Testis

Organization of Seminiferous Epithelium in Primates: Relationship to Spermatogenic Efficiency, Phylogeny, and Mating System

Abstract

The succession in time and space of specific germ cell associations, denoted as spermatogenic stages, is a typical feature of mammalian spermatogenesis. The arrangement of these stages is either single-stage (one spermatogenic stage per tubular cross-section) or multi-stage (>1 spermatogenic stage per tubular cross-section). It has been proposed that single-stage vs multi-stage arrangement is related to spermatogenic efficiency and that multi-stage arrangement is typical for Hominids. In the present work, the arrangement of spermatogenic stages and the spermatogenic efficiency of 17 primate species comprising Strepsirrhini (Prosimians: Lemuriformes, Lorisiformes), Platyrrhini (New World primates), Catarrhini (Old World primates) and Hominoidea (Great Apes and Humans) were analysed comparatively by quantitative histological and flow cytometric means. We found a predominant single-stage tubular organization in the Strepsirrhini indicating that the single-stage form represents the ancestral state. The highest degree of multi-stage complexity was found in Hominidea (except orang-utan) and in Platyrrhini but not in Catarrhini. Hence, no direct relationship between single-stage/multi-stage tubular topography and phylogeny could be established across primates. In fact, the tubule arrangement seen in Platyrrhini and Catarrhini primates is the reverse of what might be expected from phylogeny. Interestingly, spermatogenic efficiency was similar in all species. We found no correlation between single-stage/multi-stage arrangement and spermatogenic efficiency or mating system. We speculate that the presence of a single-multi-stage organization might simply reflect germ cell clonal size. Our findings further indicate that sperm competition in primates is not reflected at the testicular function.