Recent divergence in the Orchard Oriole complex: using molecular genetics and vocalizations to examine species boundaries

Understanding species boundaries and the process of speciation is a fundamental part of understanding the biodiversity of the world around us. Studies of recently diverged/diverging species can be used to examine species boundaries to better understand the nature of species/speciation. Orchard Oriole (Icterus spurius) and Fuertes' Oriole (I. fuertesi) are sister taxa with different breeding grounds and different adult plumage coloration, yet their mtDNA are intermixed, indicating a possible recent divergence event. I compared the molecular genetics (mtDNA and nuDNA) of both taxa and found that I. spurius and I. fuertesi are in the earliest stages of speciation - at a point where most neutral markers within their nuclear DNA do not yet reflect their divergence. As birdsong has the capability of diverging rapidly as two taxa speciate, I looked for evidence of divergence in the songs and jeet alarm calls of the two taxa. My analyses failed to find fixed song differences, yet the jeet calls show differentiation in a number of acoustic characteristics, such as in call duration and number of parts of the call. These differences may reflect ecological adaptation or divergence due to stochastic processes acting independently in these two taxa - indicating a degree of divergence between them. To test whether adult males were able to cue into subtle song variations that were not captured by the quantitative analyses, I conducted playback experiments on male I. spurius in Maryland - exposing focal males to homotypic songs (I. spurius), I. fuertesi songs and the songs of a negative control (I. galbula). Focal males in these experiments reacted to both conspecific and I. fuertesi songs - indicating they are identifying I. fuertesi as a potential sexual competitor. Thus, songs have not yet diverged enough that males no longer identify the other taxon's songs as potential sexual competition. However, there is some evidence that males respond more weakly to I. fuertesi songs. Regardless, song is likely not acting as a strong barrier to gene flow between these taxa. This study indicates that these two taxa are likely in the earliest stages of speciation, making them a model system to understand the process of speciation