catharusNewick

catharusNewic

Catharus_SpTree_AllDataNew_200mil

All data, species tree, Figtree fil

Microsatellites

Genotypic data for eleven microsatellites; missing data coded as zero

Catharus-SpTree_AllDataNew-Constrained_200mil

all data, constrained species tree, Figtree fil

PointLocality

Site name and GPS coordinate (latitude, longitude) in decimal degree

The Ecological and Geographic Context of Morphological and Genetic Divergence in an Understorey-Dwelling Bird

<div><p>Advances in understanding the process of species formation require an integrated perspective that includes the evaluation of spatial, ecological and genetic components. One approach is to focus on multiple stages of divergence within the same species. Species that comprise phenotypically different populations segregated in apparently distinct habitats, in which range is presently continuous but was putatively geographically isolated provide an interesting system to study the mechanisms of population divergence. Here, we attempt to elucidate the role of ecology and geography in explaining observed morphological and genetic variation in an understorey-dwelling bird endemic to southeastern Africa, where two subspecies are recognized according to phenotype and habitat affinity. We carried out a range-wide analysis of climatic requirements, morphological and genetic variation across southeast Africa to test the hypothesis that the extent of gene flow among populations of the brown scrub-robin are influenced by their distinct climatic niches. We recovered two distinct trends depending on whether our analyses were hierarchically structured at the subspecies or at the within subspecies level. Between subspecies we found pronounced morphological differentiation associated with strong reproductive isolation (no gene flow) between populations occupying divergent climatic niches characterized by changes in the temperature of the warmest and wettest month. In contrast, within subspecies, we recovered continuous morphological variation with extensive gene flow among populations inhabiting the temperate and sub-tropical forests of southern Africa, despite divergence along the climate axis that is mainly determined by minimum temperature and precipitation of the coldest months. Our results highlight the role of niche divergence as a diversifying force that can promote reproductive isolation in vertebrates.</p></div

Geographical projection of the climatic niche model of <i>Cercotrichas signata</i> and the two subspecies: <i>C. s. signata</i> and <i>C. s. tongensis</i> including a region of predicted overlap.

<p>The arrow in panel ‘overlap’ emphasizes a geographical region of niche dissimilarity and coincides with the subspecies boundary (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085903#pone-0085903-g001" target="_blank">Figure 1</a>).</p

The effect of climate on morphological traits.

<p>PC1 illustrates precipitation differences between cooler and warmer sites, PC2 explains the tropical-temperate climatic gradient. The non-linear relationship between morphology and climate was modelled by including a quadratic term.</p><p>K: number of parameters in the model.</p

Population genetic descriptive statistics by subspecies. n: number of alleles; bp: base pairs; S: segregating sites; Hd: haplotype diversity; θ^#: theta per site; Kst: genetic divergence (*p<0.01, **p<0.001).

<p>Population genetic descriptive statistics by subspecies. n: number of alleles; bp: base pairs; S: segregating sites; Hd: haplotype diversity; θ^#: theta per site; Kst: genetic divergence (*p<0.01, **p<0.001).</p

Variation in climate (a), mass (b), size (residuals of wing-length on tarsus length) (c), pairwise nuclear K<i>st</i> (d) and, mtDNA haplotypes (e) along the temperate to tropical transect (latitude −36 to −24) sampled across the range of the brown scrub-robin. K<i>st</i> is a pairwise measure of divergence; therefore, it is represented as the midpoint between two adjacent sites.

<p>Geographical distances, in km, between the main forest blocks referred to in the text are annotated at the top. The side map depicts the geographical variation in mean temperature during winter (WinterTmean = Bio11: mean temperature of the coldest quarter; light grey represents lower temperatures and dark grey higher temperatures).</p