Early life starvation has stronger intra-generational than transgenerational effects on key life-history traits and consumption measures in a sawfly

IGF-1 receptor inhibitor OSI-906 reduces growth in nestlings of a wild passerine

Young animals need to grow to a large body size fast to maximise their survival prospects until sexual maturity. However, body size varies substantially in wild populations, and neither the selection pressures maintaining this variation, nor the regulatory mechanisms are well understood. IGF-1 administration has been shown to accelerate growth, but this does not necessarily imply that natural variation in growth rate is IGF-1 dependent. To test the latter we administered OSI-906 to pied flycatcher Ficedula hypoleuca nestlings, which has an inhibitory effect on IGF-1 receptor activity. We performed the experiment in two breeding seasons to test the prediction that blocking the IGF-1 receptor downregulates growth. As predicted, OSI-906 treated nestlings had lower body mass and reached a smaller structural size than siblings receiving a vehicle only, with the mass difference being most profound at the age preceding the highest body mass growth rate. The IGF-1 receptor inhibition effect on growth varied with age and year of study, and we discuss possible explanations. The OSI-906 administration results indicate that natural variation in growth rate is regulated by IGF-1, and constitutes a novel tool to study causes and consequences of growth variation, but details of the underlying mechanism still need to be resolved.

The hunger strikes back: an epigenetic memory for autophagy

Historical and demographical human cohorts of populations exposed to famine, as well as animal studies, revealed that exposure to food deprivation is associated to lasting health-related effects for the exposed individuals, as well as transgenerational effects in their offspring that affect their diseases' risk and overall longevity. Autophagy, an evolutionary conserved catabolic process, serves as cellular response to cope with nutrient starvation, allowing the mobilization of an internal source of stored nutrients and the production of energy. We review the evidence obtained in multiple model organisms that support the idea that autophagy induction, including through dietary regimes based on reduced food intake, is in fact associated to improved health span and extended lifespan. Thereafter, we expose autophagy-induced chromatin remodeling, such as DNA methylation and histone posttranslational modifications that are known heritable epigenetic marks, as a plausible mechanism for transgenerational epigenetic inheritance of hunger.

Dietary restriction and ageing: Recent evolutionary perspectives

Dietary restriction (DR) represents one of the most robust interventions for extending lifespan. It is not known how DR increases lifespan. The prevailing evolutionary hypothesis suggests the DR response redirects metabolic resources towards somatic maintenance at the expense of investment in reproduction. Consequently, DR acts as a proximate mechanism which promotes a pro-longevity phenotype. This idea is known as resource reallocation. However, growing findings suggest this paradigm could be incomplete. It has been argued that during DR it is not always possible to identify a trade-off between reproduction and lifespan. It is also suggested the relationship between reproduction and somatic maintenance can be uncoupled by the removal or inclusion of specific nutrients. These findings have created an imperative to re-explore the nexus between DR and evolutionary theory. In this review I will address this evolutionary conundrum. My overarching objectives are fourfold: (1) to outline some of the evidence for and against resource reallocation; (2) to examine recent findings which have necessitated a theoretical re-evaluation of the link between life history theory and DR; (3) to present alternatives to the resource reallocation model; (4) to present emerging variables which potentially influence how DR effects evolutionary trade-offs.

Fluctuating Starvation Conditions Modify Host-Symbiont Relationship Between a Leaf Beetle and Its Newly Identified Gregarine Species

Gregarines are ubiquitous endosymbionts in invertebrates, including terrestrial insects. However, the biodiversity of gregarines is probably vastly underestimated and the knowledge about their role in shaping fitness-related traits of their host in dependence of fluctuating environmental conditions is limited. Using morphological and molecular analyses, we identified a new gregarine species, Gregarina cochlearium sp. n., in the mustard leaf beetle, Phaedon cochleariae. Applying a full-factorial design, we investigated the effects of a gregarine infection in combination with fluctuating starvation conditions during the larval stage on the development time and fitness-related traits of adult beetles. Under benign environmental conditions, the relationship between gregarines and the host seemed neutral, as host development, body mass, reproduction and survival were not altered by a gregarine infection. However, when additionally exposed to starvation, the combination of gregarine infection and this stress resulted in the lowest reproduction and survival of the host, which points to a parasitic relationship. Furthermore, when the host experienced starvation, the development time was prolonged and the adult females were lighter compared to non-starved individuals, independent of the presence of gregarines. Counting of gregarines in the guts of larvae revealed a lower gregarine load with increasing host body mass under stable food conditions, which indicates a regulation of the gregarine burden in dependence of the host condition. Contrary, in starved individuals the number of gregarines was the highest, hence the already weakened host suffered additionally from a higher gregarine burden. This interactive effect between gregarine infection and fluctuating starvation conditions led to an overall reduced fitness of P. cochleariae. Our study emphasizes the need to study endosymbionts as important components of the natural environment and to investigate the role of host-symbiont relationships under fluctuating environmental conditions in an evolutionary and ecological context.

Fighting over defense chemicals disrupts mating behavior

Studies on intraspecific contest behavior predominantly focus on contests between individuals of the same sex, however contest behavior is also expected to occur between individuals of the opposite sex including possible mates. Here we investigate potential trade-offs between mating and fighting behavior in the turnip sawfly (Athalia rosae). Adults of this species collect chemical defense compounds (clerodanoids) directly from plants but also indirectly by nibbling on conspecifics that have already obtained clerodanoids, a highly aggressive behavioral interaction. An A. rosae individual without clerodanoids may therefore be the potential mate or attacker of an individual of the opposite sex that has gained clerodanoids. To test the effect of clerodanoids on agonistic and mating behavior we paired females and males with or without clerodanoid access in a two-way factorial design. We show that asymmetrical clerodanoid acquisition between female-male pairs causes an increase in agonistic nibbling behavior, irrespective of sex, and moreover that conflict between individuals delays mating behavior. Our study highlights the importance of investigating agonistic intersex interactions, which can occur when adults are able to acquire valuable non-reproductive resources from a potential partner.