Strong genetic cohesiveness between Italy and North Africa in four butterfly species

The sea acts as an effective dispersal barrier for most terrestrial animal species. Narrow sea straits, therefore, often represent areas where species are able to disperse from one land mass to another. In the Mediterranean Sea, the narrowest connecting points between North Africa and Europe are the Strait of Gibraltar and the Strait of Sicily. In the past, climatic oscillations caused changing sea levels and thus influenced the permeability of these sea straits. We analysed the genetic structure of four butterfly species that all occur on both sides of the Strait of Sicily. In all four species, we observed a lack of genetic differentiation between the populations of North Africa and those of Italy. Species distribution models support the strong cohesiveness in that they show a largely continuous glacial distribution over Italy and North Africa. The data obtained reveal that there was a large exchange of individuals between Italy and the eastern Maghreb during the last ice age. This might not only be the case for the species under investigation in the present study, but also might represent a more general pattern for mobile thermophilic western Palearctic species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 818–830.     

A NEW DIPNOAN FISH FROM THE MIDDLE DEVONIAN (EIFELIAN) OF SCOTLAND

Abstract:  A new dipnoan fish, Pinnalongus saxoni gen. et sp. nov., is described from a suite of recently discovered specimens from Caithness and East Sutherland, northern Scotland. The stratum where Pinnalongus occurs is within the middle Eifelian of the Middle Devonian. Pinnalongus has a skull roof consisting of a mosaic of small bones at the anterior end, a feature more typically found in Early Devonian dipnoans. The posterior part of the skull roof is more typical of later advanced Middle Devonian dipnoans with the B-bone separating the I-bones. The postcranial body is now considered not to be so important with respect to the classification of dipnoans as originally proposed by Dollo in 1895, who thought there was an evolutionary transformation series. Nevertheless, the postcranial body of Pinnalongus has more in common with later Middle and Late Devonian dipnoans such as Scaumenacia , with a very long second dorsal fin. Based on the skull morphology, Pinnalongus is most closely related to Tarachomylax from the Lower Devonian of Severnaya Zemlya, Russia. Pinnalongus represents the earliest known complete articulated dipnoan with tooth plates.     

Germination and emergence of Ambrosia artemisiifolia L. under changing environmental conditions in China

Laboratory and greenhouse studies were conducted to determine the effects of key environmental factors on germination and seedling emergence of the invasive weed Ambrosia artemisiifolia L. (common ragweed) collected from Mudanjiang (temperate climate), Nanjing (temperate–subtropical) and Nanchang (subtropical) in China. Germination of seeds occurred at temperatures ranging from 5 to 40°C, under both a 12‐h photoperiod and continuous darkness. Germination success exceeded 48% in solutions with pH values between 4 and 12, with maximum rates occurring in distilled water at pH 5.57. Germination was greatly reduced in solutions with osmotic potentials below ?0.8 MPa. Accordingly, the final germination ratio exceeded 69% at <200 mmol/L NaCl, but only reached 8% at 400 mmol/L NaCl. Emergence was greater than 75% at burial seed depths of 1–4 cm; no seedlings emerged from a soil depth of 8 cm. Seeds collected from Mudanjiang, Nanjing and Nanchang had very similar germination traits, with the main differences occurring in relation to temperature. The great germination success of common ragweed over highly variable conditions throughout its Chinese distribution range explains its successful large‐scale invasion.     

Direct and indirect effects of nitrogen deposition on species composition change in calcareous grasslands

Atmospheric nitrogen (N) deposition has been identified as a major threat to biodiversity, but field surveys of its effects have rarely focussed on sites which are actively managed to maintain characteristic species. We analysed permanent quadrat data from 106 plots in nature reserves on calcareous grassland sites in the United Kingdom collected during a survey between 1990 and 1993 and compared the data with the results from resurvey of 48 of these plots between 2006 and 2009. N deposition showed no significant spatial association with species richness, species diversity, or the frequency of species adapted to low nutrient conditions in the 1990–1993 dataset. However, temporal analysis showed that N deposition was significantly associated with changes in Shannon diversity and evenness. In plots with high rates of N deposition, there was a decrease in species diversity and evenness, a decline in the frequency of characteristic calcareous grassland species, and a lower number of rare and scarce species. As all sites had active management to maintain a high diversity and characteristic species, our results imply that even focussed management on nature conservation objectives cannot prevent adverse effects of high rates of N deposition. Structural equation modelling was used to compare different causal mechanisms to explain the observed effects. For change in Shannon diversity, direct effects of N deposition were the dominant mechanism and there was an independent effect of change in grazing intensity. In contrast, for change in herb species number, indirect effects on soil acidity, linked to both N and S deposition, were more important than direct effects of N deposition.     

Unraveling the drivers of intensifying forest disturbance regimes in Europe

Natural disturbances like wildfire, windthrow and insect outbreaks are critical drivers of composition, structure and functioning of forest ecosystems. They are strongly climate‐sensitive, and are thus likely to be distinctly affected by climatic changes. Observations across Europe show that in recent decades, forest disturbance regimes have intensified markedly, resulting in a strong increase in damage from wind, bark beetles and wildfires. Climate change is frequently hypothesized as the main driving force behind this intensification, but changes in forest structure and composition associated with management activities such as promoting conifers and increasing standing timber volume (i.e. ‘forest change’) also strongly influence susceptibility to disturbances. Here, we show that from 1958 to 2001, forest change contributed in the same order of magnitude as climate change to the increase in disturbance damage in Europe's forests. Climate change was the main driver of the increase in area burnt, while changes in forest extent, structure and composition particularly affected the variation in wind and bark beetle damage. For all three disturbance agents, damage was most severe when conducive weather conditions and increased forest susceptibility coincided. We conclude that a continuing trend towards more disturbance‐prone conditions is likely for large parts of Europe's forests, and can have strong detrimental effects on forest carbon storage and other ecosystem services. Understanding the interacting drivers of natural disturbance regimes is thus a prerequisite for climate change mitigation and adaptation in forest ecosystem management.     

A cohesion/tension model for the gating of aquaporins allows estimation of water channel pore volumes in Chara

The water permeability (hydraulic conductivity; Lp) of turgid, intact internodes of Chara corallina decreased exponentially as the concentration of osmolytes applied in the medium increased. Membranes were permeable to osmolytes and therefore they could be applied on both sides of the plasma membrane at concentrations of up to 2.0 m (5.0 MPa of osmotic pressure). Organic solutes of different molecular size (molecular weight, MW) and reflection coefficients (σ_s) were used [heavy water HDO, MW: 19, σ_s: 0.004; acetone, MW: 58, σ_s: 0.15; dimethyl formamide (DMF), MW: 73, σ_s: 0.76; ethylene glycol monomethyl ether (EGMME), MW: 76, σ_s: 0.59; diethylene glycol monomethyl ether (DEGMME), MW: 120, σ_s: 0.78 and triethylene glycol monoethyl ether (TEGMEE), MW: 178, σ_s: 0.80]. The larger the molecular size of the osmolyte, the more efficient it was in reducing cell Lp at a given concentration. The residual cell Lp decreased with increasing size of osmolytes. The findings are in agreement with a cohesion/tension model of the osmotic dehydration of water channels (aquaporins; AQPs), which predicts both reversible exponential dehydration curves and the dependence on the size of osmolytes which are more or less excluded from AQPs (Ye, Wiera & Steudle, Journal of Experimental Botany 55, 449–461, 2004). In the presence of big osmolytes, dehydration curves were best described by the sum of two exponentials (as predicted from the theory in the presence of two different types of AQPs with differing pore diameters and volumes). AQPs with big diameters could not be closed in the presence of osmolytes of small molecular size, even at very high concentrations. The cohesion/tension theory allowed pore volumes of AQPs to be evaluated, which was 2.3 ± 0.2 nm³ for the narrow pore and between 5.5 ± 0.8 and 6.1 ± 0.8 nm³ for the wider pores. The existence of different types of pores was also evident from differences in the residual Lp. Alternatively, pore volumes were estimated from ratios between osmotic (P_f) and diffusional (P_d) water flow, yielding the number of water molecules (N) in the pores. N-values ranged between 35 and 60, which referred to volumes of 0.51 and 0.88 nm³/pore. Values of pore volumes obtained by either method were bigger than those reported in the literature for other AQPs. Absolute values of pore volumes and differences obtained by the two methods are discussed in terms of an inclusion of mouth parts of AQPs during osmotic dehydration. It is concluded that the mouth part contributed to the absolute values of pore volumes depending on the size of osmolytes. However, this can not explain the finding of the existence of two different types or groups of AQPs in the plasma membrane of Chara.     

How useful are the recommended counts and indices in the systematics of the Octopodidae (Mollusca: Cephalopoda)

A morphological dataset based on 14 standard counts and indices was constructed for 68 specimens comprising 12 species of octopuses. This was used to construct distance matrices based on morphological characters. These matrices were compared with genetic distance matrices compiled during molecular phylogenetic analyses of the same 12 species using four mitochondrial and two nuclear genes. Mantel tests showed that there was significant congruence between the phenetic and genetic matrices, suggesting that the genetic signal is reflected in the morphological data set. Matrices of geographical distance were constructed for the 12 species based on the latitude, longitude, and depth of capture of 1726 individuals. These matrices never showed significant congruence with genetic data or with morphological data. Multivariate analysis of the morphological dataset suggests that these counts and indices, traditionally used for discriminating between species in cephalopods, do not show great discrimination at species level, but provide excellent discrimination at the generic level, and, as such, might be useful for resolving the generic placement of some problematic taxa. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 205–218.