Reproductive mode of the geographic parthenogenetic mayfly Ephoron shigae, with findings from some new localities (Insecta: Ephemeroptera, Polymitarcyidae)

Abstract

The burrowing polymitarcyid mayfly Ephoron shigae is distributed widely in Japan. Some populations are bisexual, others are unisexual, and the distributions of the two types overlap broadly. Experimental evidence of parthenogenetic reproduction, long suspected in unisexual populations, is presented here, based on a comparative analysis of the developmental rate of fertilized and unfertilized eggs. The developmental rate of fertilized eggs from 20 mated females in a bisexual population was 98.4% ± 0.73% (mean ± SD), and no unfertilized eggs from 20 virgin females in that population developed. The developmental rates of unfertilized eggs in two unisexual populations were 89.0% ± 4.59% and 84.2% ± 1.96%, respectively. This article presents experimental evidence of geographic parthenogenesis in E. shigae and provides support for the previous interpretation. In addition, we discuss the relationship between the sex ratio of each population and the developmental rate of fertilized versus unfertilized eggs from the females in those populations.

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

“…The timing of their mass emergence and swarming is synchronized and lasts approximately 1 or 2 h each evening (after sunset) for several days from late August to mid‐September. Ephoron shigae exhibits strong phototaxis, and huge numbers of mayflies are attracted to car and street lights and accumulate densely along riverside roads, interfering with traffic, and sometimes even causing car accidents (Watanabe & Ishiwata, ; Tojo, Sekiné & Matsumoto, ; Sekiné, Tsuruda & Tojo, ).…”

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

“…In the Chikuma‐gawa population, no males were found (i.e. a fully unisexual population; Tojo et al. , 2006).…”

“…In the previous study on E. shigae , obligatory parthenogenesis (i.e. where parthenogenesis is the normal mode of reproduction) appears in unisexual populations (Tojo et al. , 2006).…”

“…However, the parthenogenetic ability of females in bisexual populations has not been thoroughly investigated. Although it was reported that none of the 20 females examined in the Asahi‐gawa River population (a bisexual population) demonstrated parthenogenetic ability (Tojo et al. , 2006), it is still unclear whether this parthenogenetic potential is peculiar to the unisexual populations.…”

Artificial activation of mature unfertilized eggs in the malaria vector mosquito, Anopheles stephensi (Diptera, Culicidae)

“…An indicator for whether an egg is developing would be required for evaluation of egg activation. In some aquatic insect species that lay eggs in water, such as mosquitoes, dragonflies and mayflies, coloration of the egg is often an index of normal development (Corbet, 1962;Clements, 1992;Watanabe et al, 1999;Tojo et al, 2006). Therefore, coloration of eggs could be one of the visible indices of egg activation.…”