Objective: Speckled Dace Rhinichthys osculus is small cyprinoid fish that is widespread in western North America. In California and elsewhere it is currently treated as a single species with multiple subspecies, many undescribed. However, these subspecies may represent evolutionary lineages that are cryptic species because they cannot be distinguished using standard morphometric techniques. In this study, we attempt to determine evolutionary lineages within California populations of Speckled Dace using the population genetic and genomic information. Methods: We used restriction site-associated DNA sequencing to extract thousands of single-nucleotide polymorphisms across the genome to identify genetic differences among all the samples from 38 locations in the western USA, with a focus on California. We performed principal component analysis, admixture analysis, estimated pairwise values of the genetic differentiation index F ST , and constructed molecular phylogenies to characterize population genetic and phylogenetic relationships among sampled Speckled Dace populations. Result: Our analyses detected three major lineages of Speckled Dace in California that align with geography: (1) Sacramento River, central California coast, Klamath River, and Warner Basin; (2) Death Valley and Lahontan Basin; and (3) Santa Ana River basin, in southern California. These lineages fit well with the geologic history of California, which has promoted long isolation of populations of Speckled Dace and other fishes. Conclusion: The presence of distinct evolutionary lineages indicates that SpeckledDace in California should be managed with distinct population segments to preserve within-species diversity. This study highlights the importance of genetic analyses for conservation and management of freshwater fishes.

The Speckled Dace, Rhinichthys osculus (Girard), is a small species of fish (Cypriniformes, Leuciscidae) that has the widest geographic range of any freshwater dispersing fish in western North America. The dynamic geologic history of the region has produced many isolated watersheds with endemic fish species. However, Speckled Dace from these watersheds cannot be differentiated readily by morphometrics and meristics. This has led to the widely accepted hypothesis that the dace’s adaptability and ability to cross geologic barriers has resulted in interbreeding among neighboring populations, maintaining the dace as a single species. We investigate this hypothesis by looking at Speckled Dace populations in California which are the result of at least three separate colonization events of isolated watersheds. We synthesize results from taxonomic, genetic, and zoogeographic studies in combination with the findings of a recent genomics study, to show that there are distinctive evolutionary lineages within the Speckled Dace complex. These lineages are used to designate multiple species and subspecies. We back up these designations by examining how well these lineages fit with the geologic history of the isolated basins they inhabit and with the presence of other endemic fishes. We conclude the following nine taxa can be recognized within the Speckled Dace complex in California.

Chatter is a key factor affecting tool wear, workpiece surface quality and cutting efficiency. When milling thin-walled parts, it is difficult to extract the chatter frequency band due to the time-varying characteristics of the dynamic parameters of the machining system. Variational mode decomposition (VMD) shows good performance in signal processing, but the decomposition result of this algorithm is limited by the influence of initialization parameters. Therefore, this paper proposes a scheme to determine the number of VMD decomposition layers based on the number of Fourier transform frequency peaks. The feasibility of the scheme is verified by the simulation signal and experiment signal. The results show that taking the peak number of the spectrum as the decomposition level of VMD, the spectrum distribution of the decomposed intrinsic mode function (IMF) is clear, and the frequency band containing rich chatter information can be effectively extracted.

Titanium alloy is widely used in aerospace and other fields because of its high strength, low density, good corrosion resistance and high temperature resistance. In high speed milling titanium alloy, due to the poor thermal conductivity of titanium alloy and the change of cutting mechanism caused by high speed machining, it is great significance to study the cutting temperature in high speed milling process. Based on the moving heat source method, the temperature field model of milling workpiece considering spiral edge was established, and the influence of milling speed on workpiece temperature was analyzed through the change of heat flux during milling. The thermocouple wireless temperature acquisition system was used to record the change of workpiece surface temperature in the milling process, and MATLAB was used for the simulation analysis of milling temperature. The results showed that the cutting speed mainly affected the heat flux of the heat source, thereby caused temperature rise of the workpiece. The peak temperature and response speed of measuring point are different in varying spindle speeds and measuring point positions.

The speckled dace ( Rhinichthys osculus ) is small cyprinid fish that is widespread in the Western USA. Currently treated as a single species, speckled dace consists of multiple evolutionary lineages that can be recognized as species and subspecies throughout its range. Recognition of taxonomic distinctiveness of speckled dace populations is important for developing conservation strategies. In this study, we collected samples of speckled dace from 38 locations in the American West, with a focus on California. We used RAD sequencing to extract thousands of SNPs across the genome from samples to identify genetic differences among seven California populations informally recognized as speckled dace subspecies: Amargosa, Owens, Long Valley, Lahontan, Klamath, Sacramento, and Santa Ana speckled dace. We performed principal component analysis, admixture analysis, estimated pairwise Fst, and constructed a phylogeny to explore taxonomic relationships among these groups and test if these subspecies warrant formal recognition. Our analyses show that the seven subspecies fit into three major lineages equivalent to species: western (Sacramento-Klamath), Santa Ana, and Lahontan speckled dace. Death Valley speckled dace were determined to be two lineages (Amargosa and Long Valley) within Lahontan speckled dace. Western and Lahontan speckled dace lineages had branches that can be designated as subspecies. These designations fit well with the geologic history of the region which has promoted long isolation of populations. This study highlights the importance of genetic analysis for conservation and management of freshwater fishes.