Phylogeographic structure of brown trout (Salmo trutta) in Britain and Ireland: glacial refugia, post-glacial colonisation, and origins of sympatric populations

The phylogeographical structure of brown trout Salmo trutta in Britain and Ireland was studied using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of four mitochondrial DNA segments (16S/ND1, ND5/6, COXIII/ND5 and ND5/12S). Analysis of 3636 individuals from 83 sites-morphotypes revealed a total of 25 haplotypes. These haplotypes were nested in seven two-step clades. Although there was a clear geographical patterning to the occurrence of derived clades, admixture among ancestral clades was extensive throughout the studied area. A relevant feature of the data was that some populations contained mixtures of highly divergent clades. This type II phylogeographic pattern is uncommon in nature. Clade intermixing is likely to have taken place during earlier interglacials as well as since the Last Glacial Maximum. The anadromous life history of many S. trutta populations has probably also contributed to clade mixing. Based on the data presented here and published data, postglacial colonization of Britain and Ireland most likely involved S. trutta from at least five potential glacial refuges. Probable locations for such refugia were: south of England-western France, east of the Baltic Sea, western Ireland, Celtic Sea and North Sea. Ferox S. trutta, as defined by their longevity, late maturation and piscivory, exhibited a strong association with a particular clade indicating that they share a common ancestor. Current evidence indicates that the Lough Melvin gillaroo S. trutta and sonaghen S. trutta sympatric types diverged prior to colonization of Lough Melvin and, although limited gene flow has occurred since secondary contact, they have remained largely reproductively isolated due to inlet and outlet river spawning segregation. Gillaroo S. trutta may reflect descendents of a previously more widespread lineage that has declined due to habitat alterations particularly affecting outlet rivers. The mosaic-like distribution of mtDNA lineages means that conservation prioritization in Britain and Ireland should be based on the biological characteristics of local populations rather than solely on evolutionary lineages.

Direct and indirect effects of species displacements; an invading freshwater amphipod can disrupt leaf litter processing and shredder efficiency

Invasive species may threaten the fundamental role played by native macroinvertebrate shredders in determining energy flow and the trophic dynamics of freshwater ecosystems. Functionally, amphipods have long been regarded as mainly shredders, but they are increasingly recognized as major predators of other macroinvertebrate taxa. Furthermore, intraguild predation (IGP) between native and invasive amphipods underlies many species displacements. We used laboratory mesocosms to investigate what might happen to shredders and leaf-litter processing in water bodies invaded by the highly predatory Ponto-Caspian amphipod Dikerogammarus villosus, which is spreading rapidly throughout Europe and may soon invade the North American Great Lakes. The leaf-shredding efficiency of D. villosus was significantly lower than that of 3 Gammarus species (2 native and 1 invasive) that D. villosus has either already displaced or may be currently displacing in The Netherlands. In addition, D. villosus was a major predator of all of these native and invasive amphipod shredders and of a common isopod shredder Asellus aquaticus. Leaf processing in Gammarus and Asellus mesocosms declined rapidly in the presence of D. villosus and ceased altogether within 4 d because by then, all potential shredders had been killed and consumed. Furthermore, the shredding efficiency of surviving amphipods and isopods declined significantly within 2 d of the release of D. villosus, a result indicating that predator-avoidance behavior may override leaf processing. We discuss the implications of these direct and indirect effects of D. villosus invasions and species displacements on community structure and litter processing in aquatic ecosystems. © 2011 The North American Benthological Society.


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Late Holocene linkages between decade-century scale climate variability and productivity at Lake Tanganyika, Africa

Microlaminated sediment cores from the Kalya slope region of Lake Tanganyika provide a near-annually resolved paleoclimate record between similar to 2,840 and 1,420 cal. yr B.P. demonstrating strong linkages between climate variability and lacustrine productivity. Laminae couplets comprise dark, terrigenous-dominated half couplets, interpreted as low density underflows deposited from riverine sources during the rainy season, alternating with light, planktonic diatomaceous ooze, with little terrigenous component, interpreted as windy/dry season deposits. Laminated portions of the studied cores consist of conspicuous dark and light colored bundles of laminae couplets. Light and dark bundles alternate at decadal time scales. Within dark bundles, both light and dark half couplets are significantly thinner than within light bundles, implying slower sediment accumulation rates during both seasons over those intervals.

High incidence of cryptic repeated elements in microsatellite flanking regions of galatheid genomes and its evolutionary implications

During the development of PCR primer sets for icrosatellite marker loci from enriched genomic libraries for three squat lobster species from Galatheidae (Decapoda: Anomura); Munida rugosa (Fabricius, 1775), M. sarsi (Huus, 1935), and Galathea strigosa (Linnaeus, 1761) (collectively known as squat lobsters), a number of unforeseen problems were encountered. These included PCR amplification failure, lack of amplification consistency, and the amplification of multiple fragments. Careful examination of microsatellite containing sequences revealed the existence of cryptic repeated elements on presumed unique flanking regions. BLAST analysis of these and other VNTR containing sequences (N 5 252) indicates that these cryptic elements can be grouped into families based upon sequence similarities. The unique features characterising these families suggest that different molecular mechanisms are involved. Of particular relevance is the association of microsatellites with mobile elements. This is the first reported observation of this phenomenon in crustaceans, and it also helps to explain why microsatellite primer development in galatheids has been relatively unsuccessful to date. We suggest a number of steps that can be used to identify similar problems in microsatellite marker development for other species, and also alternative approaches for both marker development and for the study of molecular evolution of species characterised by complex genome organisation. More specifically, we argue that new generation sequencing methodologies, which capitalise on parallel and multiplexed sequencing may pave the way forward for future crustacean research.

Implications of climate change for the fishes of the British Isles

Recent climatic change has been recorded across the globe. Although environmental change is a characteristic feature of life on Earth and has played a major role in the evolution and global distribution of biodiversity, predicted future rates of climatic change, especially in temperature, are such that they will exceed any that has occurred over recent geological time. Climate change is considered as a key threat to biodiversity and to the structure and function of ecosystems that may already be subject to significant anthropogenic stress. The current understanding of climate change and its likely consequences for the fishes of Britain and Ireland and the surrounding seas are reviewed through a series of case studies detailing the likely response of several marine, diadromous and freshwater fishes to climate change. Changes in climate, and in particular, temperature have and will continue to affect fish at all levels of biological organization: cellular, individual, population, species, community and ecosystem, influencing physiological and ecological processes in a number of direct, indirect and complex ways. The response of fishes and of other aquatic taxa will vary according to their tolerances and life stage and are complex and difficult to predict. Fishes may respond directly to climate-change-related shifts in environmental processes or indirectly to other influences, such as community-level interactions with other taxa. However, the ability to adapt to the predicted changes in climate will vary between species and between habitats and there will be winners and losers. In marine habitats, recent changes in fish community structure will continue as fishes shift their distributions relative to their temperature preferences. This may lead to the loss of some economically important cold-adapted species such as Gadus morhua and Clupea harengus from some areas around Britain and Ireland, and the establishment of some new, warm-adapted species. Increased temperatures are likely to favour cool-adapted (e.g. Perca fluviatilis) and warm-adapted freshwater fishes (e.g. roach Rutilus rutilus and other cyprinids) whose distribution and reproductive success may currently be constrained by temperature rather than by cold-adapted species (e.g. salmonids). Species that occur in Britain and Ireland that are at the edge of their distribution will be most affected, both negatively and positively. Populations of conservation importance (e.g. Salvelinus alpinus and Coregonus spp.) may decline irreversibly. However, changes in food-web dynamics and physiological adaptation, for example because of climate change, may obscure or alter predicted responses. The residual inertia in climate systems is such that even a complete cessation in emissions would still leave fishes exposed to continued climate change for at least half a century. Hence, regardless of the success or failure of programmes aimed at curbing climate change, major changes in fish communities can be expected over the next 50 years with a concomitant need to adapt management strategies accordingly.

Stable isotope analysis of archived roach (Rutilus rutilus) scales for retrospective study of shallow lake responses to nutrient reduction

1. There is increasing interest in the use of stable isotope analysis of archived materials to study the long-term impacts of lake perturbations, including nutrient manipulation or species invasion. We tested the utility of this approach in a shallow productive lake using the zooplanktivorous early life stages of roach ( Rutilus rutilus), a fish species that is widespread throughout Eurasian lakes.

delta C-13 and delta N-15 reveal significant differences in the coastal foodwebs of the seas surrounding Trinidad and Tobago

This study assessed nearshore, marine ecosystem function around Trinidad and Tobago (TT). The coastline of TT is highly complex, bordered by the Atlantic Ocean, the Caribbean Sea, the Gulf of Paria and the Columbus Channel, and subject to local terrestrial runoff and regional riverine inputs (e.g. the Orinoco and Amazon rivers). Coastal organisms can assimilate energy from allochthonous and autochthonous Sources, We assessed whether stable isotopes delta C-13 and delta N-15 Could be used to provide a rapid assessment of trophic interactions in primary consumers around the islands. Filter-feeding (bivalves and barnacles) and grazing organisms (gastropods and chitons) were collected from 40 marine sites during the wet season. The flesh of organisms was analysed for delta C-13 and delta N-15. Results indicate significant variation in primary consumers (by feeding guild and sampling zone). This variation was linked to different energy Sources being assimilated by consumers. Results suggest that offshore production is fuelling intertidal foodwebs; for example, a depleted delta C-13 signature in grazers from the Gulf of Paria, Columbus Channel and the Caribbean and Atlantic coastline of 9 Tobago indicates that carbon with an offshore origin (e.g. phytoplankton and dissolved organic matter) is more important than benthic or littoral algae (luring the wet season. Results also confirm findings from other studies indicating that much of the coastline is subject to Cultural eutrophication. This Study revealed that ecosystem function is spatially variable around the coastline of TT, This has clear implications for marine resource management, as a single management approach is unlikely to be successful at a national level.

A meta-analysis of latitudinal variations in life-history traits of roach, Rutilus rutilus, over its geographical range: linear or non-linear relationships?

1. We collated information from the literature on life history traits of the roach (a generalist freshwater fish), and analysed variation in absolute fecundity, von Bertalanffy parameters, and reproductive lifespan in relation to latitude, using both linear and non-linear regression models. We hypothesized that because most life history traits are dependent on growth rate, and growth rate is non-linearly related with temperature, it was likely that when analysed over the whole distribution range of roach, variation in key life history traits would show non-linear patterns with latitude.

Continuous variation in the pattern of marine v. freshwater foraging in brown trout Salmo trutta L. from Loch Lomond, Scotland

Carbon stable-isotope analysis showed that individual brown trout Salmo trutta in Loch Lomond adopted strategies intermediate to that of freshwater residency or anadromy, suggesting either repeated movement between freshwater and marine environments, or estuarine residency. Carbon stable-isotope (delta C-13) values from Loch Lomond brown trout muscle tissue ranged from those indicative of assimilation of purely freshwater-derived carbon to those reflecting significant utilization of marine-derived carbon. A single isotope, two-source mixing model indicated that, on average, marine C made a 33% contribution to the muscle tissue C of Loch Lomond brown trout. Nitrogen stable isotope, delta N-15, but not delta C-13 was correlated with fork length suggesting that larger fish were feeding at a higher trophic level but that marine feeding was not indicated by larger body size. These results are discussed with reference to migration patterns in other species. (c) 2008 The Authors Journal compilation (c) 2008 The Fisheries Society of the British Isles.

Shore exposure affects mussel population structure and mediates the effect of epibiotic algae on mussel survival in SW Ireland

On rocky shores, the relative importance of abiotic and biotic processes that regulate community structure are thought to vary with levels of shore exposure. This can lead to characteristic features found on sheltered and exposed shores. This study identified differences in the population structure of mussels on exposed and sheltered rocky shores on Atlantic coasts of south-west Ireland. Direct interactions between epibiotic algae and their host mussels were also examined to test if potential effects varied with shore exposure. Mussel beds on sheltered shores were less dense and comprised larger mussels with greater rates of individual survival and growth than those on exposed shores. The results of a field experiment showed that algal epibionts had a negative effect on mussel survival on sheltered shores but not on exposed shores. Surprisingly, the presence of algal epibionts had no effect on mussel growth on either shore type. These findings contrast with those of previous studies. The effects of shore exposure and algal epibionts on Mussels may be species-specific and may interact with other factors across different regions. This study shows that predictions of effects of exposure on mussel populations and their epibionts should only be based on specific experimental evidence and cannot be generalised across regions. (C) 2009 Elsevier Ltd. All rights reserved.

Biodiversity among mussels: separating the influence of sizes of mussels from the ages of patches

The role of habitat structure in controlling the composition of assemblages has often been studied, but is rarely manipulated so that it is distinguishable from other factors. Differences in habitat structure as determined by differences in mussel size structure may affect the diversity of assemblages associated with mussel beds. Previous studies examining the effect of the size of individual mussels in a patch on the diversity of associated macro-faunal assemblages confounded the age of the patch with the size of the mussels. We manipulated the age of mussel patches and the size of the mussels within them to test experimentally whether the size of mussels influenced the structure of associated assemblages. At one of the two locations considered, the structure of macro-faunal assemblages in patches of larger mussels differed significantly from those in patches of the same age composed of smaller mussels. At this location, the size of mussels did not affect species richness but the abundance and proportion of organisms present differed depending on the size of the mussels. Here patches of larger mussels contained greater numbers of Nematodes and Oligochaetes and a lower abundance of taxa, such as faera forsmani and Lepidonotus clava. We also found that invertebrate assemblages in general differed between the two locations. The effect of the size structure of mussels, however, varied spatially demonstrating that the effect of habitat structure on the diversity of associated assemblages is context dependent.

Effects of epibiotic algae on the survival, biomass and recruitment of mussels, Mytilus L. (Bivalvia : Mollusca)

Habitats composed of living 'ecosystem engineers', such as mussels, are subject to direct and indirect interactions with organisms that live among them. These interactions may affect the presence and structure of habitat, and hence, the associated taxa. We examined the direct effects of epibiotic algae on the Survival, biomass and recruitment of mussels (Mytilits L.) on the west coast of Ireland. A field experiment showed that the presence of epibiotic fucoid algae reduced the likelihood of survival of mussels during storms. We also found that the strength of attachment of mussels did not increase in the presence of epibionts. Another in situ experiment revealed that the presence of ephemeral epibiotic algal mats had no effect on the biomass of host mussels, suggesting no effect on mussel growth or production. The abundance of small mussels (

Do mussel patches provide a refuge for algae from grazing gastropods?

On rocky shores, cover of macroalgae is often greater growing epibiotically on mussels compared to algae growing directly attached to rock. A survey of two shores on the east coast of Ireland confirmed that mussel beds contained greater percentage algal cover and more diverse algal assemblages compared to those on rock. The reasons for this difference are not clear. It has been suggested that mussel beds provide a refuge for algae from grazing gastropods. Surprisingly, we found no evidence to support this. Using wax discs, gastropod grazing patterns were found to be similar within the mussel beds as on rock. The mussel beds do not appear to provide a refuge for algae from grazing activity at this scale and we suggest other possible mechanisms for the prevalence of epibiotic algal cover on mussels. Intertidal grazers may in fact affect the epibiotic algae on mussels and thereby affect indirectly the persistence of mussel beds.