Evidence of the sterility of allotetraploid Cobitis loaches (Teleostei, Cobitidae) using testes ultrastructure

Abstract

The diploid-polyploid populations of Cobitis distributed in Poland are usually composed of the spined loach Cobitis taenia or, less often, the Danubian loach C. elongatoides and their triploid (females) and tetraploid hybrids (females and males). The aim of this study was to determine whether tetraploid males participate in the reproduction process by analyzing their testis ultra-

Histological evidence that diploid hybrids of Cobitis taenia and C. elongatoides (Teleostei, Cobitidae) develop into fertile females and sterile males

“…Diploid hybrid males ; present study), as well as triploid (Juchno et al, unpublished) and tetraploid Cobitis males (Juchno & Boroń, 2006;Juchno et al, 2017), are infertile and disturbances in spermatogenesis begins in meiosis I. Most probably, the first signs of degeneration (shown here by pyknotic nucleus) appeared in spermatocytes I.…”

The variable presence of apoptosis in the testes of diploid and sterile allotetraploid Cobitis (Teleostei, Cobitidae) males during reproductive cycle

“…The significantly higher number of spermatozoa in testes of C. taenia from the diploid population (P<0.05; 61±2.39%) in comparison with those from the d-p population (29±3.54%) provided evidence that the steroidogenic signals triggering spermatogenesis were initiated earlier in males from the diploid population than from the d-p one. Moreover, histological sections of tetraploid Cobitis testes confirmed our previous studies (Juchno and Boron, 2006;Juchno et al, 2017) where only spermatogonia and spermatocytes were visible during the entire reproductive cycle (Fig. 1).…”

“…Importantly, tetraploid progeny were less viable than triploid ones and their number significantly decreased, reaching about 6% (Juchno et al, 2014), similar to levels that occur naturally (Boron, 2003;Juchno et al, 2007). There is evidence from C. taenia and mixed Cobitis species populations that in the reproduction processes of d-p populations, only C. taenia males are the sperm donors (Choleva et al, 2012;Juchno et al, 2014), as Cobitis tetraploid males were sterile (Juchno and Boron, 2006;Juchno et al, 2017). Therefore, the existence of allopolyploid Cobitis forms seems to be dependent upon the presence of C. taenia.…”

“…The influence of polyploidy on fish reproduction has previously been examined primarily using artificially induced triploids and, in most cases, sterility was a common outcome (for review, see Piferrer et al, 2009). Naturally occurring tetraploid males of Misgurnus anguillicaudatus produced diploid gametes (Zhao et al, 2014), whereas the ultrastructure analysis of tetraploid Cobitis testes revealed the presence of cysts with spermatogonia and spermatocytes and a lack of spermatids or spermatozoa (Juchno et al, 2017). Moreover, many cells within the cyst displayed degeneration, e.g.…”

“…Moreover, many cells within the cyst displayed degeneration, e.g. pyknotic nuclei, chromatin condensation and/or fragmentation (Juchno et al, 2017), indicating the process of cell death via apoptosis.…”