Sexual selection and cues for female choice in leks of Jackson's widowbird Euplectes jacksoni

Summary Sexual selection through female mate choice was investigated in the lekking Jackson's widowbird by applying multivariate selection analysis to observational data from four leks. Males perform a stereotyped jump display on small display courts (dance rings) constructed by the males in open grassland. Females visit the lek solely for mating and nest on their own, away from the lek area. Few cases of interference during courtship and absence of position effects on mating success indicated that female choice within the leks was not pre-empted by male-male competition. In a set of 11 male traits with mating success as the dependent fitness measure, significant selection differentials (covariances) were found for the length of the conspicuous tail and the rate of the jump display, suggesting sexual selection of these traits. They also showed the largest selection gradients (partial effects) and thereby seem to be the cues on which females base their choice. The success of males in obtaining copulations appears to depend on two components: display rate and lek attendance affect the number of female visits, whereas tail length seems to primarily influence the chance of copulating with a visiting female. Tail length was positively related to a measure of body condition, which is of interest with regard to the suggestions that sexual ornaments may serve as indicators of male viability.     

Brood sex ratio adjustment in collared flycatchers (<Emphasis Type="Italic">Ficedula albicollis</Emphasis>): results differ between populations

Recently, a number of studies have found adaptive brood sex ratio (BSR) manipulation in birds. The reason for such manipulations is thought to be the different reproductive value of male and female nestlings. Several studies have found that parental quality and food supply can affect BSR, however results are sometimes inconsistent between species and populations. We investigated BSR patterns in a Hungarian population of Collared Flycatchers (Ficedula albicollis) and compared the results with those obtained in a previous study of the same species in Sweden. We found two significant differences. First, the male forehead patch size, a heritable, sexually selected trait, affected the brood sex ratio in the Swedish population, but not in our Hungarian study population. This difference might be a consequence of the different information content of the forehead patch size in the two populations. Second, a seasonal shift in BSR (more sons late in the season) was observed in the Hungarian, but not in the Swedish population.Communicated by J. Graves     

Relationships of biological and taxonomic characteristics to chemically mediated bioactivity in Mediterranean littoral sponges

The aim of this study was to detect relationships of bioactive properties (antibacterial, antifungal, antiviral antimitotic and cytotoxic activities) of Mediterranean littoral sponges with some of their biological characteristics (growth habits, presence of symbiotic or epibiotic organisms, structural defences) and their systematic position. Antimitotic and cytotoxic activities were present in 80.6% and 73.6% of the species respectively, 42.2% of the species showed antibacterial activity, 29.8% were antiviral and 22.5% were antifungal. Only antiviral and antifungal activities were significantly dependent on taxonomical order, being especially important in the Axinellida. Antiviral, antifungal and antibacterial activities predominated in erect forms, and were poorly represented in encrusting forms, which, however, included a higher percentage of cytotoxic and antimitotic species. Nevertheless, only antiviral activity was significantly related to growth habit. All types of activities were significantly dependent on sponge skeletal features: the highest percentages of species with cytotoxic activity were found among horny and siliceous sponges. Also, antiviral and antibacterial activities were better represented in horny sponges. Antibacterial, antifungal and antiviral activities were dependent on the presence/absence of epibionts and seemed to be more efficient as antifouling defences than antimitotic and cytotoxic activities. Only cytotoxic activity was significantly more wide-spread in species harbouring cyanophyceae. Correspondence analysis revealed that cytotoxic and antimitotic activities were both related to encrusting forms, a siliceous skeleton, occasional epibiosis and the presence of cyanophyceae. Antifungal, antibacterial and antiviral activities were mainly related to erect or globular form, siliceous and horny skeleton and habitual (species-specific) epibiosis.