Aim Complex oceanographic features have historically caused difficulty in understanding gene flow in marine taxa. Here, we evaluate the impact of potential phylogeographic barriers to gene flow and assess demography and evolutionary history of a coral reef goby species complex. Specifically, we test how the Amazon River outflow and ocean currents impact gene flow. Location Western Atlantic. Taxon The bridled goby (Coryphopterus glaucofraenum) and sand‐canyon goby (C. venezuelae) species complex. Methods We used mitochondrial DNA and 2,401 genomic SNPs to investigate evolutionary history and test hypotheses of how major barriers impact species‐level differentiation. We used clustering algorithms and pairwise FST to assess population differentiation caused by minor barriers within and among regions. Finally, we tested alternate hypotheses of demographic history via coalescent simulations to determine the most plausible spread across the Western Atlantic. Results We found two unique clades of C. glaucofraenum along the Brazilian coast and the oceanic island Atol das Rocas (AR) that are more closely related to C. venzuelae. Further genetic structure within the Caribbean and separately along the Brazilian coast led to at least two distinct populations in each Province. Coalescent simulations indicated that an ancestral population of C. venezuelae split from C. glaucofraenum in the Caribbean, dispersed to Brazil, then spread to AR. Main conclusions Species‐level genetic differentiation has resulted from the Amazon River outflow and isolation of AR. Population differentiation within the Caribbean matched previous studies indicating an east‐west pattern of divergence. Brazilian population differentiation was impacted by the cold‐water upwelling filter at Cabo Frio. Overall, this research highlights how barriers to gene flow impact speciation and genetic structure within western Atlantic gobies and provides insight into the role oceanographic features have in the speciation process of fishes.

Beech leaf disease (BLD) is a recently discovered disease that is causing severe damage to American beech trees (Fagus grandifolia Ehrh.) in northeastern North America (Ewing et al., 2019). Due to the novelty of the disease, information on the general epidemiology and symptom phenology of BLD is largely unavailable.Beech leaf disease is characterized by two distinct symptom types: (1) a normal size leaf with dark green, interveinal bands that may manifest between a few or many veins and cover up to two thirds of the leaf surface referred to as "banded" or (2) a stunted leaf that is solidly darkened green, crinkled and leathery in texture, therefore, referred to as "crinkled" (Ewing et al., 2019). As the disease progresses on an infested tree, aborted buds become more frequent resulting in a loss of leaf development and thinning canopies.Aborted buds typically remain on a branch through summer before falling off. Elevated sapling mortality occurs where BLD has been present for several years and, as of yet, limited mortality of mature trees has been observed where BLD has been present 6-8 years.Since the crinkling symptoms appear more severe, we and other forest scientists initially assumed that symptoms appeared on diseased trees in a progression, with banding showing first, followed by crinkling and finally aborted buds in the subsequent growing seasons. In addition, trees that have been afflicted by BLD for years generally have more crinkled symptoms than newly infected trees, leading us to this hypothesis.

A Hopfield-type neural network has content addressable memory which emerges from its collective properties. I reinvestigate the controversial question of its critical storage capacity at zero temperature. To locate the discontinuous transition from good retrieval to bad retrieval in infinite systems the decreasing average quality of retrieved information is traced until it falls below a threshold. The cutoff points found for different system sizes are extrapolated towards infinity and yield αc=0.143±0.002.

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