S. C. Reed.
Possible Polyploidy in the Hymenoptera.
Psyche 41:164-165, 1934.

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Psyche
[September
POSSIBLE POLYPLOIDY IN THE
HYMENOPTERA
Bussey Institution, Harvard University
The Bresslau-Harnisch lists of animal chromosome num- bers (Tab. Biol. 4) include data for the twenty species of Hymenoptera whose chromosome numbers were known at that time. Records subsequently published give the num- bers in two additional species, Habrobracon juglandis and Pteronidea ribesii. The total may be summarized in this fashion :
1 species, haploid number 4
Eighteen of the twenty-two species have chromosome numbers of 4 or a multiple of 4; whereas only four species have different chromosome numbers (9 or 10). These num- bers are representative of seven families out of more than one hundred in the Hymenoptera and seem to be a random sample of what may be expected to be the situation in the other species whose chromosome numbers are yet unknown. Though the number of species which have been investigated is very small, the idea suggests itself that these chromo- some numbers may be a result of polyploidy such as is known to occur in plants.




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19341 Polyploidy in the Hymenoptera 165
There is very good evidence that about half of the Angios- perms arte polyploids. From such studies as those reviewed by Darlington (Darlington's Cytology, p. 212) we see that in polyploid series one finds many species with double the basic chromosome number, fewer with the number obtained by a second doubling and still fewer resulting from further doublings of the basic number. Such would seem to be the case even in this small sample from the Hymenoptera. A second point also demonstrated by the abundant plant ma- terial is that in polyploid series there are few species with prime numbers as their haploid count. In the Hymenoptera there are no species with prime numbers. If the chromo- some numbers in the order were entirely fortuitous, one should expect several species to show prime numbers as their haploid count.
The rareness of polyploidy in the animal kingdom and particularly in dioecious species has been considered to be due, at least in part, to thfe fact that such species are in one sex heterozygous for the sex chromosomes. Multiples of the chromosomes in the vast majority of animals would thus cause an upset of the balance between sex chromosomes and the autosomes as was suggested by Muller (Am. Nat. 59) in regard to polyploidy. He suggests, however, that polyploidy might occur in the Hymenoptera.
In the Hymenoptera it may have been possible to avoid this difficulty since they are almost unique among insects in that their males are haploid. Thus if there is any order of insects in which polyploidy is possible it would setem to be the Hymenoptera.
The suggestion that the series of chromosome numblers in the Hymenoptera may have arisen by polyploidy rests, then, on these considerations : 1, all but four of the species have chromosome numbers which are 4 or a multiple of four; 2, the 'existence of haploid males may have allowed polyploidy to occur.




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