Divergence in a transoceanic circumtropical dragonfly on a remote island

One terrestrial invertebrate that naturally spans the globe and travels vas t distances is the dragonfly Pantala flavescens (Fabricius) (Odonata: Libel lulidae). Recently, there has been a strong call to compare island with con tinental biota so as to meaningfully characterize island forms. This is don e here. The variation and differences in morphology and behaviour of an Afr ican continental (Pietermaritzburg, South Africa) and a remote island popul ation (Easter Island) of P. flavescens was investigated to determine whethe r the island population was panmictic with the migrant population, or wheth er it was a founder population. Several morphological characters were measu red in both populations, and analysed using PCA, t-tests, tests, coefficien ts of variation and Chi-square analyses. The continental and island populat ions were significantly different in body colour, head width and femur leng th. The island population had reduced hindwings, which were also more asymm etrical than the continental population, suggesting that the island individ uals were possibly more frenetically and environmentally stressed and had l ess genetic variation than the continental population. The island populatio n was also more robust and flew lower to the ground than the continental po pulation. There was no significant difference in body weight between the tw o populations because the migrant population had not begun to build up fat reserves for migration. Females were heavier than males in the continental population because they were carrying eggs. This was not the case in the is land population because the individuals were not as mature. Colour was sign ificantly different between the two populations, with island individuals ha ving darker wings and abdomens, yet a lighter synthorax colouring than the continental population. Sexual dimorphism was marked in the abdomen and win g colour of the continental population, yet the island individuals showed m ore difference between the sexes in morphological characters than in colour . The fact that P. flavescens is the only species of dragonfly on Easter Is land, and the great distance of the island from any mainland, suggests infr equent arrival of migrants arriving on the island, with resultant reduced g enetic variation. The morphological and behavioural differences between the two populations suggests divergence is occurring.