Meeting Abstract
43.1 Wednesday, Jan. 5 Snail versus crab: the biomechanics and evolution of shell ornamentation in Strombus WHITENACK, Lisa B*; HERBERT, Gregory S; SIMKINS, JR., Daniel C; Allegheny College; Univ. of South Florida; Univ. of South Florida lwhitena@allegheny.edu
The hypothesis of escalation identifies biological hazards, particularly enemies, as the major driver of evolution for most species and states that these hazards have become more severe over time. Marine communities of the western Atlantic experienced a regional mass extinction at the end-Pliocene; selection pressures conducive to escalation existed in the postextinction Pleistocene in soft-bottomed habitats. This is consistent with the frequency of repaired predation scars seen in the Strombus lineage in Florida, as well as with morphological trends in defensive features such as ornamentation and lip thickness. Ornamentation such as spines may increase the effective size of the shell with the minimal amount of material or may locally strengthen the shell. However, it is unclear if and how these changes in morphology represent increasing resistance to all predators or specific predators. The goal of this study is to address whether changes in Strombus morphology through the Plio-Pleistocene of Florida increase strength against predation by a common predator, the stone crab Menippe. We use finite element analysis to examine the effects of two potential anti-predatory features, spines and lip thickness, on the structural strength of the Strombus shell. Preliminary results indicate that while lip thickness does deter fatal attacks from Menippe, spines are not effective. These results are confirmed by feeding experiments with extant Menippe and Strombus. This suggests that spines might instead be anti-predatory feature for vertebrate predators, such as teleosts, cownose rays, and turtles, which use oral or pharyngeal jaws to crush extant Strombus. For these predators, the size of the shell may be an adequate defense against predation, as vertebrates are gape-limited.
