2 - Wood ant reproductive biology and social systems

Summary

Transmitting genes from one generation to the next is the fundamental basis of natural selection and evolution. Understanding the reproductive biology of a species is, therefore, fundamental to understanding how the species evolved and how it is adapted to its environment. In eusocial insects such as the wood ants (Formica rufa group), reproduction is invested in a specialised reproductive caste, which produces both the workers and the next generation of sexual individuals. This chapter introduces the reproductive biology of wood ants, and also gives a general view of the life cycle of a wood ant colony to put the reproductive biology in context.

Wood ant life cycle

The wood ant life cycle is strongly linked to seasonal changes in the environment. Wood ant colonies generally first become active, after winter quiescence, in early spring when the sun begins to heat the nest and, in some locations, melt the snow (Figure 2.1). The timing of the beginning of activity is strongly influenced by the local climate, altitude and nest location. In Switzerland, for example, significant colony activity usually begins in March or April (Cherix 1981; Chauternes 1988).

On warm and sunny days, early in spring, worker activity begins and the internal temperature of the nest begins to rise to between 25°C and 30°C. Nest temperature remains at this level for the entire active season, even when, during early spring, the outside temperature is close to freezing (discussed in detail in Chapter 4) (Rosengren et al. 1987). Workers gather in the warm nest core and their nutrient-producing glands become more active, converting lipids and protein into food ready to be fed to queens and future larvae (Bausenwein 1960). The queen(s) remain(s) in the warm nest core for several days and lay ‘winter eggs’. The larvae hatching from these eggs are fed by the overwintering workers, usually developing into sexuals in about 6 weeks (Otto 2005). The queen(s) then retire(s) to the lower nest chambers to start to produce ‘summer eggs’, which usually develop into workers (Otto 2005).

Reproduction generally takes place in early summer, with thousands of sexual individuals flying away from their nests and participating in nuptial flights (e.g. Cherix et al. 1991).