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Caryologia
International Journal of Cytology, Cytosystematics and Cytogenetics
ISSN: 0008-7114 (Print) 2165-5391 (Online) Journal homepage: https://www.tandfonline.com/loi/tcar
Karyological Studies on Land Planarians
(Tricladida, Terricola)
Ian R. Ball & Elizabeth J. De Vries
To cite this article: Ian R. Ball & Elizabeth J. De Vries (1983) Karyological Studies
on Land Planarians (Tricladida, Terricola), Caryologia, 36:3, 195-202, DOI:
To link to this article: https://doi.org/10.1080/00087114.1983.
Published online: 31 Jan 2014.
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CARYOLOGIA Vol. 36, n. 3: 195-202, 1983
KARYOLOGICAL STUDIES ON LAND PLANARIANS (TRICLADIDA, TERRICOLA)
IAN R. BALL and ELIZABETH J. DE VRIES
Institute of Taxonomic Zoology, University of Amsterdam, Plantage Middenlaan 53, 1018 DC Amsterdam, The Netherlands
SUMMARY - The karyotypes of two land planarians from Madeira have been determined from mitotic metaphase plates from blastema tissue. Kontikia bulbosa (Geoplanidae} possesses a diploid complement of six pairs of chromosomes, all meta- centric, and all rather small, that is less than 3 11m in mean length. Microplana terrestris shows mixoploid hyperdiploidy the presumed eudiploid complement comprising three pairs of elements, the largest, ca. 5 11m, metacentric and the two smaller ones sub- metacentric. The mosaics exhibit various types of trisomic, tetrasomic and pentasomic aneuploidy. The significance of this variation is not known.
INTRODUCTION
The karyology, cytogenetics and cytotaxonomy of freshwater planarians have been extensively studied (BENAZZI and BENAZZI-LENTATI 1976) and there has been a developing interest in the chromosomes of marine species (BALL 1976, 1979; GALLEN! and PucciNELLI 1979). The terrestrial plana- dans, however, have been almost totally neglected in this respect apart from brief notes by MINELLI ( 1977 ), who reported a probable chromosome complement of 2n = 10 from a species of Microplana (Rhynchodemidae) from the Jura Mountains, France, and WINSOR (1981) who recorded 2n = 16 in Bipalium kewense (Bipaliidae). As a result of :fieldwork on the island of Madeira by I.R. Ball and Dr. Eveline Marcus sufficient material of living terricole planarians was obtained to make it worthwhile to attempt a karyological examination of these forms. The work was undertaken not only to fill some gaps in our empirical knowledge but also in the hope of providing comparative information that may throw light on the phylogenetic relationships between the three principal suborders of the Tricladida, relationships which at the moment are rather unclear (cf. BALL 1981).
KARYOLOGICAL STUDIES ON LAND PLANARIANS (^197)
TABLE 1 - Karyometric data for the six chromosomes of the haploid set of « Kontikia bulbosa » from Madeira. Means and standard deviations from five mitotic metaphase plates. N. Chromosome Relative length Centromeric Index Size 11m Nomenclature
1 21.66 ± 2.23 46.20 ± 3.05 2.96 m 2 18.22 ± 0.68 43.38 ± 4.37 2.47 m 3 16.65 ± 0.56 43.09 ± 6.00 2.26 m 4 15.54 ± 0.57 46.22 ± 3.82 2.11 m 5 14.52 ± 0.40 43.83 ± 4.93 1.96 m 6 13.39 ± 0.74 45.09 ± 4.09 1.82 m
but variation in centromere position was high though always the centromere was in the median region. This variation may be a product of the difficulties of measurement with such small chromosomes.
Fig. 1. - Kontikia bulbosa. Living animal 30 mm long, and Idiogram based on the mean values of Table 1.
~c: ~ iOl c::
50
40
30
20
10 I^ I I (^) I (^) I
2 3 4 5 6 Chromosome
198 BALL and DE VRIES
Microplana terrestris. Study of this species revealed wide variation in chromosome number both within and between individuals (Table 2). We have interpreted this as mixo- ploid hyperdiploidy. We regard the eudiploid complement as comprising three pairs of chromosomes of which the largest pair is metacentric and the two smaller ones submetracentric, that is with the centromere in the submedian
TABLE 2 - Karyotype varzatzon in a population of « Microplana terrestris » from Madeira. Basikaryotype 2n = 2x = 6 Karyotype Complement N. Plates N. Animals Ploidv 2x = 6 2:2:2 3 3 eudiploid 2x+1 = 7 2:2:3 2 1 trisomic aneuploid 2x+1 = 7 2x+1 = 7 2x+2 = 8 2x+2 = 8 2x+2 = 8 2x+3 = 9 2x+3 = 9
trisomic aneuploid trisomic aneuploid tetrasomic aneuploid doubly trisomic aneuploid tetrasomic aneuploid triply trisomic aneuploid ?pentasomic aneuploid
Figure 3a 3b
3c
3d
3e
3f
In total some 28 metaphase plates could be counted and of these 21% showed 2x = 6, 32% 2x+1 = 7, 39% 2x+2 = 8, and 7% 2x+3 = 9. Only the first 18 plates listed above could be measured to provide the information given in Table 3.
region. Karyometric data are represented in Table 3 and an idiogram of the presumed euhaploid set, and based on Table 3 part B, is given as Figure 2. The eudiploid set together with various aneuploid derivatives are illustrated in Figure 3.
DISCUSSION
Only two other species of land planarians have hitherto been studied karyvlogically. MINELLI ( 1977) has referred to a possible complement of 2n = 10 in Microplana mahnerti but he admits incertitude concerning this figure. In the light of the polysomic mosaicism here discovered in M. terrestris it is perhaps wisest to await confirmation of this count. The other species studied is the ubiquitous Bipalium kewense for which the results have been published only in abstract form. WINSOR (1981) reports that studies of
200 BALL^ and^ DE^ VRIES
eudiploid set. Almost all possible combinations of chromosome replication have been achieved tQ a maximum of four chromosomes for the smallest, possibly five for the middle, and of three chromosomes for the largest of the set (Table 2). In general the mbrphology of the extra chromosomes agrees well with the
50
40
I
10
0 '---'L-.'--.___ 2 3 Chromosome
Fig. 2. - Microplana terrestris. Living animal 15 mm long, and Idiogram based on the mean values in Table 3 (B).
mean values for the presumed eudiploid set (Table 3) but not infrequently within a single cell the agreement was not so precise. Thus whereas one or two pairs of elements could readily be recognized the remaining elements were rather variable, and intermediate in size as, for example, in the only presumed pentasomic aneuploid seen (Table 2; Fig. 3F). For two cells observed an analysis within the framework here adopted was not possible because four pairs of elements seemed to be present. We are unable at present to ascertain whether or not the polysomic mosaicism observed corresponds with differences between the various tissues
KARYOLOGICAL STUDIES ON LAND PLANARIANS 201
of the planarians because we are unable to distinguish undifferentiated neo- blasts from dedifferentiated cells in the regenerative blastemas. But despite the almost unmanageable variation that exists, even between the cells of one animal, it seems reasonable to assume a eudiploid condition of 2x = 6 although
E ..^3 F~
Fig. 3. - Microplana terrestris. Camera Iucida drawings of six metaphase plates. Compare with Table 2.
this was not the most common number encountered. To assume otherwise, for example that 2n = 3x = 9 or 2n = 2x = 8, would require a degree of multiform aneuploidy, involving both hypo-and hyperdiploidy, which seems unlikely. As BENAZZI and BENAZZI-LENTATI ( 1976) have pointed out polysomy is widespread among some freshwater triclads and since hyperdiploid zygotes are viable aneuploidy may manifest itself in the somatic line. They also indicate that such polysomy results from non-disjunction in neoblast mitosis as well as
