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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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Results from the Structure program showing the estimated proportion of assignment of the multilocus genotypes. a. Assignment of the 632 multilocus genotypes to the clusters with K = 2 and K = 4 and b. assignment of the 203 multilocus genotypes of cluster A into 6 sub-clusters.
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Figure 4: Results from the Structure program showing the estimated proportion of assignment of the multilocus genotypes. a. Assignment of the 632 multilocus genotypes to the clusters with K = 2 and K = 4 and b. assignment of the 203 multilocus genotypes of cluster A into 6 sub-clusters.

Mentions: When K = 2, 203 MLGs of the 596 that were detected in our samples were assigned to cluster A and represented only 5% of the aphids, and 393 MLGs were assigned to cluster B, accounting for 95% of the aphids (Figure 4a). The Fst value between the clusters was 0.254. None of the MLGs that were grouped into cluster A had been described before. When K = 4, cluster A still consisted of the 203 MLGs, but cluster B was divided into three sub-clusters (Figure 4a). Cluster X consisted of 133 MLGs, representing only 4% of the individuals; cluster X also encompassed MLGs that had been previously collected on Solanum spp., pepper, cotton, citrus, strawberry and Hibiscus spp. plants. Cluster Y contained 163 MLGs, representing 73.5% of the individuals sampled and 11 MLGs that were characteristic of aphids from the Cucurbitaceae host race. Therefore, cluster Y was called the cucurbit cluster. Cluster Z, containing 97 MLGs representing 18% of the individuals sampled, contained NM1 and NM1-like MLGs that also characterised aphids from Cucurbitaceae hosts along with MLGs that were previously identified on cotton (Ivo) and Hibiscus spp. (Hib4) hosts. Therefore, cluster Z was called the NM1 cluster.


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)

Results from the Structure program showing the estimated proportion of assignment of the multilocus genotypes. a. Assignment of the 632 multilocus genotypes to the clusters with K = 2 and K = 4 and b. assignment of the 203 multilocus genotypes of cluster A into 6 sub-clusters.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: Results from the Structure program showing the estimated proportion of assignment of the multilocus genotypes. a. Assignment of the 632 multilocus genotypes to the clusters with K = 2 and K = 4 and b. assignment of the 203 multilocus genotypes of cluster A into 6 sub-clusters.
Mentions: When K = 2, 203 MLGs of the 596 that were detected in our samples were assigned to cluster A and represented only 5% of the aphids, and 393 MLGs were assigned to cluster B, accounting for 95% of the aphids (Figure 4a). The Fst value between the clusters was 0.254. None of the MLGs that were grouped into cluster A had been described before. When K = 4, cluster A still consisted of the 203 MLGs, but cluster B was divided into three sub-clusters (Figure 4a). Cluster X consisted of 133 MLGs, representing only 4% of the individuals; cluster X also encompassed MLGs that had been previously collected on Solanum spp., pepper, cotton, citrus, strawberry and Hibiscus spp. plants. Cluster Y contained 163 MLGs, representing 73.5% of the individuals sampled and 11 MLGs that were characteristic of aphids from the Cucurbitaceae host race. Therefore, cluster Y was called the cucurbit cluster. Cluster Z, containing 97 MLGs representing 18% of the individuals sampled, contained NM1 and NM1-like MLGs that also characterised aphids from Cucurbitaceae hosts along with MLGs that were previously identified on cotton (Ivo) and Hibiscus spp. (Hib4) hosts. Therefore, cluster Z was called the NM1 cluster.

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