Effect Of Predation Odor On Male-male Confliction Of Striped Field Mice (Apodemus Agrarius)

Predation is one of the strongest selective pressures. Mustelid odors have been shown to suppress breeding in voles. The mechanism behind the suppression is unknown. Social conflict is necessary for successful reproduction, and for the defense of resources. Engaging in social conflict is necessary for the formation of social structure. Social behavior interacts with the hormones and immune function in a complex bidirectional fashion. Hormones can act directly on the neural circuits that regulate specific behaviors to change the functioning of those circuits and thereby change the expression of behavior;Social encounters can regulate the levels of various hormones and influence immune function of the individuals.Measuring steroid hormone metabolites in fecal samples has become a widely appreciated technique, because it has been proved to be a powerful noninvasive tool that provides important information about an animal's endocrine status (adrenocortical activity and reproductive status). Measurement of these hormones in fecal extracts by high-performance liquid chromatography (HPLC) was validated using chemical derivatization, mass spectrometry.This study investigated: 1) to develop a method for assessment of fecal glucocorticoids (specifically cortisol and corticosterone) as a measure of stress in rodents, specifically striped field mice Apodemus agrarins, 2) the effect of social conflict on the behavior, physiology and endocrine response of male striped field mice, 3) examined the effects of predator odor on the incidence of aggressive behaviors between male striped field mice relative to unstressed controls. Themain results of this are as follow.1. A simple and sensitive method for the determination of steroid compounds extracted from mice feces using l,2-benzo-3, 4-dihydrocarbazole-9- ethyl-carbonylhydazine (BCEC) as pre-column derivatization reagent by high-performance liquid chromatography in combination with a gradient elution with fluorescence detection and mass spectrometric identification has been developed. Studies on derivatization conditions indicate that steroid compounds react with BCEC at 65 °C within a two-hour period in the presence of trichloroacetic acid (TCA) catalyst with acetonitrile as reaction co-solvent to give the corresponding sensitive fluorescence derivatives. The fluorescence excitation and emission wavelengths are set at Xex 333 and Xem390nm, respectively. The identification of steroid derivatives is performed under APCI source in positive-ion mode. Correlation coefficients for steroid derivatives are >0.9999, and detection limits (at signal-to-noise ratio of 3:1). are 47.3—71.2 fmol. The established method is sensitive and reproducible for the determination of steroid compounds from real samples with satisfactory results.2. Our data indicate that there are effects of both short-term and long-term predator odor stress on the incidence of aggressive conflicts, an effect that is correlated with the HPA axis response. Short-term stress exposure significantly elevated the incidence of aggression among stress mice relative to unstressed controls (Dayl, Z=2.21, P=0.028).Alternatively, long-term stress significantly lowered aggression among stress (day21, Z=2.26, P=0.02;day28, Z=2.1, P=0.037).3. Long-term predator odor stress significantly lowered attack latency among stress mice, and there was a significant relationship between attack latency and total aggressive behavior. Males that attacked earlier displayed more aggressive behavior overall.4. Long-term predator odor stress did not significantly alter the Liver, Spleen, Adrenal, Testis, Epididymis and Sperm count. As in other rodent species,predator odor did not affect the reproductive organs and adrenal size in adult mice.5. The male mice activate the HPA axis responses to cope with different stressful social environment. Among control mice, corticosterone levels of the winner and loser did not significantly alter. While under repeated predator odor, corticosterone levels of the winner and loser were significantly higher than baseline. Predator odor is more stressful than social contact for male mice.Presumably, the positive social interaction suppresses the HPA axis and decreases basal cortisol concentrations to eliminate the predator odor effect. Among control mice, cortisol levels of the winner were higher than that of the loser.Winning fights elevates testosterone levels in male mice and enhance future chance to win fights among control. Testosterone levels of the winner increased with prior winning experience, while predator odor can enhance the testosterone secretion and long-term exposure can inhibit secretion.