The effectiveness of some mechanisms of reproductive isolation in Arum maculatum and A. italicum (Araceae)

Mechanisms of reproductive isolation were studied in two species of Arum , A. italicum and A. maculatum , growing in England and the south of France. The study focused on three potential mechanisms for reproductive isolation: the effectiveness of dichogamy as a barrier to autogamy; the ability of self and outcrossed pollen to germinate on stigmas at different stages of anthesis and to effect pollination; and postzygotic barriers to selfing. Dichogamy was found to provide a very effective barrier to within-inflorescence selfing in these species, as no seeds were produced by spontaneous self-pollination (i.e. autogamy) in any population of either species. However, the study found that geitonogamy (cross-pollination between inflorescences of a same individual or clone) was possible, as genotypes frequently produced several inflorescences and stigmas were found to be receptive to pollen from before anthesis until their contraction at the end of the female phase of flowering. Hand pollination with self pollen from clone inflorescences produced as numerous and heavy seeds as outcross pollination. In addition, the germination and growth of geitonogamously produced seed was similar to that of outcrossed seed, suggesting that this potential postzygotic barrier is absent or weak. These findings suggest that geitonogamous seed production may be unrestricted by significant pre- or postzygotic barriers. The possible advantages of geitonogamy in Arum are discussed.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 323–328.     

Estimating fat and protein fuel from fat and muscle scores in passerines

Fat is the prime energy source for birds during prolonged exercise, but protein is also catabolized. Estimates of the amount of catabolizable fat and protein (termed fat and protein fuel) are therefore important for studying energetics of birds. As fat and protein fuel can only be measured by sacrificing individuals or by use of technically complex methods, scoring systems were invented to estimate fat and protein fuel of birds in the field. The visible subcutaneous fat deposits and the thickness of the flight muscles are each scored on an ordinal scale but these scales do not correspond linearly to fat and protein fuel within species, which is needed for analyses such as flight range estimates. We developed an anova ‐type model to estimate fat and protein fuel from fat scores (FS) and muscle scores (MS) along with total mass and a size measurement. Using data from 11 337 individuals of eight passerine species (Common Nightingale Luscinia megarhynchos, Eurasian Reed Warbler Acrocephalus scirpaceus, Melodious Warbler Hippolais polyglotta, Willow Warbler Phylloscopus trochilus, Orphean Warbler Sylvia hortensis, Garden Warbler Sylvia borin, Common Whitethroat Sylvia communis, Subalpine Warbler Sylvia cantillans) mist‐netted in Mauritania, West Africa, we tested for independence of FS and MS and for variation in the relationship between scores and associated mass in response to physiological state. FS, MS and third primary length (size) explained variation in body mass of all eight species analysed (R²: 0.56–0.77). The parameter estimates of the model showed that fat and protein fuel increased monotonically with increasing fat and muscle scores. In two species we found small differences in the estimates between physiological states (seasons). We evaluated our model by comparing the predicted body mass of birds with both FS and MS equal to 0 with the mean body mass of individuals mist‐netted with both scores equal to zero. The values were very close. The amount of fat extracted from dead Garden and Willow Warblers was within the range of predicted fat fuel derived from the model. We conclude that our model is a useful non‐invasive method to estimate simultaneously mean fat and protein fuel of small passerines and we provide recommendations on its use.     

Loading Mode Interactions in Simulations of Long Bone Cross-Sectional Adaptation

Although many bone adaptation theories have been formulated to address both trabecular and cortical adaptation, most applications have focused on trabecular adaptation. Thus far, no thorough investigations of the influence of different types of loading on predicted patterns of long bone cross-sectional adaptation have been reported. In the current study, we present a new model for long bone cross-sectional adaptation that incorporates axial, bending and torsional loading components. We found that bending moments have a strong potential to modulate cross-sectional geometry, but can produce unforseen (and unrealistic) geometric instabilities. Torsional moments have the ability to suppress these instabilities, suggesting that torsion may play a more significant role in guiding long bone development than previously recognized. Our results also call into question the concept of strict “remodeling equilibrium,” suggesting that long bones do not necessarily approach a state of uniform mechanical stimulation. This modeling approach provides an additional perspective on experimental studies, and may lead to a greater understanding of the interaction between mechanics and biology in long bone adaptation.     

Environmental control on the biogeographical distribution of Desmanella (Soricomorpha,Mammalia) in the Miocene of the Iberian Peninsula

Abstract: This paper reports the first record of Desmanella (Mammalia, Soricomorpha) from the Granada Basin in southern Iberian Peninsula, which represents its south‐westernmost occurrence in all Eurasia. It is a controversial taxon whose systematic assignment has been discussed for a long time. This genus belongs to the family Talpidae, a group of insectivores that include extant moles, shrew moles and desmans. Desmanella was very abundant in the late Miocene and early Pliocene of Eurasia, including several basins of northern Iberian Peninsula, but it has not been found until now in southern Iberia. Previous studies have shown that the faunal record and the climatic conditions during the Neogene in the Granada Basin were different from other areas of the Iberian Peninsula. The particular distribution of Desmanella supports the hypothesis that specific climatic features (wetter than neighbouring areas) prevailed in the Granada Basin during the late Turolian (late Miocene).     

Experimental shading alters leaf litter breakdown in streams of contrasting riparian canopy cover

1. Headwater stream ecosystems are primarily heterotrophic, with allochthonous organic matter being the dominant energy. However, sunlight indirectly influences ecosystem structure and functioning, affecting microbial and invertebrate consumers and, ultimately, leaf litter breakdown. We tested the effects of artificial shading on litter breakdown rates in an open‐canopy stream (high ambient light) and a closed‐canopy stream (low ambient light). We further examined the responses of invertebrate shredders and aquatic hyphomycetes to shading to disentangle the underlying effects of light availability on litter breakdown. 2. Litter breakdown was substantially slower for both fast‐decomposing (alder, Alnus glutinosa) and slow‐decomposing (beech, Fagus sylvatica) leaf litters in artificially shaded stream reaches relative to control (no artificial shading) reaches, regardless of stream type (open or closed canopy). 3. Shredder densities were higher on A. glutinosa than on F. sylvatica litter, and shading had a greater effect on reducing shredder densities associated with A. glutinosa than those associated with F. sylvatica litter in both stream types. Fungal biomass was also negatively affected by shading. Results suggest that the effects of light availability on litter breakdown rates are mediated by resource quality and consumer density. 4. Results from feeding experiments, where A. glutinosa litter incubated under ambient light or artificial shade was offered to the shredder Gammarus fossarum, suggest that experimental shading and riparian canopy openness influenced litter palatability interactively. Rates of litter consumption by G. fossarum were decreased by experimental shading in the open‐canopy stream only. 5. The results suggest that even small variations in light availability in streams can mediate substantial within‐stream heterogeneity in litter breakdown. This study provides further evidence that changes in riparian vegetation, and thus light availability, influence organic matter processing in heterotrophic stream ecosystems through multiple trophic levels.     

Multimodal signals in male European treefrog (Hyla arborea) and the influence of population isolation on signal expression

In nocturnal treefrogs, mate choice implies the use of acoustic and visual signals. Multimodality is suspected to have evolved for either information redundancy or information complementariness. It is essential to explore multimodality in a natural context to understand the selection pressures operating on the signals. In the present study, we investigated calling and coloration in relation to male biometry and condition in four populations of European treefrog (Hyla arborea) varying in size and genetic isolation. We compared the signal intensity between core and satellite populations to estimate the impact of genetic diversity on male secondary sexual traits. The results obtained show important regional variations in both traits, likely as a result of local adaptations. Call and coloration are weakly correlated within an individual, implying that these traits likely convey different information about the signaller's identity or quality, thus supporting the hypothesis of complementariness of multiple messages. By contrast to the experimental evidence, we find that call and coloration are not related to male condition (as estimated by the residual of mass over size), suggesting that the condition‐dependence of these traits may be mediated by complex mechanisms not accurately reflected by the chosen estimator. Finally, male call and colour phenotypes present no robust pattern of variation with isolation status, probably because of variation in local selective pressures and in history of population dynamics. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 633–647.     

Species richness estimation and determinants of species detectability in butterfly monitoring programmes

Abstract 1. Species richness is the most widely used biodiversity index, but can be hard to measure. Many species remain undetected, hence raw species counts will often underestimate true species richness. In contrast, capture–recapture methods estimate true species richness and correct for imperfect and varying detectability. 2. Detectability is a crucial quantity that provides the link between a species count and true species richness. For insects, it has hardly ever been estimated, although this is required for the interpretation of species counts. 3. In the Swiss butterfly monitoring programme about 100 transect routes are surveyed seven times a year using a highly standardised protocol. In July 2003, control observers made two additional surveys on 38 transects. Data from these 38 quadrats were analysed to see whether currently available capture–recapture models can provide quadrat‐specific estimates of species richness, and to estimate species detectability in relation to transect, observer, survey, region, and abundance. 4. Species richness over the entire season cannot be estimated using current capture–recapture methods. The species pool was open, preventing use of closed population models, and detectability varied by species, preventing use of current open population models. Assuming a closed species pool during two mid‐season (July) surveys, a Jackknife capture–recapture method was used that accounts for heterogeneity to estimate mean detectability and species richness. 5. In every case, more species were present than were counted. Mean species detectability was 0.61 (SE 0.01) with significant differences between observers (range 0.37–0.83). Species‐specific detection at time t+ 1 was then modelled for those species seen at t for three mid‐season surveys. Detectability averaged 0.50 (range 0.17–0.81) for individual species and 0.65, 0.44, and 0.42 for surveys. Abundant species were detected more easily, although this relationship explained only 5% of variation in species detectability. 6. These are important, although not entirely unexpected, results for species richness estimation of short‐lived animals. Raw counts of species may be misleading species richness indicators unless many surveys are conducted. Monitoring programmes should be calibrated, i.e. the assumption of constant detectability over dimensions of interest needs to be tested. The development of capture–recapture or similar models that can cope with both open populations and heterogeneous species detectability to estimate species richness should be a research priority.     

Old and stable soil organic matter is not necessarily chemically recalcitrant: implications for modeling concepts and temperature sensitivity

Soil carbon turnover models generally divide soil carbon into pools with varying intrinsic decomposition rates. Although these decomposition rates are modified by factors such as temperature, texture, and moisture, they are rationalized by assuming chemical structure is a primary controller of decomposition. In the current work, we use near edge X‐ray absorption fine structure (NEXAFS) spectroscopy in combination with differential scanning calorimetry (DSC) and alkaline cupric oxide (CuO) oxidation to explore this assumption. Specifically, we examined material from the 2.3–2.6 kg L^?1 density fraction of three soils of different type (Oxisol, Alfisol, Inceptisol). The density fraction with the youngest ¹⁴C age (Oxisol, 107 years) showed the highest relative abundance of aromatic groups and the lowest O‐alkyl C/aromatic C ratio as determined by NEXAFS. Conversely, the fraction with the oldest C (Inceptisol, 680 years) had the lowest relative abundance of aromatic groups and highest O‐alkyl C/aromatic C ratio. This sample also had the highest proportion of thermally labile materials as measured by DSC, and the highest ratio of substituted fatty acids to lignin phenols as indicated by CuO oxidation. Therefore, the organic matter of the Inceptisol sample, with a ¹⁴C age associated with ‘passive’ pools of carbon (680 years), had the largest proportion of easily metabolizable organic molecules with low thermodynamic stability, whereas the organic matter of the much younger Oxisol sample (107 years) had the highest proportion of supposedly stable organic structures considered more difficult to metabolize. Our results demonstrate that C age is not necessarily related to molecular structure or thermodynamic stability, and we suggest that soil carbon models would benefit from viewing turnover rate as codetermined by the interaction between substrates, microbial actors, and abiotic driving variables. Furthermore, assuming that old carbon is composed of complex or ‘recalcitrant’ compounds will erroneously attribute a greater temperature sensitivity to those materials than they may actually possess.