Eusociality refers to a highly complex order of social organization in animals and is epitomized by many insects such as certain species of ants and bees. These social insects are vital to most of the world’s terrestrial habitats, with ants helping to maintain nutrient levels in soil and honeybees accounting for 80 percent of pollination worldwide. The hierarchical structures employed in these societies have evolved with the division of reproductive labor at their core, often with reproductive queens and largely sterile workers that care for the brood. We spoke to sociobiologist and co-Editor-in-Chief of Frontiers in Zoology Jürgen Heinze, from the University of Regensburg, Germany, about the complex social behaviours that underpin eusocial insect communities and what led to his interest in them.
Jürgen Heinze obtained his PhD at the Technische Universität Darmstadt, Germany, where he investigated queen polymorphisms in the North American ant of the genus Leptothorax. Heinze continued his research into this genus at Harvard University, USA, in the laboratory of noted sociobiologist E.O. Wilson. He then returned to Germany, joining the University of Würzburg, Friedrich-Alexander-Universität Erlangen-Nürnberg and finally the University of Regensburg, where he now holds the position of professor and studies the evolution of group structures and reproductive tactics in social insects.
What first interested you in social insects?
Their incredible ubiquity, complexity and ecological and evolutionary success – social insects are almost everywhere, they have evolved the most diverse life histories, and they constitute one of the few pinnacles of social evolution.
You worked for some time with E.O. Wilson, perhaps one of the best known sociobiologists. How do you think this influenced the direction of your research?
Working with the wonderful ant team of E.O. Wilson and Bert Hölldobler showed me that there is always something new to discover, if you only take the time to watch carefully and ask the right questions – even in your backyard or with long studied model systems.
What are the main projects you are currently working on?
Life history evolution in social insects, in particular the proximate and ultimate causes of the links between reproduction and longevity. In addition, kin conflict and its resolution and the basics of division of labor and caste differentiation, which are everlasting hot topics in insect sociobiology.
Social insects are among the most dominant organisms on earth, how do they affect our ecosystems?
Take away the social insects and most terrestrial ecosystems will collapse. Social insects play key roles as pollinators, predators, prey, direct or indirect herbivores, and thus our world cannot possibly be imagined without them.
What is so special about the reproductive structure of social insects, which makes them different from other group living animals?
Colonies have reached a high degree of division of reproductive labor, with reproductive queens and non-reproductive workers. Though some other animals have also evolved a eusocial life history, some social insects, in particular the ants, have brought this to perfection.
What insights are gained into the organization of social insects by studying alternative reproductive tactics?
Individuals of the same species may pursue their reproductive success in different ways, e.g. males may defend a harem of females and are engage in sneak copulations unnoticed by the dominant male. In several species of social insects, alternative reproductive tactics (or strategies, if based on a genetic polymorphism) are associated with differences in morphology, e.g. fighter males versus disperser males or wingless versus winged queens. Learning more about the reproductive success of these different phenotypes not only leads to a better understanding of colony structure but in general helps to increase our knowledge about life history evolution.
How does a queen ensure that she is the only reproductively active female in the colony?
Colonies of many species of social insects may have several queens, which in most cases tolerate one another and only in a few species form reproductive hierarchies by ritualized or overtly aggressive dominance behavior. Quite generally, however, workers refrain from reproduction in the presence of a fertile queen, and this appears to be linked to chemical signals of the queen. Workers that begin to develop their own eggs in the presence of a queen may be attacked by the queen itself or by other workers, which sustains reproductive division of labor. Worker altruism thus appears in part to be maintained by mutual surveillance and policing.
There must be a huge amount of competition between males to mate with the queen, what does current research tell us about how males use reproductive tactics to ‘win’?
Males of many social Hymenoptera (ants, bees, wasps) are short-lived and die after mating. Their testes have degenerated by the time they reach sexual maturity and they start their reproductive life with a limited amount of sperm. Furthermore, mating often occurs during short and highly localized nuptial flights, in which thousands of sexuals from a large number of colonies meet for a few hours during one or a few days per year. There is little a male ant or bee can do to increase its mating success. When mating occurs in the nest, as in the ant genus Cardiocondyla, males can try to monopolize all female sexuals by eliminating their rivals – this probably explains the unique evolution of life-long spermatogenesis in these fighter males.
What do you think are the key questions that remain to be answered in the study of social insects?
We still do not fully understand the mechanisms underlying caste differentiation and how queens and workers with very different phenotype, behavior, life expectancy etc. can develop from the same genotype. Several social insect genomes have recently become available and functional genomics certainly will help to uncover the proximate mechanisms leading to phenotypic plasticity.