Stolid Flycatcher

Frontiers of Taxonomy: Divergence and Convergence in the Stolid-La-Sagra’s Flycatcher Complex.

The taxonomic status and relationships of the four subspecies currently grouped under Stolid and La Sagra’s Flycatchers present a conundrum.  When Lanyon analyzed their measurements, coloration, vocalizations, response to tape playback, he found that the Jamaican stolidus and Hispaniolan dominicensis were nearly identical, and that the Cuban sagrae and Bahamian lucaysiensis were only slightly more distinguishable from one another.  This was the original basis for recognizing La Sagra’s Flycatcher as a separate species.

However, Joseph et al.’s 2004 study of mitochondrial DNA reached a potentially conflicting result.  In essence, they found that the Jamaican stolidus (Stolid) and Cuban sagrae (La Sagra’s) are more closely related to one another by ancestry than either is to dominicensis or lucaysiensis.  Conversely, they found that the Hispaniolan dominicensis (Stolid) and Bahamian lucaysiensis (La Sagra’s) are also one another’s closest ancestral relatives.

Assuming that the genetic evidence is accurate (i.e., not somehow a fluke of the individuals sampled or the analytical methods used), this situation seems to suggest some form of coevolution.  In simplified terms, it suggests that a split occurred between two lineages (representing sagrae/stolidus and lucaysiensis/dominicensis), and that later each of these lineages diverged internally, but somehow each of the resulting four lineages “converged” with a less-related lineage—assembling the current Stolid and La Sagra’s Flycatcher species.

Although this hypothesis may seem peculiar, there may be a biogeographical mechanism that would enable it.  Lucaysiensis is found on smaller islands than the others, and is prone to wandering (e.g., regularly straying to southern Florida), while the other three subspecies appear to be mostly sedentary.  Perhaps, then, regular strays of lucaysiensis into the range of sagrae resulted in new gene flow between these forms, introducing traits of lucaysiensis into sagrae.  This would allow these subspecies to share features, rapidly spread through sexual selection, while the underlying drift in mitochrondrial DNA in the respective populations proceeded on its gradual, inexorable pace.

The argument for continuing to recognize Stolid and La Sagra’s Flycatchers as currently configured is that, as far as has been documented, stolidus and dominicensis are essentially indistinguishable in the field, as are sagrae and lucaysiensis.  Functionally, these appear to be the two species definitions that the birds themselves would likely recognize, so the current taxonomic consensus makes sense, even if it contradicts the underlying phylogenetic relationships.