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

Abstract

Characteristics of parthenogenesis in Cacopsylla ledi (Flor, 1861) were analyzed using cytological and molecular approaches. In all three populations studied from Finland, i.e. Turku, Kustavi and Siikajoki, males were present at a low frequency but were absent from a population from Vorkuta, Russia. In a follow-up study conducted in the Turku population during 2010–2016, the initial frequency of males was ca. 10 % and showed no intraseasonal variation, but then dramatically decreased down to approximately 1–2 % level in seasons 2015–2016. Male meiosis was chiasmate with some traces of chromosomal fragmentation and subsequent fusions. In most females, metaphase in mature eggs included 39 univalent chromosomes which indicated apomictic triploidy. Only a small fraction of females was diploid with 13 chiasmate bivalents. The frequency of diploid females approximately equaled that of males. COI barcode analyses showed that triploid females (N = 57) and diploids (7 females and 5 males) displayed different haplotypes, demonstrating that triploid females reproduced via obligate parthenogenesis. The rarity of diploids, along with the lack of males’ preference towards diploid females, suggested that most likely diploids were produced by rare triploid females which shared the same haplotype with the diploids (not found in the present analysis). Minimum haplotype diversity was detected in the Turku population, but it was much higher in Vorkuta with some indication for the mixed origin of the population. We suggest that functional diploids produced in a parthenogenetic population can give rise either to a new parthenogenetic lineage or even to a new bisexual species.

Description of two new species of the genus Cacopsylla Ossiannilsson, 1970 (Hemiptera, Psylloidea) from northern Fennoscandia recognized by morphology, cytogenetic characters and COI barcode sequence

“…nov. has migrated towards the north during recolonization after the last glacial period, while all other related recolonizing species, C. myrtilli , C. ledi and C. borealis sp. nov., are apomictic parthenogens (Nokkala et al 2008, 2013, 2015, 2017).…”

“…Genomic DNA was isolated from whole insects or from the head and thorax portion of individuals stored in alcohol using the DNeasy Blood and Tissue Kit (Qiagen) as described previously (Nokkala et al 2015, 2017). A fragment of the mitochondrial COI gene was amplified using the primer pair HybCacoCO / HybHCOMod.…”

“…PCR products were purified with QIAquick PCR Purfication Kit (Qiagen) and sent to Macrogen Europe (Amsterdam, the Netherlands) for sequencing. BioEdit 7.2.0 (Hall 1999) software was used to trim the sequences to span a 638 bp fragment of the gene and to align the sequences with related Cacopsylla species, C. fraudatrix (GenBank accession number JX987970 = h8) (Kuznetsova et al 2012), C. myrtilli (KF494326–KF494332 = h1–h7) (Nokkala et al 2015), C. ledi (MF978762–MF978766 = h9–h11, h13–h14) (Nokkala et al 2017) and JX987973 = h12 (Kuznetsova et al 2012). In addition, we sequenced the same gene region from a related bisexual species C. corcontum (Šulc, 1909), accession number MK184915 (= h18), used as an outgroup in phylogenetic analysis.…”

“…C. ledi is quite evenly distributed throughout the distribution range, while the distribution of C. myrtilli is concentrated towards the north and/or high altitudes. Females of both species are triploid and reproduce through apomictic parthenogenesis (Ossiannilsson 1992; Nokkala et al 2008, 2017). Quite commonly, infrequent males known as rare males exist in their populations.…”

“…Quite commonly, infrequent males known as rare males exist in their populations. Males are mainly nonfunctional in populations of C myrtilli (Nokkala et al 2013) and functional in C. ledi populations (Nokkala et al 2017). In populations with rare males, infrequent diploid females also exist among the triploids (Nokkala et al 2015).…”