Biology subjects

Burdfield-Steel, E.

Publications and source records attributed to Burdfield-Steel, E..

7 recordsLinked to original sources

bioRxiv2024

Honest signalling in predator-prey interactions: testing the resource allocation hypothesis

Warning signals are honest if they reliably deliver information about prey unprofitability to predators. One potential mechanism that may create and maintain a positive relationship between the strength of signals and defence is the resource allocation between these costly traits. Here, we test this hypothesis using the wood tiger moth Arctia plantaginis, whose females red hindwings are a warning signal to predators but show considerable variation in colouration within populations. These moths also produce a defensive chemical that is known to influence avian predator attack risk. Using dietary manipulations, image and chemical analyses, and experiments with ecologically relevant predators we demonstrate that protein availability during development can influence the strength of both the primary warning signal and the secondary defence. Our results show that females raised on a high-protein or ad libitum natural diet produced more distasteful defensive fluids than those raised on a low-protein diet or subjected to periodic food deprivation. While the patterning of the warning signal was unaffected by food deprivation, its efficacy was diminished in moths raised on a low-protein diet. However, this change was imperceptible to avian predators. Critically, resource availability influenced the relationship between signal strength and defence: moths on a high-protein diet displayed a positive correlation between warning signal strength and unpalatability, whereas this correlation was absent in moths raised on a natural diet. These findings show that resource availability can weaken the reliability of warning signals as an indicator of an individuals defensive capabilities, highlighting the complex interplay between ecological conditions and the evolution of honest signalling.

evolutionary biology↗

bioRxiv2024

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

O_LIUnderstanding the maintenance of genetic variation in reproductive strategies and polymorphisms in the wild requires a comprehensive examination of the complex interactions between genetic basis, behavior, and environmental factors. C_LIO_LIWe tested the association between three color genotypes and variation in female pheromone signaling 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. C_LIO_LIFemale attractiveness was tested by baiting traps with females of the three color genotypes both in low-(i.e., field setup) and in high-population density (i.e., large enclosure setup). Males ability to reach females was correlated to their own color genotype and antennal morphology (length, area, and lamellae count). C_LIO_LIContrary 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 color morph were linked to the males 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. C_LIO_LIOur 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 behavioral strategies and local population density. Ultimately, the combined effect of genotype-related pheromone signaling strategies of females together with environment-dependent male behavior affect male response and potentially contribute to maintaining variation in fitness-related traits. C_LI

evolutionary biology↗

bioRxiv2023

Diet influences resource allocation in chemical defence but not melanin synthesis in an aposematic moth

For animals that synthesise their chemical compounds de novo, resources, particularly proteins, can influence investment in chemical defences and nitrogen-based wing colouration such as melanin. Competing for the same resources often leads to trade-offs in resource allocation. We manipulated protein availability in the larval diet of the wood tiger moth, Arctia plantaginis, to test how early life resource availability influences relevant life history traits, melanin production, and chemical defences. We expected higher dietary protein to result in more effective chemical defences and a higher amount of melanin in the wings. According to the resource allocation hypothesis, we also expected individuals with less melanin to have more resources to allocate to chemical defences. We found that protein-deprived moths had a slower larval development, and their chemical defences were less unpalatable for bird predators, but the expression of melanin in their wings did not differ from that of moths raised on a high-protein diet. The amount of melanin in the wings, however, unexpectedly correlated positively with chemical defences, irrespective of the diet they were raised on. Our findings demonstrate that the resources available in early life have an important role in the efficacy of chemical defences, but melanin-based warning colours are less sensitive to resource variability than other fitness-related traits.

ecology↗

bioRxiv2022

Not just the sum of its parts: geographic variation and non-additive effects of pyrazines in the chemical defence of an aposematic moth

Chemical defences often vary within and between populations both in quantity and quality, which is puzzling if prey survival is dependent on the strength of the defence. We investigated the within-and between-population variability in chemical defence of the wood tiger moth (Arctia plantaginis). The major components of its defences, SBMP (2-sec-butyl-3-methoxypyrazine) and IBMP (2-isobutyl-3-methoxypyrazine) are volatiles that deter bird attacks. We expected the variation to reflect populations predation pressures and early-life conditions. To understand the role of the methoxypyrazines, we experimentally manipulated synthetic SBMP and IBMP and tested the birds reactions. We found a considerable variation in methoxypyrazine amounts and composition, both from wild-caught and laboratory-raised male moths. In agreement with the "cost of defence" hypothesis, the moths raised in the laboratory had a higher amount of pyrazines. We found that SBMP is more effective at higher concentrations and that IBMP is more effective only in combination with SBMP and at lower concentrations. Our results fit findings from the wild: the amount of SBMP was higher in the populations with higher predation pressure. Altogether, this suggests that, regarding pyrazine concentration, more is not always better, and highlights the importance of testing the efficacy of chemical defence and its components with relevant predators, rather than relying only on results from chemical analyses.

evolutionary biology↗

bioRxiv2021

Experimental evolution of a pheromone signal

Sexual signals are important in speciation, but understanding their evolution is complex as these signals are often composed of multiple, genetically interdependent components. To understand how signals evolve, we thus need to consider selection responses in multiple components and account for the genetic correlations among components. One intriguing possibility is that selection changes the genetic covariance structure of a multicomponent signal in a way that facilitates a response to selection. However, this hypothesis remains largely untested empirically. In this study, we investigate the evolutionary response of the multicomponent female sex pheromone blend of the moth Heliothis subflexa to 10 generations of artificial selection. We observed a selection response of about 3/4s of a phenotypic standard deviation in the components under selection. Interestingly, other pheromone components that are biochemically and genetically linked to the components under selection did not change. We also found that after the onset of selection, the genetic covariance structure diverged, resulting in the disassociation of components under selection and components not under selection across the first two genetic principle components. Our findings provide rare empirical support for an intriguing mechanism by which a sexual signal can respond to selection without possible constraints from indirect selection responses.

evolutionary biology↗

bioRxiv2021

Toward an understanding of the chemical ecology of alternative reproductive tactics in the bulb mite (Rhizoglyphus robini)

BackgroundUnder strong sexual selection, certain species evolve distinct intrasexual, alternative reproductive tactics (ARTs). In many cases, ARTs can be viewed as environmentally-cued threshold traits, such that ARTs coexist if their relative fitness alternates over the environmental cue gradient. Surprisingly, the chemical ecology of ARTs has been underexplored in this context. To our knowledge, no prior study has directly quantified pheromone production for ARTs in a male-polymorphic species. Here, we used the bulb mite--in which males are either armed fighters that kill conspecifics, or unarmed scramblers--as a model system to gain insight into the role of pheromones in the evolutionary maintenance of ARTs. Given that scramblers forgo investment into weaponry, we tested whether scramblers produce higher pheromone quantities than fighters, which would improve the fitness of the scrambler phenotype, e.g. through female mimicry to avoid aggression from competitors. To this end, we sampled mites from a rich and a poor nutritional environment and quantified their production of the female sex pheromone -acaridial through gas chromatography analysis. ResultsWe found a positive relationship between pheromone production and body size, but males exhibited a steeper slope in pheromone production with increasing size than females. Females exhibited a higher average pheromone production than males. We found no significant difference in slope of pheromone production over body size between fighters and scramblers. However, scramblers reached larger body sizes and higher pheromone production than fighters, providing some evidence for a potential female mimic strategy adopted by large scramblers. Pheromone production was significantly higher in mites from the rich nutritional environment than the poor environment. ConclusionFurther elucidation of pheromone functionality in bulb mites, and additional inter-and intrasexual comparisons of pheromone profiles are needed to determine if the observed intersexual and intrasexual differences in pheromone production are adaptive, if they are a by-product of allometric scaling, or diet-mediated pheromone production under weak selection. We argue chemical ecology offers a novel perspective for research on ARTs and other complex life-history traits.

evolutionary biology↗

bioRxiv2020

Geographic mosaic of selection by avian predators on hindwing warning colour in a polymorphic aposematic moth

Warning signals are predicted to develop signal monomorphism via positive frequency-dependent selection (+FDS) albeit many aposematic systems exhibit signal polymorphism. To understand this mismatch, we conducted a large-scale predation experiment in four locations, among which the frequencies of hindwing warning coloration of aposematic Arctia plantaginis differ. Here we show that selection by avian predators on warning colour is predicted by local morph frequency and predator community composition. We found +FDS to be strongest in monomorphic Scotland, and in contrast, lowest in polymorphic Finland, where different predators favour different male morphs. +FDS was also found in Georgia, where the predator community was the least diverse, whereas in the most diverse avian community in Estonia, hardly any models were attacked. Our results support the idea that spatial variation in predator and prey communities alters the strength or direction of selection on warning signals, thus facilitating a geographic mosaic of selection.

ecology↗