Interrelation of inversion systems in the midge Chironomus intertinctus (Diptera: Nematocera). II. A nonrandom association of linked inversions.

HE three most common inversions in the population of Chironomus (Kiefferulus) intertinctus Skuse at Ocean Grove, Victoria, are tied up in associations of one sort or another. The first paper in this series (MARTIN 1962) was concerned with the linkage of the Corio inversion, on the third chromosome, with the sex determining region. The present paper deals with a nonrandom association of inversions on the second chromosome, the Lonsdale inversion, with alternative sequences StLo and Lo, and the Banvon inversion, with alternative sequences StBa and Ba (MARTIN 1963). This association has been investigated for a number of years in the Ocean Grove population and also in other widely separated populations in an attempt to learn something of its basis. Many records of similar nonrandom associations appear in the literature for Drosophila (reviewed by LEVITAN 1958b). The species in which they have been recorded are D. robusta (CARSON and STALKER 1949; LEVITAN 1954 a,b, 1955, 1957, 1958a,b, 1959a,b, 1961a,b, 1964), D. guaramunu (BRNCIC 1953; LEVITAN and SALZANO 1959), D. americana (BLIGHT 1955), D. paramelanica (STALKER 1959, 1960, 1961), D. pavani (BRNCIC 1961), D. rubida (MATHER 1961, 1963), D. nigromaculata (TOYOFUKU 1962), D. euronotus (STALKER 1964) and D. subobscura (KRIMBAS 1964). For other species there appear to be only the cases of Chironomus tentans ( ACTON 1955), Simulium tuberosum (LANDAU 1962) and Simulium uittatum (PASTERNAK 1964). Also in Tendipes (= Chironomus) decorus, the results of ROTHFELS and FAIRLIE (1957) show a significant nonrandom association of inversions A and C of chromosome I, such that SA with Sc and A with C are favoured. The case of Simulium vittatum must be treated with caution since the significant deviation of inversions ZZZL-22 and 111s-2 is apparently due to deviation of the individual inversions from Hardy-Weinberg expectation, and the significance of this association disappears when the expected values are calculated from marginal totals and are made to add to the observed total. The majority of these papers simply report the presence of an association in a single population, in some cases not even giving the data upon which their conclusions are based. The only detailed studies are of Drosophila species: D.