Résumé
Parthenogenesis (reproduction through unfertilized eggs) encompasses a
variety of reproduction modes with (automixis) or without (apomixis)
meiosis. Different modes of automixis have very different genetic and
evolutionary consequences but can be particularly difficult to tease
apart. In this paper, we propose a new method to discriminate different
types of automixis from population-level genetic data. We apply this
method to diploid Artemia parthenogenetica, a crustacean whose
reproductive mode remains controversial despite a century of intensive
cytogenetic observations. We focus on A. parthenogenetica from two western
Mediterranean populations. We show that they are diploid, and that markers
remain heterozygous in cultures maintained up to ~36 generations in the
laboratory. Moreover, parallel patterns of population-wide heterozygosity
levels between the two natural populations strongly support the conclusion
that diploid A. parthenogenetica reproduce by automictic parthenogenesis
with central fusion and low, but non-zero recombination. This settles a
century-old controversy on Artemia, and, more generally, suggests that
many automictic organisms harbor steep within-chromosome gradients of
heterozygosity due to a transition from clonal transmission in
centromere-proximal regions to a form of inbreeding similar to
self-fertilization in centromere-distal regions. Such systems therefore
offer a new avenue for contrasting the genomic consequences of asexuality
and inbreeding.