852 research outputs found
Structural Variants and Speciation: Multiple Processes at Play
No full textResearch on the genomic architecture of speciation has increasingly revealed the importance of structural variants (SVs) that affect the presence, abundance, position, and/or direction of a nucleotide sequence. SVs include large chromosomal rearrangements such as fusion/fissions, inversions and translocations, as well as smaller variants such as duplications, insertions, and deletions (CNVs). Although we have ample evidence that SVs play a key role in speciation, the underlying mechanisms differ depending on the type and length of the SV, as well as the ecological, demographic and historical context. We review predictions and empirical evidence for classic processes such as underdominance due to meiotic aberrations and the coupling effect of recombination suppression before exploring how recent sequencing methodologies illuminate the prevalence and diversity of SVs. We discuss specific properties of SVs and their impact throughout the genome, highlighting that multiple processes are at play, and possibly interacting, in the relationship between SVs and speciation.Fil: Berdan, Emma L.. University Goteborg; SueciaFil: Aubier, Thomas G.. Université Paul Sabatier Toulouse III; ArgentinaFil: Cozzolino, Salvatore. University Of Naples Federico II; ItaliaFil: Faria, Rui. Universidade Do Porto; PortugalFil: Feder, Jeffrey L.. University of Notre Dame; Estados UnidosFil: Giménez, Mabel Dionisia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Gobierno de la Provincia de Misiones. Ministerio de Salud de la Provincia de Misiones. Instituto de Genética Humana;Fil: Joron, Mathieu. Universite de Montpellier; FranciaFil: Searle, Jeremy Byron. Cornell University; Estados UnidosFil: Mérot, Claire. Universite de Rennes I; Franci
Linking ecological divergence and reproductive isolation: a tale of two killifish
No full textGene flow and recombination directly oppose genetic differentiation and speciation because they homogenize allele combinations that are unique to each population/species (Felsenstein 1981; Rieseberg 2001; Ortiz-Barrientos, Reiland et al. 2002; Butlin 2005). Under divergence with gene flow, either very strong selection or some other mechanism that reduces recombination rates is needed to maintain different allelic combinations.
Decreased recombination is especially important in cases of ecological speciation with gene flow. A decade of work in evolutionary biology indicates that divergent natural selection in different habitats is usually involved in speciation (i.e. ecological speciation). While ecological selection alone can promote speciation (Schluter 2001; Rundle and Nosil 2005; Schluter and Conte 2009), a variety of species contain populations that are adapted to different habitats and yet have not undergone speciation (Hendry 2009; Nosil, Harmon et al. 2009). These conflicting outcomes suggest that ecological selection need not always lead to the evolution of reproductive isolating barriers (RIBs). When the genes under ecological selection also confer reproductive isolation, ecological speciation occurs readily (Boughman 2001; Kirkpatrick and Ravigne 2002; Gavrilets 2004). However, when the genes under ecological selection are independent of the genes conferring reproductive isolation, alleles for RIBs must somehow become associated with the alleles under ecological selection, thus providing a link between adaptation and reproductive isolation (Felsenstein 1981; Servedio 2009). To date, few studies have examined the mechanisms by which divergent natural selection can lead to the development of reproductive isolation.
I examined role of divergent natural selection in speciation using the sister species Lucania goodei and L. parva (Duggins, Karlin et al. 1983; Whitehead 2010). Lucania goodei and L. parva are differentially adapted to salinity with L. goodei being primarily freshwater and L. parva being euryhaline (able to tolerate a wide range of salinities). In my thesis I determined the extent to which divergent natural selection (with regard to salinity tolerance) has led to reproductive isolation.
First, I searched for physiological mechanisms to explain the difference in salinity tolerance between the two species. I did this by exposing individuals of both species to different salinities and then performing a real time PCR study to examine changes in mRNA transcript levels of genes known to be involved in osmoregulation. I found that L. parva expressed higher levels of the genes involved in saltwater ion/osmoregulatory regulation than did L. goodei, but that both species expressed similar levels for two of the three genes involved in freshwater osmoregulation.
Next, I examined whether or not divergent natural selection for salinity tolerance has led directly to behavioral isolation (Chapter 3). Previous work indicated that behavioral isolation was present, but did not test whether the expression of behavioral isolation varied with environmental conditions. Adaptation to different salinities may have led to differences in mating signals and perception of those signals, producing behavioral isolation as a byproduct. I tested if this had occurred by manipulating the environment the fish were in. If mating signals and preferences in L. parva are especially adapted to saltwater and those of L. goodei to freshwater, then changing the salinity should decrease the strength of behavioral isolation by interfering with these signals.
The results of this study suggested that divergent natural selection did not play a role in the evolution of behavioral isolation. However, there was a striking asymmetry in courtship between the species that was concordant with the direction of intrinsic isolation. Hence, there may have been selection for species recognition in male L. goodei due to low fitness in hybrids (i.e. reinforcement).
The classic signature of reinforcement is heightened behavioral isolation in areas of sympatry. In Chapter 4, I explicitly tested whether or not reinforcement of male preferences had occurred by comparing male preferences from sympatric and allopatric populations. Males from sympatric and allopatric populations were exposed to females of both species over two days and their behavior was monitored. Allopatric males were significantly more likely to court heterospecific females than sympatric males. This is in agreement with the expectations of reinforcement theory.
In the final two chapters of my thesis, I tested whether or not chromosomal rearrangements have led to linkage disequilibrium between genes underlying reproductive isolation and genes underlying salinity tolerance. Many closely related species differ in chromosome number and shape. Chromosomal rearrangements can be important to both adaptation and the development of reproductive isolation since rearrangements can physically link species-specific genes in areas of low recombination (White 1978; Trickett and Butlin 1994; Noor, Grams et al. 2001; Rieseberg 2001; Ortiz-Barrientos, Reiland et al. 2002; Feder, Roethele et al. 2003; Navarro and Barton 2003; Brown, Burk et al. 2004; Butlin 2005; Kirkpatrick and Barton 2006; Carneiro, Ferrand et al. 2009). I created linkage maps for both L. goodei and L. parva and analyzed them for synteny to determine if genomic rearrangements had occurred (Chapter 5). A fusion between linkage groups 13 and 14 in L. goodei has led to a large metacentric chromosome (linkage group 1 in L. parva). I performed a QTL analysis to determine if the genes underlying salinity tolerance and reproductive isolation are located within this rearrangement (Chapter 6). The fusion contained QTLs for multiple traits involved in reproductive isolation. In contrast, the genetic underpinnings of salinity tolerance had little relationship to reproductive isolation. Only one of four QTL underlying salinity tolerance mapped to the same location as a QTL involved in reproductive isolation. Thus, genetic differentiation in salinity tolerance does not seem to be strongly associated with reproductive isolation. Instead, my data suggest that chromosomal rearrangements are important in linking female and male behavioral isolation and genes related in intrinsic isolation. Linkage of behavioral isolation with intrinsic isolation is vital for reinforcement (Ortiz-Barrientos, Grealy et al. 2009). The chromosomal fusion may have aided reinforcement in this system by bringing loci underlying behavioral isolation and intrinsic isolation into linkage disequilibrium.
My dissertation indicated that divergent natural selection likely had little to do with speciation in this group and future work should concentrate on discerning the non-ecological mechanisms (i.e. reinforcement) that led to reproductive isolation.Item withdrawn by Mark Zulauf ([email protected]) on 2012-07-10T18:18:07Z
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Deleterious mutation accumulation and the long-term fate of chromosomal inversions
No full textChromosomal inversions contribute widely to adaptation and speciation, yet they present a unique evolutionary puzzle as both their allelic content and frequency evolve in a feedback loop. In this simulation study, we quantified the role of the allelic content in determining the long-term fate of the inversion. Recessive deleterious mutations accumulated on both arrangements with most of them being private to a given arrangement. This led to increasing overdominance, allowing for the maintenance of the inversion polymorphism and generating strong non-adaptive divergence between arrangements. The accumulation of mutations was mitigated by gene conversion but nevertheless led to the fitness decline of at least one homokaryotype under all considered conditions. Surprisingly, this fitness degradation could be permanently halted by the branching of an arrangement into multiple highly divergent haplotypes. Our results highlight the dynamic features of inversions by showing how the non-adaptive evolution of allelic content can play a major role in the fate of the inversion
The persistence of populations facing climate shifts and harvest
No full textMany species are expected to shift their geographic distribution as climates change, and yet climate change is only one of a suite of stressors that species face. Species that might, in theory, be able to shift rapidly enough to keep up with climate velocity (the rate and direction that isotherms move across the landscape) may not in actuality be able to do so when facing the cumulative impacts of multiple stressors. Despite empirical reports of substantial interactions between climate change and other stressors, we often lack a mechanistic understanding of these interactions. Here, we developed and analyzed a spatial population dynamics model to explore the cumulative impacts of climate with another dominant stressor in the ocean and on land: harvest. We found that critical rates of climate velocity and harvest depend on the growth rate and dispersal kernel of the population, as well as the magnitude of the other stressor. This allowed us to identify conditions under which harvesting and climate velocity can together drive populations extinct even when neither stressor would do so in isolation. Except in these extreme cases, we also found that the interaction between the declines in biomass caused by climate velocity and harvest is approximately additive. Finally, we have shown that threshold harvest rules can be effective management tools to mitigate the interaction between the two stressors, while protected areas can either help or hinder,depending on how harvesters reallocate their effort. We also have parameterized the model for black rockfish (Sebastes melanops) to demonstrate the model’s broad applicability.Received 22 December 2014; revised 25 February 2015; accepted 4 March 2015; final version received 8 May 2015; published 23 September 2015.Peer reviewe
Ritorno a Thornfield. La "storia segreta" di Adèle Varens in Thornfield Hall di Emma Tennant
No full textIn the line of the Neo-Victorian movement within postmodern literature, in 2002 British author Emma Tennant (1937-2017) re-wrote Charlotte Brontë’s 1847 Jane Eyre as Thornfield Hall. Even though its subtitle, The Hidden Story of Jane Eyre, anticipates a new appendix to Jane’s widely known adventures, the novel is in fact centred on Adèle Varens, “the French dancer’s bastard”. In particular, Tennant’s narrative looks back at the Brontean novel by exploring the Parisian milieu in which the young Adèle breathes the air of the Révolution and learns how to resist the patriarchal and political established order; and yet, later on, she seems to forget the teachings she drew from Céline Varens, her mother, and her world in a problematic intertextual twist that questions the presence of the Other – once again represented by Bertha Antoinette Mason, echoing Jean Rhys’s 1966 masterpiece Wide Sargasso Sea – but ultimately/inevitably pays homage to Brontë’s classic
Data from: A test for environmental effects on behavioral isolation in two species of killifish
No full textBehavioral isolation is a common and potent mechanism of reproductive isolation. Determining the extent to which behavioral isolation varies with environmental conditions is critical to understanding speciation and the maintenance of species boundaries. Here, we tested the effect of salinity on behavioral isolation (female species recognition, male-male competition, male species recognition) between two closely related killifish (Lucania goodei and L. parva) that differ in salinity tolerance. We performed no-choice assays and behavioral trials where males could compete and court females in fresh water (0 ppt) and brackish water (15 ppt). We found high levels of behavioral isolation that did not vary as a function of salinity. In behavioral trials, male species recognition of females was strong and asymmetric between the two species. Lucania goodei males preferred conspecifics and rarely courted or mated with L. parva females. Lucania parva males preferred conspecifics but readily courted and mated with L. goodei females. This asymmetry matches previously documented asymmetries in hybrid offspring fitness. Crosses between L. parva males and L. goodei females produce fully viable/fertile hybrids, but crosses between L. goodei males and L. parva females produce males with reduced fertility. Hence, behavioral isolation may have evolved in part due to reinforcement
Handheld-Impedance-Measurement System with seven-decade capability and potentiostatic function
No full textThis paper describes design and test of a new impedance-measurement system for nonlinear devices that exhibits a seven-decade range and works down to a frequency of 0.01 Hz. The system is specifically designed for electrochemical measurements, but the proposed architecture can be employed in many other fields where flexible signal generation and analysis are required. The system employs an unconventional signal generator based on two pulsewidth modulation (PWM) oscillators and an autocalibration system that allows uncertainties of less than 3% to be obtained over a range of 1 kΩ to 100 GΩ. A synchronous demodulation processing allows the noise superimposed to the low-amplitude input signals to be made negligibl
Genomic landscape of reproductive isolation in Lucania killifish: The role of sex loci and salinity
No full textAdaptation to different environments can directly and indirectly generate reproductive isolation between species. Bluefin killifish (Lucania goodei) and rainwater killifish (L. parva) are sister species that have diverged across a salinity gradient and are reproductively isolated by habitat, behavioral, extrinsic, and intrinsic postzygotic isolation. We asked if salinity adaptation contributes indirectly to other forms of reproductive isolation via linked selection and hypothesized that low recombination regions, such as sex chromosomes or chromosomal rearrangements, might facilitate this process. We conducted QTL mapping in backcrosses between L. parva and L. goodei to explore the genetic architecture of salinity tolerance, behavioral isolation, and intrinsic isolation. We mapped traits relative to a chromosome that has undergone a centric fusion in L. parva (relative to L. goodei). We found that the sex locus appears to be male determining (XX-XY), was located on the fused chromosome, and was implicated in intrinsic isolation. QTL associated with salinity tolerance were spread across the genome and did not overly co-localize with regions associated with behavioral or intrinsic isolation. This preliminary analysis of the genetic architecture of reproductive isolation between Lucania species does not support the hypothesis that divergent natural selection for salinity tolerance led to behavioral and intrinsic isolation as a byproduct. Combined with previous studies in this system, our work suggests that adaptation as a function of salinity contributes to habitat isolation and that reinforcement may have contributed to the evolution of behavioral isolation instead, possibly facilitated by linkage between behavioral isolation and intrinsic isolation loci on the fused chromosome.This dataset include the R markdown files used for QTL mapping and statistical analyses of genotype frequencies along with all data files necessary for those analyses.
Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB-0953716Funding provided by: National Science FoundationCrossref Funder Registry ID: http://dx.doi.org/10.13039/100000001Award Number: DEB-111065
Seawater carbonate chemistry and growth, chain length, silica content, and toxin content of four species of diatoms and one toxic dinoflagellate
No full textPhytoplankton induce defensive traits in response to chemical alarm signals from grazing zooplankton. However, these signals are potentially vulnerable to changes in pH and it is not yet known how predator recognition may be affected by ocean acidification. We exposed four species of diatoms and one toxic dinoflagellate to future pCO2 levels, projected by the turn of the century, in factorial combinations with predatory cues from copepods (copepodamides). We measured the change in growth, chain length, silica content, and toxin content. Effects of increased pCO2 were highly species specific. The induction of defensive traits was accompanied by a significant reduction in growth rate in three out of five species. The reduction averaged 39% and we interpret this as an allocation cost associated with defensive traits. Copepodamides induced significant chain length reduction in three of the four diatom species. Under elevated pCO2 Skeletonema marinoi reduced silica content by 30% and in Alexandrium minutum the toxin content was reduced by 30%. Using copepodamides to induce defensive traits in the absence of direct grazing provides a straightforward methodology to assess costs of defense in microplankton. We conclude that copepodamide signalling system is likely robust to ocean acidification. Moreover, the variable responses of different taxa to ocean acidification suggest that there will be winners and losers in a high pCO2 world, and that ocean acidification may have structuring effects on phytoplankton communities
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