Population density, sex ratio, body size and fluctuating asymmetry of Ceroglossus chilensis (Carabidae) in the fragmented Maulino forest and surrounding pine plantations

Habitat fragmentation results in new environmental conditions that may stress resident populations. Such stress may be reflected in demographical or morphological changes in the individuals inhabiting those landscapes. This study evaluates the effects of fragmentation of the Maulino forest on population density, sex ratio, body size, and fluctuating asymmetry (FA) of the endemic carabid Ceroglossus chilensis. Individuals of C. chilensis were collected during 2006 in five locations at Los Queules National Reserve (continuous forest), in five forest fragments and in five areas of surrounding pine plantations (matrix). In each location, once a season, 40 pitfall traps (20 in the centre, 20 in the edge), were opened for 72 h. Population density of C. chilensis was higher in the small fragments than in the pine matrix, with intermediate densities in the continuous forest; sex ratio did not differ significantly from 1:1 in the three habitats. Individuals from the centre of fragments were smaller than those from the centre of continuous forest, and FA did not vary significantly among habitats. These results suggest that small forest fragments maintain dense populations of C. chilensis and therefore they must be considered in conservation strategies. Although the decrease of the body size suggests that small remnants should be connected by managing the structure of the surrounding matrix, facilitating the dispersion of this carabid across the landscape and avoiding possible antagonistic interactions inside small fragments.     

Gracilaria-Mytilus interaction on a commercial algal farm in Chile

Mytilus chilensis is an invertebrate that competes for space with the alga Gracilaria chilensis in farmed areas in Chile and, for this reason, is considered a contaminant organism. Mussel beds are considered to play a role in the regeneration of nitrogen and, as a consequence, they could be an important source of ammonium for the algae. In this study, we manipulated the mussel cover in experimental plots, creating replicated areas with 0%, 30% and 60% coverage. In half of the plots the mussels were killed with a gas torch so their effect would be mechanical, without nutrient regeneration. After 15 days, each plot was planted with 12 G. chilensis bundles (100 g each) per square meter. Ammonium concentrations increased significantly in the waters around the mussel bed in contrast to areas without mussels or dead mussels. Mussel cover had a significant negative effect on the length of the G. chilensis bundles planted in the experimental plots. However, no significant differences were detected between experimental quadrats with live mussels and those with dead mussels during a 5 month period. These results indicate that the mechanical effect of the mussel can, to some extent, be responsible for the decline in G. chilensis abundance in farms where mussel beds have been established.     

Distribution,status and biology of the tortoise,Geochelone chilensis,in Río Negro Province,Argentina

Morphometric and meristic data from 32 specimens from Río Negro Province do not allow differentiation between G. donosobarrosi and G. chilensis. The significance of morphological and genetic differentiation among Argentinian tortoises is yet to be determined; southern Chaco tortoises undergo ontogenetic and sexual dichromatism. Geochelone chilensis has an extensive latitudinal range (Map 1). Field investigations indicate that Chaco tortoises occupy, and apparently excavate, burrows in the southern portion of the range, prior reports of the species’ southern limit are evaluated and the link between tortoise distribution and “monte”; vegetation is discussed. The season of reproduction and clutch size are noted. Extensive internal pet traffic has markedly affected tortoise populations in some areas; near the southern limit of the range, however, there is little commercial collecting.     

Relationship between the aerobic and anaerobic metabolic capacities and the vertical distribution of three intertidal sessile invertebrates: Jehlius cirratus(Darwin) (Cirripedia), Perumytilus purpuratus (Lamarck) (Bivalvia) and Mytilus chilensis (Hupé) (Bivalvia)

In protected areas of the southern Chilean coastline, the barnacle Jehlius cirratus dominates the upper intertidal zone, the bivalve Perumytilus purpuratus is the dominating species in the intermediate zone and Mytilus chilensis in the middle-lower zone. Varying degrees of aerial respiration were observed in the laboratory for these three sessile invertebrates: 80–100% of the immersed oxygen uptake for Jehlius cirratus, 30–50% for Perumytilus purpuratus and 5–15% for Mytilus chilensis. The pyruvate kinase/phosphoenolpyruvate carboxykinase (PK/PEPCK) ratio (adductor muscle) was higher for P. purpuratus than for M. chilensis. J. cirratus had no PEPCK activity in total soft tissues, under the assay conditions used in this study, and PK activity was higher for the cirriped than that of both bivalves. Succinate was produced in both mussels when exposed to hypoxic conditions, but it was not detected in J. cirratus. The kinetic parameters of the PK revealed that M. chilensis presented the highest _0.5 value for PEP and J. cirratus the lowest. Alanine inhibited the PK from M. chilensis to a greater extent (higher n_H value) and did not affect the PK of the cirriped. This latter enzyme also presented a marked substrate inhibition, above PEP concentrations of 0.5 mM. The evidence suggests that organisms inhabiting the upper intertidal zone could utilize an aerobic metabolism, given their high aerial respiration capacity, and that the succinate anaerobic pathway could be a more important metabolic strategy in species of the middle-lower intertidal zone. The physiological and biochemical capacities of these three species could thus be correlated with their vertical distribution in the intertidal rocky shore.     

SPORE RELEASE IN ACROCHAETIUM SP. (RHODOPHYTA) IS BACTERIALLY CONTROLLED1

The facultative red algal epiphyte Acrochaetium sp. liberated spores preferentially and recruited more successfully in laboratory cultures when its host Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira was present. The same effect was also induced by cell‐free medium from G. chilensis, suggesting it contained a molecular signal. Antibiotics prevented spore release in Acrochaetium sp., even when G. chilensis was present, suggesting a prokaryotic origin of the signal. Simultaneous application of N‐butyl‐homoserine‐lactone (BHL) restored the spore‐release capacity, which demonstrated that spore release was not directly inhibited by the antibiotics and indicated that bacterially generated N‐acyl‐homoserine‐lactones (AHLs) regulate spore release. An involvement of AHL was further indicated by the fact that two different halofuranone inhibitors of AHL receptors also inhibited spore release when they were applied at relatively low concentrations. Of seven different AHLs tested, only BHL induced the effect. However, BHL was only active at relatively high concentrations (100 μM), and it was not detected in spore‐release‐inducing medium of G. chilensis. Another water‐soluble AHL or an AHL structure analog is therefore probably the active compound in G. chilensis cultures. The data presented demonstrate that life cycle completion in Acrochaetium sp. strongly depends on bacteria, which are not always present in sufficient numbers on the alga itself. Exogenous bacteria that are associated with G. chilensis or with other potential substrates may therefore trigger timely spore liberation in Acrochaetium sp., provided that the necessary concentration of AHL is reached. This first finding of AHL perception in a red alga confirms that AHL signalling is more widespread among eukaryotes than was thought until recently. However, spore release of a second red alga, Sahlingia subintegra (Rosenv.) Kornmann, was unaffected by AHL, and the reaction observed is therefore not universal.     

CHARACTERIZATION OF GENETIC MARKERS LINKED TO SEX DETERMINATION IN THE HAPLOID‐DIPLOID RED ALGA GRACILARIA CHILENSIS1

Bulk segregant analysis, random amplified polymorphic DNA (RAPD), and sequence characterized amplified region (SCAR) methods were used to identify sex‐linked molecular markers in the haploid‐diploid rhodophyte Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira. One hundred and eighty 10 bp primers were tested on three bulks of DNA: haploid males, haploid females, and diploid tetrasporophytes. Three RAPD primers (OPD15, OPG16, and OPN20) produced male‐specific bands; and one RAPD primer (OPD12), a female‐specific band. The sequences of the cloned putative sex‐specific PCR fragments were used to design specific primers for the female marker SCAR‐D12‐386 and the male marker SCAR‐G16‐486. Both SCAR markers gave unequivocal band patterns that allowed sex and phase to be determined in G. chilensis. Thus, all the females presented only the female band, and all the males only the male band, while all the tetrasporophytes amplified both male and female bands. Despite this sex‐specific association, we were able to amplify SCAR‐D12‐386 and SCAR‐G16‐486 in both sexes at low melting temperature. The differences between male and female sequences were of 8%–9% nucleotide divergence for SCAR‐D12‐386 and SCAR‐G16‐486, respectively. SCAR‐D12‐386 and SCAR‐G16‐486 could represent degenerated or diverged sequences located in the nonrecombining region of incipient sex chromosomes or heteromorphic sex chromosomes with sequence differences at the DNA level such that PCR primers amplify only one allele and not the other in highly specific PCR conditions. Seven gametic progenies composed of 19 males, 19 females, and the seven parental tetrasporophytes were analyzed. In all of them, the two SCAR markers segregated perfectly with sexual phenotypes.     

Differential responses of tetrasporophytes and gametophytes of Mazzaella laminarioides (Gigartinales,Rhodophyta) under solar UV radiation

The effects of solar UV radiation on mycosporine‐like amino acids (MAAs), growth, photosynthetic pigments (Chl a, phycobiliproteins), soluble proteins (SP), and C and N content of Mazzaella laminarioides tetrasporophytes and gametophytes were investigated. Apical segments of tetrasporophytes and gametophytes were exposed to solar radiation under three treatments (PAR [P], PAR+UVA [PA], and PAR+UVA+UVB [PAB]) during 18 d in spring 2009, Punta Arenas, Chile. Samples were taken after 2, 6, 12, and 18 d of solar radiation exposure. Most of the parameters assessed on M. laminarioides were significantly influenced by the radiation treatment, and both gametophytes and tetrasporophytes seemed to respond differently when exposed to high UV radiation. The two main effects promoted by UV radiation were: (i) higher synthesis of MAAs in gametophytes than tetrasporophytes at 2 d, and (ii) a decrease in phycoerythrin, phycocyanin, and SPs, but an increase in MAA content in tetrasporophytes at 6 and 12 d of culture. Despite some changes that were observed in biochemical parameters in both tetrasporophytes and gametophytes of M. laminarioides when exposed to UVB radiation, these changes did not promote deleterious effects that might interfere with the growth in the long term (18 d). The tolerance and resistance of M. laminarioides to higher UV irradiance were expected, as this intertidal species is exposed to variation in solar radiation, especially during low tide.     

PHOSPHORUS AND NITROGEN NUTRITION IN CHONDRUS CRISPUS (RHODOPHYTA): EFFECTS ON TOTAL PHOSPHORUS AND NITROGEN CONTENT,CARRAGEENAN PRODUCTION,AND PHOTOSYNTHETIC PIGMENTS AND METABOLISM1

The existence of a phenomenon in phosphorus (P) nutrition comparable to the “Neish effect” in nitrogen (N) nutrition (an inverse relation between seawater N enrichment and carrageenan content) was investigated in the temperate red alga Chondrus crispus Stackhouse. Plants were preconditioned for 17 d and then cultured under varying enrichments of P (0, 3, 6, 10, 15 μM P·wk^?1) and a constant N enrichment (53.5 μM N·wk^?1) for 5 wk. Tissue total P, tissue total N, and carrageenan contents were then determined. Identical experiments were performed using C. crispus collected during the fall, winter, spring, and summer seasons. The procedure was repeated using material collected during the following fall season and cultured under constant P (6 μM P·wk^?1) and varying N enrichments (0, 3, 6, 10, 25 μM N·wk^?1). In the fall (P) experiment, carrageenan content was the highest [53.1 ± 0.3% DW (dry weight)], and tissue total P content was the lowest (1.71 ± 0.27 mg P·g DW^?1) in plants that received no P enrichment. Carrageenan content was stable (46.1 ± 1.8% DW) for plants given enrichments of 3 μM P·wk^?1 and greater. Thus, a decrease in carrageenan content, concomitant with an increase in tissue total P content, was observed, but only at tissue total P levels below 2 mg P·g DW^?1. As these levels were always higher than 2 mg P·g DW^?1 in the winter, spring, and summer experiments, carrageenan content remained constant within each season at 46.2 ± 1.3, 43.1 m 0.7, and 44.5 ± 0.6% DW, respectively. Nitrogen enrichment of plants collected in the fall did not affect carrageenan content, which was stable at 49.3 ± 0.9% DW. When these plants were compared with those of the previous fall experiment (6 μM P·wk^?1 and 53.5 μM N·wk^?1), a slight increase in carrageenan content was noted. Thus, at sufficiently high concentration, N also decreased carrageenan content in C. crispus. Phosphorus nutrition had no significant effect on photosynthesis versus irradiance parameters (P_max, α, R_d, I_c, and I_k), the contents of the photosynthetic pigments chlorophyll-a, phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC), and the ratios PE:APC and PC:APC. In contrast, N nutrition affected both P_maxand the photosynthetic pigment contents. The data indicate that N limitation reduces the number of phycobilisomes but not their size. The greater reduction in phycobiliprotein than chlorophyll-acontent corroborates the natural bleaching phenomenon regularly observed in C. crispus populations during summer when N levels are generally low in seawater. These results suggest that C. crispus in the temperate waters of the Bay of Fundy may experience N limitation, but P limitation is unlikely.     

SIZE INCREMENTS DUE TO INTERINDIVIDUAL FUSIONS: HOW MUCH AND FOR HOW LONG?1

Size increments following interindividual fusions appear as a general benefit for organisms, such as coalescing seaweeds and modular invertebrates, with the capacity to fuse with conspecifics. Using sporelings of the red algae Gracilaria chilensis C. J. Bird, McLachlan et E. C. Oliveira and Mazzaella laminarioides (Bory) Fredericq, we measured the growth patterns of sporelings built with different numbers of spores, and the magnitude and persistence of the size increments gained by fusions. Then we studied three morphological processes that could help explain the observed growth patterns. Results indicate that in these algae, coalescence is followed by immediate increase in total size of the coalesced individual and that the increment is proportional to the number of individuals fusing. However, the size increments in sporelings of both species do not last >60 d. Increasing reductions of marginal meristematic cells and increasing abundance of necrotic cells in sporelings built with increasing numbers of initial spores are partial explanations for the above growth patterns. Since sporelings formed by many spores differentiate erect axes earlier and in larger quantities than sporelings formed by one or only a few spores, differentiation, emergence, and growth of erect axes appear as a more likely explanation for the slow radial growth of the multisporic sporelings. Erect axis differentiation involves significant morphological and physiological changes and a shift from radial to axial growth. It is concluded that the growth pattern exhibited by these macroalgae after fusion differs from equivalent processes described for other organisms with the capacity to fuse, such as modular invertebrates.     

Microsatellite markers and cytoplasmic sequences reveal contrasting pattern of spatial genetic structure in the red algae species complex Mazzaella laminarioides

Mazzaella laminarioides is a common haploid‐diploid red alga that forms dense beds. This alga has a wide distributional range, covering 3,500 km of the Chilean coast, but is restricted to high rocky intertidal zones. Recently, the existence of three highly divergent genetic lineages was demonstrated for this taxon, and two cytoplasmic markers were used to determine that these lineages are distributed in strict parapatry. Here, using 454 next‐generation sequencing, we developed polymorphic microsatellite loci that cross amplify in all three cytoplasmic lineages. Six sites (i.e., two sites within each lineage) were analyzed using nine microsatellite loci. Our work shows that, although substantial cytoplasmic differentiation occurs within M. laminarioides, the microsatellite loci did not retrieve three nuclear genetic clusters as expected. Indeed, while the northernmost and southernmost cytoplasmic lineages form two strongly divergent nuclear groups characterized by diagnostic alleles, the third cytoplasmic lineage did not form a third nuclear independent group. It is possible that inter‐lineage gene exchange has occurred, particularly at sites along the contact zone between the different cytoplasmic lineages. This nuclear‐cytoplasmic incongruence in M. laminarioides could be explained by incomplete lineage sorting of the nuclear genes or asymmetric introgressive hybridization between the lineages. Finally, highly significant heterozygote deficiencies (suggesting occurrence of intergametophytic selfing) were observed in the three small northernmost sites while the large southernmost sites generally approached panmixia.     

Is top‐down control by predators driving insect abundance and herbivory rates in fragmented forests?

The effects of forest fragmentation on ecological interactions and particularly on food webs have scarcely been analysed. There is usually less herbivory in forest fragments than in continuous forests. Here we hypothesize that forest fragmentation enhances top‐down control of herbivory through an increase in insectivorous birds and a decrease in herbivorous insects, with a consequent decrease in plant reproductive success in small forest fragments. In the Maulino forest in central Chile, we experimentally excluded birds from Aristotelia chilensis (Elaeocarpaceae) trees in both forest fragments and continuous forest, and analysed herbivore insect abundance, herbivory and plant reproductive success during two consecutive growing seasons. We expected that insect abundance and herbivory would increase, and reproductive success would decrease in A. chilensis from which birds have been excluded, particularly in forest fragments where bird abundance and predation pressure on insects is higher. The abundance of herbivorous insects was lower in the forest fragments than in the continuous forest only in the first season, and herbivory was lower in forest fragments than in the continuous forest throughout the study. Moreover, during the second growing season herbivory was greater in the excluded trees than in the control trees, and as expected, there was a greater difference in the fragments than in the continuous forest, but this was not statistically significant. Exclusion of birds did not affect the reproductive success of A. chilensis. Our results, after 2 years of study, demonstrate that birds affect the levels of herbivory on A. chilensis in the Maulino forest, but do not support our hypothesis of enhanced top‐down control in fragmented forests, as the strength of the effect of excluding birds did not vary with fragmentation.     

CD40-TRAF6 and Autophagy-Dependant Anti-Microbial Activity in Macrophages

A fundamental question in host-pathogen interaction is to determine if the immune system activates fusion with the lysosomes to eradicate pathogens. We recently reported that this task is accomplished by the interaction between CD40 expressed on macrophages and CD154 expressed on activated CD4⁺ T cells. CD40 stimulation of macrophages induces vacuole-lysosome fusion through autophagy and results in killing of the obligate intracellular pathogen Toxoplasma gondii. This response is independent of IFN-gamma, STAT1 and p47 GTPases. We now report that vacuole-lysosome fusion is dependent on synergy between TRAF6 signaling downstream of CD40 and TNF-alpha. These studies identified a new paradigm by which T cells eradicate an intracellular pathogen within macrophages.

Addendum to:

CD40 Induces Macrophage Anti-Microbial Activity by Triggering Autophagy-Dependent Fusion of Pathogen-Containing Vacuoles and Lysosomes

R.M. Andrade, M. Wessendarp. M.J. Gubbels, B. Striepen and C.S. Subauste

J Clin Invest 2006; 116:2366-77     

Characterization of functionally active interleukin‐18/eGFP fusion protein expression during cell cycle phases in recombinant chicken DF1 Cells

The dependence of foreign gene expression on cell cycle phases in mammalian cells has been described. In this study, a DF1/chIL‐18a cell line that stably expresses the fusion protein chIL‐18 was constructed and the enhanced green fluorescence protein connected through a (G₄S)₃ linker sequence investigated the relationship between cell cycle phases and fusion protein production. DF1/chIL‐18a cells (1 × 10⁵) were inoculated in 60‐mm culture dishes containing 5 mL of media to achieve 50%–60% confluence and were cultured in the presence of the cycle‐specific inhibitors 10058‐F4, aphidicolin, and colchicine for 24 and 48 h. The percentage of cell density and mean fluorescence intensity in each cell cycle phase were assessed using flow cytometry. The inhibitors effectively arrested cell growth. The fusion protein production rate was higher in the S phase than in the G0/G1 and G2/M phases. When cell cycle progression was blocked in the G0/G1, S, and G2/M phases by the addition of 10058‐F4, aphidicolin, and colchicine, respectively, the aphidicolin‐induced single cells showed higher fusion protein levels than did the 10058‐F4‐ or colchicine‐induced phase cells and the uninduced control cells. Although the cells did not proliferate after the drug additions, the amount of total fusion protein accumulated in aphidicolin‐treated cells was similar to that in the untreated cultures. Fusion protein is biologically active because it induces IFN‐γ production in splenocyte cultures of chicken. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:581–591, 2016     

EFFECT OF ROCKY INTERTIDAL AMPHIPODS ON ALGAL RECRUITMENT: A FIELD STUDY1

Evidence about the potential of mobile marine invertebrates to act as algal spore dispersal agents is presently circumstantial. Using a field correlational and experimental protocol, our study tested the hypothesis that amphipods can increase the spore recruitment of the red alga Iridaea laminarioides Bory. Iridaea laminarioides spore recruitment onto glass slides was measured at a site with high amphipod abundance and a site with low density of amphipods. To evaluate the effect of an Ulva canopy on recruitment, replicated glass slides with and without a surrounding Ulva canopy were installed at both sites. The number of I. laminarioides spores recruited on the glass slides was four to eight times higher at the high amphipod abundance site than at the low density site. However, the presence of an Ulva canopy covering the glass slides did not significantly increase the recruitment of I. laminarioides. Because the abundance of I. laminarioides, the proportion of cystocarpic plants, and the percentage of open cystocarps only differed slightly between the low and high abundance amphipod sites, we suggest that the variation in recruitment between the sites is due to the differences in amphipod abundance (and their movements) and not to differences in spore production. Moreover, the presence of I. laminarioides cystocarps showing amphipod grazing scars was significantly higher at the high amphipod density site than at the low density site.     

Whitening,thallus decay and fragmentation in Gracilaria chilensis associated with an endophytic amoeba

Whitening of Gracilaria chilensis, accompanied by tissue softening and thallus fragmentation, was found to be associated with the presence of an endophytic amoeba. Although the symptoms developed originally in green mutant thalli, subsequent infections in the laboratory also affected normal, wild-type G. chilensis. Ultrastructural evidence indicates that the amoebae perforate the host cell walls of both cortical and medullary cells and digest their protoplasm. Feeding by the amoeba appears to involve both phagocytosis and enzymatic digestion of the host tissue. Destruction of the host tissue resulted in large cavities first, followed by thallus fragmentation. No other organism was found during the early stages of thallus invasion by the amoeba, although bacteria may appear once the amoeba reaches the inner tissues of the host.     

Nucleotide distribution in bacterial DNA's differing in G + C content

Summary The DNA's ofMicrococcus lysodeikticus andClostridium perfringens were fragmented to about 7 000 nucleotide pairs long by shear and fractionated with respect to buoyant density of mercury complexes in Cs₂SO₄. The distribution of G + C content in both DNA's was characteristically asymmetric. InM. lysodeikticus DNA, low G + C fragments were more numerous than high G + C fragments, whereas inC. perfringens DNA, high G + C fragments were more numerous than low G + C fragments. The G + C content of fragments ofM. lysodeikticus DNA varied from 70 to 77%, with a mean and standard deviation of 73.7 ± 1.92% G + C and that ofC. perfringens DNA varied from 27 to 34%, with a mean and standard deviation of 29.8 ± 1.34% G + C. The standard deviation was smaller than that ofEscherichia coli DNA fragments of similar size. Biological meanings of relatively low heterogeneity in nucleotide composition inM. lysodeikticus andC. perfringens are discussed.     

PLASTID DNA RESTRICTION ANALYSIS LINKS THE HETEROMORPHIC PHASES OF AN APOMICTIC RED ALGAL LIFE HISTORY1

Gymnogongrus sp. (Phyllophoraceae) from Nova Scotia, Canada, identified tentatively as G. devoniensis (Greville) Schotter, grows in association with an Erythrodermis-like that forms chains of tetrasporangia or bisporangia. The crust resembles tetrasporophytic phases of other Gymnogongrus species, but in culture both it and the G. devoniensis gametophytes cycle independently by apomictic reproduction. A method was developed for extracting organelle DNA from this carrageenophyte genus involving purification of nucleic acids by binding to hydroxylapatite. Plastid DNA from G. devoniensis and bisporangial Erythrodermis-like crusts was compared with that of G. devoniensis and G. crenulatus (Turner) J. Agardh from France and of G. furcellatus (C. Agardh) J. Agardh from Chile. Plastid genomes of all Gymnogongrus species and the Erythrodermis-like crust were approximately 175 kb long. A single 3.5-kb plasmid DNA species was found in G. devoniensis and the Erythrodermis-like bisporophyte but not in other samples. Digestion of plasted DNA with several restriction endonucleases produced identical patterns in G. devoniensis and the Erythrodermis-like bisporophyte from the same location, indicating clearly that these entities represent two phases of an uncoupled life history. These results were confirmed with heteologous probes. A restriction fragment length polymorphism was identified between two Nova Scotian G. devoniensis populations. There was no similarity in restriction patterns between G. devoniensis from Nova Scotia, G. devoniensis from France. G. crenulatus or G. furcellatus, suggesting that molecular taxonomic methods could be important in delineating members of this morphologically variable genus. Further study is necessary to determine whether either Nova Scotian G. devoniensis or French G. devoniensis corresponds to type populations of G. devoniensis from Devon, England.     

Effects of UVB Radiation on the Initial Stages of Growth of Gigartina Skottsbergii, Sarcothalia Crispata and Mazzaella Laminarioides (Gigartinales, Rhodophyta)

The effects of UVB radiation on the growth of macroalgal thalli were evaluated using tetrasporophytic fronds of the Rhodophytes Gigartina skottsbergii, Sarcothalia crispata and Mazzaella laminarioides. The tetrasporophytic fronds were collected from nature and the tetrasporophyte sporelings grown in a temperature regulated chamber at 8 ± 2 ^∘C with a 12L:12D (Light: Dark) photoperiod, Photosynthetically Active Radiation (PAR) of 55 μmol photons m⁻² s⁻¹ and seawater enriched with 20 mL L⁻¹ of Provasoli medium. We exposed the thalli of these macroalgae to PAR (55 μmol photons m⁻² s⁻¹) and three treatments using a combination of PAR with three different levels of UVB radiation (0.10, 0.15 and 0.23 W m⁻² for G. skottsbergii and S. crispata and 0.02, 0.05 and 0.10 W m⁻² for M. laminarioides) during a period of 71 days. Growth of thalli was quantified by measuring their length using digitized photographs of samples.Important differences were detected in the growth of individuals cultured under the effects of UVB radiation, when compared to the control (i.e. plants exposed to PAR only). In the case of G. skottsbergii and S. crispata higher levels of UVB radiation resulted in slower growth of thalli. In nearly all measurements for the first two species, UVB radiation levels of 0.1 W m⁻² induced differences in thallus growth, while for M. laminarioides levels of UVB radiation of 0.1 W m⁻² were effective only after a prolonged period of exposure.Differential effects of UVB radiation on G. skottsbergii, S. crispata and M. laminarioides could interfere with the natural populations of these economically important macroalgal species in southern Chile, where they occur under the annual influence of the Antarctic Ozone Hole and the general thinning of the ozone layer.     

MOLECULAR IDENTIFICATION OF TWO SIBLING SPECIES UNDER THE NAME GRACILARIA CHILENSIS (RHODOPHYTA,GRACILARIALES)1,3

Molecular markers belonging to three different genomes, mitochondrial (cox2‐3 spacer), plastid (RUBISCO spacer), and nuclear (internal transcribed spacer 1), were used to compare Gracilaria chilensis samples collected along the Chilean coast with samples ascribed to G. chilensis from the West Pacific Ocean (New Zealand and Australia). Our data are in agreement with previous studies suggesting two sibling species currently going under the name G. chilensis that co‐occur in New Zealand. One of these, a New Zealand sample previously examined by Bird and others in 1990, is conspecific with G. chilensis from Chile. Finally, our results demonstrate clearly that most of the sequences in GenBank reported as G. chilensis are based on misidentified material.     

Effects of simulated browsing on the growth of Austrocedrus chilensis saplings

In the forests of Austrocedrus chilensis (D.Don) Florin et Boutleje (Cupressaceae) it is frequent to observe numerous mutilated and dwarfed saplings which have been browsed by domestic cattle and exotic deer. One way to assess the effects of browsing on plant growth is by simulating this process through defoliation. This study includes results from four years of artificial browsing at different intensities on A. chilensissaplings. Our objective was to evaluate the possible compensatory growth by A. chilensis. To that end we measured the effects of simulated browsing on the growth of saplings kept under two different experimental conditions, with and without water stress. Treatments were applied at the end of winter of 1993 and were repeated on 1994, 1995 and 1996. Treatments consisted in pruning and cutting. Neither cutting effects nor factors interactions were found. Pruning resulted in a reduction of saplings biomass of 44% and was only significant at the more intensive level. Watering produced saplings with five times more biomass, but the general response of A. chilensis to simulated browsing was the lack of compensation regardless the intensity of pruning or the quality of site.