Non-indigenous species and their realized niche in tidepools along the South-East Pacific coast.

Non-indigenous species (NIS) have the potential to colonize and become established in a wide range of coastal habitats. Species with broad environmental tolerances can quickly adapt to local conditions and expand their niches along environmental gradients, and even colonize habitats with extreme abiotic conditions. Here we report and document the distribution of eight marine NIS (four seaweed and four invertebrate species) found in tidepools along a 3000 km latitudinal gradient along the Pacific coast of Chile (18.4°S to 41.9°S). The seaweed NIS Codium fragile, Capreolia implexa, Schottera nicaeensis and Mastocarpus latissimus were mostly distributed towards high latitudes (i.e., more southerly locations), where temperatures in tidepools were low. The invertebrate NIS Anemonia alicemartinae, Ciona robusta, Bugula neritina and Bugulina flabellata were more common towards low latitudes, where high temperatures were registered in the tidepools. Across the intertidal gradient, seaweed NIS were mostly found in pools in the mid and low intertidal zone, while invertebrate NIS occurred mostly in pools from the mid and upper intertidal zones. The realized niche spaces of NIS (based on the Outlying Mean Index, OMI) in the study area were mainly influenced by environmental conditions of temperature and salinity (along the latitudinal and intertidal gradients), while other tidepool characteristics (depth, surface area, exposition, and complexity) only had minor effects. Five of the eight NIS exhibited a realized niche space coinciding with the average tidepool environmental conditions, while marginal niches were occupied by species with affinities for specific temperatures and salinities along the latitudinal and intertidal gradients. Our results indicate that physiological tolerances to environmental factors play a fundamental role in the distribution of seaweed and invertebrate NIS in tidepools along the Chilean coast. This study confirms that tidepools offer suitable conditions for some seaweed and invertebrate NIS, potentially facilitating their invasion into new natural habitats.

Effect of UV-radiation on the physiology of the invasive green seaweed Codium fragile and its associated bacteria.

Invasive species such as seaweeds often have a broad tolerance, allowing them to colonize novel habitats. During invasion, also new epibacteria can be formed on seaweeds, which have important chemo-ecological effects. Since UV-radiation (UVR) is one of the main factors affecting seaweeds and their epibacteria, we tested its effect on intertidal and subtidal thalli of the invasive seaweed Codium fragile from three sites and monitored photosynthesis, antioxidant activity and epibacteria. Exposure to UV-radiation resulted in photoinhibition with a subsequent low recovery in subtidal thalli from 23°S compared to 27°S and 30°S, which both showed a higher and almost complete recovery. However, a high antioxidant activity was present in all thalli, permitting to explain its relatively high tolerance to new environments. UV-radiation modified the composition of the epibacteria community by reducing its diversity and evenness. Our results showed that C. fragile responds plastic to variable UV-radiation (depending on site and water depth), which contributes to its high invasion potential.

Deciphering the Non-Equivalence of Serine and Threonine O-Glycosylation Points: Implications for Molecular Recognition of the Tn Antigen by an anti-MUC1 Antibody.

The structural features of MUC1-like glycopeptides bearing the Tn antigen (α-O-GalNAc-Ser/Thr) in complex with an anti MUC-1 antibody are reported at atomic resolution. For the α-O-GalNAc-Ser derivative, the glycosidic linkage adopts a high-energy conformation, barely populated in the free state. This unusual structure (also observed in an α-S-GalNAc-Cys mimic) is stabilized by hydrogen bonds between the peptidic fragment and the sugar. The selection of a particular peptide structure by the antibody is thus propagated to the carbohydrate through carbohydrate/peptide contacts, which force a change in the orientation of the sugar moiety. This seems to be unfeasible in the α-O-GalNAc-Thr glycopeptide owing to the more limited flexibility of the side chain imposed by the methyl group. Our data demonstrate the non-equivalence of Ser and Thr O-glycosylation points in molecular recognition processes. These features provide insight into the occurrence in nature of the APDTRP epitope for anti-MUC1 antibodies.

Detection of tumor-associated glycopeptides by lectins: the peptide context modulates carbohydrate recognition.

Tn antigen (α-O-GalNAc-Ser/Thr) is a convenient cancer biomarker that is recognized by antibodies and lectins. This work yields remarkable results for two plant lectins in terms of epitope recognition and reveals that these receptors show higher affinity for Tn antigen when it is incorporated in the Pro-Asp-Thr-Arg (PDTR) peptide region of mucin MUC1. In contrast, a significant affinity loss is observed when Tn antigen is located in the Ala-His-Gly-Val-Thr-Ser-Ala (AHGVTSA) or Ala-Pro-Gly-Ser-Thr-Ala-Pro (APGSTAP) fragments. Our data indicate that the charged residues, Arg and Asp, present in the PDTR sequence establish noteworthy fundamental interactions with the lectin surface as well as fix the conformation of the peptide backbone, favoring the presentation of the sugar moiety toward the lectin. These results may help to better understand glycopeptide-lectin interactions and may contribute to engineer new binding sites, allowing novel glycosensors for Tn antigen detection to be designed.

Serine versus threonine glycosylation with α-O-GalNAc: unexpected selectivity in their molecular recognition with lectins.

The molecular recognition of several glycopeptides bearing Tn antigen (α-O-GalNAc-Ser or α-O-GalNAc-Thr) in their structure by three lectins with affinity for this determinant has been analysed. The work yields remarkable results in terms of epitope recognition, showing that the underlying amino acid of Tn (serine or threonine) plays a key role in the molecular recognition. In fact, while Soybean agglutinin and Vicia villosa agglutinin lectins prefer Tn-threonine, Helix pomatia agglutinin shows a higher affinity for the glycopeptides carrying Tn-serine. The different conformational behaviour of the two Tn biological entities, the residues of the studied glycopeptides in the close proximity to the Tn antigen and the topology of the binding site of the lectins are at the origin of these differences.

Major consequences of minor damage: impacts of small grazers on fast-growing kelps.

Damage by small herbivores can have disproportionately large effects on the fitness of individual plants if damage is concentrated on valuable tissues or on select individuals within a population. In marine systems, the impact of tissue loss on the growth rates of habitat-forming algae is poorly understood. We quantified the grazing damage by an isopod Amphoroidea typa on two species of large kelps, Lessonia spicata and Macrocystis pyrifera, in temperate Chile to test whether non-lethal grazing damage could reduce kelp growth rates and photosynthetic efficiency. For L. spicata, grazing damage was widespread in the field, unevenly distributed on several spatial scales (among individuals and among tissue types) and negatively correlated with blade growth rates. In field experiments, feeding by A. typa reduced the concentration of photosynthetic pigments and led to large reductions (~80%) in blade growth rates despite limited loss of kelp biomass (0.5% per day). For M. pyrifera, rates of damage in the field were lower and high densities of grazers were unable to reduce growth rates in field experiments. These results demonstrate that even low per capita grazing rates can result in large reductions in the growth of a kelp, due the spatial clustering of herbivores in the field and the selective removal of photosynthetically active tissues. The impacts of small herbivores on plant performance are thus not easily predicted from consumption rates or abundance in the field, and vary with plant species due to variation in their ability to compensate for damage.

Hermafroditismo funcional de la gónada de Fissurella crassa (Mollusca: Fissurellidae) / Functional hermaphrodite gonad in Fissurella crassa (Mollusca: Fissurellidae)

La costa del Pacífico sudoriental es el hábitat de las 13 especies de lapas descritas del subgénero Fissurella Brugière. En estas especies no existe dimorfismo sexual, los animales son dioicos, el sexo se reconoce explorando directa o indirectamente las gónadas y no tienen procesos de reversión sexual. La presencia de un organismo de Fissurella crassa con gónada formada por porciones de ovario y otras de testículo con capacidad para generar óvulos y espermatozoides, evidencia la potencialidad que los organismos de Fissurella poseen para desarrollar el hermafroditismo funcional. Sin embargo, el presente hallazgo no permite inferir si el agente desencadenante del desarrollo sincrónico funcional de la gónada hermafrodita es un factor endógeno y/o asociado a algún evento exógeno medio ambiental.

The coast of the Southeastern Pacific is the habitat for 13 species of described keyhole limpets of the subgenus Fissurella Brugière. In these species sexual dimorphism does not exist, the animals are dioicos, the sex is recognized exploring directly or indirectly the gonads and they do not have processes of sexual reversion. The presence of an organism Fissurella crassa with portions of ovary and testicle with ability to generate ova and sperms, demonstrates the potential that Fissurella's organisms possess to develop functional hermaphroditism. Nevertheless, the present find does not allow to infer if the trigger agent of the synchronous functional development of the hermaphrodite gonad is a factor endogenous and/or associated with any exogenous environmental event.