Karyological studies on some species of the families Echinostomatidae and Plagiorchiidae and aspects of chromosome evolution in trematodes

Abstract

The morphometric characteristics of the chromosomes and the variability of the C-heterochromatin blocks in the trematodes Echinoparyphium aconiatum, E. recurvatum, Echinostoma revolutum, E. echinatum, Hypoderaeum conoideum, Isthmiophora melis, Paryphostomum radiatum, Neoacanthoparyphium echinatoides, Plagiorchis maculosus and Opisthioglyphe ranae are determined. The terminal and subterminal localisation of the centromere is a characteristic of the taxa examined. Typical two-arm chromosomes are rare. The karyotype of the examined trematodes is asymmetrical, and this asymmetry is a result of differences in the lengths of the chromosome arms. It is proved that the regression of the lengths of the chromosome arms has a linear character with a similar angle of slope in the different species. Centric fusion and unreciprocal translocations are accepted as contributing significantly to chromosome changes. A hypothesis on the possible mechanism of chromosome changes in the trematode karyotype is proposed.

Phylogenetic relationships of some species of the family Echinostomatidae Odner, 1910 (Trematoda), inferred from nuclear rDNA sequences and karyological analysis

“…Centric fusions could be a possible mechanism for changes in the chromosomal number in this family and in the other digenean groups (Grossman et al 1981a,b, Baršienė 1993, Mutafova 1994). Pericentric inversions are also possibly involved in the karyotypic evolution of echinostomatids, since within the group of species with 2n=20 some of them have more biarmed chromosomes than others, while differences in relative length values are not so conspicuous.…”

“…with 2n=22 chromosomes gradually decreasing in size and with one-armed elements prevailing are characteristic for species of type-genus Echinostoma (Baršienė 1993; Mutafova 1994). The same chromosome morphology has been reported for species of the genus Echinopharyphium , Neoacanthoparyphium , Moliniella , Hypoderaeum , Isthmiophora (Echinostomatinae), but in these species the diploid chromosome number is lower, 2n = 20 (see Baršienė 1993 for review, Mutafova 1994). The chromosome number and morphology of Echinochasmus sp.…”

A cytogenetic study on the rodent tapewormRodentolepis myoxi

“…Generally, a hypothesis proposed by White (1973), suggesting that more evolved species possess symmetrical karyotypes with less number of biarmed, mostly metacentric chromosomes, has often been assumed in studies on several helminth families and genera (e.g. Grossman & Cain, 1981;Barsiene, 1993;Mutafova, 1994;Petkeviciute & Regel, 1994;Petkeviciute et al, 1995;Bell et al, 1998). According to the high degree of symmetry of the R. myoxi karyotype, this species could be considered a young member of the genus.…”

Echinostomes as Experimental Models for Biological Research

“…Over the past decade molecular technology has advanced at a rapid rate; techniques are now available to investigate gene expression (Schechtman et al, 1995 working on an mRN A protein in Schistosoma), to resolve protein structure and function (Davis, 1997 studying spliced leader RNAs in flatworms), to determine genome organisation (Boore, 1999 reviewed the mitochondrial genome) and for species diagnostics and vaccine development (Bergquist, 1995 looking at possible vaccines for schistosomiasis). These techniques were limited by low resolution due to a lack of variation (Mutafova, 1994). These techniques were limited by low resolution due to a lack of variation (Mutafova, 1994).…”

“…A comparison of chromosome structural and C-banding patterns could not distinguish among Echinostoma species in the 37 collar-spine group (Mutafova, 1994). Enzyme electrophoresis proved more successful with fixed differences detected among E. revolutum, E. paraensei, E. caproni and E. trivoivis (Ross et ai., 1989;Sloss et ai., 1995).…”