Molecular phylogeny of the western Atlantic species of the genus Portunus (Crustacea, Brachyura, Portunidae)

The genus Portunus encompasses a comparatively large number of species distributed worldwide in temperate to tropical waters. Although much has been reported about the biology of selected species, taxonomic identification of several species is problematic on the basis of strictly adult morphology. Relationships among species of the genus are also poorly understood, and systematic review of the group is long overdue. Prior to the present study, there had been no comprehensive attempt to resolve taxonomic questions or determine evolutionary relationships within this genus on the basis of molecular genetics. Phylogenetic relationships among 14 putative species of Portunus from the Gulf of Mexico and other waters of the western Atlantic were examined using 16S sequences of the rRNA gene. The resultant molecularly based phylogeny disagrees in several respects with current morphologically based classification of Portunus from this geographical region. Of the 14 species generally recognized, only 12 appear to be valid. We recommend that P. vossi be hereafter regarded as a junior synonym of P. spinimanus and that P. bahamensis be regarded as a junior synonym of P. depressifrons . Our analysis suggests that western Atlantic members of the genus can be subdivided into at least three well-defined clades. Pending further molecular analyses with a large subset of species, it appears that the genus is not monophyletic and that it warrants further taxonomic revision.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 211–220.     

Spread and impact of introduced conifers in South America: Lessons from other southern hemisphere regions

The history of conifers introduced earlier elsewhere in the southern hemisphere suggests that recent invasions in Argentina, Brazil, Chile and Uruguay are likely to increase in number and size. In South Africa, New Zealand and Australia, early ornamental introductions and small forestry plantations did not lead to large‐scale invasions, while subsequent large plantations were followed with a lag of about 20–30 years by troublesome invasions. Large‐scale conifer plantation forestry in South America began about 50–80 years later than in South Africa, Australia and New Zealand, while reports of invasions in South America lagged behind those in the latter nations by a century. Impacts of invading non‐native conifers outside South America are varied and include replacement of grassland and shrubland by conifer forest, alteration of fire and hydrological regimes, modification of soil nutrients, and changes in aboveground and belowground biotic communities. Several of these effects have already been detected in various parts of South America undergoing conifer invasion. The sheer amount of area planted in conifers is already very large in Chile and growing rapidly in Argentina and Brazil. This mass of reproductive trees, in turn, produces an enormous propagule pressure that may accelerate ongoing invasions and spark new ones at an increasing rate. Regulations to control conifer invasions, including measures to mitigate spread, were belatedly implemented in New Zealand and South Africa, as well as in certain Australian states, inspired by observations on invasions in those nations. Regulations in South America are weaker and piecemeal, but the existing research base on conifer invasions elsewhere could be useful in fashioning effective regulations in South America. Pressure from foreign customers in South Africa has led most companies there to seek certification through the Forestry Stewardship Council; a similar programme operates in Australia. Such an approach may be promising in South America.     

Genetic structure and population differentiation of the Mediterranean pioneer spiny broom Calicotome villosa across the Strait of Gibraltar

The region around the Strait of Gibraltar is considered to be one of the most relevant 'hot spots' of biodiversity in the Mediterranean Basin due to its historical, biogeographical, and ecological features. Prominent among these is its role as a land bridge for the migration and differentiation of species during the Pleistocene, as a consequence of the lowering of sea level and climate changes associated with the Ice Ages. In the present study, we report a multilevel hierarchical investigation of the genetic diversity of Calicotome villosa , a common pioneer legume shrub, at the regional scale. The results of genetic analysis of progeny arrays are consistent with a predominantly outcrossing mating system in all the populations analysed. Geographically, a pattern of population isolation by distance was found, but the Strait accounted for only approximately 2% of the among-population genetic differentiation. Consequently, extensive historical gene flow appears to be the rule for this species in this area. According to the natural history traits of C. villosa (pollination, dispersal, and colonization ability), we hypothesize that gene flow must be strongly influenced by seed dispersal because pollen flow is very limited. Based on the history of trade and land use, cattle and human movements across the Strait must have strongly favoured seed dispersal. We review and discuss these results and compare them with those of other reported studies of genetic and phylogenetic differentiation across the Strait of Gibraltar. It is stressed that colonization ability, which depends upon seed dispersal and life form, can be a more critical factor in gene flow than pollination.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 39–51.     

Microsporogenesis and meiotic abnormalities in the hybrid complex of Phlomis composita (Lamiaceae)

The extent of chromosome structural differences such as permanent translocations and paracentric inversions has been studied in the hybrid complex of Phlomis composita and its putative parental taxa P. lychnitis and P. crinita . They are detected as meiotic abnormalities during microsporogenesis. In total, 117 plants from 19 populations in Andalusia (southern Spain) and Levante (eastern Spain) were studied for ploidy level, chromosome clumping, multivalent or univalent formation, late bivalent disjunction with bridges, chromatin bridges and fragments, irregular polysporads and variable pollen size. All individuals had the diploid chromosome number 2 n  = 20, with no significant difference in the frequencies of the above meiotic abnormalities either at taxon or population levels. However, very different frequencies were observed on the regional scale between populations in Andalusia and Levante. The results are discussed within the theoretical framework of homoploid hybrid or recombinational speciation.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 79−85.     

MICROTUBULES IN THE SHELL OF THE INVASIVE BIVALVE CORBICULA FLUMINEA (MULLER, 1774) (BIVALVIA: HETERODONTA)

Using scanning electron and histological techniques on specimensof the bivalve Corbicula fluminea a new relationship betweenmantle, shell and periostracum has been observed, apparentlyfor the first time. Here we demonstrate that several extensionsof the mantle epithelium pierce the shell to join the innerlayer of the two-layered periostracum. The mantle extensionsare confirmed as unicellular processes. We suggest that theycould serve the animal in the mobilization of calcium from theshell for buffering the extrapalhal fluid under anaerobic conditions,when organic acids accumulate or when an extra contributionof Ca²⁺ is required (Received 5 January 1994; accepted 30 March 1994)     

Miscellania dentata gen. et sp.n. (Polychaeta: Syllidae) from the Spanish Mediterranean coast

Specimens of Miscellania dentata gen. et sp.n. were collected in Catalunya, the Balearic Islands, and Strait of Gibraltar. They are characterized by an anterior tooth and an incomplete crown of denticles on the tip of the pharynx, short and smooth antennae and cirri, bases of palps separated, and the presence of compound and simple setae. Specimens were found living inside calcareous algal concretions.     

Habitat Selection by Prairie Dogs in a Disturbed Landscape at the Edge of Their Geographic Range

ABSTRACT Although habitat attributes of black-tailed prairie dog (Cynomys ludovicianus) colonies have been described for central and northern portions of the species' geographic range, little is known about these associations at the southern edge of this species' distribution. Because high-quality habitats are expected to be scarcer at the edge of the species' geographic range, different patterns of habitat selection might emerge in these populations. We analyzed habitat selection by black-tailed prairie dogs in a human-disturbed mosaic of desert grasslands and shrublands in northwestern Chihuahua, Mexico. We contrasted 151 used and 133 unused habitat units producing 11 case-control logistic regression models to explain site occupancy by prairie dogs with different combinations of environmental variables. Prairie dogs from Chihuahua occupy sites similar in most respects to sites in more northern regions, although these prairie dogs appear to be more tolerant of increased shrub density and reduced herbage cover. We found that site occupancy was best modeled by positive effects of soil moisture level, cover of forbs, cover of unpalatable vegetation, cover of bare ground, and amount of prairie-dog colony area within 1 km and by the inverse of altitude, shrub density, herbage height, and amount of hostile habitat within 1 km. The 2 most significant variables were herbage height and shrub density, which might reflect the prominent role that visibility plays in habitat selection by prairie dogs. In contrast, we found weak evidence that human features have significant impacts on site occupancy by prairie dogs. Our results support the prediction that environmental conditions of sites used by prairie dogs in edge regions partially differ from those observed in more northern latitudes. We suggest that reserve managers focus conservation efforts on areas with short vegetation, low density of shrubs, and high herbage cover, conditions that could be promoted by controlled burns, herbage mowing, and mechanical removal of shrubs.