Nonlocal Genotypes Research Articles

Genotypic and phenotypic distinctness of restored and indigenous populations of Pimpinella saxifraga L. 8 or more years after restoration.

The recovery of altered or damaged ecosystems demands large-scale reintroductions of seeds. In the past, ecological restoration in Germany was carried out with non-local seeds of naturally occurring species. We here analysed whether the genetic pattern of the introduced non-local seeds (R=restored) of Pimpinella saxifraga are still detectable several years after application and whether the phenotype differs from that of the regional gene pool (I=indigenous) of the species. We collected material from individuals of R and I sites, conducted a common garden experiment and tested for genetic, morphological and phenotypic differences. In a cutting experiment we investigate treatment effects on indigenous and restored populations. At all investigated sites we only found P. saxifraga individuals with comparatively similar genome sizes. The population genetic analysis revealed two large and quite distinct molecular clusters, separating indigenous and restored individuals along the first axis. None of the vegetative, but two of the reproductive fitness parameters differed between individuals of the R and I sites. Cutting always had a significant influence on all analysed vegetative and reproductive fitness parameters, regardless of the individuals' origin. The effects of mowing always mask origin-specific characteristics, which then disappear. Genotypic coexistence reduces the availability of niches for the local genotype and may eventually lead to genotypic competition or introgression. We therefore recommend not to use non-local genotypes of this species in the region. Instead, we recommend using the genetically diverse local genotypes of P. saxifraga for restoration purposes.

Plant reproductive strategies vary under low and high pollinator densities

Long‐term variation in the population density of honey bees Apis mellifera across landscapes has been shown to correlate with variation in the floral traits of plant populations in these landscapes, suggesting that variations in pollinator population density and foraging rates can drive floral trait evolution of their host plants. However, it remained to be determined whether this variation in plant traits is associated with adaptive variation in plant reproductive strategies under conditions of high and low pollinator densities. Here we conducted a reciprocal transplant experiment to examine how this variation in floral traits, under conditions of either high and low pollinator density, impacted seed production in the Tibetan lotus Saussurea nigrescens. In 2014 and 2015, we recorded the floral traits, pollinator visitation rates, and seed production of S. nigrescens populations grown in both home sites and foreign sites, where sites varied in honey bee population density. Our results demonstrated that the floral traits reflected those of their original population, regardless of their current location. However, seed production varied with both population origin and transplant site. Seed number was positively correlated with flower abundance in the pollinator‐rich sites, but with nectar production in the pollinator‐poor sites. Pollinator visitation rate was also positively correlated with flower number at pollinator‐rich sites, and with nectar volume at pollinator‐poor sites. Overall, the local genotype had higher seed production than nonlocal genotypes in home sites. However, when pollen is hand‐supplemented, plants from pollinator‐rich populations had higher seed production than plants from pollinator‐poor populations, regardless of whether they were transplanted to pollinator‐rich or ‐poor sites. These results suggest that the plant genotypic differences primarily drive variation in pollinator attraction, and this ultimately drives variation in seed: ovule ratio. Thus, our results suggest that flowering plant species use different reproductive strategies to respond to high or low pollinator densities.

Integrating climate change and habitat fragmentation to identify candidate seed sources for ecological restoration

AbstractAnthropogenic change (climate change and habitat fragmentation) is driving a growing view that local seed collections may need to be supplemented with nonlocal seed as a strategy to bolster genetic diversity and thus increase evolutionary potential of plantings. While this strategy is becoming widely promoted, empirical support is limited, and there is a lack of accessible research tools to assist in its experimental testing. We therefore provide the Provenancing Using Climate Analogues (PUCA) framework that integrates the principles of the climate‐adjusted provenancing strategy with concepts from population genetics (i.e. potential inbreeding in small fragmented populations) as both a research and operational‐ready tool to guide the collection of nonlocal seed. We demonstrate the application of PUCA using the Midlands of Tasmania, Australia, a region that is currently undergoing large‐scale ecological restoration. We highlight multiple nonlocal seed sources for testing by identifying actual species distribution records that currently occupy environments similar to that projected to occur at the restoration site in the future. We discuss the assumptions of PUCA and the ecological considerations that need to be tested when moving nonlocal genotypes across the landscape.

Evolutionary applications research highlight for issue 1.

As we highlight each month in this section, the application of evolutionary theory to issues affecting the health and well-being of human, agricultural, and natural populations is gaining increasing momentum. In a recent review article written for Science, Scott Carroll et al. take on the now monumental task of synthesizing the many ways that evolutionary biology can be used to address global challenges (Carroll et al. 2014). They comprehensively explore the main problems being tackled with an evolutionary approach, ranging from populations evolving too quickly (such as emerging pathogens or pests evolving resistance to treatment) to populations not evolving quickly enough (for example those being negatively affected by human-mediated change). The authors begin by identifying what they see as the two key paradigms of applied evolutionary biology: (i) managing contemporary evolution (i.e., manipulating the rapid evolutionary response of short-lived organisms with large population sizes, such as bacterial pathogens) and (ii) altering the phenotype–environment mismatch (i.e., responding to populations of long-lived organisms such as trees that are no longer well adapted to their local environment due to shifts in climatic conditions or changes in biotic interactions). As a great example of such a mismatch, the authors highlight the increasing rates of obesity, diabetes, and heart disease in the human populations as a result of a more sedentary lifestyle with diets rich in sugars and fat. They then identify a number of promising research avenues that either have addressed or have the potential to address current global challenges, covering a wide range of approaches including the use of genetic engineering to more appropriately match genomes to their environment, the use of ‘refuges’ in agriculture and combination treatments against pests and pathogens to hinder the evolution of resistance, and introducing nonlocal genotypes which are predicted to perform better under given environmental conditions into natural populations to increase local adaptation. The article nicely separates these conceptual approaches into strategies for slowing unwanted evolution or directly influencing fitness of pests and pathogens, strategies for reducing the mismatch between phenotype and the local environment, and strategies for increasing group performance by selecting on group-level traits. For example, the authors discuss the success of artificially selecting for group yield in agricultural plots rather than individual fitness as a means for decreasing competition among plants. Critically, the piece also emphasizes the need to take a unified approach in meeting international objectives for sustainable development and suggests a need for stricter enforcement of guidelines in order to ensure best practice is achieved despite temptation to put profit or immediate success ahead of sustainable solutions. Overall, the review acts as a unique and remarkable resource both for researchers and students who are new to the field of applied evolution and those who actively contribute to the field.

QTL mapping of freezing tolerance: links to fitness and adaptive trade-offs.

Local adaptation, defined as higher fitness of local vs. nonlocal genotypes, is commonly identified in reciprocal transplant experiments. Reciprocally adapted populations display fitness trade-offs across environments, but little is known about the traits and genes underlying fitness trade-offs in reciprocally adapted populations. We investigated the genetic basis and adaptive significance of freezing tolerance using locally adapted populations of Arabidopsis thaliana from Italy and Sweden. Previous reciprocal transplant studies of these populations indicated that subfreezing temperature is a major selective agent in Sweden. We used quantitative trait locus (QTL) mapping to identify the contribution of freezing tolerance to previously demonstrated local adaptation and genetic trade-offs. First, we compared the genomic locations of freezing tolerance QTL to those for previously published QTL for survival in Sweden, and overall fitness in the field. Then, we estimated the contributions to survival and fitness across both field sites of genotypes at locally adaptive freezing tolerance QTL. In growth chamber studies, we found seven QTL for freezing tolerance, and the Swedish genotype increased freezing tolerance for five of these QTL. Three of these colocalized with locally adaptive survival QTL in Sweden and with trade-off QTL for overall fitness. Two freezing tolerance QTL contribute to genetic trade-offs across environments for both survival and overall fitness. A major regulator of freezing tolerance, CBF2, is implicated as a candidate gene for one of the trade-off freezing tolerance QTL. Our study provides some of the first evidence of a trait and gene that mediate a fitness trade-off in nature.

Influence of environmental heterogeneity on genetic diversity and structure in an endemic southern Californian oak

Understanding how specific environmental factors shape gene flow while disentangling their importance relative to the effects of geographical isolation is a major question in evolutionary biology and a specific goal of landscape genetics. Here, we combine information from nuclear microsatellite markers and ecological niche modelling to study the association between climate and spatial genetic structure and variability in Engelmann oak (Quercus engelmannii), a wind-pollinated species with high potential for gene flow. We first test whether genetic diversity is associated with climatic niche suitability and stability since the Last Glacial Maximum (LGM). Second, we use causal modelling to analyse the potential influence of climatic factors (current and LGM niche suitability) and altitude in the observed patterns of genetic structure. We found that genetic diversity is negatively associated with local climatic stability since the LGM, which may be due to higher immigration rates in unstable patches during favourable climatic periods and/or temporally varying selection. Analyses of spatial genetic structure revealed the presence of three main genetic clusters, a pattern that is mainly driven by two highly differentiated populations located in the northern edge of the species distribution range. After controlling for geographic distance, causal modelling analyses showed that genetic relatedness decreases with the environmental divergence among sampling sites estimated as altitude and current and LGM niche suitability. Natural selection against nonlocal genotypes and/or asynchrony in reproductive phenology may explain this pattern. Overall, this study suggests that local environmental conditions can shape patterns of genetic structure and variability even in species with high potential for gene flow and relatively small distribution ranges.

Outbreeding Depression Caused by Intraspecific Hybridization Between Local and Nonlocal Genotypes in Abies sachalinensis

To evaluate the effects of intraspecific hybridization of local and nonlocal genotypes on growth traits of progeny in Abies sachalinensis, we performed reciprocal crossing between nonlocal trees in a high‐elevation zone (1,100–1,200 m asl) and local trees in a low‐elevation zone (530 m asl) in Hokkaido, northern Japan, in 1979 and established a common garden experiment using local × local (female × male ), local × nonlocal , nonlocal × local , and nonlocal × nonlocal progeny in the low‐elevation zone in 1986. Survival, height, diameter at breast height (dbh), needle nitrogen content, specific leaf area (SLA), and needle area per shoot diameter (NA) of 25‐year‐old progeny were measured in 2005. The survival rate was consistently high (>85% on average). Reductions in height and dbh were apparent in F1 hybrids compared with local × local progeny. Furthermore, outbreeding depression was significant in height growth of nonlocal × local F1 hybrids and in dbh of both F1 hybrids. Reductions in growth traits may be related to morphological needle traits, such as the low values of SLA and NA. Elevation guidelines for A. sachalinensis seed zones are discussed to ensure the long‐term viability of both restored and native populations.

Dune Restoration Introduces Genetically Distinct American Beachgrass,Ammophila breviligulata, into a Threatened Local Population

There is mounting concern over the source and genetic history of plant propagules used for habitat restoration because introduced genotypes may destabilize remnant local populations through competition and introgression. We examined whether introduced dune grass,Ammophila breviligulata, from Michigan is genetically distinct from a threatened local Minnesota population by comparing local and nonlocal genotypes in well‐established stands in the field and in experimental common gardens. Both observational and experimental studies suggest that Michigan plants differed genetically and had an advantage over local plants in terms of vegetative spread and sexual reproduction. Well‐established restoration populations composed of Michigan plants produced fertile culms that were 1.8 times taller than Minnesota plants and more than twice as fecund. Introgression is unlikely, however, because Minnesota genotypes flowered on average 6.7 weeks earlier than Michigan plants and only 20% of Minnesota pollen remained viable after 4 weeks. In the common gardens, Michigan plants from two sources were larger in size, grew faster, and flowered more frequently than Minnesota plants. Plant surveys across the study area suggest that nonlocal genotypes have spread beyond documented restoration areas and into local stands, particularly in foredunes. Even if gene flow between local and nonlocal plants is limited due to differences in flowering phenology, Michigan genotypes may out‐compete plants in the threatened Minnesota population through greater vegetative and sexual reproduction. The fitness consequences of this change in the genetic composition of the local population have yet to be determined.

A question of origin: Where and how to collect seed for ecological restoration

Native plant species are routinely planted or sown in ecological restoration projects, but successful establishment and survival depend on where and how seeds are collected. Research suggests that it is important to use locally adapted seeds. Local populations often show a home-site advantage and non-local genotypes may be maladapted to local environmental conditions. Furthermore, intraspecific hybridisation of local and non-local genotypes may have a negative impact on the genetic structure of local populations via mechanisms such as outbreeding depression. Many species show a strong small-scale genetic differentiation between different habitats so that matching habitats of the restoration and donor site can be more important than minimizing geographical separation. It is a challenge to identify appropriate seed sources because strong small-scale population differentiation makes it difficult to delineate geographically defined seed zones to which seed exchange should be limited. Moreover, it is important to consider the genetic diversity of introduced material because it may be crucial to avoid genetic bottlenecks, inbreeding depression and poor establishment of plant populations. Repeated propagation in stock, which is often required to obtain a sufficient amount of seeds, can further reduce genetic diversity and may select for particular genotypes. Negative impacts of improper seed choice for nursery planting stock may become detectable only after many years, especially in long-lived and slow growing plants. Although scientific information on many species remains limited, the increasing demand for translocation of seed means that mandatory regulations are necessary. Guidelines should prescribe a specification of seed provenance, a record of genetic diversity of wild collections and rules for subsequent processing such as direct transfer and propagation of stock or seed orchards. We use a literature review to evaluate current legislation and to develop recommendations for herbaceous and woody species.

Modelling forest recolonization by an epiphytic lichen using a landscape genetic approach

The process of recolonization after disturbance is crucial for the persistence and dynamics of patch-tracking metapopulations. We developed a model to compare the spatial distribution and spatial genetic structure of the epiphytic lichen Lobaria pulmonaria within the perimeter of two reconstructed 19th century disturbances with a nearby reference area without stand-level disturbance. Population genetic data suggested that after stand-replacing disturbance, each plot was colonized by one or a few genotypes only, which subsequently spread clonally within a local neighborhood. The model (cellular automaton) aimed at testing the validity of this interpretation and at assessing the relative importance of local dispersal of clonal propagules vs. long-distance dispersal of clonal and/or sexual diaspores. A reasonable model fit was reached for the empirical data on host tree distribution, lichen distribution, and tree- and plot-level genotype diversity of the lichen in the reference area. Although model calibration suggested a predominance of local dispersal of clonal propagules, a substantial contribution of immigration of non-local genotypes by long-distance dispersal was needed to reach the observed levels of genotype diversity. The model could not fully explain the high degree of clonality after stand-replacing disturbance, suggesting that the dispersal process itself may not be stationary but depend on the ecological conditions related to disturbance.

Genetic structure in the perennial grasses Lolium perenne and Agrostis curtisii

Genetic variation was studied in unimproved grassland populations of two contrasting outbreeding perennial grass species. A total of 27 populations of Lolium perenne (perennial ryegrass) and 30 populations of Agrostis curtisii (bristle-leaved bent), sampled from seven and five regions spread across southern Britain, were assessed at three and four isozyme loci, respectively. The extent of genetic structure within and among populations was estimated using unbiased F-statistics. In A. curtisii, a nonagricultural species, populations from adjacent regions were found to be more genetically similar than those separated by greater distance. The reverse situation was observed within L. perenne, a species of major agricultural importance. It is suggested that the absence from L. perenne of the pattern of genetic variation found in A. curtisii is consistent with the occurrence of large-scale human-mediated gene flow via ‘improved’ ryegrass cultivars. If this is the case, then the disruption of natural patterns of genetic variation by the introduction of nonlocal genotypes may occur without apparent major ecological consequences.