Coupling Demographic and Genetic Variability from Archived Collections of European Anchovy (Engraulis encrasicolus)

Abstract

It is well known that temporal fluctuations in small populations deeply influence evolutionary potential. Less well known is whether fluctuations can influence the evolutionary potentials of species with large census sizes. Here, we estimated genetic population parameters from as survey of polymorphic microsatellite DNA loci in archived otoliths from Adriatic European anchovy (Engraulis encrasicolus), a fish with large census sizes that supports numerous local fisheries. Stocks have fluctuated greatly over the past few decades, and the Adriatic fishery collapsed in 1987. Our results show a significant reduction of mean genetic parameters as a consequence of the population collapse. In addition, estimates of effective population size (Ne) are much smaller than those expected in a fishes with large population census sizes (Nc). Estimates of Ne indicate low effective population sizes, even before the population collapse. The ratio Ne/Ne ranged between 10−6 and 10−8, indicating a large discrepancy between the anchovy gene pool and population census size. Therefore, anchovy populations may be more vulnerable to fishery effort and environmental change than previously thought.

Distribution of Engraulis encrasicolus eggs and larvae in relation to coastal oceanographic conditions (the South-western Adriatic Sea case study)

“…These data agree with those reported by Giannoulaki et al (2013), who found in the Mediterranean Sea a preference for spawning areas at depths of 40 -150 m, and with those of Saraux et al (2014), who identified two recurrent areas further from the coast (isobaths of ∼70 to 100 m) and unfavourable areas close to the coast in the Gulf of Lion for adult anchovy. The results of the present study show significantly different distributions of eggs and larvae over the years, in line with the notion that the biomass of small pelagic species undergoes wide fluctuations over time throughout the world (Brander, 2007;Leonori et al, 2009Leonori et al, , 2011Ruggeri et al, 2016a). The PCA data explained the environmental variability mainly in terms of depth and chlorophyll-a, but also stressed the importance of zooplankton abundance.…”

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“…As a result of this study; a significantly higher DNA yield was observed for historical otoliths treated with Protocol 2 modified by Ruggeri et al (2016) in comparison to Protocol 1 (NucleoSpin TissueXS, Magery-Nagel). Although DNA yield was generally low, the PCR amplification success rate of contemporary otolith samples were high for the full range of fragments sizes in both the Protocol 1 and 2 (Figure 2 and Figure 3).…”

Biocomplexity in Populations of European Anchovy in the Adriatic Sea

“…During population bottlenecks, the reduction in effective population size ( N e ) can produce transient genetic sweeps that lead to locally adaptive genotypes [ 81 ]. A recent study showed that the effective sizes of anchovy populations in the Adriatic are several orders of magnitude smaller than census sizes [ 82 ]. These small effective sizes appear to be in part a legacy of a severe reduction in population abundances from overharvesting in the 1980s.…”