Highly Connected Populations and Temporal Stability in Allelic Frequencies of a Harvested Crab from the Southern Pacific Coast

Abstract

For marine invertebrates with a benthic adult form and a planktonic larva phase, the connectivity among populations is mainly based on larval dispersal. While an extended larval phase will promote gene flow, other factors such as an intensive fishery and geographical barriers could lead to changes in genetic variability. In this study, the population genetic structure of the commercial crab Metacarcinus edwardsii was analyzed along 700 km of the Chilean coast. The analysis, based on eight microsatellite loci genotyped from megalopae and adult crabs, considered temporal and spatial patterns of genetic variation. The results showed no evidence of spatial patterns in genetic structure, suggesting high connectivity among the sampling sites. The temporal analysis showed no evidence of changes in allele frequencies and no evidence of a recent bottleneck. The lack of spatial structure and allele variation over time could be explained by the interaction of factors such as i) low reproductive variance due to the capability of females to store sperm in the seminal receptacle, which can be used for successive broods, ii) high larval dispersal and iii) high individual reproductive output. Using our data as priors, a genetic modelling approach coincided, predicting this temporal and spatial stability. The same analysis showed that a reduction in population size leads to the loss of genetic variability in populations, as well as of the genetic cohesiveness between populations, pointing out the importance management for species under exploitation, such as M. edwardsii.

Spatial and temporal stability in the genetic structure of a marine crab despite a biogeographic break

“…The analyses did not detect population differentiation, except for slight but significant differences in F ST when pairs of sites with small sample sizes were compared. This temporal stability has been previously described for this species; Rojas-Hernández et al 36 did not detect differences in microsatellite variability in four cohorts of megalopas (over the period 2011 to 2014) collected at Los Molinos (39° 51′ S; 73° 23′ W). To our knowledge, there is little evidence of the temporal genetic stability of populations of benthic marine organisms.…”

“…Larvae recruit in association with the estuarine environment 34 . Laboratory experiments have demonstrated a planktonic larval duration of 60 days at 15 °C 35 , and a population genetic study based on eight microsatellites found high gene flow among populations over 700 km apart 36 . However, the possible effect of the Humboldt Current on gene flow, temporal genetic stability, and population differentiation of the species across the biogeographic break at 42°S remains unknown.…”

Population genomic analyses reveal hybridization and marked differences in genetic structure of Scurria limpet sister species with parapatric distributions across the South Eastern Pacific

“…Much attention has been given to the biogeographic break located at 30°S that separates the Peruvian province from the intermediate area. This break is the distributional boundary for many species (both equatorward and poleward) and has been documented as an effective barrier to gene flow for some species that have distributions that cross this break (for examples see Haye et al, 2014Haye et al, , 2019Montecinos et al, 2012;Tellier et al, 2009) but not for others (such as in Cárdenas et al, 2009;Rojas-Hernandez et al, 2016). In addition, long-term surveys have shown that environmental characteristics, particularly upwelling, not only are highly heterogeneous along the Chilean Pacific coast but also change dramatically across the 30°S latitude (Aravena et al, 2014;Broitman et al, 2018;Lara et al, 2019;Torres et al, 2011).…”

Genetic Diversity and Population Structure of Genypterus chilensis, a Commercial Benthic Marine Species of the South Pacific

“…This iteroparous, partial spawner has a pelagic larval life span of 30-45 days, similar to other benthic marine organisms (Chong and González, 2009;Marshall and Morgan, 2011;Toledo et al, 2017). The pelagic larvae are expected to be distributed by ocean currents over wide geographic areas, contributing to panmixia (Cowen et al, 2007;Rojas-Hernandez et al, 2016). Thus, this fish is thought to have limited genetic structure due to the lack of oceanographic barriers, which promotes connectivity.…”