No abstract

Studying population structure and genetic diversity at fine spatial scales is key for a better understanding of demographic processes that influence population connectivity. This is particularly important in marine benthic organisms that rely on larval dispersal to maintain connectivity among populations. Here, we report the results of a genetic survey of the ascidian Pyura chilensis from three localities along the southeastern Pacific. This study follows up on a previous report that described a genetic break in this region among localities only 20 km apart. By implementing a hierarchical sampling design at four spatial levels and using ten polymorphic microsatellite markers, we test whether differences in fine‐scale population structure explain the previously reported genetic break. We compared genetic spatial autocorrelations, as well as kinship and relatedness distributions within and among localities adjacent to the genetic break. We found no evidence of significant autocorrelation at the scale up to 50 m despite the low dispersal potential of P. chilensis that has been reported in the literature. We also found that the proportion of related individuals in close proximity (<1 km) was higher than the proportion of related individuals further apart. These results were consistent in the three localities. Our results suggest that the spatial distribution of related individuals can be nonrandom at small spatial scales and suggests that dispersal might be occasionally limited in this species or that larval cohorts can disperse in the plankton as clustered groups. Overall, this study sheds light on new aspects of the life of this ascidian as well as confirms the presence of a genetic break at 39°S latitude. Also, our data indicate there is not enough evidence to confirm that this genetic break can be explained by differences in fine‐scale genetic patterns among localities.

Monitoring plans using environmental DNA have the potential to offer a standardized and cost-efficient method to survey biodiversity in aquatic ecosystems. Among these ecosystems, coastal wetlands are key elements that serve as transition zones between marine and freshwater ecosystems and are today the target of many conservation and restoration efforts. In this sense, eDNA monitoring could provide a rapid and efficient tool for studying and generating baseline biodiversity information to guide coastal wetland management programs. Here, we test an eDNA metabarcoding assay as a tool to characterize vertebrate biodiversity in one of the largest coastal wetlands of Chile, the Rio Cruces Wetland, a Ramsar designated site since 1981. We sampled surface water from 49 sites along the entire wetland. Our eDNA approach detected 91genera of vertebrates including amphibians, fishes, mammals, and birds, as well as identified several cryptic, exotic, and endangered species. Our results also indicated that the spatial distribution of eDNA from different species is spatially structured despite the complex hydrodynamics inherent in this wetland due to the influence of daily tidal regimes. For amphibians and fishes, the number of taxa detected with eDNA was higher in the periphery of the wetland, and increased with proximity to the ocean, a pattern consistent with small-scale spatial sensitivity for some species and eDNA accumulation downstream for others. Birds and mammals showed somewhat more idiosyncratic distributions. Taken together, our results add to the growing body of evidence showing eDNA can serve as a rapid cost-effective tool

Aim Accurate characterization of evolutionary units (species or populations) underlies all ecological and evolutionary studies and is crucial to conservation planning. Seascapes have long been thought to be highly permeable to gene flow, yet over the last decade building evidence has shown that barriers to gene flow in marine environments are much more common than previously thought. Here, we precisely characterize two barriers to gene flow in the tunicate Pyura chilensis across 26° of latitude in the southeastern Pacific, assess their magnitude and explore their congruence with current biogeographical patterns of this region. Location The southeastern Pacific (SEP), from Ilo, Perú (17°S) to Chiloé, Chile (43°S). Taxon Pyura chilensis. Methods We used a combination of highly polymorphic microsatellite markers and a 540 bp fragment of the Cytochrome Oxidase subunit I (COI) to compare individuals sampled at 26 localities spanning approximately 2500 km of the SEP. Genetic diversity was analysed using Bayesian clustering, haplotype networks, Isolation by Distance and cline models. A Coalescent simulator was used to estimate migration rates. Results The results from both the microsatellite and COI markers indicate the presence of two genetic discontinuities: one at 34°S and one at 39°S which coincide with genetic breaks reported for other species. Interestingly, we were able to determine that genetic transitions occur abruptly and within short geographical distances (~30 km) compared with previous studies of this tunicate. Coalescent simulations indicate the 34°S break is less permeable than the 39°S break, and gene flow appears to be mostly from north to south. Main conclusions Our results support other studies that show that seascapes are complex, and also highlight the importance of accurately sampling distribution ranges when making conclusions about gene flow. Overall, the two main biogeographical barriers to gene flow characterized in the southeastern Pacific are not homogeneously permeable and can be narrow (<30 km). These results are relevant for the management of fisheries in this region and specifically for this commercially important species.

Gracilaria chilensis is the main cultivated seaweed in Chile. The low genetic diversity observed in the Chilean populations has been associated with the over‐exploitation of natural beds and/or the founder effect that occurred during post‐glacial colonization from New Zealand. How these processes have affected its evolutionary trajectory before farming and incipient domestication is poorly understood. In this study, we used 2232 single nucleotide polymorphisms (SNPs) to assess how the species' evolutionary history in New Zealand (its region of origin), the founder effect linked to transoceanic dispersion and colonization of South America, and the recent over‐exploitation of natural populations have influenced the genetic architecture of G. chilensis in Chile. The contrasting patterns of genetic diversity and structure observed between the two main islands in New Zealand attest to the important effects of Quaternary glacial cycles on G. chilensis. Approximate Bayesian Computation (ABC) analyses indicated that Chatham Island and South America were colonized independently near the end of the Last Glacial Maximum and emphasized the importance of coastal and oceanic currents during that period. Furthermore, ABC analyses inferred the existence of a recent and strong genetic bottleneck in Chile, matching the period of over‐exploitation of the natural beds during the 1970s, followed by rapid demographic expansion linked to active clonal propagation used in farming. Recurrent genetic bottlenecks strongly eroded the genetic diversity of G. chilensis prior to its cultivation, raising important challenges for the management of genetic resources in this incipiently domesticated species.