Mating systems and territory in Lapwings Vanellus vanellus

In a population of Lapwings Vanellus vanellus studied for 5 years near Bergen, southwester Norway, 23–41% of the males were polygynous, having two and sometimes three mates, whereas 50–77% were monogamous and 0–21% remained unmated. Bachelors held territories in or immediately adjacent to the study area each of the years. As predicted from the Polygyny Threshold model, primary females generally laid eggs earlier than monogamous females, but the overlap in laying dates was substantial between these two classes. The number of females and start of breeding on the territories were analysed in relation to nine variables pertaining to safety from predation and to food. Of these, territory size correlated most consistently with number of females (positively) and the laying of first egg (negatively). Numbers of females observed were not significantly different from numbers expected from territory size in 4 out of 5 years; however, earlier start of breeding on large territories indicated that females did not settle according to the Neutral Mate Choice model. The Female-biased Sex Ratio hypothesis was refuted, unmated territorial males being available throughout the breeding seasons.     

Structure and Variation in the Sarcotubular System of the Extraocular Muscle Fibres in the Shark Scyliorhinus canicula L.

The microscopic anatomy of the extraocular eye muscles of the shark Scyliorhinus canicula is described. In contrast to swimming muscles, the fibres are not differentiated into distinct fibre type groups. The sarcoplasmic reticulum has narrow terminal cisternae in the Z band region, longitudinal tubules and a fenestrated cisterna in the H band region. Triads or dyads are mostly located at the Z discs. A number of variations from this general pattern is described, with main emphasis on triad location, orientation and structure. Since triads in vertebrates usually are located either at the Z disc or at the A-I junction, and with a fixed structure, these variations in shark muscles are of phylogenetic interest, as they may provide basis for an explanation of development to the two different triad locations.