Population biology of Avena

Genomic insights into local adaptation in the Asiatic toad Bufo gargarizans, and its genomic offset to climate warming

Genomic signatures of local adaptation have been identified in many species but remain sparsely studied in amphibians. Here, we explored genome-wide divergence within the Asiatic toad, Bufo gargarizans, to study local adaptation and genomic offset (i.e., the mismatch between current and future genotype-environment relationships) under climate warming scenarios. We obtained high-quality SNP data for 94 Asiatic toads from 21 populations in China to study spatial patterns of genomic variation, local adaptation, and genomic offset to warming in this wide-ranging species. Population structure and genetic diversity analysis based on high-quality SNPs revealed three clusters of B. gargarizans in the western, central-eastern, and northeastern portions of the species' range in China. Populations generally dispersed along two migration routes, one from the west to the central-east and one from the central-east to the northeast. Both genetic diversity and pairwise F ST were climatically correlated, and pairwise F ST was also correlated with geographic distance. Spatial genomic patterns in B. gargarizans were determined by the local environment and geographic distance. Global warming will increase the extirpation risk of B. gargarizans.

ESTIMATION OF GENE FLOW AND GENETIC NEIGHBORHOOD SIZE BY INDIRECT METHODS IN A SELFING ANNUAL, TRITICUM DICOCCOIDES

Rates of gene flow and neighborhood area were investigated in the selfing annual, Triticum dicoccoides. The collection of seed material was made using a spatial hierarchical sampling design in which four collection sites were 5-7 m apart, four were 15-17 m apart, and four were 100-120 m apart. Between 25 and 30 plants were scored from each site (mean sample size = 28.7). Two procedures for indirect estimation of gene flow were used on gene-frequency data from 13 polymorphic loci. The estimates of Nm using Wright's (1943a, 1943b) estimation procedure were 1.265, 0.212, and 0.357, for the closest, intermediate, and most distant distance classes, respectively. The estimates of Nm using Slatkin's (1985) private-allele procedure were 4.675 (subsample ranges: 1.544-4.675), 0.110 (subsample ranges: 0.069-0.153), and 0.670 (subsample ranges: 0.129-0.256). The results indicate a general agreement between the two procedures. Both indicate a sharp decrease in gene flow beyond the first distance class (5-7 m). The large gene-flow values and the large variation within the 5-7-m distance class are taken as evidence that a genetic neighborhood for this species may cover an area defined by a 5-m radius. The results also indicate that gene flow between populations separated by only 10 or more meters may be quite limited.

THE EFFECT OF DISTANCE FROM THE PARENTAL SITE ON OFFSPRING PERFORMANCE AND INBREEDING DEPRESSION IN IMPATIENS CAPENSIS: A TEST OF THE LOCAL ADAPTATION HYPOTHESIS

If microgeographic variation in selection within a natural plant population has resulted in local adaptation, then offspring fitness should decline with distance from the parental site. If outcrossed progeny are less well-adapted to the parental environment than inbred progeny, but perform better in environments different from that of the parent, then the fitness of inbred progeny relative to outcrossed progeny should decrease with dispersal distance from the parent. To test these predictions, we collected seedlings at 10-m intervals from a 40 times 40-m permanent grid in a natural population of Impatiens capensis, grew them in a greenhouse, and crossed them to produce outcrossed chasmogamous seeds. Seedlings from outcrossed chasmogamous and self-fertilized cleistogamous seeds were planted back into the source population in the original site of their maternal parents and in arcs 3 and 12 m from the parental location and censused weekly for survival and reproduction. The fitness of inbred offspring declined significantly and the magnitude of observed inbreeding depression increased with distance from the parental site, supporting the local adaptation hypothesis.

Temporal changes in pollen flow and neighbourhood structure in a population of Saxifraga hirculus L

The population are of flowering shoots of the perennial herb, Saxifraga hirculus, reaches a max. of 134 m² and an overall density of flowers/m² of 11.4. The flower is mainly visited by a syrphid sp., Eurimyia lineata, and to a lesser extent by another syrphid Neoscia tenur, a moth, Zygaena trifolii, and a fungus gnat, Asindulum nigrum. The distribution of the interfloral flight distance is leptokurtic. The mean flight distance of the visitors is 101 cm. 10% of the flights are much longer (2-8 m: cross-flower patch, and about 20 m: cross-population flights). If they are not included, the mean of flights (<1.7 m) becomes 28 cm. These flights become shorter with increasing flower density. The visitors do not have a nearest-neighbour foraging pattern. They visit on average the 8th nearest neighbour. The distribution of flight directions is uniform. Seed dispersal distances have a leptokurtic distribution and a mean dispersal distance of 13 cm. The ecological neighbourhood area is 66.4 m² and 64.9 m² assuming normality and allowing for leptokurtosis. Z. trifolii with its large proportion of long flights increases the size of the neighbourhood area considerably. The mean flight distance (<1.7 m) is correlated with neighbourhood area. The evolutionary impact of moths and butterflies to plant population structure is stressed.