Automictic parthenogenesis of a geographically parthenogenetic mayfly, Ephoron shigae (Insecta: Ephemeroptera, Polymitarcyidae)

Abstract

In the geographically parthenogenetic mayfly, Ephoron shigae, egg maturation and counts of chromosome number of unfertilized, parthenogenetic eggs were studied, in comparison with fertilized eggs from a bisexual population. The primary oocyte becomes mature through two successive maturation divisions. The first maturation division (meiotic division) takes place in the primary oocyte to produce a secondary oocyte and a first polar body. The second maturation division soon occurs in the secondary oocyte, in which the nucleus is divided into a mature egg nucleus (female pronucleus) and second polar body nuclei. The first polar body, in some cases, was successively divided into two polar bodies; in other instances, it was not divided. After the successive maturation division, the egg nucleus and the sister second polar body nucleus drew near to fuse into the zygote nucleus. The chromosome number was doubled in the zygote, and this conjugation initiates subsequent embryonic development. This suggests that, in E. shigae, the process of parthenogenetic recovery of diploidy is the automictic type categorized as the 'terminal fusion' pattern.

Phylogeography of the East Asian polymitarcyid mayfly genusEphoron(Ephemeroptera: Polymitarcyidae): a comparative analysis of molecular and ecological characteristics

“…A difference of karyological characters in both species, E. shigae and E. eophilum , also strongly supports molecular phylogeny. In previous studies of E. shigae , the numbers of chromosomes were 2 n = 12 (female) and 2 n = 11 (male), and the sex chromosomes exhibited an XX (female) and XO (male) pattern (Sekiné & Tojo, , 2010a, b). In the present study of E. eophilum , the numbers of chromosomes were mainly shown to be 2 n = 15 and 16 (Fig.…”

“…Upon hatching of the nymphs having soft cuticle and little yolk within the abdomen, chromosome preparations were made and chromosomes were counted for each specimen, in accordance with the method of our previous study (Sekiné & Tojo, 2007, 2010a, b). The whole nymphs (body length < 1 mm) were prepared on slides by wounding the tissue with a needle and forceps and incubating for 30 min in ion‐exchange water containing 0.005% colcemide.…”

Potential for parthenogenesis of virgin females in a bisexual population of the geographically parthenogenetic mayfly Ephoron shigae (Insecta: Ephemeroptera, Polymitarcyidae)

“…In E. shigae , Sekiné & Tojo (2007, 2009) indicate that all parthenogenetic offspring from the unisexual populations were female (2 n = 12), and that the reproductive mode of the unisexual populations can be described as diploid thelytokous parthenogenesis. These results also indicate that all of the parthenogenetic offspring from bisexual population are female (2 n = 12; Fig.…”

“…, 2006). Furthermore, it is revealed that all individuals reproduced by parthenogenesis are diploid females (2 n = 12), indicating the occurrence of thelytokous parthenogenesis (Sekiné & Tojo, 2007, 2009). However, the parthenogenetic ability of females in bisexual populations has not been thoroughly investigated.…”

Parthenogenesis in Hexapoda: Entognatha and non-holometabolous insects

“…Cytogenetic studies on Ephoron shigae (Takahashi, 1924) (Polymitarcyidae) demonstrated automictic diploid thelytoky (Sekiné and Tojo , ,b; Sekiné et al. ).…”