RESUMEN
Mercury is a widespread pollutant of increasing global concern that exhibits a broad range of deleterious effects on organisms, including birds. Because the developing brain is well-known to be particularly vulnerable to the neurotoxic insults of mercury, many studies have focused on developmental effects such as on the embryonic brain and resulting behavioral impairment in adults. It is not well understood how the timing of exposure, for example exclusively in ovo versus throughout life, influences the impact of mercury. Using dietary exposure to environmentally relevant methylmercury concentrations, we examined the role that timing and duration of exposure play on spatial learning and memory in a model songbird species, the domesticated zebra finch (Taeniopygia guttata castanotis). We hypothesized that developmental exposure was both necessary and sufficient to disrupt spatial memory in adult finches. We documented profound disruption of memory for locations of hidden food at two spatial scales, cage- and room-sized enclosures, but found that both developmental and ongoing adult exposure were required to exhibit this behavioral impairment. Methylmercury-exposed birds made more mistakes before mastering the spatial task, because they revisited unrewarded locations repeatedly even after discovering the rewarded location. Contrary to our prediction, hippocampal volume was not affected in birds exposed to methylmercury over their lifetimes. The disruption of spatial cognition that we detected is severe and would likely have implications for survival and reproduction in wild birds; however, it appears that individuals that disperse or migrate from a contaminated site might recover later in life if no longer exposed to the toxicant.
Asunto(s)
Pinzones , Mercurio , Compuestos de Metilmercurio , Humanos , Adulto , Animales , Mercurio/toxicidad , Compuestos de Metilmercurio/toxicidad , Cognición , EncéfaloRESUMEN
Students' perceptions of challenges in biology influence performance outcomes, experiences, and persistence in science. Identifying sources of student struggle can assist efforts to support students as they overcome challenges in their undergraduate educations. In this study, we characterized student experiences of struggle by 1) quantifying which external factors relate to perceptions of encountering and overcoming struggle in introductory biology and 2) identifying factors to which students attribute their struggle in biology. We found a significant effect of Course, Instructor, and Incoming Preparation on student struggle, in which students with lower Incoming Preparation were more likely to report struggle and the inability to overcome struggle. We also observed significant differences in performance outcomes between students who did and did not encounter struggle and between students who did and did not overcome their struggle. Using inductive coding, we categorized student responses outlining causes of struggle, and using axial coding, we further categorized these as internally or externally attributed factors. External sources (i.e., Prior Biology, COVID-19, External Resources, Classroom Factors) were more commonly cited as the reason(s) students did or did not struggle. We conclude with recommendations for instructors, highlighting equitable teaching strategies and practices.