A PLANT HOPPER (NOGODINIDAE) FROM THE UPPER PALAEOCENE OF ARGENTINA: SYSTEMATICS AND TAPHONOMY

Abstract:  A new taxon of plant hopper, Celinapterixini, is erected based on Celinapterix bellissima gen. et sp. nov. from the Upper Palaeocene Maíz Gordo Formation, north-west Argentina. Its phylogenetic relationships within the Fulgoroidea and Nogodinidae are discussed. The Danish Eocene species Hammapterix paucistrata (Henriksen) is transferred to the Nogodinidae and placed in a new genus, Henriksenopterix , based on wing-venation characters. The new plant hopper is an unusual case of articulated preservation from the Maíz Gordo Formation. The palaeoenvironment is interpreted as a carbonate mudflat subenvironment with a low flow of energy, created during a period of contraction of the lacustrine system. The plant hopper is considered to have sunk and been buried in a soupy substrate. Early fossil-diagenesis seems to have occurred over an extended period of time, because although the specimen preserves all original soft-body parts, these occur as an amorphous mass owing to tissue decomposition. The occurrence of three-dimensional preservation suggests the absence of fossil-diagenetic compression; the sediments seem to preserve more-or-less their original thickness.     

POPULATION GENETICS AND TAXONOMY OF CAULERPA (CHLOROPHYTA) FROM THE GREAT BARRIER REEF,AUSTRALIA1

Allozyme variation was examined in seven species and four varieties of Caulerpa sampled from the Great Barrier Reef (GBR) region, Australia. Differences between species were greater than those between populations of the same taxon sampled from different geographical locations, and typically included fixed gene differences (no alleles found in one taxon shared by the other taxon) at two or more loci. Three varieties of C. racemosa, vars imbricata, laetevirens, and racemosa, and a peltate morph of C. racemosa were as strongly distinguished genetically as the six other species examined: C. cupressoides, C. lentillifera, C. peltata, C. serrulata, C. sertularioides, and C. taxifolia. Cluster analysis did not place all of the C. racemosa varieties together and linked them with other species, but cladistic analyses showed the allozyme data gave little useful phylogenetic information. Eight of 13 plants identified initially as C. serrulata were distinguished at several loci, indicating the presence of an undetermined cryptic taxon. Population genetic analysis of polymorphism, which occurred in some taxa, demonstrated strong spatial differentiation among populations of C. cupressoides, C. racemosa vars laetevirens and racemosa, C. serrulata, and C. taxifolia and significant but variable degrees of clonality and/or inbreeding within these populations. Allozymes proved to be a useful tool for defining species boundaries and investigating population structure in Caulerpa, but not for determining phylogenetic relationships within the genus.     

BIOCHEMICAL PHENOTYPIC AND GENETIC STUDIES OF TWO INTRODUCED FIRE ANTS AND THEIR HYBRID (HYMENOPTERA: FORMICIDAE)

Two introduced fire ants, Solenopsis invicta and S. richteri, and their hybrid were studied using phenotypic markers from gas chromatographic analysis of hydrocarbons and venom alkaloids, as well as genetic markers from enzyme electrophoresis. Both methods show that extensive gene introgression is occurring over a distance of at least 120 km at the contact zone between the two forms in eastern Mississippi. Genetic analyses suggest that the hybrid population does not depart dramatically from panmixia. Also, recombinant genotypes predominate in the hybrid zone, indicating that F₁ hybrids are viable. Allele frequency clines through the hybrid zone are apparent for four polymorphic loci. Data sets generated by the chromatographic and electrophoretic methods are highly concordant in that they differentiate completely between the two forms and agree in designating colonies from the contact zone as hybrid or parental in a high proportion (90%) of cases. The two methods can serve as complementary tools for studying closely related but genetically distinct populations in this, and perhaps other, groups of insects.     

POPULATION GENETICS OF EUROPEAN ANODONTINAE (BIVALVIA: UNIONIDAE)

Enzyme electrophoresis was used to study population geneticsand molecular differentiation of European Anodontmae. The existenceof two genera (Anodonta Lamarck 1799 and Pseudanodonta Bour-guignat1876) is supported by the number of diagnostic loa (4) and Net'sD > 0.463 in all cases. In western and central Europe thereare two species of Anodonta, A. anatina (Linnaeus 1758) andA cygnea (Linnaeus 1758) while two other taxa of still uncertainrank were identified in the Mediterranean area. An estimatedmedium level of gene flow and pronounced genetic differentiationbetween-the taxa support this view. Data on genetic distancessuggest that the diversification of European Anodontinae tookplace in the middle-late Pleistocene (Received 15 August 1995; accepted 5 February 1996)     

COMPARATIVE BIOCHEMICAL GENETICS OF THREE FIRE ANT SPECIES IN NORTH AMERICA,WITH SPECIAL REFERENCE TO THE TWO SOCIAL FORMS OF SOLENOPSIS INVICTA (HYMENOPTERA: FORMICIDAE)

An electrophoretic study of the genetics of three fire ant species in North America was undertaken with the primary objective of further clarifying the genetic relationship between two social forms of Solenopsis invicta. Such social forms are common in many groups of ants and may, in some cases, represent significant intermediate stages in the speciation process. The monogyne and polygyne forms of S. invicta, while differing in a number of important biological traits, are genetically indistinguishable, in contrast to the substantial genetic differentiation observed between S. invicta and a second, closely related, introduced species, S. richteri. The native fire ant, S. geminata, is genetically the most distinct of the three species studied, in accord with its taxonomic placement in a different species complex. Hypotheses concerning the derivation of the polygyne form of S. invicta from the monogyne form which invoke their long-term reproductive isolation in South America and separate introductions to North America appear unfounded. Although S. invicta and S. richteri are known to hybridize in North America, our study provided no evidence of gene introgression between S. invicta and the native species, S. geminata, in areas where our samples were collected. Analyses of population structure in S. invicta failed to reveal significant differentiation of populations or local inbreeding. Levels of genetic diversity in the three species studied, although not significantly different, were in the order predicted from knowledge of the population biology and recent history of the taxa, with S. richteri exhibiting the least diversity, S. geminata the greatest, and S. invicta having an intermediate level.     

华南地区黒眶蟾蜍的遗传变异和地理分化

黒眶蟾蜍Bufo melanostictus(Anura,Bufonidae)是亚洲常见的蟾蜍,广泛分布于中国华南地区。由于华南地区分布着众多的大陆架岛屿及其地貌的复杂性与多样性,因而不同地区的黑眶蟾蜍种群可能存在地理上的遗传变异。本文首次采用DNA序列分析方法,检测了采自我国华南6个省市地区(福建、广东、广西、海南、香港、台湾),包括4个主要大陆架岛屿(海南岛、大屿山、南澳岛、台湾岛)的12个黑眶蟾蜍种群共84个个体,获得mtDNA控制区序列长956bp的片段,共有75个变异位点(26.3%为单个多态位点,73.7%为简约信息位点),12个插入/缺失。所获得的44个单倍型中有5个为种群间共享的单倍型。华南地区黒眶蟾蜍较高的的遗传多样性(单倍型多样性h=0.977)不但表现为海岛种群内普遍具有较高的遗传变异,而且遗传分化指数(FST)、基因流(Nm)、Amova和Samova等分析均表明种群之间已经发生了明显的遗传分化。从Amova分析和分子系统发育分析结果来看,华南地区分布于大陆与分布于海岛的种群之间并未发生明显的遗传分化,说明由陆缘浅海造成的阻隔作用(isolation by barrier)并不能很好地解释华南地区黑眶蟾蜍种群之间遗传分化的原因。遗传距离与地理距离的低度相关(Mantel测试R=0.192,P<0.001)说明华南地区黑眶蟾蜍的种群分化並不完全符合距离决定分化(isolation by distance)的假说。Samova的结果表明华南沿海大陆东部的3个种群(广东汕头、福建莆田和东山)与其它地区9个种群之间的变异最大(FCT=0.35097),因此,推测黑眶蟾蜍这2个地理区域组之间应该存在着其它地理隔离屏障,对两地黑眶蟾蜍的迁移有一定的阻隔作用,产生此隔离效应的天然地理屏障可能为莲花山脉。黑眶蟾蜍种群在历史上曾发生多次局部扩张,时间大约在距今0.025MYA左右,这与最后一次冰期结束的时间相吻合,而位于我国华南大陆周边的4个主要大陆架岛屿(海南岛、大屿山、南澳岛、台湾岛)可能是华南地区黒眶蟾蜍在第四纪冰期的"避难所"。南澳岛种群所存在的特殊单倍型验证了这一岛屿避难所的存在。本研究揭示的地理种群之间的遗传变异和分化,对进一步了解华南地区乃至亚洲的黒眶蟾蜍的生物地理关系有重要意义。     

POPULATION GENETICS OF INTRAGAMETOPHYTIC SELFING

Intragametophytic selfing is a mode of reproduction occurring in homosporous ferns where two gametes from the same haploid gametophyte form a completely homozygous sporophyte. The inbreeding equilibrium is derived for a population with partial intragametophytic selfing, selfing, and outcrossing. Procedures for directly estimating the extent of intragametophytic selfing and selfing using parent-offspring data are given. The conditions for a stable polymorphism from a heterozygous-advantage fitness model are more restrictive for partial intragametophytic selfing than for selfing. The rate of decay of gametic disequilibrium is slower for partial intragametophytic selfing than for selfing. Based on these findings, one would predict that plants with intragametophytic selfing would have less polymorphism for loci with a heterozygous advantage and more gametic disequilibrium between neutral loci than is expected for populations with an equivalent amount of selfing. Data from several studies are consistent with these predictions.     

MOLECULAR SYSTEMATICS OF CERAMIUM AND CENTROCERAS (CERAMIACEAE,RHODOPHYTA) FROM BRAZIL1

Morphological investigations identified 11 Ceramium Roth species, of the 18 previously reported from Brazil. Phylogenetic analyses of sequences of the chloroplast‐encoded rbcL gene confirmed the presence of seven of these species. Three other species are reported from Brazil for the first time. Ceramium affine Setchell & Gardner and C. filicula Harvey ex Womersley were previously known only from the Pacific Ocean (Mexico and Australia, respectively). A new species, C. fujianum Barros‐Barreto et Maggs sp. nov., is described here. Its general habit is similar to that of C. strictum sensu Harvey from Europe but it has one less periaxial cell than C. strictum; its cortical filament arrangement is closest to C. deslongchampsii Chauvin ex Duby, also from Europe, but whorled tetrasporangia partially covered by cortical cells differ strikingly from the naked protruding tetrasporangia of C. deslongchampsii. Ceramium species in which each periaxial cell cuts off transversely only a single basipetal cell formed a robust clade. The genus Ceramium as represented in Brazil is not monophyletic with respect to Centroceras Kützing and Corallophila Weber‐van Bosse; Ceramium nitens, which has axial cells completely covered by rounded cortical cells formed by acropetal and basipetal filaments, did not group with any Ceramium clade but was weakly allied to a species of Corallophila. All three Brazilian Centroceras sequences were attributed to a single species, C. clavulatum.     

CO-OCCURRENCE OF CARRAGEENANS AND AGAROIDS IN GYMNOGONGRUS TORULOSUS (GIGARTINALES, PHYLLOPHORACEAE) FROM ARGENTINA

The red seaweeds, Gigartina skottbetgii and Sarcothalia crispata , have commercial value as raw material for the industrial production of phycocolloids (carrageenans) in Argentina. The third alga with potencial possibilities for the carrageenan production is Gymnogongrus torulosus. Herein, we report the study of the polysaccharide system present in Gymnogongrus torulosus , which contribute to the estimation of the importance of this algae in the seaweed industry. Analysis of the hot water-soluble extract (C1), by FT-IR, methylation and ¹³C NMR, showed mainly the presence of iota/kappa carrageenan hybrid (molar ratio ∼ 2:1). The soluble fractions obtained after KCl fractionation (F3, 16.1 % of C1) and soluble after alkaline treatment and KCl fractionation (F3T3, 34.6% of F3T) gave negative optical rotations (−15.5 and −55.4, respectively), considerably lower than those reported for kappa/iota carrageenans (from 56.1 to 66.5). These fractions (F3 and F3T3) have significant quantities of L-galactose (11.1% and 29.8%) and L-3,6-anhydrogalactose (19.2% and 4.3%). The direct relationship between the optical rotation and the percentage of L-galactose indicated that its structural influence is similar in all the fractions. The results suggest that Gymnogongrus torulosus biosynthesizes a polysaccharide system with co-occurrence of carrageenans and agaroids in the same thallus.     

POPULATION GENETICS OF SKELETONEMA COSTATUM (BACILLARIOPHYCEAE) IN NARRAGANSETT BAY1

During a two year period 457 clones of the diatom Skeletonema costatum were isolated prior to and during the summer-fall and winter-spring blooms of this species in Narragansett Bay, R.I. Their allozyme banding patterns were examined for 5 enzyme loci. Genotypic frequencies indicated that the winter bloom populations were genetically different from the prevalent summer bloom populations of the same species. Genetic differences between seasonal blooms are as great as those found between species of terrestrial organisms, but are not accompanied by morphological variation. Although blooms have distinct prevalent forms, they are not genetically homogeneous. No single clone is ever representative of all populations of S. costatum. The dynamics of these allochronic populations appear to be governed by a form of cyclic natural selection, and are probably a regular feature of the cycles of abundance of this species in this area. These results cast doubt on some of the assumptions often made in the “autecological approach” to phytoplankton ecology. This study comprises the first quantitative examination of the population genetics of a microalga.     

POPULATION GENETICS AND COLONY STRUCTURE OF THE ARGENTINE ANT (LINEPITHEMA HUMILE) IN ITS NATIVE AND INTRODUCED RANGES

Abstract.— Introduced species often possess low levels of genetic diversity relative to source populations as a consequence of the small population sizes associated with founder events. Additionally, native and introduced populations of the same species can possess divergent genetic structuring at both large and small geographic scales. Thus, genetic systems that have evolved in the context of high diversity may function quite differently in genetically homogeneous introduced populations. Here we conduct a genetic analysis of native and introduced populations of the Argentine ant (Linepithema humile) in which we show that the population‐level changes that have occurred during introduction have produced marked changes in the social structure of this species. Native populations of the Argentine ant are characterized by a pattern of genetic isolation by distance, whereas this pattern is absent in introduced populations. These differences appear to arise both from the effects of recent range expansion in the introduced range as well as from differences in gene flow within each range. Relatedness within nests and colonies is lower in the introduced range than in the native range as a consequence of the widespread genetic similarity that typifies introduced populations. In contrast, nestmates and colony‐mates in the native range are more closely related, and local genetic differentiation is evident. Our results shed light on the problem posed for kin selection theory by the low levels of relatedness that are characteristic of many unicolonial species and suggest that the loss of genetic variation may be a common mechanism for the transition to a unicolonial colony structure.     

POPULATION BIOLOGY OF BONAMIA GRANDIFLORA (CONVOLVULACEAE): EFFECTS OF FIRE ON PLANT AND SEED BANK DYNAMICS

The effects of disturbance on reproduction and plant and seed bank dynamics in the perennial herb Bonamia grandiflora were studied by comparing populations in recently burned, mechanically disturbed, and undisturbed habitats in central Florida over a 3-year period. Plant densities, seed production, and the occurrence of herbivory and predispersal seed predation varied considerably between sites and between years, with recently disturbed sites supporting the densest and most dynamic populations. Death of established plants was rare in all sites. In each site, the soil seed bank was several-fold larger than single season seed rains suggesting that B. grandiflora seeds are long-lived and accumulate in the soil. There was no evidence that postdispersal predation or pathogens have any significant influence on the seed bank dynamics. Fire resulted in large increases in stem densities due to both increased clonal stem production and new genet recruitment from seed. Burning also caused significant increases in the percentage of flowers producing seed and the numbers of capsules and seeds per plant. The seed rain was ten to thirty times greater in the burned site relative to adjacent unburned site during the 3 years after burning. However, additions to the seed bank from the postfire seed rain were balanced by equivalent losses due primarily to seed mortality during fire, and to a much lesser extent due to germination and new genet establishment. As a result, the subsequent densities of seeds stored in the soil in these two sites were similar, indicating that fire results in a significant turnover in the seed bank population but no immediate change in its size. These effects on seed bank dynamics, in addition to new genet recruitment, suggest that periodic fires may play an important role in the maintenance of genetic variability as well as the size of these populations.     

SYSTEMATICS AND EVOLUTION OF ELEUSINE CORACANA (GRAMINEAE)

Finger millet (Eleusine coracana (L.) Gaertn. subsp. coracana) is cultivated in eastern and southern Africa and in southern Asia. The closest wild relative of finger millet is E. coracana subsp. africana (Kennedy-O'Byrne) Hilu & de Wet. Wild finger millet (subsp. africana) is native to Africa but was introduced as a weed to the warmer parts of Asia and America. Derivatives of hybrids between subsp. coracana and subsp. africana are companion weeds of the crop in Africa. Cultivated finger millets are divided into five races on the basis of inflorescence morphology. Race coracana is widely distributed across the range of finger millet cultivation. It is present in the archaeological record of early African agriculture that may date back 5,000 years. Racial evolution took place in Africa. Races vulgaris, elongata, plana, and compacta evolved from race coracana, and were introduced into India some 3,000 years ago. Little independent racial evolution took place in India.