Student Speakers

Evangeline Shank, Omland Lab

"Male and Female Eastern Bluebirds Sing Similar Songs: A New Statistical Method to Test Equivalence "

Understanding complex natural systems requires approaches with minimal statistical limitations and biases. Previously, however, the fields of behavior, ecology, and evolution generally have been restricted to evaluating statistical differences. This framework can be very powerful. Unfortunately, it has also created a bias in these, and many other fields, towards publications focusing only on phenomena in nature for which differences are present and detectable. However, there are a wide range of questions that would benefit from reversing the preexisting paradigm and testing, instead, for equivalence. We have adapted the two one-sided test (TOST), also known as equivalence testing, from pharmaceutical science to be applicable to behavioral and ecological studies, and have created a repeated measures analysis that allows researchers to statistically examine similarities between distributions. We compared song structure in male and female eastern bluebirds (Sialia sialis) as a case study for this method. We failed to find significant differences between male and female songs via a more traditional test, repeated measures ANOVA. Therefore, no conclusion could be drawn about the similarities or differences in song structure. However, our repeated measures equivalence test showed that, based on five standard measures of song complexity, male and female eastern bluebirds sing statistically equivalent songs. Our study highlights the presence of complex female song in a temperate songbird species. Additionally, we provide a new statistical test useful for expanding the statistical toolbox to assess new ecological and evolutionary questions, and to help counteract publication bias in our fields.

Rickesh Patel, Cronin Lab

"There and back again, a mantis shrimp's tale (of local navigation)"

Stomatopods, better known as mantis shrimp, are predatory crustaceans which commonly inhabit holes and crevices in benthic marine environments for use as burrows. However, many stomatopod species forage at extended distances from these burrows before returning back to their homes, risking predation. Since many mantis shrimp are central place foragers living in structurally complex environments, we hypothesized that these animals use piloting (landmark navigation), path integration (dead reckoning), or a combination of the two methods to navigate their benthic environments. To experimentally determine which mechanisms are employed, Neogonodactylus oerstedii were placed in featureless circular arenas in a glass roofed greenhouse, with their burrows submerged from view. Foraging paths in the presence and absence of a landmark adjacent to the burrow were recorded. We found that return trips in the presence of the landmark were more direct than trips in the landmark’s absence. However, the initial direction of the return trips were generally oriented towards the burrow regardless of the presence or absence of the landmark. Further, in the absence of a landmark, paths home were statistically indistinguishable to the beeline distance to the burrow before a search behavior was initiated. To determine if N. oerstedii employ path integration when returning to their burrows, animals were translocated along a platform to a new location before homeward paths were initiated. These translocated animals exhibited homeward paths oriented towards the direction of the burrow had they not been moved, rather than towards the actual direction of their burrow. These results indicate that N. oerstedii use piloting in parallel with a path integration system to return to their burrows.

Estela Monge, Gardner Lab

"Characterization of Chitin Degrading Enzymes in Cellvibrio japonicus"

Understanding the strategies used by bacteria to degrade polysaccharides constitutes an invaluable tool for biotechnological applications. Bacteria are major mediators of polysaccharide degradation in nature, however the complex mechanisms used to detect, degrade, and consume these substrates are not well understood, especially for recalcitrant polysaccharides such as chitin. It has been previously shown that the model bacterial saprophyte Cellvibrio japonicus is able to catabolize chitin, but little is known about the enzymatic machinery underlying this capability. Previous analyses of the C. japonicus genome and proteome indicated the presence of four family 18 Glycoside Hydrolase (GH18) enzymes, and studies of the proteome indicated that all are involved in chitin utilization. Using a combination of in vitro and in vivo approaches, we have studied the roles of these four chitinases in chitin bioconversion. Genetic analyses showed that only the chi18D gene product is essential for the degradation of chitin substrates. Biochemical characterization of the four enzymes showed functional differences and synergistic effects during chitin degradation, indicating non-redundant roles in the cell. Transcriptomic studies revealed complex regulation of the chitin degradation machinery of C. japonicus and confirmed the importance of CjChi18D and CjLPMO10A, a previously characterized chitin-active enzyme. With this systems biology approach, we deciphered the physiological relevance of the GH18 enzymes for chitin degradation in C. japonicus, and the combination of in vitro and in vivo approaches provided a comprehensive understanding of the initial stages of chitin degradation by this bacterium.