Population regulation in Bromus rubens and B. mollis: Life cycle components and competition

Summary A series of Bromus rubens and B. mollis populations were sampled in the coastal range and northern part of the Central Valley of California in order to study their population ecology in demographic terms. Quantitative estimates were obtained on plants collected directly in nature, and their progenies in controlled environments with randomized block design in the greenhouse.Two parameters of population growth — the intrinsic rate of increase, r, and the carrying capacity, K-were estimated by using the logistic model (r=ln R and K=equilibrium population size). It was found that B. mollis is a relatively K-type species, while B. rubens is a relatively r-type species.The effects of density on competition between individuals in pure and mixed populations of B. mollis and B. rubens were studied. In both species, increasing density induced greater mortality and a striking plastic reduction in the size and reproductive potential of the individuals. Further, B. rubens showed a relatively greater mortality and less plastic response to densities than B. mollis in both pure and mixed stands. Two different types of plasticity were considered: one in response to changing density (d-plasticity); and the other in response to changing enironmental conditions (e-plasticity). High plasticity in one of them need not imply that the other one is high too. B. rubens showed higher e-plasticity, but lower d-plasticity than B. mollis.The relationships between r, K and competitive ability were discussed. Two types of K-strategy were distinguished: one involving greater nonreproductive effort with longer life span, or lowered mortality (Type-I) and the other with density-induced adjustments in body size along with survival in higher numbers (Type-II). Different populations of these two Bromus species showed different values of r and K (Type-II) and different competitive abilities. It was found that higher r was usually accompanied by lower K (Type-II), while higher K (Type-II) was accompanied by lower competitive ability, which in turn is correlated with higher d-plasticity. In general, coexistence was predicted on the basis of estimates derived from the interspecific competition experiments.     

Genetic diversity in Mediterranean diploid and tetraploid Bromus L. (section Bromus Sm.) populations.

The levels of genetic diversity assessed from allozyme data were investigated in 25 populations of Mediterranean Bromus intermedius, B. squarrosus, B. lanceolatus, and B. hordeaceus from Algeria. The geographically restricted diploids B. intermedius and B. squarrosus displayed less genetic diversity (the mean population gene diversity of Nei (Hu) ranged from 0.03 to 0.12) than the widespread tetraploid colonizers B. lanceolatus and B. hordeaceus (Hu = 0.07-0.27). Deviations from Hardy-Weinberg expectations in diploid populations of B. intermedius and B. squarrosus were observed owing to heterozygote excess at several loci and suggested that these self-fertilizing species may have substantial amounts of allogamy. Tetraploid populations of B. lanceolatus and B. hordeaceus were largely homozygous at homologous loci and frequently exhibited intergenomic fixed heterozygosity in accordance with their alloploid origin. Genetic variation at the infraspecific level was mostly distributed within populations in the four species, B. hordeaceus showing the lowest level of interpopulation differentiation (Gst = 0.06) and the highest level of gene flow (Nm = 3.75). Consistent gene flows are in agreement with the strongest intercontinental invasive behaviour of B. hordeaceus. Less differentiation was reported in the literature among later introduced B. hordeaceus populations from England and Australia, indicating reduced differentiation under the process of colonization. Moderate divergence occured among the four taxa, with interspecific genetic identities ranging from 0.87 to 0.93. In spite of substantial genetic similarity, species were clearly differentiated, with each tetraploid being more closely related to a diploid: B. hordeaceus to B. squarrosus and B. lanceolatus to B. intermedius.     

Cryptoporic and isocryptoporic acids from the fungal cultures of Polyporus arcularius and P. ciliatus

In a chemical study of several fungal cultures of Polyporus, a methyl ester of cryptoporic H was isolated from P. ciliatus, together with cryptoporic acid H and 5-hydroxymethylfuran-3-carboxylic acid. Furthermore, two additional compounds, named isocryptoporic acids H and I, were isolated from P. arcularius. These isocryptoporic acids are isomers of the cryptoporic acids with drimenol instead of albicanol as the terpenoid fragment; their structural elucidation was determined by application of spectroscopic methods.     

Maternal behaviour in Richardson's ground squirrel (Spermophilus richardsonii richardsonii): retrieval of young by non-lactating females

Retrieval of young by females which had littered in the previous year and by virgins was investigated. More (five of six) non-parous mothers retrieved than virgins (one of seven). Those animals which did not retrieve attacked the young. Animals which retrieved also exhibited other maternal responses (cleaning, nidification, lactation position). The results suggest that previous parity has a long lasting effect on the response of non-lactating females to young.     

Multivariate analysis of morphological variation among closely related species Bromus japonicus, B. squarrosus and B. arvensis (Poaceae) in comparison with isozyme evidences

Morphological variation and taxonomic continuum of 110 specimens of Bromus arvensis, B. japonicus and B. squarrosus were analysed to assess the morphological variability of these close taxa. The importance of every morphological character was estimated by the GLM procedure. Stepwise discriminant analysis was used in order to find a set of morphological characters that maximises differences among the species. According to this, the most important characters appeared to be the length of anthers, width of lemma and lemma margin angle shape. The most important characters for the determination of Bromus arvensis was the length of anthers and for B. squarrosus width of lemma. According to the UPGMA cluster analysis, canonical discriminant, classificatory discriminant and principal component analyses, all specimens were separated into three moderately distinct groups which corresponded to the three traditional species. The study showed that qualitative characters were the best for the delimitation of the tax a by statistical analyses and demonstrated the incongruity between the pattern of morphological and genetic (allozyme) variation among the three Bromus species.     

Comparative Study of the Ploidy Series Bromus sterilis, B. diandrus and B. rigidus (Poaceae) Based on Chromosome Numbers, Morphology and Isozymes

Abstract: Chromosome numbers, morphological characters and isozymes of seven enzymes were studied to assess relationships between species of the Bromus diandrus-rigidus polyploid complex and the closely related species, B. sterilis. The four different cytotypes detected, 2n = 14, 28, 42 and 56, could be divided into two species: B. sterilis (2n = 14, 28) and B. diandrus (2n = 42, 56) by morphological features and isozymes. The shape of the scar of rachilla segments in the floret proved to be a suitable character for distinguishing the two species, but not the chromosomal races within species. The tetraploid shared homozygous isozyme phenotypes with diploid B. sterilis at all loci, except one, suggesting that it is autopolyploid. No diagnostic isozymes could be found to distinguish between hexa- and octoploid cytotypes in the B. diandrus-rigidus complex.     

Drechslera sp. (Pyrenophora chaetomioides (Speg.)), a Potential Biocontrol Agent for Bromus sterilis and Other Bromus spp.

Infection by a Drechslera sp. (perfect stage, Pyrenophora chaetomioides (Speg.)), isolated from Bromus sterilis , killed B. sterilis , B. commutatus and B. secalinus. B. diandrus and B. hordeaceus were both infected but not killed. Successful infection required a 24-h dew period. Reduction of the dew period to 8 h significantly reduced the infection of all Bromus spp. tested as determined by leaf necrosis. Inoculation with a low inoculum concentration (2 104 conidia/ml) produced little dry weight reduction, but at 2 105 conidia/ml with an 8-h dew period the dry weights of B. commutatus , B. diandrus , B. secalinus and B. sterilis were reduced by 11-25%. Extending the dew period to 24 h resulted in 77% mortality of B. sterilis and 93% mortality of B. commutatus and B. secalinus.     

Chromosomes and evolution of the ground squirrel,Spermophilus richardsonii

Summary Chromosomes were analyzed from two geographically isolated populations of Spermophilus richardsonii. The diploid chromosome number was 36 in S. r. richardonii (Montana population) and 34 in S. r. elegans (Wyoming-Colorado population). The richardsonii Karyotype differed from elegans by the presence of two pairs of acrocentric autosomes whereas the elegans Karyotype lacked acrocentric autosomes and had an extra pair of submetacentrics.A chromosomal polymorphism, produced by centric fusion, probably existed in the more primitive richardsonii population. After ancestral stock of the elegans population became geographically isolated, both populations of S. richardsonii evolved independently and developed different karyotypes derived from the original polymorphism. Although the karyotypes have evolved to a stage found in valid species, the populations may not have been separated long enough to attain reproductive isolation.This investigation was supported by a grant from the National Science Foundation (GB-503).     

Moose soup shigellosis in Alaska.

Following a community gathering held in early September 1991, an outbreak of gastroenteritis occurred in Galena, Alaska. We conducted an epidemiologic investigation to determine the cause of the outbreak. A case of gastroenteritis was defined as diarrhea or at least 2 other symptoms of gastrointestinal illness occurring in a Galena resident within a week of the gathering. Control subjects included asymptomatic residents who either resided with an affected person or were contacted by us during a telephone survey. Of 25 case-patients, 23 had attended the gathering compared with 33 of 58 controls. Among persons who attended the gathering and from whom we obtained a food consumption history, 17 of 19 case-patients and 11 of 22 controls ate moose soup. No other foods served at the gathering were associated with illness. Ten case-patients had culture-confirmed Shigella sonnei. Many pots of moose soup were served each day, and persons attended the gathering and ate moose soup on more than 1 day. Moose soup was prepared in private homes, allowed to cool, and usually served the same day. We identified 5 women who had prepared soup for the gathering and in whose homes at least 1 person had a gastrointestinal illness occur at the time of or shortly before soup preparation. This investigation suggests that eating contaminated moose soup at a community gathering led to an outbreak of shigellosis and highlights the risk of eating improperly prepared or stored foods at public gatherings.     

Serological Relationships of Bromus L. and Boissiera Hochst. ex Steud

Serological techniques have been used to compare the seed albumin and globulin fractions of species of Bromus L. and Boissiera squarrosa (Soland.) Nevski. Compared with other grass genera, Boissiera squarrosa gives a very strong reaction with Bromus antisera, resembling the reactions of Bromus section Bromus species. It is considered that this evidence of serological relationship, together with evident morphological resemblance and the same basic chromosome number, require the transference of the species to the genus Bromus. It is therefore included in that genus under the name Bromus pumilio (Trin.) P. Smith, comb. nov. The significance of reactions with Bromus antisera by seed extracts of species in the tribe Hordeae is discussed.     

Photoregulation of Germination in Freshly-harvested and Dried Seeds of Bromus sterilis L.

Freshly-harvested and dried seeds of Bromus sterilis L. withrespectively 52-54% and less than 10% moisture contents, differedmarkedly in their rates of germination and in their responsesto light. Dried seeds attained full germination in darknessat 15 ?C by 4 d from sowing and were inhibited by the formationof Pfr. In contrast, freshly-harvested seeds required 3-4 weeksto attain maximum germination and were promoted by Pfr. Themodified photoresponse of the seeds was induced only when theseeds were dried in an alternating temperature regime. The resultsare discussed in relation to the importance of desiccation asthe trigger for the transition from the developmental to thegerminative and growth phases of seed maturation of Bromus steriliswhich is well-documented in seeds of other species. Key words: Bromus sterilis, desiccation, light     

Ecological genetics of seed germination regulation in Bromus tectorum L.

Regulation of seed germination phenology is an important aspect of the life history strategy of invading annual plant species. In the obligately selfing winter annual grass Bromus tectorum, seeds are at least conditionally dormant at dispersal in early summer and lose dormancy through dry-afterripening. Patterns of germination response at dispersal vary among populations and sometimes across years within populations. To assess the relative contribution of genotype and maturation environment to this variation, we grew progeny of ten parental lines from each of six contrasting populations in a common greenhouse environment. We then tested the germination responses of recently harvested seeds of the putative full-sib progeny at five incubation temperatures. Significant germination response differences among populations were observed in greenhouse cultivation, and major differences among full-sib families were evident for some populations and traits. Among-population variation accounted for over 90% of the variance in each trait, while within-family variance accounted for 1% or less. Germination responses of greenhouse-grown progeny were positively correlated with the responses of wild-collected seeds, but there was a tendency for lowered dormancy at higher incubation temperatures. This tendency was more marked in populations from cold desert, foothill, and plains habitats, suggesting a genotype-maturation environment interaction. Differences among populations in the amount of among-family variance were more evident at lower incubation temperatures, while among-family variance was more uniformly low at summer incubation temperatures. Populations from predictable extreme environments (subalpine meadow and warm desert margin) showed significantly less variation among families than populations from less predictable cold desert, foothill, and plains environments. Low among-family variance was not specifically associated with small population size or marginality of habitat, as small marginal populations from unpredictable environments showed variance as high as that of large populations. In populations with high among-family variance for germination traits, germination responses tended to be correlated across incubation temperatures, making it possible to characterize families in terms of their general dormancy status. The results indicate that seed germination regulation in this species is probably under strong genetic control, and that habitats with temporally varying selection are occupied by populations that tend to be more polymorphic in terms of their germination response patterns. Received: 19 May 1998 / Accepted: 27 January 1999     

Ecological genetics of seed germination regulation in Bromus tectorum L.

The probability that a seed will germinate depends on factors associated with genotype, maturation environment, post-maturation history, and germination environment. In this study, we examined the interaction among these sets of factors for 18 inbred lines from six populations of Bromus tectorum L., a winter annual grass that is an important weed in the semi-arid western United States. Seeds of this species are at least conditionally dormant at dispersal and become germinable through dry-afterripening under summer conditions. Populations and inbred lines of B. tectorum possess contrasting dormancy patterns. Seeds of each inbred line were produced in a greenhouse under one of three levels of maturation water stress, then subjected to immediate incubation under five incubation regimes or to dry storage at 20°C for 4 weeks, 12 weeks, or 1 year. Dry-stored seeds were subsequently placed in incubation at 20/30°C. Narrow-sense heritability estimates based on parent-offspring regressions for germination percentage of recently harvested seeds at each incubation temperature were high (0.518–0.993). Germination percentage increased with increasing water stress overall, but there were strong interactions with inbred line and incubation temperature. Inbred lines whose seeds were non-dormant over the full range of incubation temperatures when produced at low maturation water stress showed reaction norms characterized by little or no change as a function of increasing stress. For inbred lines whose dormancy status varied with incubation temperature, incubation treatments where seeds exhibited either very low or very high levels of dormancy showed the least change in response to maturation water stress. Inbred lines also varied in their pattern of dormancy loss during storage at 20°C, but maturation water stress had only a minor effect on this pattern. For fully afterripened seeds (1 year in storage at 20°C), inbred line and maturation water stress effects were no longer evident, indicating that differences in genotype and maturation environment function mainly to regulate dormancy and dormancy loss in B. tectorum, rather than to mediate response patterns of non-dormant seeds.     

Factors influencing the numbers of branches and inflorescences of Potamogeton richardsonii (A. Benn.) Rydb.

Potamogeton richardsonii (A. Benn) Rydb., a submerged rooted aquatic plant, is common in small temperate lakes. In some regions of a Minnesota lake, P. richardsonii plants rarely branched and had few inflorescences, while in other areas of the same lake P. richardsonii plants typically had many branches and inflorescences. To identify factors affecting branch and flower number, three experiments were carried out in the two lake regions: reciprocal transplants, nutrient addition and clipping. The results from transplants of cloned material suggested that the morphological differences had neither genetic nor substrate bases. Nutrient additions were added by implanting fertilizer stakes in lake sediments. There was no significant response to nutrient addition. There was a response to clipping. When the apical meristem was removed, the numbers of leaves, branches and flowers increased significantly. Since there are both natural and anthropogenic sources of apex removal, a number of agents, including herbivores, may increase P. richardsonii reproductive potential.     

Serological Distinctness of Bromus pseudosecalinus P. SMITH sp. nov.

Immunoelectrophoretic studies of the seed proteins of material provisionally referred to B. secalinus var. or f. hirsutus have revealed that it is serologically distinct from B. secalinus. The plant has many of the characters of B. secalinus fitting that species to life as a contaminant of cereal fields, but the floret and seed sizes are much smaller, and the sheaths are normally hairy. In Britain the plant appears to contaminate small-seeded pasture grasses which are sown on roadsides. The chromosome number of this plant is 2n = 14, unlike typical B. secalinus which has 2n = 28. The plant seems to be introduced in Britain, but its native distribution is not known. In view of its distinctive morphology and its serological difference from B. secalinus and other bromes, it is proposed to name it as a new species: Bromus pseudosecalinus P. SMITH sp. nov.     

Allozyme Diversity and Interspecific Differentiation o the Two Diploid Bromegrass Species, Bromus tectorum L. and B. sterilis L (Poaceae)

Abstract: Genetic diversity among 50 accessions of Bromus tectorum and 43 of B. sterilis from different sites of their Eurasian ranges has been studied by electrophoretic analysis of ten enzymes encoded by 18 loci. The two species proved clearly differentiated by alternate allozymes at seven isozymes. Populations of both taxa showed differentiation into eleven (B. tectorum ) and six (B. sterilis ) multilocus allozyme lineages (MLALs). The extent of interspecific allozyme divergence estimated by Manhattan distance exceeded more than three times intraspecific differentiation between the multilocus lineages. Only two MLALs in each species have wide geographical distribution from the Near East to Europe. Other MLAL5 were found each for only one or two populations and were region-specific. Most geographically marginal European populations had widespread MLALs.