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opencc-zeroSep 2021View details →

Data from: Thermal tolerance in two wood ant species and their hybrids

Local populations can cope with rising temperatures, if they have adaptive potential to face the new thermal regime. Hybridization with a closely related lineage is one potential source of adaptive genetic variability and an outstanding question is whether hybridization could help contemporary populations to adapt in the face of current environmental change. We investigate thermal adaptation by testing for differences in cold and heat tolerances between Finnish populations of two mound-building wood ants, Formica polyctena and Formica aquilonia, and their naturally occurring hybrids. The results showed that parental individuals differed in both cold and heat tolerances and expressed thermal limits which reflect the global distributions of the parental species, in support to the thermal adaptation hypothesis. However, hybrids could not combine the thermal tolerance of both parental species as they were equally heat-tolerant to F. polyctena, but not equally cold-tolerant to F. aquilonia. Intriguingly, body weight had a significant role in thermal tolerance, with heavier ants coping better with higher temperatures. These results contribute to understanding the outcomes of hybridization and the potential that species possess in coping with environmental change. Wood ants are keystone species in the boreal forests and important for healthy forest ecosystems, but they are threatened by increasing global temperatures and habitat destruction. Our findings help to understand how these species may respond to global climate change.

opencc-zeroJun 2020View details →

Variation in susceptibility of Eucalyptus grandis and selected hybrid clones to two termite species Macrotermes bellicosus and M. subhyalinus in Uganda

The maximum productivity of plantation forestry and its role in climate change mitigation, adaptation and resilience cannot be met without proper management. Termites in the genus Macrotermes have been reported as a major challenge to Eucalyptus plantation forestry establishment. The current study evaluated the susceptibility of four Eucalyptus hybrid clones; GU 7, GC 796, GC 550 and GC 796/2 and E. grandis to the most damaging Macrotermes bellicosus (Smeathman) and Macrotermes subhyalinus (Rambur) to identify tolerant material that can be planted in high incidence areas. The study involved exposure of moisture dry pieces of wood from E. grandis and the four hybrid clones to damage by M. bellicosus and M. subhyalinus. Results confirmed that M. bellicosus is the most aggressive. Results further revealed that E. grandis and GC 550 are the most susceptible whereas GC 796 is the most tolerant clone. The findings from the study will contribute to improved management of termites by planting tolerant material in high risk areas.

opencc-zeroAug 2020View details →

Genetic, morphological, and niche variation in the widely hybridizing Rhus integrifolia-Rhus ovata species complex

Hybridization and introgression are common processes among numerous plant species that present both challenges and opportunities for studies of species delimitation, phylogenetics, taxonomy, and adaptation. Rhus integrifolia and R. ovata are two ecologically important shrubs native to the southwestern USA and Mexico, and are known to hybridize frequently, but the morphological, genetic, and ecological implications of hybridization in these species are poorly studied on a broad geographic scale. Analyses were conducted using leaf morphology, genetic variation of plastid and nuclear loci, and species distribution models for both species and their putative hybrid introgressants across 19 localities in California and Arizona, USA. These analyses revealed evidence for morphological and genetic distinction among localities comprising putative parental species, but a high degree of morpho-genetic intermediacy among localities with putative hybrids. Comparison of morphological and genetic population structure among localities revealed evidence for putative local adaptation or widespread phenotypic plasticity. Multiple regression models identified a weak but statistically significant negative association between leaf area and precipitation. Finally, species distribution modeling inferred northward range shifts over time, with both species predicted to occupy more coastal regions in the future, possibly increasing the frequency of hybridization among them. These findings underscore the importance of integrative assessment of multiple data sources in the study of hybridizing species and highlight the Rhus integrifolia-ovata complex as a powerful model for investigating the adaptive implications of hybridization.

opencc-zeroDec 2020View details →

The origin of the parrotfish species Scarus compressus in the Tropical Eastern Pacific: region-wide hybridization between ancient species pairs

Background: An increasing number of hybrid zones with varying evolutionary outcomes have been documented from different reef fish families. In the Tropical Eastern Pacific (TEP), four species of parrotfishes occur in sympatry on rocky reefs from Baja California to Ecuador: Scarus. compressus,S. ghobban, S. perrico, and S. rubroviolaceus; and have complex phylogeographic histories. The most divergent,S. perrico, belongs to a Tropical American clade that diverged from a Central Indo-Pacific ancestor in the late Miocene (6.6 Ma). We tested the hypothesis that S. compressuswas the result of ongoing hybridization among the other three species by sequencing four nuclear markers and a mitochondrial locus in samples spanning 2/3 of the latitudinal extent of the TEP. Results: A structure model of all samples indicated that K=3 was the best fit to the nuclear data and that individuals identified as S. compressushad admixed assignment values (Q). Power analyses indicated our data could correctly detect and assign pure adults and F1 hybrids with > 0.90 probability, and correct assignment of F2 was also high in some cases. NewHybrids models revealed that 89.8% (n= 59) of the Scarus compressus samples were F1 hybrids of crosses between divergent species pairs: S. perrico × S. ghobbanand S. perrico × S. rubroviolaceus. Similarly, S.ghobban and S. rubroviolaceuswere also hybridizing, with ½ of the admixed individuals assigned to F1 hybrids and the remainder likely deep generation hybrids. We observed strong mito-nuclear discordance in all three hybrid pairs, but found little evidence for accelerated mt vs. nuclear evolution in the paternal species. Bayesian analysis of Migrate models favours gene flow between S. perricoand S. ghobban, but not other species pairs. Conclusions: Mating between species whose ancestors diverged in the late Miocene is giving rise to region wide, hybrid complex, characterized by a high frequency of parental and F1 genotypes but a low frequency of deep generation hybrids. Trimodal structure, combined with reproductive evidence for fertility of both male and female F1 hybrids, suggest that fitness declines sharply in later generation hybrids. In contrast, the hybrid population of the two younger species had similar frequencies of F1 and > F1 hybrids. These differences are consistent with a model of accelerating post-mating incompatibility with time. Mitochondrial genotypes in hybrids, suggests indiscriminate mating by male S. perricois driving pre-zygotic breakdown, which may reflect the isolation of this endemic species in the TEP for millions of years and weak selection for conspecific mate recognition. Despite overlapping habitat use, high rates of hybridization, and evidence for historical gene flow, species boundaries are maintained by post-mating processes in this complex.

opencc-zeroDec 2018View details →

Data from: Cross-species hybridization and the origin of North African date palms

Date palm (Phoenix dactylifera L.) is a major fruit crop of arid regions that were domesticated 7,000 y ago in the Near or Middle East. This species is cultivated widely in the Middle East and North Africa, and previous population genetic studies have shown genetic differentiation between these regions. We investigated the evolutionary history of P. dactylifera and its wild relatives by resequencing the genomes of date palm varieties and five of its closest relatives. Our results indicate that the North African population has mixed ancestry with components from Middle Eastern P. dactylifera and Phoenix theophrasti, a wild relative endemic to the Eastern Mediterranean. Introgressive hybridization is supported by tests of admixture, reduced subdivision between North African date palm and P. theophrasti, sharing of haplotypes in introgressed regions, and a population model that incorporates gene flow between these populations. Analysis of ancestry proportions indicates that as much as 18% of the genome of North African varieties can be traced to P. theophrasti and a large percentage of loci in this population are segregating for single-nucleotide polymorphisms (SNPs) that are fixed in P. theophrasti and absent from date palm in the Middle East. We present a survey of Phoenix remains in the archaeobotanical record which supports a late arrival of date palm to North Africa. Our results suggest that hybridization with P. theophrasti was of central importance in the diversification history of the cultivated date palm.

opencc-zeroDec 2015View details →

Data from: Differential introgression and the maintenance of species boundaries in an advanced generation avian hybrid zone

Background: Evolutionary processes, including selection and differential fitness, shape the introgression of genetic material across a hybrid zone, resulting in the exchange of some genes but not others. Differential introgression of molecular or phenotypic markers can thus provide insight into factors contributing to reproductive isolation. We characterized patterns of genetic variation across a hybrid zone between two tidal marsh birds, Saltmarsh (Ammodramus caudacutus) and Nelson's (A. nelsoni) sparrows (n = 286), and compared patterns of introgression among multiple genetic markers and phenotypic traits. Results: Geographic and genomic cline analyses revealed variable patterns of introgression among marker types. Most markers exhibited gradual clines and indicated that introgression exceeds the spatial extent of the previously documented hybrid zone. We found steeper clines, indicating strong selection for loci associated with traits related to tidal marsh adaptations, including for a marker linked to a gene region associated with metabolic functions, including an osmotic regulatory pathway, as well as for a marker related to melanin-based pigmentation, supporting an adaptive role of darker plumage (salt marsh melanism) in tidal marshes. Narrow clines at mitochondrial and sex-linked markers also offer support for Haldane's rule. We detected patterns of asymmetrical introgression toward A. caudacutus, which may be driven by differences in mating strategy or differences in population density between the two species. Conclusions: Our findings offer insight into the dynamics of a hybrid zone traversing a unique environmental gradient and provide evidence for a role of ecological divergence in the maintenance of pure species boundaries despite ongoing gene flow.

opencc-zeroDec 2017View details →

Data from: Genetic divergence and the number of hybridizing species affect the path to homoploid hybrid speciation

Hybridization is often maladaptive, and in some instances has led to the loss of biodiversity. However, hybridization can also promote speciation, such as during homoploid hybrid speciation, thereby generating biodiversity. Despite examples of homoploid hybrid species, the importance of hybridization as a speciation mechanism is still widely debated, and we lack a general understanding of the conditions most likely to generate homoploid hybrid species. Here we show that the level of genetic divergence between hybridizing species has a large effect on the probability that their hybrids evolve reproductive isolation. We find that populations of hybrids formed by parental species with intermediate levels of divergence were more likely to mate assortatively, and discriminate against their parental species, than those generated from weakly or strongly diverged parental species. Reproductive isolation was also found between hybrid populations, suggesting differential sorting of parental traits across populations. Finally, hybrid populations derived from three species were more likely to evolve reproductive isolation than those derived from two, supporting arguments that hybridization-supplied genetic diversity can lead to the evolution of novel "adaptive systems" and promote speciation. Our results illustrate when we expect hybridization and admixture to promote hybrid speciation. Whether homoploid hybrid speciation is a common speciation mechanism in general, remains an outstanding empirical question.

opencc-zeroDec 2014View details →

Data from: Reproductive isolation in a nascent species pair is associated with aneuploidy in hybrid offspring

Speciation may occur when the genomes of two populations accumulate genetic incompatibilities and/or chromosomal rearrangements that prevent inter-breeding in nature. Chromosome stability is critical for survival and faithful transmission of the genome, and hybridization can compromise this. However, the role of chromosomal stability on hybrid incompatibilities has rarely been tested in recently diverged populations. Here, we test for chromosomal instability in hybrids between nascent species, the 'dwarf' and 'normal' lake whitefish (Coregonus clupeaformis). We examined chromosomes in pure embryos, and healthy and malformed backcross embryos. While pure individuals displayed chromosome numbers corresponding to the expected diploid number (2n = 80), healthy backcrosses showed evidence of mitotic instability through an increased variance of chromosome numbers within an individual. In malformed backcrosses, extensive aneuploidy corresponding to multiples of the haploid number (1n = 40, 2n = 80, 3n = 120) was found, suggesting meiotic breakdown in their F1 parent. However, no detectable chromosome rearrangements between parental forms were identified. Genomic instability through aneuploidy thus appears to contribute to reproductive isolation between dwarf and normal lake whitefish, despite their very recent divergence (approx. 15–20 000 generations). Our data suggest that genetic incompatibilities may accumulate early during speciation and limit hybridization between nascent species.

opencc-zeroDec 2016View details →

Data from: Hybridization increases mitochondrial production of reactive oxygen species in sunfish

Mitochondrial dysfunction and oxidative stress have been suggested to be possible mechanisms underlying hybrid breakdown, as a result of mito-nuclear incompatibilities in respiratory complexes of the electron transport system. However, it remains unclear whether hybridization increases the production of reactive oxygen species (ROS) by mitochondria. We used high-resolution respirometry and fluorometry on isolated liver mitochondria to examine mitochondrial physiology and ROS emission in naturally occurring hybrids of pumpkinseed (Lepomis gibbosus) and bluegill (L. macrochirus). ROS emission was greater in hybrids than in both parent species when respiration was supported by complex I (but not complex II) substrates, and was associated with increases in lipid peroxidation. However, respiratory capacities for oxidative phosphorylation, phosphorylation efficiency, and O2 kinetics in hybrids were intermediate between those in parental species. Flux control ratios of capacities for electron transport (measured in uncoupled mitochondria) relative to oxidative phosphorylation suggested that the limiting influence of the phosphorylation system is reduced in hybrids. This likely helped offset impairments in electron transport capacity and complex III activity, but contributed to augmenting ROS production. Therefore, hybridization can increase mitochondrial ROS production, in support of previous suggestions that mitochondrial dysfunction can induce oxidative stress and thus contribute to hybrid breakdown.

opencc-zeroDec 2014View details →

Data from: Hybridization in the Drosophila melanogaster subgroup: incomplete isolation among the three species of the yakuba complex

In the Drosophila melanogaster subgroup, the yakuba species complex, D. yakuba, D. santomea and D. teissieri have identical mitochondrial genomes in spite of nuclear differentiation. The first two species can be readily hybridized in the laboratory, and produce fertile females and sterile males. They also form hybrids in natural conditions. Nonetheless, the third species, D. teissieri, was thought to be unable to produce hybrids with either D. yakuba or D. santomea. This in turn posed the conundrum of why the three species shared a single mitochondrial genome. In this report we show that D. teissieri can indeed hybridize with both D. yakuba and D. santomea. The resulting female hybrids from both crosses are fertile, while the hybrid males are sterile. We also characterize six isolating mechanisms that might be involved in keeping the three species apart. Our results open the possibility of studying the history of introgression in the yakuba species complex and dissecting the genetic basis of interspecific differences between these three species by genetic mapping.

opencc-zeroDec 2010View details →

Data from: Genetics of hybrid male sterility among strains and species in the Drosophila pseudoobscura species group

Taxa in the early stages of speciation may bear intraspecific allelic variation at loci conferring barrier traits in hybrids such as hybrid sterility. Additionally, hybridization may spread alleles that confer barrier traits to other taxa. Historically, few studies examine within- and between-species variation at loci conferring reproductive isolation. Here, we test for allelic variation within Drosophila persimilis and within the Bogota subspecies of D. pseudoobscura at regions previously shown to contribute to hybrid male sterility. We also test whether D. persimilis and the USA subspecies of D. pseudoobscura share an allele conferring hybrid sterility in a D. pseudoobscura bogotana genetic background. All loci conferred similar hybrid sterility effects across all strains studied, though we detected some statistically significant quantitative effect variation among D. persimilis alleles of some hybrid incompatibility QTLs. We also detected allelism between D. persimilis and D. pseudoobscura USA at a 2nd chromosome hybrid sterility QTL. We hypothesize that either the QTL is ancestral in D. persimilis and D. pseudoobscura USA and lost in D. pseudoobscura bogotana, or gene flow transferred the QTL from D. persimilis to D. pseudoobscura USA. We discuss our findings in the context of population features that may contribute to variation in hybrid incompatibilities.

opencc-zeroDec 2010View details →

Data from: Interpreting the estimated timing of migration events between hybridizing species

The question of whether speciation can occur in the presence of gene flow has long been a contentious one. However, measuring the amount and timing of gene flow remains challenging. The computer program IMA2 allows researchers to estimate the timing of migration events for each locus during analyses, and these estimates have been used to infer the timing of introgression and mode of speciation. We use simulated datasets to examine the degree to which gene flow timing estimates can be used for these purposes, and what demographic conditions and datasets may be most amenable to gene flow timing estimation. We find that the 90% highest posterior density (HPD) interval of gene flow timing is almost always substantially wider than the actual window of gene flow, and increasing the information content of the dataset in terms of number of loci, number of sequences sampled, or locus length (and thus number of variable sites) has little impact on the posterior distribution over the range of values we tested. Even when simulated gene flow only occurred over the most recent 0.01% of the species' history, the HPD interval usually encompasses the inferred divergence time. Our results indicate that gene flow timing estimates made using the method currently implemented in IMA2 cannot reliably be used to make inferences about the timing of introgression between diverged species or to distinguish between speciation with gene flow and allopatric speciation followed by one or more episodes of gene flow.

FIGURE 11 in Cryptic species and hybridization in the Anolis polylepis complex, with the description of a new species from the Osa Peninsula, Costa Rica (Squamata: Polychrotidae)

FIGURE 11. Adult female of Anolis osa (not collected) at Puerto Escondido in life.

FIGURE 4 in Cryptic species and hybridization in the Anolis polylepis complex, with the description of a new species from the Osa Peninsula, Costa Rica (Squamata: Polychrotidae)

FIGURE 4. Hemipenis of Anolis osa (SMF 89260). Scale bar = 1.0 mm.

FIGURE 3 in Cryptic species and hybridization in the Anolis polylepis complex, with the description of a new species from the Osa Peninsula, Costa Rica (Squamata: Polychrotidae)

FIGURE 3. Hemipenis of Anolis polylepis (MHCH 1024). Scale bar = 1.0 mm.

FIGURE 2 in Cryptic species and hybridization in the Anolis polylepis complex, with the description of a new species from the Osa Peninsula, Costa Rica (Squamata: Polychrotidae)

FIGURE 2. Designation of dorsal color pattern types.

openother-openOct 2021View details →

Supporting data and code for: Distribution of invasive versus native whitefly species and their pyrethroid knock-down resistance allele in a context of interspecific hybridization

This is the first release of the final data and code for the article accepted for publication in Scientific Reports journal. It contains all the necessary scripts to produce most of the analyses and figures of the manuscript. All the necessary data can be found in the 'data' folder.