Article 0015 Hybrid Ambystomids
Introduction
In the wild, unisexual hybrids occur throughout the Great Lakes region to New England and the
Maritime Provinces of Canada (Petranka, 122). In this region, forms are typically polyploid
chromosomes), female, and can consist of varying combinations of genetic material from A. laterale, A. jeffersonianum,
A. texanun, and A. tigrinum. Most hybrid combinations are triploid, however, tetraploid and pentaploid
individuals occasionally occur in some populations (Bogart, 1989; Bogard and Licht 1986; Kraus 1985). Diploid
unisexual individuals possessing genomes from A. laterale and A. texanum
are common in northwestern
Ohio and southeastern Michigan (Petranka, 122).
Some unisexual biotypes have been given names, A. nothagenes, A.
platineum, and A. tremblayi. However, most hybrids are referred to by
their genomic compliments (see following).
J - A. jeffersonianum
L - A. laterale
T - A. texanum
Ti - A. tigrinum
These initials are used to describe the ploidy of a given hybrid. For example,
"JLL" describes a hybrid with one set of genes from A.
jeffersonianum, and two sets of genes from A. laterale. Positively
identified combinations include: JL, LT, JJL, JLL, JLT, JLTi, LLT, LTT, LTTi,
TTT, JJLT, JLLL, LLLL, LLLT, LLTT, LTTT, LTTi, and JLLLL (Bogart and Licht 1986;
Bogart et al. 1985, 1987; Downs 1978; Kraus et al. 1991; Licht and Bogart 1987,
1989; Lowcock and murphy 1991; Lowcock eta al. 1991, 1992; Morris and Brandon
1984; Uzzel 1964).
The "Ambystoma jeffersonianum Complex" consists of the two
bisexual diploid species A. jeffersonianum (JJ), A. laterale (LL),
and two unisexual triploids, A. platineum (JJL) and A.
tremblayi (JLL). JJL and JLL are unisexual females, as genetic
material from the male only stimulates egg development (however, there are
rare cases of male hybrids). It is though that the "Ambystoma
jeffersonianum Complex" arose as a result of one ore more hybridizations
between JJ and LL, followed by 'backcrossing' with the diploid parents, which
resulted in unisexual triploids. Unisexuals produce unreduced ova that are
stimulated to divide when a sperm of a diploid male penetrates the egg membrane.
In other words, fertilization does not ensue, so the males genes do not
contribute to the resulting embryo (Petranka, 123). This would mean that unisexuals
are sexually dependent upon bisexual diploids (Macgregor and Uzzell, 1964). A. jeffersnonianum males breed
with A. platineum females, and A. laterale males breed with A. tremblayi
females (Behler 291-292). JJL and JLL have larger cells and nuclei, larger eggs,
and smaller clutches than JJ and LL.
Morris and Brandon (1984) documented the unisexual polyploid JJLT in
Illinois. JLT and JLTi unisexuals have been found on Kelly's Island in
Lake Erie (Kraus, 1985). Specimens from Kelly's Island, A. nothagenes, have been
documented as being diploid, triploid, and tetraploid types with A. laterale,
A. texanum, and A. tigrinum genomes.
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