Genetic architecture of traits associated with reproductive barriers in Silene:
 Coupling, sex chromosomes and variation

Abstract Genetic analyses of reproductive barriers represent one of the few methods by which theories of speciation can be tested. However, genetic study is often restricted to model organisms that have short generation times and are easily propagated in the laboratory. Replicate hybrid zones with a diversity of recombinant genotypes of varying age offer increased resolution for genetic mapping experiments and expand the pool of organisms amenable to genetic study. Using 88 markers distributed across 17 chromosomes, we analyze the introgression of chromosomal segments of Helianthus petiolaris into H. annuus in three natural hybrid zones. Introgression was significantly reduced relative to neutral expectations for 26 chromosomal segments, suggesting that each segment contains one or more factors that contribute to isolation. Pollen sterility is significantly associated with 16 of these 26 segments, providing a straightforward explanation of why this subset of blocks is disadvantageous in hybrids. In addition, comparison of rates of introgression across colinear vs. rearranged chromosomes indicates that close to 50% of the barrier to introgression is due to chromosomal rearrangements. These results demonstrate the utility of hybrid zones for identifying factors contributing to isolation and verify the prediction of increased resolution relative to controlled crosses.

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GENETIC ARCHITECTURE OF ISOLATION BETWEEN TWO SPECIES OFSILENEWITH SEX CHROMOSOMES AND HALDANE'S RULE

Evolution ◽

10.1111/evo.12269 ◽

2013 ◽

Vol 68 (2) ◽

pp. 332-342 ◽

Cited By ~ 17

Author(s):

Jeffery P. Demuth ◽

Rebecca J. Flanagan ◽

Lynda F. Delph

Keyword(s):

Sex Chromosomes ◽

Genetic Architecture ◽

Haldane’S Rule ◽

Haldane's Rule

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Sex without sex chromosomes: genetic architecture of multiple loci independently segregating to determine sex ratios in the copepod Tigriopus californicus

Journal of Evolutionary Biology ◽

10.1111/jeb.12743 ◽

2015 ◽

Vol 28 (12) ◽

pp. 2196-2207 ◽

Cited By ~ 12

Author(s):

H. J. Alexander ◽

J. M. L. Richardson ◽

S. Edmands ◽

B. R. Anholt

Keyword(s):

Sex Chromosomes ◽

Genetic Architecture ◽

Sex Ratios ◽

Tigriopus Californicus ◽

Multiple Loci

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Sex chromosome evolution, heterochiasmy and physiological QTL in the salmonid Brook Charr Salvelinus fontinalis

10.1101/105411 ◽

2017 ◽

Author(s):

Ben J. G. Sutherland ◽

Ciro Rico ◽

Céline Audet ◽

Louis Bernatchez

Keyword(s):

Sex Determination ◽

Sex Chromosomes ◽

Genetic Architecture ◽

Salvelinus Fontinalis ◽

Sex Chromosome ◽

Brook Charr ◽

Determination System ◽

Males And Females ◽

Sex Determination System ◽

Sex Determination Mechanisms

ABSTRACTWhole genome duplication can have large impacts on genome evolution, and much remains unknown about these impacts. This includes the mechanisms of coping with a duplicated sex determination system and whether this has an impact on increasing the diversity of sex determination mechanisms. Other impacts include sexual conflict, where alleles having different optimums in each sex can result in sequestration of genes into non-recombining sex chromosomes. Sex chromosome development itself may involve sex-specific recombination rate (i.e. heterochiasmy), which is also poorly understood. Family Salmonidae is a model system for these phenomena, having undergone autotetraploidization and subsequent rediploidization in most of the genome at the base of the lineage. The salmonid master sex determining gene is known, and many species have non-homologous sex chromosomes, putatively due to transposition of this gene. In this study, we identify the sex chromosome of Brook Charr Salvelinus fontinalis and compare sex chromosome identities across the lineage (eight species, four genera). Although non-homology is frequent, homologous sex chromosomes and other consistencies are present in distantly related species, indicating probable convergence on specific sex and neo-sex chromosomes. We also characterize strong heterochiasmy with 2.7-fold more crossovers in maternal than paternal haplotypes with paternal crossovers biased to chromosome ends. When considering only rediploidized chromosomes, the overall heterochiasmy trend remains, although with only 1.9-fold more recombination in the female than the male. Y chromosome crossovers are restricted to a single end of the chromosome, and this chromosome contains a large interspecific inversion, although its status between males and females remains unknown. Finally, we identify QTL for 21 unique growth, reproductive and stress-related phenotypes to improve knowledge of the genetic architecture of these traits important to aquaculture and evolution.

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Genomic landscape of reproductive isolation in Lucania killifish: The role of sex chromosomes and salinity

10.1101/831867 ◽

2019 ◽

Author(s):

Emma L. Berdan ◽

Rebecca C. Fuller ◽

Genevieve M. Kozak

Keyword(s):

Reproductive Isolation ◽

Salinity Tolerance ◽

Sex Chromosomes ◽

Genetic Architecture ◽

Sex Chromosome ◽

Salinity Gradient ◽

Chromosome 1 ◽

Hybrid Male ◽

Bluefin Killifish ◽

Sex Locus

ABSTRACTUnderstanding how speciation occurs and how reproductive barriers contribute to population structure at a genomic scale requires elucidating the genetic architecture of reproductive isolating barriers. In particular, it is crucial to determine if loci underlying reproductive isolation are genetically linked or if they are located on sex chromosomes, which have unique inheritance and population genetic properties. Bluefin killifish (Lucania goodei) and rainwater killifish (L. parva) are closely related species that have diverged across a salinity gradient and are reproductively isolated by assortative mating, hybrid male infertility, viability of hybrid offspring at high salinities, as well as reduced overall fitness of F2 offspring and backcrosses to L. goodei. We conducted QTL mapping in backcrosses between L. parva and L. goodei to determine the genetic architecture of sex determination, mate attractiveness, fertility, and salinity tolerance. We find that the sex locus appears to be male determining and located on a chromosome that has undergone a Robertsonian fusion in L. parva relative to L. goodei. We find that the sex locus on the fused chromosome is involved in several genomic incompatibilities, which affect the survival of backcrossed offspring. Among the backcrossed offspring that survived to adulthood, we find that one QTL for male attractiveness to L. goodei females is closely linked to this sex locus on chromosome 1. Males homozygous for L. goodei alleles at the sex locus laid more eggs with L. goodei females. QTL associated with salinity tolerance were spread across the genome but did not tend to co-localize with reproductive isolation. Thus, speciation in this system appears to be driven by reinforcement and indirect selection against hybrids rather than direct natural selection for salinity tolerance. Our work adds to growing evidence that sex chromosome evolution may contribute to speciation.

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Adaptive introgression during environmental change can weaken reproductive isolation

10.1101/553230 ◽

2019 ◽

Cited By ~ 1

Author(s):

Gregory L. Owens ◽

Kieran Samuk

Keyword(s):

Climate Change ◽

Species Diversity ◽

Reproductive Isolation ◽

Genetic Architecture ◽

Species Boundaries ◽

Reproductive Barriers ◽

Climatic Variable ◽

Adaptive Introgression ◽

Primary Mechanism ◽

Reverse Speciation

AbstractAnthropogenic climate change is an urgent threat to species diversity. One aspect of this threat is the collapse of species reproductive barriers through increased hybridization. The primary mechanism for this collapse is thought to be the weakening of ecologically-mediated reproductive barriers, as demonstrated in many cases of “reverse speciation” . Here, we expand on this idea and show that adaptive introgression between species adapting to a shared, moving climatic optimum can readily weaken any reproductive barrier, including those that are completely independent of the climatic variable. Using genetically explicit forward-time simulations, we show that genetic linkage between alleles conferring adaptation to a changing climate and alleles conferring reproductive isolation can lead to adaptive introgression facilitating the homogenization of reproductive isolation alleles. This effect causes the decay of species boundaries across a broad and biologically-realistic parameter space. We explore how the magnitude of this effect depends upon the rate of climate change, the genetic architecture of adaptation, the initial degree of reproductive isolation and the mutation rate. These results highlight a previously unexplored effect of rapid climate change on species diversity.

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