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Future climate change is leading to the redistribution of life on Earth as species struggle to cope with rising temperatures. Local adaptation allows species to become locally optimized and persist despite environmental selection, but the extent to which this occurs in nature may be limited by dispersal and gene flow. Congeneric marine gastropod species (Littorina littorea and L. saxatilis) with markedly different developmental modes were collected from across a latitudinal thermal gradient to explore the prevalence of local adaptation to temperature. The acute response of metabolic rate (using oxygen consumption as a proxy) to up‐ramping and down‐ramping temperature regimes between 6°C and 36°C was quantified for five populations of each species. The highly dispersive L. littorea exhibited minimal evidence of local adaptation to the thermal gradient, with no change in thermal optimum (Topt) or thermal breadth (Tbr) and a decline in maximal performance (max) with increasing latitude. In contrast, the direct developing L. saxatilis displayed evidence of local optimization, although these varied idiosyncratically with latitude, suggesting a suite of selective pressures may be involved in shaping thermal physiology in this relatively sedentary species. Our results show that the biogeography of thermal traits can differ significantly between related species, and show that interpopulation differences in thermal performance do not necessarily follow simple patterns that may be predicted based on latitudinal changes in environmental temperatures. Further research is clearly required to understand the mechanisms that can lead to the emergence of local adaptation in marine systems better and allow improved predictions of species redistribution in response to climate change. [ABSTRACT FROM AUTHOR]

Surfacing behaviour is fundamental in the ecology of aquatic air-breathing organisms; however, it is only in vertebrates that the evolutionary ecology of diving has been well characterized. Here, we explore the diving behaviour of dytiscid beetles, a key group of surface-exchanging freshwater invertebrates, by comparing the dive responses of 25 taxa ( Deronectes and Ilybius spp.) acclimated at two temperatures. The allometric slopes of dive responses in these dytiscids appear similar to those of vertebrate ectotherms, supporting the notion that metabolic mode shapes the evolution of diving performance. In both genera, beetles spend more time submerged than on the surface, and surface time does not vary with the temperature of acclimation. However, presumably in order to meet increased oxygen demand at higher temperatures, Deronectes species increase surfacing frequency, whereas Ilybius species decrease dive time, an example of 'multiple solutions.' Finally, widespread northern species appear to possess higher diving performances than their geographically restricted southern relatives, something which may have contributed to their range expansion ability. [ABSTRACT FROM AUTHOR]

Aim Within clades, most taxa are rare, whilst few are common, a general pattern for which the causes remain poorly understood. Here we investigate the relationship between thermal performance (tolerance and acclimation ability) and the size of a species’ geographical range for an assemblage of four ecologically similar European diving beetles (the Agabus brunneus group) to examine whether thermal physiology relates to latitudinal range extent, and whether Brown’s hypothesis and the environmental variability hypothesis apply to these taxa. Location Europe. Methods In order to determine the species tolerances to either low or high temperatures we measured the lethal thermal limits of adults, previously acclimated at one of two temperatures, by means of thermal ramping experiments (± 1°C min−1). These measures of upper and lower thermal tolerances (UTT and LTT respectively) were then used to estimate each species’ thermal tolerance range, as total thermal tolerance polygons and marginal UTT and LTT thermal polygons. Results Overall, widespread species have higher UTTs and lower LTTs than restricted ones. Mean upper lethal limits of the Agabus brunneus group (43 to 46°C), are similar to those of insects living at similar latitudes, whilst mean lower lethal limits (−6 to −9°C) are relatively high, suggesting that this group is not particularly cold-hardy compared with other mid-temperate-latitude insects. Widespread species possess the largest thermal tolerance ranges and have a relatively symmetrical tolerance to both high and low temperatures, when compared with range-restricted relatives. Over the temperature range employed, adults did not acclimate to either high or low temperatures, contrasting with many insect groups, and suggesting that physiological plasticity has a limited role in shaping distribution. Main conclusions Absolute thermal niche appears to be a good predictor of latitudinal range, supporting both Brown’s hypothesis and the environmental variability hypothesis. Restricted-range species may be more susceptible to the direct effect of climate change than widespread species, notwithstanding the possibility that even ‘thermally-hardy’, widespread species may be influenced by the indirect effects of climate change such as reduction in habitat availability in Mediterranean areas. [ABSTRACT FROM AUTHOR]

Aquatic insects obtain oxygen either from air dissolved in water or directly from air via surfacing. Diving beetles (Coleoptera: Dytiscidae) rely on a subelytral air store, which has to be renewed periodically at the water's surface. [Correction added after publication 28 July 2007: in the preceding sentence ‘Diving beetles Ilybius montanus ( Coleoptera: Dytiscidae)’ was corrected to ‘Diving beetles (Coleoptera: Dytiscidae)’]. The way in which diving behaviour responds to changes in the insect's environment has not been previously explored, however. Here, we investigate the diving behaviour of the widespread European species Ilybius montanus (Stephens). We go on to examine how different aspects of the diving behaviour of individual insects change with temperature and water acidity, using both hydrochloric and sulphuric acids. Individual surfacing frequency was significantly higher at 20.5°C than at 14.5°C, which resulted from a shortening of the mean dive duration at higher temperatures, no associated change being seen in mean time spent exchanging at the surface. The observed reductions in dive duration may have resulted from increased metabolic rate at higher temperatures, while the constancy of surface time suggests that this represents a trade-off between gas exchange demands and selection to minimize time spent at the surface, perhaps to avoid predation. Although acidity did not affect surfacing frequency or the mean duration of individual dive parameters, it resulted in a breakdown of an individual's ability to regulate diving behaviour with temperature. This effect was most pronounced when experimental water was acidified using sulphuric acid, indicating that anion, as well as acidity itself, is of importance. As the dive response could be broken down into readily quantifiable components, and this behaviour showed marked responses to the factors considered here, we propose that diving activity could serve as an integrative organismal biomarker in these and other surface-exchanging aquatic insects. [ABSTRACT FROM AUTHOR]

1. It is increasingly recognised that adequate measures of biodiversity should include information on the 'relatedness' of species within ecological assemblages, or the phylogenetic levels at which diversity is expressed. Taxonomic distinctness measures provide a series of indices to achieve this, which are independent of sample size. Taxonomic distinctness has been employed widely in marine systems, where it has been suggested that this index can provide a reliable measure of anthropogenic impact. 2. We tested the behaviour of three related taxonomic distinctiveness indices (Average Taxonomic Distinctness, Δ+; Variation in Taxonomic Distinctness, Λ+; and Total Taxonomic Distinctness, sΔ+) in relation to putative levels of anthropogenic impact in inland waters and their potential utility in environmental monitoring, using an extensive data set for aquatic beetles from the south-east of the Iberian Peninsula. 3. Taxonomic distinctness measures were not able to identify human disturbance effects and there were no clear relationships between these new biodiversity measures and the disturbance level recorded at individual localities. Furthermore, the taxonomic distinctness measures used were apparently less sensitive to the effects of anthropogenic impact than other diversity metrics, such as species richness and rarity. 4. We conclude that taxonomic distinctness indices may not always perform as well as other metrics in the assessment of environmental quality. In addition, taxonomic distinctness measure should be interpreted with caution, as their performance and ability to detect anthropogenic disturbance may depend on the phylogenetic structure of sampled taxa within a region, and their evolutionary and ecological history. [ABSTRACT FROM AUTHOR]

Abstract The phylogeny and population history of Meladema diving beetles (Coleoptera, Dytiscidae) were examined using mitochondrial DNA sequence from 16S ribosomal RNA and cytochrome oxidase I genes in 51 individuals from 22 populations of the three extant species (M. imbricata endemic to the western Canary Islands, M. lanio endemic to Madeira and M. coriacea widespread in the Western Mediterranean and on the western Canaries), using a combination of phylogenetic and nested clade analyses. Four main lineages are observed within Meladema , representing the three recognized species plus Corsican populations of M. coriacea . Phylogenetic analyses demonstrate the sister relationship of the two Atlantic Island taxa, and suggest the possible paraphyly of M. coriacea . A molecular clock approach reveals that speciation within the genus occurred in the Early Pleistocene, indicating that the Atlantic Island endemics are not Tertiary relict taxa as had been proposed previously. Our results point to past population bottlenecks in all four lineages, with recent (Late-Middle Pleistocene) range expansion in non-Corsican M. coriacea and M. imbricata . Within the Canary Islands, M. imbricata seems to have independently colonized La Gomera and La Palma from Tenerife (although a colonization of La Palma from La Gomera cannot be discarded), and M. coriacea has independently colonized Tenerife and Gran Canaria from separate mainland lineages. In the Mediterranean basin this species apparently colonized Corsica on a single occasion, relatively early in its evolutionary history (Early Pleistocene), and has colonized Mallorca recently on multiple occasions. On the only island where M. coriacea and M. imbricata are broadly sympatric (Tenerife), we report evidence of bidirectional hybridization between the two species. [ABSTRACT FROM AUTHOR]

For some of their occupants, estuaries represent spatially discrete habitats, isolated from each other by barriers to dispersal or physiological tolerance. We present contrasting strategies for the retention or export of larvae from their estuary of origin, and consider the implications these have on population structure and divergence. Reported patterns of genetic differentiation and inferred gene flow in estuarine taxa (principally animals) are reviewed, and difficulties in the interpretation of existing genetic data discussed. Species concepts and models of speciation relevant to estuaries are outlined, and patterns of speciation of estuarine taxa reviewed. It is concluded that estuarine environments tend to restrict gene flow and impose distinct selective regimes, generating physiologically adapted populations divergent from their marine counterparts, and the potential for in situ speciation in complete or partial isolation. The resulting taxa may represent sibling or cryptic species groups of truly estuarine origin, rather than simply estuarine populations of marine eurytopes. [Copyright &y& Elsevier]

Marine nematodes, which play an important role in many ecosystems, include a number of apparently cosmopolitan taxa that exhibit broad biogeographic ranges even though there is no obvious dispersal phase in their lifecycle. In this study, standard taxonomic approaches to marine nematode identification in conjunction with multivariate statistical analysis of morphometric data were compared with molecular techniques. Specimens of the marine nematode Terschellingia longicaudata that had been identified by their morphological features were investigated from a range of localities (East and West Atlantic, Bahrain, Malaysia) and habitats (estuarine, intertidal, subtidal) using molecular approaches based on the amplification and sequencing of the small subunit ribosomal RNA (18S rRNA). The study revealed that the majority of the morphologically defined T. longicaudata specimens share a single 18S rRNA sequence and apparently belong to a single taxon distributed from the British Isles to Malaysia. In addition, 18S rRNA analysis also revealed two additional sequences. One of these sequences was found in both the British Isles and Mexico, the other was recorded only from British waters. Individuals collected in Bahrain and identified from their morphology as T. longicaudata had two highly divergent 18S rRNA sequences. Separate morphological and morphometric approaches to identification of specimens from the same sites that had been formalin-preserved did not support evidence of multiple genotypes revealed previously by molecular analysis. Current taxonomy based on morphological characters detected using light-microscopy may be unable to discriminate possible species complexes. Biodiversity of marine nematodes may often be underestimated due to the presence of morphologically cryptic species complexes. High-throughput techniques such as DNA barcoding would aid in species identification but may require thorough analysis of multiple nuclear and mitochondrial molecular markers. [ABSTRACT FROM AUTHOR]

Small metazoans such as marine nematodes are increasingly identified using both molecular and morphological techniques. Formalin is the preferred fixative for morphological analysis but specimens become unsuitable for molecular study due to formalin-induced modification of DNA. Nematodes fixed in ethanol work well for molecular studies but become unsuitable for taxonomy due to shrinkage. Here we show for the first time that formalin can be used as a short-term fixative (≤ 7 days) for marine nematodes, allowing both morphological and molecular work to be conducted on the same individual. No sequence ambiguities were detected in polymerase chain reaction (PCR) amplifications of 18S ribosomal DNA (rDNA) following short-term formalin preservation. [ABSTRACT FROM AUTHOR]

Physiological traits are key in determining the vulnerability of narrow range, highly specialized animals to climate change. It is generally predicted that species from more stable environments possess lower thermal tolerance breadths and thermal plasticity than those from more variable habitats – the so‐called 'climatic variability hypothesis'. However, evolutionary trade‐offs between thermal breadth and its plasticity are also seen in some taxa, and the evolution of thermal physiology remains poorly understood. Subterranean environments are excellent systems for exploring these issues, being characterized by stable climatic conditions, with environmental variability increasing predictably from deep to shallow habitats. Acclimation capacity will be fundamental in determining the sensitivity of subterranean species to climate change, since they have poor dispersal capacity and limited possibility to exploit thermally different microhabitats in the uniform cave environment. We assessed critical thermal maximum (CTmax) and short‐term heat acclimation capacity in three related beetles (Leiodidae: Leptodirini) with differing degrees of specialization to the subterranean environment (deep, shallow and facultatively subterranean, respectively) and therefore exposed to contrasting thermal variability in nature. Only the facultative subterranean species showed any acclimatory capacity, also having the highest CTmax across the taxa studied. However, this species might experience the highest thermal stress in its habitat under climate change. The studied subterranean specialists will be poorly able to cope physiologically with temperature increase, but in contrast exposed to lower magnitude and rate of warming. Our results fit the climatic variability hypothesis, suggesting that adaptation to cave conditions has selected against the retention of acclimation mechanisms. We show that the pathways that determine vulnerability of subterranean species to climate change depend on their degree of specialization to deep subterranean environments. This information, combined with evaluation of exposure to climatic changes at their present locations, is fundamental in identifying species or populations at greatest risk. [ABSTRACT FROM AUTHOR]

Supra-tidal plant communities fulfil a vital role in coastal protection and conservation but despite an increased likelihood of salt-water inundation from storm surges, we understand remarkably little on how salinity affects habitats like coastal grasslands or their component species. We quantified the survival and growth of a common coastal grassland plant, Plantago lanceolata when exposed to short-duration (1-, 2-, 4-, or 8-h) immersion in sea water. We also calculated root:shoot ratios (R:SR) and specific leaf area (SLA) to examine how salinity stress affects above- and below-ground resource allocation patterns and likely interactions with other trophic levels. Immersion in sea water reduced Plantago survival particularly at longer durations of 4- and 8 h, and for surviving plants, growth was also much reduced. Contrary to studies with crop plants however, we found reduced allocation to root biomass (R:SR) and increased SLA. The fact that Plantago displayed opposite ecophysiological responses to those consistently reported in the literature highlights that the response of coastal grassland plants to storm surge events cannot be assumed from conventional wisdom. In order to better protect and conserve these internationally important ecosystems from the effects of anthropogenically induced sea-level rise, a systematic exploration of the effects of sea water flooding on coastal grasslands is required. [ABSTRACT FROM AUTHOR]

Habitat structure is one of the fundamental factors determining the distribution of organisms at all spatial scales, and vegetation is of primary importance in shaping the structural environment for invertebrates in many systems. In the majority of biotopes, invertebrates live within vegetation stands of mixed species composition, making estimates of structural complexity difficult to obtain. Here we use fractal indices to describe the structural complexity of mixed stands of aquatic macrophytes, and these are employed to examine the effects of habitat complexity on the composition of free-living invertebrate assemblages that utilise the habitat in three dimensions. Macrophytes and associated invertebrates were sampled from shallow ponds in southwest England, and rapid digital image analysis was used to quantify the fractal complexity of all plant species recorded, allowing the complexity of vegetation stands to be reconstructed based on their species composition. Fractal indices were found to be significantly related to both invertebrate biomass–body size scaling and overall invertebrate biomass; more complex stands of macrophytes contained a greater number of small animals. Habitat complexity was unrelated to invertebrate taxon richness and macrophyte surface area and species richness were not correlated with any of the invertebrate community parameters. The biomass–body size scaling relationship of lentic macroinvertebrates matched those predicted by models incorporating both allometric scaling of resource use and the fractal dimension of a habitat, suggesting that both habitat fractal complexity and allometry may control density–body size scaling in lentic macroinvertebrate communities. [ABSTRACT FROM AUTHOR]

1. Nestedness is a composite property of many suites of biotas. Such patterns may be driven by dispersal limitation, species–area relationships, hierarchical niche requirements, or occur as an artefact of passive sampling. Despite its widespread occurrence, few studies have explored the factors underlying nested subset structure, and ecological distinctions between nested and non-nested (idiosyncratic) taxa within a region have been largely ignored.2. Macroinvertebrate assemblages from 45 heathland ponds in south-west England are used to (i) unravel the relative importance of processes driving nested subset structure and (ii) test spatially explicit hypotheses concerning the response of nested and idiosyncratic taxa to parameters shown to structure assemblage-level nestedness.3. Despite being dominated by taxa with good powers of inter-site dispersal, pond macroinvertebrate assemblages were found to be significantly nested. This nesting was not due to passive sampling, and was best explained by pond area, with habitat parameters and isolation being of secondary importance.4. The spatial responses of nested and idiosyncratic taxa matched predictions; nested taxa showed strong spatial structure, which was reduced when the effects of pond area and habitat were removed. In contrast, a greater proportion of idiosyncratic taxa were completely spatially random and exhibited weaker responses to factors that structure assemblage level nestedness.5. Nested and idiosyncratic species tend to differ ecologically: idiosyncratic taxa generally possess broad ecological tolerance and good dispersal capacity, whilst nested species are more likely to have narrow tolerances or limited powers of dispersal.6. Factors structuring nestedness in ponds can be viewed as probabilistic filters which act to limit the spatial distribution of species with narrow ecological tolerance or low dispersal tendency. Nestedness analysis alone fails to elucidate processes that structure assemblage composition. The additional use of spatially explicit analyses is important if processes that generate nested pattern across a region are to be understood.Journal of Animal Ecology(2005) doi: 10.1111/j.1365-2656.2004.00895.x [ABSTRACT FROM AUTHOR]

1. Dispersal ability influences the distribution and abundance of organisms, but empirical investigations of the relationship between dispersal ability and the composition of ecological assemblages are scarce. Here, we compare between-site variation in the species richness and community composition of actively and passively dispersing pond invertebrates. 2. Coleoptera (active dispersers) and microcrustacea (passive dispersers) were sampled over a season from 16 ponds within a 4-km radius in south-west England. Species richness and community composition were related to environmental variables using regression and Canonical Correspondence Analysis (CCA), respectively. 3. Coleopteran species richness was significantly and positively correlated with pond permanence and maximum area, whereas microcrustacean species richness was relatively equal across sites and did not correlate with environmental variables. The frequency of species' occurrence between sites was the same for both groups, which suggests that active and passive dispersers exhibited the same degree of dispersal. 4. Between-site variation in community composition was non-random for both groups, with pond permanence and area, together, explaining similar proportions of between-site variation for Coleoptera. Permanence was correlated most strongly with microcrustacean community composition and a high proportion (25%) of microcrustacean species were more numerous in smaller, more ephemeral ponds. 5. These data suggest that, at small spatial scales, Coleoptera which can undertake multiple dispersal events, are more likely to colonise large, more permanent ponds than passively dispersing microcrustacea. For microcrustacea, other traits (in this case those permitting existence in ephemeral habitats) may over-ride the influences of dispersal in driving between-site variation in species composition. [ABSTRACT FROM AUTHOR]

The common woodlouse Oniscus asellus can be divided into two forms on the basis of morphology, particularly male accessory genitalia. Where these taxa meet, morphological intermediates are found, and the forms were therefore described as subspecies; O. a. asellus and O. a. occidentalis. In this study allozyme loci are used to test the hypothesis that intermediate forms result from hybridization, and to study the nature of hybridization. Thirteen enzyme loci were scored across five English sites representative of each subspecies and intermediates. Ten loci showed strong frequency differences between asellus and occidentalis populations, although no loci showed completely fixed differences. These data confirm that asellus and occidentalis represent genetically distinct taxa, and that intermediate populations are of hybrid origin. There is apparently substantial population substructuring in the contact zone, as indicated by deficits of heterozygotes (FIS) and sporadic gametic (i.e. linkage) disequilibria. Population structure in the Oniscus hybrid zone appears to be analogous to that seen in plant hybrid swarms rather than the narrow hybrid zones observed in many animal taxa. Values of Nei’s genetic distance between the subspecies range from 0.65 to 0.70; these are much higher than between typical conspecific taxa and are indicative of ancient genetic divergence. However, because asellus and occidentalis do not remain distinct in areas of overlap, it is simplest to regard these taxa as members of the same species. [ABSTRACT FROM AUTHOR]

1. Water beetles were recorded from 157 sites around the Wash, England, in 1986. Most sites were ditches in arable land. Eight main types of water beetle assemblage were identified by multivariate analysis. The habitats of these assemblages were characterized by measurement of a range of physical and chemical factors. 2. Of the 130 species recorded, four are listed in the British Red Data Book and a further thirty-five are rated as Nationally Notable. Records from 1904 to 1938 for the same area indicate that only three species have been lost in the subsequent period of intensification of water management and arable farming. A rich water beetle fauna can thus survive in drainage systems in arable fen. 3. Vegetation management was important in maintaining the ‘species quality score’, proposed as a measure of conservation value, of larger ditches but management reduced the species quality of one type of assemblage associated with smaller ditches. One type of assemblage was found only in ditches subject to management. [ABSTRACT FROM AUTHOR]