Effects Of Repeated Exposure To Cat Odor On Mate Choice Of Norway Rats (Rattus Norvegicus)

Mate choice behavior of rodents is closely related to their mating system which is an important factor that affects the population dynamics.It is of great significance to clarify the mating system and its plasticity for the studies of the population structure of rodents.Norway rats(Rattus norvegicus)are the most harmful species in the world,which seriously interferes with people’s normal life.The mating system of Norway rat is promiscuity,However,the effects of kinship,familiarity,mate relationship,and individual size on mate choice have not been studied;Norway rats can recognize the odors of the predator,non-predator,and distilled water,predator odors significantly affect the behavior and physiology of Norway rats,However,the effect of predator odors on mate choice of them has not been reported.This study was undertaken by using behavioral research methods,reared and bred indoors Norway rats were used as research objects and were exposed to odorless,distilled water,and cat urine odors for 18 days.After the treatment,we measured the duration and frequencies of their visiting,caring,sniffing/licking,and attacking behaviors,to analyze the changes of mate choice behaviors,and determine the characteristics of mate choice on Norway rats.We aimed to investigate the influence of kinship,familiarity,sexual relationship,and individual body size and predator odors factors on the mate choice of Norway rats.Furtherly,revealing the plasticity and function characteristics of the mating system of Norway rats,and provides theoretical information for population prediction and hazard controls of Norway rats.The main research results were as follows:1)Mate choice of Norway rats under the odorless conditionInfluence of kinship:The male and female Norway rats showed no significant differences in the duration and frequency of visit,care,sniffing/lick,and attack behaviors between siblings and non-siblings.The results showed that the kinship factor had no significant effect on the mate choice of male and female rats.Influence of familiarity:The frequency and duration of visit,care,sniff/lick,attack of male to female strangers were significantly higher than those of familiar female rats.The results showed that the male rats preferred the stranger females under odorless condition,while the female rats showed no preference,familiarity significantly affected the mate choice of Norway rats.Influence of spouse relationship:The duration of the visit,frequency,and duration of attack of female rats to non-spouse males were significantly higher than those spouse males;The frequency and duration of attack of male rats to female strangers were significantly higher than those of female mates,but there were no significant differences in the frequency and duration of visit,care,and sniff/slick to spousing and non-spousing female rats.The results showed that female rats preferred non-spouse male rats,while spouse relationship had no significant effect on the mating choice of male rats.Influence of Body Weight:The male rats had more frequency of visit and sniff/lick to heavy female rats than light female rats,and had longer duration of visit,care and sniff/lick to heavy female rats than light rats.The result indicated that male Norway rats preferred heavier female rats,while the bodyweight factor did not influence the mating choice of female rats.2)Mate choice of Norway rats under odor exposure conditionsInfluence of Kinship:Under distilled water odor exposure conditions,the sniffing frequency and the duration of female rats to male non-siblings were significantly higher than those of male siblings;The male rats showed no significant differences in the frequency and duration of visit,care,sniff/lick and attack to male siblings and non-siblings;The results showed that female rats preferred non-sibling males under the condition of distilled water exposure,but the kinship had no effect on the mating choice of male rats.Under cat odor exposure conditions,there were no significant differences in the frequency and duration of visit,care,sniff/lick,and attack of female Norway rats to spouse male rats and non-spouse male rats;The male Norway rats showed more frequency and duration of attack to spouse females than non-spouse females,indicating that male Norway rats showed increased aggression towards female siblings when exposed to cat odor.Influence of Familiarity:Under distilled water odor exposure conditions,the female Norway rats had more frequency and duration of sniff/lick and attack to male strangers than familiar male rats,and showed more frequency of attack,as well;The male Norway rats showed more frequency of visit and attack to female strangers than familiarizes,and the duration of the attack,as well;The results showed that both male and female rats preferred to choose the stranger rats under the condition of distilled water exposure.Under cat odor exposure conditions,the frequency and duration of sniff/lick and attack of female Norway rats to strange males were higher than familiar males;The male Norway rats showed no difference in the frequency and duration of visit,care,sniff/lick and attack,indicating that female Norway rats had a preference on unfamiliar males when exposed to cat odorInfluence of spouse relationship:Under distilled water odor exposure conditions,the female Norway rats had more duration of visit,care,sniff/lick and attack to non-spouse males than spouse males,and the frequency of attack as well;And the male Norway rats showed no significant differences;The results showed that female Norway rats preferred non-mating males under the condition of distilled water exposure,but spouse relationship had no effect on the mate choice of male rats.Under cat odor exposure conditions,the female Norway rats showed more duration of sniff/lick and attack to non-spouse rats,the frequency of attack,as well;The male Norway rats showed more frequency of care and sniff/lick to non-spouse female rats,the duration of sniff/lick as well;The results showed that Norway rats tended to pair with non-siblings when exposed to cat odor.Influence of body weight:Under distilled water odor exposure conditions,there were no significant differences in the time and frequency of visit,care,sniff/lick,and attack of female Norway rats to light and heavy male rats;And the male Norway rats showed the same results,which indicated that body weight did not affect mate choice of both male and female rats under the condition of distilled water exposure.Under cat odor exposure conditions,Influence of Bodyweight:The frequency and duration of an attack of female Norway rats to lighter male rats were higher;There were no significant differences in the duration and frequency of visit,care,sniff/lick,and attack of male Norway rats.It was shown that female Norway rats increased their aggressions towards lighter males when exposed to cat odor.The above results indicated that in the absence of predator odor,the kinship factor had no significant effect on the mate choice of male and female rats.Male rats have a preference for the selection of heavy female rats,female rats have a preference for the selection of non-spouse males,but males have no preference for spouse males.It could be inferred that the mating system of Norway rats is promiscuous in the natural environment.After repeated exposure to distilled water and cat odor for 18 days,although the mating system of Norway rats is still promiscuous,the mate preference of female and male rats changed significantly.This shows that the mating system of Norway rats has certain plasticity.The familiar characteristics of mate choice behavior of Norway rats are related to its mating system.The preference of Norway rats to choose individuals with large body weight may be the main mechanism to improve the fitness of their offspring.