ENZYME ELECTROPHORESIS AND EVOLUTIONARY RELATIONSHIPS AMONG THREE SPECIES OF LASTHENIA (ASTERACEAE: HELIANTHEAE)

Enzyme electrophoresis was used to examine variation at 18 gene loci in Lasthenia burkei, L. conjugens, and L. femontii. The species consist of diploid annuals restricted to vernal pools in California; a variety of data has indicated that they are closely related. Populations of the three species are similar at isozyme loci; L. conjugens and L. fremontii are most similar with a genetic identity of 0.965. Lasthenia conjugens and L. burkei are next most similar (0.934), while L. burkei and L. fremontii have an identity of 0.909. Lasthenia burkei and L. femontii each contain a different subset of the alleles found in L. conjugens. Electrophoretic data are concordant with the view that these three species are closely related, but do not support the hypothesis that L. burkei is a stabilized hybrid derivative of L. conjugens and L. fremontii because alleles unique to each of the latter two species are not combined in the former. Rather, distribution of alleles among the three species suggests two possible alternative hypotheses of evolutionary relationships. One hypothesis considers Lasthenia conjugens a hybrid derivative of L. burkei and L. fremontii while the alternative explanation views the latter two species as independent derivatives of the former. Neither of these hypotheses appears to be concordant with morphological data.     

ALLOZYME VARIATION WITHIN SOLANUM SECT. PETOTA,SER. ETUBEROSA (SOLANACEAE)

Enzyme electrophoresis was employed to measure genetic variation within and divergence among 32 populations of three species in Solanum sect. Petota (S. brevidens, S. etuberosum, and S. fernandezianum). These species are self-compatible, diploid (2n = 2x = 24), and members of the monophyletic series Etuberosa. Solanum etuberosum is distributed in southern Chile, S. brevidens occurs in southern Chile and adjacent southern Argentina, and S. fernandezianum is endemic to Masatierra Island in the Juan Fernández Archipelago, 650 km west of continental Chile. Very low levels of observed heterozygosity (0.00–0.04) are found within populations of all three species. Interspecific mean genetic identities between S. brevidens and S. etuberosum (0.854) were similar to their intraspecific values (0.923, 0.865, respectively), with both species monomorphic for alleles at nine of the 12 loci examined. Solanum fernandezianum shows no heterozygosity and is more divergent to both S. brevidens (0.780) and S. etuberosum (0.698) than either is to each other. The divergence of S. fernandezianum to S. brevidens and S. etuberosum results from novel alleles at two of the 12 isozyme loci; in addition, it possesses only a subset of the variability found in S. brevidens and S. etuberosum at three other loci.     

ALLOZYME DIVERGENCE AMONG FIVE DIPLOID SPECIES OF ANTENNARIA (ASTERACEAE: INULEAE) AND THEIR ALLOPOLYPLOID DERIVATIVES

The Antennaria parlinii and A. neodioica agamic complexes are widely distributed across North America. Morphological data have suggested that these dioecious, perennial, entire-leaved herbs are of multiple hybrid origin from among five sexual diploid species. Antennaria neglecta, A. plantaginifolia, A. racemosa, and A. virginica are hypothesized to be the diploid progenitors of the A. neodioica complex, whereas A. parlinii sensu lato is thought to include the genomes of A. plantaginifolia, A. racemosa, and A. solitaria. An electrophoretic study was initiated to assess the degree of divergence among the five diploid species and to test the hypotheses of the hybrid (allopolyploid) origins of A. parlinii and A. neodioica. Twenty genetic loci were surveyed in 76 populations of the diploid and polyploid taxa. The diploid species are well defined morphologically, although the genetic basis of differences distinguishing them have not been determined. The species exhibit little divergence at genes specifying soluble enzymes, however each species has unique alleles in highest frequency at one or two genes. Allozymes indicate that gene diversity in the obligately outcrossing diploids occurs primarily within rather than among populations. The shale barren endemic, A. virginica, is as genetically diverse as the more edaphically diverse and widespread species. Tetraploid cytotypes of diploid (2n = 28) A. virginica possess the same allozymes as the diploids and these cytotypes appear to be of autopolyploid (non-hybrid) origin. Enzyme electrophoresis is concordant with morphological data in suggesting that A. neodioica contains the genomes of A. neglecta, A. virginica, A. plantaginifolia, A. racemosa and perhaps A. solitaria whereas the latter three species are the progenitors of A. parlinii.     

PHENOTYPIC VARIATION IN STEPHANOMERIA EXIGUA SSP. CORONARIA (COMPOSITAE) AND ITS RECENT DERIVATIVE SPECIES “MALHEURENSIS”

Phenotypic variation in 33 quantitative characters was analyzed in Stephanomeria exigua ssp. coronaria (Greene) Gottlieb and its recent derivative species, presently called “Malheurensis,” grown in a series of experimental environments. The study was made to determine whether their high genetic identity, previously revealed by electrophoresis of a sample of their enzymes, was correlated with a high similarity in quantitative traits of morphology, size, growth rates, and fecundity. The electrophoretic evidence provided correct information about the relative variability, similarity, and phylogenetic relationship of the two taxa. Thus, 90% of the between-plant variance components from the analysis of variance were higher in ssp. coronaria and, therefore, concordant with its higher genetic variability. The between-environment variance components in the two species were similar in magnitude and when ordered, from smallest to largest, were nearly identical in ranking. The quantitative study provided important additional evidence. Ssp. coronaria grew more rapidly and produced more florets than Malheurensis in all of the growth conditions and also was found to grow larger than Malheurensis in their native habitat in eastern Oregon where they grow sympatrically. These and other results indicate that the persistence of Malheurensis in nature cannot depend on advantages of size, growth rates, or number of flowers produced per individual. The large differences between the taxa in the size of their seeds was used as the basis for a model to account for the continued persistence of Malheurensis.     

ALLOZYME VARIATION,GENECOLOGY, AND PHYTOGEOGRAPHY OF ANTENNARIA ARCUATA (ASTERACEAE), A RARE SPECIES FROM THE GREAT BASIN AND RED DESERT WITH SMALL DISJUNCT POPULATIONS

Antennaria arcuata (Asteraceae: Inuleae) is a rare sexual diploid species that occurs in three disjunct regions of Idaho, Nevada, and Wyoming. Isozyme diversity in six populations of the species from the three regions utilized 26 putative loci to provide clues to its population genetic structure. Results show that, in general, the amount of genetic diversity in A. arcuata is very low in comparison to other sexual species of Antennaria. The values of several genetic statistics such as mean number of alleles per locus, proportion of loci polymorphic, and observed heterozygosity, are significantly lower than populations of any of 17 other sexual species of Antennaria that have been studied previously. It is likely that the unusual disjunct and restricted distribution of A. arcuata is partially the result of its unusual ecology, as it occurs in moist basins having high concentrations of salts that are frequently disturbed by large grazing animals. Canonical correspondence analysis shows strong relationships between several edaphic, environmental, and geographic features and the genetic variation in the populations. The migration of A. arcuata to other regions since the end of the Wisconsinan might have been inhibited by the fact that suitable habitats occur as small isolated islands in a sea of inhospitable terrain, the dry sagebrush steppe.     

LIFE HISTORY VARIATION WITHIN POPULATIONS OF AN ASEXUAL PLANT,ERIGERON ANNUUS (ASTERACEAE)

Genetic variation was measured for several morphological and life history characters in Erigeron annum, a triploid and obligately apomictic species. There was significant genetic variation for nearly all characters measured, including plant size, growth rate, time of flowering, biomass allocation to roots and shoots, seed weight, and germination response to temperature. Variance among genotypes accounted for up to 55% of the total phenotypic variance, well within the range of heritabilities observed for sexual species. These estimates of broad-sense heritability predict substantial short-term response to selection on life history characters in this asexual species.     

ALLOZYME DIVERSITY WITHIN AND DIVERGENCE AMONG FOUR SPECIES OF ROBINSONIA (ASTERACEAE: SENECIONEAE), A GENUS ENDEMIC TO THE JUAN FERNANDEZ ISLANDS,CHILE

Enzyme electrophoresis was employed to assess genetic diversity within and divergence among four species of Robinsonia (R. evenia, R. gayana, R. gracilis, R. thurifera), a genus endemic to the Juan Fernandez Islands, Chile. The genus consists of treelike perennial plants, and all species are dioecious. Morphological diversity within the genus is reflected by recognition of two subgenera, with three sections in one subgenus. Total gene diversity is highest in the two species (R. gayana and R. gracilis) that are most common and have the largest population sizes. Robinsonia evenia has only half and the rare R. thurifera only 20% of the diversity detected in the other two species. The diversity measured in R. gayana and R. gracilis is comparable to the values typical of continental species of flowering plants with similar life history attributes. The genetic identities between species range from 0.560 to 0.706, which is similar to or below many values for congeneric species, but much lower than most reports for congeners on oceanic islands. The higher diversity within and divergence among species of Robinsonia compared to many insular endemics may result from several factors. The genus probably arose from selfincompatible plants of the genus Senecio, which means that several to perhaps many colonizers carried considerable allozymic variation to the Islands. Large population sizes and obligate outcrossing are additional factors that would account for higher diversity. Sorting of alleles during radiation and the process of mutation probably combined to produce divergence among the species. Estimated divergence times calculated for the species from allozyme data range from 1.7 to 5.5 million years depending on the assumptions made in the calculations; the age of the island (Masatierra) on which these four species are confined is approximately 4.0 million years. The electrophoretic data suggest that Robinsonia arrived early in the archipelago, and radiated and speciated rapidly after colonization.     

ALLOZYME VARIATION WITHIN AND AMONG MATURE POPULATIONS OF SPECKLED ALDER (ALNUS RUGOSA) AND RELATIONSHIPS WITH GREEN ALDER (A. CRISPA)

Vegetative tissues from 14 sexually mature populations of speckled alder (Alnus rugosa (Du Roi) Sprengel) in Québec have been analyzed for electrophoretically demonstrable variation in 9 enzymes encoding a total of 15 loci. Speckled alder demonstrated a diploid-like expression for all polymorphic loci investigated. Populations were in Hardy-Weinberg equilibrium for the 9 polymorphic loci observed. The total expected heterozygosity was 0.173. Analysis of fixation indices indicated a slight deficiency of heterozygotes, relative to panmictic expectations. This was likely due to weak population differentiation, which did not follow any particular geographical trend. Qualitative estimates of interpopulation rates of gene flow were high, and in good agreement with the small pair-wise population genetic distances and among-population fixation index. Levels of genetic diversity and partition of this diversity were similar to previous observations obtained with the sympatric species A. crispa (Ait.) Pursh. However, no phenomena of interspecific hybridization were noted. The average genetic distance between these two alder species was large, with a value of 0.4, emphasizing the different ecological niches colonized by each of the two species. The estimate of divergence time between these two taxa was two million years. It is in agreement with the hypothesis of repetitive spatial isolation of each species in ice-free refugia during the Pleistocene, thus promoting their reproductive isolation. The interspecific divergence noted at the enzyme level allowed for the easy electrophoretic identification of each taxon.     

GENES WITH SOCIAL EFFECTS ARE EXPECTED TO HARBOR MORE SEQUENCE VARIATION WITHIN AND BETWEEN SPECIES

The equilibrium sequence diversity of genes within a population and the rate of sequence divergence between populations or species depends on a variety of factors, including expression pattern, mutation rate, nature of selection, random drift, and mating system. Here, we extend population genetic theory developed for maternal-effect genes to predict the equilibrium polymorphism within species and sequence divergence among species for genes with social effects on fitness. We show how the fitness effects of genes, mating system, and genetic system affect predicted gene polymorphism. We find that, because genes with indirect social effects on fitness effectively experience weaker selection, they are expected to harbor higher levels of polymorphism relative to genes with direct fitness effects. The relative increase in polymorphism is proportional to the inverse of the genetic relatedness between individuals expressing the gene and their social partners that experience the fitness effects of the gene. We find a similar pattern of more rapid divergence between populations or species for genes with indirect social effects relative to genes with direct effects. We focus our discussion on the social insects, organisms with diverse indirect genetic effects, mating and genetic systems, and we suggest specific examples for testing our predictions with emerging sociogenomic tools.     

款冬属的核形态(菊科:千里光族)

研究了款冬属的核形态。染色体间期为简单型与复杂型的过渡型;前期染色体为近基型与中间型的过渡型。染色体较小,核型不对称,具明显的二型性;数目与核型公式为2n=60=42m+10sm+6st+2t。比较发现款冬的核型明显不同于千里光族中已有的核型记载,其核型特征似乎与它独特的形态特征相联系,具有重要的系统学意义。     

MITOCHONDRIAL DNA VARIATION WITHIN AND BETWEEN SPECIES OF THE PAPILIO MACHAON GROUP OF SWALLOWTAIL BUTTERFLIES

Species limits and phylogenetic relationships in the Papilio machaon species group are potentially confounded by a complex pattern of Pleistocene range fragmentation, hybridization, and ecological race formation. Mitochondrial DNA (mtDNA) restriction-site analysis has been used to define genetic affinities and genetic population structure within this species group. The distribution of mtDNA haplotypes generally confirms prior phylogenetic hypotheses and species delineations, but there is poor correspondence between ecological races and mtDNA haplotypes. The amount and distribution of mtDNA sequence variation within species vary among species, reflecting differences in current patterns of gene flow and/or historical population structure. In spite of wing pattern characters that ally them with P. polyxenes, both P. joanae and P. brevicauda have mtDNA that is closely related to that of P. machaon. We suggest that P. joanae and P. brevicauda are of hybrid origin.     

ECOLOGICAL BARRIERS TO GENE FLOW BETWEEN RIPARIAN AND FOREST SPECIES OF AINSLIAEA (ASTERACEAE)

Understanding the role of habitat‐associated adaptation in reducing gene flow resulting in population differentiation and speciation is a major issue in evolutionary biology. We demonstrate a significant role for habitat divergence in species isolation between two naturally hybridizing riparian and nonriparian plants, Ainsliaea faurieana and A. apiculata (Asteraceae), on Yakushima Island, Japan. By analyzing the fine‐scale population structure at six sympatric sites, we found that variations in leaf shape, geography, light conditions, and genotype were strongly correlated across riverbank–forest transitions. No evidence of effective gene flow was found between the two species across the majority of the transition zones, although the NewHybrid clustering analysis confirmed interspecific hybridization. However, a relatively high level of gene flow was observed across one zone with a more diffuse ecotone and intermediate flooding and light conditions, possibly generated by human disturbances. These results suggest that the barriers to gene flow between the riparian and forest species are primarily ecological. Additional common garden experiments indicated that the two species are adaptively differentiated to contrasting flooding and light environments. Overall, our study suggests that adaptations to different habitats can lead to the formation of reproductive isolating barriers and the maintenance of distinct species boundaries.     

马铃薯叶甲属六个种的等位基因酶变异

用聚丙烯酰胺凝胶电泳测定了马铃薯叶甲属(Leptinotarsa)六个种:马铃薯叶甲(L. decemlinecta)、胡颓子叶茄叶甲(L. texana)、柔毛茄叶甲(L. rubiginosa)、膜苞菊叶甲(L. lineolata)、蒺藜叶甲(L. peninsularis)和蒺藜四条叶甲(L. tlascalana)的等位基因酶变异.分析了14种同工酶(ACPH、ADH、AMY、FUM、GDH、GOT、IDH、HBDH、LAP、MDH、ME、PGM、SORDH和XDH)的17个座位.其中单型座位有9个,多型座位有8个,后者占47.1%.六个种的平均杂合度为0.091.其中最高的是膜苞菊叶甲0.154;最低的是蒺藜四条叶甲0.042.六个种彼此之间的遗传距(D)在0.129—0.573之间,说明这六个种的亲缘关系是很密切的.     

ALLOZYME VARIATION IN SOME POPULATIONS OF THE FRESHWATER SNAILS LYMNAEA PEREGRA, L. AURICULARIA AND L. STAGNALIS (GASTROPODA: PULMONATA)

Three species of the genus Lymnaea (Gastropoda, Pulmonata, Basommatophora)were examined for genetic variation at 11 enzymatic loci insamples collected in Brittany (North-Western France). Variabilitywas greatest in L. percgra, but the limited area of samplingdid not allow specific inferences. The UPGMA clustering of unbiasedgenetic distances (Nei, 1978) isolated first L. auriculariasamples, and secondly the single L. stagnalis sample from theL. peregra set. This scheme of relationships was opposed tothe identification of alleles shared by the three species atthe studied loci Analysis of L. peregra population structure by F-statistics(Weir & Cockerham, 1984) suggested high inbreeding and raisedthe possible role of self-fertilization. The contradiction betweenhigh variability and high homozygosity is discussed. Furthermore,population differentiation was rather weak (although statisticallysignificant), despite some remarkable differences among loci.Nm estimates using Wright's (1951) and Slatkin's (1985) methodsrevealed a gene flow unable to prevent the effect of geneticdrift among populations. The relative homogeneity of populationswith weak genetic exchange is discussed (Received 24 May 1993; accepted 21 March 1994)     

GENETIC SIMILARITY IS HIGH BETWEEN INTERCONTINENTAL DISJUNCT SPECIES OF SENECIO (ASTERACEAE)

Senecio flavus (Decne.) Schultz-Bip. of the Saharo-Arabian and Namibian deserts and Senecio mohavensis Gray of the Mojave and Sonoran deserts form a pair of closely related disjunct annual taxa. The two species exhibit slight morphological differences and have different ploidy levels: all North American populations examined are tetraploid, while African and Asian populations are diploid. Senecio flavus comprises two morphologically and geographically distinct subspecies, subsp. flavus and subsp. breviflorus Kadereit. Electrophoretic examination of 13 enzymes revealed that the subsp. breviflorus has two additional isozymes relative to subsp. flavus, and that 5. mohavensis has four additional isozymes relative to subsp. breviflorus. Senecio flavus subsp. breviflorus and S. mohavensis are identical at 20 of the 21 (I = 0.952) remaining homologous loci. This value is much higher than the genetic identity values observed in other taxa with disjunct intercontinental distributions such as members of Agastache, Datisca, Liriodendron, and Styrax. This suggests that the Senecio disjunction may be of recent origin. Senecio flavus subsp. flavus from North Africa and Namibia has lower genetic identity values with S. mohavensis (0.857 and 0.805, respectively), implicating S. flavus subsp. breviflorus as the progenitor of 5. mohavensis. The complete lack of heterozygosity confirms that the plants are highly autogamous, and thus could have attained their disjunct distribution through long distance dispersal.     

PUPARIATION SITE PREFERENCE WITHIN AND BETWEEN DROSOPHILA SIBLING SPECIES

Holometabolous insects pass through a sedentary pupal stage and often choose a location for pupation that is different from the site of larval feeding. We have characterized a difference in pupariation site choice within and between sibling species of Drosophila. We found that, in nature, Drosophila sechellia pupariate within their host fruit, Morinda citrifolia, and that they perform this behavior in laboratory assays. In contrast, in the laboratory, geographically diverse strains of Drosophila simulans vary in their pupariation site preference; D. simulans lines from the ancestral range in southeast Africa pupariate on fruit, or a fruit substitute, whereas populations from Europe or the New World select sites off of fruit. We explored the genetic basis for the evolved preference in puariation site preference by performing quantitative trait locus mapping within and between species. We found that the interspecific difference is controlled largely by loci on chromosomes X and II. In contrast, variation between two strains of D. simulans appears to be highly polygenic, with the majority of phenotypic effects due to loci on chromosome III. These data address the genetic basis of how new traits arise as species diverge and populations disperse.