Dynamic gastropods: stable shell polymorphism despite gene flow in the land snail Arianta arbustorum

Based on a sequence fragment of mtDNA we analysed the genetic differentiation of the land snail Arianta arbustorum in the Alpine massif Gesäuse, where four morphotypes occur in close vicinity. We aimed at understanding actual and historical evolutionary processes among the morphotypes. With 135 haplotypes diverging up to 12.5%, genetic diversity was extremely high. Phylogenetic analyses indicated that A. arbustorum has colonized the Gesäuse several times in consecutive waves and that introgression of neutral markers across morphotypes and selection on shell shape have played an important role. Gene flow was more likely between locally close, different morphotypes than among distant populations of the same morphotype again indicating that cohesion of morphotypes was mainly due to selection. The actual distribution of morphotypes and haplotypes as well as the high genetic diversity also suggested that the area provided refugia during the Pleistocene glaciations.     

Spatial genetic structuring in a vagile species, the European wood mouse

We examined the genetic structure of natural populations of the European wood mouse Apodemus sylvaticus at the microgeographic (<3 km) and macrogeographic (>30 km) scales. Ecological and behavioural studies indicate that this species exhibits considerable dispersal relative to its home-range size. Thus, there is potential for high gene flow over larger geographic areas. As levels of population genetic structure are related to gene flow, we hypothesized that population genetic structuring at the microgeographic level should be negligible, increasing only with geographic distance. To test this, four sites were sampled within a microgeographic scale with two additional samples at the macrogeographic level. Individuals ( n =415) were screened and analysed for seven polymorphic microsatellite loci. Contrary to our hypothesis, significant levels of population structuring were detected at both scales. Comparing genetic differentiation with geographic distance suggests increasing genetic isolation with distance. However, this distance effect was non-significant being confounded by surprisingly high levels of differentiation among microgeographic samples. We attribute this pattern of genetic differentiation to the effect of habitat fragmentation, splitting large populations into components with small effective population sizes resulting in enhanced genetic drift. Our results indicate that it is incorrect to assume genetic homogeneity among populations even where there is no evidence of physical barriers and dispersal can occur freely. In the case of A. sylvaticus , it is not clear whether dispersal does not occur across habitat barriers or behavioural dispersal occurs without consequent gene flow.     

Spatial distribution of the basidiocarps of aphyllophoraceous fungi in a tropical rainforest on Borneo Island, Malaysia

The spatial distribution of basidiocarps provides much information on the dispersal abilities, habitat preferences, and inter- and intraspecific interactions of aphyllophoraceous fungi. To reveal the spatial distribution and resource utilization patterns of aphyllophoraceous fungi in Malaysia, we conducted field observations in a primary forest in 2006 and analyzed the relationships between the abundance of eight dominant fungal species and various environmental factors. The topographical characteristics were significantly patchily distributed at the 100-m scale, whereas woody debris and most fungal species were distributed randomly. Although the dominant fungal species differed among the decay classes and diameters of the woody debris, the abundance of a few dominant species was significantly correlated with environmental factors. Although the latter factors might affect the spatial distribution of these fungi, the effects appear to be so small that they would not create an aggregated distribution at a few 100-m scales.     

Families in space: relatedness in the Barents Sea population of polar bears (Ursus maritimus)

The kin structure and dispersal pattern of polar bears ( Ursus maritimus ) of the Barents Sea was investigated during the spring mating season using two complementary approaches. First, individual genotypes based on the analyses of 27 microsatellite loci of 583 polar bears were related to field information gathered from 1146 bears in order to reconstruct the animals' pedigrees and to infer geographical distances between adult bears of different relatedness categories. According to the data, the median natal dispersal distance of the male animals was 52 km while that of the females was 93 km. Second, the relatedness of pairs of adult bears was estimated and correlated to the geographical distance between them. The female dyads had a much stronger kin structure than the male dyads. The 'pedigree approach' revealed a male kin structure which could not be detected using the 'relatedness approach'. This suggests that, on a broader scale, effective dispersal is slightly male biased. Despite fidelity to natal areas, male-mediated gene flow may nevertheless prevent genetic differentiation. Males might occasionally shift their home range which could therefore lead to a male-biased breeding dispersal. Our results showed that a nonterritorial species such as the polar bear that has a high dispersal potential, lives in a highly unstable environment and migrates seasonally is still able to exhibit a distinct kin structure during the mating season.     

Genetic relatedness in groups of the humbug damselfish Dascyllus aruanus: small, similar-sized individuals may be close kin

Kin selection plays an important role in the evolution of social behaviour in terrestrial systems. The extent to which kin selection influences the evolution of social behaviour in marine systems is largely unexplored. Generally, it is considered that kin selection is irrelevant in marine systems, because it is assumed that the dispersing larval phase of marine organisms will break up kin associations. Here, we challenge this assumption and investigate the opportunity for kin selection in a coral reef fish: the humbug damselfish Dascyllus aruanus . This fish lives in groups composed of a large male and a number of smaller females and nonbreeders. We use 10 polymorphic microsatellite loci to assess the relatedness of 265 individuals from 35 groups. The mean coefficient of relatedness among group members is 0.01 ± 0.04, suggesting that individuals are not associated with close relatives. However, the distribution of pairwise relatedness of individuals within groups has an overabundance of positive values, and indicates that there might be 35 pairs of close relatives within groups. Further analyses reveal that close relatives likely are similar in size and small in size, suggesting that they might have recruited together. We conclude that it is possible for kin selection to operate in D. aruanus , but kin recognition will be a prerequisite for such selection. This study reveals that individuals can be associated with close relatives, and there is a hidden potential for kin selection, during certain parts of the life cycle of coral reef fishes.     

Restricted dispersal in a continuously distributed marine species: common bottlenose dolphins Tursiops truncatus in coastal waters of the western North Atlantic

The marine environment provides an opportunity to examine population structure in species with high dispersal capabilities and often no obvious barriers to genetic exchange. In coastal waters of the western North Atlantic, common bottlenose dolphins, Tursiops truncatus, are a highly mobile species with a continuous distribution from New York to Florida. We examine if the highly mobile nature coupled with no obvious geographic barriers to movement in this region result in a large panmictic population. Mitochondrial control region sequences and 18 microsatellite loci indicate dolphins are partitioning the habitat both latitudinally and longitudinally. A minimum of five genetically differentiated populations were identified among 404 samples collected in the range of New Jersey to northern Florida using both genetic marker types, some inhabiting nearshore coastal waters and others utilizing inshore estuarine waters. The genetic results reject the hypothesis of a single stock of coastal bottlenose dolphins put forth after the 1987–1988 epizootic that caused a large‐scale die‐off of dolphins and suggest instead the disease vector was transferred from one population to the next as a result of seasonal migratory movements of some populations. These coastal Atlantic populations also differ significantly from bottlenose dolphin samples collected in coastal waters of the northern Gulf of Mexico, implying a long‐term barrier to movement between the two basins.     

Fine-scale geographical structure of genetic diversity in inland wild beet populations

Introgression arising from crop-to-wild gene flow provides novel sources of genetic variation in plant species complexes. Hybridization within the Beta vulgaris species complex is of immediate concern; crop lineages ( B .  vulgaris ssp. vulgaris ) hybridize easily with their wild relatives ( B .  vulgaris ssp. maritima ) thereby threatening wild beet gene diversity with genetic swamping. Hybridization 'hotspots' occur in European seed production areas because inland ruderal wild beets occur and reproduce in sympatry with cultivated beets. We studied gene flow occurring between seed-producing cultivars and ruderal wild B .  vulgaris in southwestern France to determine whether feral beets, arising from unharvested cultivated seed, represent an opportunity for crop-to-wild gene flow. We surveyed 42 inland ruderal beet populations located near seed production fields for nucleo-cytoplasmic variation and used a cytoplasmic marker diagnostic of cultivated lines. Occurrence of cultivated-type cytoplasm within ruderal populations clearly reflected events of crop seed escape. However, we found no genetic signatures of nuclear cultivated gene introgression, which suggests past introgression of cultivated cytoplasm into a wild nuclear background through seed escape rather than recent direct pollen flow. Overall, patterns of genetic structure suggested that inland ruderal wild beet populations act as a metapopulation, with founding events involving a few sib groups, followed by low rates of seed or pollen gene flow after populations are established. Altogether, our results indicate that a long-lived seed bank plays a key role in maintaining cultivated-type cytoplasm in the wild and highlight the need for careful management of seed production areas where wild and cultivated relatives co-occur.     

Genetic relatedness in wintering groups of house sparrows (Passer domesticus)

Social behaviour of group-living animals is often influenced by the relatedness of individuals, thus understanding the genetic structure of groups is important for the interpretation of costs and benefits of social interactions. In this study, we investigated genetic relatedness in feeding aggregations of free-living house sparrows ( Passer domesticus ) during the nonbreeding season. This species is a frequent model system for studies of social behaviour (e.g. aggression, social foraging), but we lack adequate information on the kin structure of sparrow flocks. During two winters, we ringed and observed sparrows at feeding stations, and used resightings to identify stable flock-members and to calculate association indices between birds. We genotyped the birds using seven highly polymorphic microsatellite loci, and estimated pairwise relatedness coefficients and relatedness categories (close kin vs. unrelated) by maximum likelihood method. We found that most birds were unrelated to each other in the flocks (mean ± SE relatedness coefficient: 0.06 ± 0.002), although most individuals had at least a few close relatives in their home flock (14.3 ± 0.6% of flock-mates). Pairwise association between individuals was not significantly related to their genetic relatedness. Furthermore, there was no difference between within-flock vs. between-flock relatedness, and birds had similar proportions of close kin within and outside their home flock. Finally, relatedness among members of different flocks was unrelated to the distance between their flocks. Thus, sparrow flocks were not characterized by association of relatives, nevertheless the presence of some close kin may provide opportunity for kin-biased behaviours to evolve.     

Comparative evolution of flower and fruit morphology

Angiosperm diversification has resulted in a vast array of plant morphologies. Only recently has it been appreciated that diversification might have proceeded quite differently for the two key diagnostic structures of this clade, flowers and fruits. These structures are hypothesized to have experienced different selective pressures via their interactions with animals in dispersal mutualisms, resulting in a greater amount of morphological diversification in animal-pollinated flowers than in animal-dispersed fruits. I tested this idea using size and colour traits for the flowers and fruits of 472 species occurring in three floras (St John, Hawaii and the Great Plains). Phylogenetically controlled analyses of nearest-neighbour distances in multidimensional trait space matched the predicted pattern: in each of the three floras, flowers were more divergent from one another than were fruits. In addition, the spacing of species clusters differed for flowers versus fruits in the flora of St John, with clusters in flower space more divergent than those in fruit space. The results are consistent with the idea that a major driver of angiosperm diversification has been stronger selection for divergent floral morphology than for divergent fruit morphology, although genetic, physiological and ecological constraints may also play a role.     

A test of the social cohesion hypothesis: interactive female marmots remain at home

Individuals frequently leave home before reaching reproductive age, but the proximate causes of natal dispersal remain relatively unknown. The social cohesion hypothesis predicts that individuals who engage in more (affiliative) interactions are less likely to disperse. Despite the intuitive nature of this hypothesis, support is both limited and equivocal. We used formal social network analyses to quantify precisely both direct and indirect measures of social cohesion in yellow-bellied marmots. Because approximately 50 per cent of female yearlings disperse, we expected that social relationships and network measures of cohesion would predict dispersal. By contrast, because most male yearlings disperse, we expected that social relationships and cohesion would play a less important role. We found that female yearlings that interacted with more individuals, and those that were more socially embedded in their groups, were less likely to disperse. For males, social interactions were relatively unimportant determinants of dispersal. This is the first strong support for the social cohesion hypothesis and suggests that the specific nature of social relationships, not simply the number of affiliative relationships, may influence the propensity to disperse.