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How the ladybird got its spots: effects of resource limitation on the honesty of aposematic signals
Article first published online: 6 FEB 2012
DOI: 10.1111/j.1365-2435.2012.01961.x
© 2012 The Authors. Functional Ecology © 2012 British Ecological Society
Additional Information
How to Cite
Blount, J. D., Rowland, H. M., Drijfhout, F. P., Endler, J. A., Inger, R., Sloggett, J. J., Hurst, G. D. D., Hodgson, D. J. and Speed, M. P. (2012), How the ladybird got its spots: effects of resource limitation on the honesty of aposematic signals. Functional Ecology, 26: 334–342. doi: 10.1111/j.1365-2435.2012.01961.x
Publication History
- Issue published online: 27 MAR 2012
- Article first published online: 6 FEB 2012
- Received 4 October 2011; accepted 21 December 2011 , Handling Editor: Adam Kay
Keywords:
- aposematism;
- carotenoids;
- Coccinella septempunctata;
- coccinelline;
- phenotypic plasticity;
- precoccinelline
Summary
1. Prey species often possess defences (e.g. toxins) coupled with warning signals (i.e. aposematism). There is growing evidence that the expression of aposematic signals often varies within species and correlates with the strength of chemical defences. This has led to the speculation that such signals may be ‘honest’, with signal reliability ensured by the costliness of producing or maintaining aposematic traits.
2. We reared larval seven-spot ladybirds (Coccinella septempunctata) on a Low or High aphid diet and measured the effects on warning signal expression (elytral carotenoid pigmentation, conspicuousness, spot size), levels of defensive alkaloids (precoccinelline, coccinelline), and relationships between these traits.
3. High-diet individuals had greater total precoccinelline levels, and elytra carotenoid concentrations at adulthood which was detectable to a typical avian predator. However, larval diet did not significantly affect adult body mass or size, spot size or coccinelline levels.
4. Elytra carotenoid concentrations correlated positively with total precoccinelline levels in both diet groups and sexes. However, the relationship between elytra carotenoid concentrations and total levels of coccinelline depended on sex: in both diet groups, elytra carotenoids and coccinelline levels were positively correlated in females, but negatively correlated in males. Spot size and coccinelline levels correlated positively in Low-diet individuals, but negatively in High-diet individuals.
5. These results point to physiological linkages between components of aposematism, which are modulated by resource (i.e. food) availability and affect the honesty of signals. Developmental diet, but also sex, influenced the relationships between signals and toxin levels. Ladybirds are sexually size dimorphic, and thus in comparison with males, females may be more susceptible to resource limitation and more likely to be honest signallers.