Genetic homogeneity in the face of morphological heterogeneity in the harbor porpoise from the Black Sea and adjacent waters (Phocoena phocoena relicta).

Absence of genetic differentiation is usually taken as an evidence of panmixia, but can also reflect other situations, including even nearly complete demographic independence among large-sized populations. Deciphering which situation applies has major practical implications (e.g., in conservation biology). The endangered harbor porpoises in the Black Sea illustrates this point well. While morphological heterogeneity suggested that population differentiation may exist between individuals from the Black and Azov seas, no genetic study provided conclusive evidence or covered the entire subspecies range. Here, we assessed the genetic structure at ten microsatellite loci and a 3904 base-pairs mitochondrial fragment in 144 porpoises across the subspecies range (i.e., Aegean, Marmara, Black, and Azov seas). Analyses of the genetic structure, including FST, Bayesian clustering, and multivariate analyses revealed a nearly complete genetic homogeneity. Power analyses rejected the possibility of underpowered analyses (power to detect FST ≥ 0.008 at microsatellite loci). Simulations under various demographic models, evaluating the evolution of FST, showed that a time-lag effect between demographic and genetic subdivision is also unlikely. With a realistic effective population size of 1000 individuals, the expected "gray zone" would be at most 20 generations under moderate levels of gene flow (≤10 migrants per generation). After excluding alternative hypotheses, panmixia remains the most likely hypothesis explaining the genetic homogeneity in the Black Sea porpoises. Morphological heterogeneity may thus reflect other processes than population subdivision (e.g., plasticity, selection). This study illustrates how combining empirical and theoretical approaches can contribute to understanding patterns of weak population structure in highly mobile marine species.

Network analysis to reveal the most commonly detected compounds in predator-prey pairs in freshwater and marine mammals and fish in Europe.

Marine and freshwater mammalian predators and fish samples, retrieved from environmental specimen banks (ESBs), natural history museum (NHMs) and other scientific collections, were analysed by LIFE APEX partners for a wide range of legacy and emerging contaminants (2545 in total). Network analysis was used to visualize the chemical occurrence data and reveal the predominant chemical mixtures for the freshwater and marine environments. For this purpose, a web tool was created to explore these chemical mixtures in predator-prey pairs. Predominant chemicals, defined as the most prevalent substances detected in prey-predator pairs were identified through this innovative approach. The analysis established the most frequently co-occurring substances in chemical mixtures from AP&P in the marine and freshwater environments. Freshwater and marine environments shared 23 chemicals among their top 25 predominant chemicals. Legacy chemical, including perfluorooctanesulfonic acid (PFOS), brominated diphenyl ethers (BDEs), polychlorinated biphenyls (PCBs), hexachlorobenzene and mercury were dominant chemicals in both environments. Furthermore, N-acetylaminoantipyrine was a predominant pharmaceutical in both environments. The LIFE APEX chemical mixture application (https://norman-data.eu/LIFE_APEX_Mixtures) was proven to be useful to establish most prevalent compounds in terms of number of detected counts in prey-predator pairs. Nonetheless, further research is needed to establish food chain associations of the predominant chemicals.