Date Thesis Awarded
Bachelors of Science (BS)
J. Emmett Duffy
Jonathan D. Allen
Randolph M. Chambers
Eusociality is one of the most highly developed forms of social behavior in which groups of individuals show overlap of generations, strong reproductive skew, and cooperative care of young. Eusociality is thought to have evolved in several animal groups as a response to ecological challenges. Within the diverse tropical sponge-dwelling marine crustacean genus Synalpheus, multiple species display eusocial behavior, a trait that is not found in any other marine organisms. The eusocial species of the genus Synalpheus form large colonies often with only one reproducing female among tens to hundreds of individuals. These reproducing females, or queens, strongly influence the growth and success of a colony as they appear to be the primary source of direct recruits. In addition, the success of a eusocial Synalpheus colony is highly dependent on its ability to retain and defend its host sponge. This necessary combination of reproduction and defense presents a potential for trade-offs between the allocation of energy and resources for the queen and the colony. Because both defense and reproduction are key factors in the evolution of eusociality, I have compared the allometry of reproductive capacity and defensive weaponry to colony characteristics in queens of four eusocial Synalpheus species. Bivariate regressions and structural equation modeling were used to characterize relationships between queen fecundity, size of the major chela (fighting claw), and colony size, shedding light on the relationship between individual success and social organization in sponge-dwelling shrimp. The individual allometry of reproducing females was relatively consistent across species with body mass having strong positive effects on both major chela mass and egg number. In addition, the relationship between chela mass and egg number, or fecundity and weaponry, was negative indicating a tradeoff between reproduction and defense. Furthermore, the relationship between colony size and major chela mass was also negative indicating a buffer effect between number of cohorts in a colony and the necessity of a major chela for queen personal defense. Finally, the effect of individual allometry on colony size varied dramatically indicating that while queen allometry did significantly affect colony size, other factors outside the sphere of this study are also involved.
Bornbusch, Sarah, "Allometry of reproduction, weapon size, and colony size in social shrimp: A comparative analysis of four eusocial species in genus Synalpheus" (2013). Undergraduate Honors Theses. Paper 613.
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