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Hybridization and the spread of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae), in the northwestern United States.

Arcella T, Hood GR, Powell TH, Sim SB, Yee WL, Schwarz D, Egan SP, Goughnour RB, Smith JJ, Feder JL - Evol Appl (2015)

Bottom Line: Allele frequencies for seven microsatellites in R. pomonella were more 'R. zephyria-like' in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria.However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA.Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Notre Dame Notre Dame, IN, USA.

ABSTRACT
Hybridization may be an important process interjecting variation into insect populations enabling host plant shifts and the origin of new economic pests. Here, we examine whether hybridization between the native snowberry-infesting fruit fly Rhagoletis zephyria (Snow) and the introduced quarantine pest R. pomonella (Walsh) is occurring and may aid the spread of the latter into more arid commercial apple-growing regions of central Washington state, USA. Results for 19 microsatellites implied hybridization occurring at a rate of 1.44% per generation between the species. However, there was no evidence for increased hybridization in central Washington. Allele frequencies for seven microsatellites in R. pomonella were more 'R. zephyria-like' in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria. However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA. Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population. The dynamics of hybridization are therefore complex and nuanced for R. pomonella, with various causes and factors, including introgression for a portion, but not all of the genome, potentially contributing to the pest insect's spread.

No MeSH data available.


Related in: MedlinePlus

Association between mean allele frequency difference for 19 microsatellite loci between R. zephyria and R. pomonella populations at each of the nine paired sites plotted against each pairs geographic distance to the Tampico unincorporated community near Yakima, WA. Best fit line added to illustrate association. Note: the mean allele frequency difference at the Klickitat site was based on only 17 loci.
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fig04: Association between mean allele frequency difference for 19 microsatellite loci between R. zephyria and R. pomonella populations at each of the nine paired sites plotted against each pairs geographic distance to the Tampico unincorporated community near Yakima, WA. Best fit line added to illustrate association. Note: the mean allele frequency difference at the Klickitat site was based on only 17 loci.

Mentions: Microsatellite allele frequency differences between R. pomonella and R. zephyria populations across the nine paired sites were significantly related to geographic distance to Tampico near Yakima in central WA (Table 1, Fig. 4). Seven loci designated p4, p7, p16, p18, p25, p46, and p80, as well as the overall pattern for all 19 loci scored in the study, displayed significant trends for black hawthorn flies to become more ‘snowberry-like’ in their frequencies with geographic proximity to Yakima (Table 1, Fig. 4). As mean July to October precipitation also decreases with proximity to Yakima, overall microsatellite genetic distance for black hawthorn flies was also significantly correlated with rainfall (r = 0.729, P = 0.026, df = 8), consistent with the desiccation hypothesis. Mean allele frequency differences were also strongly correlated with summer high temperatures (r = −0.752, P = 0.019, df = 8) and winter low temperatures (r = 0.958, P < 0.0001, df = 8). The seven significant loci displaying a relationship with distance to Yakima were distributed across all five of the chromosomes for which genetic markers were scored (Table 1), implying that the pattern was not restricted to just one particular region of the genome. The increased genetic similarity of R. pomonella to R. zephyria was also reflected in the Burbank and Yakima black hawthorn populations (sites 8 and 9) being closest to snowberry flies in the genetic distance network (Fig. 2). However, allele frequencies for the remaining 12 microsatellites did not differ significantly with geographic distance, with two loci (p66 and p70) having negative, but not significant, regression coefficients (Table 1). Also, the seven significant loci described above also differed significantly between R. pomonella and R. zephyria Burbank and Yakima in central WA (Table S3). Moreover, with the exception of locus p16, every microsatellite possessed at least one private allele present in R. zephyria, but not in any of the nine co-occurring R. pomonella populations scored, even for those loci displaying significant frequency convergence between the two species with geographic proximity to Yakima. In addition, there were a total of 41 instances in which an allele was present at a microsatellite locus in only two of the total of 18 host-associated populations surveyed in the study. If introgression was appreciable between local R. pomonella and R. zephyria populations, then we would expect to observe several instances in which the rare allele was shared between the taxa at sympatric sites and not present anywhere else. However, in only one of the 41 cases was this so, which was lower than the expectation of 1.2 (= [9/306] × 41). Consequently, while the microsatellites implied hybridization, gene flow, and a degree of genetic converge between R. zephyria and R. pomonella approaching central WA, there was also evidence for introgression being restricted between the species despite hybridization.


Hybridization and the spread of the apple maggot fly, Rhagoletis pomonella (Diptera: Tephritidae), in the northwestern United States.

Arcella T, Hood GR, Powell TH, Sim SB, Yee WL, Schwarz D, Egan SP, Goughnour RB, Smith JJ, Feder JL - Evol Appl (2015)

Association between mean allele frequency difference for 19 microsatellite loci between R. zephyria and R. pomonella populations at each of the nine paired sites plotted against each pairs geographic distance to the Tampico unincorporated community near Yakima, WA. Best fit line added to illustrate association. Note: the mean allele frequency difference at the Klickitat site was based on only 17 loci.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4561572&req=5

fig04: Association between mean allele frequency difference for 19 microsatellite loci between R. zephyria and R. pomonella populations at each of the nine paired sites plotted against each pairs geographic distance to the Tampico unincorporated community near Yakima, WA. Best fit line added to illustrate association. Note: the mean allele frequency difference at the Klickitat site was based on only 17 loci.
Mentions: Microsatellite allele frequency differences between R. pomonella and R. zephyria populations across the nine paired sites were significantly related to geographic distance to Tampico near Yakima in central WA (Table 1, Fig. 4). Seven loci designated p4, p7, p16, p18, p25, p46, and p80, as well as the overall pattern for all 19 loci scored in the study, displayed significant trends for black hawthorn flies to become more ‘snowberry-like’ in their frequencies with geographic proximity to Yakima (Table 1, Fig. 4). As mean July to October precipitation also decreases with proximity to Yakima, overall microsatellite genetic distance for black hawthorn flies was also significantly correlated with rainfall (r = 0.729, P = 0.026, df = 8), consistent with the desiccation hypothesis. Mean allele frequency differences were also strongly correlated with summer high temperatures (r = −0.752, P = 0.019, df = 8) and winter low temperatures (r = 0.958, P < 0.0001, df = 8). The seven significant loci displaying a relationship with distance to Yakima were distributed across all five of the chromosomes for which genetic markers were scored (Table 1), implying that the pattern was not restricted to just one particular region of the genome. The increased genetic similarity of R. pomonella to R. zephyria was also reflected in the Burbank and Yakima black hawthorn populations (sites 8 and 9) being closest to snowberry flies in the genetic distance network (Fig. 2). However, allele frequencies for the remaining 12 microsatellites did not differ significantly with geographic distance, with two loci (p66 and p70) having negative, but not significant, regression coefficients (Table 1). Also, the seven significant loci described above also differed significantly between R. pomonella and R. zephyria Burbank and Yakima in central WA (Table S3). Moreover, with the exception of locus p16, every microsatellite possessed at least one private allele present in R. zephyria, but not in any of the nine co-occurring R. pomonella populations scored, even for those loci displaying significant frequency convergence between the two species with geographic proximity to Yakima. In addition, there were a total of 41 instances in which an allele was present at a microsatellite locus in only two of the total of 18 host-associated populations surveyed in the study. If introgression was appreciable between local R. pomonella and R. zephyria populations, then we would expect to observe several instances in which the rare allele was shared between the taxa at sympatric sites and not present anywhere else. However, in only one of the 41 cases was this so, which was lower than the expectation of 1.2 (= [9/306] × 41). Consequently, while the microsatellites implied hybridization, gene flow, and a degree of genetic converge between R. zephyria and R. pomonella approaching central WA, there was also evidence for introgression being restricted between the species despite hybridization.

Bottom Line: Allele frequencies for seven microsatellites in R. pomonella were more 'R. zephyria-like' in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria.However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA.Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Notre Dame Notre Dame, IN, USA.

ABSTRACT
Hybridization may be an important process interjecting variation into insect populations enabling host plant shifts and the origin of new economic pests. Here, we examine whether hybridization between the native snowberry-infesting fruit fly Rhagoletis zephyria (Snow) and the introduced quarantine pest R. pomonella (Walsh) is occurring and may aid the spread of the latter into more arid commercial apple-growing regions of central Washington state, USA. Results for 19 microsatellites implied hybridization occurring at a rate of 1.44% per generation between the species. However, there was no evidence for increased hybridization in central Washington. Allele frequencies for seven microsatellites in R. pomonella were more 'R. zephyria-like' in central Washington, suggesting that genes conferring resistance to desiccation may be adaptively introgressing from R. zephyria. However, in only one case was the putatively introgressing allele from R. zephyria not found in R. pomonella in the eastern USA. Thus, many of the alleles changing in frequency may have been prestanding in the introduced R. pomonella population. The dynamics of hybridization are therefore complex and nuanced for R. pomonella, with various causes and factors, including introgression for a portion, but not all of the genome, potentially contributing to the pest insect's spread.

No MeSH data available.


Related in: MedlinePlus