Vol. 36 No. 3, 1997
Karyotype Polymorphism in Hybrid Populations of Drosophila nasuta and D. albomicans
Yu1, Fei-Jann Lin2 and Hwei-yu Chang1,2,*
of Plant Pathology and Entomology, National Taiwan University, Taipei,
Taiwan 106, R.O.C.
2lnstitute of Zoology, Academia Sinica, Taipei, Taiwan
Yu, Fei-Jann Lin and Hwei-yu Chang (1997) Karyotype
polymorphism in hybrid populations of Drosophila nasuta and D. albomicans. Zoological Studies 36(3): 251-259. Drosophila albomicans (2n = 6) and D. nasuta (2n
= 8) are 2 sibling species with indistinguishable morphology; but
distinct karyotypes. The former is distributed from Japan through
Taiwan to Thailand, and the latter from India to the east coast of
Africa. Although they are completely crossable in the laboratory, no
polymorphic karyotype has ever been found in any one population of
these two species in nature. In this report, 2 questions are addressed.
First, does karyotype polymorphism exist in hybrid populations of these
2 species after long-term cultivation? Second, do the chromosomes
originating from the same species interact with each other during their
trans mission from generation to generation in hybrid offspring? To
answer these questions, 22 interspecific hybrid strains were
established. Each strain was initiated by crossing one D. nasuta male and one D. albomicans
female. Their hybrid offsprings were maintained with the
non-overlapping generation method for 2.5 y (i.e., 45 generations) and
then subjected to karyotype analysis. The origins of the 3rd, 4th, and
sex chromosomes in the hybrid offspring were identified by larval
karyotyping, while an esterase electrophoretic technique was applied
for distinguishing the origin of the 2nd chromosome. Among these hybrid
offsprings, 92% of the 4th chromosomes and 38% of the 2nd chromosomes
are derived from D. albomicans.
The frequencies of the 4th and the 2nd chromosomes are significantly
different from their initial values (50%), therefore, we may conclude
that chromosome 4 is leaning to D.
albomicans, and chromosome 2 to D. nasuta in hybrid strains. On the
contrary, 72.2% of the 3rd and X chromosomes (70.3% in male and 72.8%
in female) are derived from D.
which is close to the initial value (66.7%). Our data clearly reveal
that karyotype poly morphism exists in hybrid offspring after
long-term cultivation, and the evolution of the 3rd and X chromo somes
is apparently not associated with other chromosomes.
Key words: Hybridization, Karyotype selection.
*Correspondence: Department of Plant Pathology and Entomology,
National Taiwan University, Taipei, Taiwan 106, R.O.C.