hosts, often referred to as ‘Emery’s rule’ (Hölldobler and Wilson, 1990;
Bourke and Franks, 1995), contrasts sharply with the much more distant
taxonomic relationship between most other kinds of parasites and their
hosts, as exemplified by the other chapters in this volume.
The commingling and communal care of brood in mixed colonies
provides important additional opportunities for parasitic adaptation and
for the further elaboration and specialization of parasitic relationships
that are not possible in compound nests. In compound nests, the parasite
species must retain the ability to maintain brood, the chambers in which it
is contained and the queens that produce it. However, in mixed colonies,
where the parasite colony’s brood and queens are fully integrated into the
host colony and cared for by the host workers, the domestic abilities of the
parasite workers are no longer required; and these abilities, and often
the workers themselves, can be discarded. An evolutionary progression
towards the loss of domestic abilities in workers of obligatory slave-
making (or dulotic) species and towards the elimination of the worker
caste in inquilines is a hallmark of the highly specialized social parasites
that exist in mixed colonies (Wilson, 1971, 1975b; Dobrazanska, 1978;
Buschinger, 1986; Stuart and Alloway, 1985; Mori and Le Moli, 1988;
Hölldobler and Wilson, 1990).Compound nests
The various kinds of compound nests that have been described constitute
an array of different types of relationships, generally among distantly
related ant species. They encompass what might be fairly casual, perhaps
accidental, facultative relationships but also include some that are clearly
highly specialized obligatory social parasitism. The more rudimentary
associations might be quite common in nature and might constitute
important evolutionary precursors to the more specialized forms.Plesiobiosis
The most rudimentary and ‘least intimate’ association involving
compound nests is referred to as plesiobiosis and involves a spatially
close nesting association between species with little, if any, direct
communication between the societies. Two or more nests of different
species under the same stone but otherwise quite separate are a common
example. Plesiobiosis tends to occur among species that are not closely
related taxonomically, since closely related species rarely tolerate the
close proximity of one another’s nests. None the less, such associations
are not always completely amiable and, if the nest chambers of such
colonies are broken open, then fighting, brood pilfering and predation are
likely to ensue. The benefits from plesiobiotic associations might involve
the creation of a suitable microenvironment for one species by the
other or inadvertent protection from certain predators or competitors
(see Wheeler, 1910; Wilson, 1971).318 R.J. Stuart