Karyological observations on Turbellaria Proseriata: karyometric analysis ofMonocelis fusca,M. lineata (Monocelididae) andParotoplana macrostyla (Otoplanidae)

A karyometric analysis of the chromosome set of the marine turbellariansMonocelis fusca, M. lineata andParotoplana macrostyla has been carried out. The karyotype of the twoMonocelis species investigated (2n=6) is formed by three pairs of small and similarly sized chromosomes: InM. fusca, chromosome 1 is metacentric, chromosome 2 acrocentric and chromosome 3 is subtelocentric.M. lineata also presents one pair of metacentric chromosomes (chromosome 2), while chromosomes 1 and 3 are submetacentric.P. macrostyla (2n=12) reveals two pairs of large metacentric and four pairs of small chromosomes, three of which are metacentric, whereas the last is subtelocentric.     

Population structure of the Monocelis lineata (Proseriata, Monocelididae) species complex assessed by phylogenetic analysis of the mitochondrial Cytochrome c Oxidase subunit I (COI) gene

Monocelis lineata consists of a complex of sibling species, widespread in the Mediterranean and Atlantic Ocean. Previous genetic analysis placed in evidence at least four sibling species. Nevertheless, this research was not conclusive enough to fully resolve the complex or to infer the phylogeny/phylogeography of the group. We designed specific primers aiming at obtaining partial sequences of the mtDNA gene Cytochrome c Oxidase subunit I (COI) of M. lineata, and have identified 25 different haplotypes in 32 analyzed individuals. The dendrogram generated by Neighbor-Joining analysis confirmed the differentiation between Atlantic and Mediterranean siblings, as well as the occurrence of at least two Mediterranean sibling species. Thus validated, the method here presented appears as a valuable tool in population genetics and biodiversity surveys on the Monocelis lineata complex.     

The Gyratrix hermaphroditus species complex (Kalyptorhynchia: Polycystididae) in marine habitats of eastern Australia

A karyological and morphological analysis of 97 specimens from eastern Australia belonging to the Gyratrix hermaphroditus species complex was performed. Based on karyotype and on details of sclerotized structures of the copulatory organ, the existence of at least eight sibling species in eastern Australia could be recognised. Some of the siblings have a wide distribution across eastern and northern Australia. Populations of wide-ranging species often showed degrees of karyological and morphological differentiation. The diversity of the group is particularly high in tropical Australia. Distribution of siblings appears to be affected by ecological and physical barriers, and determined by sediment texture. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dismissal of Acoelomorpha: Acoela and Nemertodermatida are separate early bilaterian clades

We used new 18S and 28S rRNA sequences analysed with parsimony, maximum likelihood and Bayesian methods of phylogenetic reconstruction to show that Nemertodermatida, generally classified as the sister group of Acoela within the recently proposed Phylum Acoelomorpha, are a separate basal bilaterian lineage. We used several analytical approaches to control for possible long branch attraction (LBA) artefacts in our results. Parsimony and the model based phylogenetic reconstruction methods that incorporate 'corrections' for substitution rate heterogenities yielded concordant results. When putative long branch taxa were experimentally removed the resulting topologies were consistent with our total evidence analysis. Deletion of fast-evolving nucleotide sites decreased resolution and clade support, but did not support a topology conflicting with the total evidence analysis. Establishment of Acoela and Nemertodermatida as two early lineages facilitates reconstruction of ancestral bilaterian features. The ancestor of extant Bilateria was a small, benthic direct developer without coelom or a planktonic larval stage. The previously proposed Phylum Acoelomorpha is dismissed as paraphyletic.     

Karyometrical analysis of 10 species of the subfamily Monocelidinae (Proseriata,Platyhelminthes) with remarks on the karyological evolution of the Monocelididae

Ten species of the Monocelidinae have been examined. All were found to be regularly diploid. Four of them show the chromosome number n=3 and remarkably similar karyotypes (one pair of large metacentrics, one pair of medium sized metacentrics and one pair of small heterobrachial chromosomes). This set is considered as basic (plesiomorphic) for the family Monocelididae. Three species present n=4 and three species n=5, with an increase of heterobrachial chromosomes. Based on karyometrical data, it is suggested that these complements are derived from the basic complement through fission of one or both metacentric chromosomes, respectively. Further minor chromosome rearrangements, involving centromere position, were observed.     

A molecular tool for genetic surveys in the red coral (Corallium rubrum): An Inter-Simple Sequence Repeats (ISSRs) perspective

Corallium rubrum is a colonial cnidarian, distributed in Mediterranean and Atlantic rocky bottoms. The species has been largely exploited for use in jewellery since 17th century, raising increasing concerns for the sustainability of the present rate of harvesting. The aim of this study was to standardise a simple and not expensive molecular technique to perform genetic analysis on populations of C. rubrum, in order to provide a useful tool for future surveys. Twelve samples collected from one shallow-water and two deep sites located at the Capo Caccia–Isola Piana MPA (North-western Sardinia, Italy) were surveyed by means of 10 ISSR (Inter-Simple Sequence Repeat) primers. Our results confirmed the ease of use and the reliability of ISSR markers, and their usefulness in detecting genetic variability even among individuals.     

Patterns of diversity in soft-bodied meiofauna: dispersal ability and body size matter

Background

Biogeographical and macroecological principles are derived from patterns of distribution in large organisms, whereas microscopic ones have often been considered uninteresting, because of their supposed wide distribution. Here, after reporting the results of an intensive faunistic survey of marine microscopic animals (meiofauna) in Northern Sardinia, we test for the effect of body size, dispersal ability, and habitat features on the patterns of distribution of several groups.

Methodology/Principal Findings

As a dataset we use the results of a workshop held at La Maddalena (Sardinia, Italy) in September 2010, aimed at studying selected taxa of soft-bodied meiofauna (Acoela, Annelida, Gastrotricha, Nemertodermatida, Platyhelminthes and Rotifera), in conjunction with data on the same taxa obtained during a previous workshop hosted at Tjärnö (Western Sweden) in September 2007. Using linear mixed effects models and model averaging while accounting for sampling bias and potential pseudoreplication, we found evidence that: (1) meiofaunal groups with more restricted distribution are the ones with low dispersal potential; (2) meiofaunal groups with higher probability of finding new species for science are the ones with low dispersal potential; (3) the proportion of the global species pool of each meiofaunal group present in each area at the regional scale is negatively related to body size, and positively related to their occurrence in the endobenthic habitat.

Conclusion/Significance

Our macroecological analysis of meiofauna, in the framework of the ubiquity hypothesis for microscopic organisms, indicates that not only body size but mostly dispersal ability and also occurrence in the endobenthic habitat are important correlates of diversity for these understudied animals, with different importance at different spatial scales. Furthermore, since the Western Mediterranean is one of the best-studied areas in the world, the large number of undescribed species (37%) highlights that the census of marine meiofauna is still very far from being complete.     

Phylogenetic relationships within the Archiloa genus complex (Proseriata,Monocelididae)

Of the seven genera which we have recognised within the Archiloa genus complex sensu Karling (1966) the cosmopolitan genus Archilina is the most primitive and is characterised only by plesiomorphic characters, and has to be considered paraphyletic. All other species of the Archiloa genus complex are hypothesized to be derived from Archilina-like ancestors through different evolutionary lineages. One lineage led to the genera Archiloa, Inaloa, Archilopsis and Monocelopsis, taxa found in the Atlantic and the Mediterranean. These genera are monophyletic and their relationships are analyzed. The genera Mesoda (Brazil) and Tajikina (Northern Pacific) can be considered as two other separate lineages. Similarly, within what we now consider as the genus Archilina different lineages can be recognized in different regions.     

Chromosomal evolution and speciation in the Gyratrix hermaphroditus species complex (Platyhelminthes,Kalyptorhynchia): karyometric and morphological analyses of fifteen fresh-water populations from Western Europe

Fifteen fresh-water populations of the Gyratrix hermaphroditus species complex from Western Europe (Italy, Spain, France) were karyometrically analysed. All shared the same chromosome number 2n = 4. Three distinct karyotypes were recognized on the basis of the different values of the centromeric index of chromosome 2, respectively metacentric, intermediate between meta- and submetacentric, and sub-telocentric. The morphology of chromosome 1 (an isobrachial metacentric) and the length ratio of chromosomes were on the contrary constant in all the populations investigated.Differences in the size of male cuticular organs were observed accompanying the karyological differentiation.The fifteen populations are interpreted as representing at least three sibling-species.Chromosomal evolution and phylogenetical relationships with the marine species of the Gyratrix hermaphroditus complex are discussed.