H.A.H. Jansman

Genetic impoverishment of the last black grouse (Tetrao tetrix) population in the Netherlands: detectable only with a reference from the past

We have studied a small isolated population of black grouse (Tetrao tetrix) in the Netherlands to examine the impact of isolation and reduction in numbers on genetic diversity. We compared the genetic diversity in the last extant Dutch population with Dutch museum samples and three other black grouse populations (from England, Austria and Norway, respectively) representing isolated and continuous populations. We found significantly lower allelic richness, observed and expected heterozygosities in the present Dutch population compared to the continuous populations (Austria and Norway) and also to the historical Dutch population. However, using a bottleneck test on each population, signs of heterozygosity excess were only found in the likewise isolated English population despite that strong genetic drift was evident in the present Dutch population in comparison to the reference populations, as assessed both in pairwise FST and structure analyses. Simulating the effect of a population reduction on the Dutch population from 1948 onwards, using census data and with the Dutch museum samples as a model for the genetic diversity in the initial population, revealed that the loss in number of alleles and observed heterozygosity was according to genetic drift expectations and within the standard error range of the present Dutch population. Thus, the effect of the strong decline in the number of grouse on genetic diversity was only detectable when using a reference from the past. The lack of evidence for a population reduction in the present Dutch population by using the program bottleneck was attributed to a rapidly found new equilibrium as a consequence of a very small effective population size.

Genetic variability in European black grouse ( Tetrao tetrix )

We studied microsatellite genetic variation in 14 different geographic populations of black grouse (Tetrao tetrix) across the European range. Populations were grouped in three different fragmentation categories: isolated, contiguous and continuous, respectively. Genetic diversity, measured as observed heterozygosity (HO), expected heterozygosity (HE) and allelic richness, were lower in isolated populations as compared to the other two categories that did not differ amongst one another. These results imply that lowered genetic variability in black grouse populations is negatively affected by population isolation. Our results suggest that the connectivity of small and isolated populations in Western Europe should be improved or else these face an increased risk of extinction due to genetic and demographic stochasticity.

Applicability of spraints for monitoring organic contaminants in free-ranging otters (Lutra lutra).

In the current study, the use of spraints for monitoring levels of polychlorinated biphenyls (PCBs) in individual otters was experimentally validated. On the basis of a detailed pattern analysis, it is concluded that in the current study, PCB concentrations in spraints that contain relatively high concentrations of nonmetabolizable PCB congeners (PCB 138 and 153 > 42.5% of total PCB concentrations) reflect the internal PCB concentrations of the otter that produced the spraint. In general, however, spraints should be selected that contain relative concentrations of PCB138 and PCB153 > 95th percentile of these congeners in samples from local food items of otters. On the basis of relationships between levels in spraints and internal levels and on earlier reported effect concentrations, a threshold level range of 1.0 to 2.3 microg/g (lipid normalized) in such spraints is proposed. The validated methods to monitor PCBs in otters may be combined with genetic marker techniques that can assess the identity of the otter that produced the spraints. In such a design, it is feasible to monitor PCB levels in individual free-ranging otters in a truly animal friendly way.

Analyses of historical and current populations of black grouse in Central Europe reveal strong effects of genetic drift and loss of genetic diversity

Black grouse (Tetrao tetrix) in Central Europe have undergone a severe contraction of their range in recent decades with only a few small isolated remaining populations. Here we compare genetic diversity of two contemporary isolated populations (Sallandse Heuvelrug, Netherlands and Lüneburger Heide, Germany) with historical samples from the same region collected within the last one hundred years. We use markers with both putatively neutral and functional variation to test whether the present small and highly fragmented populations hold lower genetic diversity compared to the former larger population. For this we applied three different types of genetic markers: nine microsatellites and 21 single nucleotide polymorphisms (SNPs), both sets which have been found to be neutral, and two functional major histocompatibility complex (MHC) genes for which there is evidence they are under selection. The contemporary small isolated populations displayed lower neutral genetic diversity compared to the corresponding historical samples. Furthermore, samples from Denmark showed that this now extinct population displayed lower genetic variation in the period immediately prior to the local extinction. Population structure was more pronounced among contemporary populations compared to historical populations for microsatellites and SNPs. This effect was not as distinct for MHC which is consistent with the possibility that MHC has been subjected to balancing selection in the past, a process which maintains genetic variation and may minimize population structure for such markers. Genetic differentiation among the present populations highlights the strong effects of population decline on the genetic structure of natural populations, which can be ultimately attributed to habitat loss following anthropogenic land use changes.

Hidden dispersal in an urban world: genetic analysis reveals occasional long-distance dispersal and limited spatial substructure among Dutch pine martens

Especially in urbanized landscapes, habitat fragmentation and increasing numbers of infrastructural features may limit genetic exchange among wildlife populations. Yet, whether this results in genetic differentiation among individuals in different habitat fragments will depend on both the species studied and the composition of the landscape. European pine martens (Martes martes) show clear spatial structure at a Europe-wide scale, but whether gene flow among habitat patches can be maintained at a more local scale in intensively urbanized areas remained unclear. Here, we analysed genotypic data from 270 pine martens sampled from locations scattered across the Netherlands, one of the most densely populated areas in the world. Using Bayesian clustering models we show that most likely maximum two large subpopulations exist in the Netherlands. We observed relatively low levels of genetic differentiation and genetic evidence of regular long-distance dispersal by juveniles that must have crossed one or multiple major highways. Our results suggest that genetic exchange among Dutch pine martens has, until 2010, not been impacted severely by the countries’ dense infrastructural network. Furthermore this species seems to have maintained its genetic diversity despite a recent demographic bottleneck. These conclusions support the idea that the effects of habitat fragmentation may strongly differ between (groups of) species, and that prioritization and optimization of management decisions thus requires direct study of the targeted species.

Genetic impoverishment of the last Black grouse (Tetrao tetrix) population in the Netherlands

We have studied a small isolated population of black grouse (Tetrao tetrix) in the Netherlands to examine the impact of isolation and reduction in numbers on genetic diversity. We compared the genetic diversity in the last extant Dutch population with Dutch museum samples and three other black grouse populations (from England, Austria and Norway, respectively) representing isolated and continuous populations. We found significantly lower allelic richness, observed and expected heterozygosities in the present Dutch population compared to the continuous populations (Austria and Norway) and also to the historical Dutch population. However, using a bottleneck test on each population, signs of heterozygosity excess were only found in the likewise isolated English population despite that strong genetic drift was evident in the present Dutch population in comparison to the reference populations, as assessed both in pairwise FST and structure analyses. Simulating the effect of a population reduction on the Dutch population from 1948 onwards, using census data and with the Dutch museum samples as a model for the genetic diversity in the initial population, revealed that the loss in number of alleles and observed heterozygosity was according to genetic drift expectations and within the standard error range of the present Dutch population. Thus, the effect of the strong decline in the number of grouse on genetic diversity was only detectable when using a reference from the past. The lack of evidence for a population reduction in the present Dutch population by using the program bottleneck was attributed to a rapidly found new equilibrium as a consequence of a very small effective population size.

Genetic impoverishment of the last black grouse (Tetrao tetrix) population in the Netherlands: detectable only with a reference from the past: GENETIC DIVERSITY IN BLACK GROUSE

We have studied a small isolated population of black grouse (Tetrao tetrix) in the Netherlands to examine the impact of isolation and reduction in numbers on genetic diversity. We compared the genetic diversity in the last extant Dutch population with Dutch museum samples and three other black grouse populations (from England, Austria and Norway, respectively) representing isolated and continuous populations. We found significantly lower allelic richness, observed and expected heterozygosities in the present Dutch population compared to the continuous populations (Austria and Norway) and also to the historical Dutch population. However, using a bottleneck test on each population, signs of heterozygosity excess were only found in the likewise isolated English population despite that strong genetic drift was evident in the present Dutch population in comparison to the reference populations, as assessed both in pairwise FST and structure analyses. Simulating the effect of a population reduction on the Dutch population from 1948 onwards, using census data and with the Dutch museum samples as a model for the genetic diversity in the initial population, revealed that the loss in number of alleles and observed heterozygosity was according to genetic drift expectations and within the standard error range of the present Dutch population. Thus, the effect of the strong decline in the number of grouse on genetic diversity was only detectable when using a reference from the past. The lack of evidence for a population reduction in the present Dutch population by using the program bottleneck was attributed to a rapidly found new equilibrium as a consequence of a very small effective population size.