Barker, M. K. | bioRxiv Science

bioRxiv2024

Trophic level associated gut length divergence evolved under sexual conflict in Lake Malawi cichlids

Variation in gastrointestinal morphology is associated with dietary specialization across the animal kingdom. Gut length generally correlates with trophic level, and increased gut length in herbivores is a classic example of adaptation to cope with diets with lower nutrient content and a higher proportion of refractory material. However, the genetic basis of gut length variation remains largely unstudied, partly due to the inaccessibility and plasticity of the gut tissue, as well as the lack of dietary diversity within traditional model organisms relative to that observed among species belonging to different trophic levels. Here, we confirm the genetic basis of gut length variation among recently evolved Lake Malawi cichlid fish species with different dietary adaptations. We then produce interspecific, inter-trophic-level hybrids to map evolved differences in intestinal length in an F2 mapping cross between Metriaclima mbenjii, an omnivore with a relatively long gut, and Aulonocara koningsi, a carnivore with a relatively short gut. We identify numerous candidate quantitative trait loci for evolved differences in intestinal length. These quantitative trait loci are predominantly sex-specific, supporting an evolutionary history of sexual conflicts for the gut. We also identify epistatic interactions potentially associated with canalization and the maintenance of cryptic variation in the cichlid adaptive radiation. Overall, our results suggest a complex, polygenic evolution of gut length variation associated with trophic level differences among cichlids, as well as conflicts and interactions that may be involved in evolutionary processes underlying other traits in cichlids. SummaryThis study examines the genetic basis of gut length variation in Lake Malawi cichlids, which exhibit different dietary adaptations. It highlights how cichlids recapitulate a broad taxonomic trend: gut length correlates with trophic level, with herbivores and omnivores having longer intestines than carnivores. By creating hybrids of Metriaclima mbenjii (omnivore) and Aulonocara koningsi (carnivore), we identify several quantitative trait loci and epistatic interactions underlying gut length differences. These genetic associations are predominantly sex-specific, suggesting historical sexual conflicts. The results indicate complex, polygenic evolution of gut morphology in these fish, and suggest evolutionary interactions and processes shaping dietary traits across species.

genetics↗

bioRxiv2020

Supporting Student Learning and Experiences in the Lab: (How) Should We Design Their Groups?

Undergraduate science students spend a substantial amount of time working in their laboratory groups, and instructors want to make evidence-based decisions on how to best set up these groups. Despite several studies on group composition, the evidence appears to be quite context-specific, and very little has been published about lab groups. Further, many studies focus solely on conceptual learning; however, the lab is an important venue for also supporting non-content outcomes such as confidence, process skills, team skills, and attitudes. Thus, in our introductory course on molecules, cells, and physiology we were interested in the impact of group composition, on a spread of student outcomes. Students were either placed into groups by the instructor, or self-selected into groups. To assess the impact of group composition on student outcome, we collected pre/post data from >500 students over 2 semesters. Our measures assess conceptual knowledge, confidence in lab skills, attitudes toward group learning, lab grades, gender, year of study, and (via open-ended questions) student perspectives. Using a multiple regression approach, we established models that predict student outcomes based on their individual attributes and on their lab group attributes. Surprisingly, the hetero/homogeneity of the initial group, and whether the groups were student- or instructor-selected, did not affect student outcomes in these models. Further MANCOVA analysis demonstrated that student interaction outside of the lab time was the strongest predictor of positive student attitudes toward group learning. Student perspectives on group formation are mixed, and suggest that a simple and flexible choice approach may best support our students. Overall, these findings have clear implications for our course design and instructional choices: we should focus our efforts to promote positive student interactions, rather than worrying about initial composition.

scientific communication and education↗