Shifts In Genetic Composition Research Articles

Evaluation of Population Characteristic Differences between the Largemouth Bass and Its Backcross Following a Long‐Term Florida Bass Stocking Effort

AbstractManagement agencies throughout the southern United States widely stock Florida Bass (FLB) Micropterus floridanus into extant Largemouth Bass (LMB) M. salmoides populations, with the intent of increasing the trophy potential of those water bodies. These stockings commonly lead to a shift in the systemwide genetic composition toward a population dominated by hybrids, which are predominantly LMB with low levels of FLB alleles (FX‐LMB). Despite the increasing prevalence of FX‐LMB throughout the Southeast, little work has examined FX‐LMB population vital rates and whether these hybrids increase the trophy potential of a water body. Our study fills a void in existing research by comparing the population characteristics of FX‐LMB and LMB using a common garden experimental design. Lake Ouachita is a large Arkansas reservoir that was stocked with over 800,000 fingerling FLB between 2007 and 2015. In 2019, we collected 1,000 bass from throughout the reservoir and determined the level of FLB introgression for each fish by using a panel of species‐diagnostic single‐nucleotide polymorphisms. We then tested for relationships between the percentage of FLB alleles or genotype and the age at 50% maturity, total annual mortality rate, size structure, condition, and growth. In addition, we compared tournament catches of large bass during the pre‐ and poststocking time periods to test whether catch rates of 2.3‐kg and larger bass increased after FLB stockings. Our results indicated that FX‐LMB hybrids likely do not mature earlier, survive longer, have better body condition, or have greater growth potential than native LMB in Lake Ouachita. We also did not observe differences in the number of hours to catch a 2.3‐kg or larger bass or in the number of 2.3‐kg and larger bass captured per tournament between the pre‐ and poststocking time periods. We conclude that a stocking program resulting in a subtle shift in the genetic composition toward the FX‐LMB genotype will not effectively increase the trophy potential of a population.

Genetic Patterns and Climate Modelling Reveal Challenges for Conserving Sclerolaena napiformis (Amaranthaceae s.l.) an Endemic Chenopod of Southeast Australia

Sclerolaena napiformis is a perennial chenopod endemic to southeast Australia. Human-mediated habitat loss and fragmentation over the past century has caused a rapid decline in abundance and exacerbated reduced connectivity between remnant populations across three disjunct regions. To assess conservation requirements, we measured the genetic structure of 27 populations using double digest RADseq). We combined our genetic data with habitat models under projected climate scenarios to identify changes in future habitat suitability. There was evidence of regional differentiation that may pre-date (but also may be compounded) by recent habitat fragmentation. We also found significant correlation between genetic and geographic distance when comparing sites across regions. Overall, S. napiformis showed low genetic diversity and a relatively high proportion of inbreeding/selfing. Climate modelling, based on current occupancy, predicts a reduction in suitable habitat for S. napiformis under the most conservative climate change scenario. We suggest that the best conservation approach is to maximise genetic variation across the entire species range to allow dynamic evolutionary processes to proceed. We recommend a conservation strategy that encourages mixing of germplasm within regions and permits mixed provenancing across regions to maximise genetic novelty. This will facilitate shifts in genetic composition driven by individual plant fitness in response to the novel environmental conditions this species will experience over the next 50 years.

Analysis of Spatiotemporal Genetic Variability in Eastern OysterCrassostrea virginica(Gmelin, 1791) Mtdna 16S Sequences Among North Carolina Populations

ABSTRACT Spatial and temporal genetic structure of the eastern oyster Crassostrea virginica was examined along the coast of North Carolina (NC); utilizing a fragment of the mitochondrial large (16S) ribosomal subunit gene sequence known to distinguish three regional haplotypes in C. virginica—North Atlantic, South Atlantic, and Gulf of Mexico. Significant geographic genetic structure was identified among all populations studied, with little temporal genetic variation observed over the 9-y sampling period. The results are consistent with those of previous studies analyzing geographic variation in mitochondrial DNA16S sequence data, which revealed a genetic discontinuity between North and South Atlantic oyster assemblages along the NC Coast. The increased geographic resolution and duration of sampling in this study revealed a sustained significant shift in genetic composition between Pamlico Sound populations and southern NC populations of C. virginica. These results suggest that a prolonged or persistent b...

An ecological approach to measuring the evolutionary consequences of gene flow from crops to wild or weedy relatives.

Premise of the study:Agricultural practices routinely create opportunities for crops to hybridize with wild relatives, leading to crop gene introgression into wild genomes. Conservationists typically worry this introgression could lead to genetic homogenization of wild populations, over and above the central concern of transgene escape. Alternatively, viewing introgression as analogous to species invasion, we suggest that increased genetic diversity may likewise be an undesirable outcome.Methods:Here, we compare the sensitivity of conventional population genetic metrics with species diversity indices as indicators of the impact of gene flow on genetic diversity. We illustrate this novel approach using multilocus genotype data (12 allozyme loci) from 10 wild (Beta vulgaris subsp. maritima) and eight putative crop–wild hybrid beet populations (B. vulgaris subsp. vulgaris × B. vulgaris subsp. maritima) scattered throughout Europe.Results:Conventional population genetic metrics mostly failed to detect shifts in genetic composition of putative hybrid populations. By contrast, species diversity indices unambiguously revealed increased genetic diversity in putative hybrid populations.Discussion:We encourage other workers to explore the utility of our more sensitive approach for risk assessment prior to the release of transgenic crops, with a view toward widespread adoption of our method in studies aimed at detecting allelic invasion.

Population structure and recent temporal changes in genetic variation in Eurasian otters from Sweden

The Eurasian otter (Lutra lutra) population in Sweden went through a drastic decline in population size between the 1950s and 1980s, caused mostly by anthropogenic factors such as high hunting pressure and the introduction of environmental toxic chemicals into the otter’s habitats. However, after the bans of PCBs and DDT in the 1970s, the population began to recover in the 1990s. This study compares microsatellite data across twelve loci from historical and contemporary otter samples to investigate whether there has been a change in population structure and genetic diversity across time in various locations throughout Sweden. The results suggest that otters in the south were more severely affected by the bottleneck, demonstrated by a decline in genetic diversity and a shift in genetic composition. In contrast, the genetic composition in otters from northern Sweden remained mostly unchanged, both in terms of population structure and diversity. This suggests that the decline was not uniform across the country. Moreover, our analyses of historical samples provide an overview of the level of genetic variation and population structure that existed prior to the bottleneck, which may be helpful for the future management and conservation of the species.

Rise and Fall of a Hybrid Zone: Implications for the Roles of Aggression, Mate Choice, and Secondary Succession

Hybridization can be an important evolutionary force by generating new species and influencing evolution of parental species in multiple ways, including introgression and the consequences of hybrid vigor. Determining the ecological processes underlying evolution in hybrid zones is difficult however because it requires examining changes in both genotypic frequencies over time and corresponding ecological information, data that are rarely collected together. Here, we describe genetic and ecological aspects of a hybrid zone between the Eastern Fence Lizard, Sceloporus undulatus, and the Florida Scrub Lizard, Sceloporus woodi, occurring over at least 23 generations. The hybrid zone, discovered greater than 35 years ago using morphological characters, originally consisted of nearly even proportions of parental species and hybrids. Now, using genetic markers (species-diagnostic mtDNA sites and 6 nDNA microsatellite loci across a total of n = 117 individuals), we confirm not only that hybridization occurred but also that subsequent backcrossing has resulted in highly introgressed hybrids, with many hybrids containing mitochondrial DNA from one species on a nuclear DNA background of the other. Ecological aspects explaining these shifts in genetic composition include female mate choice, changes in habitat associated with secondary succession, and, most strongly, a hierarchy of male territorial advantage-ecological mechanisms likely to be involved in the emergence and disappearance of many animal hybrid zones. Our results suggest that genetic assimilation is not a significant threat to either species and that rather transient hybrid zones such as this may serve to increase genetic diversity and are candidates for causing genetic discordance in phylogeographic analyses.

Introgressive hybridization among major Columbia River Chinook salmon (Oncorhynchus tshawytscha) lineages within the Klickitat River due to hatchery practices

Major lineages of anadromous salmonids show resilience to natural introgressive hybridization; however, Klickitat River spring-run Chinook salmon (KRSC, Oncorhynchus tshawytscha ) have an enigmatic origin because of their intermediate genetic and geographic relationship among Columbia River Chinook salmon lineages. We used computer simulations to evaluate four anthropogenic and natural processes as likely causes of the apparent introgressed genetic composition of KRSC: recent admixture (∼5 generations), historical admixture (>200 generations), isolation-by-distance gene flow, and natural selection. We also genotyped 2413 fish (32 collections) across 96 single nucleotide polymorphism loci to clarify the relationship of KRSC among the three major Columbia River lineages (Lower Columbia and interior ocean- and stream-types) and to quantify introgression among collections. Between 1980 and 2000, we observed a decline of pure interior stream-type individuals in the KRSC collections. This temporal shift in genetic composition was coincident with relevant changes in hatchery practices. Based on results from the simulations and time-series samples, a recent and anthropogenically caused admixture was most likely responsible for introgression of KRSC. Potential long-term negative effects of introgression may require some form of mitigation.

Coastal upwelling is linked to temporal genetic variability in the acorn barnacle Balanus glandula

Dispersal and recruitment are central processes that shape the geographic and temporal distributions of populations of marine organisms. However, significant variability in factors such as reproductive output, larval transport, survival, and settlement success can alter the genetic identity of recruits from year to year. We designed a temporal and spatial sampling protocol to test for genetic heterogeneity among adults and recruits from multiple time points along a similar to 400 km stretch of the Oregon (USA) coastline. In total, 2824 adult and recruiting Balanus glandula were sampled between 2001 and 2008 from 9 sites spanning the Oregon coast. Consistent with previous studies, we observed high mitochondrial DNA diversity at the cytochrome oxidase I locus (884 unique haplotypes) and little to no spatial genetic population structure among the 9 sites (Phi(ST) = 0.00026, p = 0.170). However, subtle but significant temporal shifts in genetic composition were observed among year classes (Phi(ST) = 0.00071, p = 0.035), and spatial Phi(ST) varied from year to year. These temporal shifts in genetic structure were correlated with yearly differences in the strength of coastal upwelling (p = 0.002), with greater population structure observed in years with weaker upwelling. Higher levels of barnacle settlement were also observed in years with weaker upwelling (p < 0.001). These data suggest the hypothesis that low upwelling intensity maintains more local larvae close to shore, thereby shaping the genetic structure and settlement rate of recruitment year classes.

A major shift in Daphnia genetic structure after the first ice‐free winter in a German reservoir

Summary1. Climate warming may cause disruption of trophic linkages in aquatic ecosystems and lead to changes in abundance and genetic structure of zooplankton populations. We monitored the community of the Daphnia galeata‐hyalina hybrid complex in the Saidenbach Reservoir (Saxony, Germany) using allozyme electrophoresis for three consecutive years (2005–07), including one (2007) following an unusually warm winter that prevented the formation of ice cover for the first time in the history of the reservoir.2. Genetic composition during the 2007 season differed substantially from the two preceding years that experienced the usual 3‐month ice period. Three abundance peaks in June, July and October 2007 were dominated by hybrids of Daphnia galeata x hyalina, whereas in the 2005 and 2006 seasons two peaks in June and September were dominated by Daphnia hyalina genotypes.3. The genetic composition of the pool of diapausing eggs produced in autumn and the rate of change of genotype abundance during the following spring indicate recruitment of the D. hyalina subpopulation from ex‐ephippial animals during the spring population increase.4. The differing potential to contribute to the overwintering animal pool or to the inoculum from diapausing eggs was confirmed by results from laboratory life‐table experiments. Daphnia galeata clones survived longer and produced parthenogenetic offspring under winter conditions, whereas D. hyalina clones showed a shorter lifespan and produced resting eggs.5. Our results indicate a profound role of recruitment strategy in the observed shift in genetic composition. Increasing winter temperatures predicted in the context of climate change may thus favour overwintering animals, leading to an increase in the contribution of these genotypes to the population. Such microevolutionary processes may dampen possible seasonal mismatches between daphnid populations and their food or predator populations.

Microevolutionary responses in experimental populations of plants to CO2-enriched environments: parallel results from two model systems.

Despite the critical role that terrestrial vegetation plays in the Earth's carbon cycle, very little is known about the potential evolutionary responses of plants to anthropogenically induced increases in concentrations of atmospheric CO2. We present experimental evidence that rising CO2 concentration may have a direct impact on the genetic composition and diversity of plant populations but is unlikely to result in selection favoring genotypes that exhibit increased productivity in a CO2-enriched atmosphere. Experimental populations of an annual plant (Abutilon theophrasti, velvetleaf) and a temperate forest tree (Betula alleghaniensis, yellow birch) displayed responses to increased CO2 that were both strongly density-dependent and genotype-specific. In competitive stands, a higher concentration of CO2 resulted in pronounced shifts in genetic composition, even though overall CO2-induced productivity enhancements were small. For the annual species, quantitative estimates of response to selection under competition were 3 times higher at the elevated CO2 level. However, genotypes that displayed the highest growth responses to CO2 when grown in the absence of competition did not have the highest fitness in competitive stands. We suggest that increased CO2 intensified interplant competition and that selection favored genotypes with a greater ability to compete for resources other than CO2. Thus, while increased CO2 may enhance rates of selection in populations of competing plants, it is unlikely to result in the evolution of increased CO2 responsiveness or to operate as an important feedback in the global carbon cycle. However, the increased intensity of selection and drift driven by rising CO2 levels may have an impact on the genetic diversity in plant populations.

Variation in Aggressiveness and the Regulation of Numbers in House Mouse Populations

Variation in Aggressiveness and the Regulation of Numbers in House Mouse Populations