Condition-dependent signaling affects male sexual attractiveness in field crickets, Gryllus campestris

The condition dependence of sexually selected traits is an important assumption of sexual selection theory. Several laboratory studies have documented a positive relationship between food availability, body condition, and sexual display. However, these studies might not reflect the resource allocation between body maintenance, reserves, and the sexually selected trait under natural conditions. Further, the effect of condition-dependent signaling on female mate choice has hardly been investigated experimentally in the field. We therefore investigated the effect of food availability on body condition, calling behavior, and sexual attractiveness of male field crickets, Gryllus campestris, under field conditions. Food availability was manipulated for individual males by supplementing food in a confined area close to the burrow. Food-supplemented males showed a significant increase in body condition, whereas the opposite was found in the control males. Males receiving extra food called more frequently, whereas the calling-song characteristics were not affected by the treatment. Further, food-supplemented males attracted more females than did control males, and their higher attractiveness was partly explained by their superior calling rate. Our study thus indicates condition-dependent signaling as an important determinant of the sexual attractiveness of males to females under natural conditio

Forced Dissociation of Food- and Light-Entrainable Circadian Rhythms of Rats in a Skeleton Photoperiod

To investigate the control over drinking and feeding behavior by the light-entrainable circadian pacemaker, rats were maintained in a 12 h:12 h skeleton photoperiod for 36 days with both food and water restricted to the subjective day. During the restriction period most of the food and water intake was concentrated during the first 4 h of the subjective day. The subsequent release into ad lib conditions under the skeleton photoperiod or continuous dark showed that this increased ingestion during the subjective day persisted for up to 6–10 days. This may indicate the entrainment of a food-entrainable oscillator, which has hitherto been investigated solely in anticipatory activity. The daily activity rhythm returned to its original phase position. Thus the phase of the overt daily rhythm is eventually only determined by the phase of the light-entrainable oscillator (LEO) but can temporarily be influenced by the restriction of food and water access. This restriction apparently stimulated a food-entrainable oscillator in antiphase with the light-entrainable oscillator but failed to phase shift or entrain the light-entrainable oscillator.

Data from: Immune response increases predation risk

Why do individuals have an imperfect immune system? Most studies suggest trade-offs associated with immunity and metabolism, and neglect ecological factors, such as predation. We provide one of the first experimental studies demonstrating a context-dependent survival cost to immune activation. In the presence of a predator, immune-challenged male field crickets showed significantly lower survival than controls, whilst there was no difference in a predator-free environment. Immune-challenged males spent more time outside their burrows and reacted slower to a simulated predator attack. We conclude that some costs of immunity are expressed via increased susceptibility to predation, indicating the importance of integrating the ecological context when investigating optimal investment in immunity

Diel variation in a dynamic sexual display and its association with female mate-searching behaviour

Dynamic sexual signals often show a diel rhythm and may vary substantially with time of day. Diel and short-term fluctuations in such sexual signals pose a puzzle for condition capture models of mate choice, which assume a female preference for male traits that reliably reflect a male's quality. Here we experimentally manipulated the food supply of individual male field crickets Gryllus campestris in their natural habitat in two consecutive seasons to determine (i) the effect of male nutritional condition on the fine-scaled variation of diel investment in acoustic signalling and (ii) the temporal association between the diel variation in male signalling and female mate-searching behaviour. Overall food-supplemented males signalled more often, but the effect was only visible during the daytime. In the evening and the night, signal output was still high but the time spent signalling was unrelated to a male's nutritional condition. Females' mate-searching behaviour also showed a diel rhythm with peak activity during the afternoon, when differences among calling males were highest, and where signal output reliably reflects male quality. These findings suggest that males differing in nutritional condition may optimize their investment in signalling in relation to time of day as to maximize mating success

Timing of Current Reproduction Directly Affects Future Reproductive Output in European Coots

Life-history theory suggests that the variation in the seasonal timing of reproduction within populations may be explained on the basis of individual optimization. Optimal breeding times would vary between individuals as a result of trade-offs between fitness components. The existence of such trade-offs has seldom been tested empirically. We experimentally investigated the consequences of altered timing of current reproduction for future reproductive output in the European coot (Fulica atra). First clutches of different laying date were cross-fostered between nests, and parents thereby experienced a delay or an advance in the hatching date. The probability and success of a second brood, adult survival until and reproduction in the next season were then compared to the natural variation among control pairs. Among control pairs the probability of a second brood declined with the progress of season. Delayed pairs were less likely and advanced pairs were more likely to produce a second brood. These changes were quantitatively as predicted from the natural seasonal decline. The number of eggs in the second clutch was positively related to egg number in the first clutch and negatively related to laying date. Compared to the natural variation, delayed females had more and advanced females had fewer eggs in their second clutch. The size of the second brood declined with season, but there was no significant effect of delay or advance. Local adult survival was higher following a delay and reduced following an advance. The effect of the experiment on adult survival was independent of sex. Laying date and clutch size of females breeding in the next year were not affected by treatment. The study demonstrates the existence of a trade-off between increased probability of a second brood and decreased parental survival for early breeding. Timing-dependent effects of current reproduction on future reproductive output may thus play an important role in the evolution of the seasonal timing of reproduction.

Otti.etal.Behavior data

Data for behavior analysis Table S2 and Figure 2c. We would appreciate to be informed about any reuse of our data ([email protected])

Otti.etal.Survival data

Survival data for Figure 2b We would appreciate to be informed about any reuse of our data ([email protected])

Predator avoidance trait data

Data for predator avoidance traits analysis and Figure 3. We would appreciate to be informed about any reuse of our data ([email protected])

Repository data to Reinhardt et al, PLoS ONE

EXCEL File. See Excel Sheet "Description of data sets" for detail