The four paracentric autosomal chromosome inversions In(2L)r.In(2R)NS, In(3L)P and /n(JR)P are commonly polymorphic in natural populations of D. ndanogaster in Australasia, North America and Asia, with latitudinal clines in the frequencies of each inversion in each region. In each region inversion frequency decreases with increasing distance from the equator, although the precise relationship between frequency and latitude varies between inversions and, for In(2L)t and In(2R)NS, among regions. Each inversion also shows a longitudinal cline in at least one region but none show such a cline in all three. Although no inversion's frequency is associated with the same climatic variable in all three regions, inversion frequencies are generally positively related to annual maximum temperature and, more particularly, minimum temperature and minimum rainfall. The directions of the latitudinal clines and the climatic associations are consonant with evidence from D. melanogaster that inversion frequencies decline in winter. They are also consonant with evidence from some other Drosophila species that inversion heterozygosities are lower at the geographic margins than at the centre of the species' ranges.

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Infection patterns of Mycobacterium rnarinum were studied over a period of 3 yr in wild rabbitfish Siganus rivulatus populations associated with commercial mariculture cages and inhabiting various sites along the Israeli Red Sea coastline. Mycobacteriosis was first recorded from the Red Sea in 1990 in farmed sea bass Dicentrarchus labrax and is absent from records of studies on parasites and diseases of wild rabbitfish carned out in the 1970s and 1980s. A sharp increase in the prevalence of the dsease in cultured and wild fish in the region has occurred since. A total of 1142 rabbitfish were examined over a 3 yr period from inside mariculture net cages, from the cage surroundings and from several sites along the coast. Histological sections of spleens were examined for presence of granulomatous lesions. Overall prevalence levels of 50 % were recorded in the rabbitfish sampled inside the net cages and 39 % at the cages' close surroundings, 21 % at a sandy beach site 1.2 km westwards, 35 % at Eilat harbour 3 km to the south and 4 2 % at a coral reef site about 10 km south of the cages. In addition, 147 fish belonging to 18 native Red Sea species were sampled from 2 sites, the net cage farm perimeter and the coral reef area, and examined for similar lesions. None of those from the coral reef were infected with Mycobacterium; however, 9 of 14 species collected from the cage surroundings were infected. An increase in prevalence of mycobacteriosis in the manculture farm area was noted from 1995 to 1997. At the same time, a significant increase in prevalence was also apparent at the coral reef sampling site. Two M. marinum isolates from rabbitfish captured at Eilat harbour and the coral reef site were shown by 16s rDNA sequencing analysis to be identical to isolates from rabbitfish trapped inside the mariculture cages as well as isolates from locally cultured sea bass D. labrax. The implications of spreading of M, marinum infection in wild fish populations in the Gulf of Eilat are discussed.