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Abstract:
Background: Accurate formal taxonomic designations are thought to be of critical importance
for the conservation of endangered taxa. The Galápagos sea lion (GSL), being appreciated as a key
element of the Galápagos marine ecosystem, has lately been listed as 'vulnerable' by the IUCN. To
date there is, however, hardly any scientific evidence, whether it constitutes a separate entity from
its abundant Californian neighbour (CSL). In this paper, we delineate the taxonomic relationships
within the genus Zalophus being comprised of the Galápagos sea lion, the Californian sea lion and
the already extinct Japanese sea lion (JSL).
Results: Using a set of different phylogenetic reconstruction approaches, we find support for
monophyly of all three taxa without evidence of reticulation events. Molecular clock estimates
place time to common ancestry of the Galápagos sea lion and the Californian sea lion at about 2.3
± 0.5 mya. Genetic separation is further suggested by diagnostic SNPs in the mitochondrial and
nuclear genome. Microsatellite markers confirm this trend, showing numerous private alleles at
most of the 25 investigated loci. Microsatellite-based estimates of genetic differentiation between
the Galápagos sea lion and the Californian sea lion indicate significant genetic differentiation. Gene
diversity is 14% lower in the Galápagos sea lion than in the Californian sea lion, but there is no
evidence for recent bottleneck events in the Galápagos sea lion.
Conclusion: Based on molecular evidence we build a case for classifying the Galápagos sea lion
(Zalophus wollebaeki), the Californian sea lion (Zalophus californianus) and the Japanese sea lion
(Zalophus japonicus) as true species. As morphological characters do not necessarily fully reflect the
rapid divergence on the molecular level, the study can be considered as a test case for deriving
species status from molecular evidence. We further use the results to discuss the role of genetics
in conservation policy for an organism that already is under the general protection of the habitat it
lives in.
