Browsing Earth sciences by Types
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Diversification dynamics in freshwater bivalves (Unionidae) from the East African RiftInvertebrates are exceptionally diverse, but declining because of anthropogenic changes to their habitat, as exemplified by freshwater bivalves in Europe and North America. Much less information is available for African freshwater bivalves, especially for Unionidae, which comprise 9 genera and ~40 nominal species, many of which are endemic to African ancient lakes. The phylogenetic position of most of these genera and species remains uncertain, and their conservation status unassessed. Here, we present preliminary results of phylogenetic studies on the Unionidae of the East African Rift. We integrate a phylogenetic backbone based on four gene fragments with (1) sampling information to examine geographic patterns of diversity and with (2) geometric morphometrics of shell shape to examine the relation between morphological disparity and molecular diversity. African Unionidae apart from ‘Cafferia’ form a monophyletic clade, and the basal splits in this clade occur between the reciprocally monophyletic genera Pseudospatha and Grandidieria, both of which are currently endemic to Lake Tanganyika. Mweruella, Nyassunio and Prisodontopsis are also monophyletic in the preliminary analyses as is Nitia, although this latter taxon is nested within Coelatura, which highlights the need of systematic revisions. Biogeographic analyses indicate a statistically significant North-to-South colonization of the East African Rift by Coelatura sensu lato. Beyond deep phylogenetic splits among individual clades, limited molecular differentiation is observed within most clades, calling for population genetic studies. Ongoing morphometric analyses suggest strong morphological differentiation among several clades, but substantial disparity in shell shape is observed within many clades, which needs further examination.
New model systems for early land plant evolution (w16-05) Vienna, Austria, 22 - 24 June 2016Microbial communities have existed on land since at least the Neoarchean (2800 to 2500 million years), but fossil evidence indicates that the ancestors of land plants first appeared much later during the mid-Ordovician some 470 million years ago. These latter communities probably comprised varied and mixed associations of Archaea, Bacteria, arthropods, lichens, fungi, green algae and extinct land plants called ‘cryptophytes’. Little is known about the cryptophytes, but emerging evidence from fossil charcoal records minute sporophytes at the bryophyte level of complexity but with novel combinations of characteristics. Some are known to contain spores dispersed as tetrads and dyads suggesting that significant differences in sporogenesis operated in some early extinct lineages. The most intact and earliest well-preserved fossil ecosystem is the 407 million year old Rhynie Chert (Scotland). Here, plants were fossilised near to their sites of growth preserving soft tissues and organism associations. Such fossils provide unparalleled insights into the evolution of major organ systems in stem group vascular plants and lycophytes, including roots, shoots, leaves, vascular system and reproductive structures. They are helping us to understand how key plant organs evolved from precursor structures, to disentangle homology from homoplasy, to better reconstruct early life cycle evolution, and to learn about the co-evolution of plants and their fungal symbionts.