FOUR FORMS OF SIMULIUM TUBEROSUM (LUNDSTR.) IN SOUTHERN ONTARIO: A SALIVARY GLAND CHROMOSOME STUDY

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Abstract
A detailed study of the salivary gland chromosomes of Simulium tuberosum in Southern Ontario revealed four well-defined breeding units and a likely fifth, all sympatric. Except for "floating" inversions, the banding sequence differs between siblings only on the sex-determining arm, 2S. Of the seven basic arrangements of this arm, three are found in more than one breeding group, i.e. they bridge the siblings.Inversion analysis of the entire complement uncovered 83 "floating" rearrangements, generally of low frequency, and produced data on chromosomal linkage, specificity, and breakpoint concentration. Most interestingly, seven of the more widely distributed and functionally important inversions were found to be shared between two or three of the siblings.The occurrence of bridging sequences of 2S and shared "floating" inversions attests to the close genetic affinity of the four sympatric forms and is suggestive of occasional hybridization.