Abstract
BackgroundHybridogenesis (hemiclonal inheritance) is a kind of clonal reproduction in which hybrids between parental species are reproduced by crossing with one of the parental species. European water frogs (Pelophylax esculentus complex) represent an appropriate model for studying interspecies hybridization, processes of hemiclonal inheritance and polyploidization. P. esculentus complex consists of two parental species, P. ridibundus (the lake frog) and P. lessonae (the pool frog), and their hybridogenetic hybrid – P. esculentus (the edible frog). Parental and hybrid frogs can reproduce syntopically and form hemiclonal population systems. For studying mechanisms underlying the maintenance of water frog population systems it is required to characterize the karyotypes transmitted in gametes of parental and different hybrid animals of both sexes.ResultsIn order to obtain an instrument for characterization of oocyte karyotypes in hybrid female frogs, we constructed cytological maps of lampbrush chromosomes from oocytes of both parental species originating in Eastern Ukraine. We further identified certain molecular components of chromosomal marker structures and mapped coilin-rich spheres and granules, chromosome associated nucleoli and special loops accumulating splicing factors. We recorded the dissimilarities between P. ridibundus and P. lessonae lampbrush chromosomes in the length of orthologous chromosomes, number and location of marker structures and interstitial (TTAGGG)n-repeat sites as well as activity of nucleolus organizer. Satellite repeat RrS1 was mapped in centromere regions of lampbrush chromosomes of the both species. Additionally, we discovered transcripts of RrS1 repeat in oocytes of P. ridibundus and P. lessonae. Moreover, G-rich transcripts of telomere repeat were revealed in association with terminal regions of P. ridibundus and P. lessonae lampbrush chromosomes.ConclusionsThe constructed cytological maps of lampbrush chromosomes of P. ridibundus and P. lessonae provide basis to define the type of genome transmitted within individual oocytes of P. esculentus females with different ploidy and from various population systems.
Highlights
IntroductionHybridogenesis (hemiclonal inheritance) is a kind of clonal reproduction in which hybrids between parental species are reproduced by crossing with one of the parental species
Hybridogenesis is a kind of clonal reproduction in which hybrids between parental species are reproduced by crossing with one of the parental species
In this paper we perform a detailed analysis of oocyte karyotypes of P. ridibunda and P. lessonae originating from Eastern Ukraine and present comprehensive cytological maps of all parental lampbrush chromosomes of the European water frog complex, describing intraspecific variation between frogs from Ukrainian and Polish populations
Summary
Hybridogenesis (hemiclonal inheritance) is a kind of clonal reproduction in which hybrids between parental species are reproduced by crossing with one of the parental species. The European water frogs of the Pelophylax esculentus complex represent an appropriate model for studying interspecies hybridization accompanied by hemiclonal inheritance and polyploidization (reviewed in [6]). This complex consists of two parental species – the lake frog Pelophylax ridibundus (genome composition RR) and the pool frog P. lessonae (LL), as well as natural hybridogenetic form – the edible frog P. esculentus (LR), the latter arising as a result of hybridization between the two parental species [7]. These latter forms most likely appear as a result of fertilization of egg cell with two sets of chromosomes by haploid sperm or vise versa [9]
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