Does wing size shape insect biogeography? Evidence from a diverse regional stonefly assemblage

Aim Dispersal ability has traditionally been seen as a key influence on species distributions, but recent biogeographical analyses have cast doubt on the strength of this association. Here we present biogeographical evidence from New Zealand's entire plecopteran fauna (100 species) to test for associations between flight ability and species range, and to determine the extent of wing reduction that is required to influence biogeographical patterns. Location The main islands of New Zealand, representing a land area of 270,000 km(2). These islands host a diverse assemblage of endemic stoneflies, including a substantial number of wing-reduced taxa. Methods We analyse biogeographical data, encompassing over 7000 species/locality records, across all 100 stonefly taxa recorded from New Zealand's mainland. Distributional data are analysed together with morphological data, in a phylogenetic framework, to test the hypothesis that wing length (dispersal ability) has a significant association with range size. Results Our analyses indicate a strong relationship between species wing length and area of occupancy, unconfounded by phylogenetic relationships. A significant positive correlation was also observed between geographical range and relative wing length in both sexes, with consistent patterns observed in distinct families. When the analysis was confined only to macropterous species the relationship between wing length and area of occupancy remained significant. Main conclusions This study shows that rapid switches in dispersal ability are linked to dramatic biogeographical contrasts. While complete wing loss is associated with major range reduction, it is also clear that even small reductions in wing size can significantly influence biogeographical patterns. Broadly, the analysis demonstrates that by focusing on a major regional assemblage of ecologically, and phylogenetically, similar taxa, it is possible to show that even subtle morphological shifts can be correlated with substantial biogeographical change.