Physiology as a caste-defining feature

Abstract

Abstract. Division of labour is a key factor in the ecological success of social insects. Groups of individuals specializing on a particular behaviour are known as castes and are usually distinguished by morphology or age. Physiology plays a key role in both these types of caste, in either the developmental physiology which determines morphology, or the temporal changes in physiology over an insects life. Physiological correlates of morphological or temporal caste include differences in gland structure, secretory products, leanness, neuroanatomy and neurochemistry. However, purely physiological castes could also occur. Physiological castes are discrete groups of same-age same-size individuals with particular physiological competencies, or groups of individuals with similar physiology crossing age or size groups. A stable physiological caste occurs in the monomorphic Pharaohs ant, where some ants can detect old pheromone trails and retain this specialization over time. These ants differ physiologically from other workers, and the differences arise before eclosion. More temporary physiological castes occur in the ant Ectatomma where brood care specialists have more developed ovarioles than other same-aged workers, and in the honeybee where nurses, wax-workers and soldiers all differ physiologically from same-aged nestmates. Physiology is an important aspect of caste, not only in its contribution to age-related and morphological castes, but also in its own right as a caste grouping factor. While age and morphological differences make caste structures accessible for study, more cryptic physiological castes may play just as important a role in division of labour.

Reproductive status, endocrine physiology and chemical signaling in the Neotropical, swarm-founding eusocial wasp,Polybia micansDucke (Vespidae: Epiponini)

“…Eusocial insects within the order Hymenoptera (bees, wasps and ants) are characterized by the production of distinct phenotypes (caste polyphenism) in the female sex: the queen, the worker and often additional physiologically or morphologically specialized types within the worker caste (Wilson, 1971;Hunt, 2006;Hunt et al, 2007;Robinson, 2009;Tibbetts and Izzo, 2009;Shukla et al, 2013). In most caste-based societies the development of such specialized phenotypes is induced or at least biased in a pre-imaginal stage, where qualitative or quantitative differences in diet, pheromonal signals, mechanical stimuli or other environmental cues trigger endogenous signaling cascades toward alternative developmental trajectories (Wilson, 1971; Chavarría-Pizarro and West-Eberhard, 2010;Suryanarayanan et al, 2011;Hartfelder and Emlen, 2012;Penick and Liebig, 2012).…”

Experience, corpulence and decision making in ant foraging

“…Task specialisation may be enhanced further if individuals have response thresholds that change according to experience such that the threshold for a particular task decreases after that task has been performed (Ravary et al, 2007;Théraulaz et al, 1998). Threshold adjustment could be mediated quickly by learning from experience or more slowly through physiological changes, such as laying down fat reserves or activating glands (Franks and Tofts, 1994;Robinson, 2009). However, memory carries primarily individual-specific information (though acquired in a social context) whereas fat reserves may carry information about the state of both the individual and the colony, in terms of how much food has been available recently.…”

The effects of genotype, caste, and age on foraging performance in leaf-cutting ants

“…Division of labor between individuals is the defining trait of social insects, and is affected by age, experience, body size, morphology, and physiology (Hölldobler and Wilson 1990;Robinson 1992Robinson , 2009Ravary et al 2007;Johnson 2010). If genotypes vary in their ability to carry out particular tasks, or their propensity to engage in them, then colonies with a greater diversity of genotypes may be better able to respond appropriately to changing environmental conditions (Oldroyd and Fewell 2007).…”