Traffic noise exposure impacts song production in wild male field crickets (Gryllus bimaculatus) under predator and intrasexual competition contexts

Animals are known to adjust their acoustic signals in the presence of anthropogenic noise. These changes may affect fitness by altering susceptibility to predators or changing signal efficiency in intra- and intersexual interactions. Male field crickets, Gryllus bimaculatus, chirp to attract females, with chirp rate being an important success factor. Males reduce the chirp rate when exposed to predators or traffic noise and increase it in response to male competitors. However, the combined effects of these pressures on signalling are unknown. This study examined whether antipredator responses are influenced by male-male competition and variations in traffic noise exposure. We used substrate-borne vibrations to simulate a predator approaching and varied perceived male-male competition using playbacks to calling males. We found that responses to increased competition were affected by variation in traffic noise exposure, with males chirping faster as noise levels increased. Additionally, antipredator responses depended on an interaction between traffic noise and competition. Under high competition, males reduced the chirp rate as traffic noise increased. Our results demonstrate that adjustments in signal production in response to noise pollution may negatively impact communication in both antipredator and competitive contexts, indicating more pervasive effects of anthropogenic noise than previously recognized.

The evolution of preferred male traits, female preference and the G matrix: "Toto, I've a feeling we're not in Kansas anymore"

Female preference exerts selection on male traits. How such preferences affect male traits, how female preferences change and the genetic correlation between male traits and female preference were examined by an experiment in which females were either mated to males they preferred (S lines) or to males chosen at random from the population (R lines). Female preference was predicted to increase the time spent calling by males. Thirteen other song components were measured. Preference for individual traits was greatest for time spent calling(CALL), volume(VOL) and chirp rate(CHIRP) but the major contributors in the multivariate function were CALL and CHIRP, the univariate influence of VOL arising from correlations to these traits. Estimation of β, the standardized selection differential, for CALL resulting from female preference showed that it was under strong direct selection. However, contrary to prediction, CALL did not change over the course of the experiment whereas VOL, CHIRP and other song components did. Simulation of the experiment using the estimated G matrix showed that lack of change in CALL resulted from indirect genetic effects negating direct effects. Changes in song components were largely due to indirect effects. This experiment showed that female preference may exert strong selection on traits but how they respond to such selection will depend greatly upon the G matrix. As predicted, female preference declined in the R lines. The genetic correlations between preference and preferred traits did not decline significantly more in the R lines, suggesting correlations resulted from both linkage disequilibrium and pleiotropy.

Morph-linked variation in female pheromone signalling and male response in a polymorphic moth

Understanding the maintenance of genetic variation in reproductive strategies and polymorphisms in the wild requires a comprehensive examination of the complex interactions between genetic basis, behaviour and environmental factors. We tested the association between three colour genotypes and variation in female pheromone signalling and male antennal morphology in the wood tiger moth (Arctia plantaginis). These moths have genetically determined white (WW, Wy) and yellow (yy) hindwings that are linked to mating success and fitness, with heterozygotes (Wy) having an advantage. We hypothesized that attractiveness and reproductive success are correlated, with Wy females being more attractive than the other two genotypes which could contribute to maintaining the polymorphism. Female attractiveness was tested by baiting traps with females of the three colour genotypes both in low- (i.e. field set-up) and in high-population density (i.e. large enclosure set-up). Male's ability to reach females was correlated to their own colour genotype and antennal morphology (length, area and lamellae count). Contrary to our prediction, morph-related reproductive success and attractiveness were not correlated. Heavier Wy females attracted a lower proportion of males compared to WW and yy females. Specifically, an increase in weight corresponded to a decreased Wy but increased yy female attractiveness. yy females were generally more attractive than others likely due to earlier pheromone release. In males, lamellae count and genetic colour morph were linked to the male's ability to locate females. Furthermore, male traits affected their ability to reach females in a context-specific way. Males with denser antennae (i.e. higher lamellae count) and white males reached the females faster than yellows in the enclosure, while yellow males located females faster than whites in the field. Our results indicate that higher yy female attractiveness was likely affected by the combined effect of early pheromone release, female weight and higher population density. Males' searching success was affected by morph-specific behavioural strategies and local population density. Ultimately, the combined effect of genotype-related pheromone signalling strategies of females together with environment-dependent male behaviour affect male response and potentially contribute to maintaining variation in fitness-related traits.

Age-Related Plasticity Integration in Male Cicadas Tettigetta isshikii: Are Adult Cicadas Capital Breeders?

Labile traits, such as behavioural, physiological traits or body mass, vary within an individual either over time or across environments. Such changes within an individual can be linked across traits, forming within-individual trait correlations. These correlations are particularly expected when ageing causes changes in the expression of multiple traits. Moreover, the direction of these correlations depends on mechanisms that explain age-related changes in each trait, such as physiological deterioration or changes in future fitness expectations. Therefore, assessing within-individual trait correlations offers insights into trait-specific ageing patterns, their integration and age-related reproductive strategies. Here, we tracked individual male cicadas (Tettigetta isshikii) in their natural habitat, repeatedly assessing their plant use (narrow-leafed vs. large-leafed plants), calling activity and body mass. The results revealed that male cicadas lost mass, increased calling activity and a preference for narrow-leafed plants as they aged. This integration of age-related plasticity led to negative within-individual correlations between body mass and behaviours. Considering that adult cicadas consume nutritionally poor xylem sap, the negative within-individual correlations between body mass and risk-taking behaviour suggest that T. isshikii males follow a capital breeding strategy rather than an income breeding strategy. As adult cicadas may use up the energy stored during the nymph stage, an age-related increase in energetically demanding calling activity could cause an age-related decrease in body mass. The terminal investment hypothesis could also explain the age-related increase in calling activity and the preference for narrow-leafed plants. Therefore, we emphasise the importance of individual-level tracking studies in the wild to achieve a comprehensive understanding of the life-history strategies and behavioural ecology of a study animal.

Variation in local population size predicts social network structure in wild songbirds

The structure of animal societies is a key determinant of many ecological and evolutionary processes. Yet, we know relatively little about the factors and mechanisms that underpin detailed social structure. Among other factors, social structure can be influenced by habitat configuration. By shaping animal movement decisions, heterogeneity in habitat features, such as vegetation and the availability of resources, can influence the spatiotemporal distribution of individuals and subsequently key socioecological properties such as the local population size and density. Differences in local population size and density can impact opportunities for social associations and may thus drive substantial variation in local social structure. Here, we investigated spatiotemporal variation in population size at 65 distinct locations in a small songbird, the great tit (Parus major) and its effect on social network structure. We first explored the within-location consistency of population size from weekly samples and whether the observed variation in local population size was predicted by the underlying habitat configuration. Next, we created social networks from the birds' foraging associations at each location for each week and examined if local population size affected social structure. We show that population size is highly repeatable within locations across weeks and years and that some of the observed variation in local population size was predicted by the underlying habitat, with locations closer to the forest edge having on average larger population sizes. Furthermore, we show that local population size affected social structure inferred by four global network metrics. Using simple simulations, we then reveal that much of the observed social structure is shaped by social processes. Across different population sizes, the birds' social structure was largely explained by their preference to forage in flocks. In addition, over and above effects of social foraging, social preferences between birds (i.e. social relationships) shaped certain network features such as the extent of realized social connections. Our findings thus suggest that individual social decisions substantially contribute to shaping certain social network features over and above effects of population size alone.

Fencing amplifies individual differences in movement with implications on survival for two migratory ungulates

Fences have recently been recognized as one of the most prominent linear infrastructures on earth. As animals traverse fenced landscapes, they adjust movement behaviours to optimize resource access while minimizing energetic costs of coping with fences. Examining individual responses is key for connecting localized fence effects with population dynamics. We investigated the multi-scale effects of fencing on animal movements, space use and survival of 61 pronghorn and 96 mule deer on a gradient of fence density in Wyoming, USA. Taking advantage of the recently developed Barrier Behaviour Analysis, we classified individual movement responses upon encountering fences (i.e. barrier behaviours). We adopted the reaction norm framework to jointly quantify individual plasticity and behavioural types of barrier behaviours, as well as behaviour syndromes between barrier behaviours and animal space use. We also assessed whether barrier behaviours affect individual survival. Our results highlighted a high-level individual plasticity encompassing differences in the degree and direction of barrier behaviours for both pronghorn and mule deer. Additionally, these individual differences were greater at higher fence densities. For mule deer, fence density determined the correlation between barrier behaviours and space use and was negatively associated with individual survival. However, these relationships were not statistically significant for pronghorn. By integrating approaches from movement ecology and behavioural ecology with the emerging field of fence ecology, this study provides new evidence that an extraordinarily widespread linear infrastructure uniquely impacts animals at the individual level. Managing landscape for lower fence densities may help prevent irreversible behavioural shifts for wide-ranging animals in fenced landscapes.

Environment and mate attractiveness in a wild insect

The role of female choice in sexual selection is well established, including the recognition that females choose their mates based on multiple cues. These cues may include intrinsic aspects of a male's phenotype as well as aspects of the environment associated with the male. The role of the spatial location of a potential mate has been well studied in territorial vertebrates. However, despite their role as laboratory models for studies of sexual selection, the potential for insects to choose their mates on the basis of location has scarcely been studied. We studied a natural population of individually tagged crickets (Gryllus campestris) in a meadow in Northern Spain. Adults typically move between burrows every few days, allowing us to examine how pairing success of males can be predicted by the burrow they occupy, independent of their own characteristics. We observed the entirety of ten independent breeding seasons to provide replication and to determine whether the relative importance of these factors is stable across years. We find that both male ID and the ID his burrow affect the likelihood that he is paired with a female, but the burrow has a consistently greater influence. Furthermore, the two factors interact: the relative attractiveness of an individual male depends on which burrow he occupies. Our finding demonstrates a close interaction between naturally and sexually selected traits. It also demonstrates that mate choice studies may benefit from considering not only obvious secondary sexual traits, but also more cryptic traits such as microhabitat choice.