Post-embryonic development of the reproductive system of Pneumonema tiliquae (Nematoda: Rhabdiasidae)

Abstract

The post-embryonic development of the reproductive system of both generations of Pneumonema tiliquae is described from fixed and stained specimens. In recently hatched first-stage larvae all the nuclei stained alike with males having 10 nuclei and females six. The development of the genital primordium during each stage is very precise in both generations; division of the nuclei begins 4–6 h after hatching. At moult 1 the male genital primordium is clearly organized into an anterior gonoduct area of eight nuclei and 12–13 spermatogonia. The anterior gonoduct nuclei arise from a common precursor cell (Z1) whereas one distal tip cell (dtc) and the germinal nuclei that form post-hatching have a common precursor cell origin (Z4). In the female, there are 20 nuclei at moult 1, all appearing essentially similar; in the early second stage these nuclei differentiate into 12 somatic and eight germinal nuclei; the somatic nuclei are considered to be of Z1 and Z4 origin. In the male the gonoduct nuclei grow, reflex and divide before joining to the rectum during the fourth stage. At moult 4 the system is fully formed with the testis containing fully developed secondary spermatocytes; sperm are produced and ejaculated in two phases. In the second-stage larvae the female primordium differentiates into a central gonoduct area with the germinal cells formed into distal opposed regions; subsequent development is rapid and during the fourth stage a small vulva joins the uteri to the body wall. Fertilized eggs develop and hatch in utero; recently hatched first-stage larvae usually have six nuclei in the genital primordium. At moult 2 the primordium has 12 somatic and two germinal nuclei. Once established in the lizard, the reproductive system develops rapidly with development similar to that seen in the free-living generation except the system is larger and contains about four times as many nuclei. Development ceases pre-sperm development if adults remain in the body cavity of the lizard. In the lungs the system continues to grow via increase in cell size with the anterior system folding and the relative position of the vulva changing from 57 to 44% of the body length as the adult increases in length.