THE RELATIVE IMPORTANCE OF HISTORICAL EVENTS AND GENE FLOW ON THE POPULATION STRUCTURE OF A MEDITERRANEAN RAGWORT,SENECIO GALLICUS (ASTERACEAE)

Comparisons of cytoplasmic and nuclear diversity within and among natural plant populations have the potential to distinguish the relative influences of seed and pollen dispersal on contemporary gene flow, or alternatively, may permit inferences of the colonization history of a species via seed. We examined patterns of cpDNA and allozyme variation in Senecio gallicus, a diploid, annual plant that occurs in both coastal and ruderal inland areas of the Iberian Peninsula and southern France. The species appears to have a strong propensity for long-distance seed dispersal. Five cpDNA haplotypes were found by RFLP analysis among a sample of 111 individuals derived from 11 populations. Differences in haplotype frequencies across populations were most evident with respect to a dramatic increase in the frequency of a derived haplotype from coastal to inland localities. The level of cpDNA differentiation among populations within the inland group (θ₀ = 0.07) was significantly less than that seen within the coastal group (θ₀ = 0.41). In contrast, for allozymes, no significant difference in population structure was evident between collections from coastal and inland habitats. At the rangewide geographic scale, there was only a very weak association between inferred levels of gene flow and geographic distance for cpDNA, and no such association was found for allozymes. It appears that while seed movement in the species might be sufficiently great to disturb the pattern of isolation by distance for cpDNA, it cannot fully account for the nearly randomized spatial structure at polymorphic allozyme loci. It is suggested that isolation of populations in Atlantic-Mediterranean coastal refugia during previous glacial maxima, and the effects of subsequent colonization events in inland areas, have had an important effect on molding the present genetic structure of the species.     

RECONSTRUCTING ORIGINS OF LOSS OF SELF‐INCOMPATIBILITY AND SELFING IN NORTH AMERICAN ARABIDOPSIS LYRATA: A POPULATION GENETIC CONTEXT

Theoretical and empirical comparisons of molecular diversity in selfing and outcrossing plants have primarily focused on long‐term consequences of differences in mating system (between species). However, improving our understanding of the causes of mating system evolution requires ecological and genetic studies of the early stages of mating system transition. Here, we examine nuclear and chloroplast DNA sequences and microsatellite variation in a large sample of populations of Arabidopsis lyrata from the Great Lakes region of Eastern North American that show intra‐ and interpopulation variation in the degree of self‐incompatibility and realized outcrossing rates. Populations show strong geographic clustering irrespective of mating system, suggesting that selfing either evolved multiple times or has spread to multiple genetic backgrounds. Diversity is reduced in selfing populations, but not to the extent of the severe loss of variation expected if selfing evolved due to selection for reproductive assurance in connection with strong founder events. The spread of self‐compatibility in this region may have been favored as colonization bottlenecks following glaciation or migration from Europe reduced standing levels of inbreeding depression. However, our results do not suggest a single transition to selfing in this system, as has been suggested for some other species in the Brassicaceae.     

DOES MATE LIMITATION IN SELF‐INCOMPATIBLE SPECIES PROMOTE THE EVOLUTION OF SELFING? THE CASE OF LEAVENWORTHIA ALABAMICA

Genetic diversity at the S‐locus controlling self‐incompatibility (SI) is often high because of negative frequency‐dependent selection. In species with highly patchy spatial distributions, genetic drift can overwhelm balancing selection and cause stochastic loss of S‐alleles. Natural selection may favor the breakdown of SI in populations with few S‐alleles because low S‐allele diversity constrains the seed production of self‐incompatible plants. We estimated S‐allele diversity, effective population sizes, and migration rates in Leavenworthia alabamica, a self‐incompatible mustard species restricted to discrete habitat patches in rocky glades. Patterns of polymorphism were investigated at the S‐locus and 15 neutral microsatellites in three large and three small populations with 100‐fold variation in glade size. Populations on larger glades maintained more S‐alleles, but all populations were estimated to harbor at least 20 S‐alleles, and mate availabilities typically exceeded 0.80, which is consistent with little mate limitation in nature. Estimates of the effective size (N_e) in each population ranged from 600 to 1600, and estimated rates of migration (m) ranged from 3 × 10⁻⁴ to nearly 1 × 10⁻³. According to theoretical models, there is limited opportunity for genetic drift to reduce S‐allele diversity in populations with these attributes. Although pollinators or resources limit seed production in small glades, limited S‐allele diversity does not appear to be a factor promoting the incipient breakdown of SI in populations of this species that were studied.     

DIVERSITY IN THE GENUS SKELETONEMA (BACILLARIOPHYCEAE). II. AN ASSESSMENT OF THE TAXONOMY OF S. COSTATUM‐LIKE SPECIES WITH THE DESCRIPTION OF FOUR NEW SPECIES1

The morphology of strains of Skeletonema Greville emend Sarno et Zingone was examined in LM, TEM, and SEM and compared with sequence data from nuclear small subunit rDNA and partial large subunit rDNA. Eight distinct entities were identified, of which four were known: S. menzelii Guillard, Carpenter et Reimann; S. pseudocostatum Medlin emend. Zingone et Sarno; S. subsalsum (Cleve) Bethge; and S. tropicum Cleve. The other four species were new: S. dohrnii Sarno et Kooistra sp. nov., S. grethae Zingone et Sarno sp. nov., S. japonicum Zingone et Sarno sp. nov., and S. marinoi Sarno et Zingone sp. nov. Skeletonema species fell into four morphologically distinct groups corresponding to four lineages in the small subunit and large subunit trees. Lineage I included S. pseudocostatum, S. tropicum, S. grethae, and S. japonicum. All have external processes of the fultoportulae with narrow tips that connect with those of sibling cells via fork‐, knot‐, or knuckle‐ like junctions. Lineage II included only the solitary species S. menzelii. Lineage III comprised S. dohrnii and S. marinoi. This latter pair have flattened and flared extremities of the processes of the fultoportulae, which interdigitate with those of contiguous valves without forming knots or knuckles. Lineage IV only contained the brackish water species S. subsalsum. Some species also differ in their distribution and seasonal occurrence. These findings challenge the concept of S. costatum as a single cosmopolitan and opportunistic species and calls for reinterpretation of the vast body of research data based on this species.     

STRONG INBREEDING DEPRESSION IN TWO SCANDINAVIAN POPULATIONS OF THE SELF‐INCOMPATIBLE PERENNIAL HERB ARABIDOPSIS LYRATA

Inbreeding depression is a key factor influencing mating system evolution in plants, but current understanding of its relationship with selfing rate is limited by a sampling bias with few estimates for self‐incompatible species. We quantified inbreeding depression (δ) over two growing seasons in two populations of the self‐incompatible perennial herb Arabidopsis lyrata ssp. petraea in Scandinavia. Inbreeding depression was strong and of similar magnitude in both populations. Inbreeding depression for overall fitness across two seasons (the product of number of seeds, offspring viability, and offspring biomass) was 81% and 78% in the two populations. Chlorophyll deficiency accounted for 81% of seedling mortality in the selfing treatment, and was not observed among offspring resulting from outcrossing. The strong reduction in both early viability and late quantitative traits suggests that inbreeding depression is due to deleterious alleles of both large and small effect, and that both populations experience strong selection against the loss of self‐incompatibility. A review of available estimates suggested that inbreeding depression tends to be stronger in self‐incompatible than in self‐compatible highly outcrossing species, implying that undersampling of self‐incompatible taxa may bias estimates of the relationship between mating system and inbreeding depression.     

TRANSMISSION ADVANTAGE FAVORS SELFING ALLELE IN EXPERIMENTAL POPULATIONS OF SELF‐INCOMPATIBLE WITHERINGIA SOLANACEA (SOLANACEAE)

The evolution of self‐fertilization is one of the most commonly traversed transitions in flowering plants, with profound implications for population genetic structure and evolutionary potential. We investigated factors influencing this transition using Witheringia solanacea, a predominantly self‐incompatible (SI) species within which self‐compatible (SC) genotypes have been identified. We showed that self‐compatibility in this species segregates with variation at the S‐locus as inherited by plants in F1 and F2 generations. To examine reproductive assurance and the transmission advantage of selfing, we placed SC and SI genotypes in genetically replicated gardens and monitored male and female reproductive success, as well as selfing rates of SC plants. Self‐compatibility did not lead to increased fruit or seed set, even under conditions of pollinator scarcity, and the realized selfing rate of SC plants was less than 10%. SC plants had higher fruit abortion rates, consistent with previous evidence showing strong inbreeding depression at the embryonic stage. Although the selfing allele did not provide reproductive assurance under observed conditions, it also did not cause pollen discounting, so the transmission advantage of selfing should promote its spread. Given observed numbers of S‐alleles and selfing rates, self‐compatibility should spread even under conditions of exceedingly high initial inbreeding depression.     

AN INTEGRATIVE TEST OF THE DEAD‐END HYPOTHESIS OF SELFING EVOLUTION IN TRITICEAE (POACEAE)

Self‐fertilization is hypothesized to be an evolutionary dead end because reversion to outcrossing can rarely happen, and selfing lineages are thought to rapidly become extinct because of limited potential for adaptation and/or accumulation of deleterious mutations. We tested these two assumptions by combining morphological characters and molecular‐evolution analyses in a tribe of hermaphroditic grasses (Triticeae). First, we determined the mating system of the 19 studied species. Then, we sequenced 27 protein‐coding loci and compared base composition and substitution patterns between selfers and outcrossers. We found that the evolution of the mating system is best described by a model including outcrossing‐to‐selfing transitions only. At the molecular level, we showed that regions of low recombination exhibit signatures of relaxed selection. However, we did not detect any evidence of accumulation of nonsynonymous substitutions in selfers compared to outcrossers. Additionally, we tested for the potential deleterious effects of GC‐biased gene conversion in outcrossing species. We found that recombination and not the mating system affected substitution patterns and base composition. We suggest that, in Triticeae, although recombination patterns have remained stable, selfing lineages are of recent origin and inbreeding may have persisted for insufficient time for differences between the two mating systems to evolve.     

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.     

北京自然博物馆馆藏膜壳蟹科蟹类及三新种记述

本报道北京自然博物馆馆藏膜壳蟹Ｈｙｍｅｎｏｓｏｍａｔｉｄａｅ共５种,其中篦额滨蟹Ｈａｌｉｃａｒｃｉｎｕｓ ｍｅｓｓｏｒ Ｓｔｉｍｐｓｏｎ与中华拟薄板蟹Ｅｌａｍｅｎｏｐｓｉｓ ｓｉｎｅｎｓｉｓ（Ｓｈｅｎ）曾发现于中国东海,这次标本检查中发现中华拟薄板蟹在广东沿海也有分布。其它三种均为新种,分别定名为长指薄板蟹Ｅｋａｍｅｎａ ｌｏｎｇｉｄａｃｔｙｌｉｓ ｓｐ．ｎｏｖ．,长足滨蟹Ｈａｌｉｃａｒｃｉｎｕ     

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.     

PANORPIDAE (MECOPTERA) IN XIZANG, CHINA, WITH DESCRIPTION OF THREE NEW SPECIES OF THE GENUS NEOPANORPA

Abstract  Three new species of the genus Neopanorpa Weele are described and illustrated from Xizang in China. The previously reported three species from Xizang, Panorpa guttata Navas, P. davidi Navas, and P. stigmalis Navas, are verified to distribute in Sichuan Province, instead of in Xizang. The type specimens are deposited in Northwest Agricultural University and China Agricultural University separately. A key to the Tibetan species of Neopanorpa is provided.     

西藏新蝎蛉属昆虫三新种记述(长翅目:蝎岭科)(英文)

本文记述中国西藏自治区的新蝎蛉属 Ｎｅｏｐａｎｏｒｐａ Ｗｅｅｌｅ昆虫３新种：西藏新蝎岭 Ｎｅｏｐａｎｏｒｐａｔｉｂｅｔｅｎｓｉｓ Ｈｕａ ｅｔ Ｃｈｏｕ, ｓｐ． ｎｏｖ．（正模,西藏通麦, ２０５０ ｍ）,胡氏新蝎蛉 Ｎｅｏｐａｎｏｒｐａ ｈｕｓｈｅｎｇｃｈａｎｇｉＨｕａ ｅｔ Ｃｈｏｕ, ｓｐ． ｎｏｖ．（正模,西藏樟木口岸）,以及李氏新蝎蛉 Ｎｅｏｐａｎｏｒｐａ ｌｉｆａｓｈｅｎｇｉ　ｈｕａ　ｅｔ　Ｃｈｏｕ,ｓｐ． ｎｏｖ．（正模：,西藏易贡, ２３００ ｍ）。简述了西藏长翅目的分类历史和现状,证实过去记载所谓的三种西藏蝎蛉（模式产地均为马边）,即Ｐａｎｏｒｐａ　ｇｕｔｔａｔａ　Ｎａｖａｓ,Ｐ．ｄａｖｉｄｉ　Ｎａｖａｓ,和Ｐ．ｓｔｉｇｍａｌｉｓ　Ｎａｖａｓ,实际上均为四川省种类。新种模式标本分别保存在西北农业大学昆虫博物馆和中国农业大学昆虫标本室。     

中国南海北部北部湾水母类调查及三新种记述(刺胞动物门)(英文)

材料系于2007年(1,4,7,10月)、2008年(1,7月)和2009年(1月)在北部湾水域采集的,调查海区共设52站,共采集364份样品。经分析鉴定出67种水母,其中有3新种和中国2新纪录,主辐特古水母Tregouboiva perradialis Xu,Huang et Du,sp. nov.,泡真囊水母Euphysora vacuola Xu,Huang et Guo,sp. nov.,波腺侧丝水母Helgicirrha sinuatus Xu,Huang et Du,sp. nov.,艾格帝纹水母Timoides agassizi Bigelow,1904和大腺美螅水母Clytia macrogonia Bouillon,1984。此外,还报道了20种水母为北部湾新纪录。模式标本保存在中国水产科学研究院南海水产研究所。主辐特古水母,新种Tregoubovia perradialis Xu,Huang et Du,sp. nov.鉴别特征伞近钟形,外伞有16条双层向心肋; 垂管很大,近方形,约为内伞腔深度4/5;口有4个延长成触手状的口唇,具环状刺胞,无末端刺胞球;隔膜短;4个大的椭圆形生殖腺,几乎覆盖整个垂管主辐位;伞缘无缘触手或缘基球;无眼点。正模(BG 001),北部湾S30站(17°30’N,107°30’E;水深70m),2008-07-06,梁新采(南海水产研究所)。词源:新种种名源自拉丁词perradialis,意为生殖腺位于垂管主辐位。泡真囊水母,新种Euphysora vacuola Xu,Huang et Guo,sp. nov.鉴别特征伞有钝圆形顶突;垂管长椭圆形,约有1/2长度超出缘膜口外,垂管基部很宽,覆盖着浓密泡状细胞组织;4条辐管上部与扩大的垂管基部连接;生殖腺围绕着垂管壁;主触手很长,触手基球很大,呈卵圆形至球形,触手上具30～40个成排的背轴刺胞球,无末端膨大刺胞球,另3个触手基球退化,很小,同样大小,无丝状触手,每个基球具外胚层背距。正模(BG 006),北部湾C15站(20°N,109°E;水深44m),2007-07-25,梁新采(南海水产研究所)。副模(TB001),台湾海峡102站(23°40’N,118°44’E;水深54m),1988-06-29,黄加祺采(厦门大学海洋学系)。词源:新种种名源自拉丁词vacuola,意为该种在垂管基部覆盖浓密泡状细胞组织。波腺侧丝水母,新种 Helgicirrha sinuatus Xu,Huang et Du,sp.nov.鉴别特征伞略扁于半球形;胃柄长,约有1/2超出缘膜口外,垂管短小,口有4个短的略为向上弯曲折叠的口唇;生殖腺深波形,位于辐管远端1/3处; 16 ～ 24 条缘触手,每条触手具2对侧丝,每2条触手间有3～5个缘疣,具1对侧丝和3～4个平衡囊,每个平衡囊有2～4个平衡石;所有触手和缘疣基部均有向轴排泄乳突。正模(BG 007),副模(BG 008-009),北部湾S18站( 18°45’N,106°45’E;水深53m),2007-04-15,梁新采(南海水产研究所)。词源:新种种名源自拉丁词sinuatus,意为该种生殖腺深波状。     

EFFECTS OF SOCIAL AND EXTRA‐PAIR MATING ON SEXUAL SELECTION IN BLUE TITS (CYANISTES CAERULEUS)

The contribution of extra‐pair paternity (EPP) to sexual selection has received considerable attention, particularly in socially monogamous species. However, the importance of EPP remains difficult to assess quantitatively, especially when many extra‐pair young have unknown sires. Here, we combine measurements of the opportunity for selection (I), the opportunity for sexual selection (I_S), and the strength of selection on mating success (Bateman gradient, β_SS) with a novel simulation of random mating tailored to the specific mating system of the blue tit (Cyanistes caeruleus). In a population where social polygyny and EPP are common, the opportunity for sexual selection was significantly stronger and Bateman gradients significantly steeper for resident males than for females. In general, success with the social mate(s) contributed most to variation in male reproductive success. Effects of EPP were small, but significantly higher than expected under random mating. We used sibship analysis to estimate the number of unknown sires in our population. Under the assumption that the unknown sires are nonbreeding males, EPP reduced the variance in and the strength of selection on mating success, a possibility that hitherto has not been considered.     

OVERCOMING STATISTICAL BIAS TO ESTIMATE GENETIC MATING SYSTEMS IN OPEN POPULATIONS: A COMPARISON OF BATEMAN'S PRINCIPLES BETWEEN THE SEXES IN A SEX‐ROLE‐REVERSED PIPEFISH

The genetic mating system is a key component of the sexual selection process, yet methods for the quantification of mating systems remain controversial. One approach involves metrics derived from Bateman's principles, which are based on variances in mating and reproductive success and the relationship between them. However, these measures are extremely difficult to measure for both sexes in open populations, because missing data can result in biased estimates. Here, we develop a novel approach for the estimation of mating system metrics based on Bateman's principles and apply it to a microsatellite‐based parentage analysis of a natural population of the dusky pipefish, Syngnathus floridae. Our results show that both male and female dusky pipefish have significantly positive Bateman gradients. However, females exhibit larger values of the opportunity for sexual selection and the opportunity for selection compared to males. These differences translate into a maximum intensity of sexual selection () for females three times larger than that for males. Overall, this study identifies a critical source of bias that affects studies of mating systems in open populations, presents a novel method for overcoming this bias, and applies this method for the first time in a sex‐role‐reversed pipefish.     

OOGAMOUS REPRODUCTION,WITH TWO‐STEP AUXOSPORULATION,IN THE CENTRIC DIATOM THALASSIOSIRA PUNCTIGERA (BACILLARIOPHYTA)1

Thalassiosira species are common components of marine planktonic communities worldwide and are used intensively as model experimental organisms. However, data on life cycles and sexuality within the genus are fragmentary. A clone of the cosmopolitan marine diatom Thalassiosira punctigera Cleve emend. Hasle was isolated from the North Sea and oogamous sexual reproduction was observed in culture. Cells approximately 45 μm and smaller became sexualized. Oogonia were produced preferentially and spermatogenesis was infrequent. Unfertilized oogonia always aborted and their development was apparently arrested at prophase of meiosis I. Further progression through meiosis and auxospore formation occurred only after a sperm had penetrated into the oocyte. Many cells of the new large‐celled generation (approximately 90–120 μm in size) immediately became sexualized again but only oogonia were produced. A few of the large oogonia became auxospores and produced initial cells 132–153 μm in diameter. The second step of auxosporulation probably involved fertilization of large‐celled oocytes by the sperm of the small‐celled spermatogonangia that were still present in the culture. An F₁ clone obtained after selfing within the small‐celled auxosporulation size range was investigated. Like the parent clone, the F₁ clone was homothallic but no auxosporulation was observed: spermatogonangia were unable to produce viable sperm, apparently because of inbreeding depression. Aggregation and interaction of oogonia were documented, and may be relevant for understanding the mechanisms of signaling and recognition between sexualized cells and the evolution of sexuality in pennate diatoms.     

DETERMINISM IN THE DIVERSIFICATION OF HISPANIOLAN TRUNK‐GROUND ANOLES (ANOLIS CYBOTES SPECIES COMPLEX)

The evolutionary processes that produce adaptive radiations are enigmatic. They can only be studied after the fact, once a radiation has occurred and been recognized, rather than while the processes are ongoing. One way to connect pattern to process is to study the processes driving divergence today among populations of species that belong to an adaptive radiation, and compare the results to patterns observed at a deeper, macroevolutionary level. We tested whether evolution is a deterministic process with similar outcomes during different stages of the adaptive radiation of Anolis lizards. Using a clade of terrestrial–scansorial lizards in the genus Anolis, we inferred the adaptive basis of spatial variation among contemporary populations and tested whether axes of phenotypic differentiation among them mirror known axes of diversification at deeper levels of the anole radiation. Nonparallel change associated with genetic divergence explains the vast majority of geographic variation. However, we found phenotypic variation to be adaptive as confirmed by convergence in populations occurring in similar habitats in different mountain ranges. Morphological diversification among populations recurs deterministically along two axes of diversification previously identified in the anole radiation, but the characters involved differ from those involved in adaptation at higher levels of anole phylogeny.     

IDENTIFICATION OF THE MINUS MATING‐TYPE SPECIFIC GENE MTD1 FROM GONIUM PECTORALE (VOLVOCALES,CHLOROPHYTA)1

Gonium pectorale O. F. Müll. (Volvocales, Chlorophyta), a colonial 8‐ or 16‐cellular alga, is phylogenetically important as an intermediate form between isogametic unicellular Chlamydomonas and oogamous Volvox. We identified the mating‐type specific gene GpMTD1, from G. pectorale, the first homologue of Chlamydomonas reinhardtii MTD1 (CrMTD1). The GpMTD1 gene was found to be present only in the minus mating‐type locus and was expressed specifically in the gametic phase as is the case for CrMTD1, suggested to participate in development of the minus gametes. This gene is useful as a probe in analyzing the bacterial artificial chromosome (BAC) library for resolving genomic structures of the mating‐type loci in isogamous and oogamous colonial volvocaleans.     

SEQUENCES OF THE RRN18 GENES OF CHLAMYDOMONAS HUMICOLA AND C. DYSOSMOS ARE IDENTICAL,IN AGREEMENT WITH THEIR COMBINATION IN THE SPECIES C. APPLANATA (CHLOROPHYTA)1

The nuclear Rrn18 gene coding for small-subunit ribosomal RNA was amplified from Chlamydomonas humicola and C. dysosmos. The sequences were identical, in agreement with the combination of these two species under the name C. applanata on morphological and physiological grounds by Ettl and Schlösser (1992).