Microhabitat preferences of triploid Cobitis fish and diploid progenitors in two streams in Slovakia (Danube River Basin)

Abstract Loaches (genus Cobitis ) in Slovakian tributaries (Danube River Basin) are represented by diploid-polyploid hybrid complexes of C. elongatoides and C. tanaitica . Uniquely, their coexistence is made possible by the presence of polyploid (mainly triploid) females that are sexually dependant on diploid male sperm (donors) for gynogenesis. Information on the spatial distribution of Cobitis with of differing ploidy remains relatively scarce. The main aim of this study, therefore, was to identify in ploidy in the species preferred microhabitat. Overall, 345 Cobitis were recorded in Rivers Okna and Ondava (Danube Basin) between 2011 and 2015, with 316 diploid and triploid individuals detected by flow cytometry examined were studied for the microhabitat preferences with the using the point sample method. The sex ratio differed significantly between localities, while diploid-polyploid ratio not. Moreover, each of ploidy-sex forms (i.e. diploid male, diploid female, triploid female) showed a preference for a specific substrate composition, velocity, depth and distance from the bank at both localities. Mixed effect linear models identified clear differences in fine substrate between seasons for individuals from the River Okna. Similarly, non-metric multidimensional scaling detected differences in environmental variables preference for both diploid and triploid forms. These finding indicate specific spatial and temporal microhabitat preference for diploid (sexual donors) and triploid (asexuals) C. elongatoides  ×  C. tanaitica when coexisting as mixed a population.