Jouni Aspi

Genetic structure and gene flow in a metapopulation of an endangered plant species, Silene tatarica

We investigated the distribution of genetic variation within and between seven subpopulations in a riparian population of Silene tatarica in northern Finland by using amplified fragment length polymorphism (AFLP) markers. A Bayesian approach‐based clustering program indicated that the marker data contained not only one panmictic population, but consisted of seven clusters, and that each original sample site seems to consist of a distinct subpopulation. A coalescent‐based simulation approach shows recurrent gene flow between subpopulations. Relative high FST values indicated a clear subpopulation differentiation. However, amova analysis and UPGMA‐dendrogram did not suggest any hierarchical regional structuring among the subpopulations. There was no correlation between geographical and genetic distances among the subpopulations, nor any correlation between the subpopulation census size and amount of genetic variation. Estimates of gene flow suggested a low level of gene flow between the subpopulations, and the assignment tests proposed a few long‐distance bidirectional dispersal events between the subpopulations. No apparent difference was found in within‐subpopulation genetic diversity among upper, middle and lower regions along the river. Relative high amounts of linkage disequilibrium at subpopulation level indicated recent population bottlenecks or admixture, and at metapopulation levels a high subpopulation turnover rate. The overall pattern of genetic variation within and between subpopulations also suggested a ‘classical’ metapopulation structure of the species suggested by the ecological surveys.

Male courtship song frequency as an indicator of male genetic quality in an insect species, Drosophila montana

Most theoretical models on evolution of male secondary sexual characters and female preferences for these characters suggest that the male characters evolve in response to female preferences that may themselves evolve in response to direct or indirect benefits of choice. InDrosophila montana (a species of theD. virilis group), females use male song in their mate choice, preferring males that produce songs with short sound pulses and a high carrier frequency. We demonstrate here that the females get indirect benefits from their choice: in our data the frequency of the male song correlated with the survival rate of the males progeny from egg to adulthood (indirect benefit for the female), but not with the fecundity of his mating partner (no direct benefit for the female). Male wing centroid asymmetry did not correlate with male wing song characters, nor with female egg production nor the fitness of her progeny, suggesting that fluctuating asymmetry in male wings does not play a major role in sexual signalling. The fact that the male song gives the female information on the males condition/genetic quality inD. montana suggests that in this species the evolution of female preferences for male song characters could have evolved through condition–dependent viability selection presented in some ‘good genes’ models.

Genetic diversity, population structure, effective population size and demographic history of the Finnish wolf population

The Finnish wolf population (Canis lupus) was sampled during three different periods (1996–1998, 1999–2001 and 2002–2004), and 118 individuals were genotyped with 10 microsatellite markers. Large genetic variation was found in the population despite a recent demographic bottleneck. No spatial population subdivision was found even though a significant negative relationship between genetic relatedness and geographic distance suggested isolation by distance. Very few individuals did not belong to the local wolf population as determined by assignment analyses, suggesting a low level of immigration in the population. We used the temporal approach and several statistical methods to estimate the variance effective size of the population. All methods gave similar estimates of effective population size, approximately 40 wolves. These estimates were slightly larger than the estimated census size of breeding individuals. A Bayesian model based on Markov chain Monte Carlo simulations indicated strong evidence for a long‐term population decline. These results suggest that the contemporary wolf population size is roughly 8% of its historical size, and that the population decline dates back to late 19th century or early 20th century. Despite an increase of over 50% in the census size of the population during the whole study period, there was only weak evidence that the effective population size during the last period was higher than during the first. This may be caused by increased inbreeding, diminished dispersal within the population, and decreased immigration to the population during the last study period.

Male Mating Success and Survival in the Field with Respect to Size and Courtship Song Characters in Drosophila littoralis and D. montana (Diptera: Drosophilidae)

We investigated the importance of male song and morphological characters to the male mating success in a two-year field study in natural populations ofD. littoralis andD. montana. We compared the properties of mating flies with those of a random male sample taken at the same time and place. InD. littoralis the males size had no effect on his mating success, while inD. montana small males had a mating advantage in the field during the first study year. Females preferred males with short sound pulses in both species. We also examined the relationship between male morphological and song characters and viability by collecting male flies in late summer and comparing the means of male characters to those of overwintered flies the next spring. InD. littoralis male size had no effect on overwinter survival. InD. montana large flies survived better than small flies. In both species the shifts in song characters during the winter dormancy were opposite to those caused by sexual selection. Our results, accordingly, imply a possible balance between the forces of sexual and natural selection, which act in opposing directions on attractive male traits.

Effects of winter grazing by reindeer on vegetation

The structure of the flora on Calluna-Cladina heaths was studied in northwestern Finnish Lapland in relation to grazing pressure of semi-domestic reindeer. The total biomass of 11 sample areas varied from 6 ? 1 g m2 to 524 ? 12 g m2. The highest species richness was found in moderately grazed areas. The species diversity (inverse of Simpson) was rather similar in areas under very hard and moderate grazing pressure, declining for ungrazed areas. The relative abundance of reindeer lichens increased with decreasing grazing pressure and Cladonia stellaris inhibited the growth of dwarf shrubs. C. stellaris, the dominant species of climax communities, cannot withstand hard grazing pressure; it is more effectively grazed than the other Cladina species because of its compact structure. Only small-bodied moss and horn lichen species, which are also resistant to reindeer trampling, can survive under the heaviest grazing pressure. They have apparently effective dispersal mechanisms and are thus capable of occupying recently disturbed patches.

Inbreeding and outbreeding depression in male courtship song characters in Drosophila montana

In Drosophila montana, male courtship song frequency is closely associated with male courtship success and offspring survival. Other pulse characters (pulse length and cycle number) may also affect female mate choice, whereas pulse train characters (interpulse interval, pulse number and pulse train length) are not associated with these male fitness components. Inbreeding depression in these song characters was investigated by comparing the songs of inbred and outbred fly strains. The average change in most song characters as a result of inbreeding was only a few percent. However, in male song frequency the average inbreeding depression was about 14%, suggesting that this song character is associated with fitness. Outbreeding depression and the genetic architecture of song characters were investigated with interpopulation crosses and joint scaling tests. For pulse train characters the generation means show only evidence of additivity, and the existence of dominance or epistasis in these characters was strongly rejected in each case. In pulse characters the means of the F1 males were lower than the average of the parental generations. In pulse length and cycle number this difference was attributable to dominance alone. In frequency there was outbreeding depression also in the F2 generation, suggesting a break-up of favourable epistatic gene combinations. The outbreeding depression in this character in the F1 generation was caused by dominance, and in the F2 also by duplicate epistasis between dominant decreasers. The possible role of outbreeding depression and epistasis in speciation is discussed.

DISPERSAL IN AN EXPANDING WOLF POPULATION IN FINLAND

Abstract Dispersal influences distribution and genetic structure of animal populations. Dispersal in expanding wolf (Canis lupus) populations is not well documented, especially in Europe, where no studies of dispersal based on marked wolves are available. We studied the dispersal of wolves in Finland, where a peripheral wolf population (160–180 animals) increased and expanded during 1998–2004. We equipped 60 wolves from 8 neighboring wolf pack territories with radio or GPS transmitters in east-central Finland during 1998–2004, and at least 30 wolves (50%) dispersed from the home territory. Additional information was collected by detecting the natal pack of captured wolves with multilocus microsatellite genotyping and paternity analysis. In the study area, the directions formed a sun-ray pattern. Wolves usually departed their home territory as pups and yearlings, and in unimodal seasonal fashion. The dispersal distance (median 98.5, range 35–445 km) did not differ by sex (P = 0.342). Long-distance travelers (>200 km) were found only among wolves that departed at the age of 10–12 months. Survival was linked to the direction of dispersal. All marked wolves that dispersed to reindeer management areas in the north were shot before being able to reproduce, whereas elsewhere, the majority of dispersers (10 of 16) reproduced.

Courtship in Drosophila montana: the effects of male auditory signals on the behaviour of flies

Abstract In Drosophila montana (a species of the D. virilis group) the sounds produced by the courting male are a prerequisite for copulation. The mating behaviour of four experimental groups was recorded. Two groups consisted of single pairs of normal flies with successful and unsuccessful courtship, respectively. The third group consisted of single pairs of normal males and deaf females and the fourth group of single pairs of mute males and normal females. In successful courtships (i.e. those ending in copulation) touching and licking by the male led to female standing. Female standing led to male wing vibrating, male wing vibrating to female wing lifting, and female wing lifting to copulation. In unsuccessful courtships, the males did not vibrate their wings in response to female standing. In the groups lacking male auditory signals (deaf females or mute males) the females hummed their wings in response to male licking and wing vibrating. Although the males responded to wing humming by more licking and by producing more sounds, the courtships did not proceed to copulation. It is concluded that the willingness of the female to mate with a conspecific male depends on the detection of sound at the appropriate time in the courtship sequence as a response to female behaviour.

Laboratory and natural heritabilities of male courtship song characters in Drosophila montana and D. littoralis

We estimated heritabilities for several male courtship song characters in two Drosophila species using father-son regression under conditions where both fathers and sons had been raised in the laboratory. In D. montana the heritabilities of song characters were rather high (−0.23 to 0.80) and in most cases significant. In D. littoralis the heritabilities of song characters were generally lower (−0.33 to 0.18), and none of them was significantly larger than zero. We also estimated heritabilities regressing characters of wild-caught fathers with those of their laboratory reared sons, and used the method employed by Riska et al. to estimate the lower bound of heritabilities in nature. In D. montana most and in D. littoralis all of the across-environment heritabilities were non-significant (−0.15 to 0.43 and −0.04 to 0.15, respectively), and in some cases the across-environment heritabilities were significantly lower than the heritabilities measured under laboratory conditions. The low across-environment heritabilities appeared to be due to larger phenotypic variability of song characters in the field and in some cases also due to genotype-environment interactions.

Rise and fall of a wolf population: genetic diversity and structure during recovery, rapid expansion and drastic decline

The grey wolves (Canis lupus) of Finland have had a varied history, with a period of rapid population expansion after the mid‐1990s followed by a decline with a current census size of about 140 wolves. Here, we investigate the impact of unstable population size and connectivity on genetic diversity and structure in a long‐term genetic study of 298 Finnish wolves born in 1995–2009 and genotyped for 17 microsatellite loci. During the initial recovery and prior to population expansion, genetic diversity was high (1995–1997: LD‐Ne = 67.2; Ho = 0.749; He = 0.709) despite a small census size and low number of breeders (Nc < 100; Nb < 10) likely reflecting the status of the Russian source population. Surprisingly, observed heterozygosity decreased significantly during the study period (t = −2.643, P = 0.021) despite population expansion, likely a result of an increase in inbreeding (FIS = 0.108 in 2007–2009) owing to a low degree of connectivity with adjacent Russian wolf population (m = 0.016–0.090; FST = 0.086, P < 0.001) and population crash after 2006. However, population growth had a temporary positive impact on Ne and number of family lines. This study shows that even strong population growth alone might not be adequate to retain genetic diversity, especially when accompanied with low amount of subsequent gene flow and population decline.