Evolution of the Neotropical ant genus Linepithema

Abstract A comprehensive species‐level phylogeny of the ant genus Linepithema Mayr, a Neotropical group best known for the invasive Argentine ant L. humile (Mayr), is inferred for the first time using fragments from three nuclear loci [wingless (WG), long‐wavelength rhodopsin (LWR) and internal transcribed spacer (ITS‐2)] and the mitochondrial cytochrome oxidase subunit I (COI) gene. Monophyly of the genus is strongly supported in parsimony, likelihood and Bayesian analyses of the concatenated data, as is the monophyly of four species groups defined previously on the basis of morphology. An Andean species, L. oblongum (Santschi), is the sister taxon of the Argentine ant. Eight of the 11 species whose monophyly was testable in the analysis were inferred to be monophyletic. Several instances of species paraphyly and one case of mitochondrial introgression suggest that complex population genetic processes underpin the patterns of diversity in Linepithema, and that simple genetic approaches to taxonomy such as DNA barcoding should be treated with caution. A maximum likelihood reconstruction of ancestral distributions suggests that Linepithema is of southern South American origin and that populations in the Greater Antilles are the result of four independent colonization events.     

Palaeoclimatic models help to understand current distribution of Caucasian forest species

Spatial and temporal constraints on dispersal explain the absence of species from areas with potentially suitable conditions. Previous studies have shown that post‐glacial recolonization has shaped the current ranges of many species, yet it is not completely clear to what extent interspecific differences in range size depend on different dispersal rates. The inferred boundaries of glacial refugia are difficult to validate, and may bias spatial distribution models (SDMs) that consider post‐glacial dispersal constraints. We predicted the current distribution of 12 Caucasian forest plants and animals, factoring in the effective geographical distance from inferred glacial refugia as an additional predictor. To infer glacial refugia, we tested the transferability of the current SDMs based on the distribution of climatic variables, and projected the most transferable ones onto two climate scenarios simulated for the Last Glacial Maximum (LGM). We then calculated least‐cost distances from the inferred refugia, using elevation as a friction surface, and recalculated the current SDMs incorporating the distances as an additional variable. We compared the predictive powers of the initial with the final SDMs. The palaeoclimatic simulation that best matched the distribution of species was assumed to represent the closest fit to the true palaeoclimate. SDMs incorporating refugial distance performed significantly better for all but one studied species, and the Model for Interdisciplinary Research on Climate (MIROC) climatic simulation provided a more convincing pattern of the LGM climate than the Community Climate System Model (CCSM) simulation. Our results suggest that the projection of suitable habitat models onto past climatic conditions may yield realistic boundaries of glacial refugia, and that the current distribution of forest species in the study region is strongly associated with locations of former refugia. We inferred six major forest refugia throughout western Asia: (1) Colchis; (2) western Anatolia; (3) western Taurus; (4) the upper reaches of the Tigris River; (5) the Levant; and (6) the southern Caspian basin. The boundaries of the modelled refugia were substantially broader than the refugia boundaries inferred solely from pollen records. Thus, our method could be used to: (1) improve models of current species distributions by considering the dispersal histories of the species; and (2) validate alternative reconstructions of palaeoclimate with current distribution data. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 231–248.     

Completeness of the fossil record and the validity of sampling proxies at outcrop level

Abstract: Most studies of the adequacy of the fossil record have been carried out at a global or continental scale, and they have used sampling proxies that generally do not incorporate all aspects of sampling (i.e. rock volume, accessibility, effort). Nonetheless, such studies have identified positive correlations between apparent diversity and various sampling proxies. The covariation of fossil and rock record signals has been interpreted as evidence for bias or for a common cause, such as sea level change, or as evidence that the signals are in some ways redundant with each other. Here, we compare a number of proxies representing the three main aspects of sampling, (1) sedimentary rock volume, (2) rock accessibility and (3) worker effort, with palaeodiversity in a geographically and stratigraphically constrained data set, the marine Lower Jurassic outcrop of the Dorset and East Devon Coast. We find that the proxies for rock volume and accessibility do not correlate well with the other sampling proxies, nor with apparent diversity, suggesting that the total amount of sedimentary rock preserved does not influence apparent diversity at a local scale, that is, the rock record at outcrop has been sampled efficiently. However, we do find some correlations between apparent diversity and proxies for worker effort. The fact that the proxies do not correlate significantly with each other suggests that none can be regarded as an all‐encompassing sampling proxy that covers all aspects of bias. Further, the presence of some correlations between sampling proxies and diversity most probably indicates the bonanza effect, as palaeontologists have preferentially sampled the richest rock units.     

Re‐examining extreme longevity of the cave crayfish Orconectes australis using new mark–recapture data: a lesson on the limitations of iterative size‐at‐age models

1. Centenarian species, defined as those taxa with life spans that frequently exceed 100 years, have long been of interest to ecologists because they represent an extreme end point in a continuum of life history strategies. One frequently reported example of a freshwater centenarian is the obligate cave crayfish Orconectes australis, with a maximum longevity reported to exceed 176 years. As a consequence of its reported longevity, O. australis has been used as a textbook example of life history adaptation to the organic‐carbon limitation that characterises many cave‐stream food webs. 2. Despite being widely reported, uncertainties surround the original estimates of longevity for O. australis, which were based on a single study dating from the mid‐1970s. In the present study, we re‐evaluated the growth rate, time‐to‐maturity, female age‐at‐first‐reproduction and longevity of O. australis using a mark–recapture study of more than 5 years based upon more than 3800 free‐ranging individuals from three isolated cave streams in the south‐eastern United States. 3. The results of our study indicate that accurate estimates of the longevity of O. australis are ≤22 years, with only a small proportion of individuals (<5%) exceeding this age. Our estimates for female time‐to‐maturity (4–5 years) and age‐at‐first‐reproduction (5–6 years) are also substantially lower than earlier estimates. 4. These new data indicate that the age thresholds for life history events of O. australis are comparable to other estimates for a modest assemblage of cave and surface species of crayfish for which credible age estimate exists, suggesting that a cave environment per se is not required for the evolution of extreme longevity in crayfish.     

Historic parks and pasture-woodlands: The National Trust resource and its conservation

The National Trust owns and manages considerably more historic parklands and other types of pasture-woodlands than any other conservation body in the British Isles. These include one virtually intact medieval forest and fragments of others, as well as more than one hundred historic parks and many wooded commons. This special responsibility is described, both in terms of the assemblages of plants and animals now protected by the Trust, and in terms of the active management programmes for their conservation. Management issues of immediate concern on Trust properties are identified.     

The Effect of Petiolar Temperature upon the Translocation Rate of 137Cs in the Phloem of Nymphoides peltata

A fixed length of the petiole of Nymphoides peltata was subjectedto a variety of temperature treatments. A Q₁₀ is calculatedfor the velocity of flow, from the mass transport rate of ¹³⁷Csin the phloem at temperatures between 0 and 50?C. Associatedwith lowered temperatures there was a temporary interruptionof transport overriding the longer term temperature dependence.The characteristics of the interruption were dependent uponthe size of the temperature drop and the magnitude of the ‘new’temperature.     

Use of ciliate and phytoplankton taxonomic composition for the estimation of eicosapentaenoic acid concentration in lakes

1. The polyunsaturated fatty acid eicosapentaenoic acid (EPA) plays an important role in aquatic food webs, in particular at the primary producer–consumer interface where keystone species such as daphnids may be constrained by its dietary availability. Such constraints and their seasonal and interannual changes may be detected by continuous measurements of EPA concentrations. However, such EPA measurements became common only during the last two decades, whereas long‐term data sets on plankton biomass are available for many well‐studied lakes. Here, we test whether it is possible to estimate EPA concentrations from abiotic variables (light and temperature) and the biomass of prey organisms (e.g. ciliates, diatoms and cryptophytes) that potentially provide EPA for consumers. 2. We used multiple linear regression to relate size‐ and taxonomically resolved plankton biomass data and measurements of temperature and light intensity to directly measured EPA concentrations in Lake Constance during a whole year. First, we tested the predictability of EPA concentrations from the biomass of EPA‐rich organisms (diatoms, cryptophytes and ciliates). Secondly, we included the variables mean temperature and mean light intensity over the sampling depth (0–20 m) and depth (0–8 and 8–20 m) as factors in our model to check for large‐scale seasonal‐ and depth‐dependent effects on EPA concentrations. In a third step, we included the deviations of light and temperature from mean values in our model to allow for their potential influence on the biochemical composition of plankton organisms. We used the Akaike Information Criterion to determine the best models. 3. All approaches supported our proposition that the biomasses of specific plankton groups are variables from which seston EPA concentrations can be derived. The importance of ciliates as an EPA source in the seston was emphasised by their high weight in our models, although ciliates are neglected in most studies that link fatty acids to seston taxonomic composition. The large‐scale seasonal variability of light intensity and its interaction with diatom biomass were significant predictors of EPA concentrations. The deviation of temperature from mean values, accounting for a depth‐dependent effect on EPA concentrations, and its interaction with ciliate biomass were also variables with high predictive power. 4. The best models from the first and second approaches were validated with measurements of EPA concentrations from another year (1997). The estimation with the best model including only biomass explained 80%, and the best model from the second approach including mean temperature and depth explained 87% of the variability in EPA concentrations in 1997. 5. We show that it is possible to predict EPA concentrations reliably from plankton biomass, while the inclusion of abiotic factors led to results that were only partly consistent with expectations from laboratory studies. Our approach of including biotic predictors should be transferable to other systems and allow checking for biochemical constraints on primary consumers.     

Nitrogen Partitioning During Early Development of Supernodulating Soybean (Glycine max [L.] Merrill) Mutants and their Wild-Type Parent

The relative importance of fixed N², cotyledonary N, and nitratefor growth of seedlings of soybean cv. Bragg and two of itsnitrate tolerant supernodulating (nts) mutants (intermediatents 1116 and extreme nts1007) was investigated during symbioticdevelopment in the presence of nitrate (3.0 mol m^–3) using¹⁵N techniques. Newly-fixed N₂ and nitrate were both major sourcesof N for nodule development and nitrate principally supportedearly shoot and root growth in Bragg. In the nts mutants, however,all plant parts and nodules in particular, relied more on Nstored in the cotyledons. This resulted in later nodule maturityand a period of prolonged N-starvation for the seedlings ofthe extreme supernodulator, and could be responsible for theirsubsequently lowered biomass accumulation compared to the parentcultivar. Key words: Nodules, N partitioning, supernodulating soybeans     

Population regulation of brook trout (Salvelinus fontinalis) in Hunt Creek,Michigan: a 50‐year study

1. Fisheries models generally are based on the concept that strong density dependence exists in fish populations. Nonetheless, there are few examples of long‐term density dependence in fish populations. 2. Using an information theoretical approach (AIC) with regression analyses, we examined the explanatory power of density dependence, flow and water temperature on the per capita rate of change and growth (annual mean total length) for the whole population, adults, 1+ and young‐of‐the‐year (YOY) brook trout (Salvelinus fontinalis) in Hunt Creek, Michigan, USA, between 1951 and 2001. This time series represents one of the longest quantitative population data sets for fishes. 3. Our analysis included four data sets: (i) Pooled (1951–2001), (ii) Fished (1951–65), (iii) Unfished (1966–2001) and (iv) Temperature (1982–2001). 4. Principle component analyses of winter flow data identified a gradient between years with high mean daily winter flows, high daily maximum and minimum flows and frequent high flow events, and years with an opposite set of flow characteristics. Flows were lower during the Fished Period than during the Unfished Period. Winter temperature analyses elucidated a gradient between warm mean, warm minimum and maximum daily stream temperatures and a high number of minimum daily temperatures >6.1 °C, and years with the opposite characteristics. Summer temperature analyses contrasted years with warm summer stream temperatures vs years with cool summer stream temperatures. 5. Both YOY and adult densities varied several‐fold during the study. Regression analysis did not detect a significant linear or nonlinear stock–recruitment relationship. AIC analysis indicated that density dependence was present in 15 of 16 cases (four population segments × four data sets) for both per capita rate of increase (w_i values 0.46–1.00) and growth data (w_i values 0.28–0.99). The almost ubiquitous presence of density dependence in both population and growth data is concordant with results from other trout populations and other studies in Michigan.