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The spectral tuning mechanism of visual pigments is an excellent model to elucidate the mechanisms of adaptive evolution and the importance of selection as an evolutionary force. Therefore, we use a phylogenetic approach to determine whether there is evidence for differential adaptive molecular evolution on the rhodopsin (RH1) gene among closely related 'sand goby' species (Teleostei, Gobiidae). Fragments of the RH1 gene (868 bp) were sequenced and analyzed for nine 'sand goby' species that inhabit different photic environments. A high level of interspecific polymorphism at the RH1 gene was observed, including non-synonymous mutations on amino acids known as spectral tuning sites. Clear indications for positive Darwinian selection were provided by three independent methods: (1) by linking functional variation on the RH1 gene to specific light environments of the different fish habitats; (2) by constructing and comparing phylogenies based on RH1 and the 'neutral' 12S and 16S mtDNA fragments; and (3) by performing statistical tests to detect signatures of directional selection on the RH1 gene. This study shows an unusual high variability in the gobiid visual RH1 pigment, and we therefore suggest a possible role for sensory genes in the adaptive radiation of 'sand goby' species., (Copyright 2009 Elsevier Inc. All rights reserved.)

Vicariant and climatic cycling speciation hypotheses of the 'sand gobies' belonging to the genera Pomatoschistus, Gobiusculus, Knipowitschia, and Economidichthys are tested using molecular phylogenies constructed of nuclear DNA (ITS1 locus) and mitochondrial DNA (12S and 16S fragments). These gobies are among the most abundant in the Eastern Atlantic-Mediterranean region, and play an important role in the ecosystem. Considerable ITS1 length differences, primarily due to the presence of several tandem repeats, were found between species and even within individuals. Therefore, phylogenetic analyses focused on fragments of the 12S and 16S mtDNA region that have been sequenced for 16 goby taxa. The 'sand gobies' clustered as a monophyletic group as proposed on morphological grounds. However, G. flavescens, E. pygmaeus, and K. punctatissima clustered within the Pomatoschistus species, pointing to a paraphyletic origin of these genera. Furthermore, the genetic divergence between P. minutus from the Adriatic Sea versus the Atlantic-Mediterranean region was as high as the divergence within the P. minutus complex, suggesting that P. minutus from the Adriatic Sea should be considered as a distinct species. The "star" phylogeny might suggest that these gobies evolved in a very short time period, possibly linked to the drastic alterations in the Mediterranean Sea during and immediately after the Messinian salinity crisis at the end of the Miocene. The freshwater life-style appeared monophyletic; equating its origin with the salinity crisis resulted in a molecular clock estimate of 1.4% divergence per million years. The last common ancestor probably occupied sandy bottoms and a coastal niche while several species subsequently adapted to new habitats (pelagic, freshwater or stenohaline). The origin of the shallowest clades dated back to the glacial cycling during the Pleistocene epoch., (Copyright 2003 Elsevier Inc.)

The burbot (Lota lota Linnaeus, 1758) is the only freshwater species from the cod family. Various taxonomic hypotheses were tested against molecular data by sequencing the mitochondrial cytochrome b locus of 120 burbot from 41 populations together with the related species Molva molva (ling) and Brosme brosme (tusk), which represented the other Lotinae genera. Within the genus Lota two distinct phylogroups were observed: one in North America south of the Great Slave Lakes (Lota lota maculosa) and one in Eurasia and the remainder of the Nearctic region (Lota lota lota). The burbot lineage separated 10 Myr BP from the other Lotinae, while the genetic variation within burbot appeared to be approximately 1 Myr old. However, fossil evidence suggested that burbot already existed in the Early Pliocene in Europe, from were it probably colonized North America in the Early Pleistocene. While Nearctic burbot survived climatic oscillations and diverged in several refugia, the Eurasian form became extinct or was reduced to a very small population. In the Late Pleistocene the species recolonized the Palearctic region to establish its present distribution range.