Archetype

Evolution and development of castes in ants

Up until resuming posting a couple of weeks ago you may had thought I was dead. Well, fear not (nor rejoice just yet). I am now happy to report that those previous months of blogging slowness paid off: I got funding for the project I wrote during the summer.

Starting next year I will be working as a postdoc in the laboratory of Patrícia Beldade at the Instituto Gulbenkian de Ciência in Portugal. This is an evolutionary developmental biology lab, an area of research fondly know as EvoDevo.

EvoDevo ask questions that are of a different nature than the classical Neo-Darwinian ones. For example, in the latter you always presuppose that variation exists in populations and that there is a link between what you see at the level of an organism’s morphology (its phenotype) and the underlying genetics (its genotype), and you study how natural selection then goes to mess things around. In EvoDevo you don’t give these things for granted. Rather, you ask how do new features (novelties and innovations) arise in the first place and exactly how does the link between genotype and phenotype comes about through the developmental process. From there, what you seek is to understand evolution as a process of modification of development.

Now, one cool thing about the Variation: Development and Selection lab of Patrícia Beldade is that her research focuses right at the area of confluence between the two views just described. She seeks to understand the mechanism by which development generates phenotypic variation of the sort that is important for natural selection to act upon.

We will be working with ants, of course, looking at the evolution of the caste system in the group. Most studies into caste evolution take the Neo-Darwinian approach to the problem. The classical work on the subject is Oster and Wilson 1978 book Caste and Ecology in the Social Insects¹, where the authors specifically set to focus “attention on the ecological and evolutionary aspects of caste, as distinct from developmental and physiological processes”². For example, there is a lot of work in this area on optimal caste ratios, looking at the proportion of the different castes within a colony in terms of how costly they are to produce. In contrast, we will look at the problem in terms of the potential that the developmental system has to produce a variety of alternative caste morphologies as dramatic as fully winged queens versus completely wingless workers.

Worker ants are, ecologically, the most conspicuous adult forms, so we often take this caste for granted. But from a comparative perspective workers are the odd ones: the flightless form arose in the common ancestor of the group as a modified version of a winged female. Once this ability originated, once this extreme plasticity in development was gained, it evolved as ants speciated giving rise to the extraordinary diversity of castes and forms we see today. But, for the most part, queens remain fully winged individuals, so in understanding ant evolution it is important to keep in mind that we are dealing with a caste-producing developmental system– just concentrating on workers wont do.

The project was written in collaboration with Christian Peeters from the Université Pierre et Marie Curie in Paris. As I have mentioned before, he specializes in all those ant species where the queen is not a winged individual, but rather a wingless form intermediate between the typical queen and the worker. This component is also important for our project, not only because such peculiar type of queens gives us more insight in this plastic developmental system, but also because queen morphology has a direct impact in the reproductive strategy of colonies. So this is a way to tie morphology and development with behavioral ecology and thus ask questions on selection and adaptation.

Does this means I am turning away from systematics? Not at all (again, for the joy of some and fear of others). My research centers on understanding the evolution of form, and while comparative anatomy and systematics serve to establish evolutionary patterns, it is development that provides the process side of the explanation. In fact, the first part of the project is pattern oriented, our goal been to identify and characterize relevant anatomical modifications. Besides, I still have a backlog of systematic manuscripts from my PhD research that I am preparing for publication.

Expect to see more on this topic in the coming months.

Notes and references

Tags: Castes, EvoDevo, Plasticity

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