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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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Distribution of the alate and apterous A. gossypii samples according to the genetic clusters. The proportion of individuals is represented by sectors and the numbers of multilocus genotypes is shown in each sector in the four melon-growing areas according to the division into four genetic clusters.
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Figure 5: Distribution of the alate and apterous A. gossypii samples according to the genetic clusters. The proportion of individuals is represented by sectors and the numbers of multilocus genotypes is shown in each sector in the four melon-growing areas according to the division into four genetic clusters.

Mentions: We considered the distribution of the alate and apterous individuals according to the existence of the four genetic clusters A, X, Y and Z, within each of the four geographic areas (Figure 5). In the SE region, 70% of the alate individuals and 80% of the apterous individuals were assigned to cluster Y (the cucurbit cluster). In the SW region, 60% of the alate individuals and 80% of the apterous individuals were also assigned to the cucurbit cluster. In both the SE and SW areas, 20 to 25% of the individuals, either alate or apterous, belonged to cluster Z (the NM1 cluster). MLGs characteristic of cluster A were present among the alate individuals in the SW region (10%). In the W region, 5% of the alate and 28% of the apterous individuals had an MLG assigned to the cucurbit cluster, and 24 and 30% of the alate and apterous individuals, respectively, had an MLG assigned to the NM1 cluster; approximately 50% of the individuals, regardless of the morph, were assigned to cluster A. In the LA region, most of the alate and apterous individuals had an MLG assigned to the cucurbit cluster (91 to 100%), and these MLGs were not observed in the other growing areas. In all of the areas, 10 to 20% of the alate individuals but almost none of the apterous individuals exhibited an MLG from cluster X (containing MLGs that were characteristics of host races other than Cucurbitaceae). Moreover, in all of the areas, the number of individuals with an MLG assigned to the cucurbit cluster or to the NM1 cluster (known for its ability to colonise Cucurbitaceae) was significantly higher in the apterous populations than in the alate populations (Chi-square test, P < 0.0001). Notably, although the percentage of apterous individuals belonging to the Cucurbitaceae host race was equivalent in the SE and SW areas, the diversity among the cucurbit MLGs was considerably higher (Chi-square test, P < 0.0001) in the SE region (n = 93) than in the SW region (n = 28) (Figure 5).


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)

Distribution of the alate and apterous A. gossypii samples according to the genetic clusters. The proportion of individuals is represented by sectors and the numbers of multilocus genotypes is shown in each sector in the four melon-growing areas according to the division into four genetic clusters.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: Distribution of the alate and apterous A. gossypii samples according to the genetic clusters. The proportion of individuals is represented by sectors and the numbers of multilocus genotypes is shown in each sector in the four melon-growing areas according to the division into four genetic clusters.
Mentions: We considered the distribution of the alate and apterous individuals according to the existence of the four genetic clusters A, X, Y and Z, within each of the four geographic areas (Figure 5). In the SE region, 70% of the alate individuals and 80% of the apterous individuals were assigned to cluster Y (the cucurbit cluster). In the SW region, 60% of the alate individuals and 80% of the apterous individuals were also assigned to the cucurbit cluster. In both the SE and SW areas, 20 to 25% of the individuals, either alate or apterous, belonged to cluster Z (the NM1 cluster). MLGs characteristic of cluster A were present among the alate individuals in the SW region (10%). In the W region, 5% of the alate and 28% of the apterous individuals had an MLG assigned to the cucurbit cluster, and 24 and 30% of the alate and apterous individuals, respectively, had an MLG assigned to the NM1 cluster; approximately 50% of the individuals, regardless of the morph, were assigned to cluster A. In the LA region, most of the alate and apterous individuals had an MLG assigned to the cucurbit cluster (91 to 100%), and these MLGs were not observed in the other growing areas. In all of the areas, 10 to 20% of the alate individuals but almost none of the apterous individuals exhibited an MLG from cluster X (containing MLGs that were characteristics of host races other than Cucurbitaceae). Moreover, in all of the areas, the number of individuals with an MLG assigned to the cucurbit cluster or to the NM1 cluster (known for its ability to colonise Cucurbitaceae) was significantly higher in the apterous populations than in the alate populations (Chi-square test, P < 0.0001). Notably, although the percentage of apterous individuals belonging to the Cucurbitaceae host race was equivalent in the SE and SW areas, the diversity among the cucurbit MLGs was considerably higher (Chi-square test, P < 0.0001) in the SE region (n = 93) than in the SW region (n = 28) (Figure 5).

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