Models of Division of Labor and Expression of Biological Clock in the Colony of Gray-Black Spiny Ant, Polyrhachis dives Smith (Hymenoptera: Formicidae)
Date Issued
2008
Date
2008
Author(s)
Jong, Jaw-Jinn
Abstract
Typical social structure of ant is self-organized and decentralized system. The whole colony displays assembled behaviors which are composed independently by individuals'' specific behavior. Division of labor, the most basic and extensive research field of studying ant, is the backbone to assemble individual-mates behaviors. Many researches attempt to probe into task partition of individual workers in the whole colony and how to regulate division of labor in order to promote colony’s efficiency. This thesis focused on the adaptation significance of division of labor in the gray-black spiny ant, Polyrhachis dives. I attempt to understand its social structure, the regulation of sexual and non-sexual castes, and task-shift of worker subcastes. Three types of colony as queenless, monogyny and polygyny were found in nature condition. The colony funding could be either by budding or independent which could be found at the same time in the same habitat. In the nature colony, several reproductive castes, including virgin queens, queens and males, were commonly found and could perform either monoandrous (monogamous) or polyandrous (polygamous) which would result in interchange of out-breeding and in-breeding. Although virgin queens appeared twice within one year, males could be found all year long. Based on my long-term observation, P. dives could form not only independent colony, but also super-colony. The uniqueness of the super-colony of P. dives was its 4 distinguish function and structure colonies such as central colony, reproductive colony, supportive colony and reserve colony. The division of labor in super-colony also relied on temporal regulation of functions among 4 colonies. Seasonal variation was reflected on colony size, sex ratio and presence of male caste. Under detailed observation, ethogram of nurse, guard, forager and callow worker was constructed to reveal all the behavior repertoires in the nest. Although there was no significant difference on morphological characteristics among four workers, there were significant difference on resting proportion, resting duration, trophallaxis, encounter rate with nest mates, and spontaneous activity ratio. Special attention was on resting because it was the most common behavior in the nest and served as an essential stage for task shifting. Different sub-castes of worker might have different rates of task shifting which represented weak age-polyethism and flexible task partition. Since resting was a key factor of changing tasks, pulses of activity following resting to revive the whole colony was the important phenomenon to communicate with nest-mates for division of labor. The daily pulses of activity expressing free running rhythm in queenright colonies under DD condition, revealed pulse-like phenomenon in heart beat of vertebrate which was high at active phase and low at inactive phase. However, this circadian rhythm was disappeared in queenless colonies. In the study of task partition in large, small, and queenless colony, the proportion of tasks was reflecting the efficient proportion for survive of the colony. Artificial biased the proportion would trigger the task shifting to balance out the excessive tasks. Guard was the unique task found in P. dives. The recruitment of guard was depended on colony size, food quality and food density. Temporal analysis on the existence of foragers and guards at food source revealed the dynamics of task partitioning between these sub-castes. Continuous monitoring of the locomotion of the gray-black spiny ant, Polyrhachis dives, showed a diurnal nature in foraging and reproduction. Furthermore, all the castes except dominant queens and nurses expressed circadian locomotor rhythms. Since isolation could cause task-shifting in worker castes, a series of behavioral bioassays were designed to determine the task of workers at the end of locomotor detection. The differential expression of circadian locomotor rhythms among castes reflected a masking effect on locomotion by social status or task demands. This unique phenomenon is discussed in the context of the “super-organism” concept.
Subjects
division of labor
biological clock
Polyrhachis dives
Type
thesis
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