Neutral processes and taxonomic scale drive beta species-genetic diversity correlations in a submesophotic tropical reef fish.

If similar evolutionary forces maintain intra- and interspecific diversity, patterns of diversity at both levels of biological organization can be expected to covary across space. Although this prediction of a positive species-genetic diversity correlation (SGDC) has been tested for several taxa in natural landscapes, no study has yet evaluated the influence of the community delineation on these SGDCs. In this study, we focused on tropical fishes of the Indo-Pacific Ocean, using range-wide single nucleotide polymorphism data for a deep-sea fish (Etelis coruscans) and species presence data of 4878 Teleostei species. We investigated whether a diversity continuum occurred, for different community delineations (subfamily, family, order and class) and spatial extents, and which processes explained these diversity patterns. We found no association between genetic diversity and species richness (α-SGDC), regardless of the community and spatial extent. In contrast, we evidenced a positive relationship between genetic and species dissimilarities (ß-SGDC) when the community was defined at the subfamily or family level of the species of interest, and when the Western Indian Ocean was excluded. This relationship was related to the imprint of dispersal processes across levels of biological organization in Lutjanidae. However, this positive ß-SGDC was lost when considering higher taxonomic communities and at the scale of the entire Indo-Pacific, suggesting different responses of populations and communities to evolutionary processes at these scales. This study provides evidence that the taxonomic scale at which communities are defined and the spatial extent are pivotal to better understand the processes shaping diversity across levels of biological organization.

Gigantic breeding colonies of a marine fish in the Mediterranean.

While breeding colonies are well known in seabirds, they remain exceptional for marine fishes. Here, we report on fifteen massive breeding colonies of picarels (Spicara smaris), a small benthic zooplanktivorous fish, observed by chance during video transects in spring 2021 along the East coast of Corsica (French Mediterranean). In total, these colonies cover more than 134.6 hectares (ha) within a surveyed area of 712.1 ha, a single colony covering from 2.2 to 28 ha between 37 and 50 meters deep. The seabed, including the lower limit of Posidonia oceanica seagrass meadows, soft bottoms, and the predominant rhodolith beds, has been completely rebuilt in circular jointed nests measuring 55 cm in diameter on average. With a density of 2.6 nests per m2, the estimated number of nests in the colony exceeds 18 million. Each nest is guarded by a male. Females swim in groups above the nests and sometimes lay eggs. A rich macrofauna including threatened species can be observed around the nests, eating eggs or adults. This finding highlights the exceptional ecological role of this small fish as an ecosystem engineer creating oases of marine life. This warrants further studies and better protection of the area, at least during the breeding season.