Sex Determination and Female Reproductive Development in the Genus Schistosoma: A Review

Abstract

Parasites of the genus Schistosoma were among the first metazoans to develop separate sexes, which is chromosomally determined in the fertilized egg. Despite the occurrence of specific sex chromosomes, the females of most Schistosomatidae species do not complete their somatic development and reach no sexual maturity without the presence of males. Indeed, the most controversial and at the same time most fascinating aspect about the sexual development of Schistosoma females lies on discover the nature of the stimulus produced by males that triggers and controls this process. Although the nature of the stimulus (physical or chemical) is a source of controversy, there is agreement that mating is a necessary requirement for maturation to occur and for migration of the female to a definitive final site of residence in the vascular system of the vertebrate host. It has also been proposed that the stimulus is not species-specific and, in some cases, not even genus-specific. Despite a vast literature on the subject, the process or processes underlying the meeting of males and females in the circulatory system have not been determined and as yet no consensus exists about the nature of the stimulus that triggers and maintains female development. In the studies about their role, Schistosoma males have been considered, at times pejoratively, the brother, the muscles or even the liver of females. Indeed, it still remains to be determined whether the stimulus responsible for female maturation involves the transfer of hormones, nutrients, neuromediators, mere tactile stimulation or a combination of chemotactic and thigmotactic factors.

Parasitological characteristics of Schistosoma mansoni infection in swiss mice with underlying malnutrition

“…The kinetics of fecal egg-output in both experimental groups were similar to other studies indicating an initial phase with low egg-shedding, another with increasing in the egg-laying and a later decreasing (Rocha et al 1995, Ribeiro-Paes & Rodrigues 1997, Thiongo et al 1997. These data suggest that the egg passage through the intestine tissue was not hampered and its maturation did not seem to be affected.…”

Development of Schistosoma mansoni worms in mice analyzed by bright field and confocal microscopy

“…Although the adaptative explanation of this bias is unclear (Boissier et al 2004), previous reports have suggested a strategy to ensure that all female would find a partner (Basch 1990, Platt & Brooks 1997. Second, development of present-day-females is strongly dependent of male worms (Basch 1990, Ribeiro-Paes & Rodrigues 1997, Kunz 2001). However, it appears to be realized into two phases which are male-indepedent or male-dependent (Hernandez et al 2004).…”

“…As a consequence, they significantly depend on the well-muscled males which control their feeding (Basch 1990, Ribeiro-Paes & Rodrigues 1997, Oliveira et al 2000, Kunz 2001) and sexual maturity (Basch 1990, Southgate et al 1998, Kunz 2001. Various lines of evidence suggest that gene expression in the vitellaria of females is dependent on signals from the male sexual partner (LoVerde & Chen 1991, Grevelding et al 1997) and expression of the gene (p19) depends on pairing with a male (Michel et al 2003).…”

“…Morphological studies have shown that present-day-females have sacrificed structural elements including locomotory and pharyngeal muscles (Basch 1990). These losses were balanced for a significant dependency on the well-muscled males (Basch 1990) for transportation to the site of egg deposition, feeding (Basch 1990, Ribeiro-Paes & Rodrigues 1997, Kunz 2001, and possibly haemozoin synthesis (Oliveira et al 2000). In addition, long-term pairing is wanted for females to maintain their sexual maturity (Basch 1990, Kunz 2001 Grevelding et al 1997) and expression of the gene (p19) depends on pairing with a male (Michel et al 2003).…”

Morphometric study of Schistosoma mansoni adult worms recovered from undernourished infected mice

“…It is well documented that male worms intimately control and regulate the expression of a number of female genes (LoVerde & Chen 1991, Skelly et al 1998. It means that females are dependent on pairing with males in order to reach normal growth, sexual maturity, eggs production, feeding (Erasmus 1986, Basch 1990, Ribeiro-Paes & Rodrigues 1997, Kunz 2001) and possibly haemozoin synthesis (Oliveira et al 2000).…”