Research

Galápagos and Californian sea lions are separate species: Genetic analysis of the genus Zalophus and its implications for conservation management

Jochen BW Wolf^1,2,3 , Diethard Tautz¹ and Fritz Trillmich³

¹  Department of Evolution Genetics, Institute for Genetics, University of Köln, Zülpicherstraße 47, 50674 Köln, Germany

²  Max-Planck Institute of Evolutionary Biology, August-Thienemannstr. 2, 24306 Plön, Germany

³  Department of Animal Behaviour; University of Bielefeld; PO Box 10 01 31; 33501 Bielefeld; Germany

author email corresponding author email

Frontiers in Zoology 2007, 4:20doi:10.1186/1742-9994-4-20

Published:	15 September 2007

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.