Phylogeography of the chestnut‐tailed antbird (Myrmeciza hemimelaena) clarifies the role of rivers in Amazonian biogeography

Aim We examined patterns of spatial and temporal diversification of the Amazonian endemic chestnut‐tailed antbird, Mymeciza hemimelaena (Thamnophilidae), to evaluate the diversification of a widespread avian taxon across rivers that potentially represent major natural barriers. Location Lowland Amazonia. Methods Sequences of the mitochondrial ND2 and cytochrome b genes were investigated from 65 individuals distributed throughout the entire range of M. hemimelaena, and including the two currently valid subspecies M. h. hemimelaena and M. h. pallens. Based on a combination of phylogeographic tools, molecular dating, and population genetic methods, we reconstructed a spatio‐temporal scenario of diversification of M. hemimelaena in the Amazon. Results The data revealed three genetically divergent and monophyletic groups in M. hemimelaena, which can also be distinguished by a combination of morphological and vocal characters. Two of these clades correspond to the previously described taxa M. h. hemimelaena and M. h. pallens, which are separated by the upper Madeira River, a main Amazonian tributary. The third clade is distributed between the middle reaches of the Madeira River and the much smaller tributaries Jiparaná and Aripuanã, and, although currently treated as M. h. pallens, clearly constitutes an independent evolutionary lineage probably deserving separate species status. Molecular clock and population genetic analyses indicate that diversification in this group occurred throughout the Pleistocene, with demographic fluctuations assumed for M. h. hemimelaena and M. h. pallens. Main conclusions The findings implicate rivers as barriers driving diversification in the M. hemimelaena complex. Levels of mitochondrial DNA divergence and associated morphological and vocal traits support its division into at least three separate species with comparatively small ranges. The existence of a previously unrecognized lineage in the M. hemimelaena complex, and the high degree of population structuring found in M. h. hemimelaena underscore the pervasiveness of cryptic endemism throughout Amazonia and the importance of DNA‐based taxonomic and phylogeographic studies in providing the accurate estimates of diversity that are essential for conservation planning.     

Ecological and historical filters constraining spatial caddisfly distribution in Mediterranean rivers

1. Contemporary species distributions are determined by a mixture of ecological and historical filters acting on several spatial and temporal scales. Mediterranean climate areas are one of the world's biodiversity hotspots with a high level of endemicity, which is linked to complex ecological and historical factors. 2. This paper explores the ecological and historical factors constraining the distribution of caddisfly species on a large regional scale. A total of 69 taxa were collected from 140 sampling sites in 10 Iberian Mediterranean river basins. Approximately 74% of taxa can be considered rare, with the southern basins (the Baetic–Riffian region) having greater endemicity. The greatest richness, involving a mixture of northern and southern species, was found in the transitional area between the Baetic–Riffian region and the Hesperic Massif. 3. The historical processes occurring during the Tertiary (i.e. the junction of the Eurasian and African plates) explained 3.1% of species distribution, whereas ecological factors accounted for 20.7%. Only 0.3% was explained by the interaction of history and ecology. A set of multi‐scale ecological variables (i.e. basin, reach and bedform characteristics) defined five river types with specific caddisfly assemblages. The commonest caddisfly species accounted for the regional distribution pattern, while rare taxa contributed to the explanation of subtle patterns not shown by common species. 4. Despite the importance of historical factors for biogeography and the large scale used in our study, ecological variables better explained caddisfly distribution. This may be explained by the length of time since the historical process we are considering, the high dispersion and colonisation capacity of many caddisfly species, and the strong environmental gradient in the area. Because of the historical and environmental complexity of Mediterranean areas, rare taxa should be included in ecological studies so that the singularity of these ecosystems is not missed.     

Application of a microcomputer-based algal fluorescence technique for assessing toxicity: Lake St. Clair and St. Clair River examples

The use of a multi-trophic assay strategy is now being encouraged in toxicological investigations which provides for rapid and sensitive tests. Such a strategy, a microcomputer-based algal fluorescence technique, was applied for the bioassessment of Lake St. Clair and St. Clair River ecosystems. The technique was found to be rapid, sensitive, and relatively inexpensive. In addition, it permitted microscopic examination of the impact of contaminants on individual cells/organisms, a feature which is not possible by other tests using radioisotopes and enzymes. The algal fluorescence technique appears to have a considerable potential for fast screening of large numbers of environmental samples.     

Phylogeography and climatic niche evolution in live oaks (Quercus series Virentes) from the tropics to the temperate zone

Aim We investigated the phylogeography, geographical variation in leaf morphology, freezing tolerance and climatic niches of two widespread evergreen sister oak species (Quercus) in the series Virentes. Location South‐eastern USA, Mexico and Central America. Methods Nuclear microsatellites and non‐recombining nuclear and chloroplast DNA sequences were obtained from trees throughout the range of two sister lineages of live oaks, represented by Quercus virginiana in the temperate zone and Q. oleoides in the tropics. Divergence times were estimated for the two major geographical and genetic breaks. Differentiation in leaf morphology, analysed from field specimens, was compared with the molecular data. Freezing sensitivities of Q. virginiana and Q. oleoides populations were assessed in common garden experiments. Results The geographical break between Q. virginiana and Q. oleoides was associated with strong genetic differentiation of possible early Pleistocene origin and with differentiation in freezing sensitivity, climatic envelopes and leaf morphology. A second important geographical and genetic break within Q. oleoides between Costa Rica and the rest of Central America showed a mid‐Pleistocene divergence time and no differentiation in leaf morphology. Population genetic differentiation was greater but genetic diversity was lower within the temperate Q. virginiana than within the tropical Q. oleoides, and genetic breaks largely corresponded to breaks in leaf morphology. Main conclusions Two major breaks, one between Mexico and the USA at the boundary of the two species, and a more recent one within Q. oleoides between Honduras and Costa Rica, implicate climatic changes as potential causes. The latter break may be associated with the formation of the Cordillera de Guanacaste, which was followed by seasonal changes in precipitation. In the former case, an ‘out of the tropics’ scenario is hypothesized, in which the acquisition of freezing tolerance in Q. virginiana permitted colonization of and expansion in the temperate zone, while differences in climatic tolerances between the species limited secondary contact. More pronounced Pleistocene changes in climate and sea level in the south‐eastern USA relative to coastal Mexico and Central America may explain the greater population differentiation within temperate Q. virginiana and greater genetic diversity in tropical Q. oleoides. These patterns are predicted to hold for other taxa that span temperate and tropical zones of North and Central America.     

Distinct colonization waves underlie the diversification of the freshwater sculpin (Cottus gobio) in the Central European Alpine region

Ecological speciation and adaptive radiation are key processes shaping northern temperate freshwater fish diversity. Both often involve parapatric differentiation between stream and lake populations and less often, sympatric intralacustrine diversification into habitat‐ and resource‐associated ecotypes. However, few taxa have been studied, calling for studies of others to investigate the generality of these processes. Here, we test for diversification within catchments in freshwater sculpins in a network of peri‐Alpine lakes and streams. Using 8047 and 13 182 restriction site‐associated (RADseq) SNPs, respectively, we identify three deeply divergent phylogeographic lineages associated with different major European drainages. Within the Aare catchment, we observe populations from geographically distant lakes to be genetically more similar to each other than to populations from nearby streams. This pattern is consistent with two distinct colonization waves, rather than by parapatric ecological speciation after a single colonization wave. We further find two distinct depth distribution modes in three lakes of the Aare catchment, one in very shallow and one in very deep water, and significant genomewide differentiation between these in one lake. Sculpins in the Aare catchment appear to represent an early‐stage adaptive radiation involving the evolution of a lacustrine lineage distinct from parapatric stream sculpins and the repeated onset of depth‐related intralacustrine differentiation.     

Turquoise is the new green: Restoring and enhancing riparian function in the Anthropocene

Riparian ecosystems are hotspots for ecological restoration globally because of the disproportionately high value and diversity of the ecological functions and services which they support and their high level of vulnerability to anthropogenic pressures, including climate change. Degraded riparian ecosystems are associated with many serious anthropogenic problems including increased river bank erosion, water quality decline, increased flood risk and biodiversity loss. Conventional approaches to riparian restoration, however, are frequently too narrow in focus – spatially, temporally, ecologically and socially – to adequately or equitably address the goals to which they aspire. Climate change, along with the intensification of other human pressures, means that static, historically oriented restoration objectives focused solely on prior ecological composition and structure are unlikely to be defensible, achievable or appropriate in the Anthropocene. Conversely, open‐ended restoration strategies lacking clear objectives and targets entail substantial risks such as significant biodiversity losses, especially of native species. A functional approach to planning and prioritising riparian restoration interventions offers an intermediate alternative that is still framed by measurable targets but allows for greater consideration of broader temporal, spatial and cultural influences. Here, we provide an overview of major riparian functions across multiple scales and identify key drivers of, and threats to, these. We also discuss practical approaches to restoring and promoting riparian functions and highlight some key concerns for the development of policy and management of robust riparian restoration in the Anthropocene.     

Nutrients and temperature additively increase stream microbial respiration

Rising temperatures and nutrient enrichment are co‐occurring global‐change drivers that stimulate microbial respiration of detrital carbon, but nutrient effects on the temperature dependence of respiration in aquatic ecosystems remain uncertain. We measured respiration rates associated with leaf litter, wood, and fine benthic organic matter (FBOM) across seasonal temperature gradients before (PRE) and after (ENR1, ENR2) experimental nutrient (nitrogen [N] and phosphorus [P]) additions to five forest streams. Nitrogen and phosphorus were added at different N:P ratios using increasing concentrations of N (~80–650 μg/L) and corresponding decreasing concentrations of P (~90–11 μg/L). We assessed the temperature dependence, and microbial (i.e., fungal) drivers of detrital mass‐specific respiration rates using the metabolic theory of ecology, before vs. after nutrient enrichment, and across N and P concentrations. Detrital mass‐specific respiration rates increased with temperature, exhibiting comparable activation energies (E, electronvolts [eV]) for all substrates (FBOM E = 0.43 [95% CI = 0.18–0.69] eV, leaf litter E = 0.30 [95% CI = 0.072–0.54] eV, wood E = 0.41 [95% CI = 0.18–0.64] eV) close to predicted MTE values. There was evidence that temperature‐driven increased respiration occurred via increased fungal biomass (wood) or increased fungal biomass‐specific respiration (leaf litter). Respiration rates increased under nutrient‐enriched conditions on leaves (1.32×) and wood (1.38×), but not FBOM. Respiration rates responded weakly to gradients in N or P concentrations, except for positive effects of P on wood respiration. The temperature dependence of respiration was comparable among years and across N or P concentration for all substrates. Responses of leaf litter and wood respiration to temperature and the combined effects of N and P were similar in magnitude. Our data suggest that the temperature dependence of stream microbial respiration is unchanged by nutrient enrichment, and that increased temperature and N + P availability have additive and comparable effects on microbial respiration rates.