Two new species of Dugesia (Platyhelminthes, Tricladida, Dugesiidae) from the subtropical monsoon region in Southern China, with a discussion on reproductive modalities

Abstract

Background Freshwater planarians of the genus Dugesia (Platyhelminthes, Tricladida, Dugesiidae) are distributed in a major part of the Old World and Australia, although until recently only very few species were known from China. Results Two new species of Dugesia from Southern China are described on the basis of an integrative taxonomic approach. BI and ML phylogenetic trees based on the independent genes and on the concatenated dataset had similar topologies, only differing in some nodes that were weakly supported. Phylogenetic trees based on the concatenated dataset revealed that D. adunca Chen & Sluys, sp. nov. and D. tumida Chen & Sluys, sp. nov. are not closely related and belong to different clades. The two new species occupy separate long branches with high support values and, thus, are well-differentiated from their congeners. Separate species status of D. adunca and D. tumida is supported also by the genetic distances between the species included in our analysis, albeit that COI distances varied greatly among species. Dugesia adunca from Guangxi Province is characterized by the following features: living mature animals rather small; asymmetrical openings of the oviducts into the bursal canal; penis papilla with shape of an aquiline bill, albeit with a blunt tip; asymmetrical penis papilla, with a large antero-dorsal lip and a much smaller ventro-posterior lip; very large seminal vesicle, provided with trabeculae; small diaphragm; mixoploid karyotype with diploid complements of 2n = 2x = 16 and triploid complements of 2n = 3x = 24, with all chromosomes being metacentric. Dugesia tumida from Guangdong Province is characterized by a penis papilla provided with a large, symmetrical penial valve from the middle of which arises the small, distal section of the papilla; a duct intercalated between the seminal vesicle and the small diaphragm; ventrally displaced ejaculatory duct curving upwards before opening to the exterior; penis papilla highly asymmetrical, having a slim and long ventral portion and a short and stubby dorsal part; vasa deferentia separately opening into antero-dorsal portion of seminal vesicle; oviducts openings symmetrically into ventral portion of the bursal canal, near its opening into the atrium; mixoploid karyotype, with diploid chromosome portraits of 2n = 2x = 16, and triploid complements of 2n = 3x = 24, with all chromosomes being metacentric. In the context of the various kinds of mixoploidy and the sexualization of specimens, reproductive modalities within the genus Dugesia are shortly discussed. Conclusion Molecular, morphological, and karyological markers show that the two populations examined represent members of the genus Dugesia and constitute two new, distinct species.

Two New Species of Freshwater Planarian (Platyhelminthes, Tricladida, Dugesiidae, Dugesia) from Southern China Exhibit Unusual Karyotypes, with a Discussion on Reproduction in Aneuploid Species

“…In both sexual and sexualized ex-fissiparous specimens of D. musculosa, well-developed testes were present as well as hyperplasic ovaries. The presence of such hyperplasic ovaries is remarkable because generally, these ovaries coincide with abnormal oocytes, which causes infertility [6,46,54]. Such sexualized specimens with well-developed testes and hyperplasic ovaries have been reported for several specimens of D. semiglobosa as well as ex-fissiparous specimens of D. majuscula, which produce either infertile cocoons or reproduce by fission [5].…”

“…However, during the sexualization process, mixoploid individuals may be able to reconstitute the original diploid karyotype and, thus, become capable of sexual reproduction, a situation that has been reported for several mixoploid populations of D. japonica, one mixoploid population of D. gonocephala s. str., and also in D. adunca [6,35,49]. Such mixoploid, fertile specimens represent examples of gonado-somato-mosaicism, with the gonads having a ploidy level and a chromosomal development enabling successful sexual reproduction [53].…”

“…Sequence analyses were done as described previously by Wang et al [4][5][6]. In brief, ITS-1 sequences were aligned online with MAFFT (Online Version 7.247, [9]) using the G-INS-i algorithm.…”

“…Although about 110 species of the freshwater planarian genus Dugesia Girard, 1850, have been reported from the major portion of the Old World and Australia, it was only recently that taxonomic studies started to unveil its rich biodiversity in China, which forms a potential distribution hotspot for this genus [1]. From southern China, eight new species were described [2][3][4][5][6], while from northern China, thus far one new species was reported [7]. In the present paper, we add two new species of Dugesia to the alreadyknown diversity in southern China by applying an integrative approach, including morphological, karyological, histological, and molecular information.…”