The structure of the female reproductive system of nematodes from the genus Steinernema (Rhabditida: Steinernematidae)

Abstract

AbstractFemales of six species of nematodes from the genus Steinernema (S. affine, S. arenarium, S. bicornutum, S. carpocapsae, S. feltiae and S. glaseri) were studied using light microscopy. Investigation of the gonoduct morphology was completed with ultrastructural data for S. carpocapsae and S. feltiae. Except for S. bicornutum, all species studied show an overall similarity in reproductive system architecture, i.e., a swollen proximal region of the ovaries, an oviduct consisting of irregular rows with two to four cells in cross-section and a uterus divided into two morphologically distinguishable parts (except S. carpocapsae). Such a gonoduct structure is distinctive from any other known nematode gonoduct, especially the particular arrangement of the oviduct cells in mostly long irregular rows with two to four cells in cross-section (except S. bicornutum), which is, according to current knowledge, unique within the Rhabditida. These results indicate the coherence of the genus Steinernema as shown from other morphological and molecular studies. The distal swelling of the uterus is considered to be a spermatheca-uterus complex that possibly functions to store and activate sperm and as a fertilisation chamber. The diversity of the cellular architecture of the Steinernema gonoduct provides valuable information for the delineation of species within a morphologically conserved genus. Furthermore, limited results point to a congruence between the gonoduct characters and current molecular phylogenetic hypothesis within Steinernema. Future studies in this direction must ultimately lead to a better understanding of evolutionary processes within the genus.