CHROMOSOMAL EVOLUTION AND SPECIATION
131
chromosome number of C. a. maraenoides.
Kupka has figured an
embryonic somatic metaphase of C. wartmanni (2n = 72) in which 36
of the chromosomes seem to show a kind of negative heteropycnosis as
compared with the remaining 36, which are fully condensed. He interprets this observation as evidence for allopolyploidy, but his reasons for
rejecting the alternative interpretation (that one set of 36 elements is
of paternal origin and the other set maternal) are not entirely convincing.
Until more detailed and critical work, including a study of the meiotic
chromosomes, has been carried out on this group, the evidence for
polyploidy must be regarded as inconclusive.
A belief that multiple sex chromosome mechanisms are an indication
of polyploidy occurs in the work of Bauer (1947), Goldschmidt (1953),
Kushnir (1952), and Gates (1953). The first two of these authors both
concluded in favor of evolutionary polyploidy in the Dermaptera, where
five XY forms have the chromosome numbers 2n $ — 12,14,14, 24, 24; five
XiXoY forms have the numbers 21, 25, 25, 25, 25; and one X1X2X3Y
species has 2n & = 38 (Forfícula auricularia with both XY and XiX 2 Y
males has been included twice in the above count).
There is obviously an indication here that the species with higher numbers of autosomes have more complex sex chromosome mechanisms, but
there is certainly no critical evidence for polyploidy, and Goldschmidt's
discovery of an ΧχΧ 2 Υ species with 2n 0 — 21 seems to have weakened
rather than strengthened the original case in favor of polyploidy.
E. Goldschmidt's suggestion that the X1X2Y sex chromosome mechanism in the mantids might be due to evolutionary tetraploidy, rather than
to a reciprocal translocation as originally suggested by White (1940),
was based on the evidence available in 1949, which did suggest that the
chromosome numbers of the ΧχΧ 2 Υ species were higher than those of
almost all the XO forms. An up-to-date tabulation of 56 species does
not provide any real evidence for polyploidy (Table 1).
An essential feature of all the multiple sex chromosome mechanisms
of the Dermaptera, mantids, etc., is the nonhomology, or at any rate nonpairing, of the different X's in the heterogametic sex. The proponents of
the polyploidy hypothesis have either ignored this fact, or have resorted
to various awkward assumptions in order to explain it.
Gates (1953) states that the beetles of the genus Bhps, with multiple
sex chromosome mechanisms, studied by Guénin (1950, 1953) "are evidently tetraploid." The facts in this case are that in 7 species the numbers of autosomal pairs are 8, 9, 15, 15, 16, 16, 17. No relationship, either
direct or inverse, is discernible between the number of autosomes and
the complexity of the sex chromosome mechanism (i.e., the species with
9 pairs of autosomes has 12 X's and 6 Y's in the male, while the one
131
chromosome number of C. a. maraenoides.
Kupka has figured an
embryonic somatic metaphase of C. wartmanni (2n = 72) in which 36
of the chromosomes seem to show a kind of negative heteropycnosis as
compared with the remaining 36, which are fully condensed. He interprets this observation as evidence for allopolyploidy, but his reasons for
rejecting the alternative interpretation (that one set of 36 elements is
of paternal origin and the other set maternal) are not entirely convincing.
Until more detailed and critical work, including a study of the meiotic
chromosomes, has been carried out on this group, the evidence for
polyploidy must be regarded as inconclusive.
A belief that multiple sex chromosome mechanisms are an indication
of polyploidy occurs in the work of Bauer (1947), Goldschmidt (1953),
Kushnir (1952), and Gates (1953). The first two of these authors both
concluded in favor of evolutionary polyploidy in the Dermaptera, where
five XY forms have the chromosome numbers 2n $ — 12,14,14, 24, 24; five
XiXoY forms have the numbers 21, 25, 25, 25, 25; and one X1X2X3Y
species has 2n & = 38 (Forfícula auricularia with both XY and XiX 2 Y
males has been included twice in the above count).
There is obviously an indication here that the species with higher numbers of autosomes have more complex sex chromosome mechanisms, but
there is certainly no critical evidence for polyploidy, and Goldschmidt's
discovery of an ΧχΧ 2 Υ species with 2n 0 — 21 seems to have weakened
rather than strengthened the original case in favor of polyploidy.
E. Goldschmidt's suggestion that the X1X2Y sex chromosome mechanism in the mantids might be due to evolutionary tetraploidy, rather than
to a reciprocal translocation as originally suggested by White (1940),
was based on the evidence available in 1949, which did suggest that the
chromosome numbers of the ΧχΧ 2 Υ species were higher than those of
almost all the XO forms. An up-to-date tabulation of 56 species does
not provide any real evidence for polyploidy (Table 1).
An essential feature of all the multiple sex chromosome mechanisms
of the Dermaptera, mantids, etc., is the nonhomology, or at any rate nonpairing, of the different X's in the heterogametic sex. The proponents of
the polyploidy hypothesis have either ignored this fact, or have resorted
to various awkward assumptions in order to explain it.
Gates (1953) states that the beetles of the genus Bhps, with multiple
sex chromosome mechanisms, studied by Guénin (1950, 1953) "are evidently tetraploid." The facts in this case are that in 7 species the numbers of autosomal pairs are 8, 9, 15, 15, 16, 16, 17. No relationship, either
direct or inverse, is discernible between the number of autosomes and
the complexity of the sex chromosome mechanism (i.e., the species with
9 pairs of autosomes has 12 X's and 6 Y's in the male, while the one