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

Abstract

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.

Divergent selection along elevational gradients promotes genetic and phenotypic disparities among small mammal populations

“…This finding is consistent with that of previous studies on animals along elevational gradients at intraspecific (Caro et al, 2013;Eastman, Morelli, Rowe, Conroy, & Moritz, 2012;Liao, Zhang, & Liu, 2006;Wasserman & Nash, 1979) and interspecific (Du et al, 2017;Geraghty, Dunn, & Sanders, 2007;Hu, Xie, Li, & Jiang, 2011) levels. This finding is consistent with that of previous studies on animals along elevational gradients at intraspecific (Caro et al, 2013;Eastman, Morelli, Rowe, Conroy, & Moritz, 2012;Liao, Zhang, & Liu, 2006;Wasserman & Nash, 1979) and interspecific (Du et al, 2017;Geraghty, Dunn, & Sanders, 2007;Hu, Xie, Li, & Jiang, 2011) levels.…”

“…We can speculate that this morphogenetic divergence may be related to the pronounced ecological differences faced by populations at opposite ends of an elevational gradient (Caro et al, 2013;Kawecki & Ebert, 2004;Wang & Bradburd, 2014). We can speculate that this morphogenetic divergence may be related to the pronounced ecological differences faced by populations at opposite ends of an elevational gradient (Caro et al, 2013;Kawecki & Ebert, 2004;Wang & Bradburd, 2014).…”

Full Issue

“…Further experiments are necessary to test the degree to which interspecific aggression limits the distribution of Bicknell's Thrush, and whether the outcome of aggressive interactions between the 2 species is dependent on temperature. Nevertheless, our results are broadly consistent with the ''push'' hypothesis, and add to a growing body of evidence suggesting that biotic interactions may limit the distributions of montane birds (Jankowski et al 2010, Caro et al 2013, Freeman and Mason 2015 and therefore should be incorporated into models that predict species' responses to climate change.…”

Mountain colonisation, miniaturisation and ecological evolution in a radiation of direct-developing New Guinea Frogs (Choerophryne, Microhylidae)

“…4A). Detailed fine scale sampling is required to understand the processes that have shaped this endemism; elevational segregation may be an outcome rather than a driver of speciation (Caro et al, 2013; Freeman, 2015). However, regardless of the exact process, this represents the first strong evidence that endemic montane vertebrates have arisen de novo in northern New Guinea from largely lowland lineages.…”