Geology topics

Nathan L. Eckert

Publications and source records attributed to Nathan L. Eckert.

5 recordsLinked to original sources

USGS2025

Genetic analysis of Missouri’s Topeka Shiners with implications for the propagation of understudied small-bodied freshwater fishes

Objective Best practices for conservation hatcheries to conserve genetic diversity and minimize adaptation to captivity have been established for decades, but how to apply them is not clear in every circumstance. As a growing number of aquatic species are propagated in captive settings, addressing the fit of these practices to each system will help managers operate optimally while conserving hatchery resources. Small-bodied freshwater fish present a unique set of traits compared with species that are typically considered for propagation (i.e., salmonids), including a patchy distribution within a watercourse. We examine the propagation and reintroduction program that supports the Topeka Shiner Miniellus topeka , an endangered minnow in the Midwestern USA. Methods We genotyped shiners from groups with different histories (two reintroduced, three captive, and two remnant populations) at 11 microsatellite loci and compared genetic diversity, genetic structure, effective population size, and evidence of population bottlenecks. We also looked at the breeding structure by genetically assigning hatchery-reared young ( n = 148) to candidate parents. Results We documented high levels of genetic structure among the two natural populations in our study. We also noted lower diversity and evidence of bottlenecks in hatchery-reared groups. However, hatcheries may support sufficient (>50) effective population sizes with minimal space. Conclusions Hatcheries may avoid bottlenecks in other small-bodied freshwater fish by collecting wild fish from a broad area and frequently incorporating them into the captive population. Within the hatchery, we emphasize the need to reduce generational overlap by stocking all production fish and/or subdividing the captive populations.

Missouri↗

USGS2023

Glacial vicariance and secondary contact shape demographic histories in a freshwater mussel species complex

Characterizing the mechanisms influencing the distribution of genetic variation in aquatic species can be difficult due to the dynamic nature of hydrological landscapes. In North America’s Central Highlands, a complex history of glacial dynamics, long-term isolation, and secondary contact have shaped genetic variation in aquatic species. Although the effects of glacial history have been demonstrated in many taxa, responses are often lineage- or species-specific and driven by organismal ecology. In this study, we reconstruct the evolutionary history of a freshwater mussel species complex using a suite of mitochondrial and nuclear loci to resolve taxonomic and demographic uncertainties. Our findings do not support Pleurobema rubrum as a valid species, which is proposed for listing as threatened under the U.S. Endangered Species Act. We synonymize P. rubrum under Pleurobema sintoxia —a common and widespread species found throughout the Mississippi River Basin. Further investigation of patterns of genetic variation in P. sintoxia identified a complex demographic history, including ancestral vicariance and secondary contact, within the Eastern Highlands. We hypothesize these patterns were shaped by ancestral vicariance driven by the formation of Lake Green and subsequent secondary contact after the last glacial maximum. Our inference aligns with demographic histories observed in other aquatic taxa in the region and mirrors patterns of genetic variation of a freshwater fish species ( Erimystax dissimilis ) confirmed to serve as a parasitic larval host for P. sintoxia . Our findings directly link species ecology to observed patterns of genetic variation and may have significant implications for future conservation and recovery actions of freshwater mussels.

Mississippi River basin↗

USGS2015

Exposure-related effects of Pseudomonas fluorescens ( Pf -CL145A) on juvenile unionid mussels

The exposure-related effects of a commercially prepared spray-dried powder (SDP) or freeze-dried powder (FDP) formulation of Pseudomonas fluorescens (strain CL145A) on the survival of seven species of newly metamorphosed (<72 hours old) freshwater unionid mussels was evaluated. Forty unionid mussels of each species were randomly distributed to test chambers and each species independently exposed for 24 hours to a static dose of either SDP (four species: Lampsilis cardium , Lampsilis siliquoidea , Lampsilis higginsii , and Ligumia recta ) or FDP (three species: Obovaria olivaria , Actinonaias ligamentina , and Megalonaias nervosa ). Each test chamber was assigned to one of six treatment groups ( n = four chambers per group) by using a randomized block design. The six treatment groups included (1) an untreated control group, (2) groups that received applications with nominal target active ingredient (AI) concentrations of 50, 100, 200, and 300 milligrams per liter (mg/L), and (3) a group that received an application with a nominal target AI concentration of 300 mg/L of heat-deactivated test article (300 HD). After a 24-hour exposure period, water inflow to the test chambers was restored, and the unionid mussels were maintained for an additional 7 days before they were assessed for survival. Mean survival of four unionid mussels species exposed to SDP varied among species and treatment groups when compared to the untreated control groups. The results indicate that exposure to SDP-formulated P. fluorescens up to the maximum label concentration (100 mg/L AI) and up to three times the maximum label exposure duration (8 hours) is not likely to affect the survival of L. siliquoidea and L. higginsii . Low mean survival in the L. recta control group (25.0 percent) indicates that results for L. recta should be interpreted with caution. Mean survival of the L. cardium was significantly lower in all treated groups (14.4 to 40.6 percent) compared to the control group (68.8 percent). These results indicate that further investigation on the impact of SDP-formulated P. fluorescens on L. recta and L. cardium is warranted. Mean survival of three unionid mussels species exposed to FDP was not significantly different in the 50-, 100-, and 200-mg/L AI treatment groups and the 300 mg/L heat-deactivated treatment groups when compared to the control groups. Mean survival of O. olivaria and M. nervosa was significantly lower in the 300-mg/L AI treated groups (38.1 and 48.1 percent, respectively) compared to the control groups (71.9 and 88.1 percent, respectively). The results indicate that exposure to FDP-formulated P. fluorescens up to the maximum label concentration (100 mg/L AI) and up to three times the maximum label exposure duration (8 hours) is not likely to affect the survival of O. olivaria , A. ligamentina , and M. nervosa .

Open-File Report↗

USGS2015

Exposure-related effects of formulated Pseudomonas fluorescens strain CL145A to glochidia from seven unionid mussel species

The study was completed to evaluate the exposure-related effects of a biopesticide for dreissenid mussel ( Dreissena polymorpha , zebra mussel and Dreissena rostriformis bugensis , quagga mussel) control on glochidia from unionid mussels endemic to the Great Lakes and Upper Mississippi River Basins. The commercially prepared biopesticide was either a spray-dried powder (SDP) or freeze-dried powder (FDP) formulation of Pseudomonas fluorescens , strain CL145A. Glochidia of the unionid mussel species Lampsilis cardium , Lampsilis siliquoidea , Lampsilis higginsii , Ligumia recta , Obovaria olivaria , and Actinonaias ligamentina were exposed to SDP-formulated P. fluorescens and Lampsilis cardium and Megalonaias nervosa were exposed to FDP-formulated P. fluorescens . All exposures were static, 24 hours in duration, and included six treatment groups. The treatment groups included (1) an untreated control, (2) a positive control which received a nominal target active ingredient (AI) concentration of 300 milligrams per liter (mg/L) of heat-deactivated test article, and (3) treatments that received nominal target AI concentrations of 50, 100, 200, and 300 mg/L of test article. All treatment concentrations are reported based on active ingredient. Glochidia viability was reduced in two of the six species exposed to 50 mg/L SDP and in four of the six species exposed to 100 mg/L SDP when compared to untreated control groups at 6, 12, and 24 hours. Regardless of sample time, concentrations of 200 and 300 mg/L of SDP and 300 mg/L of heat-deactivated SDP (positive control) substantially reduced glochidia viability in all species except, L . higginsii . Glochidia viability was only reduced for L. cardium exposed to FDP at concentrations ≥ 200 mg/L. After 24 hours of FDP exposure, differences in glochidia viability were only detected in M . nervosa that were exposed to 300 mg/L of heat-deactivated SDP. However, given the low viability in the control group, the results for M . nervosa should be interpreted with caution.

Open-File Report↗

USGS2014

Intrinsic variability in shell and soft tissue growth of the freshwater mussel Lampsilis siliquoidea

Freshwater mussels are ecologically and economically important members of many aquatic ecosystems, but are globally among the most imperiled taxa. Propagation techniques for mussels have been developed and used to boost declining and restore extirpated populations. Here we use a cohort of propagated mussels to estimate the intrinsic variability in size and growth rate of Lampsilis siliquoidea (a commonly propagated species). Understanding the magnitude and pattern of variation in data is critical to determining whether effects observed in nature or experimental treatments are likely to be important. The coefficient of variation (CV) of L. siliquoidea soft tissues (6.0%) was less than the CV of linear shell dimensions (25.1-66.9%). Size-weight relationships were best when mussel width (the maximum left-right dimension with both valves appressed) was used as a predictor, but 95% credible intervals on these predictions for soft tissues were ~145 mg wide (about 50% of the mean soft tissue mass). Mussels in this study were treated identically, raised from a single cohort and yet variation in soft tissue mass at a particular size class (as determined by shell dimensions) was still high. High variability in mussel size is often acknowledged, but seldom discussed in the context of mussel conservation. High variability will influence the survival of stocked juvenile cohorts, may affect the ability to experimentally detect sublethal stressors and may lead to incongruities between the effects that mussels have on structure (via hard shells) and biogeochemical cycles (via soft tissue metabolism). Given their imperiled status and longevity, there is often reluctance to destructively sample unionid mussel soft tissues even in metabolic studies (e.g., studies of nutrient cycling). High intrinsic variability suggests that using shell dimensions (particularly shell length) as a response variable in studies of sublethal stressors or metabolic processes will make confident identifications of smaller effect sizes difficult.

PLoS ONE↗