Speciation and ecological divergence in three closely related shearwater taxa: insights from migratory connectivity and non-breeding habitat

Abstract

**Abstract:** In colonial seabirds, ecological divergence may occur in the absence of physical barriers, driven by the isolation of populations due to distance, or the adaptation to local environment. In migratory seabirds, the geographic segregation among breeding populations can persist year round (i.e., strong migratory connectivity) when populations breeding separately do not mix outside the breeding area either, segregating in different non-breeding grounds. This migratory connectivity can exacerbate the isolation among populations, and thus influence the genetic structure among them. We have studied the non-breeding ecological niche and the migratory connectivity among 34 colonies of three Calonectris taxa, Scopoli's (C. diomedea), Cory's (C. borealis), and Cape Verde (C. edwardsii) shearwaters (805 breeding adults in total). To understand at what spatial scale migratory connectivity and preferences in non-breeding environment operate, and whether they are favouring ecological divergence among populations, we calculated migratory connectivity and non-breeding environmental niche at a colony, population and taxa level. To define populations, we grouped colonies in distance-based groups formed by the colonies that fell within buffers of increasing radius. At a taxa level, we found ecological segregation among the three taxa, with a clear spatial segregation between Scopoli's shearwaters and the other two taxa. At a colony level, we found low migratory connectivity among colonies of both Cory's and Scopoli's shearwaters, indicating high degree of individual mixing in the non-breeding areas. However, when we grouped the colonies in distance-based populations, the migratory connectivity increased, and differing environmental preferences appeared among populations, indicating the presence of some spatial structure at a population level. Our results agree with an ecological and evolutionary segregation among Cory's, Scopoli's and Cape Verde shearwaters, highlighting the role of migratory connectivity in the process of genetic divergence of populations across a landscape without physical barriers. **Authors:** Virginia Morera-Pujol¹, Paulo Catry², Maria Magalhães³, Clara Péron⁴, José Manuel Reyes-González⁵, José Pedro Granadeiro⁶, Teresa Militão⁵, Maria Dias⁷, Daniel Oro⁸, Giacomo Dell'Omo⁹, Martina Müller¹⁰, Vítor Paiva¹¹, Benjamin Metzger¹², Verónica Neves¹³, Joan Navarro¹⁴, Georgios Karris¹⁵, Stavros Xirouchakis¹⁶, Jacopo Cecere¹⁷, Ángel Sallent¹⁸, Manuela Forero¹⁹, Fernanda de Felipe¹, Zuzana Zajková¹, Marta Cruz-Flores¹, David Grémillet²⁰, Jacob González-Solís¹, Raül Ramos¹ ¹Universitat de Barcelona, ²ISPA-Instituto Universitário, ³Regional Secretariat for the Sea, Science and Technology, Regional Directorate for Sea Affairs (DRAM, ⁴Université de Montpellier, ⁵nstitut de Recerca de la Biodiversitat (IRBio) and Departament de Biologia Evolutiva, Ecologia i Ciè, ⁶Universidade de Lisboa, ⁷BirdLife International, ⁸IMEDEA (CSIC-UIB) and Centre d'Estudis Avançats de Blanes (CSIC), ⁹Ornis Italica, ¹⁰Nagoya University, ¹¹University of Coimbra, ¹²BirdLife Malta, ¹³Universidade das Azores, ¹⁴Institut de Ciències del Mar, CSIC, ¹⁵Ionian University, ¹⁶University of Crete & Natural History Museum of Crete, ¹⁷Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA), ¹⁸University of Murcia, ¹⁹Estación Biológica de Doñana CSIC, ²⁰University of Cape Town