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Divergent natural selection rooted in differential resource use can generate and maintain intraspecific eco-morphological divergence (i.e., resource polymorphism), ultimately leading to population splitting and speciation. Differing bottom environments create lake habitats with different benthos communities, which may cause selection in benthivorous fishes. Here, we document the nature of eco-morphological and genetic divergence among local populations of the Japanese gudgeon Sarcocheilichthys (Cyprinidae), which inhabits contrasting habitats in the littoral zones (rocky vs. pebbly habitats) in Lake Biwa, a representative ancient lake in East Asia. Eco-morphological analyses revealed that Sarcocheilichthys variegatus microoculus from rocky and pebbly zones differed in morphology and diet, and that populations from rocky environments had longer heads and deeper bodies, which are expected to be advantageous for capturing cryptic and/or attached prey in structurally complex, rocky habitats. Sarcocheilichthys biwaensis, a rock-dwelling specialist, exhibited similar morphologies to the sympatric congener, S. v. microoculus, except for body/fin coloration. Genetic analyses based on mitochondrial and nuclear microsatellite DNA data revealed no clear genetic differentiation among local populations within/between the gudgeon species. Although the morphogenetic factors that contribute to morphological divergence remain unclear, our results suggest that the gudgeon populations in Lake Biwa show a state of resource polymorphism associated with differences in the bottom environment. This is a novel example of resource polymorphism in fish within an Asian ancient lake, emphasizing the importance and generality of feeding adaptation as an evolutionary mechanism that generates morphological diversification.

To grasp the documented evidences available regarding the cause of the anteriorly displaced human temporomandibular joint (TMJ) disc. With 20 specimens of human TMJ from cadavers, at first the number of heads of lateral pterygoid muscle (LPM) bundles were analysed with macroanatomical method. Secondary histological procedure with haematoxyline and eosine staining and orceine staining were carried out for the same specimens. Macroscopically, in 13 specimens an upper and a lower head of the LPM were present. In the other seven specimens, not only an upper and a lower head, but also a third inner head of the LPM covered with a separate fascia was observed. Histochemically, the specific localization of certain bundles of thick elastic fibres in the antero-medial parts of the anteriorly displaced deformed TMJ disc were observed.

A microsatellite-enriched genomic library was obtained for the Japanese gudgeon Sarcocheilichthys variegatus microoculus, and 15 dinucleotide markers were successfully isolated and characterized. These markers were also available for other Japanese congeners, Sarcocheilichthys variegatus variegatus and Sarcocheilichthys biwaensis. In three populations of Sarcocheilichthys from Lake Biwa and the Ashida River in western Japan, seven to 27 alleles were observed for each locus. Linkage equilibrium was observed among most loci, and only one locus showed significant deviation from Hardy-Weinberg equilibrium in a population. These microsatellite markers will be useful for studies of the genetic structure of the Japanese gudgeons.

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