Genome fractionation and loss of heterozygosity in hybrids and polyploids: Mechanisms, consequences for selection, and link to gene function

Hybridization and genome duplication have played crucial roles in the evolution of many animal and plant taxa. The subgenomes of parental species undergo considerable changes in hybrids and polyploids, which often selectively eliminate segments of one subgenome. However, the mechanisms underlying these changes are not well understood, particularly when the hybridization is linked with asexual reproduction that opens up unexpected evolutionary pathways. To elucidate this problem, we compared published cytogenetic and RNAseq data with exome sequences of asexual diploid and polyploid hybrids between three fish species; Cobitis elongatoides, C taenia, and C tanaitica. Clonal genomes remained generally static at chromosome-scale levels but their heterozygosity gradually deteriorated at the level of individual genes owing to allelic deletions and conversions. Interestingly, the impact of both processes varies among animals and genomic regions depending on ploidy level and the properties of affected genes. Namely, polyploids were more tolerant to deletions than diploid asexuals where conversions prevailed, and genomic restructuring events accumulated preferentially in genes characterized by high transcription levels and GC-content, strong purifying selection and specific functions like interacting with intracellular membranes. Although hybrids were phenotypically more similar to C taenia, we found that they preferentially retained C elongatoides alleles. This demonstrates that favored subgenome is not necessarily the transcriptionally dominant one. This study demonstrated that subgenomes in asexual hybrids and polyploids evolve under a complex interplay of selection and several molecular mechanisms whose efficiency depends on the organism's ploidy level, as well as functional properties and parental ancestry of the genomic region.Web of Science38125274525

Morphological characteristics of the mud loach Misgurnus fossilis (L.) (Pisces: Cobitidae) from the mid Odra and Vistula river basins

Morphological characteristics of M. fossilis was based on 139 specimens. Sexual dimorphism is manifested in 20 metric characters and in anatomical differences: structure of pectoral fins and presence of thickenings on the body sides of males. Growth of particular body parts is allometric, the main increase in the total body length falling on its mid part. Based on literature data, the material was compared with other European populations. The comparison revealed a wide variation of metric characters showing, however, no clinal pattern

Morphometrics of Pseudorasbora parva (Schlegel, 1842) (Cyprinidae: Gobioninae), a species introduced into the Polish waters

A morphological analysis of 11 meristic and 25 plastic characters, based on 72 specimens of Pseudorasbora parva from carp ponds in the region of Ruda Sułowska (Barycz R. system, SW Poland). The populations occurring in European waters display a wide morphological variability, significantly differing from one another. Sexual dimorphism is manifested in larger body size of males as well as in four plastic characters. The main length increase concerns the fish medial section (positive allometry), whereas the distal parts of the body, eye diameter and the postorbital part of head grow slower (negative allometry)

Metacercariae of digeneans occurring in Cobitis elongatoides Bacescu et Maier, 1969 (PISCES: Cobitidae)

Two encysted metacercariae: Metorchis xanthosomus (Creplin, 1846) Braun, 1902 and unidentified echinostomatide are reported for the first time from the fins of Cobitis elongatoides Bacescu et Maier, 1969 and their polyploid biotypes (C. elongatoides x Cobitis sp.). The morphology of both larvae is described, illustrated and discussed

State of knowledge of helminth fauna of freshwater fishes of Poland

A total 89 fish and lamprey species has been recorded from Polish freshwater habitats. Twenty−seven of them (30.3%) have not been surveyed for parasitic helminthes. Some of the latter fishes are either rare or not easily accessible. Other live only in specific habitats in scattered localities. An important obstacle for studying parasite faunas of some fishes may be their status on an endangered species. Among the non−surveyed fishes, are those which have been relatively recently introduced to Poland or migrated there on their own. The present paper attempts to review all hitherto not studied helminthologically fish species, their habitats, localities and current protection status