Gradients of genetic diversity and differentiation across the distribution range of a Mediterranean coral: Patterns, processes and conservation implications

Aim: How historical and contemporary eco-evolutionary processes shape the patterns of genetic diversity and þÿdifferentiation across species distribution range remain Focusing on the orange stony coral, Astroides calycularis, we (a) characterized the pattern of neutral genetic diversity across the distribution range; (b) gave insights into the underlying processes; and (c) discussed conservation implications with emphasis on a national park located on a hotspot of genetic diversity. Location: South Mediterranean Sea and Zembra National Park. Methods: We combined new data from 12 microsatellites in 13 populations located in the Centre and in the Western Periphery of the distribution range with a published dataset including 16 populations from the Western and Eastern Peripheries. We analysed the relationship among parameters of genetic diversity (He, Ar(g)) and structure (population-specific FST) and two measures of geographic peripherality. We compared two estimators of pairwise genetic structure (GST, DEST) across the distribution range. The evolutionary and demographic history of the populations following the Last Glacial Maximum was reconstructed using approximate Bayesian computations and maximum-likelihood analyses. We inferred the contemporary connectivity among populations from Zembra National Park and with the neighbouring area of Cap Bon. Results: We demonstrate a decrease in genetic diversity and an increase in genetic differentiation from the Centre to the Eastern and Western Peripheries of the distribution range. Populations from Zembra show the highest genetic diversity reported in the species. We identified a spillover effect towards Cap Bon. Main conclusions: The patterns of genetic diversity and þÿdifferentiation are most likely explained by the postglacial range expansion hypothesis rather than the þÿ central peripheral hypothesis. Enforcement of conservatio

Comparative population genetics of habitat-forming octocorals in two marine protected areas: eco-evolutionary and management implications

Current efforts to halt the decline of biodiversity are based primarily on protecting species richness. This narrow focus overlooks key components of biological diversity, particularly the infra-species genetic diversity, which is critical to consider with respect to genetic adaptation in changing environments. While comparative population genetics is recognized as a relevant approach to improve biodiversity management, it is still barely considered in practice. Here, a comparative population genetics study was conducted on two key habitat-forming octocoral species, Corallium rubrum and Paramuricea clavata, to contribute to management of two Marine Protected Areas (MPAs) in the northwestern Mediterranean. Contrasting patterns of genetic diversity and structure were observed in the two species, although they share many common biological features and live in similar habitats. Differential genetic drift effects induced by species-specific reproductive strategies and demographic histories most likely explain these differences. The translation of our results into management strategies supports the definition of four management units. We identified a coldspot of genetic diversity, with genetically isolated populations, and a hotspot of genetic diversity that has a central role in the system’s connectivity. Interestingly, they corresponded to the most recent and the oldest protected areas, respectively. This case study shows how moving from a “species pattern” perspective to an “eco-evolutionary processes” perspective can help assess and contribute to the effectiveness of biodiversity management plans.Open access funding provided by FCT|FCCN (b-on). JBL was funded by assistant researcher 2021.00855.CEECIND through national funds provided by FCT—Fundação para a Ciência e a Tecnologia. This research was supported by national funds through FCT within the scope of UIDB/04423/2020 and UIDP/04423/2020, by the MIMOSA project funded by the Foundation Prince Albert II Monaco. This work was supported by the European Union’s Horizon 2020 research and innovation program under grant agreement SEP-210597628 (FutureMARES). This study was also supported by the Spanish Government through the Smart project (CGL2012-32194) the HEATMED project (RTI2018-095346-B-I00, MCIU/AEI/FEDER, UE). RL was supported by the Agence Nationale de la Recherche (projects DISLAND ANR-20-CE32-00XXX, GENOSPACE ANR-16-CE02-0008 and INTROSPEC ANR-19-CE02-0011; and project PROLAG from the CeMEB LabEx;), and by recurrent funding from INRAe and CNRS. This research has been funded from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 869300 “FutureMARES”. SD is supported by the Fonds National de la Recherche Scientifique (FNRS, Belgium). JG and PL acknowledge the funding of the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). CL gratefully acknowledges the financial support by ICREA under the ICREA Academia program.Peer reviewe

Comparative population genetics of habitat-forming octocorals in two marine protected areas: eco-evolutionary and management implications

International audienceCurrent efforts to halt the decline of biodiversity are based primarily on protecting species richness. This narrow focus overlooks key components of biological diversity, particularly the infra-species genetic diversity, which is critical to consider with respect to genetic adaptation in changing environments. While comparative population genetics is recognized as a relevant approach to improve biodiversity management, it is still barely considered in practice. Here, a comparative population genetics study was conducted on two key habitat-forming octocoral species, Corallium rubrum and Paramuricea clavata , to contribute to management of two Marine Protected Areas (MPAs) in the northwestern Mediterranean. Contrasting patterns of genetic diversity and structure were observed in the two species, although they share many common biological features and live in similar habitats. Differential genetic drift effects induced by species-specific reproductive strategies and demographic histories most likely explain these differences. The translation of our results into management strategies supports the definition of four management units. We identified a coldspot of genetic diversity, with genetically isolated populations, and a hotspot of genetic diversity that has a central role in the system’s connectivity. Interestingly, they corresponded to the most recent and the oldest protected areas, respectively. This case study shows how moving from a “species pattern” perspective to an “eco-evolutionary processes” perspective can help assess and contribute to the effectiveness of biodiversity management plans

Insights into the genetic makeup of French Polynesian peripheral populations of the small giant clam Tridacna maxima

The small giant clam, Tridacna maxima, is distributed from the Red Sea and East African coast to French Polynesia. Across this widespread Indo‐Pacific range, T. maxima shows strong population structure, in agreement with its limited dispersal abilities. Peripheral populations may have smaller effective population sizes, increasing their vulnerability under any environmental changes. Understanding evolutionary processes at play in such regions located at the edges of T. maxima distribution is a prerequisite in the context of transfers and restocking programmes. In this study, giant clams were sampled from 14 atolls and islands within four archipelagos in the peripheral region of French Polynesia, in 2001–2002 and/or in 2012–2013, then genotyped at the COI gene and at nine microsatellite loci. Mitochondrial lineages of T. maxima from French Polynesia diverged from those sampled in Micronesia, Melanesia, the Coral Triangle and the Red Sea by 6.6–7.3%. Within French Polynesia, significant genetic structure was found, indicating restricted gene flow, and it was stable through time. Most of the genetic variation at microsatellite loci was between archipelagos. The most differentiated archipelago was the most geographically isolated (the Austral Islands). The current patterns of genetic structuring of T. maxima in French Polynesia probably result from long‐term genetic isolation with limited dispersal ability. In addition, these results underlined that sufficiently large populations of T. maxima have persisted in the Central Pacific during the last sea‐level regression. Strategies to optimize transfers and restocking programmes should be designed to preserve the genetic diversity and structure observed here, to avoid the risks of altering the genetic structure, allele loss and/or introduction of maladapted alleles in the receiving populations

Don’t mind if I do: Arctic humpback whales respond to winter foraging opportunities before migration

Migration patterns are fundamentally linked to the spatio-temporal distributions of prey. How migrating animals can respond to changes in their prey's distribution and abundance remains largely unclear. During the last decade, humpback whales (Megaptera novaeangliae) used specific winter foraging sites in fjords of northern Norway, outside of their main summer foraging season, to feed on herring that started overwintering in the area. We used photographic matching to show that whales sighted during summer in the Barents Sea foraged in northern Norway from late October to February, staying up to three months and showing high inter-annual return rates (up to 82%). The number of identified whales in northern Norway totalled 866 individuals by 2019. Genetic sexing and hormone profiling in both areas demonstrate a female bias in northern Norway and suggest higher proportions of pregnancy in northern Norway. This may indicate that the fjord-based winter feeding is important for pregnant females before migration. Our results suggest that humpback whales can respond to foraging opportunities along their migration pathways, in some cases by continuing their feeding season well into winter. This provides an important reminder to implement dynamic ecosystem management that can account for changes in the spatio-temporal distribution of migrating marine mammals