09 July 2017
© Guy Padfield
Citation: Padfield, G. (2017). A Review of: The Ecology & Evolution of Heliconius Butterflies [Online]. Available from http://www.dispar.org/reference.php?id=132 [Accessed September 22, 2017].
by Chris D. Jiggins and Supplement by Gerardo Lamas
Published by Oxford University Press, December 2016
Hardback, 288 pages. ISBN: 978-0-19-956657-0
From the publisher: "The Heliconius butterflies are one of the classic systems in evolutionary biology and have contributed hugely to our understanding of evolution over the last 150 years. Their dramatic radiation and remarkable mimicry has fascinated biologists since the days of Bates, Wallace, and Darwin. The Ecology and Evolution of Heliconius Butterflies is the first thorough and accessible treatment of the ecology, genetics, and behaviour of these butterflies, exploring how they offer remarkable insights into tropical biodiversity. The book starts by outlining some of the evolutionary questions that Heliconius research has helped to address, then moves on to an overview of the butterflies themselves and their ecology and behaviour before focussing on wing pattern evolution, and finally, speciation. Richly illustrated with 32 colour plates, this book makes the extensive scientific literature on Heliconius butterflies accessible to a wide audience of professional ecologists, evolutionary biologists, entomologists, and amateur collectors".
When Gregor Mendel proposed the existence of discrete but invisible 'factors' to explain the statistical patterns of inherited characteristics in his bean plants he had no way of knowing materially what these mystical entities were, still less how they governed the almost infinite diversity of structure and pattern in living organisms. Even when I was a student, back in the early 1980s, the actual operation of genes was essentially magic. More and more was being discovered about the mechanisms of DNA transcription and protein synthesis but at the heart of our (mine, at least) pretended understanding of genetics lay a huge leap of faith - that, somehow, what was read from the book of life in the nucleus of a cell could be rewritten in form, colour and function in the bodies of plants and animals. It had to be so, and we all believed in it, but the implied physical and biochemical pathways of cause and effect involved in the process remained as inscrutable as the workings of voodoo.
In the last few decades, and especially in the last few years, this situation has changed dramatically. Advances in biochemical and other techniques have allowed scientists to piece together in detail some of these hitherto invisible pathways. You might think this would break the spell, but as I read Chris Jiggins's book I felt more a sense of increasing awe than demystification. What I had taken for granted as magic is actually far more amazing when spelt out in step-by-step sequence. In fact, what makes evolving nature so thrilling and compelling an object of study is precisely that nothing happens by magic - everything is meticulously governed by real, physical processes.
The Heliconius butterflies of South America have long been a focus for research into genetics and evolution. This is partly because they are easy subjects to breed and study in the laboratory. They also show an amazing diversity of wing pattern and colour, making them highly suitable for tracking cause and effect in these designs. But, above all, they exhibit, in their historical and ongoing evolutionary history, fascinating patterns of convergence, divergence and coevolution with other species. Convergent evolution is manifested in the phenomenon of mimicry, first recognised by Henry Walter Bates from observations in the Amazon of Heliconius and other genera. At the same time, competition for the larval and adult food sources, together with the constant adaptive imperative for plant and butterfly to outwit each other, has led to divergence and coevolution. Where species on biochemically divergent trajectories show convergence to common morphological patterns there are particularly important opportunities for establishing the links between genetic code and morphological expression.
Jiggins tells the story of Heliconius research in a logical and very readable order, beginning with an overview of the butterflies themselves and the biological questions they raise. This is followed by detailed and fascinating accounts of their behaviour and ecology, moving on to consider how wing patterns are laid down in the larval and pupal stages and concluding with a chapter putting all this together in the context of evolution and speciation. Each chapter opens with a brief summary in accessible language, aimed particularly at those who would find the technical terminology of the larger part of the book obstructive. This is useful, but the main text is well enough written for anyone with sufficient interest to follow, whether professional biologist or general naturalist. It is lucid, coherent and convincing, representing divergent scientific positions fairly and telling an altogether compelling story. Greyscale diagrams and photographs are interspersed with the text for ease of following the argument. Many of these are duplicated in full colour in the central plates section of the book. In the course of the narrative we come to know the 40-odd Heliconius species in intimate detail. I did not know before that they were pollen feeders, able to extend their active, reproductive lives to many months by utilising this precious resource. It was intriguing to read of Passiflora plants lying in wait before putting on a sudden, sneaky growth spurt, and how butterflies patrol such dormant passion vines, hoping to catch the new shoots the moment they appear.
As intimated above, however, the focus of the book is evolution. How do random mutations at a biochemical level lead to advantageous morphological, ecological and behavioural adaptation, bearing in mind in particular the fact that many genes govern more than one character simultaneously (you would hardly expect a random alteration to be beneficial across all aspects of its expression)? Jiggins presents evidence and hypotheses building up to a convincing, if still radically incomplete picture of how this happens. Amazingly, it is possible to identify particular genes for particular wing characters and trace in considerable material and functional detail how they act. This includes explaining how a biochemical sense of space is generated, so a particular scale at a particular point on the wing 'knows' where it is and thus what colour to express. I found myself constantly pausing to marvel at the phenomenal ingenuity of nature even in the ordinary, everyday processes we take for granted.
I cannot write an honest review without expressing some personal reservation about this kind of research. Inevitably, turning magic into mechanics involves treating living organisms as so much biological material. Research into the laying down of wing colour and pattern, for example, involves dissecting larval and pupal wings at each successive stage of their development. For trained biologists, this is an entirely unexceptional (though in this case, very delicate) procedure - killing and dissecting is a basic method of biological enquiry. Nor would I accuse Jiggins and his co-researchers of any kind of callousness or cruelty. Nature herself discards most of her children (more than 99% of butterfly eggs laid never reach adulthood) and it is difficult to see a qualitative difference between being sucked dry by a forest bug, eaten by a blue tit or cut up by a biologist. Nevertheless, it is important for both consumer and generator of this kind of knowledge to maintain a sense of perspective between scientific curiosity and respect for life, so boundaries are not overstepped. There is no doubt in my mind that research involving higher animals loses this perspective.
Such reservations aside, this book offers a fascinating insight into both the lives of these amazing creatures and their biology. Many questions remain and more spring up as fast as others are answered; but Jiggins’s work shows the possibility, at least, of working some kind of rational narrative into the bewildering variety of form, function and behaviour in this most enigmatic group of organisms - and by extension, in life on earth in general.
The book is available through all good book stores, including those that are online.