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Diversity-enhancing selection acts on a female reproductive protease family in four subspecies of Drosophila mojavensis. Genetics 2011; 187:865-76. [PMID: 21212232 DOI: 10.1534/genetics.110.124743] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Protein components of the Drosophila male ejaculate are critical modulators of reproductive success, several of which are known to evolve rapidly. Recent evidence of adaptive evolution in female reproductive tract proteins suggests this pattern may reflect sexual selection at the molecular level. Here we explore the evolutionary dynamics of a five-paralog gene family of female reproductive proteases within geographically isolated subspecies of Drosophila mojavensis. Remarkably, four of five paralogs show exceptionally low differentiation between subspecies and unusually structured haplotypes that suggest the retention of old polymorphisms. These gene genealogies are accompanied by deviations from neutrality consistent with diversifying selection. While diversifying selection has been observed among the reproductive molecules of mammals and marine invertebrates, our study provides the first evidence of this selective regime in any Drosophila reproductive protein, male or female.
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Jennings JH, Etges WJ. SPECIES HYBRIDS IN THE LABORATORY BUT NOT IN NATURE: A REANALYSIS OF PREMATING ISOLATION BETWEENDROSOPHILA ARIZONAEANDD. MOJAVENSIS. Evolution 2010; 64:587-98. [DOI: 10.1111/j.1558-5646.2009.00834.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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53
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Lou M, Golding GB. Assigning sequences to species in the absence of large interspecific differences. Mol Phylogenet Evol 2010; 56:187-94. [PMID: 20067837 DOI: 10.1016/j.ympev.2010.01.002] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 12/30/2009] [Accepted: 01/02/2010] [Indexed: 10/20/2022]
Abstract
Barcoding is an initiative to define a standard fragment of DNA to be used to assign unknown sequences to existing known species groups that have been pre-identified externally (by a taxonomist). Several methods have been described that attempt to place this assignment into a Bayesian statistical framework. Here we describe an algorithm that makes use of segregating sites and we examine how well these methods perform in the absence of an interspecific 'barcoding gap'. When a barcoding gap exists, that is when the data are clearly delimited, most methods perform well. Here we have used data from the Drosophila genus because this genus includes sibling species and the species relationships within this species while complex are, arguably, better understood than in any other group. The results show that the Bayesian methods perform well even in the absence of a barcoding gap. The sequences from Drosophila are correctly identified and only when the degree of incomplete lineage sorting is extreme in simulations or within the Drosophila species, do they fail in their identifications and even then, the "correct" species has a high posterior probability.
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Affiliation(s)
- Melanie Lou
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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54
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ZHAO KAI, DUAN ZIYUAN, PENG ZUOGANG, GUO SONGCHANG, LI JUNBING, HE SHUNPING, ZHAO XINQUAN. The youngest split in sympatric schizothoracine fish (Cyprinidae) is shaped by ecological adaptations in a Tibetan Plateau glacier lake. Mol Ecol 2009; 18:3616-28. [DOI: 10.1111/j.1365-294x.2009.04274.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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55
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Comparative genomics of Drosophila mtDNA: Novel features of conservation and change across functional domains and lineages. J Mol Evol 2009; 69:94-114. [PMID: 19533212 PMCID: PMC2895726 DOI: 10.1007/s00239-009-9255-0] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2009] [Revised: 05/06/2009] [Accepted: 05/28/2009] [Indexed: 12/22/2022]
Abstract
To gain insight on mitochondrial DNA (mtDNA) evolution, we assembled and analyzed the mitochondrial genomes of Drosophila erecta, D. ananassae, D. persimilis, D. willistoni, D. mojavensis, D. virilis and D. grimshawi together with the sequenced mtDNAs of the melanogaster subgroup. Genomic comparisons across the well-defined Drosophila phylogeny impart power for detecting conserved mtDNA regions that maintain metabolic function and regions that evolve uniquely on lineages. Evolutionary rate varies across intergenic regions of the mtDNA. Rapidly evolving intergenic regions harbor the majority of mitochondrial indel divergence. In contrast, patterns of nearly perfect conservation within intergenic regions reveal a refined set of nucleotides underlying the binding of transcription termination factors. Sequencing of 5' cDNA ends indicates that cytochrome C oxidase I (CoI) has a novel (T/C)CG start codon and that perfectly conserved regions upstream of two NADH dehydrogenase (ND) genes are transcribed and likely extend these protein sequences. Substitutions at synonymous sites in the Drosophila mitochondrial proteomes reflect a mutation process that is biased toward A and T nucleotides and differs between mtDNA strands. Differences in codon usage bias across genes reveal that weak selection at silent sites may offset the mutation bias. The mutation-selection balance at synonymous sites has also diverged between the Drosophila and Sophophora lineages. Rates of evolution are highly heterogeneous across the mitochondrial proteome, with ND accumulating many more amino acid substitutions than CO. These oxidative phosphorylation complex-specific rates of evolution vary across lineages and may reflect physiological and ecological change across the Drosophila phylogeny.
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56
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Bono JM, Markow TA. Post-zygotic isolation in cactophilic Drosophila: larval viability and adult life-history traits of D. mojavensis/D. arizonae hybrids. J Evol Biol 2009; 22:1387-95. [PMID: 19508411 DOI: 10.1111/j.1420-9101.2009.01753.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Drosophila mojavensis and Drosophila arizonae are cactophilic flies that have been used extensively in speciation studies. Incomplete premating isolation, evidence of reinforcement, and a lack of recent introgression between these species point to a potentially important role for post-zygotic isolating barriers in this system. Other than hybrid male sterility, however, post-zygotic isolation between D. mojavensis and D. arizonae has received little attention. In this study, we examined viability and life-history traits of D. mojavensis/D. arizonae F(1) hybrids from sympatric crosses. Specifically, we reared hybrids and purebreds on the natural host cacti of each parental species and compared viability, development time, thorax length, and desiccation resistance between hybrids and purebreds. Interestingly, hybrid females from both crosses performed similarly or even better than purebred females. In contrast, hybrid sons of D. arizonae mothers, in addition to being sterile, had shorter average thorax length than males of both parental species, and hybrid males from both crosses had substantially lower desiccation resistance than D. mojavensis males. The probable cost to hybridization for D. mojavensis females resulting from reduced desiccation resistance of hybrid sons may have been an important selective factor in the history of reinforcement for crosses involving these females.
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Affiliation(s)
- Jeremy M Bono
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA.
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57
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Pfeiler E, Castrezana S, Reed LK, Markow TA. Genetic, ecological and morphological differences among populations of the cactophilicDrosophila mojavensisfrom southwestern USA and northwestern Mexico, with descriptions of two new subspecies. J NAT HIST 2009. [DOI: 10.1080/00222930802610535] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Haselkorn TS, Markow TA, Moran NA. Multiple introductions of the Spiroplasma bacterial endosymbiont into Drosophila. Mol Ecol 2009; 18:1294-305. [PMID: 19226322 DOI: 10.1111/j.1365-294x.2009.04085.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Bacterial endosymbionts are common in insects and can have dramatic effects on their host's evolution. So far, the only heritable symbionts found in Drosophila have been Wolbachia and Spiroplasma. While the incidence and effects of Wolbachia have been studied extensively, the prevalence and significance of Spiroplasma infections in Drosophila are less clear. These small, gram-positive, helical bacteria infect a diverse array of plant and arthropod hosts, conferring a variety of fitness effects. Male-killing Spiroplasma are known from certain Drosophila species; however, in others, Spiroplasma appear not to affect sex ratio. Previous studies have identified different Spiroplasma haplotypes in Drosophila populations, although no extensive surveys have yet been reported. We used a multilocus sequence analysis to reconstruct a robust Spiroplasma endosymbiont phylogeny, assess genetic diversity, and look for evidence of recombination. Six loci were sequenced from over 65 Spiroplasma-infected individuals from nine different Drosophila species. Analysis of these sequences reveals at least five separate introductions of four phylogenetically distinct Spiroplasma haplotypes, indicating that more extensive sampling will likely reveal an even greater Spiroplasma endosymbiont diversity. Patterns of variation in Drosophila mitochondrial haplotypes in Spiroplasma-infected and uninfected flies imply imperfect vertical transmission in host populations and possible horizontal transmission.
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Affiliation(s)
- Tamara S Haselkorn
- Department of Ecology and Evolutionary Biology Biosciences, University of Arizona, Tucson, 85721-0088, USA.
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59
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Duplication, selection and gene conversion in a Drosophila mojavensis female reproductive protein family. Genetics 2009; 181:1451-65. [PMID: 19204376 DOI: 10.1534/genetics.108.099044] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Protein components of the Drosophila male ejaculate, several of which evolve rapidly, are critical modulators of reproductive success. Recent studies of female reproductive tract proteins indicate they also are extremely divergent between species, suggesting that reproductive molecules may coevolve between the sexes. Our current understanding of intersexual coevolution, however, is severely limited by the paucity of genetic and evolutionary studies on the female molecules involved. Physiological evidence of ejaculate-female coadaptation, paired with a promiscuous mating system, makes Drosophila mojavensis an exciting model system in which to study the evolution of reproductive proteins. Here we explore the evolutionary dynamics of a five-paralog gene family of female reproductive proteases within populations of D. mojavensis and throughout the repleta species group. We show that the proteins have experienced ongoing gene duplication and adaptive evolution and further exhibit dynamic patterns of pseudogenation, copy number variation, gene conversion, and selection within geographically isolated populations of D. mojavensis. The integration of these patterns in a single gene family has never before been documented in a reproductive protein.
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60
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Pfeiler E, Bitler BG, Castrezana S, Matzkin LM, Markow TA. Genetic diversification and demographic history of the cactophilic pseudoscorpion Dinocheirus arizonensis from the Sonoran Desert. Mol Phylogenet Evol 2008; 52:133-41. [PMID: 19166949 DOI: 10.1016/j.ympev.2008.12.020] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2008] [Revised: 12/18/2008] [Accepted: 12/23/2008] [Indexed: 11/28/2022]
Abstract
Sequence data from a segment of the mitochondrial cytochrome c oxidase subunit I (COI) gene were used to examine phylogenetic relationships, estimate gene flow and infer demographic history of the cactophilic chernetid pseudoscorpion, Dinocheirus arizonensis (Banks), from the Sonoran Desert. Phylogenetic trees resolved two clades of D. arizonensis, one from mainland Sonora, Mexico and southern Arizona (clade I) and the other from the Baja California peninsula and southern Arizona (clade II). The two clades were separated by a mean genetic distance (d) of approximately 2.6%. Hierarchical analysis of molecular variance indicated highly significant population structuring in D. arizonensis (overall Phi(ST)=0.860; P<0.0001), with 80% of the genetic variation distributed among the two clades. Most pairwise comparisons of Phi(ST) among populations within each clade, however, were not significant. The results suggest that phoretic dispersal on vagile cactophilic insects such as the neriid cactus fly Odontoloxozus longicornis (Coquillett) provides sufficient gene flow to offset the accumulation of unique haplotypes within each clade of the non-vagile pseudoscorpion. Preliminary results on dispersal capability of O. longicornis were consistent with this conclusion. Tests designed to reconstruct demographic history from sequence data indicated that both clades of D. arizonensis, as well as O. longicornis, have experienced historical population expansions. Potential barriers to gene flow that may have led to genetic isolation and diversification in clades I and II of D. arizonensis are discussed.
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Affiliation(s)
- Edward Pfeiler
- Centro de Investigación en Alimentación y Desarrollo, A.C., Unidad Guaymas, Apartado Postal 284, Guaymas, Sonora 85480, Mexico.
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61
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Reed LK, LaFlamme BA, Markow TA. Genetic architecture of hybrid male sterility in Drosophila: analysis of intraspecies variation for interspecies isolation. PLoS One 2008; 3:e3076. [PMID: 18728782 PMCID: PMC2517651 DOI: 10.1371/journal.pone.0003076] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Accepted: 08/07/2008] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND The genetic basis of postzygotic isolation is a central puzzle in evolutionary biology. Evolutionary forces causing hybrid sterility or inviability act on the responsible genes while they still are polymorphic, thus we have to study these traits as they arise, before isolation is complete. METHODOLOGY/PRINCIPAL FINDINGS Isofemale strains of D. mojavensis vary significantly in their production of sterile F(1) sons when females are crossed to D. arizonae males. We took advantage of the intraspecific polymorphism, in a novel design, to perform quantitative trait locus (QTL) mapping analyses directly on F(1) hybrid male sterility itself. We found that the genetic architecture of the polymorphism for hybrid male sterility (HMS) in the F(1) is complex, involving multiple QTL, epistasis, and cytoplasmic effects. CONCLUSIONS/SIGNIFICANCE The role of extensive intraspecific polymorphism, multiple QTL, and epistatic interactions in HMS in this young species pair shows that HMS is arising as a complex trait in this system. Directional selection alone would be unlikely to maintain polymorphism at multiple loci, thus we hypothesize that directional selection is unlikely to be the only evolutionary force influencing postzygotic isolation.
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Affiliation(s)
- Laura K Reed
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, USA.
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62
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Castrezana SJ, Markow TA. Sexual isolation and mating propensity among allopatric Drosophila mettleri populations. Behav Genet 2008; 38:437-45. [PMID: 18561017 DOI: 10.1007/s10519-008-9209-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2007] [Accepted: 05/20/2008] [Indexed: 10/21/2022]
Abstract
Drosophila mettleri is found in deserts of North America breeding in soil soaked by the juices of necrotic cacti. Saguaro (Carnegiea gigantea) and cardón (Pachycereus pringlei) are the usual host cacti in Mexico and Arizona, while prickly pear (Opuntia spp.) is used by an isolated population on Santa Catalina Island off the southern California Coast. Populations of D. mettleri show significant local genetic differentiation, especially when geographical isolation is coupled with host shifts. We tested for evidence of sexual isolation among allopatric populations of D. mettleri using a variety of choice and no-choice tests. Populations exhibited significant differences in mating propensity, which translated into significant deviations from random mating. While in some cases these deviations were consistent with sexual isolation, in others, negative assortative mating was observed. No relationship between degree of genetic differentiation and the appearance of sexual isolation was detected.
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Affiliation(s)
- Sergio J Castrezana
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA
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63
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Bono JM, Matzkin LM, Castrezana S, Markow TA. Molecular evolution and population genetics of two Drosophila mettleri cytochrome P450 genes involved in host plant utilization. Mol Ecol 2008; 17:3211-21. [PMID: 18510584 DOI: 10.1111/j.1365-294x.2008.03823.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding the genetic basis of adaptation is one of the primary goals of evolutionary biology. The evolution of xenobiotic resistance in insects has proven to be an especially suitable arena for studying the genetics of adaptation, and resistant phenotypes are known to result from both coding and regulatory changes. In this study, we examine the evolutionary history and population genetics of two Drosophila mettleri cytochrome P450 genes that are putatively involved in the detoxification of alkaloids present in two of its cactus hosts: saguaro (Carnegiea gigantea) and senita (Lophocereus schottii). Previous studies demonstrated that Cyp28A1 was highly up-regulated following exposure to rotting senita tissue while Cyp4D10 was highly up-regulated following exposure to rotting saguaro tissue. Here, we show that a subset of sites in Cyp28A1 experienced adaptive evolution specifically in the D. mettleri lineage. Moreover, neutrality tests in several populations were also consistent with a history of selection on Cyp28A1. In contrast, we did not find evidence for positive selection on Cyp4D10, although this certainly does not preclude its involvement in host plant use. A surprising result that emerged from our population genetic analyses was the presence of significant genetic differentiation between flies collected from different host plant species (saguaro and senita) at Organ Pipe National Monument, Arizona, USA. This preliminary evidence suggests that D. mettleri may have evolved into distinctive host races that specialize on different hosts, a possibility that warrants further investigation.
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Affiliation(s)
- Jeremy M Bono
- Department of Ecology and Evolutionary Biology, University of Arizona, 1041 E. Lowell Street, Tucson, AZ 85721, USA.
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64
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Bulazel KV, Ferreri GC, Eldridge MDB, O'Neill RJ. Species-specific shifts in centromere sequence composition are coincident with breakpoint reuse in karyotypically divergent lineages. Genome Biol 2008; 8:R170. [PMID: 17708770 PMCID: PMC2375000 DOI: 10.1186/gb-2007-8-8-r170] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2007] [Accepted: 08/20/2007] [Indexed: 11/12/2022] Open
Abstract
The evolution of three classes of centromere sequences across nine species of macropodine marsupials were compared with that of other genes, showing that each species has experienced differential expansion and contraction of individual classes. Background It has been hypothesized that rapid divergence in centromere sequences accompanies rapid karyotypic change during speciation. However, the reuse of breakpoints coincident with centromeres in the evolution of divergent karyotypes poses a potential paradox. In distantly related species where the same centromere breakpoints are used in the independent derivation of karyotypes, centromere-specific sequences may undergo convergent evolution rather than rapid sequence divergence. To determine whether centromere sequence composition follows the phylogenetic history of species evolution or patterns of convergent breakpoint reuse through chromosome evolution, we examined the phylogenetic trajectory of centromere sequences within a group of karyotypically diverse mammals, macropodine marsupials (wallabies, wallaroos and kangaroos). Results The evolution of three classes of centromere sequences across nine species within the genus Macropus (including Wallabia) were compared with the phylogenetic history of a mitochondrial gene, Cytochrome b (Cyt b), a nuclear gene, selenocysteine tRNA (TRSP), and the chromosomal histories of the syntenic blocks that define the different karyotype arrangements. Convergent contraction or expansion of predominant satellites is found to accompany specific karyotype rearrangements. The phylogenetic history of these centromere sequences includes the convergence of centromere composition in divergent species through convergent breakpoint reuse between syntenic blocks. Conclusion These data support the 'library hypothesis' of centromere evolution within this genus as each species possesses all three satellites yet each species has experienced differential expansion and contraction of individual classes. Thus, we have identified a correlation between the evolution of centromere satellite sequences, the reuse of syntenic breakpoints, and karyotype convergence in the context of a gene-based phylogeny.
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Affiliation(s)
- Kira V Bulazel
- Department of Molecular and Cell Biology, Mansfield Rd, University of Connecticut, Storrs, CT 06269, USA
| | - Gianni C Ferreri
- Department of Molecular and Cell Biology, Mansfield Rd, University of Connecticut, Storrs, CT 06269, USA
| | - Mark DB Eldridge
- Department of Biological Sciences, Macquarie University, NSW 2109, Australia
- Molecular Biology, Australian Museum, College St, Sydney, NSW 2010, Australia
| | - Rachel J O'Neill
- Department of Molecular and Cell Biology, Mansfield Rd, University of Connecticut, Storrs, CT 06269, USA
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The molecular basis of host adaptation in cactophilic Drosophila: molecular evolution of a glutathione S-transferase gene (GstD1) in Drosophila mojavensis. Genetics 2008; 178:1073-83. [PMID: 18245335 DOI: 10.1534/genetics.107.083287] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Drosophila mojavensis is a cactophilic fly endemic to the northwestern deserts of North America. This species includes four genetically isolated cactus host races each individually specializing on the necrotic tissues of a different cactus species. The necrosis of each cactus species provides the resident D. mojavensis populations with a distinct chemical environment. A previous investigation of the role of transcriptional variation in the adaptation of D. mojavensis to its hosts produced a set of candidate loci that are differentially expressed in response to host shifts, and among them was glutathione S-transferase D1 (GstD1). In both D. melanogaster and Anopheles gambiae, GstD1 has been implicated in the resistance of these species to the insecticide dichloro-diphenyl-trichloroethane (DDT). The pattern of sequence variation of the GstD1 locus from all four D. mojavensis populations, D. arizonae (sister species), and D. navojoa (outgroup) has been examined. The data suggest that in two populations of D. mojavensis GstD1 has gone through a period of adaptive amino acid evolution. Further analyses indicate that of the seven amino acid fixations that occurred in the D. mojavensis lineage, two of them occur in the active site pocket, potentially having a significant effect on substrate specificity and in the adaptation to alternative cactus hosts.
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Machado CA, Matzkin LM, Reed LK, Markow TA. Multilocus nuclear sequences reveal intra- and interspecific relationships among chromosomally polymorphic species of cactophilic Drosophila. Mol Ecol 2007; 16:3009-24. [PMID: 17614914 DOI: 10.1111/j.1365-294x.2007.03325.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Drosophila mojavensis and Drosophila arizonae, a pair of sibling species endemic to North America, constitute an important model system to study ecological genetics and the evolution of reproductive isolation. This species pair can produce fertile hybrids in some crosses and are sympatric in a large part of their ranges. Despite the potential for hybridization in nature, however, evidence of introgression has not been rigorously sought. Further, the evolutionary relationships within and among the geographically distant populations of the two species have not been characterized in detail using high-resolution molecular studies. Both species have six chromosomes: five large acrocentrics and one 'dot' chromosome. Fixed inversion differences between the species exist in three chromosomes (X, 2 and 3) while three are colinear (4, 5 and 6), suggesting that were introgression to occur, it would be most likely in the colinear chromosomes. We utilized nucleotide sequence variation at multiple loci on five chromosomes to test for evidence of introgression, and to test various scenarios for the evolutionary relationships of these two species and their populations. While we do not find evidence of recent introgression, loci in the colinear chromosomes appear to have participated in exchange in the past. We also found considerable population structure within both species. The level of differentiation discovered among D. arizonae populations was unexpectedly high and suggests that its populations, as well as those of D. mojavensis, may be themselves undergoing incipient speciation and merit further attention.
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Affiliation(s)
- Carlos A Machado
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
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67
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Pfeiler E, Erez T, Hurtado LA, Markow TA. Genetic differentiation and demographic history in Drosophila pachea from the Sonoran Desert. Hereditas 2007; 144:63-74. [PMID: 17567443 DOI: 10.1111/j.2007.0018-0661.01997.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Genetic variation at six microsatellite DNA loci and a segment of the mitochondrial cytochrome oxidase subunit I (COI) locus was used to estimate gene flow, population structure, and demographic history in the cactophilic Drosophila pachea from the Sonoran Desert of North America, a species that shows a strict association with its senita host cactus (genus Lophocereus). For microsatellite analyses, thirteen populations of D. pachea were sampled, five in mainland Mexico and the southwestern USA, and eight on the Baja California (Baja) peninsula, covering essentially the entire range of the species. Analysis of molecular variance (AMOVA) of microsatellite data revealed that populations from both the mainland and the Baja peninsula generally showed little structure, although there were a few exceptions, suggesting some local differentiation and restriction of gene flow within both regions. Pairwise comparisons of F(ST) among each of the mainland and Baja populations showed evidence of both panmixia and population subdivision. AMOVA performed on grouped populations from both the mainland and Baja, however, revealed significant partitioning of genetic variation among the two regions, but no partitioning among localities within each region. Bayesian skyline analyses of the COI data set, consisting of four mainland and seven peninsular populations, revealed population expansions dating to the Pleistocene or late Pliocene in D. pachea from both regions, although regional differences were seen in the estimated timing of the expansions and in changes in effective population size over time.
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Affiliation(s)
- Edward Pfeiler
- Centro de Investigación en Alimentación y Desarrollo, A.C., Unidad Guaymas, Guaymas, Sonora, Mexico.
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68
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Matzkin LM, Watts TD, Bitler BG, Machado CA, Markow TA. Functional genomics of cactus host shifts in Drosophila mojavensis. Mol Ecol 2007; 15:4635-43. [PMID: 17107489 DOI: 10.1111/j.1365-294x.2006.03102.x] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Understanding the genetic basis of adaptation to novel environments remains one of the major challenges confronting evolutionary biologists. While newly developed genomic approaches hold considerable promise for addressing this overall question, the relevant tools have not often been available in the most ecologically interesting organisms. Our study organism, Drosophila mojavensis, is a cactophilic Sonoran Desert endemic utilizing four different cactus hosts across its geographical range. Its well-known ecology makes it an attractive system in which to study the evolution of gene expression during adaptation. As a cactophile, D. mojavensis oviposits in the necrotic tissues of cacti, therefore exposing larvae and even adults to the varied and toxic compounds of rotting cacti. We have developed a cDNA microarray of D. mojavensis to examine gene expression associated with cactus host use. Using a population from the Baja California population we examined gene expression differences of third instar larvae when reared in two chemically distinct cactus hosts, agria (Stenocereus gummosus, native host) vs. organpipe (Stenocereus thurberi, alternative host). We have observed differential gene expression associated with cactus host use in genes involved in metabolism and detoxification.
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Affiliation(s)
- Luciano M Matzkin
- Department of Ecology and Evolutionary Biology, University of Arizona, PO Box 210088, Tucson, AZ 85721-0088, USA.
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