Stefano Tommasini

Mitochondrial DNA Sequence Variation Suggests the Lack of Genetic Heterogeneity in the Adriatic and Ionian Stocks of Sardina pilchardus

Abstract: A genetic stock structure analysis of 11 sardine samples from the Adriatic Sea and Ionian neighboring area was carried out through sequence variation analysis of a 307-bp cytochrome b gene fragment in order to identify self-recruiting units in the Adriatic Sardina pilchardus stock. The overall lack of genetic subdivision among samples detected by analysis of molecular variance, pairwise Φst values, and the exact test of population differentiation indicates this sardine stock is part of a larger self-recruiting population whose boundaries are larger than the investigated area. This conclusion is in agreement with preliminary allozymic and mitochondrial DNA restriction fragment length polymorphism data, but contradicts the previous identification of 2 subpopulations of sardines in the Adriatic Sea argued on morphologic differences, which could be rather attributed to different hydrographic or ecologic conditions occurring in different areas of the Adriatic Sea. The reduced gene flow observed between Adriatic-Ionian and Spanish sardine geographic samples (P < 0.001) suggests that reproductively isolated populations of sardines may occur in the Mediterranean Sea.

Mitochondrial DNA variation, phylogenetic relationships, and evolution of four mediterranean genera of soles (soleidae, pleuronectiformes).

To increase knowledge about the systematics and evolution of Mediterranean soles, we assessed mitochondrial DNA variation, molecular phylogeny, and evolution in eight species from the genera Solea, Microchirus, Monochirus, and Buglossidium by large ribosomal subunit (16S) and cytochrome b (cytb) sequence analysis. Relevant molecular features are the great variation of base composition among species at the third codon in cytb and the heterogeneity of the nucleotide substitution rate. Phylogenies recovered using 16S nucleotide and cytb amino acid sequences agree with those based on morphology in assessing monophyly of Solea species and ancestry of Buglossidium luteum, but they are against the intergeneric differentiation of Microchirus and Monochirus. Conversely, phylogenetic trees based on cytb nucleotide sequences yielded relationships among taxa regardless of their evolutionary histories. The incongruities between morphological and molecular issues suggest the need for reassessing the systematic value of some morphological characters. Approximate estimates of the divergence time of Mediterranean soleid lineages range from 40 to 13 Mya (Oligocene–Miocene), indicating an ancient origin for the group.

Eggshell origin and structure in two species of Conchostraca (Crustacea, Phyllopoda)

SummaryThe development of the eggshell and the laying of eggs have been studied in two species of Conchostraca, Eoleptestheria ticinensis and Leptestheria dahalacensis. By a process of exocytosis the egg forms the vitelline envelope. This remains the only envelope from laying until hatching, thus also acquiring the functions of the eggshell. The mucous layer produced by the gonad wall glands, which then covers the eggs, only has the function of keeping the eggs together and does not protect them. Before laying, the epipodites of the central metameres of the thorax are modified in relation to the passage of the eggs inside them. The adaptation of the vitelline envelope to the eggshell function is discussed.

FUNCTIONAL MORPHOLOGY AND ULTRASTRUCTURE OF THE MALE REPRODUCTIVE SYSTEM IN THE LEPTESTHERIIDAE (BRANCHIOPODA, CONCHOSTRACA)

The paired, plurilobate testes that make up the male reproductive system of the Leptestheriidae lie on either side of the intestine, occupy most of the haemocoel and extend outwards through two short deferents located at the eleventh pair of limbs. The ample lumen within the gonads, which are wedged into the somatic muscular bundle, is full of a muco-polysaccharide fluid matrix exhibiting a few, widely scattered germinal elements. The wall consists of a simple epithelium containing somatic and germinal cells mixed together. The sperms mature in the lumen and collect in the ampulla in front of the deferents; the wall of the deferents is formed by an epithelium of vacuolated cells surrounded by a muscular bundle and their lumen is usually collapsed. The sperm is expelled along with the polysaccharide matrix by contraction of the somatic muscular bundle and of the deferents, which swell out to become ducts. The matrix condenses on the outside in a sticky, fibrous structure that coats the germinal elements so as to form a spermatophore. A functional interpretation of the male genital apparatus is discussed.

Occurrence of Limnadia Lenticularis (Linnaeus, 1761) (Conchostraca, Limnadiidae) in Emilia-Romagna, Italy

Rice-growing is only a few decades old in Italys Po River delta. Yet, the new biotope has been colonized by numerous species of Crustacea Branchiopoda, including the conchostracan Limnadia lenticularis. This species, which up till now had been found in Italy only in the Piedmont area, is for the first time reported in the Emilia-Romagna region and its geographical range in northern Italy could be confirmed. Selected taxonomical traits observed under SEM and features essential for the identification of the species are reported and discussed.

Origin and chemical composition of egg cement in Conchostraca Leptestheriidae (Crustacea, Branchiopoda)

Summary The eggs laid by the Conchostraca Leptestheriidae are kept together by a cement released from the somatic cells of the female gonadic stroma. These cells, which present a highly vacuolated cytoplasm, do not have the characteristic feature of a direct secretory activity, but in any case produce the gluish cement that is stored up in the extracellular spaces. The presence of numerous microtubules in the peripheral cytoplasm supports the hypothesis that the PAS-positive product is either soluble or of a low molecular weight and is transferred through these organules. The cementing function of the secrete enables short egg brooding between the carapace valves and the females body. This brooding has been understood as being linked to the need for the eggshells to mature.

Histological changes in the ovary of Palaemon serratus (Crustacea, Decapoda) from the North Adriatic Sea

Summary Despite its considerable commercial importance, the ovarian maturation of the prawn Palaemon serratus (Crustacea, Decapoda) has been scarcely studied, especially in the marine habitats of Italian waters. For the purpose of the present study female samples were collected in the North Adriatic Sea for one year. Gonadal tissue sections were prepared using current histological techniques. The ovaries feature a “proliferative centre” from which oocytes maturing in a centrifugal direction branch out. Oocyte (n = 554) size in μm was determined at various stages of development using a semiautomatic computerized imaging scanner. Five cohorts at around 60, 120, 180, 240, 700 μm of diameter were recorded in oocyte distribution frequency during ovary maturation (spring-summer). Only two cohorts at around 60 and 120 μm were observed in oocyte distribution frequency in the immature ovary (autumn-winter). The goal of this study was to provide a preliminary characterisation of the histological structure of the ovary throughout the reproductive cycle. Although P. serratus is a commercially valuable natural resource and has potential for artificial culture, little is known as to the reproductive biology of this species and, unless remedied, this could hinder its successful rearing.

Distribution and some biological parameters of the red gurnard, Chelidonichthys cuculus (Actinopterygii, Scorpaeniformes, Triglidae) in the north-central Adriatic Sea

Background. Red gurnard, Chelidonichthys cuculus (Linnaeus, 1758), is distributed in the Mediterranean Sea, Black Sea, and in the eastern Atlantic Ocean from Norway to Mauritania, although it is rarely found in the North Sea and on the Norwegian shelf. The aim of this work was to conduct a comprehensive study of red gurnard in the Adriatic Sea on selected aspects the population biology and some of its environmental implications . Materialsandmethods. The sampling covered the entire subdivision GSA17 (north-central Adriatic Sea) and it was based on several bottom trawl surveys of MEDITS and GRUND projects from 2000 through 2009. Biometric parameters, as well as the spatial- and depth distributions were analyzed. The parameters such as the length–weight relation, sex, gonad maturity stage, and the stomach content were determined on a subsample of 539 specimens collected seasonally (summer and autumn–winter) within 2007–2009. The data were processed statistically . Results. Chelidonichthys cuculus was mainly distributed in the central Adriatic. Juveniles showed a distribution in shallower waters while adults tended to migrate towards the Croatian coast at greater depths. The total length of the fish sampled ranged from 40 to 303 mm (TL). We assumed the length of 100 mm as a threshold separat ing juveniles from adults and the length range of 170–190 mm as the maturity size for females and males. Isometric- and allometric growth patterns were showed for the juveniles and the adults, respectively. The diet was based almost exclusively on crustaceans (IRI% > 98%) and it did not change upon reaching the sexual maturity. Chelidonichthys cuculus should be considered a specialist predator feeding mostly on necto-benthic lophogastrids (IRI% > 72%) . Conclusion. This work constitutes an attempt to summarize some environmental and biology aspects of the red gurnard in Adriatic population: differences in depth distribution and growth were found between juveniles and adults but not in diet. Males and females showed differences in growth parameters. Extending the studied area and collecting data of red gurnard in the main areas of production should help in better understanding the biolo gy and dynamics of this species .

Reproductive biology and substitution of two species of Nassariidae

Reproductive biology of Nassarius reticulatus is well known, but informations about Nassarius mutabilis are scarce; we have so undertaken a macroscopical and histological study to clear the reproductive biology of this species.

Comparative aspects of habenulae in some species of Chondrohycthes and Ostehycthes

Diencephalic habenular nuclei of several species of Chondrohycthes and Ostehycthes fishes were investigated in order to ascertain their asymmetry. Raja asterias, Squalus acanthias, Mustels mustelus, Scyliorhinus canicula and Scyllium stellare show the left habenula larger than the right, as occurs in the elasmobranchs till now investigated. Among the six species of teleostean fishes we studied, the habenulae of Liza aurata, Anguilla anguilla and Trisopterus minutus are symmetrical, while in Lepidorhombus boscii, Platichthys flesus and Solea vulgaris the habenulae are slightly asymmetrical. This finding might suggest a relation, to be better investigated, among bentic life and habenular asymmetry in teleostean.