Retention of fluid and particles in the digestive tract of the llama (Lama guanacoe f. glama)

The retention times of fluid and particles of different lengths were measured in the digestive tract of the llama. PEG was used as a fluid marker; hay particles were labelled with cerium or samarium and the samples were determined by neutron activation analysis. In compartments 1 and 2 the retention time of fluid (9.7 hr) was significantly shorter than that of particles having a length of 0.2-1.0 cm (19.2 hr) and 2.5-4.0 cm (25.0 hr). In the intestine slightly significant differences in the retention times of fluid (20.1 hr) and particles (26.2 hr) were seen. In the whole digestive tract retention times were 36.2 hr for fluid, 52.0 hr for smaller particles and 59.9 hr for larger particles.     

Conspecific brood parasitism and egg quality in blue tits Cyanistes caeruleus

Laying eggs in nests of unrelated conspecific pairs to parasitize their parental care is a common phenomenon in birds. In blue tits Cyanistes caeruleus such conspecific brood parasitism (CBP) has never been reported in the literature. However, in a situation where breeding density was extremely high, we found six nests to be parasitized with eggs of conspecific females. Natural selection may favour elevated competitiveness of parasite young, since the negative consequences of increased sibling competition are incurred on the unrelated host parents and siblings, and therefore do not act as inclusive fitness costs for the parasites. Parasitizing females could achieve such a competitive advantage for their offspring by laying larger eggs or eggs with higher concentrations of testosterone in the yolk. We analyzed these parameters of the six parasitized nests, but did not find that parasite eggs differ systematically in these aspects from host eggs, nor that parasite eggs showed resemblance to host eggs. We suggest that a shortage of available nest sites caused some females to use CBP as a best-of-a bad job strategy, but that either the occurrence of CBP is too rare to lead to strong selection for egg adjustments or that parasitizing females are unable to do so.     

A transmembrane tight junction protein selectively expressed on endothelial cells and platelets

Searching for cell surface proteins expressed at interendothelial cell contacts, we have raised monoclonal antibodies against intact mouse endothelial cells. We obtained two monoclonal antibodies, 1G8 and 4C10, that stain endothelial cell contacts and recognize a protein of 55 kDa. Purification and identification by mass spectrometry of this protein revealed that it contains two extracellular Ig domains, reminiscent of the JAM family, but a much longer 120-amino acid cytoplasmic domain. The antigen is exclusively expressed on endothelial cells of various organs as was analyzed by immunohistochemistry. Immunogold labeling of ultrathin sections of brain as well as skeletal muscle revealed that the antigen strictly colocalizes in capillaries with the tight junction markers occludin, claudin-5, and ZO-1. Upon transfection into MDCK cells, the antigen was restricted to the most apical tip of the lateral cell surface, where it colocalized with ZO-1 but not with beta-catenin. In contrast to JAM-1, however, the 1G8 antigen does not associate with the PDZ domain proteins ZO-1, AF-6, or ASIP/PAR-3, despite the presence of a PDZ-binding motif. The 1G8 antigen was not detected on peripheral blood mouse leukocytes, whereas similar to JAM-1 it was strongly expressed on platelets and megakaryocytes. The 1G8 antigen supports homophilic interactions on transfected Chinese hamster ovary cells. Based on the similarity to the JAM molecules, it is plausible that the 1G8 antigen might be involved in interendothelial cell adhesion.