Student Theses and Dissertations

Date of Award

1970

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Thesis Advisor

William Trager

Keywords

termite caste regulation, Neotermes jouteli, reproductive inhibition, pseudergates, supplementary reproductives, pheromonal control

Abstract

The southern Florida termite Neotermes jouteli (Kalotermitidae) was found to provide exceptionally suitable material for the study of caste regulation, with special reference to the regeneration of reproductive forms. It was possible to collect entire natural colonies of this termite, including the reproductive pair, and to maintain them for long periods in the laboratory. In this way the characteristics of individual colonies could be studied in a way not done in most earlier work on caste regulation. Most interesting was the finding that the capacity to regenerate lost reproductive forms was a characteristic of individual colonies. By removing groups of pseudergates (advanced larval forms that serve as workers) to experimental nests where they could be observed daily, the rate and extent of appearance of supplementary reproductive forms could be measured. A quantitative measure of a colony's regenerative intensity, IR, was developed. Low IR was found to be associated with large-sized pseudergates and soldiers and the seasonal production of alates, while the opposite characteristics were found in colonies with high IR. It was therefore concluded that IR was a function of colony age and theoretical reasons were given why this should be the case. In addition it was found that a colony's IR temporarily decreases if it is forced to regenerate reproductives. Also, in colonies with low IR it is only the pseudergates that can transform to supplementaries. Earlier stage larvae with the same morphological characteristics as pseudergates of high IR colonies lack this ability. Previous work has indicated, but by no means proved, that the presence of a reproductive pair in a termite colony prevents transformation of pseudergates into supplementary reproductives by means of postulated inhibitory pheromones. Accordingly, many different kinds of experiments were devised centering on this hypothesis. In these studies, too, the index IR was very useful. More clear-cut results than have been previously reported were obtained by focusing on high IR colonies. The present findings can be summarized as follows: 1. All pseudergates in high IR colonies are genetically capable of transformation to supplementaries. However, at any given time, only a certain proportion can immediately transform. 2. Male and female reproductives play different roles in the inhibitory process with the female totally inhibiting female pseudergates and partially inhibiting males and the male equally but partially inhibiting both sexes. In contrast to previous findings, the sum of the separate effects accounts for the total inhibition observed. The separate effects of the two sexes imply the existence of at least two inhibitory substances if the pheromone theory is accepted. In addition, a pair of reproductives of either sex is fully as inhibitory as a normal bisexual pair. 3. The extent to which a colony regenerates reproductives is proportional to the amount of time each day that reproductives are absent. The surplus inhibition experienced by female pseudergates can be seen under conditions of part-time orphaning. 4. Reproductives with sealed anuses are probably just as inhibitory as normal reproductives and therefore proctodeal feeding is not the means by which the postulated inhibitory pheromones are transmitted. Likewise, restricting pseudergates to a diet of filter paper impregnated with rectal fluid has no significant inhibitory effect. These results conflict with what has previously been reported. The results of all these studies can be interpreted most easily in terms of the pheromone theory. However, the source and nature of the pheromones remain unknown. The overall results fit into the general view that a termite colony is a "superorganism." The superorganism has differentiated parts; its members are integrated primarily through chemical interactions mediated by the behavioral systems of grooming and trophallaxis; it carries out coordinated behavioral patterns such as constructing and maintaining complex and finely regulated nests; and it has a life history of its own with physiologically different stages corresponding to the embryonic, juvenile and sexually mature stages of an individual organism. Finally, a previously unnoticed and unusual protozoan, Staurojoenina sp. is present among the hindgut symbionts of N. jouteli pseudergates. It is occasionally lost in mature colonies of the termite.

Comments

A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy

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Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 4.0 International License.

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