Disentangling allometry and response to Kellwasser anoxic events in the Late Devonian conodont genus Ancyrodella

Is the ability to respond to minor perturbations a key to survival to major crisis? This idea was supported by previous studies on Late Devonian conodonts. Genera surviving the Frasnian/Famennian (F/F) crisis, at the end of the Upper Kellwasser anoxic event, had shown a response to a similar but minor event, the Lower Kellwasser (LKW). In contrast, the genus Ancyrodella went extinct at the F/F crisis. This study aims to assess whether this extinction was associated with the absence of response to the minor LKW event. For this purpose, the shape of the P1 platform elements of the conodont Ancyrodella curvata was quantified based on their 2‐D outlines. Conodonts were extracted from two outcrops documenting the Late Devonian Kellwasser events, Coumiac (France) and Mrirt (Morocco). Ancyrodella curvata is characterized by a marked allometric growth that may blur any other source of shape difference, like response to the LKW. Hence, a multivariate method was developed to disentangle size‐free from size‐related shape variations. No coherent temporal size variations emerged from the analysis, but allometry occurring along the growth of the element indeed appeared as the prevailing source of shape variation. By isolating size‐free variations, however, we were able to evidence a morphometric response of A. curvata to the LKW independent from the allometric pattern. Hence, the extinction of A. curvata at the F/F crisis cannot be attributed to an absence of response to minor events. The amount of shape change involved in the LKW shift is, however, of minor importance in comparison with the shape variation due to allometric growth. Alternate hypotheses have been further investigated. Ancyrodella curvata appears as a rare species in the assemblages, and its distribution worldwide suggests a rather specialist taxon. Considering survivorship curves (i.e. frequency distribution of the conodont as a function of its size) A. curvata was characterized by low and constant mortality rate. This may be a clue for a long growth and progressive investment in the reproduction. These arguments support the view that A. curvata was a rather specialist, rare and ‘K‐selected’ taxon. All these factors may not be exclusive and their unfavourable conjunction might have been the key to the extinction of A. curvata.     

Spatio-temporal patterns of fish assemblages in a large regulated alluvial river

1. The River Durance, the last alpine tributary of the River Rhône, is a large, braided alluvial hydrosystem. Following large-scale regulation, flow downstream of the Serre-Ponçon dam has been maintained at 1/40th of previous annual mean discharge. To assess the effects of historical disturbances, fish assemblages and habitat use were analysed during five summers in a representative reach of the middle Durance.
2. Habitat availability and use were assessed with a multi-scale approach including the variables water depth, current velocity, roughness height of substratum, amount of woody debris and lateral/longitudinal location. Eighteen fish species were sampled by electrofishing in 289 habitat sample units.
3. Partial least square (PLS) regression showed that taxa were mainly distributed according to relationships between their total length and water depth/velocity variables. Fish assemblage composition was also related to roughness height as well as distance from the bank or to the nearest large woody debris. However, PLS regression revealed no significant differences in habitat selection between two periods of varying hydromorphological stability.
4. Fish distribution patterns and density were related to proximity to the bank and cover, indicating that local scale variables need to be considered in conservation and restoration programmes.     

Molecular phylogenetic evidence for paraphyly of the genus Sooglossus, with the description of a new genus of Seychellean frogs

The Seychelles harbour an endemic frog family, the Sooglossidae, currently containing two genera: Sooglossus , with three species, and Nesomantis , with one species. These unique frogs are generally considered to be basal neobatrachians, although their relationships to other neobatrachian taxa, except the Nasikabatrachidae, remain unresolved. Our molecular phylogeny based on a dataset consisting of fragments of the nuclear rag-1 and rag-2 genes, as well as mitochondrial 16S rRNA in representatives of the major neobatrachian lineages, confirmed the previously postulated Sooglossidae + Nasikabatrachidae clade and the placement of the South American Caudiverbera with the Australian Myobatrachidae, but did not further resolve the position of sooglossids. Our results do, however, unambiguously show sooglossids to be monophyletic but the genus Sooglossus to be paraphyletic, with the type species Sooglossus sechellensis being more closely related to Nesomantis thomasseti than to Sooglossus gardineri and Sooglossus pipilodryas , in agreement with morphological, karyological, and bioacoustic data. As a taxonomic consequence, we propose to consider the genus name Nesomantis as junior synonym of Sooglossus , and to transfer the species thomasseti to Sooglossus . For the clade composed of the species gardineri and pipilodryas , here, we propose the new generic name Leptosooglossus . A significant genetic differentiation of 3% was found between specimens of Sooglossus thomasseti from the Mahé and Silhouette Islands, highlighting the need for further studies on their possible taxonomic distinctness.   © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 347–359.     

Intra- and interspecific morphological variation in the field mouse species Apodemus argenteus and A. speciosus in the Japanese archipelago: the role of insular isolation and biogeographic gradients

Two species of field mice, Apodemus argenteus and A. speciosus, occur in sympatry across the Japanese archipelago. The inter- and intraspecific patterns of morphological differentiation have been evaluated, using a Fourier analysis of the mandible outline. The relative importance of the effect of insular isolation and latitudinal climatic gradient on the size and shape of the two species was assessed by a comparison of the populations from the large island of Honshu and the surrounding small-island populations. The size variation in A. argenteus is correlated with the climatic gradient whilst the shape variation corresponds mainly to a random differentiation of the small-island populations from a Honshu-like basic morphological pattern. A. speciosus displays increased size on small islands, and its shape variation is related to both the climatic gradient and insularity. Finally, the two species are differentiated by both the size and shape of the mandible across the Japanese archipelago, suggesting that interspecific competition between both species is reduced via niche partitioning. Our results emphasize the importance of insular isolation on shape differentiation, but a part of the morphological differentiation is also related to the latitudinal climatic gradient. Isolation on small islands could have favoured such a response to environmental factors by lowering the gene flow that prevents almost any significant differentiation within Honshu populations.     

Pharmacological Characterization of an Opioid Receptor in the Ciliate Tetrahymena

A pharmacological characterization has been performed of the opioid receptor involved in modulation of phagocytosis in the protozoan ciliate Tetrahymena. Studies on inhibition of phagocytosis by mammalian prototypic opioid agonists revealed that morphine and β-endorphin have the highest intrinsic activity, whereas all the other opioids tested can only be considered partial agonists. However, morphine (a mu-receptor agonist) is twice as potent as β-endorphin (a delta-receptor agonist). Furthermore, the sensitivity for the opioid antagonist naloxone, determined in the presence of morphine and β-endorphin, is very similar to the sensitivity exhibited by mammalian tissues rich in mu-opioid receptors. We suggest that the opioid receptor coupled to phagocytosis in Tetrahymena is mulike in some of its pharmacological characteristics and may serve as a model system for studies on opioid receptor function and evolution.