Cédric Tentelier

Parasitoids use herbivore-induced information to adapt patch exploitation behaviour

Abstract.  1. Optimal foraging models ultimately predict that female parasitoids should exploit rich host patches for longer than poorer ones. At the proximate level, mechanistic models and experimental studies show that parasitoids use both chemicals produced by their hosts and direct encounters with their hosts to estimate patch quality. Although it has been extensively studied in the context of host location, the use of herbivore‐induced plant response by insect parasitoids has never been considered in the context of patch time allocation.

Microsatellite‐based parentage analysis reveals non‐ideal free distribution in a parasitoid population

Habitat selection by dispersers is the focus of much theoretical models, most of which are based on the assumption of negative density dependence. The archetype of these models is the ideal free distribution, characterized by an evolutionary stable state where more competitors aggregate in better habitats, so that the fitness benefit of resource abundance is equally offset by the cost of competition in all habitats. In this study, we used parentage analysis on microsatellite genotypes to test the ideal free distribution in a natural population of aphid parasitoids. Parentage analysis was conducted on parasitoids emerging from aphid colonies. We inferred the number of foundress females which had reproduced in each colony, as well as the number of offspring for each foundress. As predicted by the ideal free distribution, the number of offspring per foundress per colony did not depend on the number of hosts per colony. However, contrary to ideal free distribution predictions, it was affected by the number of foundresses per colony. In surprising contrast with the basic assumption of negative density dependence, individual fitness increased with the number of foundresses. Moreover, parentage analysis revealed a very low number of offspring per foundress per colony (mean = 1.8). This observed distribution questions the validity of classical models of habitat choice based on competition. Indeed, our results provide a new illustration reinforcing a growing body of theory and data on positive density dependence. Our results also suggest that the avoidance of hyperparasitism and predation, although generally neglected, may shape the distribution of parasitoids in the field.

The concentration of plasma metabolites varies throughout reproduction and affects offspring number in wild brown trout (Salmo trutta).

In wild populations, measuring energy invested in the reproduction and disentangling investment in gametes versus investment in reproductive behavior (such as intrasexual competition or intersexual preference) remain challenging. In this study, we investigated the energy expenditure in brown trout reproductive behavior by using two proxies: variation in weight and variation of plasma metabolites involved in energy production, over the course of reproductive season in a semi natural experimental river. We estimated overall reproductive success using genetic assignment at the end of the reproductive season. Results show that triglycerides and free fatty acid concentrations vary negatively during reproduction, while amino-acids and glucose concentrations remain stable. Decrease in triglyceride and free fatty acid concentrations during reproduction is not related to initial concentration levels or to weight variation. Both metabolite concentration variations and weight variations are correlated to the number of offspring produced, which could indicate that gametic and behavioral reproductive investments substantially contribute to reproductive success in wild brown trout. This study opens a path to further investigate variations in reproductive investment in wild populations.

Inflexible wasps: the aphid parasitoid Lysiphlebus testaceipes does not track multiple changes in habitat profitability.

Bayesian updating is a form of learning by which individuals can adapt their behaviour to uncertain environments. In the particular situation of optimal foraging in a patchy habitat, animals may estimate the profitability of the patches they encounter to update their estimate of the profitability of the habitat as a whole, and adjust their foraging decisions accordingly. Recent studies have suggested that parasitoid insects may have such abilities, but were based on too few patches for clear conclusions on Bayesian updating. We studied how females of an aphid parasitoid update their estimate of habitat profitability, by recording their behaviour on a series of seven consecutive host patches, each serving both as a potential cue for habitat profitability and as a means to measure the behavioural response to previously collected information. The experiment was designed to test specific predictions based on Bayesian updating with different memory dynamics. The parasitoids clearly perceived the profitability of the patches, but the effect of previous experience on current patch use was different from our predictions. The reinterpretation of previous studies in the light of our results suggests that foraging parasitoids give more weight to early experience.

Experimental evidence of population differences in reproductive investment conditional on environmental stochasticity.

Environmental stochasticity is expected to shape life histories of species, wherein organisms subjected to strong environmental variation should display adaptive response by being able to tune their reproductive investment. For riverine ecosystems, climate models forecast an increase in the frequency and intensity of extreme events such as floods and droughts. The speed and the mechanisms by which organisms may adapt their reproductive investment are therefore of primary importance to understand how species will cope with such radical environmental changes. In the present study, we sampled spawners from two different populations of wild brown trout, originating from two environments with contrasting levels of flow stochasticity. We placed them in sympatry within an experimental channel during reproductive season. In one modality, water flow was maintained constant, whereas in another modality, water flow was highly variable. Reproductive investment of all individuals was monitored using weight and energetic plasma metabolite variation throughout the reproductive season. Only the populations originating from the most variable environment showed a plastic response to experimental manipulation of water flow, the females being able to reduce their weight variation (from 19.2% to 13.1%) and metabolites variations (from 84.2% to 18.6% for triglycerides for instance) under variable flow conditions. These results imply that mechanisms to cope with environmental stochasticity can differ between populations of the same species, where some populations can be plastic whereas other cannot.

Melanin in a changing world: brown trout coloration reflects alternative reproductive strategies in variable environments

Lisa Jacquin,a Zoé Gauthey,b Vincent Roussille,b Michel Le Hénaff,c Cédric Tentelier,b and Jacques Labonneb aUniversité Fédérale de Toulouse, Université Toulouse 3 Paul Sabatier, UPS, CNRS, ENFA, IRD; UMR 5174 EDB (Laboratoire Évolution & Diversité Biologique), 118 route de Narbonne, 31062 Toulouse, France, bEcobiop, INRA, Univ. Pau & Pays Adour, 64310 Saint-Pée-sur-Nivelle, France, and cBordeaux Science Agro, 1 cours du Gal De Gaulle, CS 40201, 33175 Gradignan, France

Are 2D space-use analyses adapted to animals living in 3D environments? A case study on a fish shoal

Lay Summary The way space and resources are shared within a group of animals reveal key aspects of the behavioral ecology of gregarious species. For species using space in 3D, multidimensional analysis would be necessary to accurately describe patterns of spatial partitioning between group-members, however, such analyses are scarce. We used a group of wild fish to test the relevance of multidimensional analysis when space-use is used to infer the feeding behavior of group-members.

The dynamics of spawning acts by a semelparous fish and its associated energetic expenses

During the reproductive season, animals have to manage both their energetic budget and gamete stock. In particular, for semelparous capital breeders with determinate fecundity and no parental care other than gametic investment, the depletion of energetic stock must match the depletion of gametic stock, so that individuals get exhausted just after their last egg is laid and fertilized. Although these budgets are managed continuously, monitoring the dynamics of mating acts and energy expenditure at a fine temporal scale in the wild is challenging. This study aimed to quantify the individual dynamics of spawning acts and the concomitant energy expenditure of female Allis shad (Alosa alosa) throughout their mating season. Using eight individual-borne accelerometers for one month, we collected tri-axial acceleration, temperature, and pressure data that we analysed to i) detect the timing of spawning acts, ii) estimate energy expenditure from tail beat frequency and water temperature, and iii) monitor changes in body roundness from the position of the dorsally-mounted tag relative to the vertical plane. Female shad had a higher probability to spawn during warmer nights, and their spawning acts were synchronized (both individually and inter-individually) within each active night. They experienced warmer temperature, remained deeper, swan more slowly and spent less energy during daytime than night time. Over one month of spawning, they performed on average 15.75 spawning acts, spent on average 6 277 kJ and died with a significant portion of residual oocytes. The acceleration-based indicator of body roundness was correlated to condition coefficient measured at capture, and globally decreased through the spawning season, although the indicator was noisy and was not correlated to changes in estimated energy expenditure. Despite significant individual variability, our results indicate that female shad exhausted their energetic stock faster than their egg stock. Water warming will increase the rate of energy expenditure, which might increase the risk that shad die with a large stock of unspent eggs. Although perfectible, the three complementary analyses of acceleration data are promising for in situ monitoring of energy expenditure related to specific behaviour.