THE ROLE OF INTROGRESSIVE HYBRIDIZATION IN THE EVOLUTION OF THE GILA ROBUSTA COMPLEX (TELEOSTEI: CYPRINIDAE)

Abstract The extent and impact of introgressive hybridization was examined in the Gila robusta complex of cyprinid fishes using mitochondrial DNA (mtDNA) sequence variation. Lower Colorado River basin populations of G. robusta, G. elegans, and G. cypha exhibited distinct mtDNAs, with only limited introgression of G. elegans into G. cypha. The impact of hybridization was significant in upper Colorado River basin populations; most upper basin fishes sampled exhibited only G. cypha mtDNA haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence. Analysis of the geographic distribution of variation identified two distinctive G. elegans lineages; however, the small number of individuals and localities sampled precluded a comprehensive analysis. Analysis of haplotype and population networks for G. cypha mtDNAs from 15 localities revealed low divergence among haplotypes; however, significant frequency differences among populations within and among drainages were found, largely attributable to samples in the Little Colorado River region. This structure was not associated with G. cypha and G. robusta, as morphotypes from the same location are more similar than conspecific forms in other locations. This indicates that morphological and mtDNA variation are affected by different evolutionary forces in Colorado River Gila and illustrates how both hybridization and local adaptation can play important roles in evolution.     

CHLOROPLAST DNA EVOLUTION AND PHYLOGENETIC RELATIONSHIPS IN CLARKIA SECT. PERIPETASMA (ONAGRACEAE)

Restriction-site analysis of chloroplast DNA in Clarkia sect. Peripetasma (Onagraceae) was done to test previously proposed phylogenetic models. One hundred nineteen restriction-site mutations were identified among the nine species using 29 restriction enzymes, and these were used to construct rooted most parsimonious trees (Wagner and Dollo). A chloroplast DNA evolutionary clock could not be statistically rejected. Branch points of this tree were statistically tested by Felsenstein's bootstrap method. This tree 1) provided an unambiguous and detailed genealogical history for the section, 2) verified a previous partial phylogenetic model for the section based on gene duplications and differential silencing, 3) provided details of the phylogenetic model not inferred or expected based on morphology and reproductive isolation, and 4) indicated that morphology evolves at markedly different rates within and between lineages in the section.     

SPECIAL PAPER: SYSTEMATICS AND EVOLUTION OF SORGHUM SECT. SORGHUM (GRAMINEAE)

The genus Sorghum Moench is subdivided into sections Chaeotosorghum, Heterosorghum, Parasorghum, Stiposorghum and Sorghum. Section Sorghum includes two rhizomatous species, S. halepense (L.) Pers. (2n = 40) and S. propinquum (Kunth) Hitchcock (2n = 20), as well as the annual S. bicolor (L.) Moench (2n = 20). Sorghum bicolor is divided into subspecies bicolor to include all domesticated grain sorghums, subspecies drummondii (Steud.) de Wet comb. nov. to include stabilized derivatives of hybridization among grain sorghums and their closest wild relatives and subspecies arundinaceum (Desv.) de Wet et Harlan to include the wild progenitors of grain sorghums. Four ecotypes of subspecies arundinaceum are recognized: race aethiopicum of the arid African Sahel. race virgatum of northeastern Africa, race arundinaceum of the African tropical forest, and race verticilliflorum of the African Savanna. The numerous, usually recognized grain sorghums are divided among five basic races, bicolor, caudatum, durra, guinea and kafir, and ten hybrid races that each combine characteristics of at least two of these basic races. Races of grain sorghum are morphologically distinct, and they maintain their unity of type through spacial and ethnological isolation.     

BIAS IN INHERITANCE OF CHLOROPLAST DNA AND MECHANISMS OF HYBRIDIZATION BETWEENWIND- AND INSECT-POLLINATED EUPATORIUM (ASTERACEAE)

Hybrids of the wind-pollinated E. capillifolium and the insect-pollinated E. serotinum were found to occur in the Coastal Plain of Louisiana, Mississippi, and southern Arkansas and on the Piedmont in three locations. Interspecific cross-pollination occurs when wind causes the flexible flowering branches of E. capillifolium to whisk over the stiff upright branches of E. serotinum plants. Interspecific pollen was found to be captured by E. serotinum more effectively than by E. capillifolium. However, analysis of cpDNA of natural field hybrids indicated that most were maternally descended from E. capillifolium. This latter bias can be explained by the far greater number of flowers, and thus greater seed producing capacity, of E. capillifolium relative to E. serotinum. Morphological variability observed among field hybrids suggests that backcrossing has occurred; however, field hybrids and progeny grown from field hybrid achenes generally had low pollen stainability, irregular meiosis, and reduced achene set. Furthermore, field hybrids were found to have a chromosome number of 2n = 20, like the parental species, whereas progeny grown from field hybrids had deficiencies and duplications of chromosome numbers. Because these chromosome number deviations were not seen in field hybrids it is logical to suggest that either they are F₁s, or that strong selective forces in the field eliminated the progeny of hybrids with deficiencies and duplications.     

蒿属腺毛蒿组和白苞蒿组的分支分类,生物地理及亲缘关系的研究

菊科蒿属Ａｒｔｅｍｉｓｉａ的腺毛蒿组和白苞蒿组共有２６种８变种,为亚洲特有植物。前主产我国西南中、高海拔地区;后主产秦岭以南横断山脉以东各省区的中、低海拔地区,少数种在亚洲南部、东南部也有分布。除泰国艾Ａ．ｂｏｒｅａｌｉ－ｓｉａｍｅｎｓｉｓ外,其余国内均产。它们在蒿属蒿亚属中进化程度较高,且与其它组有明显的区别。选择亲缘关系最近的艾组为外类群。在外类群比较原则和形态演化原则的基础上,对大量性状     

贵州大树茶的核型变异与进化

本文对贵州大树茶7种1变种11类型的核型进行了分析。结果表明,这些种类均为二倍体2n＝30。五室茶Camellia quinquelocularis 2n＝30＝24m+6sm;四球茶C．tetracocca 2n＝30=22m+8sm;大理茶C．taliensis 2n=30＝22m+8sm;秃房茶C．gymnogyna 2n＝30＝22m+6sm+2st与2n=30＝20m+8sm+2st;假秃房茶C. gymnogynoides 2n＝30=22m+6sm+2st与2n＝30=20m+8sm+2st;榕江茶C. jungkiangensis 2n＝30+20m+8sm+2st;茶C．sinensis 2n=30＝20m+8sm+2st以及变种淡红花茶C．sinensis var．ruolla 2n＝30=20m+8sm+2st;均属2A核型。染色体结构变异在茶组植物演化中起了重要作用。所划分的两大类核型,即m和sm类与m,sm,和st类是与其子房室数,即5室和3室相一致的。根据核型的不对称性程度、外部形态及生化分析,探讨了各种类的亲缘关系与系统演化途径,论证了茶组植物的原产地是位于滇、桂、黔毗邻交汇处的云贵高原,探讨了茶组植物的分类学问题。     

EVOLUTION OF THE HELIORNITHIDAE: RECIPROCAL ILLUMINATION BY MORPHOLOGY, BIOGEOGRAPHY AND DNA HYBRIDIZATION (AVES: GRUIFORMES)

Abstract— Finfoots (Heliornithidae) were chosen to test the possibility that there has been a dramatic reversal in a suite of morphological characters, intimated by an earlier phylogenetic reconstruction of Gruiformes based on DNA hybridization. There are three nodes where unstudied finfoots could stem from the existing reconstruction. The resulting alternate trees have largely exclusive implications for morphological character suite polarity, biogeography and fossil identifications. A new DNA hybridization study that includes all relevant taxa was intended to form the basis for independent evaluation of the trees, but it produced results that conflict with the earlier DNA study. So, instead, DNA trees were evaluated by their reproducibility and consensus with most-parsimonious trees, biogeography, paleontology and traditional classifications, I concur with traditional classifications that finfoots are monophyletic, and that Limpkin (Gruiformes: Aramidae) is the sister of cranes (Gruiformes: Gruidae). Limpkin is not supported as the sister of the Sungrebe ( Heliornis fulica ) or as a member of the Heliornithidae, as reported in the earlier DNA study. It is alarming that the gross lack of consensus with traditional characters and concomitant implications for character suite polarity in this case went unquestioned.     

杂交在进化中的作用及杂种的识别和分类处理

所谓杂交和杂种,可以有不同的概念。从最广义的角度来理解,凡基因型不同的个体之间的交配都叫杂交。基因杂合状态是自然界正常的现象。互交繁育的生物体,在正常情况下,在许多位点上都是不同等位基因的杂合体,也就是杂种,它们在自交和杂合时都产生有变异和分离的子代。但杂交最常用的含义是指已有生殖隔离的异种个体或甚至异     

THE atpA GENE CLUSTER OF GUILLARDIA THETA (CRYPTOPHYTA): A PIECE IN THE PUZZLE OF CHLOROPLAST GENOME EVOLUTION

We cloned and sequenced the genes of the atp A ( atp 1) cluster, together with its upstream and downstream sequences, of the chloroplast genome of the cryptomonad Guillardia theta Hill et Wetherbee and used gene signatures, predicted amino acid sequences, and gene arrangements for phylogenetic inferences. The Guillardia atp A cluster contains the genes atp I,H,G,F,D,A in the given order, thus reflecting the cyanobacterial/red algal/chromophyte gene arrangement. In addition, the order of both the upstream sequences rpo B,C₁,C₂, rps 2, tsf and the downstream sequences ycf 16/24, which is found exclusively in red algal chloroplast genomes, is conserved in Guillardia. This gene order, which presumably is the result of the reduction process of the cyanobacterial genome following primary endosymbiosis, provides strong evidence for a red algal ancestry of the Guillardia chloroplast and supports the hypothesis of secondary endosymbioses giving rise to chl a + c -containing algae. The close evolutionary relationship of the chloroplasts of Guillardia and red algae is furthermore supported by the lack of introns, high degrees of sequence similarities, and additional gene signatures, including spacers, gene overlaps, and inverted repeats. Gene cluster analysis, including the ATPase genes together with their upstream and downstream genes, is consistent with a single primary photosynthetic eukaryote that gave rise to all extant algal lineages and land plants by either direct filiation or secondary endosymbioses.     

CHROMOSOMES AND SYSTEMATICS OF ASPLENIUM SECT. HYMENASPLENIUM (ASPLENIACEAE)

Gametic and somatic chromosome numbers of eight Asian species belonging to Asplenium sect. Hymenasplenium were determined. Seven species were observed to have chromosome numbers based on x = 39, and one on x = 38. These chromosome numbers are exceptional in Asplenium which is well known to have chromosomes of n = 36 or multiples thereof. Decisions on the taxonomic status of the species of section Hymenasplenium were facilitated by cytological observations. Systematic recognition of this section is also supported by the peculiarity in the chromosome numbers, and evidence for the addition to the section of several other species is presented.     

CHLOROPLAST DNA VARIATION AND THE PHYLOGENY OF HORDEUM (POACEAE)

Restriction site variation in the chloroplast genome (cpDNA) was surveyed among 37 taxa or cytotypes (40 accessions) of the genus Hordeum. Seventeen restriction enzymes were employed, and a total of 491 restriction sites were assayed. Of these, 120 were variable among the taxa, including 70 synapomorphies. The level of sequence divergence (p) among species of Hordeum varied from 0.0 to 0.017, indicating that Hordeum possesses an about-average level of cpDNA diversity as compared to most other genera of flowering plants for which data are available. Wagner and polymorphism parsimony phytogenies were constructed from the restriction site data. These analyses divided the genus into several distinct groups; 1) American taxa; 2) diploid H. marinum; 3) Asian taxa; 4) H. vulgare-H. bulbosum; and 5) the H. murinum complex. Bootstrap-based confidence limits provided statistical support for the monophylesis of the latter three groups. The cpDNA data showed remarkably good congruence with previously published isoenzymatic, molecular, cytological, and crossing data.     

CHLOROPLAST DNA VARIATION WITHIN AND AMONG GENERA OF THE HEUCHERA GROUP (SAXIFRAGACEAE): EVIDENCE FOR CHLOROPLAST TRANSFER AND PARAPHYLY

The Heuchera group (Saxifragaceae) comprises Bensoniella, Conimitella, Elmera, Heuchera, Lithophragma, Mitella, Tellima, Tiarella, and Totmiea. Earlier studies employing morphology, karyology, and flavonoid chemistry indicated that these genera form a natural group, but failed to resolve relationships among them. Restriction site analysis of chloroplast DNA (cpDNA) suggests that Bensoniella, Tolmiea, and Lithophragma are close allies and form the sister group of a large clade containing the remaining six genera. Mitella and Heuchera are both paraphyletic based on cpDNA data. cpDNA data, in conjunction with morphological and allozyme data, suggest at least four examples of intersectional hybridization and subsequent chloroplast capture in Heuchera. Several of these events may be explained via a stepping stone model in which the chloroplast genome of a species was captured by a second species, and then ultimately by a third taxon. Two well-differentiated groups of Tellima populations were detected: one group has a unique chloroplast genome characterized by nine autapomorphies, and the second group has a chloroplast genome identical to that found in M. trifida and M. diversifolia. cpDNA and allozyme data suggest that some Tellima populations probably obtained their chloroplast genome via intergeneric hybridization with M. trifida, M. diversifolia, or the ancestor of these taxa. The occurrence of intergeneric chloroplast transfer in some populations of Tellima, as well as extensive intersectional chloroplast capture in Heuchera, not only suggests caution in the use of cpDNA restriction site data in phylogenetic reconstruction, but also demonstrates again the importance of adequate sampling of conspecific populations. If the intergeneric relationships in the Heuchera group suggested by cpDNA analysis are accurate, fundamental questions arise regarding the validity of certain morphological traits as good taxonomic characters in Saxifragaceae. Furthermore, significant taxonomic changes at the generic level would be necessary.     

ULTRASTRUCTURE AND DEVELOPMENT OF THE NEXINE AND INTINE IN THE POLLEN WALL OF SILENE ALBA (CARYOPHYLLACEAE)

Nexine and intine development in Silene alba (Caryophyllaceae) was investigated by electron microscopy and enzyme cytochemistry. Nexine-2 forms by deposition of sporopollenin along unit membrane lamellae closely associated with the microspore plasma membrane in the late tetrad stage. After the callose wall dissolves, electron density increases along the tangentially oriented fibers of the proximal primexine, forming nexine-1. When the exine is essentially complete, the intine begins to develop. In the nearly mature microspore, acid phosphatase activity appears in the peripheral cytoplasm just prior to its extrusion into the intine of the mature pollen grain.     

山茶科系统发育诠释——Ⅲ.关于金花茶组及山茶属演化若干问题

作者通过比较认为山茶属金花茶组的模式和古茶组的模式不是同一分类单位,因而取消金花茶组是不恰当的。金花茶组是一个自然的集合体。作者详细地分析了山茶属内演化的四个阶段:第一阶段表现为苞被不分化、大型、宿存、子房5室、心皮部分分离;第二阶段演化出苞被宿存和苞被脱落两个类群,前者较为原始的代表是离蕊茶织和短蕊茶组,较为进化的代表是管蕊茶组;后者较为原始的代表是半宿萼茶组、瘤果茶组、糙果茶组,较为进化的代表是油茶组、短柱茶组、红山茶组;第三阶段是苞被分化为小苞片和萼片的类群,金花茶组和长柄茶组是较为原始而茶组、超长柄茶组则是较为进化的代表;第四阶段的连蕊茶组和毛蕊茶组苞萼小型化且宿存,的代表,雌、雄蕊均高度连合,子房室不完全发育 它们只能由第三阶段具有多数小苞片的原始类群发展出来,认为把山茶属划分为四个亚属的系统是合理的。 作者还认为,花的颜色以及其他相似性状的集合是划分山茶属次级分类单位的重要依据;分类系统的自然性和实用性相结合是分类学家始终应该追随的目标,混淆不同差异的做法是不可取的。最后,作者认为山茶属没有真正的顶生花。     

THE CONTRIBUTION OF EDAPHIC HETEROGENEIYT TO THE EVOLUTION AND DIVERSITY OF BURSERACEAR TREES IN THE WESTERN AMAZON

Abstract —Environmental heterogeneity in the tropics is thought to lead to specialization in plants and thereby contribute to the diversity of the tropical flora. We examine this idea with data on the habitat specificity of 35 western Amazonian species from the genera Protium, Crepidospermum, and Tetragastris in the monophyletic tribe Protieae (Burseraceae) mapped on a molecular‐based phylogeny. We surveyed three edaphic habitats that occur throughout terra firme Amazonia: white‐sand, clay, and terrace soils in eight forests across more than 2000 km in the western Amazon. Twenty‐six of the 35 species were found to be associated with only one of three soil types, and no species was associated with all three habitats; this pattern of edaphic specialization was consistent across the entire region. Habitat association mapped onto the phylogenetic tree shows association with terrace soils to be the probable ancestral state in the group, with subsequent speciation events onto clay and white‐sand soils. The repeated gain of clay association within the clade likely coincides with the emergence of large areas of clay soils in the Miocene deposited during the Andean uplift. Character optimizations revealed that soil association was not phylogenetically clustered for white‐sand and clay specialists, suggesting repeated independent evolution of soil specificity is common within the Protieae. This phylogenetic analysis also showed that multiple cases of putative sister taxa with parapatric distributions differ in their edaphic associations, suggesting that edaphic heterogeneity was an important driver of speciation in the Protieae in the Amazon basin.     

DISENTANGLING THE CONTRIBUTION OF SEXUAL SELECTION AND ECOLOGY TO THE EVOLUTION OF SIZE DIMORPHISM IN PINNIPEDS

The positive relationship between sexual size dimorphism (SSD) and harem size across pinnipeds is often cited as a textbook example of sexual selection. It assumes that female aggregation selected for large male size via male–male competition. Yet, it is also conceivable that SSD evolved prior to polygyny due to ecological forces. We analyzed 11 life‐history traits in 35 pinniped species to determine their coevolutionary dynamics and infer their most likely evolutionary trajectories contrasting these two hypotheses. We find support for SSD having evolved prior to changes in the mating system, either as a consequence of niche partitioning during aquatic foraging or in combination with sexual selection on males to enforce copulations on females. Only subsequently did polygyny evolve, leading to further coevolution as the strength of sexual selection intensified. Evolutionary sequence analyses suggest a polar origin of pinnipeds and indicate that SSD and polygyny are intrinsically linked to a suite of ecological and life‐history traits. Overall, this study calls for the inclusion of ecological variables when studying sexual selection and argues for caution when assuming causality between coevolving traits. It provides novel insights into the role of sexual selection for the coevolutionary dynamics of SSD and mating system.