Data from: Lifetime inbreeding depression, purging, and mating system evolution in a simultaneous hermaphrodite tapeworm

Classical theory on mating system evolution suggests that simultaneous
hermaphrodites should either outcross if they have high inbreeding
depression (ID) or self-fertilize if they have low ID. However, a mixture
of selfing and outcrossing persists in many species. Previous studies with
the tapeworm Schistocephalus solidus have found worms to self-fertilize
some of their eggs despite ID. The probability for selfing to spread
depends on the relative fitness of selfers, as well as the genetic basis
for ID and whether it can be effectively purged. We bred S. solidus
through two consecutive generations of selfing and recorded several
fitness-correlates over the whole life cycle. After one round of selfing,
ID was pronounced, particularly in early-life traits, and the
conservatively estimated lifetime fitness of selfed progeny was only 9%
that of the outcrossed controls. After a second generation of selfing, ID
remained high but was significantly reduced in several traits, which is
consistent with the purging of deleterious recessive alleles (the
estimated load of lethal equivalents dropped by 48%). Severe ID, even if
it can be rapidly purged, likely prevents transitions towards pure selfing
in this parasite, though we also cannot exclude the possibility that
low-level selfing has undetected benefits.