Evolutionary drivers of the hump-shaped latitudinal gradient of benthic polychaete species richness along the Southeastern Pacific coast.

Latitudinal diversity gradients (LDG) and their explanatory factors are among the most challenging topics in macroecology and biogeography. Despite of its apparent generality, a growing body of evidence shows that 'anomalous' LDG (i.e., inverse or hump-shaped trends) are common among marine organisms along the Southeastern Pacific (SEP) coast. Here, we evaluate the shape of the LDG of marine benthic polychaetes and its underlying causes using a dataset of 643 species inhabiting the continental shelf (<200 m depth), using latitudinal bands with a spatial resolution of 0.5°, along the SEP (3-56° S). The explanatory value of six oceanographic (Sea Surface Temperature (SST), SST range, salinity, salinity range, primary productivity and shelf area), and one macroecological proxy (median latitudinal range of species) were assessed using a random forest model. The taxonomic structure was used to estimate the degree of niche conservatism of predictor variables and to estimate latitudinal trends in phylogenetic diversity, based on three indices (phylogenetic richness (PDSES), mean pairwise distance (MPDSES), and variation of pairwise distances (VPD)). The LDG exhibits a hump-shaped trend, with a maximum peak of species richness at ca. 42° S, declining towards northern and southern areas of SEP. The latitudinal pattern was also evident in local samples controlled by sampling effort. The random forest model had a high accuracy (pseudo-r2 = 0.95) and showed that the LDG could be explained by four variables (median latitudinal range, SST, salinity, and SST range), yet the functional relationship between species richness and these predictors was variable. A significant degree of phylogenetic conservatism was detected for the median latitudinal range and SST. PDSES increased toward the southern region, whereas VPD showed the opposite trend, both statistically significant. MPDSES has the same trend as PDSES, but it is not significant. Our results reinforce the idea that the south Chile fjord area, particularly the Chiloé region, was likely the evolutionary source of new species of marine polychaetes along SEP, creating a hotspot of diversity. Therefore, in the same way as the canonical LDG shows a decline in diversity while moving away from the tropics; on this case the decline occurs while moving away from Chiloé Island. These results, coupled with a strong phylogenetic signal of the main predictor variables suggest that processes operating mainly at evolutionary timescales govern the LDG.

A new species of Eunice Cuvier, 1817 (Polychaeta: Eunicidae) from the slope of the Desventuradas Islands and seamounts of the Nazca Ridge, southeastern Pacific Ocean.

A new species of Eunicidae, Eunice decolorhami sp. n., from the southeastern Pacific Ocean, is described. The species was collected at the slope of the Desventuradas Islands (San Félix and San Ambrosio) and in three nearby seamounts of the Nazca Ridge, in dead coral rubble bottoms from 180 to 340 m depth and inhabiting inside parchment-like branched tubes. Eunice decolorhami sp. n. can be distinguished from other species of the genus, mainly by the coloration pattern of the subacicular hooded hooks along the body segments, the beginning of the subacicular hooded hooks, the beginning of the branchiae, the maximum number of branchial filaments, and the maxillary formula. A key for the seven Eunice species recorded off the coast of Chile and Peru, including the new species described herein, is provided.

Patterns of association of native and exotic boring polychaetes on the southeastern Pacific coast of Chile: the combined importance of negative, positive and random interactions.

BACKGROUND: Studies of biological invasions focus on negative interactions between exotic and native biotas, emphasizing niche overlap between species and competitive exclusion. However, the effects of positive interactions and coexistence are poorly known. In this study we evaluate the importance of positive, negative, or random species associations in explaining the coexistence of native and exotic boring polychaetes inhabiting invertebrate hosts, on the southeastern Pacific coast of Chile. We assess three hypotheses to explain the observed patterns: positive species interactions, weak competitive interactions, and competitive intransitivity. METHODOLOGY: To assess the potential effect of competition between native and exotic polychaetes we analyzed patterns of co-occurrence of species pairs in northern and southern regions, using the metric of the probabilistic model. Since biotic interactions can affect not only native species, we also evaluated correlations between native and exotic polychaete abundance, using reduced major axis regression linear models. To assess the transitivity of competitive hierarchies we used metrics and analytical methods based on abundance matrices to estimate species competition and patch transition matrices. RESULTS: On average 50% of the species pairs presented significant weak negative associations, all associated with the exotic species Polydora rickettsi; the remaining 50% had random associations, and none showed positive associations. However, the relationship of abundance between native and exotic boring polychates supports a tendency towards coexistence. At local and regional scales, we observed the presence of a transitive network competition structure, where the exotic boring polychaete, P. rickettsi was generally the dominant species. CONCLUSIONS: Our results support that native and exotic boring polychaete species coexist through weak competitive interactions. Nevertheless, the large number of random interactions observed indicates that species coexistence can be accounted for by stochastic processes, as proposed by neutral theory. Coexistence may be a frequent result of interactions between native and exotic species, although less apparent than competitive exclusion. Thus, the probabilistic point-of-view used here provides a statistical tool for evaluating coexistence as a result of exotic and native species' interactions, an idea which has been proposed in invasion ecology, but largely lacks empirical support and methodologies for detecting underlying mechanisms. Finally, we found evidence that P. rickettsi is a successful invader by being competitively dominant, but not excluding other species.

Sternaspis chilensis n. sp., a new species from austral Chilean channels and fjords (Annelida, Sternaspidae).

Sternaspis chilensis n. sp. is described based on specimens collected in channels and fjords of southern Chile and previously identified as Sternaspis scutata (Ranzani, 1817), originally described from the Meditarrean Sea. Sternaspis chilensis n. sp. is described based on the features of the shield with anterior margins rounded and anterior depression shallow; marginal shield chaetal fascicles arranged with an inverted C-shaped pattern; and distribution of the integument papillae. Sternaspis chilensis is widely distributed in the Magellan Province from Estero Reloncaví (41°32'54"S, 72°19'48"W) to Strait of Magellan (53°34'S, 70°04'W), between 50 and 515 m depth.

Pectinaria chilensis NILSSON, 1928 (POLYCHAETA: PECTINARIIDAE): taxonomic characterization, new distributional records and ecological notes from the chilean coast

Se revisa Pectinaria chilensis de la costa de Chile a partir de ejemplares recolectados en fondos blandos sublitorales, entre 45 y 93m de profundidad, en cuatro localidades del norte de Chile. Estos especímenes fueron comparados con ejemplares recolectados a 17m de profundidad en Coronel, Golfo de Arauco, Chile, localidad tipo de la especie. Se incluye una caracterización taxonómica, ilustraciones, y nuevas localidades en la distribución geográfica de la especie. Se provee información del hábitat (batimetría, tipo de sedimento, contenido de materia orgánica total y O2 disuelto de fondo) y se incluye una clave para diferenciar las dos especies de Pectinariidae registradas en Chile.

The taxonomy, geographical distribution, and ecological aspects of Pectinaria chilensis are reviewed. Specimens were collected in sublittoral soft bottoms, between 45 and 93m depth, at four localities in northern Chile. These specimens are compared with individuals collected from 17m depth at Coronel, Gulf of Arauco, Chile, the type locality of the species. A taxonomic characterization, illustrations and a list of new localities in the geographical distribution of this species are presented. Ecological information (bathymetry, sediment type, total organic matter content and dissolved O2 concentration of sea water above the bottom) is included, as well as a key for differentiating the two Pectinariidae species registered in Chile to date.

Revisa-se Pectinaria chilensis da costa do Chile a partir de exemplares recolhidos em fundos brandos sub-litorais, entre 45 e 93m de profundidade, em quatro localidades ao norte do Chile. Estes espécimes foram comparados com exemplares recolhidos a 17m de profundidade em Coronel, Golfo de Arauco, Chile, localidade padrão da espécie. Se inclui uma caracterização taxonômica, ilustrações, e novas localidades na distribuição geográfica da espécie. Se fornece informação do hábitat (batimetria, tipo de sedimento, conteúdo de matéria orgânica total e O2 dissolvido de fundo) e se inclui uma clave para diferenciar as duas espécies de Pectinariidae registradas no Chile.