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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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Related in: MedlinePlus

Life cycle evolution shown on one Bayesian species tree. Pie charts at nodes show the% of trees for which the character state at this node was identified as the uniquely best state under MP optimisation (the percentage of equivocal reconstructions include reconstructions that did not yield a single best state for the node concerned, even if one state was more likely than any other): (a) life cycle evolution with facultative heteroecious species considered to be heteroecious; (b) life cycle evolution with facultative heteroecious species considered to be monoecious on trees. ML optimization under the 6 parameter model suggested that all character states were equally likely at all nodes of interest (nodes 1 to 12).
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Figure 3: Life cycle evolution shown on one Bayesian species tree. Pie charts at nodes show the% of trees for which the character state at this node was identified as the uniquely best state under MP optimisation (the percentage of equivocal reconstructions include reconstructions that did not yield a single best state for the node concerned, even if one state was more likely than any other): (a) life cycle evolution with facultative heteroecious species considered to be heteroecious; (b) life cycle evolution with facultative heteroecious species considered to be monoecious on trees. ML optimization under the 6 parameter model suggested that all character states were equally likely at all nodes of interest (nodes 1 to 12).

Mentions: Ancestral state reconstruction by MP, ML and stochastic mapping are summarised in Fig. 3 and 4 and Tables 1-2-3.


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

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

Life cycle evolution shown on one Bayesian species tree. Pie charts at nodes show the% of trees for which the character state at this node was identified as the uniquely best state under MP optimisation (the percentage of equivocal reconstructions include reconstructions that did not yield a single best state for the node concerned, even if one state was more likely than any other): (a) life cycle evolution with facultative heteroecious species considered to be heteroecious; (b) life cycle evolution with facultative heteroecious species considered to be monoecious on trees. ML optimization under the 6 parameter model suggested that all character states were equally likely at all nodes of interest (nodes 1 to 12).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Life cycle evolution shown on one Bayesian species tree. Pie charts at nodes show the% of trees for which the character state at this node was identified as the uniquely best state under MP optimisation (the percentage of equivocal reconstructions include reconstructions that did not yield a single best state for the node concerned, even if one state was more likely than any other): (a) life cycle evolution with facultative heteroecious species considered to be heteroecious; (b) life cycle evolution with facultative heteroecious species considered to be monoecious on trees. ML optimization under the 6 parameter model suggested that all character states were equally likely at all nodes of interest (nodes 1 to 12).
Mentions: Ancestral state reconstruction by MP, ML and stochastic mapping are summarised in Fig. 3 and 4 and Tables 1-2-3.

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