Biology subjects

Ottocento, C.

Publications and source records attributed to Ottocento, C..

3 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↗

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↗