Elda Gaino

Parasitic diatoms inside antarctic sponges.

Antarctic sponges may host large populations of planktonic and benthic diatoms. After settling on the sponge, these diatoms enter its body through pinacocytes (1) and form, there, large mono- or pauci-specific assemblages. Yet the total amount of carbohydrates in the invaded sponge tissue is inversely correlated with that of chlorophyll-a. We suggest, therefore, that endobiont diatoms utilize the products of the metabolism of their host as an energy source. This is the first evidence indicating that an endobiotic autotrophic organism may parasitize its animal host. Moreover, this unusual symbiotic behavior could be a successful strategy that allows the diatom to survive in darkness.

Mortality of commercial sponges: Incidence in two mediterranean areas

Abstract In 1986 a severe epidemic affecting horny sponges broke out in several areas of the Mediterranean Sea. The disease rapidly spread to species of marketing interest belonging to the genera Spongia and Hippospongia. Ultrastructural studies of Spongia officinalis evidenced two main features: 1) peculiar bacteria with irregularly dotted electron‐dense walls within the tissue; 2) profound alterations of the skeleton with bacterial damage of fibres. These lesions made the sponges unsuitable for commercial purposes. Long‐term investigation in the Marsala Lagoon (northwestern Sicily) and at the Portofino Promontory (eastern Ligurian coast) in 1986–1989 evidenced striking incidence of the disease on the abundance of sponges. Reparative processes were also present in specimens collected during the epidemic that affected even other demosponges besides horny sponges. The etiology of the disease is discussed.

Geographical and seasonal evidence of cryptic diversity in the Baetis rhodani complex (Ephemeroptera, Baetidae) revealed by means of DNA taxonomy

Previous phylogenetic investigations on the mayfly Baetis rhodani Pictet from several European countries, excluding Italy, strongly suggested the presence of cryptic species. Our paper reports a DNA-taxonomy phylogenetic analysis of B. rhodani with additional populations coming from Italian and UK sites, and aims to identify potential cryptic species with a coalescent-based method (GMYC model) and to understand the mechanisms of local coexistence of cryptic species. Twenty-five haplotypes of Italian samples and five haplotypes of UK samples were identified and added to a large European dataset. A total of 11 potential cryptic species have been recognised, and three of them co-occured in one Italian area. Such cryptic species seem to be phylogenetically over-dispersed on the tree and temporally segregated, and the seasonal substitution pattern of cryptic species could explain the apparently widespread distribution of the B. rhodani complex and its ability to adapt to different temperatures and food resources, justifying some of the differences observed in the relationship between water temperature, growth rates and phenology documented from field studies.

A sponge with acrosome: Oscarella lobularis

In this paper we describe the presence of a true acrosome in the Homosclerophorida demosponge Oscarella lobularis. Because it is the first finding of this organelle in Porifera, the general concepts of the acrosomal evolution are reviewed.

The antennal sensilla of the adult of Libellula depressa (Odonata: Libellulidae)

An ultrastructural investigation (SEM, TEM) on the antennal flagellum of the adult of the dragonfly Libellula depressa (Odonata:Libellulidae) revealed sensilla located in pits on the lateral-ventral side of the antenna. These sensilla are represented by sensilla coeloconica and by deeply sunken sensilla. The sensilla coeloconica are innervated by three unbranched dendrites, which enter the peg and show a dendrite sheath ending at the base of the peg. The peg has no socket and its cuticle is irregular with wide pore-like structures at the base of which actual pores are visible. The structure of these coeloconic sensilla is in agreement with that reported for single-walled insect chemoreceptors. The deeply sunken sensilla are represented by two kinds of sensilla styloconica, named type-1 and type-2, located at the bottom of deep cavities appearing as simple openings on the antennal surface. These sensilla are no-pore sensilla with inflexible socket and unbranched dendrites and, notwithstanding their structural differences, share common features typical of thermo/hygroreceptors. The presence of chemoreceptors in adult dragonflies sheds light on evolutionary trends in insect perception; the previously unknown occurrence of thermo/hygroreceptors in dragonflies is very important in view of the reported ability of Odonata to thermoregulate heliothermically.

Necrosis in a population of Petrosia ficiformis (Porifera, Demospongiae) in relation with environmental stress

Abstract Healthy specimens of the Mediterranean Petrosia ficiformis har bour endocellular cyanobacteria (Aphanocapsa feldmanni) caus ing a violet pigmentation of the sponge. Necrosis in P. ficiformis can be easily detected by the occurrence of white patches scat tered over the surface. Necrotic specimens were examined along the Gallinara Island coasts (Western Ligurian Sea), in coincidence with environmental stress (heavy rainfall, land run‐off, high sea‐water temperature). The appearance of white patches is due to the gradual sloughing of the pinacodermal covering, as evidenced by scanning electron microscopic observations. Sloughing leads to progressive tissue degeneration in the deeper parts. Histologi‐cal sections showed that, concomitantly with the loss of the su perficial layer, internal sponge tissues degenerate and the sponge body becomes exposed to the invasion of ciliates. Spicule bun dles of the skeletal network separate damaged tissues from the healthy ones, thereby slowing down spread of necrosis and en abling successful recovery.

Ultrastructural study of spermatogenesis in Oscarella lobularis (Porifera, Demospongiae)

Summary The various phases of spermatogenesis in the demosponge Oscarella lobularis were studied by electron microscopy. Spermatogenesis occurs within spermatic cysts, which are presumed to derive from choanocyte chambers by transformation of choanocytes into spermatogonia. Germ cells develop asynchronously within spermatocysts, and cytoplasmic bridges, indicating incomplete cells division, connect several germ cells. Attached spermatogonia suggest gonial generations. Spermatocytes I typically show the presence of synaptonemal complexes indicating meiotic divisions. Spermatocytes II have a small size probably because of the meiotic divisions of spermatocytes I. Spermatids are characterized by an acrosome, a big mitochondrion and a peripheral sheath of condensed chromatin surrounding a clearer central area in the nucleus. The mature spermatozoon shows a lateral flagellum and a flattened acrosome capping the nucleus. The phylogenetic implications of some features of the spermatozoon are suggested.

Olfaction in dragonflies: Electrophysiological evidence

The problem of olfaction in Paleoptera (Odonata, Ephemeroptera) cannot be considered fully elucidated until now. These insects have been traditionally considered anosmic, because their brain lacks glomerular antennal lobes, typically involved in Neoptera odor perception. In order to understand if the presumed coeloconic olfactory receptors described on the antennal flagellum of adult Odonata are really functioning, we performed an electrophysiological investigation with electroantennogram (EAG) and single cell recordings (SCR), using Libellula depressa L. (Odonata, Libellulidae) as a model species. Odors representing different chemical classes such as (Z)-3-hexenyl acetate (acetate ester), (E)-2-hexenal, octanal (aldehydes), (Z)-3-hexen-1-ol (alcohol), propionic acid, butyric acid (carboxylic acids), and 1,4-diaminobutane (amine) were tested. Most of the tested chemicals elicited depolarizing EAG responses in both male and female antennae; SCR show unambiguously for the first time the presence of olfactory neurons in the antennae of L. depressa and strongly support the olfactory function of the coeloconic sensilla located on the antennal flagellum of this species. Electrophysiological activity may not necessarily indicate behavioral activity, and the biological role of olfactory responses in Odonata must be determined in behavioral bioassays. This study represents a starting point for further behavioral, electrophysiological, neuroanatomical and molecular investigation on Odonata olfaction, a research field particularly interesting owing to the basal position of Paleoptera, also for tracing evolutionary trends in insect olfaction.

Ootaxonomic investigation of the Italian species of the genus Electrogena (Ephemeroptera, Heptageniidae)

Abstract The egg chorion of the Italian species of the genus Electrogena was investigated using the scanning electron microscope (SEM). The eggs examined showed distinctive chorionic patterns. Electrogena grandiae, E. lateralis and E. zebrata showed attachment structures characterized by knob‐terminated coiled threads (KCTs). These structures were uniformly scattered over the egg surface in E. grandiae, while in E. lateralis they differed in size and position. In E. zebrata, the attachment structures were of uniform size and formed a dense mat over the whole egg surface. In contrast, no specialized sculptures were found in E. fallax and E. gridellii. The different chorionic patterns allowed specific identifications. The affinities and the taxonomic position of the species examined are discussed.

The Role of Sponges in the Terra Nova Bay Ecosystem

One hundred and twenty five demosponge species are known from the Ross Sea, 49 of which have been recorded in Terra Nova Bay within the framework of the PNRA ecological project. The most common species are Tedania charcoti, Axociella nidificata, Calyx arcuarius, Isodictya erinacea, I. cactoides, I. conulosa, Gellius rudis, Gellius spp., Myxilla elongata and Phorbas glaberrima. Two of the 49 species we found are new for Antarctica: Esperiopsis informis and Isodictya conulosa. Most of the sponges were collected at 70–120m depth, where a great substrate heterogeneity allows the coexistence of different biocoenoses.