Around 1930 northern cardinals (Cardinalis cardinalis) were introduced to three islands within the Hawaiian archipelago (Hawaii Island, Oahu, and Kauai), where they have since established and spread throughout the archipelago. Interestingly, during the short time since the cardinal’s introduction we have witnessed divergent morphologies in several key avian features (e.g. tail length and wing chord) among the three initially introduced island populations. We know from historical records that approximately 300 were transported from San Francisco by boat, but during this time there were no cardinals in the San Francisco area and the record does not indicate from where and how these cardinals were acquired. The range for northern cardinals consists of the northeast United States to the southeast, and extends as far west as New Mexico and south into the Yucatan peninsula. Previous work has shown this range contains six genetically distinct mitochondrial DNA (mDNA) clades, but we do not know which or how many of these were the source of the introduction and how founders were disseminated across the three islands. Here we use a combination of morphological and molecular techniques to explore the role their invasion history into the Hawaiian archipelago may have had on this morphological divergence.
Results/Conclusions
In our results we update the morphological analyses previously conducted to assess the divergence among the three initially introduced islands, as well as adding a population that cardinals colonized on their own (Maui). We show that morphological metrics do indeed diverge among all islands, and using principal component analysis (PCA) and multivariate analysis of variance (MANOVA) show that Hawaiian populations have diverged significantly from native sources and appear to be shifting toward more insular morphology. Our phylogeographic analysis indicated the native source clade was the eastern (and largest) clade, but did not provide any specific detail on where exactly the native source was. The Approximate Bayesian Computation (ABC) analysis allowed us elucidate the source of this clade by dividing it into two regions (west and east), and indicated the most likely source was the eastern region. Additionally, using ABC we found the most likely introduction scenario of the cardinals into the archipelago, as well as the most likely island to colonize the Maui population. Overall our results indicate that the introduction history of the northern cardinal did not play a significant role in the divergence we see presently, indicating there are external factors likely driving the result we see.