Rare diploid females coexist with rare males: a novel finding in triploid parthenogenetic populations in the psyllid Cacopsylla myrtilli (W. Wagner, 1947) (Hemiptera, Psylloidea) in northern Europe

Abstract

Using a cytological approach, diploid females were found coexisting with rare males in triploid apomictic parthenogenetic populations of the psyllid Cacopsylla myrtilli (W. Wagner, 1947) in Norway, Sweden, Finland and northwest Russia. Diploid females were easily distinguished from triploid apomictic females by the presence of 13 chiasmate bivalents instead of 39 univalent chromosomes at metaphase I. Abundance equaled that of males, but the proportion of males and diploid females was significantly greater in high altitude compared with low altitude populations. Males mated with females but showed no mating preference for diploid females. Lack of genuine bisexual reproduction owing to either asynaptic meiosis in males, or rarity of males with normal meiosis, suggests that diploids are produced in every generation by parthenogenetic females as reversals from triploidy, with their production being enhanced by environmental factor(s) associated with high altitude. This is further supported by the observation that within a population the COI haplotype found in rare males was the same as that in parthenogenetic triploid females. Thus, in northern Europe parthenogenesis in C. myrtilli is obligate, geographic parthenogenesis. Bisexual populations of C. myrtilli should be looked for in Central and Southern Europe. From the evolutionary point of view, the presence of males and diploid females with normal meiosis in parthenogenetic populations could be significant as they exhibit the potential to re-evolve either a new sexual species of parthenogenetic ancestry or a new parthenogenetic species by contagious parthenogenesis.

Characteristics of parthenogenesis in Cacopsylla ledi (Flor, 1861) (Hemiptera, Sternorryncha, Psylloidea): cytological and molecular approaches

“…Our findings show that details of parthenogenesis in C. ledi are similar to those found previously in C. myrtilli (Nokkala et al 2015). Parthenogenetic females of C. ledi are triploid showing apomictic oogenesis in which normal meiosis is replaced by a modified mitosis.…”

“…In addition to triploid females, there were also diploids showing normal chiasmate meiosis. Moreover, the presence of diploid females among obligate triploid parthenogenetic females was discovered for the first time in populations of C. myrtilli collected at various altitudes on the hill Rindhovda in southern Norway (Nokkala et al 2015). Diploid females showing conventional meiosis were found at frequencies similar to those of rare males at three different altitudes.…”

“…A fragment of cytochrome c oxidase subunit I ( COI ) gene was amplified using Applied Biosystems 2720 Thermal Cycler. Initially, the C. myrtilli specific primers HybCamyCO (forward) and HybymaCCO (reverse) were used and PCR reactions were carried out as described by Nokkala et al (2015). Later on, to check the sequence at 5’ and 3’ ends, flanking primers HybCacoCO 5’-T7Promoter(F)-CTAACCATAARACTATTGGAAC-3’ (specifically designed forward primer) and a modified HCO (Folmer et al 1994) reverse primer HybHCOMod 5’-T3-TAAACTTCAGGGTGACAAAAAATCA-3’ were used.…”

“…PCR products were purified with QIAquick PCR Purfication Kit (Qiagen) and sequenced by Macrogen Europe (Amsterdam, the Netherlands). The sequences were trimmed to span a 638 bp stretch of the gene to match the available sequences of related C. myrtilli (Nokkala et al 2015). Sequences obtained during this study have been deposited in GenBank under the accession numbers MF978762-MF978766.…”

“…Cytological analysis has also discovered diploid females coexisting with the rare males especially at high altitude. These rare males, although being nonfunctional, copulate randomly with both parthenogenetic and “sexual” diploid females (Nokkala et al 2015). …”