Sexual differences in post-hatching Saunders's gulls: size, locomotor activity, and foraging skill.

Various selection pressures induce the degree and direction of sexual size dimorphism in animals. Selection favors either larger males for contests over mates or resources, or smaller males are favored for maneuverability; whereas larger females are favored for higher fecundity, or smaller females for earlier maturation for reproduction. In the genus of Larus (seagulls), adult males are generally known to be larger in size than adult females. However, the ontogeny of sexual size dimorphism is not well understood, compared to that in adults. The present study investigates the ontogeny of sexual size dimorphism in Saunders's gulls (Larus saundersi) in captivity. We artificially incubated fresh eggs collected in Incheon, South Korea, and measured body size, locomotor activity, and foraging skill in post-hatching chicks in captivity. Our results indicated that the sexual differences in size and locomotor activity occurred with the post-hatching development. Also, larger males exhibited greater foraging skills for food acquisition than smaller females at 200 days of age. Future studies should assess how the adaptive significance of the sexual size dimorphism in juveniles is linked with sexual divergence in survival rates, intrasexual contests, or parental effort in sexes.

Limitations to the comparative proteomic analysis of thrombopoietin producing Chinese hamster ovary cells treated with sodium butyrate.

Sodium butyrate (NaBu) is known to enhance the specific productivity of Chinese hamster ovary cells expressing human thrombopoietin. In order to better understand the intracellular responses of these cells resulting from NaBu treatment, the proteomic profiles of cells treated with various concentrations of NaBu (0-3mM) were compared using two-dimensional electrophoresis (2-DE). Based on spot intensities, 80 high intensity protein spots were selected. Fifty-six of the 80 protein spots, which represent 28 different kinds of proteins, were identified by MALDI-TOF-MS and MS/MS. Compared to control without NaBu treatment, the expression levels of 2 proteins (glucose regulated protein 78 (GRP 78) and peroxiredoxin 4) were increased over two fold with NaBu treatment and the expression level of phosphopyruvate hydratase was decreased over two fold with NaBu treatment. Due to multiplicity (multiple spots for one protein), a change in one single spot intensity from a 2-DE gel image may not represent the total change in expression level for that protein. Western blot analyses of GRP78, HSC70 and ERp57 confirmed the results of the MS analyses. However, a degree of change in expression level differed between the two methods, suggesting the necessity of a validating method to determine the total amount of the protein.