Making the in vitro breeding of Schistocephalus solidus more flexible.

Schistocephalus solidus is one of the few cestodes that can be bred in vitro. Worms have typically been bred in pairs, so the parents of each offspring can clearly be assigned. From a genetic perspective, it would be useful to be able to mate an individual worm to multiple partners while still being able to distinguish among different parents. As each adult S. solidus possesses numerous reproductive complexes, cutting worms and breeding the pieces separately would facilitate such breeding designs. We halved worms before in vitro breeding and evaluated whether this affected outcrossing rates and reproductive output. Cutting did not influence clutch mass, i.e. egg number and size, or outcrossing rates, but eggs from cut worms had a lower hatching rate than eggs from uncut worms. We found that when two anterior worm halves were bred together, they produced fewer, smaller eggs with higher hatching rates, compared to two posterior halves. Moreover, once we controlled for this effect of 'worm half', the two halves of an individual worm tended to reproduce similarly under comparable circumstances. We conclude that cutting plerocercoids increases the flexibility with which this tapeworm can be experimentally bred without dramatically affecting the production of viable, outcrossed eggs.