SEX-RATIO BIAS WITH ASYMMETRIC EXCHANGE OF POLLEN BETWEEN DEMES

In a patch of hermaphroditic plants, with a low level of pollen migration between patches, a prevailing wind creates a gradient, within the patch, in the strength of local competition among pollen for reproductive success. This leads to a sex ratio gradient, with a male (pollen) bias in downwind individuals, which can be quite strong even for large patches. The effect can be understood as follows: downwind individuals have relatively low reproductive value and respond by putting more resources into the gamete (pollen) with the best long-range (extra-patch) reproductive success.     

Isozyme differentiation among sibling species and among populations of the Echinogammarus berilloni-group (Crustacea, Amphipoda)

The sibling species of the Echinogammarus berilloni-group are endemic for the Iberian Peninsula and southern France. These species show wide morphological variability with some overlap in their dianostic characters making their distinction difficult. Reroductive isolation and enzmatic jivergence amon allopatric and sympatric populations of four species sharing the same chromosome number has been studied. The results show a clear genetic differentiation of E. longiserosus and E. calvus versus the other two species. However, E. margalefi and E. echinosetosus show no clear genetic differentiation between them, confirming their crose relationship. All four species often coexist in the same drainage system. Isozme analysis was employed to check the hypothesis Of Margalef that sympathy would occur age, long-term phenomena of speciation inside of a given basin with subsequent contact and overlap between the differentiated forms. Electrophoretic data were also used to determine whether one flow among gammarids populations exists. A model proosed by other authors according to which the heterozyosity decreases towards the headwaters foes not fit to the data we have obtained from E. calvus. Thus, populations of this species from sources and springs of the Duero basin show the hiFhest values of mean heterozygosity. The differentiation in this basin can be explained by drift. Migration between populations of different rivers is prevented by natural barriers. The lowest river stretches are without amhipods interrupting the gene flow amon populations. A correction between genetic and geographic fistances among subbasins and basins was found applying a double logarithmic model. A model of migration of E. calvus in the Duero basin is proposed on the basis of allelic frequencies and on the distribution of mean hetero-zygosities.     

PEAK SHIFTS AND POLYMORPHISM DURING PHASE THREE OF WRIGHT'S SHIFTING-BALANCE PROCESS

The third phase of Wright's shifting-balance theory involves the export of adaptive gene combinations from one subpopulation to another. Previous results have demonstrated that this can occur at very low migration rates, but it has been argued that this simply reflects the ability of migration to overcome selection and fix any (even deleterious) alleles. Here, previous analyses are extended by concentrating on the critical balance between forward and reverse migration rates that still allows phase III to proceed. It is shown that selective advantage, dominance, recombination rate, and the number of loci all affect the ability of a genotype to invade and become fixed in a new subpopulation, but it is unlikely that phase III will occur in the absence of differential migration unless the invading genotype consists of a few dominant loci with a large selection advantage, spreading into a few populations of lower fitness. Therefore, as was envisioned by Wright, differential migration from more to less fit populations will be necessary for phase III to occur under most circumstances.     

运用分支系统学方法对逆珊瑚亚科的修订

运用分支系统学方法，考察有可能归入Ａｎｔｉｐｈｙｌｌｉｎａｅ亚科的各属。根据个体发育极向标准对选取的７个性状进行分析，这７个性状为：主隔壁的长短，主内沟的形状和大小，对隔壁的长短和加厚程度，侧隔壁的长度，一级隔壁的排列，一级隔壁从轴部退缩程度，轴部构造等。据以上各性状在每个属中的表现编制出性状极向数据矩阵，输入计算机运算，得到分支图。并得到以下结果：ＡｎｔｉｐｈｙｌｌｉｎａｅＩｌｉｎａ应包括下列１０属：ＡｃｔｉｎｏｐｈｒｅｎｔｉｓＩｖａｎｏｗｓｋｉ，１９６７；ＦａｌｓｉａｍｐｌｅｘｕｓＦｅｄｏｒｏｗｓｋｉ，１９８７；ＬｏｎｇｉｃｌａｖａＥａｓｔｏｎ，１９６２；ＬｙｔｖｏｌａｓｍａＳｏｓｈｋｉｎａ，１９２５：ＮｅｏｚａｐｈｒｅｎｌｉｓＧｒｏｖｅ，１９３５；ＭｏｎｏｐｈｙｌｌｕｍＦｏｍｉｃｈｅｖ，１９５３：ＦａｓｃｉｃｕｌｏｐｈｙｌｌｕｍＴｈｏｍｓｏｎ．１８８３：ＢｒａｄｙｐｈｙｌｌｕｍＧｒａｂａｕ．１９２８：ＲｏｔｉｐｈｙｌｌｕｍＨｕｄｓｏｎ，１９４２；ＣｌａｖｉｐｈｙｌｌｕｍＨｕｄｓｏｎ，１９４２。     

Nucleotide polymorphism in the chalcone synthase-A locus and evolution of the chalcone synthase multigene family of common morning glory Ipomoea purpurea

Chalcone synthase (CHS) is a small multigene family with at least four members (CHS-A, B, C and PS) in common morning glory Ipomoea purpurea ROTH. The chalcone synthase enzyme performs the initial condensation reaction that results in the 15-carbon three-ring structure that is the backbone of flavonoid biosynthesis. The biochemical pathway that commences with CHS is important in plant disease defence, pigment biosynthesis and UV protection. Accordingly, it is of substantial interest to characterize levels and patterns of molecular diversity for genes that encode this important enzyme. We report the sequence of 19 CHS-A alleles from Mexican and American populations of common morning glory. American populations of this annual self-compatible vine are believed to have been introduced from Mexico, where the species is native. Individual plants were sampled from populations of common morning glory throughout Mexico and the south-eastern USA. Four American alleles were sequenced and these, together with one allele from Mexico City, were identical in primary nucleotide sequence. These data suggest a restricted origin for the American population, probably as a consequence of selection for domestication by pre-Columbian peoples. Additionally the Mitontic (Chiapas, Mexico) population is significantly more homogeneous than expected by chance indicating that this population may also have experienced a recent population bottleneck. Estimates of nucleotide diversity from the Mexican CHS-A alleles were high. We present evidence that these estimates may, in part, result from low to moderate levels of interlocus recombination/gene conversion. We also present evidence that the ancient duplication of the CHS gene family, preceding the origin of the genus Ipomoea, was associated with heterogeneity in the rate of substitution between the resulting gene family members. The group of gene family members whose sequences possess a signature amino acid of the closely related Stilbene synthase exhibit a significantly faster proportional rate of nonsynonymous substitution.     

Postglacial expansion and genome subdivision in the European grasshopper Chorthippus parallelus

A noncoding nuclear DNA marker sequence (Cpnl-1) was used to investigate subdivision in the grasshopper Chorthippus parallelus and deduce postglacial expansion patterns across its species range in Europe. Investigation of the spatial distribution of 71 Cpnl-1 haplotypes and estimation of levels of genetic differentiation (K_ST values) between populations and geographic regions provided evidence for subdivision of C. parallelus into at least five major geographic regions and indicated that the French form of C. parallelus originated after range expansion from a Balkan refugium, Further evidence for subdivision of C. parallelus between Italy and northern Europe suggests that the Alps may have formed a significant barrier to gene flow in this grasshopper.     

Is population subdivision different from speciation? From phylogeography to species delimitation

Species‐level diversity and the underlying mechanisms that lead to the formation of new species, that is, speciation, have often been confounded with intraspecific diversity and population subdivision. The delineation between intraspecific and interspecific divergence processes has received much less attention than species delimitation. The ramifications of confounding speciation and population subdivision are that the term speciation has been used to describe many different biological divergence processes, rendering the results, or inferences, between studies incomparable. Phylogeographic studies have advanced our understanding of how spatial variation in the pattern of biodiversity can begin, become structured, and persist through time. Studies of species delimitation have further provided statistical and model‐based approaches to determine the phylogeographic entities that merit species status. However, without a proper understanding and delineation between the processes that generate and maintain intraspecific and interspecific diversity in a study system, the delimitation of species may still not be biologically and evolutionarily relevant. I argue that variation in the continuity of the divergence process among biological systems could be a key factor leading to the enduring contention in delineating divergence patterns, or species delimitation, meriting future comparative studies to help us better understand the nature of biological species.     

A microsatellite-based estimation of clonal diversity and population subdivision in Zostera marina, a marine flowering plant

We examined the genetic population structure in eelgrass (Zostera marina L.), the dominant seagrass species of the northern hemisphere, over spatial scales from 12 km to 10 000 km using the polymorphism of DNA microsatellites. Twelve populations were genotyped for six loci representing a total of 67 alleles. Populations sampled included the North Sea (four), the Baltic Sea (three), the western Atlantic (two), the eastern Atlantic (one), the Mediterranean Sea (one) and the eastern Pacific (one). Microsatellites revealed substantial genetic variation in a plant group with low allozyme diversity. Average expected heterozygosities per population (monoclonal populations excluded) ranged from 0.32 to 0.61 (mean = 0. 48) and allele numbers varied between 3.3 and 6.7 (mean = 4.7). Using the expected frequency of multilocus genotypes within populations, we distinguished ramets from genetic individuals (i.e. equivalent to clones). Differences in clonal diversity among populations varied widely and ranged from maximal diversity (i.e. all ramets with different genotype) to near or total monoclonality (two populations). All multiple sampled ramets were excluded from further analysis of genetic differentiation within and between populations. All but one population were in Hardy-Weinberg equilibrium, indicating that Zostera marina is predominantly outcrossing. From a regression of the pairwise population differentiation with distance, we obtained an effective population size Ne of 2440-5000. The overall genetic differentiation among eelgrass populations, assessed as rho (a standardized estimate of Slatkin's RST) was 0.384 (95% CI 0.34-0.44, P < 0.001). Genetic differentiation was weak among three North Sea populations situated 12-42 km distant from one another, suggesting that tidal currents result in an efficient exchange of propagules. In the Baltic and in Nova Scotia, a small but statistically significant fraction of the genetic variance was distributed between populations (rho = 0.029-0. 053) at scales of 15-35 km. Pairwise genetic differentiation between European populations were correlated with distance between populations up to a distance of 4500 km (linear differentiation-by-distance model, R2 = 0.67). In contrast, both Nova Scotian populations were genetically much closer to North Sea and Baltic populations than expected from their geographical distance (pairwise rho = 0.03-0.08, P < 0.01). A biogeographical cluster of Canadian with Baltic/North Sea populations was also supported using a neighbour-joining tree based on Cavalli-Sforza's chord distance. Relatedness between populations may be very different from predictions based on geographical vicinity.     

Random amplified polymorphic DNA analysis of southern brown bandicoot (Isoodon obesulus) populations in Western Australia reveals genetic differentiation related to environmental variables

Random amplified polymorphic DNA (RAPD) markers were used to analyse genetic variation within and between populations of Isoodon obesulus in Western Australia. Genetically controlled geographical variation in body size associated with habitat type and rainfall exists in this species, raising the question of whether local conditions may influence gene flow in I. obesulus. The RAPD markers displayed substantial genetic variation, with all animals possessing unique RAPD phenotypes over 39 polymorphic bands produced by three primers. Significant geographical subdivision was apparent (PhiST = 0.208) with southwest locations being divergent from all others, despite there being no physical barriers to gene flow. The pattern of subdivision was unrelated to physical distance between the locations, but was related to both annual rainfall and habitat type. Therefore, the most reasonable explanation for this pattern of subdivision appears to be that gene flow is restricted by selection against migrants between local populations with substantially different habitat type or rainfall. Restriction of gene flow through selection against migrants is rarely investigated, and the results of this study suggest that the importance of this process in the formation of population structure may be underestimated.