Substrate Temperature Constrains Recruitment and Trail Following Behavior in Ants

In many ant species, foragers use pheromones to communicate the location of resources to nestmates. Mass-recruiting species deposit long-lasting anonymous chemical trails, while group-recruiting species use temporary chemical trails. We studied how high temperature influenced the foraging behavior of a mass-recruiting species (Tapinoma nigerrimum) and a group-recruiting species (Aphaenogaster senilis) through pheromone decay. First, under controlled laboratory conditions, we examined the effect of temperature on the trail pheromone of both species. A substrate, simulating soil, marked with gaster extract was heated for 10 min. at 25°, 35°, 45°, or 55 °C and offered to workers in a choice test. Heating gaster extract reduced the trail following behavior of the mass-recruiters significantly more than that of the group-recruiters. Second, analyses of the chemicals present on the substrate indicated that most T. nigerrimum gaster secretions vanished at 25 °C, and only iridodials persisted up to 55 °C. By contrast, A. senilis secretions were less volatile and resisted better to elevated temperatures to some extent. However, at 55 °C, the only chemicals that persisted were nonadecene and nonadecane. Overall, our results suggest that the foraging behavior of the group-recruiting species A. senilis is less affected by pheromone evaporation than that of the mass-recruiting species T. nigerrimum. This group-recruiting species might, thus, be particularly adapted to environments with fluctuating temperatures. © 2012 Springer Science+Business Media, LLC.Peer Reviewe

Non-target effects of ten essential oils on the egg parasitoid Trichogramma evanescens

Essential oils (EOs) are increasingly used as biopesticides due to their insecticidal potential. This study addresses their non-target effects on a biological control agent: the egg parasitoid Trichogramma evanescens. In particular, we tested whether EOs affected parasitoid fitness either directly, by decreasing pre-imaginal survival, or indirectly, by disrupting parasitoids' orientation abilities. The effect of Anise, Fennel, Sweet orange, Basil, Coriander, Oregano, Peppermint, Mugwort, Rosemary and Thyme EOs were studied on five strains of T. evanescens. Specific experimental setups were developed, and data obtained from image analysis were interpreted with phenomenological models fitted with Bayesian inference. Results highlight the fumigant toxicity of EOs on parasitoid development. Anise, Fennel, Basil, Coriander, Oregano, Peppermint and Thyme EOs are particularly toxic and drastically reduce the emergence rate of T. evanescens. Most EOs also affect parasitoid behavior: (i) Basil, Coriander, Oregano, Peppermint, Mugwort and Thyme EOs are highly repellent for naive female parasitoids; (ii) Anise and Fennel EOs can have repellent or attractive effects depending on strains; and (iii) Sweet orange, Oregano and Rosemary EOs have no detectable impact on orientation behavior. This study shows that EOs fumigation have non-target effects on egg parasitoids. This highlights the need to cautiously precise the deployment framework of biopesticides in an agroecological perspective

A neuronal circuit driven by GLP-1 in the olfactory bulb regulates insulin secretion

Glucagon-like peptide 1 (GLP-1) stimulates insulin secretion and holds significant pharmacological potential. Nevertheless, the regulation of energy homeostasis by centrally-produced GLP-1 remains partially understood. Preproglucagon cells, known to release GLP-1, are found in the olfactory bulb (OB). We show that activating GLP-1 receptors (GLP-1R) in the OB stimulates insulin secretion in response to oral glucose in lean and diet-induced obese male mice. This is associated with reduced noradrenaline content in the pancreas and blocked by an α2-adrenergic receptor agonist, implicating functional involvement of the sympathetic nervous system (SNS). Inhibiting GABAA receptors in the paraventricular nucleus of the hypothalamus (PVN), the control centre of the SNS, abolishes the enhancing effect on insulin secretion induced by OB GLP-1R. Therefore, OB GLP-1-dependent regulation of insulin secretion relies on a relay within the PVN. This study provides evidence that OB GLP-1 signalling engages a top-down neural mechanism to control insulin secretion via the SNS

Trade-offs and foraging activity in Mediterrannean and Communities

[FR] Une question fondamentale en Écologie des Communautés est la compréhension des mécanismes permettant la coexistence des espèces. Dans les communautés de fourmis, le rôle de la compétition inter-spécifique est prépondérant. Certaines espèces dites comportementalement dominantes monopolisent les ressources, privant ainsi les espèces dites comportementalement subordonnées. La coexistence des espèces dominantes et subordonnées repose sur des compromis évolutifs concernant les capacités compétitives. Dans les communautés de fourmis méditerranéennes, les capacités compétitives des espèces sont liées à leurs stratégies d’approvisionnement. Les espèces les plus dominantes font généralement preuve d’un plus grand degré de communication pour collecter la nourriture. Cette thèse étudie comment les stratégies d’approvisionnement contribuent aux compromis évolutifs et articulent la diversité des communautés de fourmis. La première partie s’intéresse au rôle des stratégies d’approvisionnement dans l’alternative entre découvrir vite les ressources et être capable de les soustraire au contrôle des compétiteurs. Ce compromis entre la découverte et le contrôle des ressources se base sur une répartition des ouvrières de la colonie entre celles qui recherchent la nourriture, et celles qui l’exploitent et la défendent. Les modèles mathématiques proposés sont développés à l’échelle évolutive et démontrent que ce principe simple peut expliquer la diversification des stratégies d’approvisionnement. La structure théorique proposée peut être élargie et servir de base conceptuelle à l’étude de la dynamique évolutive de traits d’histoire de vie chez les insectes eusociaux. La seconde partie est centrée sur le compromis évolutif entre la dominance comportementale et la tolérance thermique. Les espèces dominantes sont généralement plus sensibles aux températures stressantes, i.e. élevées dans les communautés méditerranéennes. L’hypothèse sous-jacente concerne le rôle de la phéromone dans la communication chez les fourmis. Les composés chimiques étant détériorés par les températures élevées, l’avantage présenté par des stratégies d’approvisionnement reposant sur la communication chimique peut être nuancé. Dans les écosystèmes méditerranéens soumis à des importantes variations de température à la fois saisonnières et journalières, la diversité des stratégies d’approvisionnement contribue ainsi à la diversité des communautés de fourmis.[ES] Una cuestión fundamental en la Ecología de Comunidades es comprender los mecanismos que permiten la coexistencia de las especies. En las comunidades de hormigas, el papel de la competencia interespecifica es preponderante. Algunas especies, llamadas dominantes comportamentales, monopolizan los recursos, privando así las especies llamadas subordinadas comportamentales del acceso al recurso. La coexistencia de especies dominantes y subordinadas está basada en unos compromisos evolutivos referidos a las capacidades competitivas. En las comunidades mediterráneas de hormigas, las capacidades competitivas de las especies están vinculadas a sus estrategias de aprovisionamiento. Las especies más dominantes usan, generalmente, un grado más elevado de comunicación para la recolección del alimento. Esta tesis estudia cómo las estrategias de aprovisionamiento contribuyen a los compromisos evolutivos y articulan la diversidad de las comunidades de hormigas. La primera parte está enfocada a estudiar el papel de las estrategias de aprovisionamiento frente a la alternativa entre descubrir rápidamentente los recursos o ser capaz de expulsar a los competidores de los mismos. Este compromiso entre el descubrimiento y el control de los recursos está basado en una repartición de las obreras de la colonia entre las exploradoras que buscan la comida y las reclutadas que explotan y defienden los recursos. Los modelos matemáticos propuestos están desarollados a una escala evolutiva y demuestran que este principio simple puede explicar la diversidad de las estrategias de aprovisionamiento. La estructura teórica propuesta puede extenderse y servir de base conceptual para el estudio de la dinámica evolutiva de los caracteres de estrategias vitales (life-history traits) en los insectos sociales. La segunda parte se centra sobre el compromiso evolutivo entre la dominancia comportamental y la tolerancia térmica. Las especies dominantes son, generalmente, más sensibles a las temperaturas estresantes, i.e. elevadas en las comunidades mediterráneas. La hipótesis subyacente concierne al papel de la feromona en la comunicación entre las hormigas. Los compuestos químicos se deterioran por las temperaturas altas, y la ventaja presentada por las estrategias de aprovisionamiento basadas en la comunicación química puede resultar atenuada. En los ecosistemas mediterráneos, sometidos a variaciones de temperaturas importantes, tanto estacionales como diarias, la diversidad de las estrategias de aprovisionamiento contribuye así a la diversidad de las comunidades de hormigasPeer reviewe

An Evolutionary Dynamics Model Adapted to Eusocial Insects

This study aims to better understand the evolutionary processes allowing species coexistence in eusocial insect communities. We develop a mathematical model that applies adaptive dynamics theory to the evolutionary dynamics of eusocial insects, focusing on the colony as the unit of selection. The model links long-term evolutionary processes to ecological interactions among colonies and seasonal worker production within the colony. Colony population dynamics is defined by both worker production and colony reproduction. Random mutations occur in strategies, and mutant colonies enter the community. The interactions of colonies at the ecological timescale drive the evolution of strategies at the evolutionary timescale by natural selection. This model is used to study two specific traits in ants: worker body size and the degree of collective foraging. For both traits, trade-offs in competitive ability and other fitness components allows to determine conditions in which selection becomes disruptive. Our results illustrate that asymmetric competition underpins diversity in ant communities. © 2013 van Oudenhove et al.Peer Reviewe

Temperature limits trail following behaviour through pheromone decay in ants

In Mediterranean habitats, temperature affects both ant foraging behaviour and community structure. Many studies have shown that dominant species often forage at lower temperature than subordinates. Yet, the factors that constrain dominant species foraging activity in hot environments are still elusive. We used the dominant ant Tapinoma nigerrimum as a model species to test the hypothesis that high temperatures hinder trail following behaviour by accelerating pheromone degradation. First, field observations showed that high temperatures (> 30°C) reduce the foraging activity of T. nigerrimum independently of the daily and seasonal rhythms of this species. Second, we isolated the effect of high temperatures on pheromone trail efficacy from its effect on worker physiology. A marked substrate was heated during 10 min (five temperature treatments from 25°C to 60°C), cooled down to 25°C, and offered in a test choice to workers. At hot temperature treatments (>40°C), workers did not discriminate the previously marked substrate. High temperatures appeared therefore to accelerate pheromone degradation. Third, we assessed the pheromone decay dynamics by a mechanistic model fitted with Bayesian inference. The model predicted ant choice through the evolution of pheromone concentration on trails as a function of both temperature and time since pheromone deposition. Overall, our results highlighted that the effect of high temperatures on recruitment intensity was partly due to pheromone evaporation. In the Mediterranean ant communities, this might affect dominant species relying on chemical recruitment, more than subordinate ant species, less dependent on chemical communication and less sensitive to high temperatures. © 2011 Springer-Verlag.Peer Reviewe

Substrate Temperature Constrains Recruitment and Trail Following Behavior in Ants

In many ant species, foragers use pheromones to communicate the location of resources to nestmates. Mass-recruiting species deposit long-lasting anonymous chemical trails, while group-recruiting species use temporary chemical trails. We studied how high temperature influenced the foraging behavior of a mass-recruiting species (Tapinoma nigerrimum) and a group-recruiting species (Aphaenogaster senilis) through pheromone decay. First, under controlled laboratory conditions, we examined the effect of temperature on the trail pheromone of both species. A substrate, simulating soil, marked with gaster extract was heated for 10 min. at 25°, 35°, 45°, or 55 °C and offered to workers in a choice test. Heating gaster extract reduced the trail following behavior of the mass-recruiters significantly more than that of the group-recruiters. Second, analyses of the chemicals present on the substrate indicated that most T. nigerrimum gaster secretions vanished at 25 °C, and only iridodials persisted up to 55 °C. By contrast, A. senilis secretions were less volatile and resisted better to elevated temperatures to some extent. However, at 55 °C, the only chemicals that persisted were nonadecene and nonadecane. Overall, our results suggest that the foraging behavior of the group-recruiting species A. senilis is less affected by pheromone evaporation than that of the mass-recruiting species T. nigerrimum. This group-recruiting species might, thus, be particularly adapted to environments with fluctuating temperatures. © 2012 Springer Science+Business Media, LLC.Peer Reviewe

Dominance-discovery and discoveryexploitation trade-offs promote diversity in ant communities

In ant communities, species coexist by using different foraging strategies. We developed an adaptive dynamics model to gain a better understanding of the factors that promote the emergence and maintenance of strategy diversity. We analysed the consequences of both interspecific competition and resource distribution for the evolutionary dynamics of social foraging in ants. The evolution of social foraging behaviour was represented using a stochastic mutation-selection process involving interactions among colonies. In our theoretical community, ant colonies inhabit an environment where resources are limited, and only one resource type is present. Colony interactions depend on colony-specific foraging strategies (defined as the degree of collective foraging), resource distribution patterns, and the degree of competition asymmetry. At the ecological timescale, we have created a model of foraging processes that reflects trade-offs between resource discovery and resource exploitation and between resource discovery and ant behavioural dominance. At the evolutionary timescale, we have identified the conditions of competition and resource distribution that can lead to the emergence and coexistence of both collective and individual foraging strategies. We suggest that asymmetric competition is an essential component in the emergence of diverse foraging strategies in a sympatric ant community.Peer reviewe

Parasitoid response to herbivore induced plant volatiles: a meta-analysis.

International audienceIn reaction to herbivore attack, plants attract herbivores’ natural enemies by emitting a chemical signal. Based on a litterature review, we documented the response of parasitoids to these Herbivore Induced Plant Volatiles (HIPV): the behavior of 60 parasitoid species was characterized, and general patterns emerged between the way parasitoids respond to HIPV, and some ecological characteristics of the species. Contrary to what was expected according to the concept of dietary specialization and infochemical use (Vet and Dicke, 1992), parasitoids of herbivores that feed on a reduced diversity of plants do not respond more innately to HIPV than more generalist parasitoids. However, parasitoids of adult herbivores tend to respond less innately than larval or pupal parasitoids. According to response specificity, as was predicted by Vet and Dicke (1992), parasitoids with a broad host range tends to respond less specifically to HIPV than do specialist parasitoids