Abstract
Structural and functional traits of organisms are known to be related to the size of individuals and to the size of their colonies when they belong to one. Among such traits, propensity to inquilinism in termites is known to relate positively to colony size. Larger termitaria hold larger diversity of facultative inquilines than smaller nests, whereas obligate inquilines seem unable to settle in nests smaller than a threshold volume. Respective underlying mechanisms, however, remain hypothetical. Here we test one of such hypotheses, namely, that nest defence correlates negatively to nest volume in Constrictotermes cyphergaster termites (Termitidae: Nasutitermitinae). As a surrogate to defence, we used ‘patrolling rate’, i.e., the number of termite individuals attending per unit time an experimentally damaged spot on the outer wall of their termitaria. We found that patrolling rate decayed allometrically with increasing nest size. Conspicuously higher patrolling rates occurred in smaller nests, while conspicuously lower rates occurred in larger nests presenting volumes in the vicinity of the threshold value for the establishment of inquilinism. This could be proven adaptive for the host and guest. At younger nest age, host colonies are smaller and presumably more vulnerable and unstable. Enhanced defence rates may, hence, prevent eventual risks to hosts from inquilinism at the same time that it prevents inquilines to settle in a still unstable nest. Conversely, when colonies grow and maturate enough to stand threats, they would invest in priorities other than active defence, opening an opportunity for inquilines to settle in nests which are more suitable or less risky. Under this two-fold process, cohabitation between host and inquiline could readily stabilize.
Highlights
Body size affects structure and function of organisms and, is of particular relevance for ecological and evolutionary processes
Traits ranging from morphology, physiology, and behaviour, to community ecology and biogeography are directly linked to some quantity describing size in organisms in general [1,2,3], and in social insects [4,5,6,7,8,9,10,11] and termites [12,13,14,15,16] in particular
We found that patrolling rate decayed allometrically with increasing nest size, and that conspicuously lower patrolling rates occurred at volumes in the vicinity of the threshold value for the establishment of inquilinism
Summary
Body size affects structure and function of organisms and, is of particular relevance for ecological and evolutionary processes. Traits ranging from morphology, physiology, and behaviour, to community ecology and biogeography are directly linked to some quantity (e.g. mass, volume) describing size in organisms in general [1,2,3], and in social insects [4,5,6,7,8,9,10,11] and termites [12,13,14,15,16] in particular. There is a minimum host nest volume below which inquiline colonies seem unable to settle in [19]
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