Rachel is interested in molluscan shell form. Animals’ shells defend them from a variety of environmental dangers and predatory attacks, including a multitude of low-magnitude, repeated stresses, which could cumulatively cause lethal fatigue damage. She studies how shell features—from composition and microstructure to overall morphology—contribute to fatigue resistance. By developing new mechanical techniques to test shell fatigue resistance, she hopes to answer questions about the evolution of shell shape and the ecological interactions between hard-shelled molluscs, their predators, and the environment.
Rachel received her B.A. in Biology from Swarthmore College where she worked with Rachel Merz studying worm burrowing and distribution in the muddy intertidal zone. She then worked as the lab manager in Sheila Patek’s lab at Duke University examining the behavioral strategies that mantis shrimp use when hammering open hard-shelled prey
Smashing mantis shrimp strategically impact shells.
The Journal of experimental biology
2018; 221 (Pt 11)
Many predators fracture strong mollusk shells, requiring specialized weaponry and behaviors. The current shell fracture paradigm is based on jaw- and claw-based predators that slowly apply forces (high impulse, low peak force). However, predators also strike shells with transient intense impacts (low impulse, high peak force). Toward the goal of incorporating impact fracture strategies into the prevailing paradigm, we measured how mantis shrimp (Neogonodactylus bredini) impact snail shells, tested whether they strike shells in different locations depending on prey shape (Nerita spp., Cenchritis muricatus, Cerithium spp.) and deployed a physical model (Ninjabot) to test the effectiveness of strike locations. We found that, contrary to their formidable reputation, mantis shrimp struck shells tens to hundreds of times while targeting distinct shell locations. They consistently struck the aperture of globular shells and changed from the aperture to the apex of high-spired shells. Ninjabot tests revealed that mantis shrimp avoid strike locations that cause little damage and that reaching the threshold for eating soft tissue is increasingly difficult as fracture progresses. Their ballistic strategy requires feed-forward control, relying on extensive pre-strike set-up, unlike jaw- and claw-based strategies that can use real-time neural feedback when crushing. However, alongside this pre-processing cost to impact fracture comes the ability to circumvent gape limits and thus process larger prey. In sum, mantis shrimp target specific shell regions, alter their strategy depending on shell shape, and present a model system for studying the physics and materials of impact fracture in the context of the rich evolutionary history of predator-prey interactions.
View details for DOI 10.1242/jeb.176099
View details for PubMedID 29903746
Mechanical properties of sediment determine burrowing success and influence distribution of two lugworm species
JOURNAL OF EXPERIMENTAL BIOLOGY
2017; 220 (18): 3248–59
We apply new perspectives on how organisms burrow by examining the association of in situ variation in sediment mechanical properties with burrowing ability and species distribution of two sympatric lugworms, Abarenicola pacifica and Abarenicola claparedi We quantified the sediment's resistance to penetration and its grain size distribution at sites inhabited by each species. Abarenicola pacifica individuals were found in significantly harder to penetrate, more heterogeneous sediments. We compared worm burrowing ability using reciprocal transplant experiments. Worms from firmer sediments, A. pacifica, were able to make successful steep burrows in sediments characteristic of either species. In contrast, A. claparedi individuals often failed to complete successful burrows in the firmer A. pacifica sediment. To examine how morphological differences could explain these patterns, we compared body wall musculature and measured how well individuals support their own bodies when draped over a cantilever. Lugworms from the firmer sediment had thicker body wall musculature and held their bodies more rigidly than did worms from softer sediments. Additionally, we observed subtle differences in the papillae on the proboscises' surfaces, which could affect worm-sediment interactions, but we found no differences in the chaetae of the two species. Abarenicola claparedi produced more mucus, which could be important in shoring up burrow walls in their shifting, sandy habitat. This study presents the first example of using field-based experiments to determine how sediment mechanical properties and worm burrowing ability could act to determine organismal distribution. Our findings have broader ecological implications because of the role of lugworms as ecosystem engineers.
View details for DOI 10.1242/jeb.156760
View details for Web of Science ID 000411199600012
View details for PubMedID 28931717