More Like this

1. Gene Flow Increases Phylogenetic Structure and Inflates Cryptic Species Estimations: A Case Study on Widespread Philippine Puddle Frogs ( Occidozyga laevis )

   https://doi.org/10.1093/sysbio/syab034  

   Chan, Kin Onn ; Hutter, Carl R ; Wood, Perry L ; Su, Yong-Chao ; Brown, Rafe M ( May 2021 , Systematic Biology)

   Burbrink, Frank (Ed.)

   Abstract In cryptic amphibian complexes, there is a growing trend to equate high levels of genetic structure with hidden cryptic species diversity. Typically, phylogenetic structure and distance-based approaches are used to demonstrate the distinctness of clades and justify the recognition of new cryptic species. However, this approach does not account for gene flow, spatial, and environmental processes that can obfuscate phylogenetic inference and bias species delimitation. As a case study, we sequenced genome-wide exons and introns to evince the processes that underlie the diversification of Philippine Puddle Frogs—a group that is widespread, phenotypically conserved, and exhibits high levels of geographically based genetic structure. We showed that widely adopted tree- and distance-based approaches inferred up to 20 species, compared to genomic analyses that inferred an optimal number of five distinct genetic groups. Using a suite of clustering, admixture, and phylogenetic network analyses, we demonstrate extensive admixture among the five groups and elucidate two specific ways in which gene flow can cause overestimations of species diversity: 1) admixed populations can be inferred as distinct lineages characterized by long branches in phylograms; and 2) admixed lineages can appear to be genetically divergent, even from their parental populations when simple measures of genetic distance are used. We demonstrate that the relationship between mitochondrial and genome-wide nuclear $p$-distances is decoupled in admixed clades, leading to erroneous estimates of genetic distances and, consequently, species diversity. Additionally, genetic distance was also biased by spatial and environmental processes. Overall, we showed that high levels of genetic diversity in Philippine Puddle Frogs predominantly comprise metapopulation lineages that arose through complex patterns of admixture, isolation-by-distance, and isolation-by-environment as opposed to species divergence. Our findings suggest that speciation may not be the major process underlying the high levels of hidden diversity observed in many taxonomic groups and that widely adopted tree- and distance-based methods overestimate species diversity in the presence of gene flow. [Cryptic species; gene flow; introgression; isolation-by-distance; isolation-by-environment; phylogenetic network; species delimitation.] 

   more » « less
2. Gene Flow Increases Phylogenetic Structure and Inflates Cryptic Species Estimations: A Case Study on Widespread Philippine Puddle Frogs (Occidozyga laevis)

   KIN ONN CHAN, CARL R. ( January 2021 , Systematic biology)

   null (Ed.)

   In cryptic amphibian complexes, there is a growing trend to equate high levels of genetic structure with hidden cryptic species diversity. Typically, phylogenetic structure and distance-based approaches are used to demonstrate the distinctness of clades and justify the recognition of new cryptic species. However, this approach does not account for gene flow, spatial, and environmental processes that can obfuscate phylogenetic inference and bias species delimitation. As a case study, we sequenced genome-wide exons and introns to evince the processes that underlie the diversification of Philippine Puddle Frogs—a group that is widespread, phenotypically conserved, and exhibits high levels of geographically based genetic structure. We showed that widely adopted tree- and distance-based approaches inferred up to 20 species, compared to genomic analyses that inferred an optimal number of five distinct genetic groups. Using a suite of clustering, admixture, and phylogenetic network analyses, we demonstrate extensive admixture among the five groups and elucidate two specificways in which gene flowcan cause overestimations of species diversity: 1) admixed populations can be inferred as distinct lineages characterized by long branches in phylograms; and 2) admixed lineages can appear to be genetically divergent, even from their parental populations when simple measures of genetic distance are used. We demonstrate that the relationship between mitochondrial and genome-wide nuclear p-distances is decoupled in admixed clades, leading to erroneous estimates of genetic distances and, consequently, species diversity. Additionally, genetic distance was also biased by spatial and environmental processes. Overall, we showed that high levels of genetic diversity in Philippine Puddle Frogs predominantly comprise metapopulation lineages that arose through complex patterns of admixture, isolation-bydistance, and isolation-by-environment as opposed to species divergence. Our findings suggest that speciation may not be the major process underlying the high levels of hidden diversity observed in many taxonomic groups and that widely adopted tree- and distance-based methods overestimate species diversity in the presence of gene flow. 

   more » « less
3. Gene Flow Increases Phylogenetic Structure and Inflates Cryptic Species Estimations: A Case Study on Widespread Philippine Puddle Frogs (Occidozyga laevis)

   KIN ONN CHAN, CARL R. ( January 2021 , Systematic biology)

   null (Ed.)

   In cryptic amphibian complexes, there is a growing trend to equate high levels of genetic structure with hidden cryptic species diversity. Typically, phylogenetic structure and distance-based approaches are used to demonstrate the distinctness of clades and justify the recognition of new cryptic species. However, this approach does not account for gene flow, spatial, and environmental processes that can obfuscate phylogenetic inference and bias species delimitation. As a case study, we sequenced genome-wide exons and introns to evince the processes that underlie the diversification of Philippine Puddle Frogs—a group that is widespread, phenotypically conserved, and exhibits high levels of geographically based genetic structure. We showed that widely adopted tree- and distance-based approaches inferred up to 20 species, compared to genomic analyses that inferred an optimal number of five distinct genetic groups. Using a suite of clustering, admixture, and phylogenetic network analyses, we demonstrate extensive admixture among the five groups and elucidate two specificways in which gene flowcan cause overestimations of species diversity: 1) admixed populations can be inferred as distinct lineages characterized by long branches in phylograms; and 2) admixed lineages can appear to be genetically divergent, even from their parental populations when simple measures of genetic distance are used. We demonstrate that the relationship between mitochondrial and genome-wide nuclear p-distances is decoupled in admixed clades, leading to erroneous estimates of genetic distances and, consequently, species diversity. Additionally, genetic distance was also biased by spatial and environmental processes. Overall, we showed that high levels of genetic diversity in Philippine Puddle Frogs predominantly comprise metapopulation lineages that arose through complex patterns of admixture, isolation-bydistance, and isolation-by-environment as opposed to species divergence. Our findings suggest that speciation may not be the major process underlying the high levels of hidden diversity observed in many taxonomic groups and that widely adopted tree- and distance-based methods overestimate species diversity in the presence of gene flow. 

   more » « less
4. Counting the genetic ancestors from source populations in members of an admixed population

   https://doi.org/10.1093/genetics/iyae011  

   Agranat-Tamir, Lily ; Mooney, Jazlyn_A ; Rosenberg, Noah_A ; Novembre, ed., J. ( January 2024 , GENETICS)

   In a genetically admixed population, admixed individuals possess genealogical and genetic ancestry from multiple source groups. Under a mechanistic model of admixture, we study the number of distinct ancestors from the source populations that the admixture represents. Combining a mechanistic admixture model with a recombination model that describes the probability that a genealogical ancestor is a genetic ancestor, for a member of a genetically admixed population, we count genetic ancestors from the source populations—those genealogical ancestors from the source populations who contribute to the genome of the modern admixed individual. We compare patterns in the numbers of genealogical and genetic ancestors across the generations. To illustrate the enumeration of genetic ancestors from source populations in an admixed group, we apply the model to the African-American population, extending recent results on the numbers of African and European genealogical ancestors that contribute to the pedigree of an African-American chosen at random, so that we also evaluate the numbers of African and European genetic ancestors who contribute to random African-American genomes. The model suggests that the autosomal genome of a random African-American born in the interval 1960–1965 contains genetic contributions from a mean of 162 African (standard deviation 47, interquartile range 127–192) and 32 European ancestors (standard deviation 14, interquartile range 21–43). The enumeration of genetic ancestors can potentially be performed in other diploid species in which admixture and recombination models can be specified.

    

   more » « less
5. Genomics reveal the origins and current structure of a genetically depauperate freshwater species in its introduced Alaskan range

   https://doi.org/10.1111/eva.13556  

   Campbell, Matthew A. ; Hale, Matthew C. ; Jalbert, Chase S. ; Dunker, Kristine ; Sepulveda, Adam J. ; López, J. Andrés ; Falke, Jeffrey A. ; Westley, Peter A. H. ( May 2023 , Evolutionary Applications)

   Invasive species are a major threat to global biodiversity, yet also represent large‐scale unplanned ecological and evolutionary experiments to address fundamental questions in nature. Here we analyzed both native and invasive populations of predatory northern pike (Esox lucius) to characterize landscape genetic variation, determine the most likely origins of introduced populations, and investigate a presumably postglacial population from Southeast Alaska of unclear provenance. Using a set of 4329 SNPs from 351 individual Alaskan northern pike representing the most widespread geographic sampling to date, our results confirm low levels of genetic diversity in native populations (average 𝝅 of 3.18 × 10⁻⁴) and even less in invasive populations (average 𝝅 of 2.68 × 10⁻⁴) consistent with bottleneck effects. Our analyses indicate that invasive northern pike likely came from multiple introductions from different native Alaskan populations and subsequently dispersed from original introduction sites. At the broadest scale, invasive populations appear to have been founded from two distinct regions of Alaska, indicative of two independent introduction events. Genetic admixture resulting from introductions from multiple source populations may have mitigated the negative effects associated with genetic bottlenecks in this species with naturally low levels of genetic diversity. Genomic signatures strongly suggest an excess of rare, population‐specific alleles, pointing to a small number of founding individuals in both native and introduced populations consistent with a species' life history of limited dispersal and gene flow. Lastly, the results strongly suggest that a small isolated population of pike, located in Southeast Alaska, is native in origin rather than stemming from a contemporary introduction event. Although theory predicts that lack of genetic variation may limit colonization success of novel environments, we detected no evidence that a lack of standing variation limited the success of this genetically depauperate apex predator.

    

   more » « less