Dataset Information

Divergence and isolation of cryptic sympatric taxa within the annual legume Amphicarpaea bracteata.

ABSTRACT: The amphicarpic annual legume Amphicarpaea bracteata is unusual in producing aerial and subterranean cleistogamous flowers that always self-fertilize and, less commonly, aerial chasmogamous flowers that outcross. Although both morphologic and genetic variants are known in this highly selfing species, debate continues over whether this variation is continuous, reflecting the segregation of standing genetic variation, or discontinuous, reflecting distinct taxa that rarely intercross. We characterized SNP variation in 128 individuals in southern Wisconsin to assess within- and among-population variation at 3928 SNPs. We also assessed genotype and leaf morphology in an additional 76 individuals to connect phenotypic variation with genetic variation. Genetic variation maps onto three strongly divergent and highly inbred genetic groups showing little relation to site location. Each group has a distinct phenotype, but the divergence of these groups differs from the varietal divisions previously identified based on morphological characters. Like previous authors, we argue that the taxonomy of this species should be revised. Despite extensive sympatry, estimates of among-group migration rates are low, and hybrid individuals were at low frequency (<2%) in our dataset. Restricted gene flow likely results from high selfing rates and partial reproductive incompatibility as evidenced by the U-shaped distribution of pairwise F ST values reflecting "islands" of genomic divergence. These islands may be associated with hybrid incompatibility loci that arose in allopatry. The coexistence of lineages within sites may reflect density-dependent attack by species-specific strains of pathogenic fungi and/or root-nodulating bacteria specializing on distinct genotypes.

SUBMITTER: Kartzinel RY

PROVIDER: S-EPMC4833626 | biostudies-literature | 2016 May

REPOSITORIES: biostudies-literature

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Divergence and isolation of cryptic sympatric taxa within the annual legume Amphicarpaea bracteata.

Kartzinel Rebecca Y RY Spalink Daniel D Waller Donald M DM Givnish Thomas J TJ

Ecology and evolution 20160412 10

The amphicarpic annual legume Amphicarpaea bracteata is unusual in producing aerial and subterranean cleistogamous flowers that always self-fertilize and, less commonly, aerial chasmogamous flowers that outcross. Although both morphologic and genetic variants are known in this highly selfing species, debate continues over whether this variation is continuous, reflecting the segregation of standing genetic variation, or discontinuous, reflecting distinct taxa that rarely intercross. We characteri ...[more]

PMID: 27103991

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Project description:Abstract A cryptic lineage is a genetically diverged but morphologically unrecognized variant of a known species. Clarifying cryptic lineage evolution is essential for quantifying species diversity. In sympatric cryptic lineage divergence compared with allopatric divergence, the forces of divergent selection and mating patterns override geographical isolation. Introgression, by supplying preadapted or neutral standing genetic variations, can promote sympatric cryptic lineage divergence via selection. However, most studies concentrated on extant species introgression, ignoring the genetic legacy of introgression from extinct or unsampled lineages (“ghost introgression”). Cycads are an ideal plant for studying the influence of ghost introgression because of their common interspecific gene flow and past high extinction rate. Here, we utilized reference‐based ddRADseq to clarify the role of ghost introgression in the evolution of a previously identified sympatric cryptic lineage in Cycas revoluta. After re‐evaluating the evolutionary independency of cryptic lineages, the group‐wise diverged single‐nucleotide polymorphisms among sympatric and allopatric lineages were compared and functionally annotated. Next, we employed an approximate Bayesian computation method for hypothesis testing to clarify the cryptic lineage evolution and ghost introgression effect. SNPs with the genomic signatures of ghost introgression were further annotated. Our results reconfirmed the evolutionary independency of cryptic lineage among C. revoluta and demonstrated that ghost introgression to the noncryptic lineage facilitated their divergence. Gene function related to heat stress and disease resistance implied ecological adaptation of the main extant populations of C. revoluta. Previous population genetics study revealed a sympatric cryptic lineage of Cycas revoluta in Taiwan. By detecting the SNP outliers and annotating its functions of lineages sympatric and allopatric to the cryptic lineage, plus approximate Bayesian computation model selection, this article provided a mechanism of the sympatric cryptic lineage divergence by ghost introgression.

Project description:BACKGROUND:The evolution of ecological divergence in closely related species is a key component of adaptive radiation. However, in most examples of adaptive radiation the mechanistic basis of ecological divergence remains unclear. A classic example is seen in the young benthic and limnetic stickleback species pairs of British Columbia. In each pair the benthic species feeds on littoral macroinvertebrates whereas the limnetic feeds on pelagic zooplankton. Previous studies indicate that in both short-term feeding trials and long-term enclosure studies, benthics and limnetics exhibit enhanced performance on their own resource but fare more poorly on the other species' resource. We examined the functional basis of ecological divergence in the stickleback species pair from Paxton Lake, BC, using biomechanical models of fish feeding applied to morphological traits. We examined the consequences of morphological differences using high speed video of feeding fish. RESULTS:Benthic stickleback possess morphological traits that predict high suction generation capacity, including greatly hypertrophied epaxial musculature. In contrast, limnetic stickleback possess traits thought to enhance capture of evasive planktonic prey, including greater jaw protrusion than benthics and greater displacement advantage in both the lower jaw-opening lever system and the opercular four-bar linkage. Kinematic data support the expectations from the morphological analysis that limnetic stickleback exhibit faster strikes and greater jaw protrusion than benthic fish, whereas benthics exert greater suction force on attached prey. CONCLUSIONS:We reveal a previously unknown suite of complex morphological traits that affect rapid ecological divergence in sympatric stickleback. These results indicate that postglacial divergence in stickleback involves many functional systems and shows the value of investigating the functional consequences of phenotypic divergence in adaptive radiation.

Dataset Information

Divergence and isolation of cryptic sympatric taxa within the annual legume Amphicarpaea bracteata.

Publications

Divergence and isolation of cryptic sympatric taxa within the annual legume Amphicarpaea bracteata.

Similar Datasets

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