Candidate genes for colour and vision exhibit signals of selection across the pied flycatcher (Ficedula hypoleuca) breeding range.

The role of natural selection in shaping adaptive trait differentiation in natural populations has long been recognized. Determining its molecular basis, however, remains a challenge. Here, we search for signals of selection in candidate genes for colour and its perception in a passerine bird. Pied flycatcher plumage varies geographically in both its structural and pigment-based properties. Both characteristics appear to be shaped by selection. A single-locus outlier test revealed 2 of 14 loci to show significantly elevated signals of divergence. The first of these, the follistatin gene, is expressed in the developing feather bud and is found in pathways with genes that determine the structure of feathers and may thus be important in generating variation in structural colouration. The second is a gene potentially underlying the ability to detect this variation: SWS1 opsin. These two loci were most differentiated in two Spanish pied flycatcher populations, which are also among the populations that have the highest UV reflectance. The follistatin and SWS1 opsin genes thus provide strong candidates for future investigations on the molecular basis of adaptively significant traits and their co-evolution.

Polyandry in coal tits Parus ater: fitness consequences of putting eggs into multiple genetic baskets.

Females of many species mate with multiple males within a single reproductive cycle. One hypothesis to explain polyandry postulates that females benefit from increasing within-brood genetic diversity. Two mechanisms may render sire genetic diversity beneficial for females, genetic bet-hedging vs. non-bet-hedging. We analysed whether females of the socially monogamous coal tit (Parus ater) benefit via either of these mechanisms when engaging in extra-pair (i.e. polyandrous) mating. To obtain a measure of within-brood genetic diversity as a function of paternal genetic contributions, we calculated a sire diversity index based on the established Shannon-Wiener Index. In 246 broods from two consecutive years, sire genetic diversity had no effect on either the mean or the variance in brood fitness measured as offspring recruitment within 4 years after birth. The hypothesis that benefits of increasing sire diversity contribute to selection for female extra-pair mating behaviour in P. ater was therefore not supported.

Concavities as basic features in visual search: evidence from search asymmetries.

Concave cusps and negative curvature minima play an important role in many theories of visual shape perception. Cusps and minima are taken to be part boundaries, used to segment an object into parts. Because of their important role in determining object structure and because there is some evidence that object structure is processed in parallel, it might be expected that concave cusps and negative curvature minima are processed preferentially. We tested this conjecture in several visual search experiments. Visual search for a target with a concave cusp among totally convex distractors yields nearly flat slopes (< 10 msec/item) for both present and absent trials. Reversing the roles of the target and the distractor results in inefficient search. The same asymmetry is found when the concave cusp is replaced by other types of concavity. We conclude, therefore, the concavities can serve as basic features in visual search experiments. This conclusion implies that the unit of selection in a visual search task is an object, rather than a location.

Oesophageal cancer in three regions of South Africa.

Cancer of the oesophagus is the commonest cancer in South African black males. The highest incidence rates occur in the south of Transkei. The rate among urban blacks, especially in Soweto, is also high. This study determined risk factors for oesophageal cancer in patients in three different environments--urban Soweto, rural Ciskei and rural-urban Bophuthatswana. Males were affected more than females. The majority of patients in all three regions were smokers. With regard to alcohol consumption, most Sowetans (84%) and Ciskeians (91%), but only 57% of patients from Bophuthatswana, were drinkers. Home-brewed drinks were the main source of alcohol. Oesophageal cancer occurs in both rural and urban environments, affects people without regard to tribal ethnicity, and occurs mainly in the 6th decade; moreover, almost all patients present with advanced disease.

Ten-year observation of peptic ulceration at Ga-Rankuwa Hospital, Pretoria--1979-1988.

For the 10-year period 1979-1988, the incidence of endoscopically diagnosed peptic ulceration at Ga-Rankuwa Hospital was studied with particular reference to: type of ulcer; age, sex and place of residence of the patients; and patient's occupations. The incidence of peptic ulceration remained unchanged. In this area, gastric ulceration is a rare disease among black people. Early urbanisation had no influence on incidence but more patients from developing rural areas were seen as the study progressed. There was a peak incidence during August.

Malignant disease of the gastro-intestinal tract in blacks. Incidence and frequency distribution by age, sex and site at Ga-Rankuwa Hospital, Pretoria, 1976-1986.

The pathology records of Ga-Rankuwa Hospital for the years 1976 - 1986 were studied in respect of the numbers of gastro-intestinal malignant diseases diagnosed. Some tumours were seen more frequently in recent years, i.e. carcinoma of the oesophagus, stomach, colon and rectum. Whether this increased occurrence represents a true increase in this type of malignant disease is not proven. In comparison with other hospital reports, carcinoma of the oesophagus is very common and is certainly showing no decrease.