Intercellular junctions in the uterine epithelium of Salamandra salamandra (L.) (Amphibia,Urodela)

Summary Intercellular junctions in the uterine epithelium of the ovoviviparous urodele Salamandra salamandra were studied in pregnant and non-pregnant females by freeze-fracture technique. Junctional complexes consist of zonulae occludentes (tight junctions) and numerous maculae adhaerentes (desmosomes); z. adhaerentes and nexuses (gap junctions) could not be identified. Tight junctions are of the flexible type exhibiting loosely interconnected fibrils. The fibrillary network appears stretched more often in pregnant females possibly due to the mechanical stress of pregnancy. The structure and occurrence of the junctions identified, especially that of the tight junctions, is discussed with regard to the functions of the uterus during pregnancy.Zusammenfassung Mit Hilfe der Gefrierbruchtechnik wurden im Uterus-epithel trächtiger und nichtträchtiger Feuersalamanderweibchen (Salamandra salamandra) Zonulae occludentes und Maculae adhaerentes, jedoch keine Z. adhaerentes sowie Nexus identifiziert. Die Z. occludentes sind flexibel. Ihr fibrilläres Netzwerk ist bei trächtigen Weibchen öfter gestreckt; das ist möglicherweise auf die stärkere Ausdehnung des Uterusgewebes während der Trächtigkeit zurückzuführen. Das Vorkommen der verschiedenen Kontakt-strukturen, namentlich das der Z. occludentes, wird im Hinblick auf die Funktionen des Uterus während der Trächtigkeit diskutiert.We are indebted to Mrs. K. Ott for excellent technical assistance and to Miss Dr. U. Beigel for linguistic help     

Anatomy and reproduction of viviparous Pisidium (Parapisidium) reticulatum Kuiper, 1966: Implications for the phylogeny of Sphaeriidae (Mollusca: Bivalvia: Heterodonta)

The pea clams Sphaeriidae represent a major molluscan freshwater radiation with cosmopolitan distribution in all kinds of lotic and lentic habitats. Their phylogenetic relationships are still controversial, with comprehensive taxonomic sampling and examination of morphological characters still challenging. Here, based on rare and rediscovered original material, we study in detail the anatomy and aspects of brood protection of the African Pisidium reticulatum Kuiper, 1966. Representing the monotypic subgenus Parapisidium Kuiper, 1966, this species is characterized by its peculiar combination of shell and anatomical features of potentially high phylogenetic relevance. While similar to other congeners in several anatomical characters (e.g. reduction of inhalant siphon and descending lamella of outer demibranch, simplified structure of intestine coil and nephridium), P. reticulatum differs from other Pisidium species in retaining both pairs of retractor muscles of the inhalant siphon, and particularly in its peculiar mode of brooding. The yolky eggs are relatively large (160–170 μm in diameter) and are incubated in the gill, albeit in the absence of the formation of brood pouches. During later stages of incubation the larvae are surrounded by large cells similar to nourishing cells in other sphaeriids and probably with similar function. This unique combination of reproductive features is hypothesized to represent an intermediate stage between the typical ovoviviparity of Euperidae and euviviparity (i.e. nourishment by the parent animal) as found exclusively in Sphaeriidae, the latter being characterized by the possession of closed brood pouches. Phylogenetic analyses based on a comprehensive set of morphological characters reveal Parapisidium as the most basal lineage within a clade Pisidium. Evaluating the phylogenetic reconstructions based also on available molecular data for Sphaeriidae, we discuss alternative scenaria of (parallel) evolution of brood pouches and viviparity in this group.     

Ovoviviparity and morphology of the female reproductive system in Palumbina (Lepidoptera,Gelechiidae, Thiotrichinae)

Ovoviviparity is reported for the genus Palumbina of Thiotrichinae. The females of eight species were found to retain a hatched first instar larva or a fully developed embryo in the oviduct (vestibulum), which suggests that the females may deposit larvae or mature eggs that are ready to hatch. In the mature embryos, the mandibles and a head capsule were visible and enclosed in chorion. Taking this into consideration, the embryos may contain sufficient nutrition for development within the eggshell, which indicates an ovoviviparous reproduction. The embryos in the oviduct were not dissolved while the early-stage embryos in the anterior portion of the abdomen were destroyed by the treatment of KOH. Therefore, the formation of chorion likely takes place in the oviduct. The female reproductive system of Palumbina displayed typical morphology of ditrysian Lepidoptera although it showed minor variations among the species. The paired reservoirs of the colleterial gland were rather reduced in the species that carried larvae. We assume that this might be related to the ovoviviparous reproductive physiology. The lagena of the spermatheca was present or absent, and if present, the shape and the size were various even in the same species. The species without lagena had a numerous thorn-like structures on the utriculus. The function is possibly related to the maintenance of sperm, but the correlation between the structure and the absence of the lagena remains unclear. Further detailed studies are required to reveal the comprehensive mechanism of the ovoviviparous reproduction in Palumbina.     

The embryonic moult in diplogastrids (Nematoda) - homology of developmental stages and heterochrony as a prerequisite for morphological diversity

Video analysis of developing eggs showed that diplogastrids, in contrast to the majority of nematodes, moult from J1 to J2 before they hatch from the egg. This embryonic moult leads to a conflict between the terminology for the J1-J4 postembryonic stages and the definition for the embryonic period that ranges from fertilization to hatching. The nature of developmental stages is discussed on the occasion of this terminological problem. Stages as “embryo”, J1, J2,… are defined as periods of time between certain developmental events and are called instars, whereas other stages as “tadpole stage” refer to characters. Character-defined stages refer to the temporal aspect of developmental characters. Only character-defined stages can be homologized between species. It is proposed to ignore the conflict of the J1-J4 terminology with the embryonic-postembryonic dichotomy as an embryonic stage cannot be satisfyingly defined. The biological relevance of the heterochronic shift of the first moult into the egg period is the possibility to omit secretion of the J1 stoma and pharynx cuticle as the diplogastrid J1 does not feed. Thereby the time slot for stoma morphogenesis that must be finished before cuticle deposition is prolonged. Within Diplogastridae this time slot facilitated the evolution of a tremendous diversity of complex stoma morphologies that is unique within “Rhabditida”.     

Biological attributes discriminating invasive from native European stream macroinvertebrates

Rising economic and ecological costs caused by invasive organisms revived research on biological attributes associated with invasiveness, focussing on the question: do invasive taxa have biological attributes favouring (1) propagule pressure; (2) dispersal; and (3) establishment and population growth? Using a literature-derived database on 312 stream macroinvertebrate genera occurring at 527 least human-impacted European sites, we quantitatively examined this question. Compared with native genera, genera with invasive invertebrate species (1) tended to reproduce more frequently and to have higher abundances (i.e. higher propagule pressure); (2) had no particular resistance stages to survive during dispersal; and (3) had significantly more ovoviviparity (enabling colonization by a single individual that typically releases viable offspring), larger size and longer life (providing resistance against mortality), food and feeding habits exploiting food resources in streams more effectively, and tended to be more dominant in their communities (all favouring establishment and population growth). Repeating these analyses excluding “native” flying insects (i.e. genera that presumably invaded from glacial refuges unnoticed by biologists), fewer biological attributes were significantly associated with invasiveness. For both data sets (all genera or insects excluded), their affinity to few biological traits (e.g. ovoviviparity, gill respiration) assigned the same 13 of the 19 invasive genera to the top 19 ranks on a gradient of potential invasiveness, together with native genera that risk to become invasive (e.g. Pisidium, Unio), but also with one endangered native genus (Margaritifera). Overall, our data support the idea that invasiveness can be predicted using biological attributes.     

Comparative ultrastructural investigations of the uterine epithelium in the viviparous Salamandra atra Laur. and the ovoviviparous Salamandra salamandra (L.) (Amphibia,Urodela)

The uterine epithelium of the viviparous Salamandra atra and the ovoviviparous Salamandra salamandra was studied in non pregnant and ovulating females and in females during different stages of pregnancy. The epithelium of both species is organized in a monolayer. The epithelial cells are characterized by a moderate secretory activity, a variable amount of apical granules which include PAS-positive material and by some apical and basal exo- or endocytotic vesicles. Adjacent cells are joined by junctional complexes. The lateral surfaces form a tortuous boundary with adjoining cells which suggest that the epithelium is involved in transport. Sporadic light cells possess highly variable cytoplasmic inclusions and are not joined with neighbouring cells. Possibly they represent migratory cells. The entire epithelium, except for a small cranial portion of the uterus in S. atra, undergoes no remarkable morphological changes during the different physiological stages examined except that flattened cells seem to be more numerous in pregnant females. The results are discussed with regard to the possible supply of the developing young by the mother.     

Patterns of parental investment,dispersal and size among coral-reef fishes

Synopsis Coral-reef fishes have been selected to produce propagules for dispersal because they live in a patchy environment, and the adults cannot migrate between patches. For large species (>100 mm SL) and widely separated patches, numerous propagules are needed, often with specialized pelagic intervals. Individuals of small species are confined to portions of the reef. They are unable to produce enough eggs for effective longrange dispersal, and so they keep their vulnerable eggs and young out of the plankton until they are well developed enough to seek out and settle onto the appropriate habitat before dispersing.Guarded demersal eggs, requiring a greater individual investment by the small short-lived species, further reduces their individual fecundity. These costs to fecundity, and the reduction in vagile young appear to account for the lack of postzygotic investment in larger longlived species.All coral-reef fishes are selected to disperse, usually with a young planktonic propagule interval. Both large and small species produce a mixed outcome, with some propagules returned to, or retained at the home reef, while others disperse more widely. The smaller the species the greater the proportion of propagules retained.     

Early intrauterine embryonic development of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost Merluccius merluccius (L., 1758) (Gadiformes: Merlucciidae)

The early intrauterine embryonic development of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost Merluccius merluccius (L., 1758), was studied by means of light (LM) and transmission electron microscopy (TEM). Contrary to the generic diagnosis given in the CABI Keys to the cestode parasites of vertebrates, the eggs of C. crassiceps, the type of species of Clestobothrium Lühe, 1899, are operculate and embryonated. Our LM and TEM results provide direct evidence that an operculum is present and that the eggs exhibit various stages of intrauterine embryonic development, and in fact represent a good example of early ovoviviparity. The intrauterine eggs of this species are polylecithal and contain numerous vitellocytes, generally ∼ 30, which are pushed to the periphery and remain close to the eggshell, whereas the dividing zygote and later the early embryo remain in the egg centre. During early intrauterine embryonic development, several cleavage divisions take place, which result in the formation of three types of blastomeres, i.e. macro-, meso- and micromeres. These can be readily differentiated at the TEM level, not only by their size, but also by the ultrastructural characteristics of their nuclei and cytoplasmic organelles. The total number of blastomeres in these early embryos, enclosed within the electron-dense eggshells, can be up to ∼ 20 cells of various sizes and characteristics. Mitotic divisions of early blastomeres were frequently observed at both LM and TEM levels. Simultaneously with the mitotic cleavage divisions leading to blastomere multiplication and their rapid differentiation, there is also a deterioration of some blastomeres, mainly micromeres. A similar degeneration of vitellocytes begins even earlier. Both processes show a progressive degeneration of both vitellocytes and micromeres, and are good examples of apoptosis, a process that provides nutritive substances, including lipids, for the developing embryo.     

卵胎生硬骨鱼褐菖鲉卵巢的周期发育研究

经组织学观察表明 ,褐菖鲉 (Sebastiscusmarmoratus)的卵巢由卵巢壁、卵巢绒毛和卵巢腔构成。卵巢壁的肌层较厚 ,卵巢上皮具分泌功能。卵巢绒毛位于卵巢腔中 ,呈树枝状。在卵巢绒毛上分布着滤泡。滤泡由卵母细胞和滤泡膜构成。滤泡膜包括内层的颗粒层和外层的鞘膜层。鞘膜层上有丰富的毛细血管。滤泡靠滤泡柄悬挂在卵巢绒毛上。卵巢发育分 7个时期。成熟卵排放在卵巢腔中受精。胚胎浸置在卵巢液中发育。卵巢发育、卵巢成熟系数和卵巢壁厚度随季节呈年周期变化。     

卵胎生硬骨鱼褐菖()卵巢的周期发育研究

经组织学观察表明,褐菖()(Sebastiscus marmoratus)的卵巢由卵巢壁、卵巢绒毛和卵巢腔构成.卵巢壁的肌层较厚,卵巢上皮具分泌功能.卵巢绒毛位于卵巢腔中,呈树枝状.在卵巢绒毛上分布着滤泡.滤泡由卵母细胞和滤泡膜构成.滤泡膜包括内层的颗粒层和外层的鞘膜层.鞘膜层上有丰富的毛细血管.滤泡靠滤泡柄悬挂在卵巢绒毛上.卵巢发育分7个时期.成熟卵排放在卵巢腔中受精.胚胎浸置在卵巢液中发育.卵巢发育、卵巢成熟系数和卵巢壁厚度随季节呈年周期变化.