidad) exhibited a posterior shift in body allocation and more elongate bodies in predator populations. This morphological shift applied not only across species, but across age/gender classes, particular predator species and gross habitat types. Each species also had unique features of divergence, which may reflect peculiarities unique to their natal environments. We hypothesize much of the predator-associated morphology enhances fitness in the presence of predators but decreases fitness in the absence of predators. Preliminary evidence supports this hypothesis. We additionally found gonopodium size divergence in both Gambusia species that was opposite a trend previously found in P. reticulata. Partitioning phenotypic variation for multiple species into shared and unique responses across environmental gradients is a useful tool for elucidating general and localized mechanisms of diversification. Divergent natural selection (DNS) is a powerful mechanism that generates and maintains phenotypic diversity (Rice and Hostert 1993; Orr and Smith 1998; Schluter 2000b). DNS is created by functional trade-offs between alternative environments (Robinson and Wilson 1994; Robinson et al. 1996; Schluter 2000b). Depending on how environments vary (e.g. fine- or coarse-grained variation; sensu Levins 1968), DNS can lead to evolution of either canalized genetic differences between populations or phenotypic plasticity (West-Eberhard 1989; Robinson and Wilson 1994; Orr and Smith 1998; Schluter 2000b). DNS results in population differentiation through either of these mechanisms. That is, populations may differ from each other because of fixed genetic differences or because each is similarly plastic but their current environments differ. Environmental differences that typically produce population divergence include predation, competition, or abiotic stresses (Magurran and May 1999; Schluter 2000b). Consider the case where the sign of selection on focal traits differs across environments. Consider also that several species are evolving adaptive solutions in these environments. Some elements of evolutionary response will be similar across species. For example, species A and B may largely respond in a similar manner. Yet other aspects of response to DNS will be speciesspecific (A responds one way; B responds differently). In theory, after accounting for gross differences between species, the unique and shared elements of response to DNS can be identified. This approach allows one to integrate the study of phenotypic variation across selective environments, populations and species. Empirical studies of diversification in vertebrates has focused on resource competition and niche partitioning (Robinson and Wilson 1994; Van Valkenburgh and Wayne 1994; Smith and Skulason 1996; Schluter 2000a). However, predation is among the most important factors structuring natural populations (Sih et al. 1985; Kerfoot and Sih 1987; Jackson et al. 2001). Predators should not only change the distribution and abundance of species (via lethal and behavioral impacts on prey), but should also produce diversification—changes in the distribution and abundance of phenotypes within species (Endler 1995; DeWitt et al. 2000; Trussell 2000; Van Buskirk and Schmidt 2000). Although predation is often thought responsible for the evolution of inducible defenses among invertebrates (Harvell 1986; Havel 1987; Tollrian and Harvell 1999), studies investigating the importance of predation in vertebrate diversification are less common. Most studies of vertebrate evolutionary responses to predation center on life history changes (e.g. Skelly and Werner 1990; Rodd and Reznick 1997; Belk 1998; Johnson and Belk 2001; Reznick et al. 2001). Investigation of morphological divergence between alternative predator environments in vertebrates is less common (Brönmark and Miner 1992; Van Buskirk et al. 1997; Walker 1997; Lardner 2000; Relyea 2001). In this study, we examined body shape divergence in three species of livebearing fishes across alternative predator regimes. Furthermore we evaluate trends within and between species to identify both unique and shared aspects of diversification among prey species

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Erratum: Corrigendum: Sequence and comparative analysis of the chicken genome provide unique perspectives on vertebrate evolution

International Chicken Genome Sequencing Consortium. The Original Article was published on 09 December 2004. Nature432, 695–716 (2004). In Table 5 of this Article, the last four values listed in the ‘Copy number’ column were incorrect. These should be: LTR elements, 30,000; DNA transposons, 20,000; simple repeats, 140,000; and satellites, 4,000. These errors do not affect any of the conclusions in our paper. Additional information. The online version of the original article can be found at 10.1038/nature0315

Comparison of Fish Assemblages in Restored and Natural Mangrove Habitats Along an Urban Shoreline

The installation of living shorelines is one strategy used to ameliorate habitat degradation along developed coastlines. In this process, existing hard structures, such as sea walls and riprap revetments, are supplemented with habitat forming species, e.g., oysters and mangrove trees, to improve habitat quality and function. Shoreline restorations in Biscayne Bay, Florida, USA, often utilize red mangroves, Rhizophora mangle (Linneaus, 1753), in addition to riprap revetments, to help stabilize the shoreline. This riprap-mangrove habitat provides structure for marine organisms to utilize and is believed to improve shoreline habitats in areas previously cleared of mangroves. We examined whether habitat provisioning was similar between restored mangrove habitat with the inclusion of riprap boulders and natural mangrove shorelines. We compared fish assemblages between natural mangrove and riprapmangrove habitats within two areas of northern Biscayne Bay. Fish community structure and certain benthic cover types varied between mangroves and riprap-mangrove habitats. Total fish abundance was greater in mangrove habitat, while taxonomic richness was highest in riprap-mangrove sites in the northern part of the bay. Our findings suggest that fish assemblages and community structure are different between these habitat types, although the geographic context may mediate the effect of habitat type. Therefore, it is likely that these restored mangroves provide different ecological services than unaltered mangrove shorelines

Economic Valuation of the Chinook Salmon Sport Fishery of the Gulkana River, Alaska, under Current and Alternate Management Plans

This paper extends the standard travel cost method (TCM) to develop estimates of the economic value of recreational chinook salmon fishing on the Gulkana River, Alaska, under existing and hypothetical fishery management conditions. Respondents were asked to state how the number of trips that they took to the study area would change if alternative fishery management practices were imposed. Three hypothetical management conditions were considered: a doubled 1992 sport fish harvest, a doubled daily bag limit, and a season bag limit of five. Each of the hypothetical fishery management conditions provides increased economic returns to anglers.

Data from: Anthropogenic ecosystem fragmentation drives shared and unique patterns of sexual signal divergence among three species of Bahamian mosquitofish

When confronted with similar environmental challenges, different organisms can exhibit dissimilar phenotypic responses. Therefore, understanding patterns of phenotypic divergence for closely related species requires considering distinct evolutionary histories. Here, we investigated how a common form of human-induced environmental alteration, habitat fragmentation, may drive phenotypic divergence among three closely related species of Bahamian mosquitofish (Gambusia spp.). Focusing on one phenotypic trait (male coloration), having a priori predictions of divergence, we tested whether populations persisting in fragmented habitats differed from those inhabiting unfragmented habitats and examined the consistency of the pattern across species. Species exhibited both shared and unique patterns of phenotypic divergence between the two types of habitats, with shared patterns representing the stronger effect. For all species, populations in fragmented habitats had fewer dorsal-fin spots. In contrast, the magnitude and trajectory of divergence in dorsal-fin color, a sexually selected trait, differed among species. We identified fragmentation-mediated increased turbidity as a possible driver of these trait shifts. These results suggest that even closely related species can exhibit diverse phenotypic responses when encountering similar human-mediated selection regimes. This element of unpredictability complicates forecasting the phenotypic responses of wild organisms faced with anthropogenic change – an important component of biological conservation and ecosystem management