Androgenetic Reproduction in a Freshwater Diploid Clam Corbicula fluminea (Bivalvia: Corbiculidae)

Abstract

Two shell color types of the exotic bivalve Corbicula fluminea were collected in Kyoto city, Japan. DNA microfluorometry revealed that both types were diploids with non-reductional spermatozoa. Maternal chromosomes were found to be extruded as two polar bodies at the first meiosis, and the second meiosis could not be observed. Only the male pronucleus was present in the egg cytoplasm and became metaphase chromosomes at the first mitosis. The present study indicates that the diploid C. fluminea in Japan has the same mode of androgenetic reproduction as the triploid C. leana.

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

“…Until now, obligate androgenesis is known in only the following organisms (Table 1): the Tassili cypress tree Cupressus dupreziana , the little fire ant Wasmannia auropunctata (Fournier et al, 2005) and several species of the clam genus Corbicula Ishibashi et al, 2003). The mechanisms of androgenesis differ widely across these three obligately androgenetic lineages.…”

“…Corbicula is found globally in fresh and brackish waters, and includes both dioecious sexual species and hermaphroditic androgenetic species (Table 2). Androgenesis in Corbicula occurs in lineages with the derived characteristics of hermaphroditism and unreduced biflagellate sperm (that is, sperm containing the same number of nuclear chromosomes as somatic cells), as opposed to dioecious sexuals with uniflagellate reduced sperm (for example, Ishibashi et al, 2003; Table 2). In androgenetic Corbicula, cytological studies show that the oocyte is fertilized by an unreduced sperm.…”

“…On the other hand, the dioecious, sexually reproducing Corbicula species produce reduced sperm: the DNA content of spermatozoa is half of that of somatic cells. Ishibashi et al (2003) concluded that, in Corbicula, unreduced biflagellate sperm could be considered indicative of androgenesis. The presence of biflagellate sperm in the invasive lineages in the Americas (Lee et al, 2005; Table 2 and Figure 3) and Europe (Pigneur et al, 2011b; Table 2 and Figure 3) suggests that androgenesis is the most likely reproductive mode in invasive Corbicula.…”

“…Owing to the peculiar orientation of the spindle, all maternal chromosomes are expelled (see Figure 1 for the detailed mechanism of zygote development). In C. leana and C. fluminea, the oocyte never goes through meiosis II, as the entire maternal nuclear genome is extruded during the first round of meiosis, and thus the reproductive mode is androgenetic Ishibashi et al, 2003). Komaru et al (1998) hypothesized that this unusual phenomenon of axis orientation and complete expulsion of maternal chromosomes in androgenetic Corbicula would result from a 'meiosis-specific mutation' , leading to the alteration of the orientation of the axis of the meiotic spindle.…”

Androgenesis: where males hijack eggs to clone themselves

“…As we explain in the following sections, whether and how diploidization occurs, and under which form of sex determination, greatly affects the predicted fate of androgenetic lineages. While androgenesis is rare in nature, it is 'normal' in some natural populations, including clams of the genus Corbicula [3][4][5], a conifer [6][7][8], a few ants [9][10][11][12] and stick insects [13][14][15][16], and most likely an Australian carp gudgeon [17] (table 1). Androgenesis is also seen sporadically in some species, particularly hymenopterans (ants, bees and wasps), and in some monocots, dicots and gymnosperms (table 1).…”