SPATIAL VARIATION PATTERNS IN THE MARINE MACROALGA XIPHOPHORA GLADIATA SSP. GLADIATA (PHAEOPHYTA). II. MORPHOLOGICAL VARIATION OVER LARGE SPATIAL SCALES1

The geographic expression of inter-regional morphological variation in Xiphophora gladiata ssp. gladiata was examined using a combination of discriminant function analyses, canonical correlation analysis and linear regression analysis. The pattern of that expression is an irregularly-stepped cline over scales of hundreds of kilometers, superimposed on a weak complex of microclines driven by exposure and (perhaps) other locally-varying environmental factors. The large-scale irregular cline is probably a response to the physico-chemical characteristics of regional water masses.     

SEASONAL PATTERNS OF MORPHOLOGICAL VARIABILITY IN SARGASSUM POLYCERATIUM (PHAEOPHYTA)1

Temporal variability in certain morphological and taxonomically important features was quantified for Sargassum polyceratium Mont. from a population in the Content Keys, Florida (U.S.A.). Patterns of blade development, senescence, and loss caused pronounced seasonal changes in blade length-width ratios. Blade length and width were maximal early in the growing season (August-November) and decreased as the annual stems matured. Early in the growing season, plants had broader blades with randomly distributed cryptostomata. Late in the growing season (February-April), plants had more linear blades with cryptostomata approximately arranged in two rows, one on each side of the midrib. The length-width ratio of blades increased acropetally along the stems and were directly correlated to the size of the cryptostomatal opening and inversely correlated with the number of cryptostomata. The branching pattern of the annual stems ranged from short spur branches to well-developed, lateral axillary branches. The frequency of bifurcated blades increased significantly late in the growing season. Vesicle shape and size and pedicel length were temporally stable. Alated pedicels and mucronate vesicles occurred in low frequencies. The variability of the morphological features used to delineate species within the genus Sargassum on the tropical eastern coasts of the Americas is poorly understood.     

VARIATION IN NITROGEN PHYSIOLOGY AND GROWTH AMONG GEOGRAPHICALLY ISOLATED POPULATIONS OF THE GIANT KELP,MACROCYSTIS PYRIFERA (PHAEOPHYTA)1

Three geographically isolated populations of the giant kelp, Macrocystis pyrifera (L.) C. Ag., were examined for responses to nitrate availability in batch culture experiments using juvenile sporophytes reared from spores in the laboratory. Although maximum rates of nitrate-saturated growth were similar among groups, there were significant quantitative differences in the response to nitrate limitation that can be related to natural patterns of nutrient availability at these sites. Plants from Santa Catalina Island (most oligotrophic) achieved maximum growth rates at ambient nitrate concentrations that were lower than those for plants from Monterey Bay, California (most eutrophic), or Refugio State Beach (near Santa Barbara, California). Tissue nitrogen and amino acid concentrations were highest in plants cultured from Santa Catalina Island populations at all external nitrate concentrations, suggesting that differences in nitrate requirements for growth may reflect the efficiency of nitrate uptake and assimilation at subsaturating nitrate concentrations. Given the different physical environments from which these plants came, the data suggest that geographically isolated populations of M. pyrifera have undergone genetic divergence that can be explained by ecotypic adaptation to unique habitat conditions at these sites.     

CONTRIBUTION OF TEMPORAL AND SPATIAL COMPONENTS TO MORPHOLOGICAL VARIATION IN THE KELP ECKLONIA (LAMINARIALES)1

Environmental conditions that are known to cause morphological variation in algae (e.g., wave exposure) often vary in both space and time and are superimposed onto the distinct seasonal growth cycles of most temperate macroalgae. We tested the hypothesis that the morphology of the small kelp Ecklonia radiata (C. Agardh) J. Agardh is the product of an interaction between site (five reefs of different wave exposure) and the time of year that sampling occurs (summer vs. winter 2004). We determined that wave exposure had a strong directional effect on kelp morphology, with “Reefs” accounting for up to 43.4% of variation in individual morphological characters. “Times” had a narrowly nonsignificant effect on overall morphology but accounted for up to 31% of variation in individual characters. Many characters were affected by wave exposure, whereas only a few were (strongly) affected by time (e.g., thallus biomass). Interactive effects between “Reefs” and “Times” were generally small, accounting for 15.8% of variation in lamina thickness, but much less for most other characters. We conclude that wave exposure exerts a strong control over the morphology of E. radiata, but that the nature of the effect depends on the magnitude of wave exposure. We also conclude that most of the effects of wave exposure are consistent through time and do not interact with cycles of growth and pruning in any major way.     

RESTRICTION ENDONUCLEASE ANALYSIS OF RIBOSOMAL DNA SEQUENCE VARIATION IN LAMINARIA (PHAEOPHYTA)1

The taxonomy and evolutionary relationships of species in the genus Laminaria are poorly understood. Previous studies have demonstrated significant plasticity of morphological characters used to describe taxa, and interfertility has been reported among putative species. We analyzed nuclear ribosomal DNA (rDNA) sequence variation in eight species of Laminaria (L. agardhii Kjell., L. digitata (Huds.) Lamour., L. groenlandica Rosenv. [sensu Druehl 1968], L. longicruris De la Pyl., L. longipes Bory, L. saccharina (L.) Lamour., L. setchellii Silva, and L. yezoensis Miyabe) to elucidate evolutionary relationships in this genus. Restriction maps were constructed using a small subunit rDNA probe from Costaria costata (Turn.) Saunders, an rDNA repeat from the nematode Caenorhabditis elegans, and 11 hexameric restriction endonucleases in an annealing analysis of genomic DNA. Laminaria rDNA restriction maps were compared to each other and to that of the outgroup taxon, C. costata. rDNA restriction maps of Laminaria species and C. costata were similar. Restriction fragment length polymorphisms mapped to both the coding regions and the nontranscribed spacer of rDNA. Laminaria species were distinguished with this method. The restriction maps of L. agardhii, L. saccharina, and L. longicruris were identical, supporting a previous hypothesis that these species are conspecific. Comparison of restriction maps of Laminaria species suggested that the generic subdivision of Sections Simplices and Digitatae may be invalid.     

PATTERNS OF ALLOZYME VARIATION IN DIPLOID AND TETRAPLOID CENTAUREA JACEA AT DIFFERENT SPATIAL SCALES

Abstract.— The extent and spatial patterns of genetic variation at allozyme markers were investigated within and between diploid and autotetraploid knapweeds (Centaurea jacea L. sensu lato, Asteraceae) at contrasted geographic scales: (1) among populations sampled from a diploid‐tetraploid contact zone in the northeastern part of the Belgian Ardennes, and (2) within mixed populations from that zone where diploids and tetraploids coexist. Our data were also compared with a published dataset by Sommer (1990) describing allozyme variation in separate diploid and tetraploid knapweeds populations collected throughout Europe. Genetic diversity was higher in tetraploids. In the Belgian Ardennes and within the mixed populations, both cytotypes had similar levels of spatial genetic structure, they were genetically differentiated, and their distributions of allele frequencies were not spatially correlated. In contrast, at the European scale, diploids and tetraploids did not show differentiated gene pools and presented a strong correlation between their patterns of spatial genetic variation. Numerical simulations showed that the striking difference in patterns observed at small and large geographic scales could be accounted for by a combination of (1) isolation by distance within cytotypes; and (2) partial reproductive barriers between cytotypes and/or recurrent formation of tetraploids. We suggest that this may explain the difficulty of the taxonomic treatment of knapweeds and of polyploid complexes in general.     

GEOGRAPHIC VARIATION IN THE LIFE HISTORY OF MASTOCARPUS PAPILLATUS (RHODOPHYTA)1

Variation in the geographic distribution of the life histories of Mastocarpus papillatus was investigated. Carpospores were isolated from 377 female gametophytes collected from eight localities on the Pacific coast of Baja California, Mexico, and California, U.S.A., and grown in laboratory culture. All carpospores from a single female gave rise either to basal discs with gametophyte-like uprights or crustose plants formerly referred to the genus Petrocelis. Early stages in the development of each type of germling were observed, and environmental factors affecting development were suggested. Based on carpospore germlings, females from each location were scored as having either the 1) sexual life history (crustose germlings) or 2) direct-development life history (discoid germlings with uprights). All females from the two southernmost locations in Baja California exhibited the sexual life history. In the three locations from the central-southern California coast, 70-95% of the females exhibited the sexual life history and the remainder exhibited the direct-development life history. In two of the three populations from the central-northern California coast, 70-90% of the females exhibited the direct-development life history and the remainder the sexual life history. In the third location from the central-northern California coast, the northernmost location sampled in the current study, 60% of the females exhibited the sexual life history and 40% the direct-development life history. The relative ecological advantages and disadvantages of the life histories are unknown as are the environmental factors that produced the ratios of sexual to direct-development females observed at each location.     

THE OCCURRENCE OF FLAGELLATED EGGS IN LAMINARIA ANGUSTATA (PHAEOPHYTA,LAMINARIALES)1

Eggs of laminaria angustata Kjellman were shown to have two flagella. Compared with flagella of other phaeophycean swarmers, those of Laminaria eggs have several unique characters such as lack of mastigonemes, widely spaced basal bodies and no flagellar rootlets. The flagella abscise during egg liberation.     

GEOGRAPHIC PATTERNS OF VARIATION IN OFFSHORE SPOTTED DOLPHINS (STENELLA ATTENUATA) OF THE EASTERN TROPICAL PACIFIC OCEAN

The spotted dolphin (Stenella attenuata), a species commonly associated with the tuna fishery, is widely distributed in the eastern tropical Pacific Ocean (ETP). Geographic patterns in morphological characteristics of this dolphin were evaluated for 36 skull measurements of 574 museum specimens allocated to 5° latitude-longitude blocks. A strong subdivision between northern and southern offshore populations was demonstrated using principal components, canonical variates and cluster (UPGMA and function-point) analyses of block means derived from standardized, sex-adjusted measurements. Classification functions derived from a stepwise multiple discriminant analysis correctly identified more than 87 percent of the specimens as being from either a northern or southern locality. These results support recognition of southern spotted dolphins as a separate management stock. Dolphins from a sample representing a far-western locality show similarities with those from the south. Patterns of geographic variation in morphology were evaluated using Mantel tests and matrix correlations; 17 of the 36 characters showed regional patterning and 18 exhibited local patterning. Morphological trends were also assessed with respect to 14 oceanographic measures that characterize environmental variability in the ETP. In general, clinal variation in morphology mirrors a north-south trend found in several environmental variables. Overall, the most striking associations between morphological and environmental variables involved Solar Insolation (Jan.). Sea surface temperatures also exhibited a strong association with morphological variables; the highest correspondence was found between width of the temporal fossa and sea surface temperature in July. In addition, the thickness of the oxygen minimum layer exhibited a pattern of variation that was statistically associated with 58 percent of the skull characters. The geographic patterns found for cranial morphology and environmental measures are strongly clinal and in general congruent, suggesting that oceanographic conditions in part determine trends in morphological characteristics of spotted dolphins.     

AN IN VITRO NITRATE REDUCTASE ASSAY FOR MARINE MACROALGAE: OPTIMIZATION AND CHARACTERIZATION OF THE ENZYME FOR FUCUS GARDNERI (PHAEOPHYTA)1

Measurement of the activity of the enzyme nitrate reductase (NR) may provide a useful index of nitrogen metabolism in marine macroalgae. In several species, including Fucus gardneri P. C. Silva, in vitro assays previously failed to detect NR activity, necessitating the use of in situ (or so-called“in vivo”) assays, which are more loosely controlled and lead to dafficulties in assessing enzyme characteristics such as the half-saturation constant (K_m). In this paper, we describe an in vitro NR assay developed for F. gardneri, in which tissue was homogenized using liquid nitrogen prior to the assay. In contrast to previous studies, enzyme activity was always detectable in F. gardneri collected directly from the field at levels up to 30 nmol nitrate converted to nitrite·min^?1·g^?1 wet weight. The effect of a variety of compounds, commonly added to NR extraction buffers, were tested. Additions of protease inhibitors, bovine serum albumin, and ethylenediamine tetraacetic acid had no consistent effects on NR activity, while polyvinyl pyrrolidone, potassium ferricyanide, and flavin adenine dinucleotide significantly decreased activity. The half-saturation constant (K_m) for NADH was 0.18 (± 0.05) mM and for nitrate, K_m=0.99 (±0.41) mM. Significant NR activity was detected without the addition of nitrate, suggesting that internal pools of nitrate averaging approximately 20 μmol NO₃^?·g^?1 wet weight were present in F. gardneri in February. The distribution of NR activity within the plant was highly variable between individuals, but activities were approximately 5-fold lower in the stipe than in midregions. In plants freshly sampled from the field, NR activity increased 7-fold from February to March, then fell to near-February levels by April. These changes in activity may correspond to seasonal changes in growth rate. The assay, optimized for F. gardneri, was used in several different macroalgal species from different taxa: Porphyra sp., Coralina vancouveriensis Yendo, Ulva sp., Enteromorpha intestinalis (Linnaeus) Nees, Macrocystis integrifolia Bory; and Costaria costatum (C. Agardh) Saunders. For all species tested, NR activity was detectable and, except for one species (Porphya sp.), was equal to or greater than activities measured by other workers using in vivo or in vitro assays for plants under similar conditions.     

AN ELECTRON MICROSCOPE STUDY OF GAMETE RELEASE AND SETTLING IN THE COMPLANATE FORM OF SCYTOSIPHON (SCYTOSIPHONACEAE,PHAEOPHYTA)1

This paper describes the ultrastructural characteristics of gametes and their liberation from the gametangia in Scytosiphon sp., a brown alga showing only slight sexual differentiation. Both male and female gametes are released initially into a central cavity which forms in the gametangial sorus by the extensive dissolution of the internal cell walls. Scytosiphon sp. gametes possess structural features in common with the zoids of other species of brown algae. Gamete fine structure is discussed in relation to cell function. After release from the gametangial sorus, female gametes can be distinguished from males by the presence of a large number of Golgi-derived vesicles with electron dense cores. It is possible that these vesicles contain the sex attractant compound. When gametes settle they become spherical, the flagella and eyespot are withdrawn into the cell and adhesive material, apparently originating from the activity of the Golgi body, appears on the surface of the cell.     

EFFECT OF HIGH IRRADIANCE ON RECRUITMENT OF THE GIANT KELP MACROCYSTIS (PHAEOPHYTA) IN SHALLOW WATER1

Laboratory and field experiments were done hi Still-water Cove, Carmel Bay, California, and Monterey Harbor, California, to determine the effect of photosynthetically active radiation (PAR) on the shallow (upper) limit of giant kelp, Macrocystis pyrifera (L.) C. Agardh. At shallow depths, M. pyrifera did not recruit or grow to macroscopic size from gametophytes or embryonic sporophytes transplanted to vertical buoy lines; sharp decreases in PAR with depth coincided with observed recruitment and sporophyte distributions. Shade manipulations indicated that settlement of M. pyrifera zoospores was decreased, but not prohibited, by high PAR. Postsettlement stages (gametophytes and embryonic sporophytes), however, survived only under shade. These results suggest that high PAR can inhibit the recruitment of M. pyrifera to shallow water by killing its postsettlement stages; whether or not ultraviolet (UV) radiation also inhibits recruitment was not tested. In either case, however, it appears that high irradiance (PAR and/or UV) regulates the shallow limit of M. pyrifera prior to temperature and desiccation stresses inherent to intertidal regions. In an additional experiment, recruitment or growth of transplanted gametophytes or embryonic sporophytes of Macrocystis integrifolia Bory also did not occur at shallow depths, suggesting that this shallow water species accesses high irradiance regions via a method other than sexual reproduction.     

INTRASPECIFIC VARIATION IN THE DINOFLAGELLATE GAMBIERDIZSCUS TOXICUS (DINOPHYCEAE). I. ISOZYME ANALYSIS

Intraspecific variation among 19 isolates of the ciguatera-causing dinoflagellate Gambierdiscus toxicus Adachi & Fukuyo (Dinophyceae) collected from French Polynesia, New Caledonia, and the French West Indies was investigated by isozyme analysis. Comparison of their cell sizes and growth rates revealed that significant variation exists among these clones. Comparison of electrophoretic patterns for seven enzyme systems indicated that G. toxicus is comprised of numerous biochemically distinct strains. Isolates from Tubuai and Hao appeared to be the most distantly related. Tahitian strains of G. toxicus also showed a remarkably low degree of similarity with the Tubuai isolates. The latter, which were taken from the same locale in Tubuai, also exhibited highly heterogeneous electrophoretic Profiles when compared to each other, suggesting a multiclonal origin. The single isolate analyzed from the Atlantic Ocean was most closely related to Tahitian isolates, despite their geographic separation. Finally, no clear relationship was found between the electrophoretic profiles of these isolates and their capacity to produce ciguatoxic compounds .     

EFFECTS OF VARIATION IN TEMPERATURE. I. ON THE BIOCHEMICAL COMPOSITION OF EIGHT SPECIES OF MARINE PHYTOPLANKTON1

The influence of temperature on the biochemical composition of eight species of marine phytoplankton was investigated. Thalassiosira pseudonana Hasle and Heim-dal, Phaeodactylum tricornutum Bohlin and, Pavlova lutheri Droop (three of eight species studied) had minimum values of carbon and nitrogen quotas at intermediate temperatures resulting in a broad U-shaped response in quotas over the temperature range of 10 to 25°C. Protein per cell also had minimum values at intermediate temperatures for six species. For T. pseudonana, P. tricornutum, and P. lutheri, patterns of variation in carbon, nitrogen, and protein quotas as a function of temperature were similar. Over all species, lipid and carbohydrate per cell showed no consistent trends with temperature. Only chlorophyll a quotas and the carbon: chlorophyll a ratios (θ) showed consistent trends across all species. Chlorophyll a quotas were always lower at 10°C than at 25°C. Carbon: chlorophyll a ratios (θ) were always higher at 10°C than at 25°C. We suggest that although θ consistently increases at lower temperatures, the relationship between temperature and θ ranges from linear to exponential and is species specific. Accordingly, the interspecific variance in θ that results from species showing a range of possible responses to temperature increases as temperature declines and reaches a maximum at low temperatures. High photon flux densities appear to increase the potential interspecific variance in the carbon: chlorophyll a ratio and therefore exacerbate these trends.     

VARIATION IN NUMBER OF APICAL RAMIFICATIONS AND VEGETATIVE CELL LENGTH IN FRESHWATER POPULATIONS OF CLADOPHORA (ULVOPHYCEAE,CHLOROPHYTA)1

Populations of Cladophora with two different levels of ploidy, n = 18/2n = 36 (18/36) and n = 24/2n = 48 (24/48), are present in creeks in the southern part of the province of Buenos Aires, Argentina. The goals of our study were to 1) relate the number of apical branches · mm^?2 in 18/36 and 24/48 populations with the water velocity at the collection site; 2) correlate the number of apical ramifications · mm^?2 in plants of the same population (24/48) growing in sectors with distinct water velocities; 3) compare cell length among populations with different ploidy levels, analyzing the sources of variation in different sectors of the same creek and in different plants of the same sector; and 4) analyze the sources of variation in cell length in 24/48 populations, including variations among different creeks. Our results suggest that 1) the number of branches · mm^?2 tends to increase with higher water velocity; 2) the 24/48 populations have more ramifications · mm^?2 than the 18/36 ones; 3) the length of vegetative cells is not an adequate criterion for differentiating between 18/36 and 24/48 populations; and 4) variations in vegetative cell length in 24/48 populations are highly significant among plants from different sectors of the same creek.     

COMPARISON OF CHLOROPLAST DNA AND ALLOZYME VARIATION IN WINTER STRAINS OF THE MARINE DIATOM SKELETONEMA COSTATUM(BACILLARIOPHYTA)1

Restriction fragment length polymorphisms (RFLPs) were examined in 12 winter strains of the marine diatom Skeletonema costatum (Grev.) Cleve using homologous chloroplast gene probes. The winter strains included eight different allozyme genotypes exhibiting physiological differences. These 12 winter strains were representative of the least diverse genetic group present in Narragansett Bay populations. Five chloroplast DNA probes and four different restriction enzymes were used to analyze the 12 Narragansett Bay strains and a reference strain “Skel.” A total of 46 restriction fragments were identified. All 12 of the winter strains had identical patterns. Strain Skel exhibited two RFLPs in comparison to the Narragansett Bay strains. Calculated diversity within the winter strain group was 0.0 and 0.85 for the chloroplast DNA and allozyme data, respectively. The chloroplast DNA polymorphisms revealed by this study are expected to represent a minimum level of the chloroplast DNA diversity present in Narragansett Bay seasonal populations.     

PARTITIONING THE EFFECTS OF SPATIAL ISOLATION,NEST HABITAT,AND INDIVIDUAL DIET IN CAUSING ASSORTATIVE MATING WITHIN A POPULATION OF THREESPINE STICKLEBACK

Assortative mating is measured as a phenotypic or genotypic correlation between mates. Although biologists typically view assortative mating in terms of mate preference for similar partners, correlations between mates can also arise from phenotypic spatial structure arising from spatial isolation or habitat preferences. Here, we test whether diet‐assortative mating within an ecologically variable population of threespine stickleback results from small‐scale geographic isolation or microhabitat preference. We find evidence for assortative mating in the form of a positive correlation between mated pairs’ diets (measured using stable isotopes). Stable isotopes reveal diet differences between different nesting areas and among individuals using different nest habitat within a nesting area. This spatial segregation of diet types should generate some assortative mating, but is insufficient to explain the observed assortment strength. Significant male–female isotope correlations remain after controlling for spatial variables. We therefore conclude that sticklebacks’ diet‐assortative mating arises from additional behavioral preference. More generally, our results illustrate the point that spatial segregation can only drive appreciable levels of phenotypic assortative mating when environment‐phenotype correlations are parallel and strong in both sexes. Consequently, intraspecific assortative mating may typically entail mating preferences rather than just spatial cosegregation of phenotypes.