Juan I. Cañete

Molecular phylogeny and historical biogeography of Nacella (Patellogastropoda: Nacellidae) in the Southern Ocean

The evolution and the historical biogeography of the Southern Ocean marine benthic fauna are closely related to major tectonic and climatic changes that occurred in this region during the last 55 million years (Ma). Several families, genera and even species of marine organisms are shared between distant biogeographic provinces in this region. This pattern of distribution in marine benthic invertebrates has been commonly explained by vicariant speciation due to plate tectonics. However, recent molecular studies have provided new evidence for long-distance dispersion as a plausible explanation of biogeographical patterns in the Southern Ocean. True limpets of the genus Nacella are currently distributed in different biogeographic regions of the Southern Ocean such as Antarctica, Kerguelen Province, southern New Zealand Antipodean Province, North-Central Chile and South American Magellanic Province. Here, we present phylogenetic reconstructions using two mitochondrial DNA markers (Cytochrome Oxidase I and Cytochrome b) to look into the relationships among Nacella species and to determine the origin and diversification of the genus. Phylogenies were reconstructed using two methods, Maximum Parsimony and Bayesian Inference, while divergence time among Nacella species was estimated following a relaxed Bayesian approach. For this purpose, we collected inter- and subtidal species belonging to four biogeographic regions in the Southern Ocean: Antarctica, Kerguelen Province, Central Chile, and Magellanic Province. Our molecular results agree with previous morphological and molecular studies supporting the monophyly of Nacella and its sister relationship with Cellana. Two rounds of diversification are recognized in the evolution of Nacella. The first one occurred at the end of the Miocene and gave rise to the main lineages, currently distributed in Antarctica, South America or Kerguelen Province. Large genetic divergence was detected among Nacella species from these distant biogeographic provinces emphasizing the significance of trans-oceanic discontinuities and suggesting long-distance dispersal was relatively unimportant. The second diversification round consisted of a more recent Pleistocene radiation in the Magellanic region. In this province, different morphological species of Nacella exhibit extreme low levels of genetic divergence with absence of reciprocal monophyly among them. According to our time estimation, the origin and diversification of Nacella in the Southern Ocean is more recent (<15 MY) than the expected under the hypothesis of vicariant speciation due to plate tectonics. The evolution of this genus seems to be closely related to drastic climatic and oceanographic changes in the Southern Ocean during the middle-Miocene climatic transition. In spite of the high number of species described for the Magellanic Province, molecular results indicate that these species are the most derived ones in the evolution of the genus and therefore that the Magellanic region does not need to correspond to the origin center of Nacella. The absence of genetic divergence among these species supports a very recent radiation process accompanied by rapid morphological and ecological diversification.

Concerted genetic, morphological and ecological diversification in Nacella limpets in the Magellanic Province

Common inhabitants of Antarctic and Subantarctic rocky shores, the limpet genus Nacella, includes 15 nominal species distributed in different provinces of the Southern Ocean. The Magellanic Province represents the area with the highest diversity of the genus. Phylogenetic reconstructions showed an absence of reciprocal monophyly and high levels of genetic identity among nominal species in this Province and therefore imply a recent diversification in southern South America. Because most of these taxa coexist along their distribution range with clear differences in their habitat preferences, Nacella is a suitable model to explore diversification mechanisms in an area highly affected by recurrent Pleistocene continental ice cap advances and retreats. Here, we present genetic and morphological comparisons among sympatric Magellanic nominal species of Nacella. We amplified a fragment of the COI gene for 208 individuals belonging to seven sympatric nominal species and performed geometric morphometric analyses of their shells. We detected a complete congruence between genetic and morphological results, leading us to suggest four groups of Nacella among seven analysed nominal species. Congruently, each of these groups was related to different habitat preferences such as bathymetric range and substrate type. A plausible explanation for these results includes an ecologically based allopatric speciation process in Nacella. Major climatic changes during the Plio‐Pleistocene glacial cycles may have enhanced differentiation processes. Finally, our results indicate that the systematics of the group requires a deep revision to re‐evaluate the taxonomy of Nacella and to further understand the Pleistocene legacy of the glacial cycles in the southern tip of South America.

Towards a model of postglacial biogeography in shallow marine species along the Patagonian Province: lessons from the limpet Nacella magellanica (Gmelin, 1791)

BackgroundPatagonia extends for more than 84,000 km of irregular coasts is an area especially apt to evaluate how historic and contemporary processes influence the distribution and connectivity of shallow marine benthic organisms. The true limpet Nacella magellanica has a wide distribution in this province and represents a suitable model to infer the Quaternary glacial legacy on marine benthic organisms. This species inhabits ice-free rocky ecosystems, has a narrow bathymetric range and consequently should have been severely affected by recurrent glacial cycles during the Quaternary. We performed phylogeographic and demographic analyses of N. magellanica from 14 localities along its distribution in Pacific Patagonia, Atlantic Patagonia, and the Falkland/Malvinas Islands.ResultsMitochondrial (COI) DNA analyses of 357 individuals of N. magellanica revealed an absence of genetic differentiation in the species with a single genetic unit along Pacific Patagonia. However, we detected significant genetic differences among three main groups named Pacific Patagonia, Atlantic Patagonia and Falkland/Malvinas Islands. Migration rate estimations indicated asymmetrical gene flow, primarily from Pacific Patagonia to Atlantic Patagonia (Nem=2.21) and the Falkland/Malvinas Islands (Nem=16.6). Demographic reconstruction in Pacific Patagonia suggests a recent recolonization process (< 10 ka) supported by neutrality tests, mismatch distribution and the median-joining haplotype genealogy.ConclusionsAbsence of genetic structure, a single dominant haplotype, lack of correlation between geographic and genetic distance, high estimated migration rates and the signal of recent demographic growth represent a large body of evidence supporting the hypothesis of rapid postglacial expansion in this species in Pacific Patagonia. This expansion could have been sustained by larval dispersal following the main current system in this area. Lower levels of genetic diversity in inland sea areas suggest that fjords and channels represent the areas most recently colonized by the species. Hence recolonization seems to follow a west to east direction to areas that were progressively deglaciated. Significant genetic differences among Pacific, Atlantic and Falkland/Malvinas Islands populations may be also explained through disparities in their respective glaciological and geological histories. The Falkland/Malvinas Islands, more than representing a glacial refugium for the species, seems to constitute a sink area considering the strong asymmetric gene flow detected from Pacific to Atlantic sectors. These results suggest that historical and contemporary processes represent the main factors shaping the modern biogeography of most shallow marine benthic invertebrates inhabiting the Patagonian Province.

Divergence time estimations and contrasting patterns of genetic diversity between Antarctic and southern South America benthic invertebrates

La diversidad, abundancia y composicion de grupos taxonomicos en el oceano Austral difiere de otros lugares del planeta debido a que su biogeografia refleja la compleja interaccion de la tectonica, oceanografia, clima y elementos biologicos desde el Eoceno. Algunos grupos de organismos marinos bentonicos muestran altos niveles de divergencia genetica entre provincias de esta region, apoyando la existencia de procesos vicariantes por tectonica de placas mientras que otros grupos, con alta capacidad dispersiva, muestran procesos de divergencia mas recientes. Mas aun, el reciente descubrimiento de larvas de decapodos no Antarticos en peninsula Antartica sugiere que algunos grupos podrian cruzar la Corriente Circumpolar Antartica. Se analizaron los niveles de divergencia genetica en especies congenericas en invertebrados bentonicos del Oceano Austral con potencial dispersivo. Para esto, se incluyo en los analisis secuencias del gen COI de un equinoideo (Sterechinus), un gastropodo (Nacella), y un bivalvo (Yoldia). Considerando los niveles de diferenciacion genetica y asumiendo la Hipotesis del Reloj Molecular, estimamos la separacion entre grupos de ambos continentes. Tambien comparamos los niveles de variacion genetica entre especies antarticas y subantarticas de Nacella y Sterechinus para determinar el efecto de los episodios glaciales del Cuaternario en su demografia. Detectamos claras diferencias geneticas entre especies congenericas antarticas y subantarticas de Sterechinus, Nacella y Yoldia. La instalacion de una barrera efectiva entre antartica y subantartica ocurrio casi al unisono (3.7 a 5.0 Ma) para estos grupos de organismos, y muy posterior a la separacion fisica de ambos continentes. Comparaciones geneticas entre especies antarticas y subantarticas detectaron menores niveles de diversidad genetica en especies antarticas sugiriendo un efecto mas pronunciado de los episodios glaciales en Antartica que en Sudamerica. Estos resultados podrian reflejar el dramatico efecto de los ciclos glaciales del Cuaternario en los tamanos poblacionales antarticos, especialmente en grupos con rangos batimetricos estrechos. El presente estudio provee nueva evidencia de los procesos de diferenciacion entre organismos antarticos y sudamericanos. Ninguno de los generos analizados mostro evidencia de flujo genico recurrente a traves de la Corriente Circumpolar Antartica desde el Mio-Plioceno. Las comparaciones geneticas indican que especies antarticas y subantarticas fueron diferencialmente afectadas por los periodos glaciales.

Proposición de un índice de vigilancia ambiental basado en la variabilidad temporal de la abundancia de dos especies de poliquetos bentónicos de bahía Quintero, Chile

An Environmental Monitoring Index based on the temporal variations in the abundance of two benthic polychaetes (Nepthys impressa Baird, 1871 and Prionospio p...

Pseudione tuberculata Richardson, 1904 (Isopoda: Bopyridae): a parasite of juveniles of the king crab Lithodes santolla (Molina, 1782) (Anomura: Lithodidae) in the Magellan Strait, Chile

El isopodo parasito Pseudione tuberculata Richardson, 1904 infesta la cavidad branquial de especies de la familia Lithodidae en el extremo sur de Sudamerica. Ha sido descrito previamente como parasito de Neolithodes en el Archipielago de los Chonos, Chile, y en Paralomis granulosa (Jacquinot, 1847) y Lithodes santolla (Molina, 1782) en aguas someras del canal Beagle, Argentina. Es la primera vez que el parasito es documentado en Chile en el estrecho de Magallanes, ubicado alrededor de 640 km al norte del canal Beagle, parasitando juveniles de L. santolla (23,0 a 51,6 mm LC en hembras y entre 24,0 a 48,7 mm en machos). La frecuencia del parasito en centollas fue de 27,97% en hembras y 21,43% en machos. La frecuencia de infestacion fue mayor a la descrita en otros crustaceos chilenos parasitados por Pseudione. Cada centolla portaba una pareja de P. tuberculata dentro de la cavidad branquial en el lado izquierdo del caparazon. Las altas tasas de parasitismo de P. tuberculata en centollas juveniles en el area podria ocurrir en aguas someras habitadas por Macrocystis pyrifera debido a su efecto en las condiciones hidrodinamicas locales, la reduccion del flujo y la amortiguacion del oleaje, proporcionando habitats para diversos organismos marinos. Se concluye que P. tuberculata como parasito de L. santolla, en el estrecho de Magallanes, responde de manera similar al compararse con los valores de infestacion de estudios previos desarrollados en el canal Beagle, Argentina, en donde ha sido reportada infestando P. granulosa y L. santolla.

Phylogeography in Galaxias maculatus (Jenyns, 1848) along Two Biogeographical Provinces in the Chilean Coast.

Major geologic and climatic changes during the Quaternary exerted a major role in shaping past and contemporary distribution of genetic diversity and structure of aquatic organisms in southern South America. In fact, the northern glacial limit along the Pacific coast, an area of major environmental changes in terms of topography, currents, and water salinity, represents a major biogeographic transition for marine and freshwater species. We used mitochondrial DNA sequences (D-loop) to investigate the consequences of Quaternary glacial cycles over the pattern of genetic diversity and structure of G. maculatus (Pisces: Galaxiidae) along two biogeographical provinces in the Chilean coast. Extreme levels of genetic diversity and strong phylogeographic structure characterize the species suggesting a low amount of influence of the last glacial cycle over its demography. However, we recognized contrasting patterns of genetic diversity and structure between main biogeographical areas here analyzed. Along the Intermediate Area (38°–41° S) each estuarine population constitutes a different unit. In contrast, Magellanic populations (43°–53° S) exhibited low levels of genetic differentiation. Contrasting patterns of genetic diversity and structure recorded in the species between the analyzed biogeographic areas are consistent with the marked differences in abiotic factors (i.e., different coastal configurations, Quaternary glacial histories, and oceanographic regimes) and to inherent characteristics of the species (i.e., salt-tolerance, physiology, and reproductive behavior).

Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile

We studied the ascidian fauna from two zones located in subantarctic (Punta Arenas, latitude 53º) and temperate Chile (Coquimbo, latitude 29º). The different oceanographic features of the two zones, with influence of the Humboldt Current in the north and the Cape Horn Current System and freshwater inputs in the south, led to markedly different ascidian faunas. A total of 22 species were recorded, with no shared species across the two areas (11 species each). The new species Polyzoa iosune is described, Lissoclinum perforatum is found for the first time in the Pacific Ocean, and Synoicum georgianum and Polyzoa minor are new to the Chilean fauna. The populations of Ciona in the Coquimbo area (formerly attributed to Ciona intestinalis) correspond to the species Ciona robusta. A total of 35 Cytochrome oxidase (COI) sequences of the standard barcode region have been obtained for 17 of the 22 species reported.

Egg-laying behaviour and intracapsular development of Argobuccinum pustulosum (Gastropoda: Ranellidae) in temperate waters at the South coast of Chile

Abstract Egg-laying behaviour, egg masses and intracapsular development of the ranellid snail Argobuccinum pustulosum are described here. Snails were collected by diving, at Corral Bay (39°53′S; 73°25′W) in the south of Chile, and adult individuals were reared in tanks with circulating seawater at ambient temperature to obtain their egg masses. The spawn produced is an irregular flat mass, taking between 3 and 9 days for the females to complete the egg deposition. Peduncleless tube-shaped capsules of 9–12 mm in length, amounted to 47–149 per mass (average = 100; n=9 masses). Eggs measured 168 µm in mean diameter. Number of eggs/embryos per capsule varied between 2500 and 5400. At mean temperatures of about 11.2–11.7°C, the intracapsular development lasted approximately 54–56 days, with the hatching of numerous planktotrophic veliger larvae of about 260 µm in shell length. Maximum production of larvae by a female is estimated at over 650,000 per spawn, and under multiple spawns it could exceed a million per breeding season. Capsule wall (100 µm thickness) consists of six laminae with protein fibres whose laminar arrangement permits a high light transmittance, accounting for the marked transparency of these capsules. Attributes of the development and of their hatching larvae, suggest a long period of planktonic larval dispersal for this snail. This would promote connectivity among geographically separated populations, thus in turn explaining the wide geographic distribution showed by this species in Southern oceans.

Caprella ungulina Mayer, 1903 (Amphipoda: Caprellidae): epizoo de Paralomis granulosa (Hombron & Jacquinot, 1846) (Decapoda: Lithodidae) en aguas de Magallanes, Chile

Caprella ungulina Mayer, 1903 is recorded from shallow waters (50 to 100 m depth) off Navarino Island (55o03’ S, 67o33’ W) and Dawson Island (54o04’ S, 70o24’ W), austral Chile. The material examined (N=289 caprellids) was collected mainly in the mouthparts (55%) of the edible crustacean Paralomis granulosa during 2016 fishery season. The percentage of epibiosis varied between 1.8 and 14.8% of the total host sampled, being collected mainly one caprellid by crab. The mortality of C. ungulina by effects of the P. granulosa fishery during 2015 in Magallanes (l,965 ton) produced between 255,450 and 1,061,100 specimens (mean epibiosis of 6.7% ± 4,1%). The mortality by fishing on P. granulosa could affect negatively the population dynamic of C. ungulina if is confirmed a high specificity for this biohabitat and the remotion of juveniles that could not reach the reproductive maturity. It is proposed that the ecological relationship between C. ungulina and P. granulosa could be defined as comensalism under