Rapid local adaptation: Can it explain the invasive success of the red-whiskered bulbul (Pycnonotus jocosus)?

Background/Question/Methods

The Red-whiskered bulbul is a very successful invasive bird, native from south Asia and often considered as an agricultural pest. In Reunion Island, a study conducted 20 years after the introduction of this species showed that several morphotypes of bulbul occur in contrasted environments. The authors concluded that the observed morphological diversity resulted from rapid local adaptation and explains the colonization success of this species. Here we investigate the hypothesis that the morphological diversity is a result of several introduction events from different sources. Our objectives were twofold, first to find the source of the introduced populations using a phylogeographic analysis, and second to compare morphologies between native and invasive populations in relation to their phylogenetic relationships. We studied Reunion and two other islands where the Red-whiskered bulbul has been introduced at different times and with similar environmental heterogeneity (Mauritius and Oahu, Hawaii). With this comparative approach, we were able to assess the likelihood of bulbuls rapidly adapting to local conditions. In our phylogeographic study, we used two mitochondrial coding gene fragments (COI, ND2) and anonymous nuclear loci obtained from microsatellite flanking regions. For the morphometric study, we used body measurements and landmarks taken on pictures of the bulbuls’ beak.

Results/Conclusions

Phylogeography: preliminary analyses show that the nine subspecies of Red-whiskered bulbul are divided in two groups, one for the Indian subspecies and the other with the subspecies from the Indochina peninsula. These results suggest that the subspecies previously described are not genetically supported. Interestingly, all the studied invasive populations fall in the Indian group, although their precise origin is not established yet. Morphometrics: in the native area, we identified three morphotypes corresponding to the geographic origin of the individuals (India, Northern and Southern Indochina peninsula). On Reunion Island, the morphs defined in the previous study were also identified. While we found a small morphological diversity on Mauritius where the bulbul has been introduced more than a hundred years ago, we did not detect any morphological structure on Oahu where the bulbuls have been introduced about 40 years ago, like on Reunion. Our results indicate that rapid local adaptation on Reunion is unlikely as the same range of environmental conditions is found on Oahu. An alternative hypothesis to explain this diversity is the existence of founding effects associated with different introduction events. A population genetics study on these data is in progress to investigate this hypothesis.