Folco Giusti

The spermatozoon of arthropoda: XXIII. The “9+9+3” spermatozoon of simuliid diptera

The authors describe a new model of sperm axoneme, the “9 + 9 + 3,” which is characteristic of simuliid Diptera. Each of the three central tubules has a row of very long side projections rich in ATPase activity, but the flagellum lacks the central sheath. Sperm motility is normal, like that of sperm having a “9 + 9 + 2” axoneme model and accessory bodies.

MORPHOLOGICAL AND ETHOLOGICAL ASPECTS OF MATING IN TWO SPECIES OF THE FAMILY HELICIDAE (GASTROPODA PULMONATA): THEBA PISANA (MÜLLER) AND HELIX APERTA BORN

SUMMARY The mating behaviour of two Helicidae (Gastropoda Pulmonata) species, Theba pisana (Muller) and Helix (Cantareus) aperta Born, is described. Comparison with prior studies suggests that the position assumed for mating is not determined by the ecology of the species but is an occasionally acquired element. Each partner reacts to the stimuli of the other. The stimuli are necessary for the initiation of the approach and the realization of a correct mating position and appear to induce one snail to accept the other. If one of the subjects is not sufficiently motivated the stimuli are ineffective. The stimuli are not specific and responses indicating a simple cause-effect relationship were not observed. The shooting of the dart marks the beginning of attempts at copulation and occurs when, after repeated stimulation, a threshold of excitement is exceeded. In T. pisana and H. aperta, although the darts are shot simultaneously after the contact organs have been pressed closely together, this happens only ...

Peri-tyrrhenian phylogeography in the land snail Solatopupa guidoni (Pulmonata)

ABSTRACT The land snail Solatopupa guidoni has an interesting disjunct distribution in the peri-Tyrrhenian area, with a few scattered populations in Sardinia, Corsica, and Elba Island. The species is strictly bound to limestone and has poor dispersal capacity. Here, we used sequences of two mitochondrial genes, cytochrome oxidase I (COI) and 16S rRNA (16S), to reconstruct the species phylogeography. The study is based on nine of the 13 populations reported in the literature. Phylogenetic methods and nested clade analysis failed to retrieve reciprocally monophyletic lineages on each island. Sardinian and Elba Island populations were found to be embedded within those of Corsica. These results contrast with previous phylogeographic studies of other organisms with similar distribution patterns, showing major phylogeographic breaks between islands. Molecular clock estimates suggest that species diversification occurred less than 2.5 Myr ago, in line with a previous study that dated the split of S. guidoni from its continental sister species at 3–5 Myr. Corsican populations can be tentatively sorted into two haplo-groups. A first group includes haplotypes found in central inland Corsica only, whereas haplotypes found in northern coastal locations cluster in a second haplo-group. The latter also includes Sardinian and Elba Island populations. Molecular data indicate that a combination of vicariance and dispersal events provide the best explanation of the distribution of this species.

Historical biogeography of Tyrrhenian land snails: The Marmorana–Tyrrheniberus radiation (Pulmonata, Helicidae)

The few studies available on Tyrrhenian land snails support high diversification in the Italian Peninsula and groups structured mainly by vicariant events. Here we investigated the phylogeny of a conchologically diversified group of Tyrrhenian land snails assigned to the genera Marmorana and Tyrrheniberus. We constructed a molecular phylogeny by sequencing two commonly used mtDNA genes (cytochrome oxidase I and the large ribosomal subunit). We also carried out conchological and anatomical analysis. Morphological (shell and genitalia) and genetic data (mitochondrial genes) showed paraphyly of Marmorana. Plio-Pleistocene events in the Tyrrhenian area may have structured relationships between species at regional scale while isolation by distance probably played a role in diversification between populations on a local scale. Continental populations experienced dispersal during interglacial periods and fragmentation and reduction during the dry cold climatic phases. Areas inhabited by Apennine Marmorana could represent relict and/or glacial refugia, with extinction in some areas along the Apennines and survival in the south. The results support a reassessment of taxonomy both at genus and species level and call for further analysis.

The morphological peculiarities of the typical spermatozoa of Theodoxus fluviatilis (L.) (Neritoidea) and their implications for motility.

A detailed examination of the typical sperm of Neritoidea shows it to be characterized by a unique flagellar structure. During the spermiogenesis of Theodoxus fluviatilis (L.), the flagellum breaks into two parts, one folded back on the other. The first length of the flagellum is constituted of a normal axoneme with a protein fiber associated with doublet 1. It is encircled by a cytoplasmic sheath containing two mitochondrial cylinders and numerous glycogen granules. This first part of the flagellum terminated in correspondence with a cap-shaped electron-dense body which gives origin to the second part of the flagellum which contains only the axoneme. The second half of the flagellum therefore develops parallel to the first but in the opposite direction. This particular conformation could account for the abnormal movement of this sperm, in which the tail precedes the head.

The seminal receptacle and sperm storage in Cochlostoma montanum (Issel) (Gastropoda: Prosobranchia)

Females of Cochlostoma montanum (Prosobranchia, Cochlostomatidae) have a seminal receptacle which is not a separate diverticulum of the oviduct. The seminal receptacle derives from a differentiated portion of the renal oviduct which has an inner wall composed of only one layer of cells. These cells are of two different types, both actively involved in secretory activity. One type is represented by goblet cells filled with large vesicles containing an electron‐dense, homogeneous, and partially paracrystalline material. This material is expelled into the lumen through macro‐apocrine or holocrine types of secretion. The other type is represented by ciliated cells rich in small vesicles containing granular material. Probably neither kind of secretion has a nutritive function; rather they serve as matrix for spermatozoa that immobilize them and prevent their expulsion from the receptacular portion of the oviduct. Spermatozoa are inserted in invaginations of the apex of both these epithelial cells. The sperm plasma membrane covering the acrosome forms long digitations which expand toward the corresponding invaginations of the receptaculum cells. This type of adhesion is a novelty for Mollusca and resembles that in seminal receptacles of some Annelida.

The fine structure of the mature spermatozoon of Onchidella celtica (Cuvier) (Mollusca: gastropoda) and its phylogenetic implications

The spermatozoon of Onchidella celtica shows many peculiar features. The acrosome is formed by an apical vesicle and a pedestal consisting of a principal body which is flanked by two electron-dense elliptical elements. The mitochondrial derivative consists of three different components: peripheral layers of paracrystalline material, concentric cisterns, and two cylindrical compartments. The 9 + 9 + 2 axoneme shows 9 small deposits of glycogen granules in correspondence with the axonemal “spokeheads,” and a small assembly of possibly proteic material lying close to the two central tubules. Another intraaxonemal deposit of glycogen granules is present at the level of the “glycogen piece.” Most of the observed features are in substantial agreement with those of another species of the Onchidiidae. This confirms the constancy of sperm structure among the members of a single family of the Gastropoda.

A question of time: the land snail Murella muralis (Gastropoda: Pulmonata) reveals constraints on past ecological speciation

The lively debate about speciation currently focuses on the relative importance of factors driving population differentiation. While many studies are increasingly producing results on the importance of selection, little is known about the interaction between drift and selection. Moreover, there is still little knowledge on the spatial‐temporal scales at which speciation occurs, that is, arrangement of habitat patches, abruptness of habitat transitions, climate and habitat changes interacting with selective forces. To investigate these questions, we quantified variation on a fine geographical scale analysing morphological (shell) and genetic data sets coupled with environmental data in the land snail Murella muralis, endemic to the Mediterranean island of Sicily. Analysis of a fragment of the mitochondrial DNA cytochrome oxidase I gene (COI) and eight nuclear microsatellite loci showed that genetic variation is highly structured at a very fine spatial scale by local palaeogeographical events and historical population dynamics. Molecular clock estimates, calibrated here specifically for Tyrrhenian land snails, provided a framework of palaeogeographical events responsible for the observed geographical variations and migration routes. Finally, we showed for the first time well‐documented lines of evidence of selection in the past, which explains divergence of land snail shell shapes. We suggest that time and palaeogeographical history acted as constraints in the progress along the ecological speciation continuum. Our study shows that testing for correlation among palaeogeography, morphology and genetic data on a fine geographical scale provides information fundamental for a detailed understanding of ecological speciation processes.

THE REPRODUCTIVE CYCLE AND THE GLOCHIDIUM OF ANODONTA CYGNE A L. FROM LAGO TRASIMENO (CENTRAL ITALY)

SUMMARY The different phases of the biological cycle of Anodonta cygnea L. living in lake Trasimeno (Central Italy) are described in the present paper. Researches have been carried out on histological sections of germinal tissues and gills of specimens of both sexes sacrificed every month and verified by following the course of the parasitic phase of life of glochidia on the fish of the lake. Moreover, the various species of fish heavily infested by glochidia have been identified and the glochidium infestation frequency has been determined. The structure of the glochidium shell has been studied with the scanning microscope for a better understanding of the mechanism of attachment to fish and to collect more information in order to compare the species of Anodonta from lake Trasimeno with those of other parts of Europe.

The spermatozoon of arthropoda. XXV. A new model of tail having up to 170 doublets: Monarthropalpus buxi

Abstract The spermatozoon of M. buxi which belongs to the Cecidomyiidae family have been studied. The spermatozoa have an aberrant flagellum somewhat similar to that of Sciaridae formed by about 170 doublets ranged in rows to form a compact bundle. Accessory tubules and all the other axonemal structures are missing. The sperm is characterized by the lack of acrosome, and by the presence of normal mitochondria apically gathered before the nucleus.