Are environmental factors responsible for geographic variation in the sex ratio of the Greenlandic seed‐bugNysius groenlandicus?

Abstract

Until recently nothing indicated an unequal sex ratio in the widespread Greenland seed‐bug Nysius groenlandicus (Zetterstedt) (Heteroptera: Lygaeidae). However, recently populations more or less devoid of males were discovered in high arctic Northeast Greenland. This initiated an inspection of the entire material of the species collected in Greenland and now preserved at the Zoological Museum, University of Copenhagen. It was found that the sex ratio varied significantly among different locations. In most cases females were most abundant, but males were either scarce or absent only in samples from Northeast Greenland, indicating that here the species reproduces asexually. This paper demonstrates that the differing sex distributions can be explained by climatic factors (temperature, precipitation) and that the degree of continentality (distance from the open sea) promotes female‐biased sex ratios.

Interglacial insects and their possible survival inGreenland during the last glacial stage

“…The recent findings of parthenogenetic populations in NE Greenland also point in this direction (Böcher & Nachman , ). A prerequisite is the existence during the last glacial stage of areas without snow in summer, with vegetation ( N. groenlandicus is a polyphagous seed‐eater; Böcher ) and with a high incidence of sunshine, so that microclimatic conditions would provide this highly thermophilic and xerophilic species with sufficient day‐degrees to fulfil their needs (obligate monocyclism with overwintering eggs and nymphal development during one summer; Böcher , ; Böcher & Nachman , , ). If N. groenlandicus could – as it appears – live in Greenland during the entire last glacial stage, many other invertebrates and plants certainly would also be able to.…”

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“…Even in the cold climate of northern Greenland this species retains the capacity for flight even though they can fly only at temperatures of 30 o C and then for distances of only about 1 m. However, they do show a habit of laying eggs on seeds and fruits adapted to wind dispersal (Böcher & Nachman 2010). The sex ratio of Greenland populations varies in ways related to temperature and precipitation and some populations in the most continental environments are parthenogenetic (Böcher & Nachman 2010. Collection: We have not collected North American specimens, but one would suspect they occur in protected, sun-warmed sites at the side of plant tussocks and hummocks on well drained soils.…”

The evolutionary ecology of the Lygaeidae

“…This is supported by the finding that differing sex ratios can be explained by climatic factors, with the female bias increasing with distance from the coast. As inland climatic conditions are more predictable than those along the coast it would seem that asexual reproduction provides a benefit in relatively stable environments while sexual reproduction remains the preferred mode of reproduction in the more changeable coastal regions (Bocher and Nachman ). However, it is also possible that these asexual populations are the result of a male‐killing parasite, like those described earlier, rather than an adaptation.…”