Assessment and diversity of fish communities in non-wadeable tributaries of the Missouri and Mississippi rivers

As the geographical centers of riverscapes, rivers support fish populations at local and basin-wide scales. However, refinements to fish sampling protocols and theories underpinning basin-wide community ecology have been slowed by the inherent complexity and immensity of rivers. I conducted three extensive studies in non-wadeable tributaries of the lower Missouri and middle Mississippi rivers (Missouri, USA) to illuminate processes structuring riverine fish communities. In Chapter 2, I tested the efficacy of a six-gear fish community sampling protocol by repeatedly sampling nine sites in spring, 07, and fall (N = 36 surveys). I identified an efficient four-gear sub protocol that consistently detected 90% of observed species richness at sites and only required 52% of initial survey effort. In comparison, an electrofishing-only protocol detected lower percentages of fish richness, varied seasonally between 07 and fall, and was nearly twice as variable. In Chapters 3 and 4, I contrasted fish communities inhabiting the Grand (10 sites, prairie region) and Meramec (12 sites, Ozark region) river systems. Chapter 3 examined tributary use by large-river specialist fishes (LRS), a guild of fishes that likely disperse into tributaries from the Missouri (Grand R.) and Mississippi (Meramec R.) rivers. I tested whether mean annual discharge consistently structured richness of LRS fishes at sites ([alpha] richness) within tributaries, and if habitat and downriver connectivity to the Missouri and Mississippi rivers explained additional variation in LRS [alpha] richness. Although species-discharge relationships were positive, discharge effect sizes varied between rivers revealing discharge did not consistently structure LRS [alpha] richness. After accounting for river-specific effects of discharge, downriver connectivity explained residual variation in LRS [alpha] richness, indicating dispersal into tributaries likely structured LRS [alpha] richness. Consequently, LRS [alpha] richness solely estimated from discharge might be underestimated in connected network branches and overestimated in isolated mainstem reaches. Chapter 4 expanded the research scope beyond LRS species to test whether regional connectivity (distance to dispersal source) or site-level habitat diversity (multivariate dispersion of nine habitat variables) explained α richness of three stream size guilds at sites: LRS species, headwater species likely sourced from [less than or equal to]3rd Strahler order streams, and core riverine fishes. In both river systems, downriver connectivity (distance upriver from mouth of mainstem river) and habitat diversity positively related to LRS- (R2 = 0.44 in Grand R, 0.91 in Meramec R.) and core-species (R2 = 0.37 in Grand R., 0.57 in Meramec R.) richness, respectively. Headwaters within 25 km of sites positively related to headwater species richness in the Grand River system (R2 = 0.85), but not in the Meramec River system where headwater richness was better explained by an inverse relationship with discharge (R2 = 0.32). Increasing LRS richness (13â€"17 spp.) downriver caused sites supporting the highest total species richness ([greater than or equal to]75th percentiles) to skew towards lower-midcourse reaches, rather than in midcourses where core-species richness and habitat diversity peaked. Because riverine fish richness manifests from regional dispersal and local habitat diversity, conserving areas of high richness will likely require management actions aimed at local and regional scales. Altogether these studies collecting 146 species and 145,147 individuals revealed non-wadeable tributaries are key riverscape elements that provide diverse riverine habitats and corridors for members of multiple regional fish species pools.

Functional connectome contractions in temporal lobe epilepsy: microstructural underpinnings and associations to surgical outcome

Temporal lobe epilepsy (TLE) is the most common drug-resistant epilepsy in adults. While commonly related to hippocampal pathology, increasing evidence suggests structural changes beyond the mesiotemporal lobe. Functional anomalies and their link to underlying structural alterations, however, remain incompletely understood. We studied 30 drug-resistant TLE patients and 57 healthy controls using multimodal magnetic resonance imaging analyses. We developed a novel framework that parameterizes functional connectivity distance, consolidating functional and geometric properties of macroscale networks. Compared to controls, TLE showed connectivity distance reductions in temporo-insular and prefrontal networks, suggesting topological segregation of functional networks. Our novel approach furthermore allowed for the testing of morphological and microstructural associations, and revealed that functional connectivity contractions occurred independently from TLE-related cortical atrophy but were mediated by microstructural changes in the underlying white matter. All patients underwent a comparable resective surgery after our study and a regularized supervised machine learning paradigm with 5-fold cross-validation demonstrated that patient-specific functional anomalies predicted post-surgical seizure outcome with 74±8% accuracy, outperforming classifiers operating on clinical and structural imaging features. Our findings suggest connectivity distance contractions as a clinically relevant pathoconnectomic substrate of TLE. Functional topological isolation may represent a microstructurally mediated network mechanism that tilts the balance towards epileptogenesis.

Gradients of connectivity distance in the cerebral cortex of the macaque monkey

Cortical connectivity conforms to a series of organizing principles that are common across species. Spatial proximity, similar cortical type, and similar connectional profile all constitute factors for determining the connectivity between cortical regions. We previously demonstrated another principle of connectivity that is closely related to the spatial layout of the cerebral cortex. Using functional connectivity from resting-state fMRI in the human cortex, we found that the further a region is located from primary cortex, the more distant are its functional connections with other areas of the cortex. However, it remains unknown whether this relationship between cortical layout and connectivity extends to other primate species. Here, we investigated this relationship using both resting-state functional connectivity as well as gold-standard tract-tracing connectivity in the macaque monkey cortex. For both measures of connectivity, we found a gradient of connectivity distance extending between primary and frontoparietal regions. As in the human cortex, the further a region is located from primary areas, the stronger its connections to distant portions of the cortex, with connectivity distance highest in frontal and parietal regions. The similarity between the human and macaque findings provide evidence for a phylogenetically conserved relationship between the spatial layout of cortical areas and connectivity.