Eusocial insect societies are analogous to organisms in that the demography, development and regulation of workers within are shaped by selection acting on whole colony
characteristics. Just as relative investment varies across the lifetime and reproductive cycle of a traditional organism, adaptive patterns of worker allocation are expected to vary with
colony development and need across each annual cycle. Despite these predictions, adaptive patterns of labor allocation remain un-described for most social insect societies. This dissertation
identifies a seasonal pattern of forager allocation in colonies of the Florida harvester ant (Pogonomyrmex badius) and describes its relationship to colony demography, size, reproduction,
worker development rate, death rate, longevity, and neighborhood dynamics. Aging P. badius workers progress through a sequence of interior labor roles before leaving the nest to forage. By
marking and recapturing foragers, forager population size was estimated and foragers were identified as a discrete, age-correlated labor group that resides only in the top 12cm of nests that
may be more than 200cm deep. Excavation and census of whole colonies revealed that foragers were present in a consistent ratio to the colony's larval population from May through August, but
that forager allocation was not a response to larval presence. Proportional allocation to foraging followed an annual pattern, shaped by the interaction of seasonal phases of colony growth
and worker development rate. Forager allocation began in March or April and increased to a peak of approximately 40% of the colony in June, as colonies provisioned alates for mating flights
in the days surrounding the summer solstice. In spring, proportion foraging increased due to an increase in forager number combined with a reduction in colony size. Beginning in late summer,
proportional allocation to foraging decreased, as colonies grew through new worker birth and forager replacement declined. This annual pattern was shaped by a five-fold difference in the age
of summer and autumn-born workers when they entered the forager population (43 vs. 200+ days). The chronological age of foragers was revealed by collecting whole colonies across two annual
cycles, marking age cohorts with colored wire-belts, releasing each colony into a field nest created from melting buried ice chambers, then monitoring the forager population for the
appearance of each marked cohort. Slow-developing workers, produced from late August until mid-October each year, dominated the forager population the following March through mid-July; while
fast developing workers appeared in early June and developed rapidly to become foragers the following month, overlapping with their older sisters. While wild foragers of both types lived an
average maximum of 27 days after entering the forager population, these same foragers were capable of surviving for hundreds of days in the laboratory. Likewise, restricting the foraging
range of wild foragers increased forager longevity by 57%, demonstrating that foraging carries mortality risks and the observed age at death was not part of a developmental program involving
senescence in P. badius. By removing neighboring colonies, this study also showed that interactions with conspecific neighbors can influence the labor thresholds of individual workers, and
the demographic structure of whole colonies, as neighbors account for 30% of forager mortality in the spring. At the colony level, increased forager longevity suppressed the movement of new
workers into the forager population, increasing their time in earlier labor roles and promoting colony growth. In contrast, both removing 50% of the forager population and doubling the larval
population did not induce forager replacement or increase the daily rate of new foragers added within seven days. Together, these results suggest a unidirectional control of labor allocation
in P. badius, where the forager population size is not maintained by workers detecting colony need and filling vacancies, but by workers developing at a rate selected to allow forager
replacement. In essence, the annual cycle of forager allocation emerges as P. badius workers 'age' into behavioral roles at environmentally appropriate times, in the same proportions, on
nearly the same dates each year and experience a predictable death rate. This process allows colonies to divide a limited number of workers between competing functions without a leader.The
findings of this study reinforce our understanding of the organism-like nature of social insect colonies. Like cells in a body, the thousands of individual insects in a P. badius colony are
organized into functional labor groups, which are responsive to cycles of growth, reproduction and dormancy through self-regulating processes. The emergence of measurable, colony-level traits
from the accumulation of thousands of transient individuals, from multiple generations is one of the most striking feats of social organization across taxa. / A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2014. / October 2, 2014. / ant colony behavior, division of labor, Florida harvester ant, Pogonomyrmex badius, labor allocation, social inhibition, superorganism / Includes bibliographical references. / Walter R. Tschinkel, Professor Directing Dissertation; Emily H. DuVal, Committee Member; Lisa C. Lyons, Committee Member; Jeanette L. Wulff, Committee
Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_252854 |
| Contributors | Kwapich, Christina L. (authoraut), Tschinkel, Walter R. (Walter Reinhart), 1940- (professor directing dissertation), Davis, Frederick Rowe, 1965- (university representative), DuVal, Emily H. (committee member), Lyons, Lisa C. (committee member), Wulff, Jeanette L. (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Biological Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (79 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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