CYTOGENETIC MECHANISMS IN SILKWORMS
203
There exists a correlation between parthenogenesis and polyploidy in
nature (Suomalainen, 1950). Although the first thoroughly investigated
polyploids in silkworms (triploids, tetraploids, and even single hexaploids) were produced by centrifugation and heating of inseminated eggs
(Hasimoto, 1933a, 1934a; Kawaguchi, 1936a,b; 1938b), the method of
thermal artificial parthenogenesis opened some new and great possibilities
for easy production and investigation of different polyploid types. Besides
diploid, triploid and tetraploid clones were soon obtained which could
be indefinitely reproduced through artificial thermoactivation. Although
these parthenoclones contained only females, some unexpected possibilities to produce autotetraploid moths of both sexes were opened in
crosses of mixoploid 3 n/6 n parthenofemales with normal 2 n males.
Unfortunately, autotetraploid males proved to be almost completely
sterile so that true breeding of a bisexual tetraploid line appeared to be
impossible.
Recently, allotetraploids of both sexes were produced through polyploid parthenogenesis and remote hybridization between domestic Bombyx mori L. and its "wild ancestor" Bombyx mandarina Moore (Astaurov
and Vereiskaya, 1960; Vereiskaya and Astaurov, 1962). Tetraploid males
were proved to be partially fertile and, despite their low fertility,
allotetraploids could be reproduced bisexually so that up to now an
allotetraploid line has reproduced inter se already during eight generations (Astaurov and Vereiskaya, 1963a; Vereiskaya and Astaurov, 1965).
As far as the author knows, this is the first example of bisexual propagation of experimental polyploids in animals with constant preservation
of the degree of polyploidy.
When referring to experimental polyploidy in animals, reviewers
limit themselves almost exclusively to the vertebrates, especially amphibians (Beatty, 1957; Bungenberg de Jong, 1957). Experimental data
gathered on amphibians are undoubtedly very important, yet data concerning experimental polyploidy in insects, in Bombyx in particular, are
in some respects no less instructive and are worth mentioning (Astaurov,
1965).
Another trend of research is connected with experimental androgenesis
(merogony). Bombyx mori appeared to be the first insect, if not the
first animal, in which androgenetic development was successfully obtained
up to the adult stage. At first this was achieved by heating freshly
inseminated eggs in air (Hasimoto, 1934b), and independently by a
somewhat different method of heating in water eggs freshly laid by an
X-irradiated female (Astaurov, 1936b, 1937).
This merogonial "formation of an Individuum by the union of two
sperm nuclei" (Hasimoto, 1934a), or "dispermic androgenesis" (Astaurov, 1937) provided some insight into nucleocytoplasmic interrelations
203
There exists a correlation between parthenogenesis and polyploidy in
nature (Suomalainen, 1950). Although the first thoroughly investigated
polyploids in silkworms (triploids, tetraploids, and even single hexaploids) were produced by centrifugation and heating of inseminated eggs
(Hasimoto, 1933a, 1934a; Kawaguchi, 1936a,b; 1938b), the method of
thermal artificial parthenogenesis opened some new and great possibilities
for easy production and investigation of different polyploid types. Besides
diploid, triploid and tetraploid clones were soon obtained which could
be indefinitely reproduced through artificial thermoactivation. Although
these parthenoclones contained only females, some unexpected possibilities to produce autotetraploid moths of both sexes were opened in
crosses of mixoploid 3 n/6 n parthenofemales with normal 2 n males.
Unfortunately, autotetraploid males proved to be almost completely
sterile so that true breeding of a bisexual tetraploid line appeared to be
impossible.
Recently, allotetraploids of both sexes were produced through polyploid parthenogenesis and remote hybridization between domestic Bombyx mori L. and its "wild ancestor" Bombyx mandarina Moore (Astaurov
and Vereiskaya, 1960; Vereiskaya and Astaurov, 1962). Tetraploid males
were proved to be partially fertile and, despite their low fertility,
allotetraploids could be reproduced bisexually so that up to now an
allotetraploid line has reproduced inter se already during eight generations (Astaurov and Vereiskaya, 1963a; Vereiskaya and Astaurov, 1965).
As far as the author knows, this is the first example of bisexual propagation of experimental polyploids in animals with constant preservation
of the degree of polyploidy.
When referring to experimental polyploidy in animals, reviewers
limit themselves almost exclusively to the vertebrates, especially amphibians (Beatty, 1957; Bungenberg de Jong, 1957). Experimental data
gathered on amphibians are undoubtedly very important, yet data concerning experimental polyploidy in insects, in Bombyx in particular, are
in some respects no less instructive and are worth mentioning (Astaurov,
1965).
Another trend of research is connected with experimental androgenesis
(merogony). Bombyx mori appeared to be the first insect, if not the
first animal, in which androgenetic development was successfully obtained
up to the adult stage. At first this was achieved by heating freshly
inseminated eggs in air (Hasimoto, 1934b), and independently by a
somewhat different method of heating in water eggs freshly laid by an
X-irradiated female (Astaurov, 1936b, 1937).
This merogonial "formation of an Individuum by the union of two
sperm nuclei" (Hasimoto, 1934a), or "dispermic androgenesis" (Astaurov, 1937) provided some insight into nucleocytoplasmic interrelations