Spatial ecology of closely related taxa: the case of the little shearwater complex in the North Atlantic Ocean

Abstract

Seabirds inhabiting vast water masses provide numerous examples where opposing phenomena, such as natal and breeding philopatry vs. vagility have dug cryptic taxonomic boundaries among closely related taxa. The taxonomy of little shearwaters of the North Atlantic Ocean (Little–Audubon’s shearwater complex, Puffinus assimilis–lherminieri) still remains unclear, and complementary information on non-breeding distributions and at-sea behaviour becomes essential to unravel divergent local adaptations to specific habitats. Using miniaturized light-level geolocators from seven study areas in the North Atlantic, we evaluate the spatial and habitat segregation, estimate the timing of their key life-cycle events and describe the at-sea behaviour of three taxa of these little shearwaters year-round to distinguish ecological patterns and specializations that could ultimately unravel potential lineage divergences. We also assess morphometric data from birds that were breeding at each study area to further discuss potential adaptations to specific habitats. Our results show that, while birds from different taxa segregated in space and habitats, they share ecological plasticity, similar annual phenology and diel foraging behaviour. These ecological inconsistencies, while defining the evolutionary stressors faced by these taxa, do not suggest the existence of three Evolutionary Significant Units. However, they confirm the recent evolutionary divergence among the three little shearwaters of the North Atlantic.

Integrating Sequence Capture and Restriction Site-Associated DNA Sequencing to Resolve Recent Radiations of Pelagic Seabirds

“…Thus, these two species may have hybridized during the Pleistocene. In addition, P. boydi and P. lherminieri show some contemporary overlap in their wintering areas ( Ramos et al 2020 ), which may be a relic of a previously higher overlap in distribution. Future studies should use population genomics data in order to confirm whether the observed patterns are due to ancestral introgression between these two species or to ancestral population structure.…”

Sea surface temperature, rather than land mass or geographic distance, may drive genetic differentiation in a species complex of highly dispersive seabirds

“…Even foraging ecology, which strongly depends on SST, may be an important process shaping divergence among lineages, as segregation of foraging areas among populations is an important factor of differentiation among seabirds (Friesen, 2015; Friesen et al, 2007), shearwaters (Genovart et al, 2007; Gómez‐Díaz et al, 2006), petrels (Gangloff et al, 2013; Welch et al, 2012), storm‐petrels (Deane, 2013; Smith et al, 2007), and albatrosses (Alderman et al, 2005; Burg & Croxall, 2001). Assessment of nonbreeding and breeding distributions at sea of the little shearwaters complex revealed that all three Atlantic taxa show rather separated foraging and wintering areas (Ramos et al, 2021), and further suggest that boydi rather than lherminieri was ancestral in the North Atlantic. Indeed, boydi is more flexible in its foraging ecological niche, suggesting ancestral behavior (Zajková et al, 2017; see map in Ramos et al, 2021).…”

“…Using this single marker, three distinct lineages were recognized in the North Atlantic: lherminieri in the Caribbean and off Brazil, baroli in the Azores, Canaries, and Madeira, and boydi in Cape Verde (Figure 1). In the North Atlantic, lineages are characterized by nonoverlapping breeding and nonbreeding distributions at sea (Ramos et al, 2021) and are thus geographically separated. Still, they are morphologically and ecologically highly similar (Precheur et al, 2016), a pattern typical of the first stages of the speciation process, the so‐called gray zone (De Queiroz, 2007).…”

Paleoceanographic changes in the late Pliocene promoted rapid diversification in pelagic seabirds

“…In addition to the aforementioned species pairs, other shearwater species showed weak patterns of population structure and genetic distances within the interval among different subspecies: P. boydi and P. baroli , and the three Atlantic Calonectris species. These species complexes are the subject of ongoing taxonomic debate (Genovart et al, 2013;Gomez-Diaz et al, 2009;Olson, 2010;Sangster, Collinson, Helbig, Knox, & Parkin, 2005;Ramos et al, 2020). As a final consideration, our genomic data, together with ongoing taxonomic debate, suggest that these taxa should not be granted species status.…”

“…Most extant Puffinus species are short-distance migrants or dispersers that remain close to their breeding sites throughout the year (e.g. Ramos et al, 2020). Their lower dispersal compared to other shearwater genera may have reduced gene flow and promoted higher species richness.…”