Linking environmental warming to the fitness of the invasive clam Corbicula fluminea

Climate warming is discussed as a factor that can favour the success of invasive species. In the present study, we analysed potential fitness gains of moderate warming (3 °C above field temperature) on the invasive clam Corbicula fluminea during summer and winter. The experiments were conducted under seminatural conditions in a bypass-system of a large river (Rhine, Germany). We showed that warming in late summer results in a significant decrease in the clams' growth rates (body mass and shell length increase) and an increase in mortality rate. The addition of planktonic food dampens the negative effect of warming on the growth rates. This suggests that the reason for the negative growth effect of temperature increase in late summer is a negative energetic balance caused by an enhanced metabolic rate at limited food levels. Warming during early summer revealed contrasting effects with respect of body mass (no warming effect) and shell length (increased shell growth with warming). This differential control of both parameters further enhances the loss of the relative (size-specific) body mass with warming. In contrast, warming in winter had a consistently positive effect on the clams' growth rate as demonstrated in two independent experiments. Furthermore, the reproduction success (as measured by the average number of larvae per clam) during the main breeding period (April) was strongly enhanced by experimental warming during winter, i.e. by eight times during the relatively cold winter 2005/2006 and by 2.6 times during the relatively warm winter 2007/2008. This strong, positive effect of moderate winter warming on the clams' fitness is probably one reason for the recent invasion success of C. fluminea in the northern hemisphere. However, warm summer events might counteract the positive winter warming effect, which could balance out the fitness gains.     

FOSSIL DIAGENESIS IN THE BURGESS SHALE

Abstract:  Current models for the exceptional preservation of Burgess Shale fossils have focused on either the HF-extractable carbonaceous compressions or the mineral films identified by elemental mapping. BSEM, EDX and microprobe analysis of two-dimensionally preserved Marpolia , Wiwaxia and Burgessia identifies the presence of both carbonaceous and aluminosilicate films for most features, irrespective of original lability. In the light of the deep burial and greenschist facies metamorphism documented for the Burgess Shale, the aluminosilicate films are identified as products of late-stage volatilization and coincident mineralization of pre-existing compression fossils, whereas the three-dimensionally preserved gut-caecal system of Burgessia is interpreted as an aluminosilicate replacement of a pre-existing carbonate phase. The case for late diagenetic emplacement of aluminosilicate minerals is supported by the extensive aluminosilicification of trilobite shell and (originally) calcareous veinlets in the Burgess Shale, as well as documentation of other secondarily aluminosilicified compression fossils. By distinguishing late diagenetic alteration from the early diagenetic processes responsible for exceptional preservation, it is possible to reconcile the range of preservational modes currently expressed in the Burgess Shale.     

Historical DNA from museum type specimens clarifies diversity of Asian leaf turtles (Cyclemys)

Species boundaries in Asian leaf turtles of the genus Cyclemys are difficult to define on the basis of morphology, primarily because many populations exhibit considerable ontogenetic variation in shell and head coloration. Two recent molecular phylogenetic hypotheses of Cyclemys species relationships, based largely on market and pet-trade samples of uncertain provenance, were highly incongruent. We used historical DNA methods to sequence fragments of the mitochondrial cytochrome  b gene from eight type specimens of Cyclemys (including one collected by Alfred Russel Wallace), and phylogenetically placed these type sequences into the context of published cytochrome  b variation. Our phylogenetic hypothesis supports the recognition of four named species ( Cyclemys atripons , Cyclemys dentata , Cyclemys oldhamii , and C. pulchristriata ), as well as a fifth species of unknown geographical provenance obtained from the Hong Kong pet trade. The type sequences show that previous molecular phylogenetic studies were hampered by misidentifications, supporting the notion that Cyclemys of unknown provenance are not reliably identified to species solely on the basis of morphology.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 131–141.     

Shell structure, ontogeny and affinities of the Lower Cambrian bivalved problematic fossil Mickwitzia muralensis Walcott, 1913

Exceptionally preserved carbonate- and shale-hosted Mickwitzia muralensis from the Lower Cambrian Mural Formation, southern Canadian Rocky Mountains, complement one another to yield an unusually complete account of its ontogeny, ecology and phylogenetic relationships. The shell of M. muralensis is composed of dense phosphatic layers interspersed with porous organic-rich layers. At the insertion of shell-penetrating tubes, shell layers deflect inwards to produce inwardly pointing cones. The tubes are interpreted as having hosted setae that were secreted by outer-epithelial follicles. Follicular setae also occurred at the mantle margin, where they were oriented within the plane of the shell as in modern brachiopods. During ontogeny, the initial setae oriented in the plane of the shell occurred before the first shell-penetrative setae. In the juvenile and early-mature stages of shell secretion, a posterior opening was present between both valves and was used for the protrusion of an attachment structure. In the late-mature shell, this opening became fixed in the ventral valve. Based on the posterior margin and the shell microstructure, a close relationship between Mickwitzia and the paterinids is proposed with differences interpreted as heterochronic. The shell-penetrative setal apparatus of M. muralensis is distinct from that previously described of Micrina, though both types are conceivably homologous to adult and juvenile setae of modern brachiopods.