Chromosome bands in freshwater triclads

Abstract

Four species of Triclads belonging to three families, Dugesia polychroa and Dugesia mediterranea (Dugesiidae), Planaria torva (Planariidae) and Dendrocoelum lacteum (Dendrocoelidae) were studied for chromosome banding : C-banding for all the species, ASG banding for Dugesia polychroa and G-banding for Dugesia polychroa and Dugesia mediterranea . C-banding results for Dugesia lugubris-polychroa group suggest a high level of heterochromatin evolution in the group . Small bands strictly limited to the centromeric region were seen in Dugesia lugubris and this pattern is similar to the patterns of some species belonging to other families, notably Planaria torva and Dendrocoelum lacteum . This could be considered a primitive character. In contrast numerous heterochromatin bands which are useful to characterize the different karyotypes were seen in Dugesia polychroa and Dugesia mediterranea. Our data suggest that heterochromatin is important in freshwater triclad speciation .

An adaptable chromosome preparation methodology for use in invertebrate research organisms

“…Many times, karyograms have been used as a powerful tool for species identification, among both planarians and mollusks [ 21 , 52 ]. We showed that when planarians are collected in the wild, it can be difficult to identify the species only on the basis of morphological features.…”

“…Historically, planarian species identification relies on the anatomy of sexual reproductive organs [ 18 , 53 , 54 ], which leaves the cohort of asexual planarian species largely uncatalogued. A proper characterization of the karyotypes of both sexual and asexual species would facilitate the identification and cataloging of planarian species, while also providing a rich resource for the understanding of karyotype evolution [ 21 ]. Similarly, over the years, the Gastropoda class has been reorganized multiple times in subclasses and families, and new species have been integrated, but the lack of a unique and established method for species identification has created multiple incongruences [ 55 , 56 ].…”

“…Furthermore, solution osmolarity, incubation temperature and time, and centrifugation speed are all complex factors to optimize for karyotyping an invertebrate species of interest. The variety of protocols used in the past for chromosome preparation in planarians and the difficulties in comparing the obtained results [ 21 ] clearly demonstrate the necessity to develop a universal protocol that can be easily adapted to as many species as possible.…”