Genomic divergence in a ring species complex

  title={Genomic divergence in a ring species complex},
  author={Miguel Alcaide and Elizabeth S C Scordato and Trevor D. Price and Darren E. Irwin},
Ring species provide particularly clear demonstrations of how one species can gradually evolve into two, but are rare in nature. In the greenish warbler (Phylloscopus trochiloides) species complex, a ring of populations wraps around Tibet. Two reproductively isolated forms co-exist in central Siberia, with a gradient of genetic and phenotypic characteristics through the southern chain of populations connecting them. Previous genetic evidence has proven inconclusive, however, regarding whether… 

Ring Species and Speciation

The study of species with ring distributions has provided information about the processes that cause population divergence through time, and the use of new genomics and modelling tools could provide valuable insights into how geographic speciation, with or without adaptive divergence, could occur.

Population genomics of an emergent tri-species hybrid zone

Field observations and genomic analysis are used to study an emergent hybrid zone involving two colliding hybrid zones of three woodpecker species, and selection against hybrids is invoked as a likely mechanism maintaining species boundaries.

Ongoing production of low-fitness hybrids limits range overlap between divergent cryptic species

Examination of genomic variation shows evidence for only a single backcrossing event in the distant past of the Pacific Wren and Winter Wren, and a sizeable rate of hybridization combined with very low fitness of F1 hybrids is expected to result in a population sink in the contact zone.

Ongoing production of low‐fitness hybrids limits range overlap between divergent cryptic species

Examination of genomic variation shows evidence for only a single backcrossing event many generations ago in Pacific wren and winter wren, and the moderate rate of hybridization combined with very low F1 hybrid fitness is expected to result in a population sink in the contact zone, largely explaining the narrow overlap of the two species.

Digest: Why are there no ring species? *

    N. Vijay
    Evolution; international journal of organic evolution
  • 2017
In this issue, Martins and de Aguiar (2016) simulate the evolution of ring species and evaluate the importance of exogenous versus endogenous barriers, compare different spatial distributions, and highlight the conditions that will favor the emergence of ringspecies.

Genomic variation across the Yellow-rumped Warbler species complex

It is shown that genomic variation is highly heterogeneous between some taxa and that these regions of high differentiation are relatively small compared to those in other study systems, and it is found that the clusters of highly differentiated markers between taxa occur in gene-rich regions of the genome and exhibit low within-population diversity.

A tree of tree frogs around the Black Sea

Genetic variation and ecological niche modelling are used to show that a ring of populations of the eastern tree frog surrounding the Black Sea had a complex history of geographic differentiation, reminiscent of those found in ring species.

The evolutionary ecology of a species ring: a test of alternative models

Song sparrows do fit some aspects of a classic ring species that formed via expansion around a barrier; however, admixture rather than complete reproductive isolation occurred when populations met at the terminus of the ring in southern California.

Ring distribution patterns—diversification or speciation? Comparative phylogeography of two small mammals in the mountains surrounding the Sichuan Basin

This study reveals a case of two sympatric small mammals following a ring‐shaped diversification pattern, and provides insight into the process of differentiation, under the barrier effect of the Sichuan Basin.

Barriers to gene flow and ring species formation

This model simulates the evolution of ring species assuming that individuals become sexually isolated if the genetic distance between them is above a certain threshold, and incorporates two forms of dispersal limitation: exogenous geographic barriers that limit the population range and endogenous barriers that result in genetic structuring within the populationrange.

Ring species as bridges between microevolution and speciation.

Analysis of proposed cases of ring species suggests that differences could have arisen even with gene flow, and that parallel rather than divergent ecological changes have led to divergence in sexually selected traits and subsequent speciation.

Speciation in a ring

This work reconstructs the pathway to speciation between two reproductively isolated forms of greenish warbler and shows how gradual divergence in a trait involved in mate choice leads to theformation of new species.

Speciation by Distance in a Ring Species

These findings provide the strongest evidence yet for “speciation by force of distance” in the face of ongoing gene flow in greenish warblers.

Evolution and stability of ring species

Simulating the expansion of a population around a barrier to form a ring species, in which the two ends of the population are reproductively isolated despite ongoing gene flow around the ring, implies that simulations can be used to accurately describe empirical data for complex spatial–genetic traits of an individual species.

The Caribbean slipper spurge Euphorbia tithymaloides: the first example of a ring species in plants

    N. I. CachoD. Baum
    Environmental Science
    Proceedings of the Royal Society B: Biological Sciences
  • 2012
These data show that Euphorbia tithymaloides is the first compelling example of a ring species in plants, and that the species complex originated in the area where Mexico and Guatemala meet, and expanded around the Caribbean basin along two distinct fronts.


Division of this complex into separate species on the basis of the observed patterns of monophyly for mitochondrial DNA is unwarranted because further sampling could reveal additional instances of paraphyly across subspecies and, more generally, because mtDNA alone should not be used to infer species boundaries.

Limits to Speciation Inferred from Times to Secondary Sympatry and Ages of Hybridizing Species along a Latitudinal Gradient

It is estimated that secondary sympatry takes on the order of millions of years following population splitting and hence could impose an important limit on the rate of range expansion, thereby limiting further rounds of species formation.

Call divergence is correlated with geographic and genetic distance in greenish warblers (Phylloscopus trochiloides): a strong role for stochasticity in signal evolution?

The results support the importance of stochastic evolution of communication systems in the evolution of new species, particularly within a geographically variable species complex, the greenish warblers.

Local Adaptation along Smooth Ecological Gradients Causes Phylogeographic Breaks and Phenotypic Clustering

    D. Irwin
    The American Naturalist
  • 2012
Simulations show that relatively weak selection for local adaptation can lead to strong phylogeographic structure, in which highly divergent genealogical groups are geographically localized and differentially adapted, and dramatically increased standing variation compared to neutral expectations.

Geographic variation, speciation, and clines.

    J. Endler
    Monographs in population biology
  • 1977
Professor Endler shows how geographic differentiation and speciation may develop in spite of continuous gene flow, and considers the interpretation of natural clines and the associated geographic patterns of subspecies and species.