The evolution of iridescent blue colour in Heliconius butterflies and its role in behaviour


The evolution of iridescent blue colour in Heliconius butterflies and its role in behaviour

 

Lead supervisor: Dr Nicola Nadeau, Univeristy of Sheffield, APS
Co-supervisors: Dr Mike Speed, Institute of Integrative Biology, University of Liverpool.

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We are seeking an enthusiastic student with interests in evolution and behaviour to work on a project investigating the role of iridescent structural colour in predator avoidance and mate choice in Heliconius butterflies. The bright wing colours of these butterflies act as warnings to predators and mimicry between species facilitates predator learning and reduces attack rates. Wing colours are also used for mate choice and attraction. The main colours used are red, yellow and black, due to pigments, but a small number of species also exhibit iridescent blue/green, due to sub-micron scale structures. The role of these colours in deterring predators and attracting mates is less well understood. The project can be tailored to the interests of the student but would likely involve experiments using captive butterfly populations in South/Central America and the UK, and could involve experiments with wild or captive avian predators or theoretical modelling. The project would also tie in with ongoing work on the genetic basis of these traits.

Structural colours, and in particular their UV reflective colours, are used for mate choice in many species and in several cases have also been shown to be condition dependent (1). We do not know if this is also the case in Heliconius, and female mate choice in general in this group has not been studied extensively. This is particularly interesting given recent findings of sexual dimorphism in both UV reflectance (unpublished) and UV perception (2). Condition dependence could also influence predator avoidance behaviour if it reflects variation in toxicity (3). However, iridescent colours could be hard for predators to learn because their appearance changes with angle, but when combined with movement the bright flash effects they produce could be effective warnings.

Therefore, the dual selection pressures for both predator avoidance and mate attraction could have either conflicting or reinforcing effects on the evolution of these colours leading to interesting evolutionary dynamics. However, structural colours also have the potential to contain private information channels that are visible to the butterflies but not their avian predators. They reflect strongly in the UV range, which is perceived differently by birds and butterflies, and produce polarised reflections, which can be detected by butterflies but not birds.

References:
1. Kemp DJ. Resource-mediated condition dependence in sexually dichromatic butterfly wing coloration. Evolution 2008, 62(9):2346–58.
2. McCulloch KJ, Osorio D, Briscoe AD. Sexual dimorphism in the compound eye of Heliconius erato: a nymphalid butterfly with at least five spectral classes of photoreceptor. Journal of Experimental Biology 2016, 219:2377-2387.
3. Lee TJ, Speed MP, Stephens PA, Honest Signaling and the Uses of Prey Coloration. The American Naturalist 2011, 178:E1–9.

Further information:
• Merrill RM, Dasmahapatra KK, Davey JW, Dell’Aglio DD, Hanly JJ, Huber B, et al. The diversification of Heliconius butterflies: what have we learned in 150 years? J Evol Biol. 2015 Aug 1;28(8):1417–38.
• http://nadeau-lab.group.shef.ac.uk/
• http://www.heliconius.org/

How to apply

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Please select ‘Standard Ph.D.’

Department: Animal and Plant Sciences Department

Project title: The evolution of iridescent blue colour in Heliconius butterflies and its role in behaviour

Supervisor(s): Dr. Nicola Nadeau, Dr. Mike Speed

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