An integrated genetic-demographic model to unravel the origin of genetic structure in European eel (Anguilla anguilla L.)

Abstract

The evolutionary enlightened management of species with complex life cycles often requires the development of mathematical models integrating demographic and genetic data. The genetic structure of the endangered European eel (Anguilla anguilla L.) has been thoroughly analyzed in several studies in the past years. However, the interpretation of the key demographic and biologic processes that determine the observed spatio-temporal genetic structure has been very challenging owing to the complex life cycle of this catadromous species. Here, we present the first integrated demographic-genetic model applied to the European eel that explicitly accounts for different levels of larval and adult mixing during oceanic migrations and allows us to explore alternative hypotheses on genetic differentiation. Our analyses show that (i) very low levels of mixing occurring during larval dispersal or adult migration are sufficient to erase entirely any genetic differences among sub-populations; (ii) small-scale temporal differentiation in recruitment can arise if the spawning stock is subdivided in distinct reproductive groups; and (iii) the geographic differentiation component might be overestimated if a limited number of temporal recruits are analyzed. Our study can inspire the scientific debate on the interpretation of genetic structure in other species characterized by complex life cycle and long-range migrations.

No apparent genetic bottleneck in the demographically declining European eel using molecular genetics and forward-time simulations

“…At present, the European eel shows a historically low recruitment abundance, following a 90-99% decline in comparison with the recruitment observed in the 1970s (Dekker 2000(Dekker , 2003. Glass eel recruitment has been decimated to 2.0 9 10 9 individuals per year (Andrello et al 2010). Most data sets also show a decline in fishing yield and landings of yellow and silver eels from the mid 1960s on (Dekker 2003;ICES 2008).…”

“…In addition, the 95% confidence interval (CI) for " F 0 and c N e was calculated by a non-parametric approach bootstrapping all the individual F values from each combination of locus and pair of consecutive cohorts. Values of l i (i.e., the probability of a newborn fish to survive to age i) were estimated for each age class from the annual survival rates reported by Andrello et al (2010). In order to estimate the relative reproductive success p i at different ages, first we estimated the proportion of breeders (silver eel survival fraction in the year of spawning migration) per age class according to Andrello et al (2010).…”

“…Values of l i (i.e., the probability of a newborn fish to survive to age i) were estimated for each age class from the annual survival rates reported by Andrello et al (2010). In order to estimate the relative reproductive success p i at different ages, first we estimated the proportion of breeders (silver eel survival fraction in the year of spawning migration) per age class according to Andrello et al (2010). Mean number of offspring per male (b m i ) and female (b f i ) of age class i were obtained from Andrello et al (2010), after correcting the values so as to result in a constant population size (i.e., net reproductive rate, R 0 = P l i b i = 1, for each sex).…”

“…In order to estimate the relative reproductive success p i at different ages, first we estimated the proportion of breeders (silver eel survival fraction in the year of spawning migration) per age class according to Andrello et al (2010). Mean number of offspring per male (b m i ) and female (b f i ) of age class i were obtained from Andrello et al (2010), after correcting the values so as to result in a constant population size (i.e., net reproductive rate, R 0 = P l i b i = 1, for each sex). Finally, p i was estimated using the age-specific estimates of b i and l i by giving the sexes equal weight:…”

The influence of genotype on habitat selection of fish and the analysis of population structure

“…Investigations of diversity of microsatellite loci in European eel indicated a weak, but significant, differentiation between fish sampled in different regions (references in Palm et al, 2009;Andrello et al, 2011). However, the studies mentioned did not take into account temporal dynamics of microsatellite frequencies, while the analysis of samples collected in different years at the same geographical point is crucial for the analysis of the population structure of any species.…”