Predators and Dangerous Prey in the Fossil Record: Evolution of the Busyconine Whelk-Mercenaria Predator-Prey System.

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Title: Predators and Dangerous Prey in the Fossil Record: Evolution of the Busyconine Whelk-Mercenaria Predator-Prey System.
Author: Dietl, Gregory Paul
Advisors: Reese E. Barrick, Committee Member
James A. Rice, Committee Co-Chair
Patricia H. Kelley, Committee Co-Chair
Brian M. Wiegmann, Committee Member
Abstract: Escalation is enemy-driven evolution. This top-down view of a predator-prey evolutionary arms race downplays the role of prey in driving the predator's evolution. In the related process of coevolution, species change reciprocally in response to one another; prey are thought to drive the evolution of their predator, and vice versa. In the fossil record, the two processes are distinguished most reliably when the predator-prey system is viewed within the context of other species that may influence the interaction. I examined the interaction between busyconine whelks and their bivalve prey Mercenaria to evaluate whether reciprocal adaptation (coevolution) was likely to occur in this predator-prey system. Species of busyconines either employ a wedging or a chipping mode of predation when feeding on bivalve prey that often results in breakage to the predator's own shell. Prey in this interaction have been hypothesized to be 'dangerous' because they are able to inflict damage to the predator as a consequence of the interaction; such damage may lead to decreased growth, reproduction and increased probability of mortality for individual whelks. Asymmetry in selection pressure (which is thought to preclude reciprocity of adaptation) is reduced when predators interact with damage-inducing prey. The likelihood of a reciprocal selection response of the predator in the interaction involving the shell-chipping whelk Sinistrofulgur sinistrum and the bivalve Mercenaria mercenaria was viewed by regressing the frequency of shell breakage in encounters with prey (an index of predator fitness) on prey phenotype (a function of size). Experimental results indicate interaction with Mercenaria has strong highly significant and predictable selective consequences for Sinistrofulgur, suggesting that evolutionary response of the predator to prey adaptation is likely in this system. The late Oligocene to Recent fossil record of whelk predation traces on shells of Mercenaria species was analyzed to determine the temporal window of possible coevolution between shell-chipping whelks and Mercenaria. Based on the fossil record of successful and unsuccessful whelk predation traces, chipping behavior evolved in the Busycon-Sinistrofulgur clade in the early late Pliocene, which constrains tests of reciprocal adaptation to the Pliocene to Recent record of the interaction. Temporal trends in the frequency of successful and unsuccessful whelk predation traces on Mercenaria suggest predation intensity, and the likelihood of prey adaptation in response to whelk predation, increased through the Plio-Pleistocene record of the interaction in Florida. Mercenaria evolutionary size increase is best explained as coevolutionary response to whelk predators. Temporal trends in decreased prey effectiveness (ratio of unsuccessful to total predation attempts) and increase in minimum boundary of a size refuge from predation suggest that, although prey responded evolutionarily to whelk predation pressure, whelk predators also were increasing their prey capture capabilities. Sinistrofulgur evolutionary size increase is best explained as reciprocal coevolutionary response to prey adaptation (which decreased the likelihood of shell breakage when encounters with damage-inducing prey occur) coupled with (or reinforced by) an escalation response to the whelk's own enemies, such as fasciolariid gastropods and durophagous crabs. Coevolution between predator and dangerous prey best explains temporal behavior-related changes in the predator that led to a decrease in frequency of chipping-induced damage to the predator when encounters with prey occur, and an increase in predator site-selective stereotypy of attack position.
Date: 2002-08-09
Degree: PhD
Discipline: Zoology

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