Clonopsis gallica, a stick insect parthenogen exploiting different egg maturation mechanisms over its range

Abstract

Clonopsis gallica is an obligate parthenogen which in Morocco has a structurally diploid but numerically triploid karyotype, while in Europe it is of uncertain structure. The egg maturation mechanism of this species was thought to be apomictic, but up to now no cytological evidence was available. Time-scheduled investigations on laid eggs revealed that in C. gallica females from Morocco a unique mitosis occurs to allow egg development, while in Italian and Spanish specimens meiotic-like modes have been observed. The first mode gives a strictly clonal progeny, while the meiotic-like ones appear to allow recombination, as it has also been found in other parthenogenetic phasmids. Clonopsis soumiae, a numerically tetraploid parthenogen, very closely related to and sympatric with Moroccan C. gallica, shares the same simple mitotic mechanisms of egg maturation. These co-occurring modes appear to account for both fixed heterozygosities and the great variety of clones reported in the literature, when mixed samples were analyzed. Also their colonization ability and distribution pattern seem in line with these alternative modes of egg maturation, since only the clones experiencing the meiotic modes appear to be widely spread. These features point to a polyphyletic origin of this taxon that could be better considered as a parthenogenetic complex of strains.