Systematic overview of Krigia (Asteraceae-Lactuceae)

Cytological and morphological variation among Krigia species is examined. Krigia exhibits a broad range of chromosome numbers including n = 4, 5, 6, 9, 10, 15, and 30. Section Krigia is characterized by reflexed phyllaries and a base chromosome number of x = 5, while section Cymbia is characterized by erect phyllaries and chromosome numbers of n = 4, 6, and 9. The micromorphological characteristics of achenes, pappus, styles, corolla, pollen, stomata, and trichomes are documented using scanning electron microscopy. Among these, the pappus shows the greatest diversity and three major types are identified: 1) a pappus of many bristles and scales, as in K. dandelion, K. montana, and K. biflora; 2) a pappus of five bristles and five scales, as in K. virginica and K. occidentalis; and 3) an absent or highly reduced pappus, as in the K. cespitosa complex and K. wrightii. Thirty-five cytological and morphological characters are subjected to phylogenetic analyses. The two sections, Krigia and Cymbia, form monophyletic lineages. Within section Krigia, the annual species, K. virginica, forms an independent clade, while the perennial species, K. dandelion, K. biflora, and K. montana, form a monophyletic clade. Krigia montana and K. biflora are identified as sister species and a hybrid between these has been identified. The hybrid is more similar morphologically to K. montana than K. biflora. Within section Cymbia, phylogenetic relationships among K. wrightii, K. occidentalis, and K. cespitosa are uncertain. Nine taxa of Krigia are herein recognized: K. dandelion, K. biflora, K. biflora var. viridis (comb. nov.), K. montana, K. virginica, K. wrightii (comb. nov.), K. occidentalis, K. cespitosa, and K. cespitosa f. gracilis (comb. nov.). Phylogenetic relationships among 12 taxa of Krigia species are compared using various combinations of morphology, chloroplast DNA, and nuclear ribosomal DNA data. Tree topologies from different combinations of data are largely congruent. The most resolved phylogenetic tree is obtained using the combined data from morphology, chloroplast DNA, and nuclear ribosomal DNA.     

Different maternal genome donor to Kengyilia species inferred from chloroplast trnL-F sequences

To reveal the maternal donor of species in genus Kengyilia, the chloroplast trnL-F sequences of 14 Kengyilia species and several related diploid species were analyzed by using Maximum Parsimony (MP) and Bayesian Inference (BI) methods. The species in Kengyilia were clustered in different clades, which indicated that Agropyron (P) is the likely maternal genome donor to Kengyilia melanthera, K. mutica and K. thoroldiana, while the maternal donor to Kengyilia batalinii, K. nana, K. kokonorica, K. kaschgarica, K. hirsuta, K. alatavica, K. gobicola, K. zhaosuensis, K. rigidula, K. longiglumis and K. grandiglumis was St or Y Roegneria genome.     

Rice potassium transporter OsHAK1 is essential for maintaining potassium‐mediated growth and functions in salt tolerance over low and high potassium concentration ranges

Potassium (K) absorption and translocation in plants rely upon multiple K transporters for adapting varied K supply and saline conditions. Here, we report the expression patterns and physiological roles of OsHAK1, a member belonging to the KT/KUP/HAK gene family in rice (Oryza sativa L.). The expression of OsHAK1 is up‐regulated by K deficiency or salt stress in various tissues, particularly in the root and shoot apical meristem, the epidermises and steles of root, and vascular bundles of shoot. Both oshak1 knockout mutants in comparison to their respective Dongjin or Manan wild types showed a dramatic reduction in K concentration and stunted root and shoot growth. Knockout of OsHAK1 reduced the K absorption rate of unit root surface area by ～50–55 and ～30%, and total K uptake by ～80 and ～65% at 0.05–0.1 and 1 mm K supply level, respectively. The root net high‐affinity K uptake of oshak1 mutants was sensitive to salt stress but not to ammonium supply. Overexpression of OsHAK1 in rice increased K uptake and K/Na ratio. The positive relationship between K concentration and shoot biomass in the mutants suggests that OsHAK1 plays an essential role in K‐mediated rice growth and salt tolerance over low and high K concentration ranges.     

Improving rice tolerance to potassium deficiency by enhancing OsHAK16p:WOX11‐controlled root development

Potassium (K) deficiency in plants confines root growth and decreases root‐to‐shoot ratio, thus limiting root K acquisition in culture medium. A WUSCHEL‐related homeobox (WOX) gene, WOX11, has been reported as an integrator of auxin and cytokinin signalling that regulates root cell proliferation. Here, we report that ectopic expression of WOX11 gene driven by the promoter of OsHAK16 encoding a low‐K‐enhanced K transporter led to an extensive root system and adventitious roots and more effective tiller numbers in rice. The WOX11‐regulated root and shoot phenotypes in the OsHAK16p:WOX11 transgenic lines were supported by K‐deficiency‐enhanced expression of several RR genes encoding type‐A cytokinin‐responsive regulators, PIN genes encoding auxin transporters and Aux/IAA genes. In comparison with WT, the transgenic lines showed increases in root biomass, root activity and K concentrations in the whole plants, and higher soluble sugar concentrations in roots particularly under low K supply condition. The improvement of sugar partitioning to the roots by the expression of OsHAK16p:WOX11 was further indicated by increasing the expression of OsSUT1 and OsSUT4 genes in leaf blades and several OsMSTs genes in roots. Expression of OsHAK16p:WOX11 in the rice grown in moderate K‐deficient soil increased total K uptake by 72% and grain yield by 24%–32%. The results suggest that enlarging root growth and development by the expression of WOX11 in roots could provide a useful option for increasing K acquisition efficiency and cereal crop productivity in low K soil.     

Characterisation of soil potassium supply as derived from sorption–desorption experiments

PlantK uptake depends on soil K supply and this can be modelled using the K concentration in the soil solution (C _K), the soil K buffer power (S _K) and the effective K diffusion coefficient. With the appropriate sorption–desorption curve, the parameters C _K and S _K can be estimated from the equilibrium K concentration (C _K,0) and from the slope of the curve at C _K,0 (S _K,0). However, buffer power is frequently estimated by the ratio of the soil exchangeable K content (E _K) to C _K. Up to now, S _K,0 had not been compared with this ratio, nor had C _K,0 been compared with any C _K estimate from soil solution extract measurements. To address this question, we collected 45 soil samples from 15 K fertilisation trials in France. The soils differed widely in their physicochemical characteristics, soil solution K concentration and buffer power. For each soil sample, a sorption–desorption curve was established from 16-h experiments performed at the estimated Ca concentration of the soil solution. The C _K,0 estimates were compared with the K concentrations measured in the soil solution obtained either by direct centrifugation (^C C _K) or by centrifugation with 1,1,2-trichlorotrifluoroethane (^TFE C _K). On average, ^C C _K values were 16% higher than ^TFE C _K values, whereas C _K,0 values were intermediate between the two. The K buffer power increased when CEC increased and when C _K decreased. Multiple linear regressions using either CEC at the soil pH and ^TFE C _K ^–1 or E _K and ^TFE C _K ^–1 as independent variables accounted for more than 98 or 95% of the variability of S _K,0. The buffer power estimated by the ratio of E _K to ^TFE C _K overestimated by 100% the S _K,0 value obtained from the sorption–desorption curves.     

The cole-moore effect in nodal membrane of the frogRana ridibunda: Evidence for fast and slow potassium channels

Summary The K conductance (g _K) kinetics were studied in voltage-clamped frog nodes (Rana ridibunda) in double-pulse experiments. The Cole-Moore translation forg _K–t curves associated with different initial potentials (E) was only observed with a small percentage of fibers. The absence of the translation was found to be caused by the involvement of an additional, slow,g _K component. This component cannot be attributed to a multiple-state performance of the K channel. It can only be accounted for by a separate, slow K channel, the fast channel being the same as then ⁴ K channel inR. pipiens.The slow K channel is characterized by weaker sensitivity to TEA, smaller density, weaker potential (E) dependence, and somewhat more negativeE range of activation than the fast K channel. According to characteristics of the slow K system, three types of fibers were found. In Type I fibers (most numerous) the slow K channel behaves as ann ⁴ HH channel. In Type II fibers (the second largest group found) the slow K channel obeys the HH kinetics within a certainE range only; beyond this range the exponential decline of the slowg _K component is preceded by anE-dependent delay, its kinetics after the delay being the same as those in Type I fibers. In Type III fibers (rare) the slow K channel is lacking, and it is only in these fibers that the Cole-Moore translation of the measuredg _K–t curves can be observed directly.The physiological role of the fast and slow K channel in amphibian nerves is briefly discussed.     

Diphenolases from <Emphasis Type="Italic">Anoxybacillus kestanbolensis</Emphasis> strains K1 and K4 <Superscript>T</Superscript>

Summary Diphenolases from Anoxybacillus kestanbolensis strains K1 and K4^T, highly active against 4-methylcatechol were characterized in terms of pH- and temperature-optima, pH- and temperature-stability, kinetic parameters, and inhibition/activation behaviour towards some general polyphenol oxidase (PPO) inhibitors and metal ions. The temperature-activity optima, for Anoxybacillus kestanbolensis K1 and K4^T catecholases in the presence of 4-methylcatechol, were 80 and 70 °C, respectively. Although catecholase from A. kestanbolensis K4^T lost no activity after a period of 1 h incubation at its optimum temperature, the enzyme pH from K1 was stimulated by keeping at 80 °C. Both of the enzymes possessed pH optima at 9.5, and the pH-stability profiles showed that cathecholases from both preparations retained their activities at alkaline pH values. Both A. kestanbolensis K1 and K4^T catecholase activities were totally inhibited by addition of 0.01 mM sodium metabisulphite, ascorbic acid and l-cysteine. 1 mM Mn²⁺ increased the activities of A. kestanbolensis K1 and K4^T catecholases by 6.4- and 5.3-fold, respectively. These results indicate that both A. kestanbolensis K1 and K4^T strains possess thermo- and alkalostable catecholases.     

ON THE IDENTITY OF KARLODINIUM VENEFICUM AND DESCRIPTION OF KARLODINIUM ARMIGER SP. NOV. (DINOPHYCEAE), BASED ON LIGHT AND ELECTRON MICROSCOPY,NUCLEAR‐ENCODED LSU RDNA,AND PIGMENT COMPOSITION1

An undescribed species of the dinoflagellate genus Karlodinium J. Larsen (viz. K. armiger sp. nov.) is described from Alfacs Bay (Spain), using light and electron microscopy, pigment composition, and partial large subunit (LSU) rDNA sequence. The new species differs from the type species of Karlodinium (K. micrum (Leadbeater et Dodge) J. Larsen) by lacking rows of amphiesmal plugs, a feature presently considered to be a characteristic of Karlodinium. In K. armiger, an outer membrane is underlain by a complex system of cisternae and vacuoles. The pigment profile of K. armiger revealed the presence of chlorophylls a and c, with fucoxanthin as the major carotenoid. Phylogenetic analysis confirmed K. armiger to be related to other species of Karlodinium; thus forming a monophyletic genus, which, in the LSU tree, occupies a sister group position to Takayama de Salas, Bolch, Botes et Hallegraeff. The culture used by Ballantine to describe Gymnodinium veneficum Ballantine (Plymouth 103) was examined by light and electron microscopy and by partial LSU rDNA. Ultrastructurally, it proved identical to K. micrum (cultures Plymouth 207 and K. Tangen KT‐77D, the latter also known as K‐0522), and in LSU sequence, differed in only 0.3% of 1438 bp. We consider the two taxa to belong to the same species. This necessitates a change of name for the most widely found species, K. micrum, to K. veneficum. The three genera Karlodinium, Takayama, and Karenia constitute a separate evolutionary lineage, for which the new family Kareniaceae fam. nov. is suggested.     

INTERSPECIFIC CROSSES IN KALMIA

Interspecific crosses among Kalmia species are reported for the first time. All possible crosses between K. angustifolia, K. cuneata, K. latifolia, K. hirsuta, K. polifolia var. rosmarinifolia and K. p. var. microphylla were attempted. Several crosses yielded no hybrids, many produced albino or yellow-green inviable seedlings, and six combinations produced at least a few seedlings with near-normal growth habit. Stylar inhibition of pollen tube growth prevented some species from hybridizing; reciprocal differences in crossability and pollen tube growth were noted. Kalmia species are highly heterozygous, but no evidence was found within a species for geographic variation of combining ability except for the two varieties of K. polifolia which had different crossing patterns with the other species. The anthocyaninless form of K. angustifolia, in contrast to the normal, has unique combining ability with K. latifolia. No genetic evidence was found to support the placement of K. hirsuta in another genus (Kalmiella) or to designate K. angustifolia var. caroliniana as a distinct species. Use of all the species to breed improved ornamentals is limited by genetic barriers and sterility of F₁ hybrids.     

The relationship of abnormal chromosome 10 to B-chromosomes in maize

Abnormal chromosome 10 (K10) is known to increase recombination in maize and to induce preferential segregation in knobbed heterozygotes during megasporogenesis. In spite of the considerable interest generated by these findings, the origin of the K10 chromosome is unknown. It has been postulated that the extra segment of K10 arose by simple translocation between normal 10 and a B-chromosome. This hypothesis was tested by comparing meiosis in haploids with either K10 or the normal 10 and carrying a single B-chromosome. The frequency of bivalent configurations was found to be similar in the two types of haploids suggesting that the K10 and B-chromosomes do not share homologies that lead to chiasma formation. These results lend no support to the hypothesis that the K10 chromosome came from a B type. The implications of these results to the action of K10 at meiosis are also discussed.     

Taxonomic revision of the Koeleria splendens C. Presl group (Poaceae) in Italy based on morphological characters

Abstract

The Italian populations of Koeleria splendens C. Presl, critical group of the Mediterranean flora, are examined from the taxonomic and nomenclatural viewpoints. On the basis of literature data, herbarium investigations and field surveys, many morphologically well-differentiated taxa have been recognized. This group is widespread in the Italian peninsula and Sicily, where it is represented by the following units: K. splendens C. Presl, with four subspecies [subsp. splendens, subsp. grandiflora (Bertol. ex Schultes) Domin, subsp. brutia Brullo, Gangale & Uzunov, and subsp. ophiolitica subsp. nova], K. lucana sp. nova, K. subcaudata (Ascherson & Graebner) Ujhelyi, K. australis Kerner, K. callieri (Domin) Ujhelyi, and K. insubrica sp. nova. As concerns their distribution, both K. splendens and K. lucana are endemic to the Italian territory, while the other species occur also in some eastern Mediterranean countries. The taxonomic position of K. lobata, recently treated by some authors as a synonym of K. splendens, is also examined. A phylogenetic analysis was performed using morphological characters. Finally, a detailed iconography of the main morphological features and an analytical key of the Italian taxa (K. lobata included) are given.     

Hybridization studies within the genus Kluyveromyces van der Walt emend. van der Walt

Hybridization studies based on the prototrophic selection technique, involving the use of auxotrophic mutants of strains of all accepted species of the genus Kluyveromyces, are reported. Two main groups of mutually interfertile taxa were established within the genus. The first group comprises Kluyveromyces bulgaricus, K. cicerisporus, K. dobzhanskii, K. drosophilarum, K. fragilis, K. lactis; K. marxianus, K. phaseolosporus, K. vanudenii and K. wikenii. The second group consists of K. dobzhanskii, K. drosophilarum, K. lactis, K. vanudenii and K. wickerhamii. Hybrids were also detected in crosses involving K. drosophilarum and K. waltii as well as K. marxianus and K. thermotolerans.In terms of the concept of the biological species and in compliance with the requirements of the International Code of Botanical Nomenclature, taxa which hybridize with K. marxianus and form fertile recombinants at frequencies observed in intraspecific crosses, are accepted as varieties of K. marxianus.     

Role of interspecies interactions in dual-species biofilms developed in vitro by uropathogens isolated from polymicrobial urinary catheter-associated bacteriuria

Most catheter-associated urinary tract infections are polymicrobial. Here, uropathogen interactions in dual-species biofilms were studied. The dual-species associations selected based on their prevalence in clinical settings were Klebsiella pneumoniae–Escherichia coli, E. coli–Enterococcus faecalis, K. pneumoniae–E. faecalis, and K. pneumoniae–Proteus mirabilis. All species developed single-species biofilms in artificial urine. The ability of K. pneumoniae to form biofilms was not affected by E. coli or E. faecalis co-inoculation, but was impaired by P. mirabilis. Conversely, P. mirabilis established a biofilm when co-inoculated with K. pneumoniae. Additionally, E. coli persistence in biofilms was hampered by K. pneumoniae but not by E. faecalis. Interestingly, E. coli, but not K. pneumoniae, partially inhibited E. faecalis attachment to the surface and retarded biofilm development. The findings reveal bacterial interactions between uropathogens in dual-species biofilms ranged from affecting initial adhesion to outcompeting one bacterial species, depending on the identity of the partners involved.     

The potential threat of algal blooms to the abalone (Haliotis midae) mariculture industry situated around the South African coast

Toxic algal blooms are common world-wide and pose a serious problem to the aquaculture and fishing industries. Dinoflagellate species such as Karenia brevis, Karenia mikimotoi, Heterosigma akashiwo and Chatonella cf. antiqua are recognised toxic species implicated in various faunal mortalities. Toxic blooms of Karenia cristata were observed on the south coast of South Africa for the first time in 1988 and were responsible for mortalities of wild and farmed abalone. K. cristata and various other dinoflagellate species common along the South African coast, as well as K. mikimotoi (Isolation site: Norway, Univ. of Copenhagen) and K. brevis (Isolation site: Florida, BIGELOW), were tested for toxicity by means of a bioassay involving Artemia larvae as well as abalone larvae and spat. K. cristata, like K. brevis, contains an aerosol toxin; however, the toxin present in K. cristata has not yet been isolated and remains unknown. K. brevis was, therefore, used to determine which developmental phase of the bloom would affect abalone farms most, and whether ozone could be used as an effective mitigating agent. Of the 17 dinoflagellate species tested, K. cristata, Akashiwo sanguinea, K. mikimotoi and K. brevis pose the greatest threat to the abalone mariculture industry. K. brevis was most toxic during its exponential and stationary phases. Results suggest that ozone is an effective mitigation agent but its economic viability for use on abalone farms must still be investigated.     

Recognition of a new species of Kallymenia (Gigartinales,Rhodophyta) from Croatia (Mediterranean Sea) based on morphology and DNA barcode

The Mediterranean red algal flora is diverse but current knowledge of its diversity is at best fragmentary. Here, a new species of Kallymenia from Croatia is described based on morphological and molecular data. Members of the genus Kallymenia share similar morphology making their generic identification relatively easy, whereas species level identification is notoriously difficult. In this paper an integrative systematics study using three gene markers, cox1 (COI), rbcL and nuclear LSU, allowed us to (i) confirm the identity of four existing members of this genus inhabiting the Mediterranean Sea: K. feldmannii, K. lacerata, K. patens and K. requienii; (ii) detect the presence of K. reniformis only in the Atlantic, and (iii) reveal the presence of a new member of Kallymenia from the Mediterranean Sea, K. ercegovicii Vergés & Le Gall, sp. nov., which is described based on distinctive morphological and molecular characters. Kallymenia ercegovicii is distinguished, using three molecular markers, from all Kallymenia species for which these sequences are available. Morphologically, the new species can be distinguished from other polycarpogonial Kallymenia by a set of characters including a deeply lobed thallus, large inner cortical cells, stellate but non-glanglionic medullary cells and non-ostiolate cystocarps surrounded by a filamentous net composed of elongated cells forming fascicles. An initial phylogeny of the genus Kallymenia was inferred from cox1 (COI), rbcL and nuclear LSU sequences. Kallymenia ercegovicii was resolved with full support within the same lineage as K. reniformis (the generitype), K. feldmannii and K. patens, whereas K. lacerata and K. requienii were only distantly related.     

Agrobacterium radiobacter strains K84, K1026 and K84 Agr‐ produce an antibiotic‐like substance,active in vitro against A. tumefaciens and phytopathogenic Erwinia and Pseudomonas spp.

Agrobacterium radiobacter strains K84, K1026 and K84 Agr^‐ produced in vitro an antibiotic‐like substance (ALS 84), different from agrocin 84 and observed in mannitol‐glutamate medium. Twenty five out of 39 A. tumefaciens strains of biovars 1, 2 and 3 were sensitive to ALS 84 regardless of their sensitivity to agrocin 84. Sensitivity in A. tumefaciens strain C58 was not encoded by the Ti‐plasmid. Most isolates tested of Erwinia carotovora subsp. carotovora E. carotovora subsp. atroseptica, Pseudomonas corrugata P. cichorii and unidentified isolates from galls were also sensitive to this substance. ALS 84 was not affected by the proteases studied, nor by treatment at 62°C for 30 min and had a bacteriostatic effect. The production of ALS 84 might play a role in the complex mechanism of biological control of crown gall, especially in strains resistant to agrocin 84 and sensitive to ALS 84, and by the creation of an ecological niche favourable to A. radiobacter strains K84, K1026 or K84 Agr^‐.     

Modulation of Serine/Threonine Protein Kinase Activity in Chloramphenicol-Resistant Mutants of Streptomyces avermitilis

A mutation to chloramphenicol resistance (Cml^r) stimulates production of macrolide avermectin in Streptomyces avermitilis; production starts in the early stationary phase. By labeling in vivo, the Cml^r mutation was shown to stimulate phosphorylation of Ser and Thr in several proteins in the same growth phase. Autophosphorylation of active protein kinases (PK) was analyzed in gel after one- or two-dimensional PAGE for the original S. avermitilis strain ATCC 31272, its Cml^r mutant, and a Cml^s revertant. An increase in in vivo phosphorylation was associated with an increase in autophosphorylation of Ser/Thr-PK 41K, 45K, 52K, 62K, and 85K and complete suppression of autophosphorylation of PK 66K. Comparison of the PK molecular weights and pI with the parameters deduced for putative PK encoded by S. avermitilis genes identified the 41K, 45K, 52K, 62K, and 85K proteins as pkn 24, pkn 32, pkn 13, pkn12, and pkn5, respectively. Prenylamine lactate, a modulator of calmodulin-dependent processes, substantially reduced the avermectin production, impaired the Cml resistance, and selectively inhibited Ca²⁺-dependent PK 85K in the Cml^r mutant. It was assumed that PK 85K is involved in regulating the avermectin production.     

Ca2+/calmodulin-dependent invasion of microvascular endothelial cells of human brain by Escherichia coli K1

Escherichia coli K1 invasion of microvascular endothelial cells of human brain (HBMEC) is required for E. coli penetration into the central nervous system, but the microbial-host interactions that are involved in this invasion of HBMEC remain incompletely understood. We have previously shown that FimH, one of the E. coli determinants contributing to the binding to and invasion of HBMEC, induces Ca²⁺ changes in HBMEC. In the present study, we have investigated in detail the role of cellular calcium signaling in the E. coli K1 invasion of HBMEC, the main constituents of the blood-brain barrier. Addition of the meningitis-causing E. coli K1 strain RS218 (O18:K1) to HBMEC results in transient increases of intracellular free Ca²⁺. Inhibition of phospholipase C with U-73122 and the chelating of intracellular Ca²⁺ by BAPTA/AM reduces bacterial invasion of HBMEC by approximately 50%. Blocking of transmembrane Ca²⁺ fluxes by extracellular lanthanum ions also inhibits the E. coli invasion of HBMEC by approximately 50%. In addition, E. coli K1 invasion is significantly inhibited when HBMEC are pretreated by the calmodulin antagonists, trifluoperazine or calmidazolium, or by ML-7, a specific inhibitor of Ca²⁺/calmodulin-dependent myosin light-chain kinase. These findings indicate that host intracellular Ca²⁺ signaling contributes in part to E. coli K1 invasion of HBMEC. This work was supported by the American Heart Association (grant SDG 0435177N to Y.K.) and by NIH grants (to K.S.K.).     

Chemical Response of the Toxic Dinoflagellate Karenia mikimotoi Against Grazing by Three Species of Zooplankton

We investigated the toxicity of Karenia mikimotoi toward three model grazers, the cladoceran Moina mongolica, the copepod Pseudodiaptomus annandalei, and the crustacean Artemia salina, and explored its chemical response upon zooplankton grazing. An induction experiment, where K. mikimotoi was exposed to grazers or waterborne cues from the mixed cultures revealed that K. mikimotoi might be toxic or nutritionally inadequate toward the three grazers. In general, direct exposure to the three grazers induced the production of hemolytic toxins and the synthesis of eicosapentaenoic acid (EPA). Both EPA and the hemolytic toxins from K. mikimotoi decreased the survival rate of the three grazers. In addition, the survival rates of M. mongolica, P. annandalei, and A. salina in the presence of induced K. mikimotoi that had previously been exposed to a certain grazer were lower than their counterparts caused by fresh K. mikimotoi, suggesting that exposure to some grazers might increase the toxicity of K. mikimotoi. The chemical response and associated increased resistance to further grazing suggested that K. mikimotoi could produce deterrents to protect against grazing by zooplankton and that the substances responsible might be hemolytic toxins and EPA.     

Biological vs. physical explanations for the non-random pattern of host occupation by a macroalga attaching to infaunal bivalve molluscs

Summary On a shallow sand flat at Princess Royal Harbour near Albany, Western Australia, the brown macrophyte Hormosira banksii attaches to shells of infaunal bivalves. Hormosira occupies shells of Katelysia rhytiphora in preference to K. scalarina. We proposed and tested four hypotheses to explain this host occupation pattern. First, by following the fate of nearly one thousand marked clams of each species, we rejected the hypothesis that K. rhytiphora exhibits greater longevity and simply possesses more frequent Hormosira because of a longer temporal integration of settlement events. Second, we rejected the hypothesis that K. rhytiphora exhibits higher densities in the top 5 mm of sediment and accumulates more Hormosira because its shell is more abundant in the depth range occupied by the attaching base of Hormosira. Third, we showed that K. rhytiphora because of its larger size is more difficult to dislodge from the sediments than K. scalarina, supporting the hypothesis that Hormosira is rare on K. scalarina because storm waves selectively dislodge and carry to the beach Hormosira attached to K. scalarina. This physical explanation for the Hormosira occupation pattern gets further support from the observation that a third infaunal bivalve, the mussel Brachidontes erosus, has a far higher frequency of Hormosira occupation than either Katelysia species, while providing a much more robust anchor because of its extensive byssal attachments to neighboring mussels. The sizes of Hormosira plants also vary consistently with this physical transport hypothesis: Hormosira is smallest on K. scalarina and largest on B. erosus. Successful colonization of initially unoccupied Katelysia during five 3–9 month periods was also more frequent on K. rhytiphora than on K. scalarina. This suggests a fourth explanation for the Hormosira distribution pattern: that spore settlement is selective for K. rhytiphora in preference to K. scalarina. Although this hypothesis requires further testing, evolution of selective spore settlement would be reasonable given the different likelihoods of subsequent host dislodgement during storm waves.