Cytogenetics of a parthenogenetic Arctic species of Micropsectra (Diptera, Chironomidae)

Parthenogenesis in dipterans: a genetic perspective

Parthenogenesis has been documented in almost every phylum of animals, and yet this phenomenon is largely understudied. It has particular importance in dipterans since some parthenogenetic species are also disease vectors and agricultural pests. Here, we present a catalogue of parthenogenetic dipterans, although it is likely that many more remain to be identified, and we discuss how their developmental biology and interactions with diverse environments may be linked to different types of parthenogenetic reproduction. We discuss how the advances in genetics and genomics have identified chromosomal loci associated with parthenogenesis. In particular, a polygenic cause of facultative parthenogenesis has been uncovered in Drosophila mercatorum, allowing the corresponding genetic variants to be tested for their ability to promote parthenogenesis in another species, Drosophila melanogaster. This study probably identifies just one of many routes that could be followed in the evolution of parthenogenesis. We attempt to account for why the phenomenon has evolved so many times in the dipteran order and why facultative parthenogenesis appears particularly prevalent. We also discuss the significance of coarse genomic changes, including non-disjunction, aneuploidy, and polyploidy and how, together with changes to specific genes, these might relate to both facultative and obligate parthenogenesis in dipterans and other parthenogenetic animals.

Life cycle and phenology of an Antarctic invader: the flightless chironomid midge, Eretmoptera murphyi

Knowledge of the life cycles of non-native species in Antarctica is key to understanding their ability to establish and spread to new regions. Through laboratory studies and field observations on Signy Island (South Orkney Islands, maritime Antarctic), we detail the life stages and phenology of Eretmoptera murphyi (Schaeffer 1914), a brachypterous chironomid midge introduced to Signy in the 1960s from sub-Antarctic South Georgia where it is endemic. We confirm that the species is parthenogenetic and suggest that this enables E. murphyi to have an adult emergence period that extends across the entire maritime Antarctic summer season, unlike its sexually reproducing sister species Belgica antarctica which is itself endemic to the Antarctic Peninsula and South Shetland Islands. We report details of previously undescribed life stages, including verification of four larval instars, pupal development, egg gestation and development, reproductive viability and discuss potential environmental cues for transitioning between these developmental stages. Whilst reproductive success is limited to an extent by high mortality at eclosion, failure to oviposit and low egg-hatching rate, the population is still able to potentially double in size with every life cycle.

Mitochondrial DNA suggests a single maternal origin for the widespread triploid parthenogenetic pest species, Paratanytarsus grimmii, but microsatellite variation shows local endemism

Parthenogenesis is common among invasive pest species, with many parthenogenetic species also showing polyploidy. Parthenogenetic polyploid species often have multiple hybrid origins and the potential to rapidly spread over vast geographical areas. In this study, we examine patterns of mitochondrial and microsatellite variation in a widespread triploid parthenogenetic chironomid pest species, Paratanytarsus grimmii. Based on samples from five countries, including Australia, England, Germany, Japan, and Canada, we found extremely low mitochondrial diversity (<0.14%), with most individuals sharing a common and widespread haplotype. In contrast, microsatellite diversity revealed 41 clonal variants, which were regionally endemic. These findings suggest a single invasive maternal lineage of P. grimmii is likely to have recently spread over a broad geographical range. High levels of genotypic endemism suggest P. grimmii populations have remained relatively isolated after an initial spread, with little ongoing migration. This, in part, can be attributed to rapid genetic differentiation via mutations of common clonal genotypes after P. grimmii spread, but multiple polyploidization and subsequent founder events are also likely to be contributing factors.