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A principal goal in ecology is to identify the determinants of species abundances in nature. Body size has emerged as a fundamental and repeatable predictor of abundance, with smaller organisms occurring in greater numbers than larger ones. A biogeographic component, known as Bergmann’s rule, describes the preponderance, across taxonomic groups, of larger-bodied organisms in colder areas. Although undeniably important, the extent to which body size is the key trait underlying these patterns is unclear. We explored these questions in diatoms, unicellular algae of global importance for their roles in carbon fixation and energy flow through marine food webs. Using a phylogenomic dataset from a single lineage with worldwide distribution, we found that body size (cell volume) was strongly correlated with genome size, which varied by 50-fold across species and was driven by differences in the amount of repetitive DNA. However, directional models identified temperature and genome size, not cell size, as having the greatest influence on maximum population growth rate. A global metabarcoding dataset further identified genome size as a strong predictor of species abundance in the ocean, but only in colder regions at high and low latitudes where diatoms with large genomes dominated, a pattern consistent with Bergmann’s rule. Although species abundances are shaped by myriad interacting abiotic and biotic factors, genome size alone was a remarkably strong predictor of abundance. Taken together, these results highlight the cascading cellular and ecological consequences of macroevolutionary changes in an emergent trait, genome size, one of the most fundamental and irreducible properties of an organism. 

Undergraduate science students who volunteer within a research laboratory group, or participate in funded research opportunities, in general are those who have the opportunity to engage in authentic research. In this article, we report the findings from two different iterations of a semester-long collaboration between a biology faculty member and a science education faculty member at a major research institution in the Southeastern United States. Specifically, the faculty members designed an ecology laboratory course for upper-level undergraduate students (primarily biology majors) where they would engage in an original and highly authentic ecological research project. The goal of this course was to have students explicitly learn about the nature of science (NOS), and authentic scientific practices such as inquiry and experimentation in the context of their own research. In the second year of the course, the global COVID-19 pandemic forced us to modify our approach to accomplish the same goals, but now in a remote and online format. Using questionnaires, concept inventories, and semi-structured interviews, the impact of the course on students’ understandings of NOS, inquiry, and experimentation, in addition to their perspectives on the experience within the course compared to prior laboratory coursework, was investigated. We found that students showed modest gains in each of the aforementioned desirable outcomes. These gains were generally comparable in both face-to-face and remote course settings. Additionally, students shared with us their preference for authentic laboratory work as compared with the typical laboratory work with its given research question and step-by-step instructions. Our research demonstrates what is possible in both face-to-face and remote undergraduate laboratory courses in biology and the positive impact that was observed in our students. We hope it serves as a model for other scientists and science educators as they collaborate to design authentic research-based coursework for undergraduate biology students. 

Determining the effects of parasites on host reproduction is key to understanding how parasites affect the underpinnings of selection on hosts. Although infection is expected to be costly, reducing mean fitness, infection could also increase variation in fitness costs among hosts, both of which determine the potential for selection on hosts. To test these ideas, we used a phylogenetically informed meta-analysis of 118 studies to examine how changes in the mean and variance in the outcome of reproduction differed between parasitized and non-parasitized hosts. We found that parasites had severe negative effects on mean fitness, with parasitized hosts suffering reductions in fecundity, viability and mating success. Parasite infection also increased variance in reproduction, particularly fecundity and offspring viability. Surprisingly, parasites had similar effects on viability when either the male or female was parasitized. These results not only provide the first synthetic, comparative, and quantitative summary of the strong deleterious effects of parasites on host reproductive fitness, but also reveal a consistent role for parasites in shaping the opportunity for selection.