Abstract
Correct species identification is a crucial issue in systematics with key implications for prioritising conservation effort. However, it can be particularly challenging in recently diverged species due to their strong similarity and relatedness. In such cases, species identification requires multiple and integrative approaches. In this study we used multiple criteria, namely plumage colouration, biometric measurements, geometric morphometrics, stable isotopes analysis (SIA) and genetics (mtDNA), to identify the species of 107 bycatch birds from two closely related seabird species, the Balearic (Puffinus mauretanicus) and Yelkouan (P. yelkouan) shearwaters. Biometric measurements, stable isotopes and genetic data produced two stable clusters of bycatch birds matching the two study species, as indicated by reference birds of known origin. Geometric morphometrics was excluded as a species identification criterion since the two clusters were not stable. The combination of plumage colouration, linear biometrics, stable isotope and genetic criteria was crucial to infer the species of 103 of the bycatch specimens. In the present study, particularly SIA emerged as a powerful criterion for species identification, but temporal stability of the isotopic values is critical for this purpose. Indeed, we found some variability in stable isotope values over the years within each species, but species differences explained most of the variance in the isotopic data. Yet this result pinpoints the importance of examining sources of variability in the isotopic data in a case-by-case basis prior to the cross-application of the SIA approach to other species. Our findings illustrate how the integration of several methodological approaches can help to correctly identify individuals from recently diverged species, as each criterion measures different biological phenomena and species divergence is not expressed simultaneously in all biological traits.
Highlights
Species have long been recognized as one of the fundamental units of biology
In the case of the linear biometric data, cluster 1 included the 10 YS breeding at Hyeres Islands, the bycatch Balearic shearwaters (BS) ringed in Menorca (5070034, see cyan circle in Fig. 4) and 43 bycatch birds, while the cluster 2 included the bycatch BS ringed in Mallorca (5042990, see dark blue circle in Fig. 4) and 62 bycatch birds
Concerning stable isotope clusters, the cluster 1 included the 10 YS from Hyeres Islands, the bycatch BS ringed in Menorca (5070034, see cyan circle in Fig. 8) and 46 bycatch birds, while the cluster 2 included the bycatch BS ringed in Mallorca (5042990, see dark blue circle in Fig. 8) and 59 bycatch birds
Summary
Species have long been recognized as one of the fundamental units of biology. After endless debates and controversies about the concept of species, the emphasis is shifting towards species delimitation [1,2,3]. While discussion of different operational methods to identify species has previously been restricted mostly to taxonomists, species delimitation and identification is underpinned by a growing concern over threats to biodiversity [2], [5]. [6]), species is the key unit for conservation biology since it is the basic unit used in international conventions and agreements and for providing lists of threatened organisms [7]. Since many human activities are responsible for the direct death of billions of animals each year [8], the unequivocal identification of individuals to the species level is crucial for an accurate evaluation of the anthropogenic impact, among threatened species
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