Evolution of Oligo-Miocene talpids (Mammalia,Talpidae) in Europe: focus on the genera Myxomygale and Percymygale n. gen.

Abstract

New material recovered in the Oligocene locality St-Martin-de-Castillon (Vaucluse, France; MP24) provides a better knowledge of the characteristics of the species vauclusensis in its type-locality, hitherto assigned to the genus Myxomygale (Talpinae, tribe Urotrichini). In Europe, the species assigned to Myxomygale range from Late Eocene/Early Oligocene to the end of the Middle Miocene (MN 7/8). However noticeable differences can be observed in mandibles of these taxa, sometimes even coexisting in the same localities. We propose for the plesiomorphic branch (including M. vauclusensis and M. minor) a new genus, Percymygale, closely related to Myxomygale. Percymygale is consequently also assigned to the tribe Urotrichini. Today, the tribe Urotrichini (American and Japanese shrew-moles) is composed of terrestrial, semi-fossorial species, not well adapted to digging but able to climb small bushes, and foraging in grasslands, forests and covered landscapes. As a result, their limbs protrude laterally from the body (unlike in moles) and their humeri are usually longer with very limited adaptations to digging. Humeri are poorly known for Myxomygale and only fragmentary humeri are known for Percymygale n. gen. making comparisons difficult. However the muzzle development in Percymygale and Myxomygale suggests that Myxomygale was perhaps a better burrower than Percymygale.

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http://www.zoobank.org/urn:lsid:zoobank.org:act:17E4DD37-24A4-4C7A-A7FEB421CF90F89C     

13C-NMR spectroscopic investigation of α- and β-1,4-D-glucose homooligomers

A complete, unambiguous assignment of all the ¹³C signals of cellobiose and maltose has been achieved using methods such as selective proton decoupling, ¹³C selective spin labeling, and isotopic chemical shift induced by deuterium. The chemical-shift variation of the ¹³C signals with the degree of polymerization in each α or β (1 → 4) series is discussed. The chemical-shift dependence on temperature and solvent in these two series is shown and interpreted in terms of modifications of the solvation and of the conformation.     

Nitrogen availability increases in a tundra ecosystem during five years of experimental permafrost thaw

Perennially frozen soil in high latitude ecosystems (permafrost) currently stores 1330–1580 Pg of carbon (C). As these ecosystems warm, the thaw and decomposition of permafrost is expected to release large amounts of C to the atmosphere. Fortunately, losses from the permafrost C pool will be partially offset by increased plant productivity. The degree to which plants are able to sequester C, however, will be determined by changing nitrogen (N) availability in these thawing soil profiles. N availability currently limits plant productivity in tundra ecosystems but plant access to N is expected improve as decomposition increases in speed and extends to deeper soil horizons. To evaluate the relationship between permafrost thaw and N availability, we monitored N cycling during 5 years of experimentally induced permafrost thaw at the Carbon in Permafrost Experimental Heating Research (CiPEHR) project. Inorganic N availability increased significantly in response to deeper thaw and greater soil moisture induced by Soil warming. This treatment also prompted a 23% increase in aboveground biomass and a 49% increase in foliar N pools. The sedge Eriophorum vaginatum responded most strongly to warming: this species explained 91% of the change in aboveground biomass during the 5 year period. Air warming had little impact when applied alone, but when applied in combination with Soil warming, growing season soil inorganic N availability was significantly reduced. These results demonstrate that there is a strong positive relationship between the depth of permafrost thaw and N availability in tundra ecosystems but that this relationship can be diminished by interactions between increased thaw, warmer air temperatures, and higher levels of soil moisture. Within 5 years of permafrost thaw, plants actively incorporate newly available N into biomass but C storage in live vascular plant biomass is unlikely to be greater than losses from deep soil C pools.     

An investigation of astroglial morphology in Torpedo and Scyliorhinus

The distribution and morphology of GFAP-immunoreactive cells was investigated in two elasmobranch species, Scyliorhinus canicula and Torpedo marmorata, in an attempt to distinguish between Horstmann's (1954) hypothesis that the presence of cells resembling mammalian astrocytes is a function of the thickness of the ventricular walls, and Cajal's (1911) hypothesis that astrocytes are a phylogenetic novelty found only in birds and mammals. Two types of GFAP-reactive elements were observed, but the distribution of these differed markedly between the two species. In Scyliorhinus, radial glial cells were predominant and astrocytes relatively rare. In Torpedo, on the other hand, a species in which the ventricles are atrophied and the ventricular walls extremely thick, the overwhelming majority of GFAP-labelled structures strongly resembled astrocytes; occasionally, GFAP-positive cells were observed in the ependyma of the spinal cord. These findings, together with previous results obtained by others in hagfish, provide strong evidence in favour of Horstmann's hypothesis.     

A genetic screen for increased loss of heterozygosity in Saccharomyces cerevisiae

Loss of heterozygosity (LOH) can be a driving force in the evolution of mitotic/somatic diploid cells, and cellular changes that increase the rate of LOH have been proposed to facilitate this process. In the yeast Saccharomyces cerevisiae, spontaneous LOH occurs by a number of mechanisms including chromosome loss and reciprocal and nonreciprocal recombination. We performed a screen in diploid yeast to identify mutants with increased rates of LOH using the collection of homozygous deletion alleles of nonessential genes. Increased LOH was quantified at three loci (MET15, SAM2, and MAT) on three different chromosomes, and the LOH events were analyzed as to whether they were reciprocal or nonreciprocal in nature. Nonreciprocal LOH was further characterized as chromosome loss or truncation, a local mutational event (gene conversion or point mutation), or break-induced replication (BIR). The 61 mutants identified could be divided into several groups, including ones that had locus-specific effects. Mutations in genes involved in DNA replication and chromatin assembly led to LOH predominantly via reciprocal recombination. In contrast, nonreciprocal LOH events with increased chromosome loss largely resulted from mutations in genes implicated in kinetochore function, sister chromatid cohesion, or relatively late steps of DNA recombination. Mutants of genes normally involved in early steps of DNA damage repair and signaling produced nonreciprocal LOH without an increased proportion of chromosome loss. Altogether, this study defines a genetic landscape for the basis of increased LOH and the processes by which it occurs.     

Asymmetrical food web responses in trophic-level richness, biomass, and function following lake acidification

We tested for disproportional changes in annual and seasonal species richness and biomass among five trophic levels (phytoplankton, herbivorous, omnivorous, and carnivorous zooplankton, and fish) as well as altered trophic structure and ecosystem function following the 5-year experimental acidification of Little Rock Lake (Wisconsin, USA) from pH 6.1 to 4.7. Abiotic and biotic controls of trophic level response during acidification were also identified. Asymmetric reductions of species richness among trophic levels, separated by life stage and feeding type, were evident and changes in trophic structure were most pronounced by the end of the acidification period. Relative declines in richness of fish and zooplankton were greater than phytoplankton, which were generally unaffected, leading to a reduction of upper trophic level diversity. Each of the lower four trophic levels responded to a distinct combination of abiotic and biotic variables during acidification. pH was identified as a direct driver of change for only carnivorous zooplankton, while all other trophic levels were affected more by indirect interactions caused by acidification. Fluctuations in ecosystem function (zooplankton biomass and primary production) were also evident, with losses at all trophic levels only detected during the last year of acidification. The acidified basin displayed a tendency for greater variation in biomass for upper trophic levels relative to reference conditions implying greater unpredictability in ecosystem function. Together, these results suggest that trophic asymmetry may be an important and recurring feature of ecosystem response to anthropogenic stress.