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Evolutionary lability of a complex life cycle in the aphid genus Brachycaudus.

Emmanuelle J, Gwenaelle G, Armelle Cd - BMC Evol. Biol. (2010)

Bottom Line: There have been many shifts in feeding behaviour but we found no significant correlation between life cycle changes and changes in diet.Life cycle changes, whether corresponding to the loss or acquisition of a primary host, necessarily promote speciation, by inducing shifts of the reproductive phase on different plants.We suggest that the evolutionary lability of life cycle may have driven speciation events in the Brachycaudus genus.

View Article: PubMed Central - HTML - PubMed

Affiliation: INRA, UMR CBGP (INRA/IRD/Cirad/Montpellier SupAgro), Campus international de Baillarguet, CS 30016, F-34988 Montferrier-sur-Lez cedex, France. jousseli@supagro.inra.fr

ABSTRACT

Background: Most aphid species complete their life cycle on the same set of host-plant species, but some (heteroecious species) alternate between different hosts, migrating from primary (woody) to secondary (herbaceous) host plants. The evolutionary processes behind the evolution of this complex life cycle have often been debated. One widely accepted scenario is that heteroecy evolved from monoecy on woody host plants. Several shifts towards monoecy on herbaceous plants have subsequently occurred and resulted in the radiation of aphids. Host alternation would have persisted in some cases due to developmental constraints preventing aphids from shifting their entire life cycle to herbaceous hosts (which are thought to be more favourable). According to this scenario, if aphids lose their primary host during evolution they should not regain it. The genus Brachycaudus includes species with all the types of life cycle (monoecy on woody plants, heteroecy, monoecy on herbs). We used this genus to test hypotheses concerning the evolution of life cycles in aphids.

Results: Phylogenetic investigation and character reconstruction suggest that life cycle is evolutionary labile in the genus. Though ancestral character states can be ambiguous depending on optimization methods, all analyses suggest that transitions from monoecy on herbs towards heteroecy have occurred several times. Transitions from heteroecy towards monoecy, are also likely. There have been many shifts in feeding behaviour but we found no significant correlation between life cycle changes and changes in diet.

Conclusions: The transitions from monoecy on herbs towards heteroecy observed in this study go against a widely accepted evolutionary scenario: aphids in the genus Brachycaudus seem to be able to recapture their supposedly ancestral woody host. This suggests that the determinants of host alternation are probably not as complicated as previously thought. Definitive proofs of the lability of life cycle in Brachycaudus will necessitate investigation of these determinants. Life cycle changes, whether corresponding to the loss or acquisition of a primary host, necessarily promote speciation, by inducing shifts of the reproductive phase on different plants. We suggest that the evolutionary lability of life cycle may have driven speciation events in the Brachycaudus genus.

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Phylogenetic reconstruction of Brachycaudus. ML topology and branch lengths are shown. Pp and ML bootstrap values are indicated above nodes. Taxonomic subdivisions (following [2]) are indicated on the left.
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Figure 1: Phylogenetic reconstruction of Brachycaudus. ML topology and branch lengths are shown. Pp and ML bootstrap values are indicated above nodes. Taxonomic subdivisions (following [2]) are indicated on the left.

Mentions: We obtained a well resolved phylogenetic tree (Fig. 1), in which most of the nodes were supported by high ML bootstrap and pp values. The phylogenetic relationships obtained here were very similar to those reported previously [23,24], and the addition of a nuclear marker confirmed the previously reported phylogenetic relationships between the species sampled. Two additional species from Central Asia, Brachycaudus pilosus (Mordvilko, 1929) and Brachycaudus cerasicola (Mordvilko, 1929), not included in previous reconstructions, clustered together with relatively long branches as a sister group to the species of the subgenus Acaudus. However, support for this branch was poor, suggesting possible long branch attraction [25].


Evolutionary lability of a complex life cycle in the aphid genus Brachycaudus.

Emmanuelle J, Gwenaelle G, Armelle Cd - BMC Evol. Biol. (2010)

Phylogenetic reconstruction of Brachycaudus. ML topology and branch lengths are shown. Pp and ML bootstrap values are indicated above nodes. Taxonomic subdivisions (following [2]) are indicated on the left.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2958166&req=5

Figure 1: Phylogenetic reconstruction of Brachycaudus. ML topology and branch lengths are shown. Pp and ML bootstrap values are indicated above nodes. Taxonomic subdivisions (following [2]) are indicated on the left.
Mentions: We obtained a well resolved phylogenetic tree (Fig. 1), in which most of the nodes were supported by high ML bootstrap and pp values. The phylogenetic relationships obtained here were very similar to those reported previously [23,24], and the addition of a nuclear marker confirmed the previously reported phylogenetic relationships between the species sampled. Two additional species from Central Asia, Brachycaudus pilosus (Mordvilko, 1929) and Brachycaudus cerasicola (Mordvilko, 1929), not included in previous reconstructions, clustered together with relatively long branches as a sister group to the species of the subgenus Acaudus. However, support for this branch was poor, suggesting possible long branch attraction [25].

Bottom Line: There have been many shifts in feeding behaviour but we found no significant correlation between life cycle changes and changes in diet.Life cycle changes, whether corresponding to the loss or acquisition of a primary host, necessarily promote speciation, by inducing shifts of the reproductive phase on different plants.We suggest that the evolutionary lability of life cycle may have driven speciation events in the Brachycaudus genus.

View Article: PubMed Central - HTML - PubMed

Affiliation: INRA, UMR CBGP (INRA/IRD/Cirad/Montpellier SupAgro), Campus international de Baillarguet, CS 30016, F-34988 Montferrier-sur-Lez cedex, France. jousseli@supagro.inra.fr

ABSTRACT

Background: Most aphid species complete their life cycle on the same set of host-plant species, but some (heteroecious species) alternate between different hosts, migrating from primary (woody) to secondary (herbaceous) host plants. The evolutionary processes behind the evolution of this complex life cycle have often been debated. One widely accepted scenario is that heteroecy evolved from monoecy on woody host plants. Several shifts towards monoecy on herbaceous plants have subsequently occurred and resulted in the radiation of aphids. Host alternation would have persisted in some cases due to developmental constraints preventing aphids from shifting their entire life cycle to herbaceous hosts (which are thought to be more favourable). According to this scenario, if aphids lose their primary host during evolution they should not regain it. The genus Brachycaudus includes species with all the types of life cycle (monoecy on woody plants, heteroecy, monoecy on herbs). We used this genus to test hypotheses concerning the evolution of life cycles in aphids.

Results: Phylogenetic investigation and character reconstruction suggest that life cycle is evolutionary labile in the genus. Though ancestral character states can be ambiguous depending on optimization methods, all analyses suggest that transitions from monoecy on herbs towards heteroecy have occurred several times. Transitions from heteroecy towards monoecy, are also likely. There have been many shifts in feeding behaviour but we found no significant correlation between life cycle changes and changes in diet.

Conclusions: The transitions from monoecy on herbs towards heteroecy observed in this study go against a widely accepted evolutionary scenario: aphids in the genus Brachycaudus seem to be able to recapture their supposedly ancestral woody host. This suggests that the determinants of host alternation are probably not as complicated as previously thought. Definitive proofs of the lability of life cycle in Brachycaudus will necessitate investigation of these determinants. Life cycle changes, whether corresponding to the loss or acquisition of a primary host, necessarily promote speciation, by inducing shifts of the reproductive phase on different plants. We suggest that the evolutionary lability of life cycle may have driven speciation events in the Brachycaudus genus.

Show MeSH
Related in: MedlinePlus