Heredity

Routley, Matthew B; Mavraganis, Katherine; Eckert, Christopher G

doi: 10.1038/sj.hdy.6885220pmid: 10383672

In self-compatible plants, small populations may experience reduced outcrossing owing to decreased pollinator visitation and mate availability. We examined the relation between outcrossing and population size in eastern Ontario populations of Aquilegia canadensis. Experimental pollinations showed that the species is highly self-compatible, and can achieve full seed-set in the absence of pollinators via automatic self-pollination. We estimated levels of outcrossing (t) and parental inbreeding coefficients (F) from allozyme variation in naturally pollinated seed families for 10 populations ranging in size from 32 to 750 reproductive individuals. The proportion of seeds produced through outcrossing was generally low (mean = 0.29 ± 0.02 SE) and varied widely among populations (range = 0.00–0.83). Accordingly, estimates of F were large (mean = 0.26 ± 0.05) and significantly greater than zero in seven populations. As expected, four small populations (N < 40) outcrossed less (0.17 ± 0.03) than six large populations (N > 90; 0.38 ± 0.03). However, parental plants were not significantly more inbred in small than large populations (P= 0.18). There was no difference in the germination of seeds from hand self- and cross-pollinations. However, population genetic estimates of inbreeding depression for survival expressed from seed to reproductive maturity were very high (mean δ = 1 − relative fitness of selfed seed = 0.88 ± 0.14). The combination of self-compatibility and automatic self-pollination makes the mating system of A. canadensis sensitive to variation in ecological factors that affect the likelihood of cross-pollination.

Surridge, Alison K; Bell, Diana J; Ibrahim, Kamal M; Hewitt, Godfrey M

doi: 10.1038/sj.hdy.6885110pmid: 10383667

The European wild rabbit (Oryctolagus cuniculus) is an introduced species in Britain, and populations have been profoundly influenced by both man and disease. In stable environmental conditions, distinct social behaviour is observed, and this social structure leads to significant genetic structuring at the intrapopulation level. In this study, European wild rabbits were sampled from 17 sites across the East Anglian region of Britain and genotyped with nine microsatellite loci. Genotypical proportions deviated significantly from Hardy–Weinberg equilibrium, reflecting a degree of population subdivision and non-random mating. Several estimates of measures of population genetic structure revealed that populations are genetically distinct and have small effective population sizes. These distinctive properties are seen to be the combined effects of the social structure and random drift acting on bottlenecked populations after myxomatosis. It is concluded that the genetic structure seen in rabbit populations today is unlikely to reflect historical structuring present before myxomatosis, but that it results from recent events.

Kvist, Laura; Ruokonen, Minna; Lumme, Jaakko; Orell, Markku

doi: 10.1038/sj.hdy.6885130pmid: 10383669

The colonization history and present-day population structure of the European subspecies of the great tit Parus major major were studied using mitochondrial control region sequences. One major haplotype was found in all but one of the eight sampled populations from Spain to northern Finland. The other haplotypes differed from the common one by just a few substitutions; the overall nucleotide diversity was 0.00187 and haplotype diversity 0.8633. No population structuring was detected. The mismatch distribution followed the expected distribution of an expanding population. The estimated time to the most recent common ancestor coincides with the last glacial period. The results suggest that P. m. major survived the last glacial period in a single isolated refuge probably by the Mediterranean Sea. This was followed by rapid colonization of the European continent and population growth. The most recent range expansion northwards is still occurring. Gene flow between the sampled populations is extensive. It is aided by juvenile dispersal, long-distance movements of juvenile flocks and partial migration in the northern parts of the great tit’s range.

Chapuisat, Michel; Keller, Laurent

doi: 10.1038/sj.hdy.6885340pmid: 10383666

Sex allocation data in eusocial Hymenoptera (ants, bees and wasps) provide an excellent opportunity to assess the effectiveness of kin selection, because queens and workers differ in their relatedness to females and males. The first studies on sex allocation in eusocial Hymenoptera compared population sex investment ratios across species. Female-biased investment in monogyne (= with single-queen colonies) populations of ants suggested that workers manipulate sex allocation according to their higher relatedness to females than males (relatedness asymmetry). However, several factors may confound these comparisons across species. First, variation in relatedness asymmetry is typically associated with major changes in breeding system and life history that may also affect sex allocation. Secondly, the relative cost of females and males is difficult to estimate across sexually dimorphic taxa, such as ants. Thirdly, each species in the comparison may not represent an independent data point, because of phylogenetic relationships among species. Recently, stronger evidence that workers control sex allocation has been provided by intraspecific studies of sex ratio variation across colonies. In several species of eusocial Hymenoptera, colonies with high relatedness asymmetry produced mostly females, in contrast to colonies with low relatedness asymmetry which produced mostly males. Additional signs of worker control were found by investigating proximate mechanisms of sex ratio manipulation in ants and wasps. However, worker control is not always effective, and further manipulative experiments will be needed to disentangle the multiple evolutionary factors and processes affecting sex allocation in eusocial Hymenoptera.

Nichols, Richard A

doi: 10.1038/sj.hdy.6885562pmid: N/A

Utelli, Anna-Barbara; Roy, Barbara A; Baltisberger, Matthias

doi: 10.1038/sj.hdy.6885070pmid: 10383678

The Aconitum lycoctonum complex is a widespread yellow-flowered group of species found in central and southern Europe. Because of extreme morphological variability, the systematics of this group is confusing, and hybridizations among taxa are often hypothesized. To determine whether hybridization, realized mating system within populations or colonization from different Pleistocene refugia might explain some of the morphological variation, the genetic structure of 19 populations from central and southern Europe was studied using starch gel electrophoresis and 10 enzyme loci, of which eight were polymorphic. A pattern typical of an outcrossing species was expected because A. lycoctonum flowers are adapted to pollination by long-tongued bumblebees. However, heterozygosity was very low (between 0.031 and 0.150), which is atypical of either widespread or outcrossing species. The inbreeding coefficient, F IS, also suggested inbreeding in more than half the populations. Analysis of molecular variance showed that 31% of the genetic variation is found among populations, again suggesting inbreeding. A neighbour-joining tree based on Reynolds’s genetic distance showed a clear separation between the central/eastern European populations and the samples from the Iberian peninsula and Alpes Maritimes. These data are consistent with the hypothesized refugia and the phylogeographical histories of several European forest trees. The genetic identity of all populations was very high, suggesting that all investigated populations belong to the same species despite high morphological variability. Hybridization was not supported by the data.

Kephart, Susan R; Brown, Erica; Hall, Jeremy

doi: 10.1038/sj.hdy.6885250pmid: 10383675

Recent studies have found moderate to high levels of selfing in plants despite high inbreeding depression. Because both factors influence the evolution and persistence of rare plants, we conducted glasshouse and field studies of pollination and inbreeding in Silene douglasii var. oraria, a perennial tetraploid endemic to coastal prairies. We detected: (i) variation in reproduction or inbreeding depression among life stages, years and maternal families; (ii) partial selfing yet higher relative fitness in outcrossed than selfed progeny; (iii) differing values of selfing and inbreeding depression using population means vs. matched maternal families. Fruit and seed production varied significantly with pollination treatment and year in flowers manipulated in situ during three seasons of growth. Hand-pollinations providing pollen in excess of ovule production in 1996 yielded more seeds than marked, open-pollinated flowers, implying pollen limitation of seed production. However, among-year differences in reproductive success after open-pollination (i.e. values equivalent to autogamy, selfing or outcrossing) suggest that pollination levels also vary temporally. In pollinations matched by maternal family, selfing yielded significantly fewer seeds than outcrossing. Fitness differences between inbred and outbred progeny were significant (P < 0.05) for seed production, percentage germination, and biomass or fecundity, but not for survival. Maternal family data gave selfing rates intermediate between obligate outcrossers and predominant selfers (S = 0.34–0.51), but population-wide means gave unusually high values (S = 1.1–1.6). Cumulative inbreeding depression was 76% for maternal families, and 70–85% using population means; in all cases, inbreeding depression values were high in early and late life stages, and lowest for survival. Thus far, reproductive assurance offers the most cogent explanation for the coexistence of moderate selfing and high inbreeding depression in this strongly protandrous Silene once thought to be highly outcrossing. This possibility merits further study in other rare plants with mixed-mating systems, where inbreeding depression and pollinator scarcity may both compromise population persistence and raise the threshold below which selfing is favoured by evolution.

Doi, Asako; Suzuki, Hiromi; Matsuura, Etsuko T

doi: 10.1038/sj.hdy.6885080pmid: 10383676

In artificially induced mitochondrial DNA (mtDNA) heteroplasmy in Drosophila, the effects of chromosome substitution on temperature-dependent selection in mtDNA transmission were investigated. Using two strains of D. melanogaster, bw;e 11 and y;bw;st, which showed a different temperature dependency in mtDNA transmission, chromosomes were substituted reciprocally, and mtDNA of D. mauritiana was introduced into each newly constructed strain. For each heteroplasmy, the transmission of mtDNA was examined at 25°C and 19°C. When either the second or the third chromosome of the y;bw;st strain was substituted with that of the bw;e 11 strain, the temperature-dependent selection in mtDNA transmission was altered. The selection was not changed when either the second or the third chromosome of the bw;e 11 strain was substituted with that of the y;bw;st strain, or even when both the second and the third chromosomes of the bw;e 11 strain were substituted with those of the y;bw;st strain. These results suggest that the temperature-dependent selection in mtDNA transmission is co-operatively regulated by gene products that are encoded by the X, second and third chromosomes.

Triantafyllidis, A; Abatzopoulos, T J; Economidis, P S

doi: 10.1038/sj.hdy.6885140pmid: 10383670

Mitochondrial DNA diversity of seven Silurus glanis populations (six from Greece and one from the Danube Delta) and three populations of the endemic Greek Silurus aristotelis was investigated. RFLP analysis of four regions of mitochondrial DNA (cytochrome b, D-loop, ND-5/6) amplified by PCR was used. Ten and nine haplotypes were found in S. glanis and S. aristotelis, respectively. No haplotype was shared between the two species. Significant geographical substructuring was observed in the distribution of haplotypes, with most populations possessing private haplotypes. These haplotypes can serve as genetic ‘tags’ and therefore warrant protection. Haplotype diversity was very low for all Greek S. glanis populations, possibly because the small size and large annual fluctuations of Greek inland waters do not support large fish populations. Nucleotide divergence was in the range of 0.00–0.52% among S. glanis populations, and 0.00–0.11% among S. aristotelis populations. Historical factors such as glaciations could account for these low values. The value of 6.75% sequence divergence of the two species refutes the classification of the two species in different genera, as proposed by some authors. This study constitutes the first attempt, based on mitochondrial molecular data, to address the complicated evolutionary history of the two species which belong to the widely distributed and economically important Siluridae family.

Miedzybrodzka, Zosia

doi: 10.1038/sj.hdy.6885563pmid: N/A