Distribution of the Medea factor M4 in populations of Tribolium castaneum (Herbst) in the United States

The distribution of the maternally acting, selfish gene Medea(4) (M-4) was determined in populations of the red flour beetle, Tribolium castaneum (Herbst), collected in the southern and midwestern United States. We found clear evidence for the existence of two major regional subpopulations, with a boundary that roughly corresponds to 33degreesN latitude. All 26 strains collected in 10 states north of this latitude were homozygous for the M-4 allele, while only two of 29 strains collected in six states south of this latitude were homozygous for the allele. Of the remaining 27 southern strains, 21 lacked the M-4 allele entirely, while six contained a mixture of M-4 and non-M-4 alleles. This is the first evidence of either the existence of biotypes or the presence of major barriers to gene flow in wild populations of this ubiquitous insect species. Published by Elsevier Science Ltd.