Bioerosion of shells by terrestrial gastropods

Empty shells of terrestrial gastropods remain intact and become fossilized only under particular conditions. The usually thin shells are readily dissolved by rainwater, a process starting often during life. Results indicate that with this chemical weathering they may lose some 1% in weight per month. But this is not the only process by which shell biominerals disappear. During field experiments, living terrestrial gastropods have been observed to actively remove calcareous material from empty shells apparently to use for building their own shell. Empty shells lost ∼30% of their weight in 2 months, indicating this process to be much more important than simple dissolution, and explaining the rapid disappearance of empty shells in the field. Previously, mainly anecdotal mention has been made of this shell scraping. Bones of birds were not scraped by terrestrial gastropods; they lost ∼1% in weight per month at the start due to chemical weathering alone, but weight loss decreased with time and was only 6.5% after 16 months.     

The use of structural reduction in phylogenetic reconstruction of decapods and a phylogenetic hypothesis for 15 genera of Majidae: testing previous larval hypotheses and assumptions

Summary

Using larval data of zoeae from selected genera of majids, we determined tree topologies, levels of homoplasy, and frequencies of reduction under three different assumptions of character argumentation: ordered reduction events, unordered reduction events, and outgroup comparison. Under each assumption we provided a phylogenetic hypothesis for some majid genera and evaluated the assumption that structural reduction can be assumed a priori as a criterion to infer character transformation polarity in phylogenetic reconstruction of decapods. The results indicate that the a priori assumption of “reduction” as the derived condition is not justified because under this assumption, reduction is not always maintained throughout the resulting phylogenetic hypothesis. Furthermore, we also found that this criterion fails to provide the most parsimonious explanation of the data set. Therefore, we reject the use a “reduction=derived” criterion to infer polarity in phylogenetic reconstruction. Phylogenetic analysis using outgroup comparison provided a phylogenetic hypothesis with a better fit and a lower frequency of reduction events. However, we found that statements of homology may be problematic when the number of larval stages in the outgroup differ from those of the ingroup. To overcome this problem, we suggest that, in the absence of evidence for developmental homology, all larval stages should be considered as potential homologues. Using this approach to homology of larval stages, we provide a new phylogenetic hypothesis for 15 genera of majids based on larval morphology. Within Majidae, representative members of Majinae formed a highly nested monophyletic group with the following topology: ((Jacquinotia+Notomithrax) (Leptomithrax+Maja)). In contrast, the Oregoniinae (Hyas+Chionoecetes) formed a basal monophyletic group. Contrary to established ideas for the monophyly of Inachinae, Macrocheira is basal to the Oregoniinae. Other taxa did not form monophyletic groupings based on classical assignment to subfamilies.     

Zur Anatomie und systematischen Stellung der Architectonicidae (Mollusca, Allogastropoda)

The anatomy of the Architectonicidae is described. The family combines prosobranch and pentaganglionate (=euthyneuran) traits, but has evolved in a very specialized way as cnidaria-feeders. There is no close relationship to the Epitoniidae, and the taxon 'Heterogastropoda' is regarded as artificial. The closest relatives of the Architectonicidae are the Mathildidae and the Pyramidellidae, all united in a taxon Allogastropoda. This taxon is regarded as a connecting link between basal marine Caenogastropoda and the most primitive Pentaganglionata (e.g. Acteon, Ringicula ). The relationships of the Architectonicidae to the Rissoellidae and Omalogyridae are briefly discussed.     

Drought turns a Central European Norway spruce forest soil from an N2O source to a transient N2O sink

Based on current climate scenarios, a higher frequency of summer drought periods followed by heavy rainfall events is predicted for Central Europe. It is expected that drying/rewetting events induce an increased matter cycling in soils and may contribute considerably to increased emissions of the greenhouse gas N₂O on annual scales. To investigate the influence of drying/rewetting events on N₂O emissions in a mature Norway spruce forest in the Fichtelgebirge area (NE Bavaria, Germany), a summer drought period of 46 days was induced by roof installations on triplicate plots, followed by a rewetting event of 66 mm experimental rainfall in 2 days. Three nonmanipulated plots served as controls. The experimentally induced soil drought was accompanied by a natural drought. During the drought period, the soil of both the throughfall exclusion and control plots served as an N₂O sink. This was accompanied by subambient N₂O concentrations in upper soil horizons. The sink strength of the throughfall exclusion plots was doubled compared with the control plots. We conclude that the soil water status together with the soil nitrate availability was an important driving factor for the N₂O sink strength. Rewetting quickly turned the soil into a source for atmospheric N₂O again, but it took almost 4 months to turn the cumulative soil N₂O fluxes from negative (sink) to positive (source) values. N₂O concentration and isotope analyses along soil profiles revealed that N₂O produced in the subsoil was subsequently consumed during upward diffusion along the soil profile throughout the entire experiment. Our results show that long drought periods can lead to drastic decreases of N₂O fluxes from soils to the atmosphere or may even turn forest soils temporarily to N₂O sinks. Accumulation of more field‐scale data on soil N₂O uptake as well as a better understanding of underlying mechanisms would essentially advance our knowledge of the global N₂O budget.     

How Much Water is in the Tank? Model Calculations for Two Epiphytic Bromeliads

Water-impounding foliage (=tank) characterizes many bromeliadspecies but, to date, a quantitative evaluation of the effectivenessof these structures to bridge rainless periods is not available.We present a model that analyses the capacity of these phytotelmatato supply moisture to the bromeliad as a function of plant size,and parameterize it for two epiphyte species,Tillandsia fasciculataandGuzmaniamonostachya. All parameters related to the recharging of a tank(e.g. catchment area, or tank capacity) and those related towater loss from the tank (e.g. tank water surface, or waterabsorption from the tank by the plant) changed with plant size.For both species a similar qualitative size-related patternemerged: smaller individuals dried out much faster than largerconspecifics. Modelling the changes in tank water content foran entire year revealed that in the seasonal climate of BarroColorado Island, Panama, tanks of smaller plants (1 g d. wt)are expected to lack water for up to 110 d (inT. fasciculata).Regardless of plant size, individuals ofG. monostachyawere consistentlymore efficient thanT. fasciculatain maintaining moisture intheir tanks. Our results provide insight into the limitationsof water-impounding tanks as an adaptation to cope with an intermittentwater supply typical for epiphytic habitats. These limitationsare particularly pronounced for smaller individuals.Copyright1999 Annals of Botany Company. Epiphytes, water relations, Barro Colorado Island, bromeliads, water tanks, phytotelmata.     

THE LATE TRIASSIC BLACK SHALES OF THE GUANLING AREA, GUIZHOU PROVINCE, SOUTH-WEST CHINA: A UNIQUE MARINE REPTILE AND PELAGIC CRINOID FOSSIL LAGERSTÄTTE

Abstract:  Black shales of the lower member of the Carnian Xiaowa Formation (previously known as the Wayao Member of the Falang Formation or as the Wayao Formation) in the Guanling area, Guizhou Province, south-west China, are yielding a rich marine reptile fauna and exceptional remains of pelagic crinoids. The black shales represent deposition on the drowned southern margin of the Yangtze Platform during a Maximum Flooding Interval. The relatively reduced sedimentation rates led to the formation of the Lagerstätte through the accumulation of fossils in the anoxic bottom sediments over a prolonged period of time. Invertebrate fossils represent almost exclusively pelagic forms, such as a diverse ammonite fauna and halobiid bivalves. The spectacular finds of colonies of large (stem lengths > 11 m) crinoids of the genus Traumatocrinus attached to driftwood prove that this crinoid was the first to evolve a pseudoplanktonic life style. The other crinoid is the planktonic roveacrinid Osteocrinus . The marine reptile fauna, represented by probably hundreds of skeletons, is numerically dominated by three species of ichthyosaurs and four species of thalattosaurs. The thalattosaurs fill a palaeobiogeographic gap between the Alpine thalattosaur faunas and those from western North America. Two species of placodonts are rare finds. As for the thalattosaurs, the placodont occurrences greatly expand the geographic range of the group because placodonts have been known previously only from the Mediterranean region, the Alps and the Muschelkalk Basin. The unique abundance of thalattosaurs contrasts with a scarcity of fishes. Although we suggest that the fauna is authochthonous and inhabited surface waters, it must have represented an unusual ecosystem. However, the possibility remains that both the marine reptiles and the Traumatocrinus colonies were concentrated in the region by currents and do not reflect the biocoenosis.     

Electric organ discharge variability of Mormyridae (Teleostei: Osteoglossomorpha) in the Upper Volta system

The electric organ discharges (EODs) of five mormyrid species ( Marcusenius senegalensis , Brevimyrus niger , Petrocephalus bovei , Pollimyrus isidori , Hippopotamyrus pictus ) from different sampling sites from the Upper Volta system in West Africa were investigated. EOD waveforms were recorded at high sampling rates in order to compare signal waveform parameters of the different species from different locations. Except for H. pictus , EODs within a species differed significantly from one another in some parameters and waveform variability at least between some sampling sites. In addition, each species showed a continuous spectrum of waveform variations, all or only parts of which were found at certain localities. Although there was variability and sometimes similarities between species, the EOD waveforms were species specific. Knowing their variation spectrum, they can be used for species determination and are probably used for species recognition by the mormyrids. Similarities or differences in EOD waveform expression within a species were not related to geographical distance. By contrast, we suggest that biotic environmental factors at a given location influence the expression of EOD waveforms. These factors affect absolute measurements such as EOD duration and fast Fourier transformation peak frequency as well as the amount of variation for certain waveform parameters across species in a similar manner for a given site. Although EOD waveform might be important for the establishment of reproductive barriers between species, our results suggest that differences in waveforms may not necessarily reflect different species or speciation processes in progress.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 61–80.     

Anatomy and affinities of cocculinid limpets (Mollusca, Archaeogastropoda)

The anatomy of seven cocculinid species, representing four genera, is described. Two new genera are erected, Paracocculina and Coccocrater, and a comparative account of all cocculinid species so far anatomically investigated is given. Definitions of six genera, mainly based on anatomical data, are presented. Variation at the species level is also discussed. The closest relatives of the Cocculinidae are found in the Bathysciadiidae, sharing a distinct gill type and similar coelomic conditions. Therefore, both families are united as the Cocculinoidea. The Lepetelloidea (Lepetellidae, Pseudococculinidae, Osteopeltidae, Bathyphytophilidae (?), Cocculinellidae, Addisoniidae and Choristellidae) are more distantly related and are classified, together with the Cocculinoidea, within the suborder Cocculiniformia. The Cocculiniformia are regarded as one of the earliest offshoots at the archaeogastropod level of organization, being secondarily modified in several respects.