An experimental, NADPH-diaphorase histochemical and immunocytochemical study of Mesocestoides vogae tetrathyridia.

In order to test the role of nitric oxide in flatworms, Mesocestoides vogae tetrathyridia were incubated together with L-arginine, which is the substrate for nitric oxide synthesis, or with NG-nitro-L-arginine, which is an irreversible inhibitor of nitric oxide synthase. Normally, tetrathyridia attach to each other with the aid of their suckers, forming clusters. The rate of cluster formation was followed during the incubations. L-Arginine stimulated, and NG-nitro-L-arginine clearly inhibited, the cluster formation. This is the first time that an effect of nitric oxide has been observed in a flatworm. In addition, the pattern of the NADPH-diaphorase histochemical reaction in the nervous system and the pattern of F-actin filaments in the musculature stained with TRITC-labelled phalloidin were studied. NADPH-d staining occurred in the brain and the main nerve cords but also followed the muscle fibres stained with phalloidin. The pattern of the NADPH-d reaction was compared with that of 5-HT immunoreactivity. The implications of the results are discussed in relation to the background of data on neuronal signal substances in M. vogae.     

The dispersal of Halimeda in northern hemisphere mid-latitudes: Palaeobiogeographical insights

The bryopsidalean alga Halimeda gained an important role as carbonate producer in Cenozoic tropical coral reefs and became a significant constituent of the modern Mediterranean seaweed flora. There are, however, open questions at which time the thermophile alga appeared in the cooler Mediterranean Sea and why it is not detected in coral reefs of the modern Persian Gulf. To unravel the biogeography and ecology of Halimeda at its northern margin of distribution, we use fossil Halimeda records of the Central Paratethys/Medditerranean for comparison of the geological, (palaeo)ecological and evolutionary dispersal constraints of the alga in the Miocene and Holocene Persian Gulf. The revealed spatial and temporal distribution patterns of Halimeda in the regions of the Mediterranean and Arabian seas identify water temperature as the major ecological constraint and the extreme Plio-Pleistocene climate changes as the motor for the dispersal and evolution of Halimeda in higher latitudes. Generally, the distribution of tropical species in higher latitudes was related to warm climate intervals during the Neogene. Accordingly, the available (palaeo)biogeographic data implies that the warm-adapted ancestors of the present-day Mediterranean H. tuna population possibly entered the Mediterranean Sea during the mid-Pliocene global warmth and became isolated during subsequent cooling. It also implies that the warm Persian Gulf water is probably unsuitable for the cool-adapted H. discoidea population in the Gulf of Oman and that its tropical ancestors could have reached the Gulf of Oman only during a Pleistocene glacial phase when monsoon-induced upwelling of cold water in the Arabian Sea was reduced and the Persian Gulf fell dry. This example demonstrates the limitation of the actualistic palaeontological approach when using biota at the edges of their distribution range as palaeoclimate proxy.     

Lungs and mesopneumonia of scincomorph lizards (Reptilia: Squamata)

Mesopneumonia of 28 and lungs of 44 species of scincomorph lizards are described, representing mesopneumonia in six of the seven scincomorph families and lungs of all seven families of this taxon. Except for gymnophthalmids and scincids, a family typical organization of mesopneumonia occurs. In cordylids, gerrhosaurids, xantusiids and lacertids the complete right ventral mesopneumonium (VMp) inserts cranially on the posterior vena cava and caudally on the dorsal surface of the right liver lobe. The left VMp is attached to the ventrolateral body wall in cordylids and lacertids; in gerrhosaurids the left VMp is short and inserts on the pericardium and the posterior vena cava; in xantusiids the left VMp is reduced and the lungs are fused cranially with the pericardium. In scincids the VMp of both sides vary in length and insert on the ventral mesentery, or may be lacking completely. The visceral topology of the gymnophthalmids Calyptommatus and Notobachia differs from the general scincomorph pattern, with the liver and stomach elongated and situated on the right and left side of the body cavity, respectively. The left and the right VMp extend over the entire length of the lungs and insert on the ventral mesentery. All lungs examined in the study are single-chambered and show no major structural variability of the inner surfaces, except in lacertids, some gerrhosaurids, Cordylus, and two genera of gymnophthalmids (Echinosaura and Neusticurus). In these groups, rows of dorsomedial niches are present.See also Electronic Supplement at: http://www.senckenberg.de/odes/05-06.htm     

Nestmate recognition in the unicolonial ant Formica paralugubris

In unicolonial populations of ants, individuals can mix freelywithin large networks of nests that contain many queens. Ithas been proposed that the absence of aggression in unicolonialpopulations stems from a loss of nest mate recognition, butfew studies have tested this hypothesis. We investigated patternsof aggression and nest mate recognition in the unicolonial woodant, Formica paralugubris. Little aggression occurred, evenbetween workers from nests separated by up to 5 km. However,when aggression took place, it was directed toward non–nestmates rather than nest mates. Trophallaxis (exchange of liquidfood) occurred very frequently, and surprisingly, workers performedsignificantly more trophallaxis with non–nest mates thanwith nest mates (bias 2.4:1). Hence, workers are able to discriminatenest mates from non–nest mates. Higher rates of trophallaxisbetween non–nest mates may serve to homogenize the colonyodor or may be an appeasement mechanism. Trophallaxis rate andaggression level were not correlated with geographical distanceand did not differ within and between two populations separatedby several kilometers. Hence, these populations do not representdifferentiated supercolonies with clear-cut behavioral boundaries.Overall, the data demonstrate that unicoloniality can evolvedespite well-developed nest mate recognition. Reduced levelsof aggression might have been favored by the low rate of interactionswith foreign workers, high cost of erroneously rejecting nestmates, and low cost of accepting foreign workers.