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Approximately 70% of the Earth’s surface is covered by water, yet birds have colonized the oceanic realm beyond the continental shelves only a few times during evolutionary history. Despite constraints associated with a pelagic lifestyle, seabirds are diverse in their ecological and behavioural traits, including, for example, dynamic soaring by albatrosses vs. wing-propelled diving by shearwaters, nesting on sea cliffs in fulmars vs. subterranean burrows in storm petrels, and foraging solitarily vs. in association with other marine predators. Seabirds are keenly adapted to their pelagic habitat, and it's likely that ecological differentiation, along with other processes like vicariance and genetic drift, have driven the divergence of species through time. However, understanding the evolutionary relationships of seabirds has been difficult: there have often been bursts of rapid radiation at several points in time, during which incipient species may have exchanged genes, thus obscuring the phylogenetic signal. It is critically important that we resolve these uncertainties and further examine the taxonomy of seabirds because they face threats both at terrestrial breeding colonies and at sea, and are among the most endangered groups of birds in the world.
Recently, we investigated the utility of two different reduced representation sequencing techniques (RADs, Restriction site-associated DNA sequencing and UCEs, ultra conserved elements) for resolving rapid radiations. These two types of loci evolve at different rates, and thus can provide information about evolutionary histories at different points in time. We found that combining these data helps disentangle the causes of phylogenetic discordance, helping to distinguish between incomplete lineage sorting (when ancestral genetic variants are retained in species after they have split) and past hybridisation during incipient species. We used them to investigate the case of the shearwaters, one of the most phylogenetically controversial and endangered bird groups.
The Scopoli’s Shearwater (Calonectris diomedea)
Beyond being charismatic and interesting in their own right, seabirds provide an excellent system for studying how factors such as body size (one proxy for metabolic for metabolic rate), life history factors (such as longevity, population size, etc), and hand-wing index (a proxy for metabolic rate during flight) are related to substitution rates. One common assumption is that animals with high metabolism (e.g. those with small body sizes, inefficient flyers, and short generation times) have a higher mutation rate because of the release of more free radicals as a result of increased rates of cellular respiration. Our work, using a genome-scale phylogeny of the order Procellariiformes (Albatrosses, petrels and shearwaters) shows that in these seabirds, which differ 900 fold in body size and exhibit striking variation in hand-wing index and other life history traits, shows that no single trait is strongly correlated with substitution rate, and instead many traits are weakly linked instead.
Body size in Procellariiformes seabirds. A. Silhouettes of the Least Storm-Petrel (Oceanodroma microsoma; wingspan 36 cm) and Wandering Albatross (Diomedea exulans; wingspan 3.5 m), to scale. B. Distribution of body mass in various groups of Procellarii- formes in our study, which range from 18.2 g to 16.1 kg
Ferrer-Obiol J, James HF, Chesser RT, Bretagnolle V, González-Solís J, Rozas J, Riutort M, Welch AJ. 2021. Integrating sequence capture and restriction-site associated DNA sequencing to resolve recent radiations of pelagic seabirds. Systematic Biology 70:976-996. PDF.
Estandía A; Chesser RT, James HF, Levy M, Ferrer-Obiol J, Bretagnolle V, González-Solís J, Welch AJ. Substitution rate variation in a robust Procellariiform seabird phylogeny is not solely explained by body mass, flight efficiency, population size or life history traits. bioRxiv.
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