Giacinta Angela Stocchino

Molecular barcoding and phylogeography of sexual and asexual freshwater planarians of the genus Dugesia in the Western Mediterranean (Platyhelminthes, Tricladida, Dugesiidae)

Planarians of the genus Dugesia have a worldwide distribution with high species diversity in the Mediterranean area. In this area, populations with a triploid karyotype that reproduce by fissiparity are exceptionally frequent, outnumbering the sexual populations. This situation poses interesting questions, such as the age of these asexual lineages, whether they all belong to the same species or whether the triploidization event is recurrent, and what factors (climatic, geographical, historical...) explain the prevalence of these asexual forms. However, asexual populations cannot be assigned to a species due to the lack of copulatory apparatus--the main structure used in species identification. In this study, we have developed a DNA barcoding method, based on COI and ITS-1 sequences, which allows the assignment of the fissiparous forms to sexual species. At the same time, phylogenetic analysis from species of the western Mediterranean have unveiled the presence of species with highly differentiated populations alongside species with a wide distribution and almost no genetic variation. The roles of habitat instability, dispersal capacity and human activities are briefly discussed.

Schmidtea mediterranea phylogeography: an old species surviving on a few Mediterranean islands?

BackgroundSchmidtea mediterranea (Platyhelminthes, Tricladida, Continenticola) is found in scattered localities on a few islands and in coastal areas of the western Mediterranean. Although S. mediterranea is the object of many regeneration studies, little is known about its evolutionary history. Its present distribution has been proposed to stem from the fragmentation and migration of the Corsica-Sardinia microplate during the formation of the western Mediterranean basin, which implies an ancient origin for the species. To test this hypothesis, we obtained a large number of samples from across its distribution area. Using known and new molecular markers and, for the first time in planarians, a molecular clock, we analysed the genetic variability and demographic parameters within the species and between its sexual and asexual populations to estimate when they diverged.ResultsA total of 2 kb from three markers (COI, CYB and a nuclear intron N13) was amplified from ~200 specimens. Molecular data clustered the studied populations into three groups that correspond to the west, central and southeastern geographical locations of the current distribution of S. mediterranea. Mitochondrial genes show low haplotype and nucleotide diversity within populations but demonstrate higher values when all individuals are considered. The nuclear marker shows higher values of genetic diversity than the mitochondrial genes at the population level, but asexual populations present lower variability than the sexual ones. Neutrality tests are significant for some populations. Phylogenetic and dating analyses show the three groups to be monophyletic, with the west group being the basal group. The time when the diversification of the species occurred is between ~20 and ~4 mya, although the asexual nature of the western populations could have affected the dating analyses.ConclusionsS. mediterranea is an old species that is sparsely distributed in a harsh habitat, which is probably the consequence of the migration of the Corsica-Sardinia block. This species probably adapted to temperate climates in the middle of a changing Mediterranean climate that eventually became dry and hot. These data also suggest that in the mainland localities of Europe and Africa, sexual individuals of S. mediterranea are being replaced by asexual individuals that are either conspecific or are from other species that are better adapted to the Mediterranean climate.

The freshwater planarian Dugesia sicula Lepori from Sardinia (Platyhelminthes, Tricladida)

Fissiparous strains of freshwater triclads of the Dugesia gonocephala group were collected from 12 localities in Sardinia all situated not more than 5 kilometers from the coast. Some environmental factors and the sexual status of the specimens were noted at the time of collection. During the laboratory rearing 30% of individuals of each strain became sexual (ex-fissiparous individuals). All the examined strains showed common karyological and morphological characteristics suggestive of the species Dugesia sicula Lepori. The chromosome complement, which was a constant 27+2–3 B chromosomes, was classified as aneutriploid, due to its clearly documented characteristics. The fissiparous populations of D. sicula appear to have a high degree of tolerance to variations in environmental factors, especially temperature. Within the D. gonocephala group this species has the broadest distribution in the Mediterranean region.

African planarians: Dugesia aethiopica sp. n. (Platyhelminthes, Tricladida) from Lake Tana (NW Ethiopia)

Abstract A new species of Dugesia from East Africa is described as a first report of Platyhelminthes from Lake Tana. Dugesia aethiopica sp. n. is characterized by the shape of its bursa copulatrix; length, diameter, course, and opening of the bursal canal; opening of the oviducts; shape of the penis papilla; penial parenchymatic cavity. The taxonomic position of the new species within the D. gonocephala group is discussed in comparison with the other African and Madagascan species.

Sponges of marine caves: Notes on the status of the Mediterranean palaeoendemic Petrobiona massiliana (Porifera: Calcarea: Lithonida) with new records from Sardinia

The discovery of conspicuous populations of the rare species Petrobiona massiliana is reported from shallow water karstic caves of Sardinia. The morphological comparative analysis versus previous data from the entire geographic range highlights that spicular traits seem to be highly conservative in contrast with a notable plasticity of growth form. Lifestyle and adaptive strategies that favoured the successful spread of P. massiliana in karstic caves and its persistence as extremely isolated populations in a fragmented habitat are discussed together with potential environmental constraints. The data indicate that conservation of this Mediterranean palaeoendemic species with a spot‐like distribution may be a challenge for the western Mediterranean Marine Protected Areas to confer protection to numerous co‐occurring cave‐dwelling species.

A new species of freshwater planarian belonging to the genus Dugesia (Platyhelminthes, Tricladida) from Sardinia

Abstract Dugesia leporii sp. n. from SW Sardinia is described. It is characterised by a comparatively small copulatory apparatus, the shape of the penial papilla, and the course and opening of the ejaculatory duct. The penial papilla, which has a penial valve, protrudes into an undivided atrium and is not provided with accessory structures. The taxonomic position of the new species within the D. gonocephala group is discussed.

Overview of life cycles in model species of the genus Dugesia (Platyhelminthes: Tricladida)

Abstract An overview of the reproductive patterns of seven model species of triclads belonging to the genus Dugesia from circum-Mediterranean and Afrotropical freshwater is provided. Populations can reproduce exclusively sexually or exclusively asexually by fissiparity but the coexistence of both reproductive modes is displayed by some lineages. The comparison of data on the life cycles as documented in the literature with new data highlights a wide array of potentialities to shift from an asexual to a sexual state and vice versa in species with fissiparous populations. Life cycles are poorly diversified in species reproducing only sexually. Among fissiparous populations, planarians may sexualise, displaying various grades of reproductive functionality under laboratory conditions. Unexpectedly, asexual reproduction by fission occurred spontaneously in two species during the sexual state of ex-fissiparous individuals. The capacity to develop or reduce the reproductive apparatus during the life cycle either in sexual or in ex-fissiparous individuals illustrates the considerable morphogenetic plasticity in planarians. The Dugesia case contributes to the modelling of reproductive patterns and strategies in basal Metazoa as a continuum from sexual to asexual reproduction and vice versa, rather than a simple clear-cut alternative.

African planarians: Morphology and karyology of Dugesia maghrebiana sp. n. (Platyhelminthes, Tricladida) from Tunisia

Extensive surveys were made of Tunisian freshwaters, yielding freshwater planarians at only one locality in southeastern Tunisia, representing a new species. Dugesia maghrebiana sp. n. is characterized by the presence of the following features: ventral course of the ejaculatory duct, terminal opening of the ejaculatory duct, double diaphragm, symmetrical openings of the oviducts into the bursal canal, and by a typical condition of mixoploidy with a double aneuploidic chromosome complement. The taxonomic position of the new species is discussed in relation to other African and Mediterranean species.

Endemic freshwater planarians of Sardinia: Redescription of Dugesia hepta (Platyhelminthes, Tricladida) with a comparison of the Mediterranean species of the genus

The endemic freshwater planarian Dugesia hepta from Sardinia was described mainly by karyology and karyotype analysis and by geographic distribution. The present paper reports on the detailed morphological study of the copulatory apparatus and highlights the fact that the exclusive diagnostic characters of D. hepta are the shape of the penis papilla, the course and opening of the ejaculatory duct and the openings of the shell glands. A neotype is designated on the basis of a detailed description, and the geographic range of the species is better defined. The two phylogenetically important traits represented by the course and opening of the ejaculatory duct show an unknown condition in the genus Dugesia, diverging from the typical one displayed by the other 69 species. A comparative analysis of morphological traits of the 20 Mediterranean species of the genus Dugesia was made.

A new and aberrant species of Dugesia (Platyhelminthes, Tricladida, Dugesiidae) from Madagascar

Abstract In this paper we report a new species of Dugesia of the family Dugesiidae from Madagascar, representing the fourth species of freshwater planarian known from this global biodiversity hotspot. In some respects the new species is aberrant, when compared with its congeners, being characterized by a head with smoothly rounded auricles, a peculiar course of the oviducts, including the presence of a common posterior extension, and by the asymmetrical openings of the vasa deferentia at about halfway along the seminal vesicle. Further, it is characterized by a ventral course of the ejaculatory duct with a terminal opening, very long spermiducal vesicles and unstalked cocoons. Its diploid chromosome complement with 18 chromosomes represents an uncommon feature among fissiparous species of Dugesia.