Limits...
Dispersal strategies of phytophagous insects at a local scale: adaptive potential of aphids in an agricultural environment.

Lombaert E, Boll R, Lapchin L - BMC Evol. Biol. (2006)

Bottom Line: The spread of agriculture greatly modified the selective pressures exerted by plants on phytophagous insects, by providing these insects with a high-level resource, structured in time and space.The life history, behavioural and physiological traits of some insect species may have evolved in response to these changes, allowing them to crowd on crops and to become agricultural pests.Dispersal, which is one of these traits, is a key concept in evolutionary biology but has been over-simplified in most theoretical studies.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unité de Lutte Biologique, INRA, 06903 Sophia-Antipolis, France. lombaert@antibes.inra.fr

ABSTRACT

Background: The spread of agriculture greatly modified the selective pressures exerted by plants on phytophagous insects, by providing these insects with a high-level resource, structured in time and space. The life history, behavioural and physiological traits of some insect species may have evolved in response to these changes, allowing them to crowd on crops and to become agricultural pests. Dispersal, which is one of these traits, is a key concept in evolutionary biology but has been over-simplified in most theoretical studies. We evaluated the impact of the local-scale dispersal strategy of phytophagous insects on their fitness, using an individual-based model to simulate population dynamics and dispersal between leaves and plants, by walking and flying, of the aphid Aphis gossypii, a major agricultural pest, in a melon field. We compared the optimal values for dispersal parameters in the model with the corresponding observed values in experimental trials.

Results: We show that the rates of walking and flying disperser production on leaves were the most important traits determining the fitness criteria, whereas dispersal distance and the clustering of flying dispersers on the target plant had no effect. We further show that the effect of dispersal parameters on aphid fitness depended strongly on plant characteristics.

Conclusion: Parameters defining the dispersal strategies of aphids at a local scale are key components of the fitness of these insects and may thus be essential in the adaptation to agricultural environments that are structured in space and time. Moreover, the fact that the effect of dispersal parameters on aphid fitness depends strongly on plant characteristics suggests that traits defining aphid dispersal strategies may be a cornerstone of host-plant specialization.

Show MeSH

Related in: MedlinePlus

Observed leaf-scale dispersal rates. Observed leaf-scale dispersal rates (points) of walking dispersers mw(n) and flying dispersers mf(n) during experiment 1, expressed in terms of the total number of aphids on a given leaf n. The line shows the values predicted by nonlinear regression analysis (see methods).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC1622755&req=5

Figure 1: Observed leaf-scale dispersal rates. Observed leaf-scale dispersal rates (points) of walking dispersers mw(n) and flying dispersers mf(n) during experiment 1, expressed in terms of the total number of aphids on a given leaf n. The line shows the values predicted by nonlinear regression analysis (see methods).

Mentions: From Experiment 1 (see methods), estimated values of dispersal rate parameters were Aw = 0.0238 and Bw = 0.01 for walking dispersers (F2, 165 = 597.66; P < 10-4), and Af = 2.16E-9 and Bf = 1.97 for flying dispersers (F2, 165 = 387.71; P < 10-4) (Fig. 1). The exponent parameter Bw was not significantly different from 0 (95% CI: [-0.07; 0.09]). The rate mw(n) (see methods, eq. 4) can thus be considered to be independent of aphid density. In contrast, the rate mf(n) (see methods, eq. 5) increased strongly with the number of aphids on the source plant. We compared the distribution of dispersing apterous aphids on the target leaves with a uniform distribution in which half the aphids settled on each of the two leaves, by carrying out a Chi-squared test for every day and plant with more than 20 apterous dispersers. Eleven times in twelve, the numbers of aphids on the upper and lower target leaves differed significantly, with a 5% type 1 error threshold. Moreover, there were always more aphids moving towards the third leaf than towards the first leaf (means of 82 % vs. 18 %; sign test: P < 0.0005). Thus, the dispersal of walking aphids was preferentially towards the younger of the two target leaves.


Dispersal strategies of phytophagous insects at a local scale: adaptive potential of aphids in an agricultural environment.

Lombaert E, Boll R, Lapchin L - BMC Evol. Biol. (2006)

Observed leaf-scale dispersal rates. Observed leaf-scale dispersal rates (points) of walking dispersers mw(n) and flying dispersers mf(n) during experiment 1, expressed in terms of the total number of aphids on a given leaf n. The line shows the values predicted by nonlinear regression analysis (see methods).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1622755&req=5

Figure 1: Observed leaf-scale dispersal rates. Observed leaf-scale dispersal rates (points) of walking dispersers mw(n) and flying dispersers mf(n) during experiment 1, expressed in terms of the total number of aphids on a given leaf n. The line shows the values predicted by nonlinear regression analysis (see methods).
Mentions: From Experiment 1 (see methods), estimated values of dispersal rate parameters were Aw = 0.0238 and Bw = 0.01 for walking dispersers (F2, 165 = 597.66; P < 10-4), and Af = 2.16E-9 and Bf = 1.97 for flying dispersers (F2, 165 = 387.71; P < 10-4) (Fig. 1). The exponent parameter Bw was not significantly different from 0 (95% CI: [-0.07; 0.09]). The rate mw(n) (see methods, eq. 4) can thus be considered to be independent of aphid density. In contrast, the rate mf(n) (see methods, eq. 5) increased strongly with the number of aphids on the source plant. We compared the distribution of dispersing apterous aphids on the target leaves with a uniform distribution in which half the aphids settled on each of the two leaves, by carrying out a Chi-squared test for every day and plant with more than 20 apterous dispersers. Eleven times in twelve, the numbers of aphids on the upper and lower target leaves differed significantly, with a 5% type 1 error threshold. Moreover, there were always more aphids moving towards the third leaf than towards the first leaf (means of 82 % vs. 18 %; sign test: P < 0.0005). Thus, the dispersal of walking aphids was preferentially towards the younger of the two target leaves.

Bottom Line: The spread of agriculture greatly modified the selective pressures exerted by plants on phytophagous insects, by providing these insects with a high-level resource, structured in time and space.The life history, behavioural and physiological traits of some insect species may have evolved in response to these changes, allowing them to crowd on crops and to become agricultural pests.Dispersal, which is one of these traits, is a key concept in evolutionary biology but has been over-simplified in most theoretical studies.

View Article: PubMed Central - HTML - PubMed

Affiliation: Unité de Lutte Biologique, INRA, 06903 Sophia-Antipolis, France. lombaert@antibes.inra.fr

ABSTRACT

Background: The spread of agriculture greatly modified the selective pressures exerted by plants on phytophagous insects, by providing these insects with a high-level resource, structured in time and space. The life history, behavioural and physiological traits of some insect species may have evolved in response to these changes, allowing them to crowd on crops and to become agricultural pests. Dispersal, which is one of these traits, is a key concept in evolutionary biology but has been over-simplified in most theoretical studies. We evaluated the impact of the local-scale dispersal strategy of phytophagous insects on their fitness, using an individual-based model to simulate population dynamics and dispersal between leaves and plants, by walking and flying, of the aphid Aphis gossypii, a major agricultural pest, in a melon field. We compared the optimal values for dispersal parameters in the model with the corresponding observed values in experimental trials.

Results: We show that the rates of walking and flying disperser production on leaves were the most important traits determining the fitness criteria, whereas dispersal distance and the clustering of flying dispersers on the target plant had no effect. We further show that the effect of dispersal parameters on aphid fitness depended strongly on plant characteristics.

Conclusion: Parameters defining the dispersal strategies of aphids at a local scale are key components of the fitness of these insects and may thus be essential in the adaptation to agricultural environments that are structured in space and time. Moreover, the fact that the effect of dispersal parameters on aphid fitness depends strongly on plant characteristics suggests that traits defining aphid dispersal strategies may be a cornerstone of host-plant specialization.

Show MeSH
Related in: MedlinePlus