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What do spring migrants reveal about sex and host selection in the melon aphid?

Thomas S, Boissot N, Vanlerberghe-Masutti F - BMC Evol. Biol. (2012)

Bottom Line: Moreover, an analysis of the genetic composition of these alate and apterous populations in four geographic regions suggested differences in life-history strategies, such as host choice and reproductive mode, and questioned the common assertion that A. gossypii is an anholocyclic species throughout its distribution area, including Europe.Our results clearly demonstrate that the melon plant acts as a selective filter against the reproduction of non-specialised individuals.We showed that olfactory cues are unlikely to be decisive in natura for host recognition by spring-migrant aphid populations that are not specialised on Cucurbitaceae.

View Article: PubMed Central - HTML - PubMed

Affiliation: INRA, UMR1062 CBGP, F-34988 Montferrier-sur-Lez, France.

ABSTRACT

Background: Host plants exert considerable selective pressure on aphids because the plants constitute their feeding, mating and oviposition sites. Therefore, host specialisation in aphids evolves through selection of the behavioural and chemical mechanisms of host-plant location and recognition, and through metabolic adaptation to the phloem content of the host plant. How these adaptive traits evolve in an aphid species depends on the complexity of the annual life cycle of that species. The purpose of this field study was to determine how winged spring-migrant populations contribute to the evolution and maintenance of host specialisation in Aphis gossypii through host-plant choice and acceptance. We also assessed whether host-specialised genotypes corresponded exclusively to anholocyclic lineages regardless of the environmental conditions.

Results: The spring populations of cotton-melon aphids visiting newly planted melon crops exhibited an unexpectedly high level of genetic diversity that contrasted with the very low diversity characterising the host-specialised populations of this aphid species. This study illustrated in natura host-plant-selection pressure by showing the great differences in genetic diversity between the spring-migrant populations (alate aphids) and the melon-infesting populations (the apterous offspring of the alate aphids). Moreover, an analysis of the genetic composition of these alate and apterous populations in four geographic regions suggested differences in life-history strategies, such as host choice and reproductive mode, and questioned the common assertion that A. gossypii is an anholocyclic species throughout its distribution area, including Europe.

Conclusions: Our results clearly demonstrate that the melon plant acts as a selective filter against the reproduction of non-specialised individuals. We showed that olfactory cues are unlikely to be decisive in natura for host recognition by spring-migrant aphid populations that are not specialised on Cucurbitaceae. The agroecosystem structure and history of the four studied regions may have partially shaped the genetic structure of the spring-migrant populations of A. gossypii. Cucurbitaceae-specialised genotypes corresponded exclusively to anholocyclic lineages, regardless of the environmental conditions. However, some genotypes that were genetically close to the host-specialised genotypes and some genotypes that probably originated from wild plants had never been previously sampled; both were holocylic.

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Clonal diversity of the alate and apterous A. gossypii samples collected in 2008 and 2009 in the four melon-growing areas. R is the index of clonal richness, D* is the unbiased Simpson's complement and is the probability that two individuals chosen at random have different genotypes and can thus be considered as an exact measure of the clonal heterogeneity and V is the Simpson evenness index and is an equitability index that describes the distribution of the components and the relative amount of clones. The confidence intervals were derived from jack-knifing procedures (p = 0.05). ✮ V was not estimated because D* was maximal.
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Figure 3: Clonal diversity of the alate and apterous A. gossypii samples collected in 2008 and 2009 in the four melon-growing areas. R is the index of clonal richness, D* is the unbiased Simpson's complement and is the probability that two individuals chosen at random have different genotypes and can thus be considered as an exact measure of the clonal heterogeneity and V is the Simpson evenness index and is an equitability index that describes the distribution of the components and the relative amount of clones. The confidence intervals were derived from jack-knifing procedures (p = 0.05). ✮ V was not estimated because D* was maximal.

Mentions: The four SE locations had similar values for these indexes for both the alate populations and apterous populations (See additional file 1: figure S1). For example, in the alate populations sampled in 2004, the Simpson's evenness index (V) was 0.86 ± 0.05 in Saint-Andiol, 0.83 ± 0.03 in Montfavet and 0.81 ± 0.01 in Eyragues (with a confidence of 95%). No strong differences were observed in these three indexes over the different years in each location. The comparison between the alate and apterous populations showed a significant decrease in the clonal richness of the apterous populations, regardless of the location or the area (See additional file 1: figure S1). We decided to pool the data from the four locations within the SE area for further analyses. The comparison of the four areas (Figure 3) revealed that the lowest diversity of the alate populations was observed within the populations from the LA region and that the highest diversity was observed within the populations from the W region. An intermediate level of diversity was observed in the populations from the SE and SW areas. The clonal richness (R) was significantly higher in the SW populations than in the SE populations, while the Simpson's evenness index (V) was significantly higher in the populations sampled from the SE area than in the populations sampled from the SW area (no overlapping intervals of confidence at 5%, Figure 3). In all of the cases, a significant decrease in the clonal richness was observed from the alate to the apterous populations (Figure 3).


What do spring migrants reveal about sex and host selection in the melon aphid?

Thomas S, Boissot N, Vanlerberghe-Masutti F - BMC Evol. Biol. (2012)

Clonal diversity of the alate and apterous A. gossypii samples collected in 2008 and 2009 in the four melon-growing areas. R is the index of clonal richness, D* is the unbiased Simpson's complement and is the probability that two individuals chosen at random have different genotypes and can thus be considered as an exact measure of the clonal heterogeneity and V is the Simpson evenness index and is an equitability index that describes the distribution of the components and the relative amount of clones. The confidence intervals were derived from jack-knifing procedures (p = 0.05). ✮ V was not estimated because D* was maximal.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3368726&req=5

Figure 3: Clonal diversity of the alate and apterous A. gossypii samples collected in 2008 and 2009 in the four melon-growing areas. R is the index of clonal richness, D* is the unbiased Simpson's complement and is the probability that two individuals chosen at random have different genotypes and can thus be considered as an exact measure of the clonal heterogeneity and V is the Simpson evenness index and is an equitability index that describes the distribution of the components and the relative amount of clones. The confidence intervals were derived from jack-knifing procedures (p = 0.05). ✮ V was not estimated because D* was maximal.
Mentions: The four SE locations had similar values for these indexes for both the alate populations and apterous populations (See additional file 1: figure S1). For example, in the alate populations sampled in 2004, the Simpson's evenness index (V) was 0.86 ± 0.05 in Saint-Andiol, 0.83 ± 0.03 in Montfavet and 0.81 ± 0.01 in Eyragues (with a confidence of 95%). No strong differences were observed in these three indexes over the different years in each location. The comparison between the alate and apterous populations showed a significant decrease in the clonal richness of the apterous populations, regardless of the location or the area (See additional file 1: figure S1). We decided to pool the data from the four locations within the SE area for further analyses. The comparison of the four areas (Figure 3) revealed that the lowest diversity of the alate populations was observed within the populations from the LA region and that the highest diversity was observed within the populations from the W region. An intermediate level of diversity was observed in the populations from the SE and SW areas. The clonal richness (R) was significantly higher in the SW populations than in the SE populations, while the Simpson's evenness index (V) was significantly higher in the populations sampled from the SE area than in the populations sampled from the SW area (no overlapping intervals of confidence at 5%, Figure 3). In all of the cases, a significant decrease in the clonal richness was observed from the alate to the apterous populations (Figure 3).

Bottom Line: Moreover, an analysis of the genetic composition of these alate and apterous populations in four geographic regions suggested differences in life-history strategies, such as host choice and reproductive mode, and questioned the common assertion that A. gossypii is an anholocyclic species throughout its distribution area, including Europe.Our results clearly demonstrate that the melon plant acts as a selective filter against the reproduction of non-specialised individuals.We showed that olfactory cues are unlikely to be decisive in natura for host recognition by spring-migrant aphid populations that are not specialised on Cucurbitaceae.

View Article: PubMed Central - HTML - PubMed

Affiliation: INRA, UMR1062 CBGP, F-34988 Montferrier-sur-Lez, France.

ABSTRACT

Background: Host plants exert considerable selective pressure on aphids because the plants constitute their feeding, mating and oviposition sites. Therefore, host specialisation in aphids evolves through selection of the behavioural and chemical mechanisms of host-plant location and recognition, and through metabolic adaptation to the phloem content of the host plant. How these adaptive traits evolve in an aphid species depends on the complexity of the annual life cycle of that species. The purpose of this field study was to determine how winged spring-migrant populations contribute to the evolution and maintenance of host specialisation in Aphis gossypii through host-plant choice and acceptance. We also assessed whether host-specialised genotypes corresponded exclusively to anholocyclic lineages regardless of the environmental conditions.

Results: The spring populations of cotton-melon aphids visiting newly planted melon crops exhibited an unexpectedly high level of genetic diversity that contrasted with the very low diversity characterising the host-specialised populations of this aphid species. This study illustrated in natura host-plant-selection pressure by showing the great differences in genetic diversity between the spring-migrant populations (alate aphids) and the melon-infesting populations (the apterous offspring of the alate aphids). Moreover, an analysis of the genetic composition of these alate and apterous populations in four geographic regions suggested differences in life-history strategies, such as host choice and reproductive mode, and questioned the common assertion that A. gossypii is an anholocyclic species throughout its distribution area, including Europe.

Conclusions: Our results clearly demonstrate that the melon plant acts as a selective filter against the reproduction of non-specialised individuals. We showed that olfactory cues are unlikely to be decisive in natura for host recognition by spring-migrant aphid populations that are not specialised on Cucurbitaceae. The agroecosystem structure and history of the four studied regions may have partially shaped the genetic structure of the spring-migrant populations of A. gossypii. Cucurbitaceae-specialised genotypes corresponded exclusively to anholocyclic lineages, regardless of the environmental conditions. However, some genotypes that were genetically close to the host-specialised genotypes and some genotypes that probably originated from wild plants had never been previously sampled; both were holocylic.

Show MeSH
Related in: MedlinePlus