Landscape genetic structure of chestnut (Castanea sativa Mill.) in Spain

The current need for forest conservation and management has driven a rapid expansion of landscape genetics approach. This discipline combines tools from molecular genetics, landscape ecology and spatial statistics and is decisive for improving not only ecological knowledge but also for properly managing population genetic resources. This approach could be appropriate to sweet chestnut (Castanea sativa Mill.), a multipurpose species of great economic importance in the Mediterranean basin and a species considered to be a good model of integration between natural and human-driven distribution of diversity. Sixteen chestnut populations, covering the distribution range of the species in Spain, were analysed using seven microsatellite markers. Results revealed a high level of genetic diversity in Spanish chestnut populations, which in part followed a geographical pattern, although distribution was not homogeneous. Likewise, areas particularly rich in diversity were detected, facilitating the development of a hypothesis about the history of chestnut in Spain. In conclusion, these results provide valuable baseline data for more in-depth studies on chestnut landscape genetics that can contribute to its conservation.     

Experimentally induced endosymbiont loss and re-acquirement in the hydrothermal vent bivalve Bathymodiolus azoricus

Invertebrates harbouring endosymbiotic chemoautotroph bacteria are widely distributed in a variety of reducing marine habitats, including deep-sea hydrothermal vents. In these species mechanisms of symbiont transmission are likely to be key elements of dispersal strategies that remained partially unresolved because the early life stages are not available for developmental studies. To study cessation and re-establishment of symbiosis in the host gill a laboratory experiment was conducted over 45 days in a controlled set-up (LabHorta) that endeavour re-creation of the hydrothermal vent chemical environment. Our animal model was the vent bivalve Bathymodiolus azoricus from the Menez Gwen vent site of the Mid Atlantic Ridge (MAR). Animals were exposed to conditions lacking inorganic S supply for 30 days, which is vital for their symbionts, and then re-acclimatized in sulphide-supplied seawater for an additional 15 days.Gradual disappearance of bacteria from the symbiont-bearing gill cells was observed in animals kept in seawater free of dissolved sulphide for up to 30 days, and was evidenced by histological, ultrastructural observations and Polymerase Chain Reaction tests. Following re-acclimatisation in S-supplied seawater, proliferation of sulphur-bacteria in the gill bacteriocytes confirms the functionality of our sulfide-feeding system in supporting chemoautotrophic symbionts. It may also indicate a horizontal endosymbiont acquisition, i.e. from the environment to the host by means of phagocytosis-like mechanism involving special “pit-like” structures on the apical cell membrane.The present work reports the first laboratory set-up successfully used to maintain the hydrothermal vent bivalve B. azoricus for prolonged periods of time by supplying inorganic sulphur as an energy source for its bacterial endosymbionts. Survival of symbiont bacteria is a critical factor influencing the host physiology and thus the methods reported here represent great potential for future studies of host-symbiont dynamics and for post-capture experimental investigations.     

Pollinator foraging modifies nectar sugar composition in Helleborus foetidus (Ranunculaceae):An experimental test

We experimentally tested the hypothesis that the extensive within-plant variation of nectar sugar composition in Helleborus foetidus (Ranunculaceae) and other species results from differences between flowers and nectaries in pollinator visitation history. Experiments were conducted to mimic single-nectary visits by wild-caught individuals of the main bee pollinators of H. foetidus, which were assayed for their capacity to modify the sugar composition of natural and artificial nectar. Experimental nectar probing with bee mouthparts induced extensive changes in proportional sugar composition 48 h after treatment, and bee taxa differed widely in their effects. Nectar probing by Andrena, medium-sized Anthophoridae, Apis mellifera, and Lasioglossum had no subsequent effects on nectar sugar composition, while probing by Bombus terrestris and B. pratorum induced an extensive reduction in percentage sucrose, a marked increase in percentage fructose, and a slight increase in percentage glucose. Results support the hypothesis that stochastic variations among flowers or nectaries in the taxonomic identity of recent visitors and their relative visitation frequencies may eventually generate very small-scale mosaics in nectar sugar composition. Changes in nectar sugar composition following bumblebee probing may be the consequence of nectar contamination with pollinator-borne nectarivorous yeasts.     

Mutations in cytochrome b that affect kinetics of the electron transfer reactions at center N in the yeast cytochrome bc1 complex

We have examined the pre-steady-state kinetics and thermodynamic properties of the b hemes in variants of the yeast cytochrome bc1 complex that have mutations in the quinone reductase site (center N). Trp-30 is a highly conserved residue, forming a hydrogen bond with the propionate on the high potential b heme (bH heme). The substitution by a cysteine (W30C) lowers the redox potential of the heme and an apparent consequence is a lower rate of electron transfer between quinol and heme at center N. Leu-198 is also in close proximity to the b(H) heme and a L198F mutation alters the spectral properties of the heme but has only minor effects on its redox properties or the electron transfer kinetics at center N. Substitution of Met-221 by glutamine or glutamate results in the loss of a hydrophobic interaction that stabilizes the quinone ligands. Ser-20 and Gln-22 form a hydrogen-bonding network that includes His-202, one of the carbonyl groups of the ubiquinone ring, and an active-site water. A S20T mutation has long-range structural effects on center P and thermodynamic effects on both b hemes. The other mutations (M221E, M221Q, Q22E and Q22T) do not affect the ubiquinol oxidation kinetics at center P, but do modify the electron transfer reactions at center N to various extents. The pre-steady reduction kinetics suggest that these mutations alter the binding of quinone ligands at center N, possibly by widening the binding pocket and thus increasing the distance between the substrate and the bH heme. These results show that one can distinguish between the contribution of structural and thermodynamic factors to center N function.     

The intrastriatal injection of thrombin in rat induced a retrograde apoptotic degeneration of nigral dopaminergic neurons through synaptic elimination

We have performed intrastriatal injection of thrombin and searched for distant effects in the cell body region. In striatum, thrombin produced a slight loss of striatal neurons as demonstrated by neural nuclei immunostaining – a non-specific neuronal marker – and the expression of glutamic acid decarboxylase 67 mRNA, a specific marker for striatal GABAergic interneurons, the most abundant phenotype in this brain area. Interestingly, striatal neuropil contained many boutons immunostained for synaptic vesicle protein 2 and synaptophysin which colocalize with tyrosine hydroxylase (TH), suggesting a degenerative process with pre-synaptic accumulation of synaptic vesicles. When we studied the effects on substantia nigra, we found the disappearance of dopaminergic neurons, shown by loss of TH immunoreactivity, loss of expression of TH and dopamine transporter mRNAs, and disappearance of FluoroGold-labelled nigral neurons. The degeneration of substantia nigra dopaminergic neurons was produced through up-regulation of cFos mRNA, apoptosis and accumulation of α-synuclein shown by colocalization experiments. Thrombin effects could be mediated by protease-activated receptor 4 activation, as protease-activated receptor 4-activating peptide mimicked thrombin effects. Our results point out the possible relationship between synapse elimination and retrograde degeneration in the nigral dopaminergic system.     

Larval development of the Patagonian brotula Cataetyx messieri (Pisces, Bythitidae) from fjords of southern Chile

Larvae of Cataetyx messieri (Bythitidae) are described from 14 individuals (12·3–27·9 mm body length) collected in deep fjords and channels of the inland sea of southern Chile (41–55° S), between 137 and 604 m depth. The larvae are elongate, with a large, flattened mouth and a coiled gut. They are lightly pigmented and show three distinctive features: a band of melanophores from the snout to the opercle, melanophores spread over the dorsolateral surface of the stomach and the intestine and a band of melanophores on both dorsal and ventral margins of the tip of the tail and adjacent finfold.     

Middle Eastern and European mtDNA lineages characterize populations from eastern Crete

Throughout centuries, the geographic location of the island of Crete has been one of the leading factors shaping the composition of its population. Invasions and commercial and cultural ties at various time periods with European, Middle Eastern, and North African civilizations have created a collage of genetic and/or cultural influences from each of these regions within the island. Previous Y-chromosome diversity analyses uncovered pronounced differences in the frequency distribution of haplogroups from a mountain refugium and surrounding lowland populations of eastern Crete. In this study, the current geographic stratification of mtDNA haplotypes in eastern Crete was explored to elucidate potential sources of maternal gene flow. Our work includes a comparative characterization of two lowland collections from the Heraklion and Lasithi Prefectures in eastern Crete, as well as of an isolated mountain population from the Lasithi Plateau, all three previously examined using Y-chromosome markers. In addition to the presence of European mtDNA haplogroups in all three collections, our analyses reveal a significant contribution of Middle Eastern and Central Asian genetic signatures in the island of Crete, and particularly in the two populations from the Lasithi region at the eastern-most portion of the island. Close association between these Cretan groups and the Balkans can also be discerned, which in the case of the Lasithi Plateau corroborates previously uncovered Y-chromosome affiliations with the same geographic region.