The role of parthenogenesis in the biology of two species of mayfly (Ephemeroptera)

Abstract

1. From a single founder virgin female of each species, nine and seven successive parthenogenetic generations of Cloeon dipterum and Cloeon simile, respectively, were reared: all offspring were female. Eggs were removed from final instar nymphs, subimagos and virgin imagos of each generation and their development assessed. The life cycles of 487 individual C. dipterum and 315 C. simile were recorded, together with details of growth rate, egg production and adult size of these and other representatives of each generation. In order to distinguish between the effects of parthenogenesis and the effects of culture conditions, fertilized eggs of both species were reared under the same laboratory conditions. 2. Fewer unfertilized than fertilized eggs hatched. There was no consistent trend in the percentage hatch in successive parthenogenetic generations. In both species the time taken for parthenogenetic individuals to complete a generation varied considerably, and no relationship was found between generation length and the number of parthenogenetic generations that had passed, the developmental stage of the donor, or the time taken for the eggs to hatch. After 50 weeks there was, in both species, an overlap of up to six generations. The number of eggs produced by both species was significantly greater in the first parthenogenetic generation than in later generations but the numbers for later generations lie within the recorded range of egg number in imagos captured in the field. 3. To find if parthenogenetic individuals occur in the field, the sex ratios of last instar nymphs and subimagos of C. simile were measured in samples collected over 13 successive years from a set of small isolated pools. There was a female bias both in winter and at the start of the emergence season. It is possible that, when mature nymphs and emerging subimagos are damaged by predators, the eggs which are released from them survive and develop. 4. Mature, egg‐containing nymphs of both species were present in the field throughout the year, although their numbers were small at the beginning of winter. 5. Oviposition by imagos captured from mating swarms and by virgin imagos, of both species, was recorded for the first time, showing that C. dipterum is not always ovoviviparous. It is suggested that early instar nymphs occurring in mid‐winter come not only from unfertilized eggs released from injured nymphs and subimagos, but also from fertilized eggs laid in autumn.

Emergent body size of mayfly survivors

“…Although female parthenogenesis (virgin females laying eggs) has been widely described in some mayfly genera, it is generally thought that entirely female populations are unstable and contribute to an overall reduction in fitness (Funk, Jackson & Sweeney, 2006). Harker (1997) has previously reported that unfertilized eggs take longer and are less probably to hatch in two mayfly species. Although this study did not detect effects on female mayfly emergence patterns or body size for either Baetis or Epeorus, future studies should evaluate egg hatching success.…”

Asexual reproduction: Genetics and evolutionary aspects

“…Equally, the term apomixis (apomictic thelytoky) is sometimes used when referring to animals [74] . Thelytoky Hexapoda Odonata Exceptional [34] and Ephemeroptera Very common [35] Deuterotoky Blattoptera Very common [11,36] Mantoptera Very common [11] Isoptera Very common [11] Plecoptera Rare [37] Orthoptera Very common [11] Embioptera Occurs in Oligotomidae [11] Phasmida Very common [11] Psocoptera Less than 4 % [38] Phthiraptera Bovicola sp (Mallophaga) [39] Hemiptera Common, universal in aphids [11,40] Thysanoptera Some species [41] Strepsiptera One possible example [42] Thelytoky and Hexapoda Coleoptera (beetles) 54 Curculionidae, 11 Chrysomelidae, rare in other families [11,40,43] Deuterotoky Hymenoptera Very common [11] Diptera Found in several families [11] Lepidoptera Several Psychidae exceptional elsewhere [40] Echinodermata Asteroidea and Stelleroidea Rare or absent [44] Vertebrata Pisces About eight species (Poeciliidae, Cyprinidae, Atherinidae and Cobitidae) [45] Amphibia About three Ambystoma [45] Reptilia About 36 lizards and two snakes [46][47][48][49][50][51][52][53][54][55] R: Reduced eggs; F: fertilisation of eggs; C: equivalent to clonality. * Except for certain automicts (see Figures 1-3).…”

Parthenogenesis in Hexapoda: Entognatha and non-holometabolous insects

“…There are numerous studies on parthenogenesis of other mayflies. Usually, parthenogenesis is suggested or demonstrated via reproductive experiments (Huff and McCafferty 1974;Friesen and Flannagan 1976;Grant and Masteller 1987;Harker 1997;Glazaczow 2001;Funk et al 2006Funk et al , 2010Sekin e et al 2015).…”