Phylogeography and genetic structure of the edible sea urchin Paracentrotus lividus (Echinodermata: Echinoidea) inferred from the mitochondrial cytochrome b gene

Phylogeographical analysis of Paracentrotus lividus was carried out by means of sequencing the mitochondrial cytochrome b gene (1143 bp) of 260 individuals collected at 22 Mediterranean and four Atlantic localities. Against a background of high haplotype diversity and shallow genetic structuring, we observed significant genetic divergence between the Adriatic Sea and the rest of the Mediterranean, as well as between the Mediterranean and the Atlantic sample groups. Furthermore, on the largest spatial scale, isolation by distance was detected. Three main haplogroups were identified by network and Bayesian assignment analyses. The relative proportions of haplogroups were different in the four regions considered, with the exception of Western and Eastern Mediterranean that showed a similar pattern. This result together with the outcome of S_nn statistics, analysis of molecular variance and network analyses allowed to identify three weakly differentiated populations corresponding to the Atlantic, Western + Eastern Mediterranean, and Adriatic seas. Analyses of mismatch distribution and neutrality tests were consistent with the presence of genetic structuring and past demographic expansion(s). From a fisheries perspective, the results obtained in the present study are consistent with genetic sustainability of current exploitation; local depleted stocks are recurrently replenished by recruits that may have originated from nonharvested areas. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 910–923.     

Exploring the history of Serapias politisii (Orchidaceae), a narrow endemic on the opposite coasts of the Otranto channel: insights from molecular investigations

Knowledge of genetic spatial structure may provide insights into the causes of population disjunctions in plants. Serapias politisii is a narrow endemic with only a few populations scattered along the opposite coasts of the Otranto strait (southern Adriatic Sea). It was originally considered to be of hybrid origin between S. vomeracea ssp. laxiflora and S. parviflora, a possibility suggested also by a DNA phylogenetic study that grouped Italian and Greek populations in two distinct clades. In this study we have carried out additional plastid DNA sequencing and an AFLP analysis of the three taxa. Whereas the geographical distribution of four plastid DNA haplotypes supports the likelihood of a double hybrid origin or of a plastid capture, AFLP data do not support such a hypothesis, because S. politisii shows several private alleles, some of which are shared by Italian and Greek populations. In light of the floristic specificity of the coasts bordering the Otranto strait, we consider that the present‐day disjunction of S. politisii could have originated either by a long‐distance seed dispersal or by a fragmentation of an old polymorphic population. The pairwise mismatch distribution excludes a recent expansion of the populations examined. In light of recent evidence concerning the Mediterranean Lago‐Mare period and the westward haplotype evolution detected in some Euro‐Mediterranean trees, we argue that fragmentation of a previously continuous population could be an intriguing possibility. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 572–580.     

Woody biomass production during the second rotation of a bio-energy Populus plantation increases in a future high CO2 world

The quickly rising atmospheric carbon dioxide (CO₂)‐levels, justify the need to explore all carbon (C) sequestration possibilities that might mitigate the current CO₂ increase. Here, we report the likely impact of future increases in atmospheric CO₂ on woody biomass production of three poplar species (Populus alba L. clone 2AS‐11, Populus nigra L. clone Jean Pourtet and Populus×euramericana clone I‐214). Trees were growing in a high‐density coppice plantation during the second rotation (i.e., regrowth after coppice; 2002–2004; POPFACE/EUROFACE). Six plots were studied, half of which were continuously fumigated with CO₂ (FACE; free air carbon dioxide enrichment of 550 ppm). Half of each plot was fertilized to study the interaction between CO₂ and nutrient fertilization. At the end of the second rotation, selective above‐ and belowground harvests were performed to estimate the productivity of this bio‐energy plantation. Fertilization did not affect growth of the poplar trees, which was likely because of the high rates of fertilization during the previous agricultural land use. In contrast, elevated CO₂ enhanced biomass production by up to 29%, and this stimulation did not differ between above‐ and belowground parts. The increased initial stump size resulting from elevated CO₂ during the first rotation (1999–2001) could not solely explain the observed final biomass increase. The larger leaf area index after canopy closure and the absence of any major photosynthetic acclimation after 6 years of fumigation caused the sustained CO₂‐induced biomass increase after coppice. These results suggest that, under future CO₂ concentrations, managed poplar coppice systems may exhibit higher potential for C sequestration and, thus, help mitigate climate change when used as a source of C‐neutral energy.     

Crossing barriers between the unrewarding Mediterranean orchids Serapias vomeracea and Serapias cordigera

Understanding the genetic architecture of admixed hybridizing populations helps in evaluating the nature of species boundaries and the levels of gene exchange between co-occurring species. In the present study, we examined a contact zone between Serapias vomeracea and Serapias cordigera , two unrewarding Mediterranean orchid species with a non-specific pollination strategy. Fruit production and seed viability from interspecific hand-pollination treatments pointed out the weaknesses of post-pollination barriers. The occurrence of hybridization was molecularly confirmed in the genus Serapias for the first time, as parts of plants with a transitional morphology were observed in both alleles of the parental LEAFY intron. Amplified fragment length polymorphism analysis revealed that plants with uncertain morphology and classified as one of the other parental species are actually backcrosses, attesting to an extensive interspecific gene exchange. Overall, the contact zone is more similar to a hybrid zone of Ophrys species, well known for their highly specialized pollination, than to a hybrid zone of unspecialized food-deceptive orchids. Therefore, species boundaries in Serapias are maintained by pre-pollination mechanisms that need to be better investigated. In light of the intriguing similarities between Serapias and Ophrys underlined by the present study, we hypothesize that the emission of floral scents could be involved in the maintenance of species boundaries in Serapias .     

Habitat preferences of Eurasian Bitterns Botaurus stellaris booming in ricefields: implications for management

The Eurasian Bittern Botaurus stellaris suffered declines in western Europe during the 20th century, partly because of wetland reclamation. The species has been traditionally considered a reedbed specialist but recent studies identified a greater ecological plasticity than previously believed. We investigated habitat associations of a Eurasian Bittern population that has started to breed in the ricefields of northwest Italy since the early 1990s. Booming Bitterns had a higher probability of occurring in ricefields with taller rice plants, more vegetated field banks, more weeds, a larger surface and closer to remaining natural wetlands. The positive effect of field bank vegetation height on the probability that a ricefield hosted a booming Bittern declined late in the season, in contrast to the effects of weeds and ricefield area, which were stronger later in the season. A decreasing importance of vegetation on field banks to booming Bitterns may be a consequence of seasonal changes in habitat structure through the Bittern’s breeding period. The degree of flooding did not affect the probability of occurrence of booming Bitterns, probably because most ricefields were homogeneously flooded during the peak breeding season (June–July). Our findings have important implications for the management of Bittern populations breeding in the ricefields of northwest Italy. We propose simple conservation actions that may favour the occurrence of booming Bitterns and help the species spread in this novel habitat.     

The unicellular freshwater cyanobacterium Synechococcus and mixotrophic flagellates: evidence for a functional association in an oligotrophic, subalpine lake

1. We applied Reynolds's approach to the study of phytoplankton ecology through functional associations of species to identify possible algal species, which associate with the freshwater cyanobacterium Synechococcus. Previously an association among Synechococcus spp. and small‐celled chlorophytes (association Z) has been recognised by evaluating phytoplankton associations according to functional criteria. 2. Biomass data for phytoplankton and picocyanobacteria from Lago Maggiore spanning more years were organised in a matrix and a cluster analysis was performed. The results showed four groups separated at a linkage distance of 0.20. Mixotrophic species which clustered with Synechococcus spp. were Ceratium hirundinella, Chrysochromulina parva, Cryptomonas erosa, Cryptomonas ovata, Dinobryon bavaricum, Dinobryon sociale, Rhodomonas minuta and Uroglena americana. The redundancy analysis (RDA) consolidated the association of Synechococcus with C. hirundinella and R. minuta showing greater probability of occurrence than random aggregates of species. 3. The association Synechococcus spp. –C. hirundinella also appeared from temporal variation of their biomass. In early summer both these species increased at the same time; later, the peak of C. hirundinella (potential predator) coincided with a minimum of Synechococcus spp. suggesting a possible predator‐prey interaction. This implied that phytoplankton assemblages which form a functional group cannot only have similar adaptations and requirements but can also exhibit trophic interactions. 4. We propose to enlarge the association Z and create an association Z_MX (where _MX stands for mixotrophs) which would include Synechococcus spp. and C. hirundinella as the most representative of the mixotrophic species found in the oligotrophic Lago Maggiore.