More Like this

1. Phenotypic disruption of cuticular hydrocarbon production in hybrids between sympatric species of Hawaiian picture-wing Drosophila

   https://doi.org/10.1038/s41598-022-08635-w  

   Fezza, Thomas J. ; Siderhurst, Matthew S. ; Jang, Eric B. ; Stacy, Elizabeth A. ; Price, Donald K. ( March 2022 , Scientific Reports)

   Interspecies hybrids can express phenotypic traits far outside the range of parental species. The atypical traits of hybrids provide insight into differences in the factors that regulate the expression of these traits in the parental species. In some cases, the unusual phenotypic traits of hybrids can lead to phenotypic dysfunction with hybrids experiencing reduced survival or reproduction. Cuticular hydrocarbons (CHCs) in insects are important phenotypic traits that serve several functions, including desiccation resistance and pheromones for mating. We used gas chromatography mass spectrometry to investigate the differences in CHC production between two closely related sympatric Hawaiian picture-wingDrosophilaspecies,Drosophila heteroneuraandD. silvestris, and their F1 and backcross hybrid offspring. CHC profiles differed between males of the two species, with substantial sexual dimorphism inD. silvestrisbut limited sexual dimorphism inD. heteroneura. Surprisingly, F1 hybrids did not produce three CHCs, and the abundances of several other CHCs occurred outside the ranges present in the two parental species. Backcross hybrids produced all CHCs with greater variation than observed in F1 or parental species. Overall, these results suggest that the production of CHCs was disrupted in F1 and backcross hybrids, which may have important consequences for their survival or reproduction.

    

   more » « less
2. Genome‐wide differentiation in closely related populations: the roles of selection and geographic isolation

   https://doi.org/10.1111/mec.13740  

   Safran, R_J ; Scordato, E_S_C ; Wilkins, M_R ; Hubbard, J_K ; Jenkins, B_R ; Albrecht, T. ; Flaxman, S_M ; Karaardıç, H. ; Vortman, Y. ; Lotem, A. ; et al ( July 2016 , Molecular Ecology)

   Population divergence in geographic isolation is due to a combination of factors. Natural and sexual selection may be important in shaping patterns of population differentiation, a pattern referred to as ‘isolation by adaptation’ (IBA).IBAcan be complementary to the well‐known pattern of ‘isolation by distance’ (IBD), in which the divergence of closely related populations (via any evolutionary process) is associated with geographic isolation. The barn swallowHirundo rusticacomplex comprises six closely related subspecies, where divergent sexual selection is associated with phenotypic differentiation among allopatric populations. To investigate the relative contributions of selection and geographic distance to genome‐wide differentiation, we compared genotypic and phenotypic variation from 350 barn swallows sampled across eight populations (28 pairwise comparisons) from four different subspecies. We report a draft whole‐genome sequence forH. rustica, to which we aligned a set of 9493 single nucleotide polymorphisms (SNPs). Using statistical approaches to control for spatial autocorrelation of phenotypic variables and geographic distance, we find that divergence in traits related to migratory behaviour and sexual signalling, as well as geographic distance, together explain over 70% of genome‐wide divergence among populations. Controlling forIBD, we find 42% of genomewide divergence is attributable toIBAthrough pairwise differences in traits related to migratory behaviour and sexual signalling alone. By (i) combining these results with prior studies of how selection shapes morphological differentiation and (ii) accounting for spatial autocorrelation, we infer that morphological adaptation plays a large role in shaping population‐level differentiation in this group of closely related populations.

    

   more » « less
3. Convergence without divergence in North American red-flowering Silene

   https://doi.org/10.3389/fpls.2022.945806  

   Berardi, Andrea E. ; Betancourt Morejón, Ana C. ; Hopkins, Robin ( September 2022 , Frontiers in Plant Science)

   Combinations of correlated floral traits have arisen repeatedly across angiosperms through convergent evolution in response to pollinator selection to optimize reproduction. While some plant groups exhibit very distinct combinations of traits adapted to specific pollinators (so-called pollination syndromes), others do not. Determining how floral traits diverge across clades and whether floral traits show predictable correlations in diverse groups of flowering plants is key to determining the extent to which pollinator-mediated selection drives diversification. The North AmericanSilenesectionPhysolychnisis an ideal group to investigate patterns of floral evolution because it is characterized by the evolution of novel red floral color, extensive floral morphological variation, polyploidy, and exposure to a novel group of pollinators (hummingbirds). We test for correlated patterns of trait evolution that would be consistent with convergent responses to selection in the key floral traits of color and morphology. We also consider both the role of phylogenic distance and geographic overlap in explaining patterns of floral trait variation. Inconsistent with phenotypically divergent pollination syndromes, we find very little clustering of North AmericanSileneinto distinct floral morphospace. We also find little evidence that phylogenetic history or geographic overlap explains patterns of floral diversity in this group. White- and pink-flowering species show extensive phenotypic diversity but are entirely overlapping in morphological variation. However, red-flowering species have much less phenotypic disparity and cluster tightly in floral morphospace. We find that red-flowering species have evolved floral traits that align with a traditional hummingbird syndrome, but that these trait values overlap with several white and pink species as well. Our findings support the hypothesis that convergent evolution does not always proceed through comparative phenotypic divergence, but possibly through sorting of standing ancestral variation.

    

   more » « less
4. Incomplete reproductive isolation and low genetic differentiation despite floral divergence across varying geographic scales in Castilleja

   https://doi.org/10.1002/ajb2.1700  

   Wenzell, Katherine E. ; McDonnell, Angela J. ; Wickett, Norman J. ; Fant, Jeremie B. ; Skogen, Krissa A. ( July 2021 , American Journal of Botany)

   Divergence depends on the strength of selection and frequency of gene flow between taxa, while reproductive isolation relies on mating barriers and geographic distance. Less is known about how these processes interact at early stages of speciation. Here, we compared population‐level differentiation in floral phenotype and genetic sequence variation among recently divergedCastillejato explore patterns of diversification under different scenarios of reproductive isolation.

   Using target enrichment enabled by the Angiosperms353 probe set, we assessed genetic distance among 50 populations of fourCastillejaspecies. We investigated whether patterns of genetic divergence are explained by floral trait variation or geographic distance in two focal groups: the widespreadC. sessilifloraand the more restrictedC. purpureaspecies complex.

   We document thatC. sessilifloraand theC. purpureacomplex are characterized by high diversity in floral color across varying geographic scales. Despite phenotypic divergence, groups were not well supported in phylogenetic analyses, and little genetic differentiation was found across targeted Angiosperms353 loci. Nonetheless, a principal coordinate analysis of single nucleotide polymorphisms revealed differentiation withinC. sessilifloraacross floral morphs and geography and less differentiation among species of theC. purpureacomplex.

   Patterns of genetic distance inC. sessiliflorasuggest species cohesion maintained over long distances despite variation in floral traits. In theC. purpureacomplex, divergence in floral color across narrow geographic clines may be driven by recent selection on floral color. These contrasting patterns of floral and genetic differentiation reveal that divergence can arise via multiple eco‐evolutionary paths.

    

   more » « less
5. High sexual display trait diversity without measured genetic divergence in a montane hybrid zone involving young species ( Habronattus americanus subgroup, Araneae: Salticidae)

   https://doi.org/10.1093/isd/ixae001  

   Bougie, Tierney ; Brelsford, Alan ; Hedin, Marshal ; Esposito, ed., Lauren ( January 2024 , Insect Systematics and Diversity)

   Genetic introgression, allele exchange across species boundaries, is a commonly recognized feature of animal evolution. Under such a paradigm, contemporary contact zones provide first-hand insight into the geographic, phenotypic, and genetic details of introgression. Also, when mate choice phenotypes are conspicuous and variable in hybrids, contact zones provide potential insight into how sexual selection interacts with species boundary maintenance, particularly when postzygotic reproductive isolation is weak. The Habronattus americanus subgroup includes several recently evolved jumping spider species, with an estimated age of about 200,000 yr, and substantial evidence for hybridization and introgression. We explored a contact zone involving H. americanus (Keyserling, 1885) and H. kubai (Griswold, 1979) on Mount Shasta, CA, in alpine habitats that would have been unavailable (under ice) at the Last Glacial Maximum. We characterized morphological diversity within the contact zone, including the fine-scale geographic distribution of hybrid and parental individuals, and assessed genetic variation using ddRADseq data. Combined results indicate a lack of measured genomic differentiation between specimens with distinct morphologies, including individuals with phenotypes of the parental species. We identified a diverse array of hybrid morphologies, with phenotypic evidence for backcrossing, essentially forming a phenotypic bridge between parental taxa. The study area is characterized by more hybrid than parental individuals, with a significantly larger number of red-palped morphologies than white- and/or yellow-palped morphologies; the novel, white-palped phenotype is perhaps transgressive. Overall, these results contribute to a better understanding of the expected ebb and flow of lineage interactions during the early stages of speciation.

    

   more » « less