Andrzej Oleksa

Increased inbreeding and strong kinship structure in Taxus baccata estimated from both AFLP and SSR data

Habitat fragmentation can have severe genetic consequences for trees, such as increased inbreeding and decreased effective population size. In effect, local populations suffer from reduction of genetic variation, and thus loss of adaptive capacity, which consequently increases their risk of extinction. In Europe, Taxus baccata is among a number of tree species experiencing strong habitat fragmentation. However, there is little empirical data on the population genetic consequences of fragmentation for this species. This study aimed to characterize local genetic structure in two natural remnants of English yew in Poland based on both amplified fragment length polymorphism (AFLP) and microsatellite (SSR) markers. We introduced a Bayesian approach that estimates the average inbreeding coefficient using AFLP (dominant) markers. Results showed that, in spite of high dispersal potential (bird-mediated seed dispersal and wind-mediated pollen dispersal), English yew populations show strong kinship structure, with a spatial extent of 50–100 m, depending on the population. The estimated inbreeding levels ranged from 0.016 to 0.063, depending on the population and marker used. Several patterns were evident: (1) AFLP markers showed stronger kinship structure than SSRs; (2) AFLP markers provided higher inbreeding estimates than SSRs; and (3) kinship structure and inbreeding were more pronounced in denser populations regardless of the marker used. Our results suggest that, because both kinship structure and (bi-parental) inbreeding exist in populations of English yew, gene dispersal can be fairly limited in this species. Furthermore, at a local scale, gene dispersal intensity can be more limited in a dense population.

Isolation by distance in saproxylic beetles may increase with niche specialization

Species confined to temporally stable habitats are usually susceptible to habitat fragmentation, as living in long-lasting habitats is predicted to constrain evolution of dispersal ability. In Europe, saproxylic invertebrates associated with tree hollows are currently threatened due to the severe fragmentation of their habitat, but data on the population genetic consequences of such habitat decline are still scarce. By employing AFLP markers, we compared the spatial genetic structure of two ecologically and taxonomically related beetle species, Osmoderma barnabita and Protaetia marmorata (Cetoniidae). Both species are exclusively associated with tree hollows, but O. barnabita has a more restricted host preferences compared to P. marmorata. Analyses of spatial autocorrelation showed, in line with the predicted low dispersal potential of these saproxylic beetles, that both species are characterized by a strong kinship structure, which was more pronounced in the specialist O. barnabita than in the generalist P. marmorata. Individuals of both species sampled within single trees showed high relatedness (≈0.50 in O. barnabita and ≈0.15 in P. marmorata). Interestingly, groups of pheromone-emitting O. barnabita males sampled on the same tree trunk were found to be full brothers. Whether this result can be explained by kin selection to increase attraction of conspecific females for mating or by severe inbreeding of beetles within individual tree hollows needs further study. Although our studied populations were significantly inbred, our results suggest that the dispersal ability of Osmoderma beetles may be one order of magnitude greater than suggested by previous dispersal studies and acceptable levels of habitat fragmentation for metapopulation survival may be bigger than previously thought.

Nuclear and mitochondrial patterns of introgression into native dark bees (Apis mellifera mellifera) in Poland

Summary The genetic diversity of the north and western European subspecies of honey bee, Apis mellifera mellifera (the “dark bee”) is severely endangered due to hybridization with introduced bees of evolutionary branch C. Genetic variability of native honey bees in the north-eastern part of Poland, including a special isolated breeding zone in the Augustów Forest, has been investigated using mitochondrial DNA and nuclear microsatellites. These involve analysis for alien haplotypes of the tRNAleu-COII region and presence of diagnostic alien alleles respectively, in conjunction with a Bayesian model based approach. We found that approximately 10 to 30% of the nuclear gene pool and 3 to 50% of mitochondria in the studied populations were derived from non-native bees. Our data revealed the presence of hybrids in populations formerly considered to be the most pure populations of dark bees in Poland. We suggest that the Bayesian analysis of admixture based on nuclear microsatellites provides a reliable tool for measuring introgression in dark bees, which should be routinely used for evaluation during conservation programmes.

Partial reproductive isolation between European subspecies of honey bees

Northern Poland is inhabited by native Apis mellifera mellifera (AMM) and the non-native A. m. carnica (AMC) which was introduced by beekeepers. However, hybrids between the two subspecies of honey bee are relatively rare. The lower than expected proportion of hybrids is hypothesised to be related to reproductive isolation between AMM and AMC. To verify this hypothesis, we allowed the AMM and AMC queens to be naturally inseminated in an area inhabited by both AMM and AMC drones. Genotype of the queens and their sexual partners were derived based on random samples of their worker offspring. Assignment of parental genotypes to the two subspecies was performed with a Bayesian clustering method. In colonies headed by AMM queens, workers were fathered mainly by AMM drones. On the other hand, in colonies headed by AMC queens workers were fathered by drones of both subspecies. The partial reproductive isolation reported here between AMM and AMC may facilitate conservation of the declining population of AMM.

Genetic evidence of reproductive isolation in a remote enclave of Quercus pubescens in the presence of cross-fertile species

Peripheral populations may be crucial for understanding processes underlying adaptive genetic variation. Their evolution and ecology are driven by various genetic and demographic processes, such as selection, gene flow and bottleneck. Peripheral populations often experience a reduction in density resulting in the Allee effect. The presence of interfertile species increases the opportunity for hybridisation, which allows for a rescue from the Allee effect, but at the risk of genetic extinction through introgression. In this article we investigated a peripheral population of Quercus pubescens, a European tree species. The study population is located in Poland, several hundred kilometres northwards from the main species range. Due to geographic separation, the study population exists under strong pressure of introgression from potentially inter-fertile Q. petraea and Q. robur, which are the only common oaks in Poland. The intermediate morphology between typical Q. pubescens and a common oak species found in the study population supports the introgression hypothesis, which could be in line with the earlier studies of this species complex conducted in the main range of Q. pubescens. Alternatively, the intermediate morphology could reflect the founder effect or selection at an ecological extreme. We attempted to verify these hypotheses using microsatellites and a reference of common oak species. The results showed that the study population is genetically distinct from both Q. petraea and Q. robur. Additionally, the population is characterised by a low effective population size and limited gene dispersal. This suggests that the study population reveals strong reproductive isolation from common species, implying alternative sources of atypical morphology.

Variable rates of random genetic drift in protected populations of English yew: implications for gene pool conservation

Protecting populations in their natural habitat allows for the maintenance of naturally evolved adaptations and ecological relationships. However, the conservation of genetic resources often requires complementary practices like gene banks, translocations or reintroductions. In order to minimize inbreeding depression and maximize the adaptive potential of future populations, populations chosen for ex situ conservation should be selected according to criteria that will result in a reduction of global coancestry in the population. Generally, large populations should reveal lower coancestry and higher genetic variation than small populations. If detailed knowledge about coancestry is lacking, census population number (Nc) can be used as a proxy for required characteristics. However, a simple measure of Nc may be misleading in particular cases as genetic processes rely on effective population size (Ne) rather than Nc and these two measures may differ substantially due to demographic processes. We used an example of English yew to address whether Nc can be a good predictor of genetic parameters when used in conservation programs. Using microsatellite markers, we estimated allelic richness, inbreeding and coancestry coefficients of six relatively large yew populations in Poland. Each population was characterized by Ne using the linkage disequilibrium method. Our results showed that populations of English yew were subject to substantial divergence and genetic drift, with both being inversely proportional to the effective subpopulation size (Ne). Additionally, allelic richness appeared proportional to Ne but not to Nc. However, the Ne/N ratio differed greatly among populations, which was possibly due to different population histories. From the results we concluded that choosing source populations based only on their census size can be fairly misleading. Implications for conservation are briefly discussed.

Could the vulnerable great Capricorn beetle benefit from the introduction of the non-native red oak?

Introduced plants are often identified as the major conservation concern worldwide, however, they also may offer conservation benefits, among others, provide habitat and/or food resources to protected animals. Here we aimed to assess the ability of the great Capricorn beetle Cerambyx cerdo, a highly specialised species associated with mature oaks, to use non-native red oak Quercus rubra as a host plant. To test which factors influenced oak colonisation, we surveyed native and non-native oaks in ‘Nowosolska Dolina Odry’, a site within the ‘Natura 2000’ network (Western Poland). The beetle was detected in 34 native oaks (10.9% of examined trees), demonstrating clear preferences for trees in a more open environment. Comparison of observed numbers of occupied oaks and values expected from their random colonisation showed that C. cerdo avoided non-native red oaks. Logistic regression revealed that variables with the greatest predictive importance for C. cerdo occurrence were canopy extent around the tree and trunk diameter, followed by an autocovariate (distance-weighted number of occupied trees in the neighbourhood of the target tree). Oak species was a poor predictor of tree occupancy, however, it added considerably to the predictive capability of the models when combined with the remaining variables. We argue that physicochemical properties of the wood and/or phloem and structure of the cortex may also influence colonisation of trees. Our results do not provide arguments for the introduction of non-native oaks to benefit C. cerdo. Instead, we recommend maintaining semi-open conditions around host trees and high density of old oaks in the landscape.

There are still Bee Trees in Europe

In Europe honey bees are considered as domesticated animals. Beekeepers provide them with hives, feed them, protect against parasites and manage them extensively. However, the number of colonies in central and northern Europe is declining, Feral colonies of honey bees once present in Europe have also seen a sharp decline in recent years.