Why do schistosomes have separate sexes?

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).…”

“…Thus, the origin of dioicism would be associated with the origin of endothermy, the development of a more sophisticated immune system in endothermic vertebrates and habitat changes, from arterial to venous blood (Platt & Brooks 1997). 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).…”

“…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).…”

“…It is believed that the genus Schistosoma would be evolved from a hermaphroditic trematode of blood system that lived in reptiles of Mesozoic (Basch 1990). Thus, the origin of dioicism would be associated with the origin of endothermy, the development of a more sophisticated immune system in endothermic vertebrates and habitat changes, from arterial to venous blood (Platt & Brooks 1997).…”

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).…”