Jaana Kekkonen

Genetic variation and structure of house sparrow populations: is there an island effect?

Population genetic structure and intrapopulation levels of genetic variation have important implications for population dynamics and evolutionary processes. Habitat fragmentation is one of the major threats to biodiversity. It leads to smaller population sizes and reduced gene flow between populations and will thus also affect genetic structure. We use a natural system of island and mainland populations of house sparrows along the coast of Norway to characterize the different population genetic properties of fragmented populations. We genotyped 636 individuals distributed across 14 populations at 15 microsatellite loci. The level of genetic differentiation was estimated using F‐statistics and specially designed Mantel tests were conducted to study the influence of population type (i.e. mainland or island) and geographic distance on the genetic population structure. Furthermore, the effects of population type, population size and latitude on the level of genetic variation within populations were examined. Our results suggest that genetic processes on islands and mainland differed in two important ways. First, the intrapopulation level of genetic variation tended to be lower and the occurrence of population bottlenecks more frequent on islands than the mainland. Second, although the general level of genetic differentiation was low to moderate, it was higher between island populations than between mainland populations. However, differentiation increased in mainland populations somewhat faster with geographical distance. These results suggest that population bottleneck events and genetic drift have been more important in shaping the genetic composition of island populations compared with populations on the mainland. Such knowledge is relevant for a better understanding of evolutionary processes and conservation of threatened populations.

Heterozygosity in an Isolated Population of a Large Mammal Founded by Four Individuals Is Predicted by an Individual-Based Genetic Model

Background Within-population genetic diversity is expected to be dramatically reduced if a population is founded by a low number of individuals. Three females and one male white-tailed deer Odocoileus virginianus, a North American species, were successfully introduced in Finland in 1934 and the population has since been growing rapidly, but remained in complete isolation from other populations. Methodology/Principal Findings Based on 14 microsatellite loci, the expected heterozygosity H was 0.692 with a mean allelic richness (AR) of 5.36, which was significantly lower than what was found in Oklahoma, U.S.A. (H = 0.742; AR = 9.07), demonstrating that a bottleneck occurred. Observed H was in line with predictions from an individual-based model where the genealogy of the males and females in the population were tracked and the populations demography was included. Conclusion Our findings provide a rare within-population empirical test of the founder effect and suggest that founding a population by a small number of individuals need not have a dramatic impact on heterozygosity in an iteroparous species.

Tawny owl reproduction and offspring sex ratios under variable food conditions

Tawny owl reproduction and offspring sex ratios have been considered to depend on the abundance of small voles. We studied reproductive performance (laying date, clutch and brood size) during 1995–2003 and offspring sex ratios from 1999 to 2003 in relation to the abundance of small voles and food delivered to the nest in a tawny owl population in southern Finland. Abundance of small voles (field and bank voles) was based on trappings in the field, and estimates of food delivery was based on diet analysis of food remains in the nest boxes. In this population, reproductive output was not related to the abundance of small voles. Analysis of food delivered to the nest showed that the prey weight per offspring varied more than twofold between years and revealed that this difference was mainly related to the proportion of water voles in the diet. Only the number of water voles correlated with laying dates. Offspring sex ratios were weakly male biased (55%) but did not differ from parity. Sex ratios were not related to the abundance of small voles, and we found no evidence that parents delivered more food to nests with proportionally more offspring of the larger (female) sex. Our results underline the notion that populations may differ in their sex allocation pattern, and suggest such differences may be due to diet.

Size differentiation in Finnish house sparrows follows Bergmann's rule with evidence of local adaptation

Bergmanns rule predicts that individuals are larger in more poleward populations and that this size gradient has an adaptive basis. Hence, phenotypic divergence in size traits between populations (PST) is expected to exceed the level of divergence by drift alone (FST). We measured 16 skeletal traits, body mass and wing length in 409 male and 296 female house sparrows Passer domesticus sampled in 12 populations throughout Finland, where the species has its northernmost European distributional margin. Morphometric differentiation across populations (PST) was compared with differentiation in 13 microsatellites (FST). We find that twelve traits phenotypically diverged more than FST in both sexes, and an additional two traits diverged in males. The phenotypic divergence exceeded FST in several traits to such a degree that findings were robust also to strong between‐population environmental effects. Divergence was particularly strong in dimensions of the bill, making it a strong candidate for the study of adaptive molecular genetic divergence. Divergent traits increased in size in more northern populations. We conclude that house sparrows show evidence of an adaptive latitudinal size gradient consistent with Bergmanns rule on the modest spatial scale of ca. 600 km.

Using heterozygosity–fitness correlations to study inbreeding depression in an isolated population of white-tailed deer founded by few individuals

A heterozygosity–fitness correlations (HFCs) may reflect inbreeding depression, but the extent to which they do so is debated. HFCs are particularly likely to occur after demographic disturbances such as population bottleneck or admixture. We here study HFC in an introduced and isolated ungulate population of white-tailed deer Odocoileus virginianus in Finland founded in 1934 by four individuals. A total of 422 ≥ 1-year-old white-tailed deer were collected in the 2012 hunting season in southern Finland and genotyped for 14 microsatellite loci. We find significant identity disequilibrium as estimated by g2. Heterozygosity was positively associated with size- and age-corrected body mass, but not with jaw size or (in males) antler score. Because of the relatively high identity disequilibrium, heterozygosity of the marker panel explained 51% of variation in inbreeding. Inbreeding explained approximately 4% of the variation in body mass and is thus a minor, although significant source of variation in body mass in this population. The study of HFC is attractive for game- and conservation-oriented wildlife management because it presents an affordable and readily used approach for genetic monitoring that allowing identification of fitness costs associated with genetic substructuring in what may seem like a homogeneous population.

Temporal Genetic Monitoring of Declining and Invasive Wildlife Populations: Current State and Future Directions

Human actions constantly change the environmental conditions for other organisms, which are inevitably affected by these rapid shifts. We need to monitor the changes we induce in the populations, whether they are for conservation purposes of species which become threatened or for measuring and controlling the spread of invasive species. Genetic methods developed in recent decades provide valuable tools for monitoring changes in populations over time. With these methods knowledge, which is difficult or even impossible to gain otherwise, is gained. Genetic monitoring can provide crucial information on genetic diversity, connectivity, fitness, and viability of populations. Furthermore, the origins of invasive species, their expansion routes, and predictions of future evolutionary trajectories can be resolved. In this chapter, methods and implications of temporal genetic monitoring are presented through case studies of declining populations and invasive species. The use of museum and other biological collections in temporal genetic monitoring is discussed, and future directions, especially in terms of measuring adaptive genetic variation, are suggested. There is great and unrealized potential in temporal genetic monitoring and this chapter hopefully encourages its wider application in wildlife management.

Growth and Age Structure in an Introduced and Hunted Cervid Population: White-Tailed Deer in Finland

White-tailed deer were introduced to Finland in 1934 from Minnesota, North America. The population has expanded and is now an important wildlife species, managed through hunting. We determined the age of 451 individuals harvested in the 2012 hunting season. Hunters measured their body mass after slaughter and we measured the dimensions of the lower jaw (in both sexes) as well as skull dimensions and antler scores (in males). The sample indicated a deficit of older males in the population. Females seem to gain their size at the age of two while males continue to increase their body size and that of skeletal traits until the age of four. The size traits measured were similar to those in the North American studies. Based on population growth patterns and introduction history, the white-tailed deer population is performing well in Finland but the potentially skewed sex-specific age distribution warrants further attention.

Pollutants in Urbanized Areas: Direct and Indirect Effects on Bird Populations

Industrialization, traffic, intensification of agriculture, and development of human lifestyle in general during the last century have resulted in elevated levels of various chemical compounds in our environment. Especially in urbanized areas, harmful substances are produced in such quantities that they can have a deleterious effect on the development, survival, and reproduction of organisms. Many bird species have adapted to living alongside with humans and even discovered new resources within the urban lifestyle. However, these birds are in greatest risk of being harmfully effected by various chemicals.

Diet and reproduction in coastal and inland populations of the Tawny Owl Strix aluco in southern Finland

In generalist predators the energy needed for reproduction is derived from various prey categories, the profitability of which may vary according to the biomass or accessibility of the prey items. We examined the relationships between the diet and production of young in two Tawny Owl (Strix aluco) populations in southern Finland. We found a positive correlation between the amount of remnants of different prey in samples of litter collected from the nest bottoms after breeding and the production of young. Three important prey categories in the diet of owls during the nestling period, i.e. Water Voles, Field Voles and thrush-sized birds, seemed to be significantly related to the number of fledglings. However, only thrush-sized birds showed a significant relationship to the number of fledglings when all prey variables were analysed together in one model. The total prey mass was the best predictor of owl brood size. There were no significant local differences between the effects of different prey categories on the production of Tawny Owl young. Our results, combined with some earlier findings, outline the relationship between food supply and the production of Tawny Owl young in southern Finland. With regards to the Tawny Owl this outline can be generalized to other areas with other kinds of food supply within the distribution range of the species. Similar outlines are probably applicable also to many other generalist predators.ZusammenfassungNahrung und Reproduktion von Küsten- und Inlandspopulationen des WaldkauzesStrix alucoin SüdfinnlandBei generalistischen Beutegreifern setzt sich die für die Reproduktion aufgewendete Energie aus den verschiedenen Beutekategorien zusammen, die je nach Biomasse und Verfügbarkeit der Beutestücke variieren können. Wir untersuchten die Beziehung zwischen Nahrung und Jungenproduktion in zwei Waldkauzpopulationen in Südfinnland. Wir fanden eine positive Korrelation zwischen der Anzahl an Beuteresten in Proben aus der Neststreu nach der Brut und der Jungenproduktion der Käuze. Drei bedeutende Beutekategorien in der Nahrung der Käuze während der Nestlingszeit schienen signifikant mit der Anzahl an Flügglingen zusammenzuhängen: Schermäuse, Erdmäuse und drosselgroße Vögel. Lediglich drosselgroße Vögel zeigten jedoch eine signifikante Beziehung in der Kombination mit allen Beutekategorien. Die gesamte Beutemasse erklärte die Brutgröße der Käuze am besten. Es gab keine signifikanten räumlichen Unterschiede zwischen den Effekten verschiedener Beutekategorien auf die Jungenproduktion der Käuze. In Kombination mit einigen früheren Ergebnissen liefern unsere Resultate einen Grundzusammenhang zwischen Nahrungsbereitstellung und der Produktion von jungen Waldkäuzen in Südfinnland. Innerhalb des Verbreitungsgebietes der Art kann dieser Grundzusammenhang generalisierend auf andere Gegenden mit anderen Arten der Nahrungsbereitstellung angewendet werden. Ähnliche Zusammenhänge sind außerdem vermutlich auch auf viele andere generalistischen Beutegreifer anwendbar.

Tawny owl prey remains indicate differences in the dynamics of coastal and inland vole populations in southern Finland

Some studies suggest that mild winters decrease overwinter survival of small mammals or coincide with decreased cyclicity in vole numbers, whereas other studies suggest non-significant or positive relationships between mild winter conditions and vole population dynamics. We expect for the number of voles to be higher in the rich and low-lying habitats of the coastal areas than in the less fertile areas inland. We assume that this geographical difference in vole abundances is diminished by mild winters especially in low-lying habitats. We examine these relationships by generalized linear mixed models using prey remains of breeding tawny owls Strix aluco as a proxy for the abundance of voles. The higher number of small voles in the coastal area than in the inland area suggest that vole populations were denser in the coastal area. Vole populations of both areas were affected by winter weather conditions particularly in March, but these relationships differed between areas. The mild ends of winter with frequent fluctuations of the ambient temperature around the freezing point (“frost seesaw”) constrained significantly the coastal vole populations, while deep snow cover, in general after hard winters, was followed by significantly lowered number of voles only in the inland populations. Our results suggest that coastal vole populations are more vulnerable to mild winters than inland ones. We also show that tawny owl prey remains can be used in a meaningful way to study vole population dynamics.