Role of oceanography in shaping the genetic structure in the North Pacific hake Merluccius productus

Abstract

Determining the relative influence of biotic and abiotic factors on genetic connectivity among populations remains a major challenge in evolutionary biology and in the management and conservation of species. North Pacific hake (Merluccius productus) inhabits upwelling regions in the California Current ecosystem from the Gulf of California to the Gulf of Alaska. In this study, we examined mitochondrial DNA (mtDNA) and microsatellite variation to estimate levels of genetic differentiation of M. productus in relation to the role of oceanographic features as potential barriers to gene flow. Samples were obtained from nine sites spanning a large part of the geographic range of the species, from Puget Sound, Washington to Costa Rica. The microsatellite results revealed three genetically discrete populations: one spanning the eastern Pacific coast, and two apparently resident populations circumscribed to the Puget Sound and the northern Gulf of California (FST = 0.032, p = 0.036). Cytochrome b sequence data indicated that isolation between the Puget Sound and northern Gulf of California populations from the coastal Pacific were recent phenomena (18.5 kyr for Puget Sound and 40 kyr for the northern Gulf of California). Oceanographic data obtained from the Gulf of California support the hypothesis that permanent fronts within the region, and strong gradients at the entrance to the Gulf of California act as barriers to gene flow. A seascape genetics approach found significant genetic–environment associations, where the daytime sea surface temperature and chlorophyll concentrations were the best predictive variables for the observed genetic differentiation. Considering the potential causes of genetic isolation among the three populations, e.g. spawning areas in different latitudes associated with upwelling processes, oceanographic barriers, asymmetric migration and specialized diet, oceanographic barriers appear to be a likely mechanism restricting gene flow.

Catch rate, length, and sex ratio of Pacific hake (Merluccius productus) in the northern Gulf of California

“…Pacific hake in NGC spawn only during December-May, peaking in December-February (Denton Castillo, 2018). The difference in spawning times and sites between these stocks could serve as a gene flow barrier that fosters the genetic isolation indicated by results of other studies (Iwamoto et al, 2015;García De León et al, 2018). Our results indicate that Pacific hake in the NGC pres ent sex dimorphism because adult females had greater maximum lengths, weights, and allometric coefficients than males.…”

“…It has been hypothesized that this population belongs to a different species, the Cor tez hake (M. hernandezi) (Mathews, 1985), mainly because of its maximum size of 107 cm total length (TL), much larger than that of the unfished population of what had been considered Panama hake (M. angustimanus), a spe cies that was also called the dwarf hake, from the southern Gulf of California and Baja California Sur (33.5 cm TL) (Mathews, 1975;Balart Páez, 2005). Nevertheless, results from molecular and meristic studies indicate the presence of a single species, M. productus, in North America with different population units (Silva Segundo et al, 2011;García De León et al, 2018).…”

Genetic diversity and structure of circumtropical almaco jack, Seriola rivoliana: tool for conservation and management

“…The magnitude of estimated F ST values also suggests potential IBD along the eastern Pacific coast, a pattern reported for a number of species with wide distributions, including hake Merluccius productus (Ayres 1855) (García‐De León et al ., 2018), sardine and anchovy (Lecomte et al ., 2004) and the brown smoothhound shark (Chabot et al ., 2015); nonetheless, the Mantel test was non‐significant. Though there are no obvious geographical barriers in this region, the environmental characteristics associated with the current of California create a transition between sub‐tropical and subarctic water bodies (Spalding et al ., 2012) that could promote genetic differentiation between northern and more‐southern populations in the eastern Pacific; such a dynamic has been suggested for yellowfin tuna, T. albacares (Díaz‐Jaimes & Uribe‐Alcocer, 2006).…”

Phylogenetic prospecting for cryptic species of the genus Merluccius (Actinopterygii: Merlucciidae)

“…Several of those morphotypes have been recently taken as synonymous with extant species. For instance, the three stocks of M. productus believed to exist in the northeast Pacific corridor from Washington State to Costa Rica 25,26 likely belong to a single hake species 27,28 . The high variability and overlap of meristic traits between M. hernandezi and M. angustimanus suggests they are synonymous forms 13 and that M. angustimanus is a subpopulation of M. productus confined to the northern Gulf of California 27 .…”