Histology and ultrastructure of the testes of Cobitis loaches from diploid-tetraploid populations

Abstract

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The diploid-polyploid complexes of Cobitis distributed in Poland are usually composed of one 2n parental species, C. taenia or C. elongatoides, triploid hybrid females and intriguingly tetraploid hybrids of both sexes. Earlier histological examinations revealed that spermatozoa not detected in the testes of tetraploids. The aim of the preliminary studies presented here for the first time was the ultrastructure of the testes of C. taenia and tetraploid Cobitis from diploid-tetraploid population in Pilica and Kortówka Rivers (Poland) during the reproductive season. The structure of C. taenia testes represents a typical for most Teleostei cystic type of spermatogenesis. So, the developing germ cells are enclosed within cysts, whose borders are formed by the Sertoli cells. The testes of C. taenia were filed with spermatozoa over the entire reproductive season. We described morphologically the different germ cell stages of spermatogenesis (spermatogonia, spermatocytes, spermatids and spermatozoa) of C. taenia. In the testes of tetraploid males only cysts with normal spermatogonia and spermatocytes (pachyten or leptoten stages), containing synaptonemal complexes were observed. Any spermatids or spermatozoa have not been observed. In many cysts of postmeiotic stages we observed planty of degenerative cells showing signs of apoptosis and characterized by strange ultrastructure. Frequently, portions of electron-dense material were observed suggesting degenerative process as a result of chromatin defragmentation. Thereby we confirmed that investigated tetraploid Cobitis males are sterile.

Keywords

• Spermatogenesis
• testes
• ultrastructure
• polyploid
• Cobitis