Coexistence of bisexual and unisexual populations of Nysius groenlandicus in the Zackenberg Valley,Northeast Greenland

The seed‐feeding true bug Nysius groenlandicus (Zetterstedt) (Heteroptera: Lygaeidae) has temperature and humidity preferences similar to many desert‐inhabiting insects. Nevertheless, it is widely distributed in Greenland and occurs even in high arctic areas. This seeming paradox implies that the species has developed physiological, ecological, and behavioral mechanisms that enable it to cope with the extreme arctic environment. One of these adaptations is its ability to reproduce both sexually and asexually. Sexual reproduction is most common in coastal populations, whereas asexual reproduction (parthenogenesis) occurs mainly in inland populations. Preliminary data from the Zackenberg Valley in Northeast Greenland indicated that both reproductive strategies occurred within the same area. We therefore decided to focus on this area to find evidence of (1) coexistence of unisexual and bisexual populations, (2) factors that correlate with the distribution of the two reproductive types, and (3) morphological differences between females from sexual and asexual populations. We sampled N. groenlandicus at 51 sites within the Zackenberg area. Males and females were found in almost equal numbers in only four of the samples, and only in samples taken close to the coast line, whereas samples from the inner part of the valley consisted almost entirely of females. Thus, the distribution of uni‐ and bisexual populations at the local scale agreed with the pattern previously found for Greenland as a whole. Using data obtained from two climate stations operated in the area, we showed that average summer temperatures tend to be more favorable for N. groenlandicus in the inner part of the valley than at the coast. The inland populations inhabited small isolated patches, whereas the sexual populations were found in the more homogeneous areas along the coast. Data support the hypothesis that coexistence of the two reproductive types is maintained by a combination of environmental variability, which gives sexual reproduction an advantage, and metapopulation dynamics characterized by frequent extinctions and re‐colonizations, which favors asexual reproduction. Head width of females from unisexual populations was on average 7% larger than that of females from bisexual populations. The mechanism behind this morphological difference needs further investigation.