We report experiments using two closely related species of alysiine braconids directed at underst... more We report experiments using two closely related species of alysiine braconids directed at understanding how gregarious development evolved in one subfamily of parasitoid wasps. Theoretical models predict that once siblicide between parasitoid wasps has evolved, it can only be lost under stringent conditions, making the transition from solitary to gregarious development exiguous. Phylogenetic studies indicate, however, that gregariousness has independently arisen on numerous occasions. New theoretical models have demonstrated that if gregarious development involves reductions in larval mobility, rather than a lack of fighting ability (as in the older models), the evolution of gregariousness is much more likely. We tested the predictions of the older tolerance models (gregariousness based on non-fighting larval phenotypes) and the reduced mobility models (gregariousness based on non-searching larval phenotypes) by observing larval movement and the outcome of interspecific competition between Aphaereta genevensis (solitary) and A. pallipes (gregarious) under multiparasitism. Differences in larval mobility matched the prediction of the reduced mobility model of gregarious development, with the solitary A. genevensis having larvae that are much more mobile. The proportion of hosts producing the solitary species significantly declined after subsequent exposure to females of the gregarious species. This contradicts the prediction of the older models (fighting vs non-fighting phenotypes), under which any competitive interactions between solitary and gregarious larvae will result in a highly asymmetrical outcome, as the solitary species should be competitively superior. The observed outcome of interspecific competition offers evidence, with respect to this subfamily, in favour of the new models (searching vs non-searching phenotypes).
Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps... more Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps due to the evolution of brood reduction behaviour in larvae competing for developmental resources. Despite this, many species of parasitoid wasp develop in small gregarious broods. Here, I catalogue the life-history properties of 87 such species, and attempt to explain their apparent stability in brood size. Small gregarious broods are taxonomically widespread, occurring in at least 15 of the 26 families containing gregarious species. The life-histories represented in this species list are extremely varied. Several species display properties consistent with an increase in the stability of non-siblicidal behaviour, but few of these properties are common to a large proportion of species. This suggests that either several factors contribute towards clutch size stability, or some important unknown variable is responsible. I discuss stochasticity in brood size as a novel but widespread factor contributing to the stability of non-siblicidal behaviour.
Entomologia Experimentalis Et Applicata, Oct 1, 2005
Behavioural interactions among relatives may have consequences for many other traits. We tested t... more Behavioural interactions among relatives may have consequences for many other traits. We tested the hypothesis that solitary parasitoids (displaying siblicidal behaviour in their larvae) have narrower host ranges than gregarious parasitoids (with tolerant larvae). In laboratory experiments, we compared parasitization success in two sister species of braconid wasp [ Aphaereta genevensis (Fischer), solitary, and Aphaereta pallipes (Say), gregarious (Hymenoptera: Braconidae: Alysiini)] on eight Drosophila species or strains. Host species or strain was the most important factor affecting parasitization success, and some of this variation was accountable to host physiological defences. Although two hosts were more suitable for the solitary species, and one more suitable for the gregarious species, these differences were small, and there was no consistent difference across all hosts. Wasp body size was positively correlated with parasitization success in both wasp species. This may be because body size increases oviposition success, or the motivation to oviposit. In A. pallipes parasitization success peaked after 3-4 days, but later in A. genevensis. This is likely due to low life expectancy and high egg loads increasing oviposition tendency in young A. pallipes , and egg limitation decreasing oviposition tendency in old A. pallipes. These data suggest that interactions among wasp larvae do not greatly affect the size of the fundamental niche examined here. However, they show the potential for life history traits, which differ between the species as a likely consequence of larval interactions, to affect the extent of the realized niche.
Across animal species, body size and clutch size often form part of a suite of associated life hi... more Across animal species, body size and clutch size often form part of a suite of associated life history traits, exemplified by the ''fast Á/slow continuum'' in mammals. Across the parasitoid Hymenoptera however, a major axis of life history variation is the development mode of the larva (koinobiosis versus idiobiosis), and body size and clutch size do not seem to form clear associations with this major axis. Here we use a large comparative data set and the latest phylogenetic information to explore hypotheses that might explain the variation in body size and clutch size across species in parasitoids. We find evidence for three novel evolutionary correlations: changes in the stage of host attacked by the parasitoid (i.e. egg, larva, pupa) significantly predict changes in both body size and clutch size, whilst in gregarious species changes to higher latitudes are associated with reduced clutch size. We also find a number of hypothesized cross-species (phenotypic) associations that, however, we cannot demonstrate are the result of evolutionary correlations: large bodied species in our data tend to lay small clutches; koinobionts are larger than idiobionts attacking the same host stage; tropical species are smaller than temperate species (Bergmann's rule). Our results provide support for theoretical models of trait evolution in parasitoids, whilst the associations between latitude and life history may help explain why species richness in the family Ichneumonidae peaks at intermediate latitudes. Our results also show the continuing value of phylogenetically-based comparative analyses and demonstrate that recent work on parasitoid phylogenetics has produced significant benefits for our understanding of life history evolution.
Deep time is geologic time, extending to the origin of the planet. For biologists in search of an... more Deep time is geologic time, extending to the origin of the planet. For biologists in search of an understanding of extinction, the relevant portion of deep time is that in which life has existed on the planet— about the last 4 billion years (Cowen, 2000). Extinctions are first recorded when the fossil record is robust enough to offer insights into the arrival and disappearance of groups of organisms (Benton and Harper, 2009). Extinctions in deep time can therefore be identified only over about the last 600 million years, an interval of time dominated by the Phanerozoic eon (540 million years ago to present).
Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial... more Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial glasshouses, have had limited success. The ability of one of its parasitoids, Aphaereta debilitata Morley, to control shore fly populations was investigated on lettuce crops within six experimental glasshouse units, over 26 weeks. The six shore fly populations, either with or without a single release of 150
bioRxiv (Cold Spring Harbor Laboratory), Jul 8, 2019
1. Insect abundance changes are well-established in some datasets, but far less is known about ho... more 1. Insect abundance changes are well-established in some datasets, but far less is known about how this translates into biomass changes. Moths (Lepidoptera) provide particularly good opportunities to study trends and drivers of biomass change at large spatial and temporal scales, given the existence of long-term abundance datasets for moths. This requires estimation of the body mass of moths sampled over time, but such data do not currently exist. 2. We collected empirical data in 2018 on the forewing length and dry mass of sampled moths, and used these to train and test a statistical model that predicts the body mass of moth species from their forewing lengths (with refined parameters for Crambidae, Erebidae, Geometridae and Noctuidae). We tested the relationships between biomass, abundance and species richness of samples of moths for our 2018 samples, and over a 16-year period using long-term historical moth data (with model-estimated biomass) from a single site. 3. Modelled biomass was positively correlated with measured biomass of moth species (R 2 = 0.910) and mixed-species samples of moths (R 2 = 0.915), showing that it is possible to predict biomass accurately. Biomass correlated with moth abundance and species richness in our 2018 data and in the historical dataset, revealing biomass declined by 65.9 % over a 16-year period. 4. By allowing biomass to be estimated for historical moth abundance datasets, our approach creates opportunities to investigate trends and drivers of insect biomass change over long timescales and broad geographic regions.
We report experiments using two closely related species of alysiine braconids directed at underst... more We report experiments using two closely related species of alysiine braconids directed at understanding how gregarious development evolved in one subfamily of parasitoid wasps. Theoretical models predict that once siblicide between parasitoid wasps has evolved, it can only be lost under stringent conditions, making the transition from solitary to gregarious development exiguous. Phylogenetic studies indicate, however, that gregariousness has independently arisen on numerous occasions. New theoretical models have demonstrated that if gregarious development involves reductions in larval mobility, rather than a lack of fighting ability (as in the older models), the evolution of gregariousness is much more likely. We tested the predictions of the older tolerance models (gregariousness based on non-fighting larval phenotypes) and the reduced mobility models (gregariousness based on non-searching larval phenotypes) by observing larval movement and the outcome of interspecific competition between Aphaereta genevensis (solitary) and A. pallipes (gregarious) under multiparasitism. Differences in larval mobility matched the prediction of the reduced mobility model of gregarious development, with the solitary A. genevensis having larvae that are much more mobile. The proportion of hosts producing the solitary species significantly declined after subsequent exposure to females of the gregarious species. This contradicts the prediction of the older models (fighting vs non-fighting phenotypes), under which any competitive interactions between solitary and gregarious larvae will result in a highly asymmetrical outcome, as the solitary species should be competitively superior. The observed outcome of interspecific competition offers evidence, with respect to this subfamily, in favour of the new models (searching vs non-searching phenotypes).
Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps... more Theory predicts that small gregarious brood sizes are evolutionarily unstable in parasitoid wasps due to the evolution of brood reduction behaviour in larvae competing for developmental resources. Despite this, many species of parasitoid wasp develop in small gregarious broods. Here, I catalogue the life-history properties of 87 such species, and attempt to explain their apparent stability in brood size. Small gregarious broods are taxonomically widespread, occurring in at least 15 of the 26 families containing gregarious species. The life-histories represented in this species list are extremely varied. Several species display properties consistent with an increase in the stability of non-siblicidal behaviour, but few of these properties are common to a large proportion of species. This suggests that either several factors contribute towards clutch size stability, or some important unknown variable is responsible. I discuss stochasticity in brood size as a novel but widespread factor contributing to the stability of non-siblicidal behaviour.
Entomologia Experimentalis Et Applicata, Oct 1, 2005
Behavioural interactions among relatives may have consequences for many other traits. We tested t... more Behavioural interactions among relatives may have consequences for many other traits. We tested the hypothesis that solitary parasitoids (displaying siblicidal behaviour in their larvae) have narrower host ranges than gregarious parasitoids (with tolerant larvae). In laboratory experiments, we compared parasitization success in two sister species of braconid wasp [ Aphaereta genevensis (Fischer), solitary, and Aphaereta pallipes (Say), gregarious (Hymenoptera: Braconidae: Alysiini)] on eight Drosophila species or strains. Host species or strain was the most important factor affecting parasitization success, and some of this variation was accountable to host physiological defences. Although two hosts were more suitable for the solitary species, and one more suitable for the gregarious species, these differences were small, and there was no consistent difference across all hosts. Wasp body size was positively correlated with parasitization success in both wasp species. This may be because body size increases oviposition success, or the motivation to oviposit. In A. pallipes parasitization success peaked after 3-4 days, but later in A. genevensis. This is likely due to low life expectancy and high egg loads increasing oviposition tendency in young A. pallipes , and egg limitation decreasing oviposition tendency in old A. pallipes. These data suggest that interactions among wasp larvae do not greatly affect the size of the fundamental niche examined here. However, they show the potential for life history traits, which differ between the species as a likely consequence of larval interactions, to affect the extent of the realized niche.
Across animal species, body size and clutch size often form part of a suite of associated life hi... more Across animal species, body size and clutch size often form part of a suite of associated life history traits, exemplified by the ''fast Á/slow continuum'' in mammals. Across the parasitoid Hymenoptera however, a major axis of life history variation is the development mode of the larva (koinobiosis versus idiobiosis), and body size and clutch size do not seem to form clear associations with this major axis. Here we use a large comparative data set and the latest phylogenetic information to explore hypotheses that might explain the variation in body size and clutch size across species in parasitoids. We find evidence for three novel evolutionary correlations: changes in the stage of host attacked by the parasitoid (i.e. egg, larva, pupa) significantly predict changes in both body size and clutch size, whilst in gregarious species changes to higher latitudes are associated with reduced clutch size. We also find a number of hypothesized cross-species (phenotypic) associations that, however, we cannot demonstrate are the result of evolutionary correlations: large bodied species in our data tend to lay small clutches; koinobionts are larger than idiobionts attacking the same host stage; tropical species are smaller than temperate species (Bergmann's rule). Our results provide support for theoretical models of trait evolution in parasitoids, whilst the associations between latitude and life history may help explain why species richness in the family Ichneumonidae peaks at intermediate latitudes. Our results also show the continuing value of phylogenetically-based comparative analyses and demonstrate that recent work on parasitoid phylogenetics has produced significant benefits for our understanding of life history evolution.
Deep time is geologic time, extending to the origin of the planet. For biologists in search of an... more Deep time is geologic time, extending to the origin of the planet. For biologists in search of an understanding of extinction, the relevant portion of deep time is that in which life has existed on the planet— about the last 4 billion years (Cowen, 2000). Extinctions are first recorded when the fossil record is robust enough to offer insights into the arrival and disappearance of groups of organisms (Benton and Harper, 2009). Extinctions in deep time can therefore be identified only over about the last 600 million years, an interval of time dominated by the Phanerozoic eon (540 million years ago to present).
Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial... more Biological control efforts against the shore fly Scatella tenuicosta Collin, a pest of commercial glasshouses, have had limited success. The ability of one of its parasitoids, Aphaereta debilitata Morley, to control shore fly populations was investigated on lettuce crops within six experimental glasshouse units, over 26 weeks. The six shore fly populations, either with or without a single release of 150
bioRxiv (Cold Spring Harbor Laboratory), Jul 8, 2019
1. Insect abundance changes are well-established in some datasets, but far less is known about ho... more 1. Insect abundance changes are well-established in some datasets, but far less is known about how this translates into biomass changes. Moths (Lepidoptera) provide particularly good opportunities to study trends and drivers of biomass change at large spatial and temporal scales, given the existence of long-term abundance datasets for moths. This requires estimation of the body mass of moths sampled over time, but such data do not currently exist. 2. We collected empirical data in 2018 on the forewing length and dry mass of sampled moths, and used these to train and test a statistical model that predicts the body mass of moth species from their forewing lengths (with refined parameters for Crambidae, Erebidae, Geometridae and Noctuidae). We tested the relationships between biomass, abundance and species richness of samples of moths for our 2018 samples, and over a 16-year period using long-term historical moth data (with model-estimated biomass) from a single site. 3. Modelled biomass was positively correlated with measured biomass of moth species (R 2 = 0.910) and mixed-species samples of moths (R 2 = 0.915), showing that it is possible to predict biomass accurately. Biomass correlated with moth abundance and species richness in our 2018 data and in the historical dataset, revealing biomass declined by 65.9 % over a 16-year period. 4. By allowing biomass to be estimated for historical moth abundance datasets, our approach creates opportunities to investigate trends and drivers of insect biomass change over long timescales and broad geographic regions.
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Papers by Peter Mayhew