Mating systems and the evolutionary transition between
haploidy and diploidy
Biological Journal of the Linnean Society, 57 (3):
197--218 (1996)DOI: 10.1111/j.1095-8312.1996.tb00309.x
Abstract
According to the ‘masking hypothesis’, diploids
gain an immediate fitness advantage over haploids
because diploids, with two copies of every gene, are
better able to survive the effects of deleterious
recessive mutations. Masking in diploids is, however, a
double-edged sword: it allows mutations to persist over
tine. In contrast, deleterious mutations are revealed
in haploid individuals and are more rapidly eliminated
by selection, creating genetic associations that are
favourable to haploidy. We model various mating schemes
and show that assortative mating, selfing, and apomixis
maintain the genetic associations that favour haploidy.
These results suggest that a correlation should exist
between mating system and ploidy level, with
outcrossing favouring diploid life cycles and
inbreeding or asexual reproduction favouring haploid
life cycles. This prediction can be tested in groups,
such as the Chlorophyta, with extensive variation both
in life cycle and in reproductive system. Confirming or
rejecting this prediction in natural populations would
constitute the first empirical test of the masking
hypothesis as a force shaping the evolution of life
cycles.