Genetic structure, phylogeography, and demography of Anadara tuberculosa (Bivalvia) from East Pacific as revealed by mtDNA: Implications to conservation

Abstract

Wild populations of the pustulose ark, Anadara tuberculosa (Bivalvia), an emblematic species of the East Pacific mangrove ecosystem declined in South American countries (Colombia, Ecuador, and Peru) mainly due to overharvesting and habitat loss or degradation. Understanding the genetic aspects of geographic variations and population structure of A. tuberculosa, currently unknown, appears as a priority to fishery authorities in order to elaborate integrated and collaborative conservation policies for fishery management, aquaculture, and stock enhancement programs. We used mtDNA sequence data to investigate haplotype diversity, genetic structure, and demography of A. tuberculosa. Results indicate genetic homogeneity of populations distributed north and south of the equator, respectively. However, statistically significant differentiation emerged between northern and southern populations with pairwise ф _ST values ranging between 0.036 and 0.092. The oceanic current system acting in the area (Panama Current and Humboldt Current) might play a role in limiting the larval dispersal of the species, still poorly understood. Demography reconstruction supported recent population expansion, possibly started after last glacial maximum. Our results would suggest separate and independent management of populations north and south of the equator.

Keywords: aquaculture; aquatic animal stock; last glacial maximum; mangrove habitat; mollusk; oceanic current.

Figure 1

Sampling sites: 1) Tumaco (Colombia), 2) Esmeralda, 3) Guayas, 4) El Oro (Ecuador), 5) Tumbes (Peru). Surface oceanic circulation observed in February 2018 (a) and March 2018 (b). Current convergence (periodic median values) in the equatorial region comprised between latitude 1.8 S and 0.2 N and longitude 82.2 W and 80.2 W, from 1992 to 2015 (c). The red line indicates the equator. The overall pattern of circulation, although with some variation, tends to be stable over time

Figure 2

Statistical parsimony network illustrating the genealogical relationships among different haplotypes (threshold of statistical significance = 95%). The size of the circle corresponds to the haplotype frequency. Pie charts indicate the proportion at which each haplotype occurs at each location

Figure 3

Mismatch distributions (pairwise differences) in Groups 1 and 2. Dotted and dashed lines indicate expected distributions under constant size and expansion models, respectively. Solid line indicates observed distributions

Figure 4

Bayesian skyline plots for Groups 1 and 2. X‐axis indicates time expressed in mutation per site units. Y‐axis indicates population size expressed as the product of N _e (effective population size) and μ (mutation rate)