Ecological speciation along an elevational gradient in a tropical passerine bird?

Local adaptation of populations along elevational gradients is well known, but conclusive evidence that such divergence has resulted in the origin of distinct species in parapatry remains lacking. We integrated morphological, vocal, genetic and behavioural data to test predictions pertaining to the hypothesis of parapatric ecological speciation associated with elevation in populations of a tropical montane songbird, the Grey-breasted Wood-wren (Henicorhina leucophrys: Troglodytidae), from the Sierra Nevada de Santa Marta, Colombia. We confirmed that two distinct populations exist along the elevational gradient. Phylogenetic analyses tentatively indicate that the two populations are not sister taxa, suggesting they did not differentiate from a single ancestor along the gradient, but rather resulted from separate colonization events. The populations showed marked divergence in morphometrics, vocalizations and genetic variation in mitochondrial and nuclear loci, and little to no evidence of hybridization. Individuals of both populations responded more strongly to their own local songs than to songs from another elevation. Although the two forms do not appear to have differentiated locally in parapatry, morphological and vocal divergence along the elevational gradient is consistent with adaptation, suggesting a possible link between adaptive evolution in morphology and songs and the origin of reproductive isolation via a behavioural barrier to gene flow. The adaptive value of phenotypic differences between populations requires additional study.

Caro LM ，Caycedo-Rosales PC ，Bowie RC ，Slabbekoorn H ，Cadena CD ... -  《-》

Habitat-dependent song divergence at subspecies level in the grey-breasted wood-wren.

Dingle C ，Halfwerk W ，Slabbekoorn H 《-》

Asymmetric response patterns to subspecies-specific song differences in allopatry and parapatry in the gray-breasted wood-wren.

Song divergence between closely related taxa may play a critical role in the evolutionary processes of speciation and hybridization. We explored song variation between two Ecuadorian subspecies of the gray-breasted wood-wren (Henicorhina leucophrys) and tested the impact of song divergence on response behaviors. Songs were significantly different between the two subspecies, even between two parapatric populations 10 km apart. Playback experiments revealed an asymmetric response pattern to these divergent subspecies specific songs; one subspecies responded more to songs of its own subspecies than to the other subspecies' songs, whereas the second responded equally strongly to songs of both subspecies. While song parameters revealed a mixed pattern of divergence between allopatric and parapatric populations, the majority of spectral characteristics showed increased divergence in parapatry, suggestive of character displacement. This increased song divergence in parapatry appeared to affect behavioral responses to playback as discriminating responses were most prominent in parapatry and against parapatric songs. The clear behavioral impact of subspecies-specific song differences supports a potential role for song as an acoustic barrier to gene flow. The asymmetric nature of the responses suggests that song divergence could affect the direction of gene flow and the position of the subspecies-specific transition.

Dingle C ，Poelstra JW ，Halfwerk W ，Brinkhuizen DM ，Slabbekoorn H ... -  《-》

Ecological adaptation and species recognition drives vocal evolution in neotropical suboscine birds.

Seddon N 《EVOLUTION》

Testing alternative mechanisms of evolutionary divergence in an African rain forest passerine bird.

Smith TB ，Calsbeek R ，Wayne RK ，Holder KH ，Pires D ，Bardeleben C ... -  《JOURNAL OF EVOLUTIONARY BIOLOGY》