Sara M Francisco and Joana I Robalo
Background: Species with planktonic larvae are more likely to show temporal genetic variation, due to differences in larval mortality and dispersal ability. The shanny Lipophrys pholis is a typical benthic rocky intertidal fish with its dispersion limited to a long larval stage. In contrast, the sand smelt Atherina presbyter has a very short planktonic life, small size and weak swimming capabilities, which translates into reduced dispersion potential.
Methods: A total of 226 shanny specimens (collected in 2003, 2013 and 2014) and 281 sand smelts (collected in 2005, 2012, 2013 and 2014) were screened for genetic variation using the mitochondrial control region. Genealogies, genetic diversities, temporal structures and contemporary effective population sizes were assessed.
Results: Haplotype networks showed deep genealogies with multiple levels of diversification and no temporal structure. Genetic diversity indices showed little variation among sampling periods and were generally high. For L. pholis significant genetic differentiation was detected between 2013 and 2014, while no significant differences were detected between sampling periods in A. presbyter. The shanny showed lower effective population size per generation when compared to the sand smelt (which yielded lack of evidence for genetic drift for the first two periods of the study).
Conclusion: These results highlight the fact that temporal changes in the gene pool composition need to be considered when evaluating population structure, especially for species with long pelagic larval dispersion, more vulnerable to fluctuations in the recruitment.
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