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

Abstract

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.

Fine‐scale hierarchical genetic structure and kinship analysis of the ascidianPyura chilensisin the southeastern Pacific

“…Three well-differentiated mitochondrial clades have also been found for P. chilensis, and one of these is only found in Los Molinos. More recently, three genetically distinct groups along the southeastern Pacific have been identified according to single nucleotide polymorphisms and Los Molinos has been highlighted again as the location where the highest degree of genetic differentiation occurs(Segovia et al, 2017). Our results and those fromGiles et al (2017) indicate that Los Molinos is not an outlier locality but rather a site in close proximity to a pronounced genetic break.…”

“…P. chilensis is a digonic hermaphrodite with external fertilization. Previous studies have investigated the population genetic structure of P. chilensis using multiple markers such as allozymes (Astorga & Ortiz, 2006), nuclear and mitochondrial genes (Haye & Muñoz-Herrera, 2013), and single nucleotide polymorphisms (Segovia, Gallardo-Escárate, Poulin, & Haye, 2017). After this time, the larva seeks a substrate on which to settle and metamorphose to its sessile adult life form (Cea, 1973).…”

“…In the last 20 years, populations of this species have been dramatically exploited (Davis, 1995). Previous studies have investigated the population genetic structure of P. chilensis using multiple markers such as allozymes (Astorga & Ortiz, 2006), nuclear and mitochondrial genes (Haye & Muñoz-Herrera, 2013), and single nucleotide polymorphisms (Segovia, Gallardo-Escárate, Poulin, & Haye, 2017). All of these previous studies have utilized samples taken hundreds of kilometers apart, but a recent study has shown that genetic differences exist between localities that are separated by only 20 km (Giles, Petersen-Zúñiga, Morales-González, Quesada-Calderon, & Saenz-Agudelo, 2017).…”

“…). More recently, three genetically distinct groups along the southeastern Pacific have been identified according to single nucleotide polymorphisms and Los Molinos has been highlighted again as the location where the highest degree of genetic differentiation occurs(Segovia et al, 2017). Three well-differentiated mitochondrial clades have also been found for P. chilensis, and one of these is only found in Los Molinos.…”

Thermal physiological traits and plasticity of metabolism are sensitive to biogeographic breaks in a rock-pool marine shrimp

“…This thus reflects local variation in solar irradiation (Broitman et al, 2001), the influence of atmospheric circulation and rainfall variability (Barros and Silvestri, 2002), and the effect of other oceanographic processes (Thiel et al, 2007). In contrast, our results suggest that metabolic plasticity is higher in populations subjected to seasonal upwelling in the intermediate area and also in populations located near environmental discontinuities at the biogeographic breaks (for similar results, see Aravena et al, 2014;Segovia et al, 2017). Ectotherms that occupy heterogeneous thermal environments are hypothesized to have evolved greater thermal plasticity to optimize performance despite exposure to environmental variability (Angilletta, 2009;Chown and Terblanche, 2007;Ghalambor et al, 2006;Janzen, 1967).…”