Population variation alters aggression-associated oxytocin and vasopressin expressions in brains of Brandt\u2019s voles in field conditions

Shuli Huang,Xinrong Wan,Wei Lu,Jing Liu,Zhibin Zhang,Jidong Zhao,Wenxuan Han,Zuoxin Wang,Charles J Krebs,Yongliang Pan,Xin Zhang,Guoliang Li

doi:10.1186/s12983-021-00441-w

Abstract

Density-dependent change in aggressive behavior contributes to the population regulation of many small rodents, but the underlying neurological mechanisms have not been examined in field conditions. We hypothesized that crowding stress and aggression-associated oxytocin (OT) and arginine vasopressin (AVP) in specific regions of the brain may be closely related to aggressive behaviors and population changes of small rodents. We analyzed the association of OT and AVP expression, aggressive behavior, and population density of Brandt’s voles in 24 large semi-natural enclosures (0.48 ha each) in Inner Mongolia grassland. We tested the effects of population density on the OT/AVP system and aggressive behavior by experimentally manipulating populations of Brandt’s voles in the grassland enclosures. High density was positively and significantly associated with more aggressive behavior, and increased expression of mRNA and protein of AVP and its receptor, but decreased expression of mRNA and protein of OT and its receptor in specific brain regions of the voles. Our study suggests that changes in OT/AVP expression are likely a result of the increased psychosocial stress that these voles experience during overcrowding, and thus the OT/AVP system can be used as indicators of density-dependent stressors in Brandt’s voles.

Highlights

Understanding the mechanisms of population regulation in small mammals has long been a fundamental topic in population ecology [1, 2]
Our results suggest that changes in OT/AVP expression are likely a result of increased psychosocial stress of voles experienced during overcrowding
We showed that high population density increased AVP/ AVPR expression but decreased the OT/OT and its receptor (OTR) expression, and aggression behavior of voles was increased in semi-natural conditions

Summary

Introduction

Understanding the mechanisms of population regulation in small mammals has long been a fundamental topic in population ecology [1, 2]. The genetic regulation hypothesis [6], the physiological regulation hypothesis [7, 12] and the social behavioral regulation hypothesis [8] are widely used to explain density-dependence in populations of small rodents. The physiological regulation hypothesis posits that high population density induces high aggression and high social stress, which result in impairment of the hypothalamus–pituitary–adrenal (HPA) axis and the hypothalamic–pituitary–gonadal (HPG) axis including increases in corticosterone (CORT), decreases in growth or reproductive hormones, followed by a population crash or decline [7, 13]. It is notable that all the three core hypotheses include the role of density-dependent aggressive behavior in regulating population fluctuations. How population density affects aggressive behavior (and population growth) of animals via neurobiological pathways has not been investigated in field conditions

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Discussion

Conclusion