Natural selection maintains species despite frequent hybridization in the desert shrub Encelia

Natural selection is an important driver of genetic and phenotypic differentiation between species. For species in which potential gene flow is high but realized gene flow is low, adaptation via natural selection may be a particularly important force maintaining species. For a recent radiation of New World desert shrubs (Encelia: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions. After finding evidence for extremely strong selection at both hybrid zones, we use a combination of field experiments, high-resolution imaging, and physiological measurements to determine the ecological basis for selection at one of the hybrid zones. Our results identify multiple ecological mechanisms of selection (drought, salinity, herbivory, and burial) that together are sufficient to maintain species boundaries despite high rates of hybridization. Given that multiple pairs of Encelia species hybridize at ecologically divergent parapatric boundaries, such mechanisms may maintain species boundaries throughout Encelia.

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Natural selection maintains species despite widespread hybridization in the desert shrub Encelia

10.1101/2020.01.23.917021 ◽

2020 ◽

Cited By ~ 1

Author(s):

Christopher D DiVittorio ◽

Sonal Singhal ◽

Adam B Roddy ◽

Felipe Zapata ◽

David D Ackerly ◽

...

Keyword(s):

Gene Flow ◽

Natural Selection ◽

Field Experiments ◽

Population Genomics ◽

Coastal Dunes ◽

Species Boundaries ◽

Hybrid Zones ◽

Desert Shrubs ◽

Species Complexes ◽

Species Pairs

ABSTRACTNatural selection is an important driver of genetic and phenotypic differentiation between species. A powerful way to test the role of natural selection in the formation and maintenance of species is to study species complexes in which potential gene flow is high but realized gene flow is low. For a recent radiation of New World desert shrubs (Encelia: Asteraceae), we use fine-scale geographic sampling and population genomics to determine patterns of gene flow across two hybrid zones formed between two independent pairs of species with parapatric distributions. After finding evidence for extremely strong selection at both hybrid zones, we use a combination of field experiments, high-resolution imaging, and physiological measurements to determine the ecological basis for selection at one of the hybrid zones. Our results identify multiple ecological mechanisms of selection (drought, salinity, herbivory, and burial) that together are sufficient to maintain species boundaries despite high rates of hybridization. Given that multiple pairs of species hybridize at ecologically divergent parapatric boundaries in the adaptive radiation of Encelia, such mechanisms may maintain species boundaries throughout this group.SIGNIFICANCE STATEMENTIn Baja California, the deserts meet the coastal dunes in a narrow transition visible even from satellite images. We study two species pairs of desert shrubs (Encelia) that occur across this transition. Although these species can interbreed, they remain distinct. Using a combination of genetics, field experiments, 3D-imaging, and physiological measurements, we show that natural selection counteracts the homogenizing effects of gene exchange. The different habitats of these species create multiple mechanisms of selection - drought, salinity, herbivory, and burial, which together maintain these species in their native habitats and their hybrids in intermediate habitats. This study illustrates how environmental factors influence traits and fitness and how this in turn maintain species, highlighting the importance of natural selection in speciation.

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Species delimitation with gene flow: A methodological comparison and population genomics approach to elucidate cryptic species boundaries in Malaysian Torrent Frogs

Molecular Ecology ◽

10.1111/mec.14296 ◽

2017 ◽

Vol 26 (20) ◽

pp. 5435-5450 ◽

Cited By ~ 22

Author(s):

Kin Onn Chan ◽

Alana M. Alexander ◽

L. Lee Grismer ◽

Yong-Chao Su ◽

Jesse L. Grismer ◽

...

Keyword(s):

Gene Flow ◽

Cryptic Species ◽

Species Delimitation ◽

Population Genomics ◽

Species Boundaries ◽

Methodological Comparison

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The future of research with carnivorous plants

10.1093/oso/9780198779841.003.0029 ◽

2018 ◽

Author(s):

Aaron M. Ellison ◽

Lubomír Adamec

Keyword(s):

Natural Selection ◽

Population Biology ◽

Field Experiments ◽

Evolutionary Dynamics ◽

Species Concept ◽

Intraspecific Variability ◽

Carnivorous Plants ◽

Assisted Migration ◽

Transcriptomic Data ◽

Phylogenetic Framework

The material presented in the chapters of Carnivorous Plants: Physiology, Ecology, and Evolution together provide a suite of common themes that could provide a framework for increasing progress in understanding carnivorous plants. All speciose genera would benefit from more robust, intra-generic classifications in a phylogenetic framework that uses a unified species concept. As more genomic, proteomic, and transcriptomic data accrue, new insights will emerge regarding trap biochemistry and regulation; interactions with commensals; and the importance of intraspecific variability on which natural selection works. Continued elaboration of field experiments will provide new insights into basic physiology; population biology; plant-animal and plant-microbe relationships; and evolutionary dynamics, all of which will aid conservation efforts and contribute to discussions of assisted migration as the climate continues to change.

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Landscape resistance constrains hybridization across contact zones in a reproductively and morphologically polymorphic salamander

Scientific Reports ◽

10.1038/s41598-021-88349-7 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Guillermo Velo-Antón ◽

André Lourenço ◽

Pedro Galán ◽

Alfredo Nicieza ◽

Pedro Tarroso

Keyword(s):

Contact Zone ◽

Environmental Heterogeneity ◽

Evolutionary Dynamics ◽

Morphological Differentiation ◽

Phenotypic Traits ◽

Hybrid Zones ◽

Landscape Resistance ◽

Phenotypic Differentiation ◽

Contact Zones

AbstractExplicitly accounting for phenotypic differentiation together with environmental heterogeneity is crucial to understand the evolutionary dynamics in hybrid zones. Species showing intra-specific variation in phenotypic traits that meet across environmentally heterogeneous regions constitute excellent natural settings to study the role of phenotypic differentiation and environmental factors in shaping the spatial extent and patterns of admixture in hybrid zones. We studied three environmentally distinct contact zones where morphologically and reproductively divergent subspecies of Salamandra salamandra co-occur: the pueriparous S. s. bernardezi that is mostly parapatric to its three larviparous subspecies neighbours. We used a landscape genetics framework to: (i) characterise the spatial location and extent of each contact zone; (ii) assess patterns of introgression and hybridization between subspecies pairs; and (iii) examine the role of environmental heterogeneity in the evolutionary dynamics of hybrid zones. We found high levels of introgression between parity modes, and between distinct phenotypes, thus demonstrating the evolution to pueriparity alone or morphological differentiation do not lead to reproductive isolation between these highly divergent S. salamandra morphotypes. However, we detected substantial variation in patterns of hybridization across contact zones, being lower in the contact zone located on a topographically complex area. We highlight the importance of accounting for spatial environmental heterogeneity when studying evolutionary dynamics of hybrid zones.

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Introgression between non-sister species of honeyeaters (Aves: Meliphagidae) several million years after speciation

Biological Journal of the Linnean Society ◽

10.1093/biolinnean/blz129 ◽

2019 ◽

Vol 128 (3) ◽

pp. 583-591

Author(s):

Leo Joseph ◽

Alex Drew ◽

Ian J Mason ◽

Jeffrey L Peters

Keyword(s):

Gene Flow ◽

Reproductive Isolation ◽

Sex Chromosomes ◽

Common Ancestor ◽

Sister Species ◽

Species Boundaries ◽

North Eastern ◽

The City

Abstract We reassessed whether two parapatric non-sister Australian honeyeater species (Aves: Meliphagidae), varied and mangrove honeyeaters (Gavicalis versicolor and G. fasciogularis, respectively), that diverged from a common ancestor c. 2.5 Mya intergrade in the Townsville area of north-eastern Queensland. Consistent with a previous specimen-based study, by using genomics methods we show one-way gene flow for autosomal but not Z-linked markers from varied into mangrove honeyeaters. Introgression barely extends south of the area of parapatry in and around the city of Townsville. While demonstrating the long-term porosity of species boundaries over several million years, our data also suggest a clear role of sex chromosomes in maintaining reproductive isolation.

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The Use of Protein Electrophoresis for Determining Species Boundaries in Amphipods

Crustaceana ◽

10.1163/156854093x00603 ◽

1993 ◽

Vol 65 (2) ◽

pp. 265-277 ◽

Cited By ~ 13

Author(s):

Barbara A. Stewart

Keyword(s):

Gene Flow ◽

Genetic Differentiation ◽

Morphological Variation ◽

Protein Electrophoresis ◽

Species Boundaries ◽

Allopatric Populations ◽

A Value ◽

Electrophoretic Data

AbstractThe use of protein electrophoretic data for determining species boundaries in amphipods is addressed. Analysis of published literature on genetic differentiation in amphipods showed that pairs of allopatric populations which have genetic identities (I) above a value of 0.85 probably represent intraspecific populations, whereas pairs of populations which have genetic identities below about 0.45 probably represent different species. It was recommended that if I values fall between 0.45 and 0.85, additional factors such as evidence of a lack of gene flow between the populations, and concordant morphological variation should be considered.

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Population structure, gene flow and natural selection in populations of Euphydryas phaeton

Heredity ◽

10.1038/hdy.1975.50 ◽

1975 ◽

Vol 34 (3) ◽

pp. 407-415 ◽

Cited By ~ 9

Author(s):

Peter F Brussard ◽

A Thomas Vawter

Keyword(s):

Population Structure ◽

Gene Flow ◽

Natural Selection

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Ecological Divergence and the Origins of Intrinsic Postmating Isolation with Gene Flow

International Journal of Ecology ◽

10.1155/2011/435357 ◽

2011 ◽

Vol 2011 ◽

pp. 1-15 ◽

Cited By ~ 24

Author(s):

Aneil F. Agrawal ◽

Jeffrey L. Feder ◽

Patrik Nosil

Keyword(s):

Linkage Disequilibrium ◽

Gene Flow ◽

Natural Selection ◽

Theoretical Models ◽

Ecological Speciation ◽

Divergent Selection ◽

Postmating Isolation ◽

Divergent Natural Selection ◽

Mathematical Exploration ◽

Neutral Gene

The evolution of intrinsic postmating isolation has received much attention, both historically and in recent studies of speciation genes. Intrinsic isolation often stems from between-locus genetic incompatibilities, where alleles that function well within species are incompatible with one another when brought together in the genome of a hybrid. It can be difficult for such incompatibilities to originate when populations diverge with gene flow, because deleterious genotypic combinations will be created and then purged by selection. However, it has been argued that if genes underlying incompatibilities are themselves subject to divergent selection, then they might overcome gene flow to diverge between populations, resulting in the origin of incompatibilities. Nonetheless, there has been little explicit mathematical exploration of such scenarios for the origin of intrinsic incompatibilities during ecological speciation with gene flow. Here we explore theoretical models for the origin of intrinsic isolation where genes subject to divergent natural selection also affect intrinsic isolation, either directly or via linkage disequilibrium with other loci. Such genes indeed overcome gene flow, diverge between populations, and thus result in the evolution of intrinsic isolation. We also examine barriers to neutral gene flow. Surprisingly, we find that intrinsic isolation sometimes weakens this barrier, by impeding differentiation via ecologically based divergent selection.

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Mismatch induced speciation in Salmonella : model and data

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2006.1925 ◽

2006 ◽

Vol 361 (1475) ◽

pp. 2045-2053 ◽

Cited By ~ 82

Author(s):

Daniel Falush ◽

Mia Torpdahl ◽

Xavier Didelot ◽

Donald F Conrad ◽

Daniel J Wilson ◽

...

Keyword(s):

New Species ◽

Natural Selection ◽

Dna Sequence ◽

Computer Simulations ◽

De Novo ◽

Sequence Data ◽

Biological Species ◽

Species Boundaries ◽

Population Subdivision ◽

Geographical Population

In bacteria, DNA sequence mismatches act as a barrier to recombination between distantly related organisms and can potentially promote the cohesion of species. We have performed computer simulations which show that the homology dependence of recombination can cause de novo speciation in a neutrally evolving population once a critical population size has been exceeded. Our model can explain the patterns of divergence and genetic exchange observed in the genus Salmonella , without invoking either natural selection or geographical population subdivision. If this model was validated, based on extensive sequence data, it would imply that the named subspecies of Salmonella enterica correspond to good biological species, making species boundaries objective. However, multilocus sequence typing data, analysed using several conventional tools, provide a misleading impression of relationships within S. enterica subspecies enterica and do not provide the resolution to establish whether new species are presently being formed.

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