Thermal change alters the outcome of behavioural interactions between antagonistic partners

1. Concerns about climate change often trigger the question whether physiological and behavioural responses of species will enable them to persist. However, species do not exist alone and are largely dependent on interactions with others within communities. 2. In the present study, a mechanistic approach is used to test the hypothesis that inter‐specific differences in metabolic response to unpredictable short‐term thermal changes can change the outcome of host–parasitoid behavioural interactions. 3. The effect of a drop or a rise of 5 °C on resting metabolic rates (RMR) of the main aphid pest of cereal crops in Western Europe, the host Sitobion avenae Fabricius and its main natural enemy, the parasitoid Aphidius rhopalosiphi De Stefani‐Perez was measured. Also, defence and attack behaviours were measured for host and parasitoid separately as well as in interaction, since behavioural strategies of both species largely determine parasitism success. 4. The results showed that, when no change in temperature occurred, parasitoids had the highest oviposition rate. However, only with a rise of temperature behavioural interactions were disrupted: the parasitoid attack rate decreased whereas the aphid defence rate increased. This alteration in behaviour was associated with a stronger thermal response of RMR in hosts than in parasitoids, suggesting that species‐specific thermal responses of RMR could give valuable information on changes in the outcome of species interactions under warm spells but not under cold ones. 5. It was shown that relatively modest thermal changes with non‐lethal effects can have profound consequences for interacting co‐evolved species which may affect ecosystem services, such as biological control of pest populations.     

Functional ecological implications of intraspecific differences in wing melanization in Colias butterflies

Variation in the degree of insect wing melanin affects thermoregulation, and is expected to be adapted to local environmental conditions, for example over an elevational gradient. The effects of melanization on flight activity and egg maturation rate were assessed in the closely related butterflies Colias philodice eriphyle and C. eurytheme using experimental manipulation of wing darkness and transplant experiments between high and low elevation sites. Experimental manipulation of wing darkness in C. p. eriphyle demonstrated that light males had reduced flight activity at high elevations, and darkened males had reduced flight activity at low elevations. In contrast, the transplant experiments revealed asymmetrical adaptation for male C. p. eriphyle . At high elevations darker, high-elevation males had higher flight activity than lighter, low-elevation males, but there was no difference between the two groups at low elevation. For females, melanization had no effect on flight activity. However, an increase in female C. eurytheme wing darkness led to a significantly higher egg maturation rate at cold ambient temperatures, which may increase female reproductive output under natural conditions. Therefore, dispersers moving down in elevation may be more successful than those moving up.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 79–87.     

Adapt or disperse: understanding species persistence in a changing world

The majority of studies on environmental change focus on the response of single species and neglect fundamental biotic interactions, such as mutualism, competition, predation, and parasitism, which complicate patterns of species persistence. Under global warming, disruption of community interactions can arise when species differ in their sensitivity to rising temperature, leading to mismatched phenologies and/or dispersal patterns. To study species persistence under global climate change, it is critical to consider the ecology and evolution of multispecies interactions; however, the sheer number of potential interactions makes a full study of all interactions unfeasible. One mechanistic approach to solving the problem of complicated community context to global change is to (i) define strategy groups of species based on life‐history traits, trophic position, or location in the ecosystem, (ii) identify species involved in key interactions within these groups, and (iii) determine from the interactions of these key species which traits to study in order to understand the response to global warming. We review the importance of multispecies interactions looking at two trait categories: thermal sensitivity of metabolic rate and associated life‐history traits and dispersal traits of species. A survey of published literature shows pronounced and consistent differences among trophic groups in thermal sensitivity of life‐history traits and in dispersal distances. Our approach increases the feasibility of unraveling such a large and diverse set of community interactions, with the ultimate goal of improving our understanding of community responses to global warming.     

Fatty acid composition remains stable across trophic levels in a gall wasp community

Acquiring sufficient nutrients is particularly important for insects that are unable to synthesize certain nutrient types de novo, as is the case for numerous parasitoid species that do not synthesize lipids. The lipid reserves of parasitoids are acquired from a single host during larval development. This imposes constraints on the quantity and quality of available lipids. In the present study, the lipid dynamics throughout the trophic cascade are investigated by measuring lipogenic ability, modifications in fatty acid composition and host exploitation efficiency in species at different trophic positions within the community of parasitoids associated with the gall wasp Diplolepis rosae L. (Hymenoptera: Cynipidae). The results obtained show that lipid levels remain stable or decline after feeding in all species, indicating that none of the wasps synthesize lipids. Fatty acid composition is highly similar between the gall wasp, parasitoid and hyperparasitoid species, with the exception of the parasitoid Orthopelma mediator Thunberg (Hymenoptera: Ichneumonidae). The divergence of fatty acid composition in O. mediator suggests that this species is able to modify its fatty acid composition after the consumption of host lipids. The efficiency of exploitation of host resource, in terms of dry body mass acquired, varies among the species (41–70%), although it is high overall compared with the efficiencies reported in other animals. Hence, for parasitoid wasps that lack lipid synthesis capabilities, the efficiency of host exploitation is high and fatty acids are consumed directly from the host without modification, leading to stable fatty acid compositions throughout the trophic cascade.     

Feeding strategies in drosophilid parasitoids: the impact of natural food resources on energy reserves in females

1. Adult feeding strongly increases longevity and fecundity in parasitic wasps. Searching for food resources involves costs; therefore, it is advantageous to be able to feed on the breeding substrate.
2. Cohorts of females of four drosophilid parasitoid species were assigned to different food treatments including starvation. Fat contents were measured and compared after 5 days. In this way the nutritional value of breeding substrates to females could be expressed in terms of energy reserves.
3. Three of the four species tested fed on natural breeding substrates. A fourth species did not produce evidence of such feeding. However, this species fed on honey when fat reserves were low.
4. Feeding is related to: (i) the species' natural breeding substrate, (ii) the energy allocation and lifetime expectancy of the female, and (iii) time of the season.
5. Because feeding strongly influences longevity and fecundity, it is argued that the different feeding strategies found may affect competitive relationships between these drosophilid parasitoid species.     

Habitat-specific differences in thermal plasticity in natural populations of a soil arthropod

When populations experience substantial variation in environmental conditions, they may evolve phenotypic plasticity in response to these varying selection pressures. Evolutionary theory predicts differentiation in the level of phenotypic plasticity among different habitats. We evaluated temperature-induced phenotypic responses in juvenile growth rate in natural populations of the springtail Orchesella cincta , inhabiting forest and heathland. These habitats typically co-occur but differ strongly with respect to, for example, thermal regime, relative humidity, and structure. Offspring of females from the two habitats were reared at different temperatures in climate rooms and the temperature response of juvenile growth rate and egg size was measured. We found a habitat-specific difference in plasticity of juvenile growth rate. The reaction norms of the forest populations were steeper than the reaction norms for heath populations at two replicated sampling sites. Egg weight itself was demonstrated to be a plastic trait with a higher egg weight at low temperatures, but the thermal response did not differ between habitats. We conclude that these populations have diverged due to strong local natural selection. Our results support the argument that the level of phenotypic plasticity itself can be under selection and that differentiation in reaction norms can occur even in neighbouring habitats with no barrier to gene flow.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 265–271.