1,552 research outputs found
Phenotypic integration of brain size and head morphology in Lake Tanganyika Cichlids
[Background]
Phenotypic integration among different anatomical parts of the head is a common phenomenon across vertebrates. Interestingly, despite centuries of research into the factors that contribute to the existing variation in brain size among vertebrates, little is known about the role of phenotypic integration in brain size diversification. Here we used geometric morphometrics on the morphologically diverse Tanganyikan cichlids to investigate phenotypic integration across key morphological aspects of the head. Then, while taking the effect of shared ancestry into account, we tested if head shape was associated with brain size while controlling for the potentially confounding effect of feeding strategy.[Results]
The shapes of the anterior and posterior parts of the head were strongly correlated, indicating that the head represents an integrated morphological unit in Lake Tanganyika cichlids. After controlling for phylogenetic non-independence, we also found evolutionary associations between head shape, brain size and feeding ecology.[Conclusions]
Geometric morphometrics and phylogenetic comparative analyses revealed that the anterior and posterior parts of the head are integrated, and that head morphology is associated with brain size and feeding ecology in Tanganyikan cichlid fishes. In light of previous results on mammals, our results suggest that the influence of phenotypic integration on brain diversification is a general process.This study was funded through the student exchange support program (scholarship for long-term study abroad) from the Japanese Student Services Organization (JASSO) to M. Tsuboi, a JAE-Doc postdoctoral fellowship from the Consejo Superior de Investigaciones Científicas to A. Gonzalez-Voyer and a Swedish Research Council grant to N. Kolm.Peer Reviewe
Study of Magnetic Excitation in Singlet-Ground-State Magnets CsFeCl and RbFeCl by Nuclear Magnetic Relaxation
The temperature dependences of spin-lattice relaxation time of
Cs in CsFeCl and Rb in RbFeCl were measured in the
temperature range between 1.5 K and 22 K, at various fields up to 7 T applied
parallel (or perpendicular) to the c-axis, and the analysis was made on the
basis of the DCEFA. The mechanism of the nuclear magnetic relaxation is
interpreted in terms of the magnetic fluctuations which are characterized by
the singlet ground state system. In the field region where the phase transition
occurs, exhibited the tendency of divergence near , and
this feature was ascribed to the transverse spin fluctuation associated with
the mode softening at the -point. It was found that the damping constant of
the soft mode is remarkably affected by the occurrence of the magnetic ordering
at lower temperature, and increases largely in the field region where the phase
transition occurs.Comment: 12 pages, 18 figures, submitted to J. Phys. Soc. Jp
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