Movement of Anopheles gambiae s.l. malaria vectors between villages in The Gambia

ovement of mosquitoes belonging to the Anopheles gambiae complex (mixed wild populations of An.arabiensis, An.gambiae and An.melas ) between three neighbouring rural villages in The Gambia was investigated by mark-release-recapture. A total of 12,872 mosquitoes were collected in bednets, marked with a magenta fluorescent powder and released over a 15-day period in one of the villages. A further 15,507 mosquitoes were collected in exit traps, marked with a yellow powder and released over the same period. Mosquitoes were captured daily in all three villages using pyrethrum spray catches, as well as bednet and exit trap catches. The catching period extended for 6 days after the last day of release.
Of the mosquitoes released, 372 (1.3%) were recaptured 2–21 days later. Of these recaptures, 272 were caught in the release village, and 98 were caught in other villages situated 1–1.4 km away. The 'movement index' between villages was calculated as 17.2% (12.2–22.4% confidence limits) for mosquitoes released after feeding and 20.1% (14.7–25.3%) for those released unfed.
These results suggest that movement of mosquitoes between neighbouring villages in The Gambia seriously affects the entomological evaluation of pyrethroid-impregnated bednet programmes in areas where treated and untreated villages are interspersed.     

Assortative mating among rock-dwelling cichlid fishes supports high estimates of species richness from Lake Malawi

It has been estimated that Lake Malawi, Africa, contains 500–650 endemic species of cichlid fishes, the largest number of vertebrate species endemic to any comparable sized area on the planet. As many of these putative species cannot be distinguished anatomically, these estimates of species richness depend to a great extent on the assumption that sympatrically occurring male colour morphs represent biological species. We have tested this assumption using a combination of behavioural observations of courtship and microsatellite DNA analysis for six putative species of the Pseudotropheus ( Tropheops ) complex and three of the Pseudotropheus ( Maylandia ) complex occurring sympatrically at Nkhata Bay. We were unable to demonstrate assortative courtship for the species pairs Pseudotropheus ( Maylandia ) zebra / P . 'gold zebra' or P. ( Tropheops ) 'band'/ P. ( T .) 'rust' because we were unable to distinguish between the females of these taxa. All other taxa showed clear assortative courtship, except for P. ( T .) 'deep', a deep-water species which was rarely observed. Fixation indices (θ_ST for the infinite allele model, and R _ST for the stepwise mutation model) calculated from six microsatellite DNA loci demonstrated significant deviations from panmixia in all pairwise comparisons of putative species, indicating little or no gene flow between populations. All taxa showed high levels of allelic diversity providing evidence that genetic bottlenecking may have been of limited importance in the speciation process. Assortative mating among taxa differing only in male colouration is supportive of theories that speciation in these fishes has been driven by sexual selection by female choice.     

Developing methods for quantifying the apparent abundance of fiddler crabs (Ocypodidae: Uca) in mangrove habitats

Counting the number of individuals emerging from burrows is the most practical method for estimating the apparent abundance of Australian Uca species living in mangrove habitats. Experiments were conducted to investigate the effect on counts of quadrat design, distance of observer, quadrat size, recovery time and observational technique. Significant differences in the apparent abundance of one species were found when the subjects were within 2 m of the observer, and when a conspicuous quadrat was used. The largest quadrat tested provided the least variability in counts but an intermediate size (0.56 m²) was more practical. Most Uca active within a 30-min period emerged during the first 10 min regardless of site, species, sex or season. There was a linear correlation between scanning and continuous observation indicating that the former method could be useful when sampling time was limited. Temporal changes in the apparent abundance of Uca suggest that long-term sampling and more detailed studies will be worthwhile.     

A quantitative study of worker reproduction in queenright colonies of the Cape honey bee, Apis mellifera capensis

Reproduction by workers is rare in honey bee colonies that have an active queen. By not producing their own offspring and preventing other workers from producing theirs, workers are thought to increase their inclusive fitness due to their higher average relatedness towards queen-produced male offspring compared with worker-produced male offspring. But there is one exception. Workers of the Cape honey bee, Apis mellifera capensis, are able to produce diploid female offspring via thelytokous parthenogenesis and thus produce clones of themselves. As a result, worker reproduction and tolerance towards worker-produced offspring is expected to be more permissive than in arrhenotokous (sub)species where worker offspring are male. Here we quantify the extent to which A. m. capensis workers contribute to reproduction in queenright colonies using microsatellite analyses of pre-emergent brood. We show that workers produced 10.5% of workers and 0.48% of drones. Most of the workers' contribution towards the production of new workers coincided with the colonies producing new queens during reproductive swarming.     

Elevated CO2 decreases seed germination in Arabidopsis thaliana

The impact of elevated [CO₂] on seed germination was studied in different genotypes of Arabidopsis thaliana from natural populations. Two generations of seeds were studied: the maternal generation was produced in the greenhouse (present-day conditions), the offspring generation was produced in two chambers where the CO₂ concentration was either the present atmospheric concentration (about 350 ppm) or elevated (700 ppm). The seeds were tested for proportion of germinated seeds and mean germination time in both chambers to study the impact of elevated [CO₂] during seed production and germination. Elevated [CO₂] during maturation of seeds on the mother-plants decreased the proportion of germinated seeds, while elevated [CO₂] during germination had no effect on the proportion of germinated seeds. However, when seeds were both produced and germinated under elevated [CO₂] (situation expected by the end of next century), germination was slow and low. Moreover, the effect of the [CO₂] treatment differs among genotypes of Arabidopsis: there is a strong treatment × genotype interaction. This means that there is ample genetic variance for a selective response modiying the effects of high levels of [CO₂] in natural populations of Arabidopsis thaliana. The outcome at the community level will depend on what seeds are available, when they germinate and the resulting competition following germination.     

ACOUSTIC SIGNALS OF THE NOCTURNAL LIZARD GEKKO GECKO: ANALYSIS OF THE ‘LONG COMPLEX SEQUENCE’

ABSTRACT

Four types of vocalizations of the nocturnal lizard Gekko gecko (the ‘Tokay’) are described. A bark of intimidation, distress calls, a short not very intense call, apparently related to sexual inter-action, and a long, complex sequence. This ‘long sequence’ is considered to be a territorial proclamation which also functions as a mating-call. It has been analysed in detail with special emphasis on the intra-individual variations. The mean duration of this sequence is 22.3 s, the intensity is 70 dB at 1m and the maximum of energy is between 300 and 4000 Hz. This sequence is composed of three phases. The first one consists of several multipulse sounds called ‘rattles’, the second of bi-motifs which sound like a two syllable tok-kay, and the third, not always present, is a kind of ‘grumble’. The number of motifs and the occurrence of the third phase may vary but the duration of the motifs is relatively stable.     

Transformation of the Mesonephros into Epididymis in the Cock: Fate of Collecting and Secretory Tubule Antigens

By means of purified rabbit anti-adult chicken kidney antibodies two types of antigens have been identified in the mesonephros: one (PS), localized in the cells of the proximal secretory tubules, the other (CT) characteristic of the collecting segments.
During the conversion of certain mesonephric tubules into epididymal ductules in the male, the CT-antigen disappears, whereas the PS-antigen not only persists but can also be detected in the cells of the parietal layers of Bowman's capsules as they transform before connecting with the rete testis. In the adult cock, the PS-antigen is found at the apical part of the cells of the ductuli efferentes, whereas the ductuli conjugentes and ductus epididymidis are negative.
In the female, the PS-antigen is also found to persist in the cells of the proximal segment and to appear in the cells of the parietal layers of Bowman's capsules. However, between 2 and 3 months after hatching it disappears, although perfectly well preserved tubuli of mesonephric origin can be observed at much later stages.
In the epididymal tubuli of the sexually mature cock, large sheets of the epithelial walls are seen to detach and to fall into the lumina where they disintegrate. The cellular contents thus released mix with the mass of the spermatozoa. Arguments tending to exclude a fixation artifact are presented and the possibility that the observation reflects a cyclic physiological process is discussed.