A lack of genetic diversity and minimal adaptive evolutionary divergence in introduced Mysis shrimp after 50 years.

The successes of introduced populations in novel habitats often provide powerful examples of evolution and adaptation. In the 1950s, opossum shrimp (Mysis diluviana) individuals from Clearwater Lake in Minnesota, USA were transported and introduced to Twin Lakes in Colorado, USA by fisheries managers to supplement food sources for trout. Mysis were subsequently introduced from Twin Lakes into numerous lakes throughout Colorado. Because managers kept detailed records of the timing of the introductions, we had the opportunity to test for evolutionary divergence within a known time interval. Here, we used reduced representation genomic data to investigate patterns of genetic diversity, test for genetic divergence between populations, and for evidence of adaptive evolution within the introduced populations in Colorado. We found very low levels of genetic diversity across all populations, with evidence for some genetic divergence between the Minnesota source population and the introduced populations in Colorado. There was little differentiation among the Colorado populations, consistent with the known provenance of a single founding population, with the exception of the population from Gross Reservoir, Colorado. Demographic modeling suggests that at least one undocumented introduction from an unknown source population hybridized with the population in Gross Reservoir. Despite the overall low genetic diversity we observed, F ST outlier and environmental association analyses identified multiple loci exhibiting signatures of selection and adaptive variation related to elevation and lake depth. The success of introduced species is thought to be limited by genetic variation, but our results imply that populations with limited genetic variation can become established in a wide range of novel environments. From an applied perspective, the observed patterns of divergence between populations suggest that genetic analysis can be a useful forensic tool to determine likely sources of invasive species.

A genetically based ecological trade-off contributes to setting a geographic range limit.

Understanding the ecological factors that shape geographic range limits and the evolutionary constraints that prevent populations from adaptively evolving beyond these limits is an unresolved question. Here, we investigated why the euryhaline fish, Poecila reticulata, is confined to freshwater within its native range, despite being tolerant of brackish water. We hypothesised that competitive interactions with a close relative, Poecilia picta, in brackish water prevents P. reticulata from colonising brackish water. Using a combination of field transplant, common garden breeding, and laboratory behaviour experiments, we find support for this hypothesis, as P. reticulata are behaviourally subordinate and have lower survival in brackish water with P. picta. We also found a negative genetic correlation between P. reticulata growth in brackish water versus freshwater in the presence of P. picta, suggesting a genetically based trade-off between salinity tolerance and competitive ability could constrain adaptive evolution at the range limit.

In Niemann-Pick C1 mouse models, glial-only expression of the normal gene extends survival much further than do changes in genetic background or treatment with hydroxypropyl-beta-cyclodextrin.

The Npc1nmf164 allele of Npc1 provides a mouse model for Niemann-Pick disease type C1 (NPC1), a genetic disease known to have a widely variable phenotype. The transfer of the Npc1nmf164 mutation from the C57BL/6J inbred strain to the BALB/cJ inbred strain increased the mean lifespan from 117.8days to 153.1days, confirming that the severity of the NPC1 phenotype is strongly influenced by genetic background. The transfer of another Npc1 allele, Npc1nih, to this background also extended survival of the homozygotes indicating that the modifying effect of BALB/cJ is not limited to a single allele of Npc1. The increased longevity due to the BALB/cJ background did not map to a previously mapped modifier on chromosome 19, indicating the presence of additional genes impacting disease severity. The previously studied Glial Fibrillary Acidic Protein promoter-Npc1 cDNA transgene (GFAP-Npc1) which only expresses NPC1 in astrocytes further extended the lifespan of Npc1nmf164 homozygotes on a BALB/cJ background (up to 600days). Hydroxypropyl-ß-cyclodextrin (HPßCD) treatment, not previously tested in the Npc1nmf164 mutant, extended life in the Npc1nmf164 homozygotes but not the transgenic, Npc1nmf164 mice on the BALB/cJ background. In all cases, lack of weight gain and early cerebellar symptoms of loss of motor control were found. At termination, the one mouse sacrificed for histological studies showed severe, diffuse pulmonary alveolar proteinosis suggesting that pulmonary abnormalities in NPC1 mouse models are not unique to the Npc1nih allele.

Relative efficacy of nicotinamide treatment of a mouse model of infantile Niemann-Pick C1 disease.

Nicotinamide delivered in drinking water at about 2 g/kg/day significantly prolonged survival and showed a suggestive improvement on memory in the Npc1 nih / Npc1 nih mouse model of infantile NPC1 disease. It is likely that this role is due to its function as a histone deacetylase (HDAC) inhibitor although another HDAC inhibitor, valproic acid, was without effect. Nicotinamide could also work by preventing/reversing oxidative stress.

Variation of DaTSCAN quantification between different gamma camera types.

OBJECTIVE: To acquire data from a 123I filled Alderson phantom on different gamma cameras types and compare the relative uptake results from processing using the QuantiSPECT program (GE Healthcare). METHODS: A DaTSCAN phantom was filled using the standard protocol and imaged on seven different gamma camera types and on two identical cameras of the same type. The standard GE Healthcare protocols for the given cameras were used. Aliquots of the striatum and brain background were counted in a gamma counter to determine variations in filling concentration. All the raw DaTSCAN SPECT data was imported into QuantiSPECT and processed by the three different algorithms (two box, three box and crescent) to determine the relative uptake in the striatum. Inter-operater and intra-operator variation was also determined. RESULTS: The 10% variation in filling concentration found across the sites was compensated for in the final results. There was a 5-15% variation between cameras depending on the processing algorithm used. There was an intra-operator variation of between 5 and 12% which reflected the proportion of operator intervention within the processing method. There was no statistical variation between operators. CONCLUSIONS: The transfer of a DaTSCAN database between camera types is feasible, but ideally all data would be acquired on a single camera type and phantom data used to normalize the database accordingly.

Comparison of different methods of DatSCAN quantification.

BACKGROUND: The quantification of DaTSCAN images can be used as an adjunct to visual assessment to differentiate between Parkinson's syndrome and essential tremor. Many programs have been written to assess the relative uptake in the striatum. AIM: To compare two of the commercially available programs: QuantiSPECT, which analyses isolated data in two dimensions, and BRASS, which performs three-dimensional processing referencing a normal image template. METHOD: Twenty-two patients (11 with Parkinson's syndrome and 11 with essential tremor) were visually assessed by two nuclear medicine consultants. The patient data were then processed using two commercial programs to determine the relative uptake in the striatum. A comparison of the results from the programs was performed, together with a comparison with the visual assessment. The inter-operator and intra-operator variabilities were also ascertained. RESULTS: All programs and processing methods could distinguish between Parkinson's syndrome and essential tremor. There was also a good correlation between the results from the three- and two-dimensional methods. The intra-operator and inter-operator variabilities were dependent on the amount of operator intervention. CONCLUSION: Both programs allowed statistical differentiation between Parkinson's syndrome and essential tremor. Strict operator protocols are needed with QuantiSPECT to reduce inter- and intra-operator variation. The three-dimensional method (BRASS) gave greater concordance than the two-dimensional method (QuantiSPECT) with the visual assessment, but at a cost of increased operator time.