The importance of listening: juvenile allocation shifts in response to acoustic cues of the social environment

The social environment has a strong effect on the strength and direction of sexual selection. Juveniles, however, often have social cues that signal the current competitive environment which may provide cues of future competitive challenges. Here we demonstrate that juvenile crickets (Teleogryllus commodus) use the calls of surrounding adult males as a cue of the quality and density of rivals/mates they are likely to encounter. We reared hatchling crickets in six acoustic environments that varied in the density and quality of calls and demonstrate that individuals modified their development rate, phenotype and behaviour at maturity. Males matured more rapidly at a smaller size and called more when reared in a low competition environment. In contrast, males delayed maturity to grow larger when faced with an increased density of high-quality males. Females matured more rapidly when reared in a high density of high-quality males and allocated proportionately more resources towards egg production. A second experiment limiting nutrient availability demonstrates sex-specific allocation shifts in the last stadium when cues are most reliable. Our results demonstrate that the social environment significantly affects allocation strategies and phenotypes, highlighting the importance of juvenile experience and competitive context when examining fitness and selection.

Authors: Michael M. Kasumovic, Matthew D. Hall, Heather Try & Robert C. Brooks

Link: http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2011.02267.x/abstract

Inbreeding and courtship calling in the cricket Teleogryllus commodus

Male field crickets produce two acoustic signals for mating: advertisement calls and courtship calls. While the importance of advertisement calling in mate attraction is well understood, the function of courtship calling is less clear. Here, we tested if the courtship call of male crickets Teleogryllus commodus signals aspects of male quality by comparing the calls of inbred and outbred males. We examined the effect of one generation of full sibling mating on fine-scale call structure, along with several life history traits. Inbreeding reduced nymph survival but had no significant effect on weight or development time. Inbreeding resulted in a small but significant change in two of the six call parameters measured. We then tested if inbreeding affects call trait combinations that are important to females by using the results of a previous selection analysis to compare the multivariate attractiveness of the calls of inbred and outbred males. There was no difference. We conclude that the courtship call of T. commodus is not a reliable signal of aspects of male quality that are affected by inbreeding (which generally reduces fitness-enhancing traits). It might, however, signal components of male fitness that are not affected by changes in heterozygosity.

Authors: Jean M. Drayton, Richard M. C. Miller, Matthew D. Hall & Michael D. Jennions

Link: http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2010.02135.x/full

The adaptive value of functional and life-history traits across fertility treatments in an annual plant

Background and Aims: Plant functional traits are assumed to be adaptive. As selection acts on individuals and not on traits, interpreting the adaptive value of a trait not may be straightforward. For example, productive leaves are associated with fertile environments. However, it is not clear if productive leaves confer an advantage in these habitats, or if they are an advantage as part of a suite of coordinated traits.

Methods Genotypes of Arabidopsis thaliana were grown in high and low nutrient treatments and low, neutral and high pH treatments. Nutrient availability is reduced in acidic or basic soils relative to neutral pH soils. pH treatments were used to alter the availability of resources rather than the amount of resources.

Key Results: Leaf function (specific leaf area, SLA) and life history (size at reproduction, age at reproduction) were variable across genotypes and were plastic. High nutrient availability induced higher SLA and larger size at reproduction. Genotypes that reproduced at large size in high nutrient conditions at neutral pH had the greatest fruit production. SLA was only indirectly related to fruit production through a causal relationship with rosette size; in high nutrient conditions, plants with high SLA were large at reproduction and had higher fruit production. In high nutrient and high pH treatments, plants were large at reproduction, but large size at reproduction was associated with low fecundity. This suggests that large size is adaptive under high nutrient availability.

Conclusions: Interpreting the adaptive value of functional traits will sometimes only be possible when these traits are considered as a suite of correlated and coordinated traits. Leaf functional traits may be important in defining adaptive strategies in A. thaliana but only through how they affect plant life history. Finally, manipulating soil pH can be a valuable tool in assessing adaptive plasticity on nutrient gradients.

Authors: Stephen P. Bonser, Brenton Ladd, Keyne Monro, Matthew D. Hall and Michael A. Forster.

Link: http://aob.oxfordjournals.org/content/early/2010/09/29/aob.mcq195.abstract

Performance is no proxy for genetic quality: trade-offs between locomotion, attractiveness, and life history in crickets

The genetic relationships among traits contributing to overall fitness are an important subject of inquiry because such relationships influence how suites of traits respond to selection. Within the field of sexual selection, these relationships are also of interest for assessing whether any given trait can be used as a proxy for total fitness. A growing number of studies have demonstrated close links between whole-organism performance traits and determinants of individual fitness; however, an understanding of the genetic relationships between performance and important aspects of genetic quality is currently lacking. We present the results of a quantitative genetic study in which we estimate covariation between a locomotor performance trait (maximal jumping ability), calling effort, sexual attractiveness, and life-history traits in male Teleogryllus commodus crickets. We show that the major axis of genetic variation (g_max) is characterized by a contrast between jump performance and life-history traits associated with mating success. Moreover, two additional axes of significant multivariate genetic variation exist, each characterized by strong contrasts among traits. These results argue against the existence of a single axis representing genetic quality, favoring instead the idea that resource allocation strategies shape multiple dimensions of genetic quality through trade-offs among key life-history traits, including performance.

Authors: Simon P. Lailvaux, Matthew D. Hall, and Robert C. Brooks

Link: http://www.esajournals.org/doi/abs/10.1890/09-0963.1