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Evidence for gene flow between two sympatric mealybug species (Insecta; Coccoidea; Pseudococcidae).

Kol-Maimon H, Ghanim M, Franco JC, Mendel Z - PLoS ONE (2014)

Bottom Line: In the present study we found evidence of gene flow between two sympatric, genetically related scale insect species--the citrus mealybug Planococcus citri (Risso) and the vine mealybug Planococcus ficus (Signoret).Our results showed attraction to P. ficus pheromones of all tested populations of P. citri males but not vice versa.We offer two hypotheses for these results. 1) The occurrence of phenotypic and genotypic traits of P. ficus in P. citri populations may be attributed to both ancient and contemporary gene flow between their populations; and 2) we cannot rule out that an ancient sympatric speciation by which P. ficus emerged from P. citri might have led to the present situation of shared traits between these species.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology, Volcani Center (ARO), Bet Dagan, Israel.

ABSTRACT
Occurrence of inter-species hybrids in natural populations might be evidence of gene flow between species. In the present study we found evidence of gene flow between two sympatric, genetically related scale insect species--the citrus mealybug Planococcus citri (Risso) and the vine mealybug Planococcus ficus (Signoret). These species can be distinguished by morphological, behavioral, and molecular traits. We employed the sex pheromones of the two respective species to study their different patterns of male attraction. We also used nuclear ITS2 (internal transcribed spacer 2) and mitochondrial COI (Cytochrome c oxidase sub unit 1) DNA sequences to characterize populations of the two species, in order to demonstrate the outcome of a possible gene flow between feral populations of the two species. Our results showed attraction to P. ficus pheromones of all tested populations of P. citri males but not vice versa. Furthermore, ITS2 sequences revealed the presence of 'hybrid females' among P. citri populations but not among those of P. ficus. 'hybrid females' from P. citri populations identified as P. citri females according to COI sequences. We offer two hypotheses for these results. 1) The occurrence of phenotypic and genotypic traits of P. ficus in P. citri populations may be attributed to both ancient and contemporary gene flow between their populations; and 2) we cannot rule out that an ancient sympatric speciation by which P. ficus emerged from P. citri might have led to the present situation of shared traits between these species. In light of these findings we also discuss the origin of the studied species and the importance of the pherotype phenomenon as a tool with which to study genetic relationships between congener scale insects.

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Pherotype frequency distribution among males whose mothers (gravid females) were sampled from various locations (see Table 1).The males were divided into four groups: (1) F- males – attracted to one or both P. ficus pheromones; (2) C- males – attracted only to P. citri pheromone; (3) FC- males – attracted to P. citri pheromone and also to one or both of P. ficus pheromones; (4) N- males – not attracted to any of the tested pheromones. Unless otherwise specified, the sampled hosts originated from Israel. The numbers preceding the host names are the serial numbers shown in Table 2; the numbers in parentheses are the numbers of tested males per tested population. The species of the populations were determined by COI sequencing and comparison with gene bank references (P. ficus: JN120845, EU250573, DQ238220; P. citri: AB439517, AF483204).
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pone-0088433-g002: Pherotype frequency distribution among males whose mothers (gravid females) were sampled from various locations (see Table 1).The males were divided into four groups: (1) F- males – attracted to one or both P. ficus pheromones; (2) C- males – attracted only to P. citri pheromone; (3) FC- males – attracted to P. citri pheromone and also to one or both of P. ficus pheromones; (4) N- males – not attracted to any of the tested pheromones. Unless otherwise specified, the sampled hosts originated from Israel. The numbers preceding the host names are the serial numbers shown in Table 2; the numbers in parentheses are the numbers of tested males per tested population. The species of the populations were determined by COI sequencing and comparison with gene bank references (P. ficus: JN120845, EU250573, DQ238220; P. citri: AB439517, AF483204).

Mentions: Male pherotypes and their distributions among the sampled populations from diverse locations and various host plants, arranged according to mealybug species are displayed in Fig. 2. All examined P. citri populations included male pherotypes that were attracted to either P. citri or P. ficus pheromones, or both. Males attracted solely to the sex pheromone of P. ficus were detected in 20 out of the 23 tested populations of P. citri. In all tested populations of each species considerable numbers of males were indifferent to all three tested pheromones, i.e., they were N pherotype. Among P. citri populations, an average of 29.8% of the males (range, 11–54%) were C pherotype, i.e., attracted to P. citri pheromone only; 39.4% of the males (range, 14–66%) were FC, i.e., attracted to both P. citri and P. ficus pheromones; 9.3% of the males (range, 0–13%) were F pherotype, i.e., attracted only to P. ficus pheromones; and the remaining 21.4% (range, 5–56%) were N pherotype, i.e., showing no attraction to either of the tested pheromones. All 11 examined P. ficus populations consisted of male pherotypes that were attracted to P. ficus pheromones (LS, LI or both). On average, 70.4% (range, 52–83%) of males of the P. ficus populations were F pherotype and the remaining 29.6% (range, 17–48%) were N pherotype. Pearson contingency analysis showed that pherotype distributions differed significantly between the P. citri populations (P<0.0001; χ2 = 310.7 between hosts; P<0.0001; χ2 = 291.8 between origins) and within P. ficus populations (P<0.001; χ2 = 10.8 between hosts; P<0.0001; χ2 = 49.7 between origins), but a significantly larger distance was found between species (P<0.0001; χ2 = 1793) than within species. Pearson contingency analysis further showed a larger variance or heterogeneity within the P. citri group than within the P. ficus group, probably because of higher pherotype variability among males of the former group.


Evidence for gene flow between two sympatric mealybug species (Insecta; Coccoidea; Pseudococcidae).

Kol-Maimon H, Ghanim M, Franco JC, Mendel Z - PLoS ONE (2014)

Pherotype frequency distribution among males whose mothers (gravid females) were sampled from various locations (see Table 1).The males were divided into four groups: (1) F- males – attracted to one or both P. ficus pheromones; (2) C- males – attracted only to P. citri pheromone; (3) FC- males – attracted to P. citri pheromone and also to one or both of P. ficus pheromones; (4) N- males – not attracted to any of the tested pheromones. Unless otherwise specified, the sampled hosts originated from Israel. The numbers preceding the host names are the serial numbers shown in Table 2; the numbers in parentheses are the numbers of tested males per tested population. The species of the populations were determined by COI sequencing and comparison with gene bank references (P. ficus: JN120845, EU250573, DQ238220; P. citri: AB439517, AF483204).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3921159&req=5

pone-0088433-g002: Pherotype frequency distribution among males whose mothers (gravid females) were sampled from various locations (see Table 1).The males were divided into four groups: (1) F- males – attracted to one or both P. ficus pheromones; (2) C- males – attracted only to P. citri pheromone; (3) FC- males – attracted to P. citri pheromone and also to one or both of P. ficus pheromones; (4) N- males – not attracted to any of the tested pheromones. Unless otherwise specified, the sampled hosts originated from Israel. The numbers preceding the host names are the serial numbers shown in Table 2; the numbers in parentheses are the numbers of tested males per tested population. The species of the populations were determined by COI sequencing and comparison with gene bank references (P. ficus: JN120845, EU250573, DQ238220; P. citri: AB439517, AF483204).
Mentions: Male pherotypes and their distributions among the sampled populations from diverse locations and various host plants, arranged according to mealybug species are displayed in Fig. 2. All examined P. citri populations included male pherotypes that were attracted to either P. citri or P. ficus pheromones, or both. Males attracted solely to the sex pheromone of P. ficus were detected in 20 out of the 23 tested populations of P. citri. In all tested populations of each species considerable numbers of males were indifferent to all three tested pheromones, i.e., they were N pherotype. Among P. citri populations, an average of 29.8% of the males (range, 11–54%) were C pherotype, i.e., attracted to P. citri pheromone only; 39.4% of the males (range, 14–66%) were FC, i.e., attracted to both P. citri and P. ficus pheromones; 9.3% of the males (range, 0–13%) were F pherotype, i.e., attracted only to P. ficus pheromones; and the remaining 21.4% (range, 5–56%) were N pherotype, i.e., showing no attraction to either of the tested pheromones. All 11 examined P. ficus populations consisted of male pherotypes that were attracted to P. ficus pheromones (LS, LI or both). On average, 70.4% (range, 52–83%) of males of the P. ficus populations were F pherotype and the remaining 29.6% (range, 17–48%) were N pherotype. Pearson contingency analysis showed that pherotype distributions differed significantly between the P. citri populations (P<0.0001; χ2 = 310.7 between hosts; P<0.0001; χ2 = 291.8 between origins) and within P. ficus populations (P<0.001; χ2 = 10.8 between hosts; P<0.0001; χ2 = 49.7 between origins), but a significantly larger distance was found between species (P<0.0001; χ2 = 1793) than within species. Pearson contingency analysis further showed a larger variance or heterogeneity within the P. citri group than within the P. ficus group, probably because of higher pherotype variability among males of the former group.

Bottom Line: In the present study we found evidence of gene flow between two sympatric, genetically related scale insect species--the citrus mealybug Planococcus citri (Risso) and the vine mealybug Planococcus ficus (Signoret).Our results showed attraction to P. ficus pheromones of all tested populations of P. citri males but not vice versa.We offer two hypotheses for these results. 1) The occurrence of phenotypic and genotypic traits of P. ficus in P. citri populations may be attributed to both ancient and contemporary gene flow between their populations; and 2) we cannot rule out that an ancient sympatric speciation by which P. ficus emerged from P. citri might have led to the present situation of shared traits between these species.

View Article: PubMed Central - PubMed

Affiliation: Department of Entomology, Volcani Center (ARO), Bet Dagan, Israel.

ABSTRACT
Occurrence of inter-species hybrids in natural populations might be evidence of gene flow between species. In the present study we found evidence of gene flow between two sympatric, genetically related scale insect species--the citrus mealybug Planococcus citri (Risso) and the vine mealybug Planococcus ficus (Signoret). These species can be distinguished by morphological, behavioral, and molecular traits. We employed the sex pheromones of the two respective species to study their different patterns of male attraction. We also used nuclear ITS2 (internal transcribed spacer 2) and mitochondrial COI (Cytochrome c oxidase sub unit 1) DNA sequences to characterize populations of the two species, in order to demonstrate the outcome of a possible gene flow between feral populations of the two species. Our results showed attraction to P. ficus pheromones of all tested populations of P. citri males but not vice versa. Furthermore, ITS2 sequences revealed the presence of 'hybrid females' among P. citri populations but not among those of P. ficus. 'hybrid females' from P. citri populations identified as P. citri females according to COI sequences. We offer two hypotheses for these results. 1) The occurrence of phenotypic and genotypic traits of P. ficus in P. citri populations may be attributed to both ancient and contemporary gene flow between their populations; and 2) we cannot rule out that an ancient sympatric speciation by which P. ficus emerged from P. citri might have led to the present situation of shared traits between these species. In light of these findings we also discuss the origin of the studied species and the importance of the pherotype phenomenon as a tool with which to study genetic relationships between congener scale insects.

Show MeSH