Cryptic Ponto-Caspian Bighead Gobies (genus Ponticola, Gobiidae, Perciformes)

Ekaterina D. Vasil'Eva 1* , Dmitry A. Medvedev 2 and Victor P. Vasil'Ev 2 • 1 Moscow State University, Biological Department, Russia • 2 A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Russia Earlier karyological studies have proved that the Ponto-Caspian Bighead goby is represented by two independent species with very similar morphological features and colour pattern: Ponticola kessleri in the Black Sea basin and P. gorlap in the Caspian Sea. In 2012 several samples of gobies, corresponding to the diagnostic features of the Caspian Bighead goby P. gorlap, were collected in the Mangyshlak Peninsula (the Eastern Caspian, Kazakhstan). These fishes were subjected to karyological study (157 metaphase plates from 12 males, 2 females, and 13 juveniles were totally analyzed); fin clips from 11 specimens were used to extract genomic DNA for amplification of mitochondrial cyt b gene fragment (about 1098 bp); 14 specimens were used for detailed morphological analysis to define their taxonomic status and divergence level between them and other samples of P. gorlap. A total of seven karyological morphs with the chromosome numbers (2n) ranging from 38 to 44 and the stable number of chromosome arms NF=46 were revealed among goby specimens from the inshore sea regions and the Karakol Lake. This karyotype noticeably differs from the karyotype of P. gorlap distributed in the western, southern, and northern Caspian, as well as from the karyotype of P. kessleri from the Black Sea basin, in the number of chromosomes and the presence of one pair of marker submetacentrics. This data confirms the validity of the species P. iljini previously described by the type specimens from the Caspian Sea off the Mangyshlak Peninsula and included in synonyms of P. gorlap. The comparative morphological study demonstrated the low level of morphological divergent between P. iljini and P. gorlap sensu stricto. P. iljini is characterized by wider head (wider than deep) and upper lip (its width is 0.7-08 distance from the lip to the orbit), longer snout (significantly larger than horizontal eye diameter), strongly compressed caudal peduncle (its width at the base of the anal fin usually does not reach 40% of its length), and nape and upper part of opercle covered with cycloid scales only. However, all of morphometric characters of P. iljini and P. gorlap significantly overlap. All 9 haplotypes revealed in P. iljini, are species-specific. Both the maximum likelihood and maximum parsimony analyses of the haplotypes from different Ponto- Caspian goby species, deposited in the GenBank, demonstrated enough similar topologies of their trees. The haplotypes of P. iljini were combined in a separate phylogenetic lineage within the clade of Ponticola species; the most related phylogenetic lineage was formed by the haplotypes of P. gorlap. Both these lineages were combined with a separate group, consisted from two other lineages represented by haplotypes of P. kessleri and the same of P. eurycephalus. In this way, P. iljini, P. gorlap, and P. kessleri represent a group of distinct allopatric cryptic species with very low morphological divergence. The start of the divergence between P. kessleri and the Caspian species can be dated no earlier than the end of the Miocene (5.8-5.0 million years ago) when the Pontian sea-lake has divided into two separate brackish pools: the later Pontian sea-lake basin and Babadzhanskoe sea-lake in the southern part of the Caspian depression. But, at the same time, it can be dated not later than Pleistocene (2.0-0.7 Ma), when the last connection of the Caspian and the Black Sea through the Manych has been stopped. The ancestors of P. iljini could penetrate to the east coast of the Caspian Sea during the period of the largest transgressions, Akchagyl (2.5-2.0 Ma) or Apsheron (2.0-0.7 Ma). Their isolation in the Mangyshlak Peninsula region from other Caspian Bighead goby populations has been provided by two hypersaline bays, limiting the peninsula from the north (Mërtvyj Kultuk and Kajdak bays with salinity of 30 ‰ and above) and from the south (Kara-Bogaz-Gol Bay with salinity of 300-350 ‰ and above), as well as the lack of a network of rivers on the peninsula.

Acknowledgements

The study was financially supported by the project no 14-50-00029 of the Russian Scientific Fond.

Keywords: cryptic species, Ponto-Caspian gobies, Karyology, morphology, mtDNA, evolution Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Oral Presentation

Topic: Phylogeny, Systematics and Genetics Citation: Vasil'Eva ED, Medvedev DA and Vasil'Ev VP (2015). Cryptic Ponto-Caspian Bighead Gobies (genus Ponticola, Gobiidae, Perciformes). Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.FMARS.2015.03.00067 Received: 11 Nov 2015; Published Online: 12 Nov 2015. * Correspondence: Dr. Ekaterina D Vasil'Eva, Moscow State University, Biological Department, Moscow, 125009, Russia, [email protected]