Pilar A. Haye

Phylogeographic Structure in Benthic Marine Invertebrates of the Southeast Pacific Coast of Chile with Differing Dispersal Potential

The role of dispersal potential on phylogeographic structure, evidenced by the degree of genetic structure and the presence of coincident genetic and biogeographic breaks, was evaluated in a macrogeographic comparative approach along the north-central coast of Chile, across the biogeographic transition zone at 30°S. Using 2,217 partial sequences of the mitochondrial Cytochrome Oxidase I gene of eight benthic invertebrate species along ca. 2,600 km of coast, we contrasted dispersal potential with genetic structure and determined the concordance between genetic divergence between biogeographic regions and the biogeographic transition zone at 30°S. Genetic diversity and differentiation highly differed between species with high and low dispersal potential. Dispersal potential, sometimes together with biogeographic region, was the factor that best explained the genetic structure of the eight species. The three low dispersal species, and one species assigned to the high dispersal category, had a phylogeographic discontinuity coincident with the biogeographic transition zone at 30°S. Furthermore, coalescent analyses based on the isolation-with-migration model validate that the split between biogeographic regions north and south of 30°S has a historic origin. The signatures of the historic break in high dispersers is parsimoniously explained by the homogenizing effects of gene flow that have erased the genetic signatures, if ever existed, in high dispersers. Of the four species with structure across the break, only two had significant albeit very low levels of asymmetric migration across the transition zone. Historic processes have led to the current biogeographic and phylogeographic structure of marine species with limited dispersal along the north-central coast of Chile, with a strong lasting impact in their genetic structure.

Species replacement along a linear coastal habitat: phylogeography and speciation in the red alga Mazzaella laminarioides along the south east pacific

BackgroundThe Chilean shoreline, a nearly strait line of coast expanding across 35 latitudinal degrees, represents an interesting region to assess historical processes using phylogeographic analyses. Stretching along the temperate section of the East Pacific margin, the region is characterized by intense geologic activity and has experienced drastic geomorphological transformations linked to eustatic and isostatic changes during the Quaternary. In this study, we used two molecular markers to evaluate the existence of phylogeographic discontinuities and detect the genetic footprints of Pleistocene glaciations among Patagonian populations of Mazzaella laminarioides, a low-dispersal benthic intertidal red seaweed that inhabits along ~3,700 km of the Chilean coastal rocky shore.ResultsThree main genetic lineages were found within M. laminarioides. They are distributed along the Chilean coast in strict parapatry. The deep divergence among lineages suggests that they could be considered putative genetic sibling species. Unexpectedly, genetic breaks were not strictly concordant with the biogeographic breaks described in the region. A Northern lineage was restricted to a broad transition zone located between 30°S and 33°S and showed signals of a recent bottleneck. The reduction of population size could be related to warm events linked to El Niño Southern Oscillation, which is known to cause massive seaweed mortality in this region. To the south, we propose that transient habitat discontinuities driven by episodic tectonic uplifting of the shoreline around the Arauco region (37°S-38°S); one of the most active forearc-basins in the South East Pacific; could be at the origin of the Central/South genetic break. The large beaches, located around 38°S, are likely to contribute to the lineages’ integrity by limiting present gene flow. Finally, the Southern lineage, occupies an area affected by ice-cover during the last glaciations. Phylogeny suggested it is a derived clade and demographic analyses showed the lineage has a typical signature of postglacial recolonization from a northern glacial refugium area.ConclusionsEven if environmental adaptation could have strengthened divergence among lineages in M. laminarioides, low dispersal capacity and small population size are sufficient to generate phylogeographic discontinuities determined by genetic drift alone. Interestingly, our results confirm that seaweed population connectivity over large geographic scales does not rely only on dispersal capacity but also seem to depend highly on substratum availability and population density of the receiving locality.

Heterochronic phenotypic plasticity with lack of genetic differentiation in the southeastern Pacific squat lobster Pleuroncodes monodon

SUMMARY Two forms of the squat lobster Pleuroncodes monodon can be found along the Pacific coast of South America: a smaller pelagic and a larger benthic form that live respectively in the northern and southern areas of the geographic distribution of the species. The morphological and life history differences between the pelagic and benthic forms could be explained either by genetic differentiation or phenotypic plasticity. In the latter case it would correspond to a heterochronic phenotypic plasticity that is fixed in different environments (phenotype fixation). The aim of this study was to evaluate whether the two forms are genetically differentiated or not; and thus to infer the underlying basis—heritable or plastic—of the existence of the two forms. Based on barcoding data of mitochondrial DNA (the COI gene), we show that haplotypes from individuals of the pelagic and benthic forms comprise a single genetic unit without genetic differentiation. Moreover, the data suggest that all studied individuals share a common demographic history of recent and sudden population expansion. These results strongly suggest that the differences between the two forms are due to phenotypic plasticity.

LISTA SISTEMATICA DE ESPECIES DE PERACARIDOS DE CHILE (CRUSTACEA, EUMALACOSTRACA)

Los crustaceos peracaridos comprenden un diverso grupo de invertebrados, comunes en ambientes terrestres, acuaticos dulceacuicolas y marinos. En este trabajo se revisa la diversidad de especies de los ordenes Amphipoda, Cumacea, Isopoda, y Tanaidacea, actualmente reportada para Chile. Otros grupos taxonomicos comunmente incluidos en Peracarida no han sido citados aun para Chile. Presentamos en este trabajo una lista sistematica de los taxa de peracaridos y su distribucion geografica en Chile desde los 18°S hasta los 56°S, incluyendo el Archipielago de Juan Fernandez e Isla de Pascua. En un analisis preliminar, la distribucion de las especies registradas para Chile sugiere que la diversidad de especies aumenta de norte a sur. El hecho que aun existen importantes areas geograficas con inusualmente bajos numeros de especies, y que muchas especies registradas para Chile tienen registros unicos, refuerza la necesidad de trabajos taxonomicos futuros, con el objeto de obtener un mas adecuado conocimiento de la diversidad de especies de este importante grupo de invertebrados.

Multiple transisthmian divergences, extensive cryptic diversity, occasional long‐distance dispersal, and biogeographic patterns in a marine coastal isopod with an amphi‐American distribution

Abstract Excirolana braziliensis is a coastal intertidal isopod with a broad distribution spanning the Atlantic and Pacific tropical and temperate coasts of the American continent. Two separate regional studies (one in Panama and one in Chile) revealed the presence of highly genetically divergent lineages, implying that this taxon constitutes a cryptic species complex. The relationships among the lineages found in these two different regions and in the rest of the distribution, however, remain unknown. To better understand the phylogeographic patterns of E. braziliensis, we conducted phylogenetic analyses of specimens from much of its entire range. We obtained DNA sequences for fragments of four mitochondrial genes (16S rDNA, 12S rDNA, COI, and Cytb) and also used publicly available sequences. We conducted maximum likelihood and Bayesian phylogenetic reconstruction methods. Phylogeographic patterns revealed the following: (1) new highly divergent lineages of E. braziliensis; (2) three instances of Atlantic–Pacific divergences, some of which appear to predate the closure of the Isthmus of Panama; (3) the distributional limit of highly divergent lineages found in Brazil coincides with the boundary between two major marine coastal provinces; (4) evidence of recent long‐distance dispersal in the Caribbean; and (5) populations in the Gulf of California have closer affinities with lineages further south in the Pacific, which contrasts with the closer affinity with the Caribbean reported for other intertidal organisms. The high levels of cryptic diversity detected also bring about challenges for the conservation of this isopod and its fragile environment, the sandy shores. Our findings underscore the importance of comprehensive geographic sampling for phylogeographic and taxonomical studies of broadly distributed putative species harboring extensive cryptic diversity.

Lineage divergence, local adaptation across a biogeographic break, and artificial transport, shape the genetic structure in the ascidian Pyura chilensis

Marine benthic organisms inhabit a heterogeneous environment in which connectivity between populations occurs mainly through dispersive larval stages, while local selective pressures acting on early life history stages lead to non-random mortality, shaping adaptive genetic structure. In order to test the influence of local adaptation and neutral processes in a marine benthic species with low dispersal, in this study we used Genotyping by Sequencing technology to compare the neutral and putatively selected signals (neutral and outlier loci, respectively) in SNPs scattered throughout the genome in six local populations of the commercially exploited ascidian Pyura chilensis along the southeast Pacific coast (24°–42°S). This species is sessile as an adult, has a short-lived larval stage, and may also be dispersed by artificial transport as biofouling. We found that the main signal in neutral loci was a highly divergent lineage present at 39°S, and a subjacent signal that indicated a separation at 30°S (north/south), widely reported in the area. North/south separation was the main signal in outlier loci, and the linage divergence at 39°S was subjacent. We conclude that the geographic structure of the genetic diversity of outlier and neutral loci was established by different strengths of environmental, historical and anthropogenic factors.

A rose by any other name: systematics and diversity in the Chilean giant barnacle Austromegabalanus psittacus (Molina, 1782) (Cirripedia)

We analyzed the population structure of the edible barnacle Austromegabalanus psittacus (Molina, 1782) along most of the coast of Chile. The analysis of population structure was based on nucleotide sequences of the mitochondrial cytochrome oxidase I (COI) gene region. We also tested for differences between the regions to the north and south of 30-33°S, as these latitudes represent a recognized biogeographic break and important oceanographic transitions occur in that area. No geographic differentiation was evident when using Hudson’s nearest-neighbor ( S nn ) statistic to analyze genetic differences between all populations. F st values nevertheless showed overall genetic structure among sites. Significant geographic structure was found using S nn and analysis of molecular variance (AMOVA) when locations were separated into northern and southern regions, with a stronger signal when the geographic division is set at 33°S. Our results support the idea that oceanographic transitions can affect the genetic structure in species with pelagic larvae. We also discuss observations on size structure differences within the natural range of A. psittacus and this barnacle’s sympatric occurrence with another barnacle, Megabalanus concinnus (Darwin, 1854) in its northern range.

IDENTIFICACION MORFOLOGICA DE LAS ALETAS DE LOS PRINCIPALES TIBURONES PELAGICOS COMERCIALIZADOS EN CHILE: AZULEJO (PRIONACE GLAUCA LINNAEUS), MARRAJO (ISURUS OXYRHINCHUS RAFINESQUE), Y TINTORERA (LAMNA NASUS BONNATERRE)

La carencia de registros de desembarque especie-especificos ha producido dificultades en la evaluacion de stock de tiburones en Chile. Debido a que los registros son insuficientes para realizar evaluaciones pesqueras, es imperativo contar con caracteristicas fidedignas para la identificacion de las especies o partes de estas (como las aletas). El presente estudio describe caracteres morfologicos para la identificacion de las aletas de las tres especies mas importantes de tiburones pelagicos comercializados en Chile (P glauca, I. oxyrhinchusyL. nasus) y provee de claves dicotomicas para la identificacion de estas especies usando ya sea la aleta pectoral, la primera dorsal o la caudal. Los resultados revelaron que existen caracteres diagnosticos para identificar las aletas de cada una de estas especies. Ya que las especies estudiadas son las que mas se comercializan, las descripciones de las aletas y las claves taxonomicas por tipo de aleta desarrolladas en este estudio prometen ser de gran utilidad para los fiscalizadores, en particular aquellos que se enfrenten a los desembarques de sacos de aletas. Ademas, el poder conocer tanto la cantidad como la proporcion de especies comercializadas, es importante para futuras evaluaciones pesqueras y el establecimiento de planes de manejo especie-especificos.

The cost of ignoring cryptic diversity in macroecological studies: Comment on Martínez et al. (2017)

Despite ample evidence indicating that Excirolana braziliensis corresponds to a species complex, Martínez et al. (2017; Mar Ecol Prog Ser 583:137−148) considered this isopod as a single species with a wide distribution along the Atlantic and Pacific coasts of the Americas, to evaluate the abundant-centre hypothesis (ACH). Multiple studies, however, have documented the presence of highly divergent lineages within this isopod, some of which may have separated millions of years ago, and with morphological differences reported among some of the lineages. The assumption of a single widespread species has led to misleading inferences regarding the underlying causes of ecological variation in this isopod, as indicated in recent phylogeographic studies. Therefore, it is surprising that a new macroecological study is considering E. braziliensis as a single widespread species again. The cost of ignoring its cryptic diversity is that the Martínez et al. (2017) study does not really contribute to our understanding of the ACH.

Transcriptome characterization of the ascidian Pyura chilensis using 454-pyrosequencing data from two distant localities on the southeast Pacific

This study describes the results from transcriptomes sequenced by 454-pyrosequencing from two populations separated by 10° of latitude of the endemic tunicate Pyura chilensis. Most transcripts were assembled in 43,972 contigs with an average length of 842 nucleotides. De novo assembly revealed that less than 30% of the contigs were annotated to Gene Ontology terms. A total of 71,662 single nucleotide polymorphisms (SNPs) were detected in 14,712 contigs. In silico differential expression of contigs annotated for SNPs revealed several genes differentially expressed in individuals collected from both populations. The present genomic resource will provide the basis to perform functional genomics on the species via the localization of genomic markers that can aid in determining levels of local adaptation, overall genetic structure and the genetic assessment of restocking programs for this species.