Papers by Pierre-Francois PELISSON
Physiological Entomology, 2012
Insects comprise relevant biological models for investigating nutrient acquisition and allocation... more Insects comprise relevant biological models for investigating nutrient acquisition and allocation processes in the context of life-history ecology and evolution. However, empirical investigations are still partly limited by the lack of availability of simple methods for simultaneously estimating the four major energetic components (i.e. lipids, free sugars, glycogen and proteins) in the same individual. In the present work, we validate a fast, reproducible and cheap method for overcoming this problem that uses different solvents successively. First, proteins are solubilized in a phosphate-lysis buffer and then quantified according to the classical Bradford assay procedure. In a second step, a chloroform-methanol mixture is added to the aqueous phase, which allows assay of the total lipid fraction, as well as the free sugars and glycogen in the same insect homogenate. In addition, a micro-separation procedure is adapted to partition the total lipids into neutral (mainly stored lipids) and polar (mainly structural lipids) components. Although these assays are conducted sequentially in the same individual, the sensitivity of our method remains high: the estimated amount of each energetic compartment does not differ from that obtained with former, partial methods. Our method should thus largely improve our knowledge about nutrient acquisition and allocation among insects not only in laboratory-reared individuals, but also in animals caught in the wild. Descriptions and recommendations are given at each step of the protocol to adapt the procedure to various insect species. Finally, to prevent misinterpretation of data generated in accordance with this protocol, the limits of our method are discussed in the light of life-history studies. To assess nutrient contents of individuals, most ecological studies rely on the colourimetric methods first proposed by van Handel. These assays were initially developed to quantify both glycogen and free sugars in one individual (van Handel, 1985a) and lipids in another individual . More recently, these methods have been modified to simultaneously estimate, in the same individual, the three main categories
Functional Ecology, 2012
1. The evolution of strategies of resource acquisition and allocation is often considered to be c... more 1. The evolution of strategies of resource acquisition and allocation is often considered to be closely dependent on the degree of environmental variability. Within this framework, female insects that experience stochastic fluctuations in the availability of their egg-laying sites in time or space can be expected to be fully synovigenic (i.e. they start maturing eggs after a delay once reaching adulthood), which allows them to tailor their reproductive investment to variations in the resource. Proovigenic females (that have most of their eggs already mature at the onset of their adult life, which corresponds to a capital breeding strategy), on the contrary, should have an advantage when the availability of the egg-laying sites is predictable. There is, however, a dearth of empirical studies testing these predictions.
Because of their significant impact on forests, tree-killing bark beetles have been widely studie... more Because of their significant impact on forests, tree-killing bark beetles have been widely studied at epidemic
population densities. However, bark-beetle outbreaks emerge from populations at low, endemic
levels, where population maintenance and growth depend on scarce, ephemeral resources such as lightning-
struck trees, weakened and suppressed standing trees or wind-felled trees, depending on the species.
The longevity of these resources strongly influences population dynamics, but very little is known
in this respect.
We tested the hypothesis that the driving factor reducing the availability of fallen trees is the decrease
of their nutritional quality. We analysed the qualitative changes of the phloem of spruces artificially
uprooted at different times (2–17 month before the experiment started) and simultaneously exposed
during the same flight season to attacks of the major forest pest in Eurasia, Ips typographus.We also measured
the impact of resources’ decay on the insects’ fecundity and the quality of their offspring.
Our results show a surprisingly slow decrease of phloem quality over time. The beetles could develop
on the oldest (17 month-old) resources with no significant differences in terms of fecundity, progeny
body mass and global energy acquisition.
Although they retain their nutritional quality over long periods, transient resources are exposed to
other factors that make them rapidly unsuitable for I. typographus. We suggest that interspecific competition
is probably the most influential of them, and acts as a major driver in the beetles’ race for new
resources.
There is empirical evidence of many diversified ways for energy to be acquired and allocated to r... more There is empirical evidence of many diversified ways for energy to be acquired and allocated to reproduction, notably with strategies ranging from strict income breeding (females fueling their gametes with energy gained concomitantly during reproduction) to strict capital breeding (females storing nutrients prior reproduction). Until now, the question of whether diversification of these strategies might impact the way communities are organized has not been considered.
1. The evolution of strategies of resource acquisition and allocation is often considered to be c... more 1. The evolution of strategies of resource acquisition and allocation is often considered to be closely dependent on the degree of environmental variability. Within this framework, female insects that experience stochastic fluctuations in the availability of their egg-laying sites in time or space can be expected to be fully synovigenic (i.e. they start maturing eggs after a delay once reaching adulthood), which allows them to tailor their reproductive investment to variations in the resource. Proovigenic females (that have most of their eggs already mature at the onset of their adult life, which corresponds to a capital breeding strategy), on the contrary, should have an advantage when the availability of the egg-laying sites is predictable. There is, however, a dearth of empirical studies testing these predictions.
2. Here, we tested the hypothesis that four phytophagous insect species of the genus Curculio, which coexist on a strongly fluctuating resource that they exploit for egg-laying purposes, would all be synovigenic as strict proovigeny should be counterselected. The resource consisted of the acorns of oak trees Quercus spp. We conducted field surveys to determine the date of adult emergence in each weevil species and the ability of newly emerged females to produce eggs. We also analysed the stable isotope profile of wild-caught females as a proxy for their feeding activity. Finally, we tested females under laboratory conditions for their ability to produce mature eggs when not fed and investigated whether dietary intake influenced their longevity.
3. Taken together, our results show that, contrary to the usual predictions, the four weevil species that were all exposed to a markedly fluctuating environment exhibited sharply contrasting strategies of resource acquisition and allocation: three species were synovigenic, while the fourth was proovigenic. Unexpectedly, therefore, our findings show that a strict capital breeding species might not always be counterselected in a temporally stochastic environment. They further suggest that fluctuations in the environment should not promote a sole, optimal strategy of energy acquisition and allocation to reproduction but instead should favour their diversification.
Background
One major challenge in understanding how biodiversity is organized is finding out whet... more Background
One major challenge in understanding how biodiversity is organized is finding out whether communities of competing species are shaped exclusively by species-level differences in ecological traits (niche theory), exclusively by random processes (neutral theory of biodiversity), or by both processes simultaneously. Communities of species competing for a pulsed resource are a suitable system for testing these theories: due to marked fluctuations in resource availability, the theories yield very different predictions about the timing of resource use and the synchronization of the population dynamics between the competing species. Accordingly, we explored mechanisms that might promote the local coexistence of phytophagous insects (four sister species of the genus Curculio) competing for oak acorns, a pulsed resource.
Methodology/Principal Findings
We analyzed the time partitioning of the exploitation of oak acorns by the four weevil species in two independent communities, and we assessed the level of synchronization in their population dynamics. In accordance with the niche theory, overall these species exhibited marked time partitioning of resource use, both within a given year and between different years owing to different dormancy strategies between species, as well as distinct demographic patterns. Two of the four weevil species, however, consistently exploited the resource during the same period of the year, exhibited a similar dormancy pattern, and did not show any significant difference in their population dynamics.
Conclusions/Significance
The marked time partitioning of the resource use appears as a keystone of the coexistence of these competing insect species, except for two of them which are demographically nearly equivalent. Communities of consumers of pulsed resources thus seem to offer a promising avenue for developing a unifying theory of biodiversity in fluctuating environments which might predict the co-occurrence, within the same community, of species that are ecologically either very similar, or very different.
Insects comprise relevant biological models for investigating nutrient acquisition and allocation... more Insects comprise relevant biological models for investigating nutrient acquisition and allocation processes in the context of life-history ecology and evolution. However, empirical investigations are still partly limited by the lack of availability of simple methods for simultaneously estimating the four major energetic components (i.e. lipids, free sugars, glycogen and proteins) in the same individual. In the present work, we validate a fast, reproducible and cheap method for overcoming this problem that uses different solvents successively. First, proteins are solubilized in a phosphate-lysis buffer and then quantified according to the classical Bradford assay procedure. In a second step, a chloroform–methanol mixture is added to the aqueous phase, which allows assay of the total lipid fraction, as well as the free sugars and glycogen in the same insect homogenate. In addition, a micro-separation procedure is adapted to partition the total lipids into neutral (mainly stored lipids) and polar (mainly structural lipids) components. Although these assays are conducted sequentially in the same individual, the sensitivity of our method remains high: the estimated amount of each energetic compartment does not differ from that obtained with former, partial methods. Our method should thus largely improve our knowledge about nutrient acquisition and allocation among insects not only in laboratory-reared individuals, but also in animals caught in the wild. Descriptions and recommendations are given at each step of the protocol to adapt the procedure to various insect species. Finally, to prevent misinterpretation of data generated in accordance with this protocol, the limits of our method are discussed in the light of life-history studies.
Aquatic Microbial Ecology. 54:71-82., 2009
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Papers by Pierre-Francois PELISSON
population densities. However, bark-beetle outbreaks emerge from populations at low, endemic
levels, where population maintenance and growth depend on scarce, ephemeral resources such as lightning-
struck trees, weakened and suppressed standing trees or wind-felled trees, depending on the species.
The longevity of these resources strongly influences population dynamics, but very little is known
in this respect.
We tested the hypothesis that the driving factor reducing the availability of fallen trees is the decrease
of their nutritional quality. We analysed the qualitative changes of the phloem of spruces artificially
uprooted at different times (2–17 month before the experiment started) and simultaneously exposed
during the same flight season to attacks of the major forest pest in Eurasia, Ips typographus.We also measured
the impact of resources’ decay on the insects’ fecundity and the quality of their offspring.
Our results show a surprisingly slow decrease of phloem quality over time. The beetles could develop
on the oldest (17 month-old) resources with no significant differences in terms of fecundity, progeny
body mass and global energy acquisition.
Although they retain their nutritional quality over long periods, transient resources are exposed to
other factors that make them rapidly unsuitable for I. typographus. We suggest that interspecific competition
is probably the most influential of them, and acts as a major driver in the beetles’ race for new
resources.
2. Here, we tested the hypothesis that four phytophagous insect species of the genus Curculio, which coexist on a strongly fluctuating resource that they exploit for egg-laying purposes, would all be synovigenic as strict proovigeny should be counterselected. The resource consisted of the acorns of oak trees Quercus spp. We conducted field surveys to determine the date of adult emergence in each weevil species and the ability of newly emerged females to produce eggs. We also analysed the stable isotope profile of wild-caught females as a proxy for their feeding activity. Finally, we tested females under laboratory conditions for their ability to produce mature eggs when not fed and investigated whether dietary intake influenced their longevity.
3. Taken together, our results show that, contrary to the usual predictions, the four weevil species that were all exposed to a markedly fluctuating environment exhibited sharply contrasting strategies of resource acquisition and allocation: three species were synovigenic, while the fourth was proovigenic. Unexpectedly, therefore, our findings show that a strict capital breeding species might not always be counterselected in a temporally stochastic environment. They further suggest that fluctuations in the environment should not promote a sole, optimal strategy of energy acquisition and allocation to reproduction but instead should favour their diversification.
One major challenge in understanding how biodiversity is organized is finding out whether communities of competing species are shaped exclusively by species-level differences in ecological traits (niche theory), exclusively by random processes (neutral theory of biodiversity), or by both processes simultaneously. Communities of species competing for a pulsed resource are a suitable system for testing these theories: due to marked fluctuations in resource availability, the theories yield very different predictions about the timing of resource use and the synchronization of the population dynamics between the competing species. Accordingly, we explored mechanisms that might promote the local coexistence of phytophagous insects (four sister species of the genus Curculio) competing for oak acorns, a pulsed resource.
Methodology/Principal Findings
We analyzed the time partitioning of the exploitation of oak acorns by the four weevil species in two independent communities, and we assessed the level of synchronization in their population dynamics. In accordance with the niche theory, overall these species exhibited marked time partitioning of resource use, both within a given year and between different years owing to different dormancy strategies between species, as well as distinct demographic patterns. Two of the four weevil species, however, consistently exploited the resource during the same period of the year, exhibited a similar dormancy pattern, and did not show any significant difference in their population dynamics.
Conclusions/Significance
The marked time partitioning of the resource use appears as a keystone of the coexistence of these competing insect species, except for two of them which are demographically nearly equivalent. Communities of consumers of pulsed resources thus seem to offer a promising avenue for developing a unifying theory of biodiversity in fluctuating environments which might predict the co-occurrence, within the same community, of species that are ecologically either very similar, or very different.
population densities. However, bark-beetle outbreaks emerge from populations at low, endemic
levels, where population maintenance and growth depend on scarce, ephemeral resources such as lightning-
struck trees, weakened and suppressed standing trees or wind-felled trees, depending on the species.
The longevity of these resources strongly influences population dynamics, but very little is known
in this respect.
We tested the hypothesis that the driving factor reducing the availability of fallen trees is the decrease
of their nutritional quality. We analysed the qualitative changes of the phloem of spruces artificially
uprooted at different times (2–17 month before the experiment started) and simultaneously exposed
during the same flight season to attacks of the major forest pest in Eurasia, Ips typographus.We also measured
the impact of resources’ decay on the insects’ fecundity and the quality of their offspring.
Our results show a surprisingly slow decrease of phloem quality over time. The beetles could develop
on the oldest (17 month-old) resources with no significant differences in terms of fecundity, progeny
body mass and global energy acquisition.
Although they retain their nutritional quality over long periods, transient resources are exposed to
other factors that make them rapidly unsuitable for I. typographus. We suggest that interspecific competition
is probably the most influential of them, and acts as a major driver in the beetles’ race for new
resources.
2. Here, we tested the hypothesis that four phytophagous insect species of the genus Curculio, which coexist on a strongly fluctuating resource that they exploit for egg-laying purposes, would all be synovigenic as strict proovigeny should be counterselected. The resource consisted of the acorns of oak trees Quercus spp. We conducted field surveys to determine the date of adult emergence in each weevil species and the ability of newly emerged females to produce eggs. We also analysed the stable isotope profile of wild-caught females as a proxy for their feeding activity. Finally, we tested females under laboratory conditions for their ability to produce mature eggs when not fed and investigated whether dietary intake influenced their longevity.
3. Taken together, our results show that, contrary to the usual predictions, the four weevil species that were all exposed to a markedly fluctuating environment exhibited sharply contrasting strategies of resource acquisition and allocation: three species were synovigenic, while the fourth was proovigenic. Unexpectedly, therefore, our findings show that a strict capital breeding species might not always be counterselected in a temporally stochastic environment. They further suggest that fluctuations in the environment should not promote a sole, optimal strategy of energy acquisition and allocation to reproduction but instead should favour their diversification.
One major challenge in understanding how biodiversity is organized is finding out whether communities of competing species are shaped exclusively by species-level differences in ecological traits (niche theory), exclusively by random processes (neutral theory of biodiversity), or by both processes simultaneously. Communities of species competing for a pulsed resource are a suitable system for testing these theories: due to marked fluctuations in resource availability, the theories yield very different predictions about the timing of resource use and the synchronization of the population dynamics between the competing species. Accordingly, we explored mechanisms that might promote the local coexistence of phytophagous insects (four sister species of the genus Curculio) competing for oak acorns, a pulsed resource.
Methodology/Principal Findings
We analyzed the time partitioning of the exploitation of oak acorns by the four weevil species in two independent communities, and we assessed the level of synchronization in their population dynamics. In accordance with the niche theory, overall these species exhibited marked time partitioning of resource use, both within a given year and between different years owing to different dormancy strategies between species, as well as distinct demographic patterns. Two of the four weevil species, however, consistently exploited the resource during the same period of the year, exhibited a similar dormancy pattern, and did not show any significant difference in their population dynamics.
Conclusions/Significance
The marked time partitioning of the resource use appears as a keystone of the coexistence of these competing insect species, except for two of them which are demographically nearly equivalent. Communities of consumers of pulsed resources thus seem to offer a promising avenue for developing a unifying theory of biodiversity in fluctuating environments which might predict the co-occurrence, within the same community, of species that are ecologically either very similar, or very different.