Lw. Beukeboom et al., DISTRIBUTION AND ORIGIN OF CHROMOSOMAL RACES IN THE FRESH-WATER PLANARIAN DUGESIA-POLYCHROA (TURBELLARIA, TRICLADIDA), Hereditas, 124(1), 1996, pp. 7-15
We present a karyotypic survey of the European freshwater planarian Du
gesia polychroa, detailing frequencies of diploid and polyploid forms
from 35 localities in seven countries. In this hermaphroditic species,
diploids reproduce sexually and polyploids by pseudogamous parthenoge
nesis. Previous laboratory studies have shown that the two reproductiv
e modes can interbreed, which may lead to new tri-, tetra-, and pentap
loid lineages. We found four pure sexual, 25 pure parthenogenetic, and
six mixed populations. Although some polyploid populations consisted
entirely of triploids, most contained triploid and tetraploid individu
als. Pentaploids were rare and reported for the first time from the fi
eld. In most populations, the higher ploidy levels were represented by
fewer individuals. Our results indicate that occasional fertilisation
of parthenogenetic eggs leading to genome addition is responsible for
the maintainance of polyploid forms in natural populations of D. poly
chroa.