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THE SEX CHROMOSOME CONSTITUTION OF CHIRONOMID INTERSEXES PARASITIZED BY NEMATODES

1962; NRC Research Press; Volume: 4; Issue: 1 Linguagem: Inglês

10.1139/g62-013

0008-4093

J. G. Rempel, J. M. Naylor, Klaus Rothfels, B. Ottonen,

Insect and Arachnid Ecology and Behavior

Intersexuality in Cliironomidae induced by nematode parasitism is relatively comn~on phenomenon. Thus Wiillter ( 1961) found that in Tmzytarsus larvae the ,percentage of parasitism may approach one hundred. Townes (1915) observed that in C13ir01zo7nzrs ~ I Z L I ? Z O S Z L S more than 25 per cent may be intersexes. A summary of the literature on this subject is given by Wiilker ( 1961) and Thienemann (1951). Rempel (1940) made an extensive study of the plienoiuenon in species identified as C. hygerborezrs Staeg. Because the typical intersexual form possessed female body and inale hypopygiuin he concluded that the intersex is a female which through loss of its reproductive glands has developed male external genitalia, and male reproductive duct. H e based his conclusion largely on the following: unparasitized chironoillid larvae near pupation show marlted sexual difference in size, the female larva being larger than the male larva; parasitized larvae are frequently larger than normal male larvae; the adult intersex is largely female. Although it was difficult to explain how genetically female individual could develop illale hypopygiun~ in all its details, it would have been infinitely more difficult to explain how genetically male larva could retain its normal reproductive system and build around it female body. When this study was conducted (1936) it was impossible to separate the sexes of the larvae on the basis of the chromosomal con~plen~ent (Bauer, 1935, 1936; Gilchrist and Haldane, 1917; Beerniann, 1955). Recently Beermann (1955a) showed that in Cnnrptochiro~zonzzrs tentnus, C. pnllidivithtus and Chiro1z07nns annz~lnr-iz~s it \vas possible to determine the sex of larvae on the basis of salivary gland chromosomes. IViilker (1961) then demonstrated that in cliironomids, male and female larvae are subject to parasitism by nematodes to an equal degree, and that the former, i.e. infected $male larvae, develop into the typical intersex (Gonopoden-Intersex, female body and male genitalia) and the latter into females in which the 8th sternum mav show tendencv toward maleness J J (Sternit-Intersex). Since these findings are in contradiction to those of Rempel, it seemed desirable to reexamine the latter's findings. The original investigations were conducted with species identified as Chiro7zonzus hyperboreus Staeg. Thienemann (1942) showed that the Canadian form could not be identified with the European form under that name and he assigned it new name, C. rmzpelii. Townes (1945) called the latter C. anthracinzes Zett., but Thienemann (1954) pointed out that C. nnthrncinus belongs to the thumnzi-bathophilus groups, while C. rempelii belongs to the plumosus group. Also, Wiilker (1961) stated that sex-chromosome inversion has not