Androgenesis: a review through the study of the selfish shellfish Corbicula spp.

Abstract

Among the asexual reproductive modes, androgenesis is probably one of the most astonishing and least studied mechanisms. In this 'paternal monopolization', the maternal nuclear genome fails to participate in zygote development and offspring are paternal nuclear clones. Obligate androgenesis is known in only a few organisms, including multiple species of clam in the genus Corbicula. Corbicula is a good system to review the evolutionary consequences of this 'all-male asexuality' because the cytological mechanisms of androgenetic reproduction have been described. In Corbicula, sperm are unreduced and, after fertilization, the maternal nuclear chromosomes are extruded as two polar bodies. Hermaphroditic lineages of Corbicula have a worldwide distribution and seem to reproduce through androgenesis, whereas their sexual relatives have restricted ranges. The invasive success of these androgenetic Corbicula lineages may be linked to their asexual mode of reproduction. We review the phenomenon of androgenesis, focusing on evolutionary perspectives, using the genus Corbicula as an exemplar system.

Androgenesis: where males hijack eggs to clone themselves

“…By contrast, in areas where they are invasive in North America and Europe, the populations are exclusively androgenetic [2,108,109]. Invasive strains of the ant W. auropunctata are also androgenetic, while some native populations are sexual [110,111].…”

“…The mechanisms behind androgenetic reproduction in C. leana and C. fluminea are well characterized and have been reviewed several times [2,47,48]. After fertilization by a diploid (or polyploid) sperm, the maternal nuclear genome is eliminated from the oocyte via two polar bodies [3][4][5] so that the only maternal genetic material retained resides in the mitochondria.…”

“…Androgenetic parasitism of other species does not always result in complete maternal genome elimination. Indeed, partial retention of different maternal genomes is likely to have contributed to the considerable genetic divergence between androgenetic strains and species [2,24,48]. In the most extreme case, maternal genome elimination fails completely and the haploid maternal nucleus fuses with the diploid sperm, resulting in polyploid strains [25].…”

“…In its original definition, androgenesis referred to when a sperm or pollen nucleus fuses with an egg nucleus, but the nuclear genome of the mother is eliminated by the paternal genome (figure 1) [1]. Alternative mechanisms of androgenesis are, however, recognized [2], particularly the development of an embryo from a male gamete in an egg that lacks a maternal nucleus (see §2; figure 1). When such a 'non-nucleate' egg is fertilized by sperm or by pollen it develops into an offspring whose entire nuclear genome is of paternal origin.…”

Sex Determining Mechanisms in Bivalves

“…Female-to-male sex change may be driven by low available resources intake ( Figure 1 and below for more details). Hermaphroditic species of freshwater Corbicula clams (Corbiculidae) are also protogynous, with eggs present year-round and sperm produced in response to seasonal changes in temperature (Pigneur et al 2012). Corbicula clams, together with the little fire ant, Wasmannia auropunctata, only two cases of obligate androgenesis in animals, and the only one for which the cytological mechanisms of androgenetic reproduction have been well described (see Pigneur et al 2012 for a review).…”