| Mating system is most important in animal behavioural ecology. Although there are closely relationships between species, rodents of the genus Microtus show diverse patterns of social organization and mating system. In addition, differences in mating system are based on diversity of physiological procedures, so the comparative study between different mating systems may reveal different mechanisms for the formation of social behavior. Therefore, Microtus rodents provide a comparative animal model for studying the underlying mechanism of the mating system and the evolution of monogamy. As the expression of breeding behaviors, mating system results from the long-term evolution, and it is plastic to some extent. Even in different living environments, same species of voles from different populations display diverse patterns of social organization and mating system. With environmental conditions differed, mating system exhibited certain plasticity. Previous studies reported that in the different populations of same species of voles, patterns of social organization and neuroendocrine features are significantly different. Recently, the studies for neuroendocrine mechanism of mating system mainly focused on oxytocin, vasopressin and estrogen, which play a great role in regulating social behaviors associated with mating system. However, these studies were conducted in different species, with little information was available in intraspecific variation. In previous study, body weight, anxiety related behaviors, the levels of sociability, partner preferences and parental care differed between two wild populations from different ecological environments. Mandarin voles from Chengcun area possess monogamous traits, and animals from Xinzheng possess polygamous traits. Differences were also found in the central patterns of ERα-IR neurons. Then in the laboratory, whether the F1 generation voles respectively reared from two wild populations, displayed above similar differences? Whether central oxytocin and vasopressin expression differed between two populations? These issues are still unclear. The purpose of the present study was to compare the social behaviors and neuroendocrine differences between the F1 generation voles of two populations, and to explore the neuroendocrine mechanism of the evolution of monogamy.The present study was conducted using the behavioural and immunohisochemical methods. The behavioural tests include open field, social interaction, partner preference and parental care tests. In addition, the distribution patterns of ERαin MPOA, BNST, Arc, VMH and MeA were compared between F1 generation voles. We also examined OT and AVP expression in PVN and SON. The main findings are as follow:1. F1 generation Chengcun and Xinzheng mandarin voles displayed less sexual dimorphism with respect to body weight. This result indicated that F1 generation mandarin vole possess monogamous traits for sexual dimorphism of body mass. However, Xinzheng males were significantly heavier than Chengcun males whatever in wild or F1 generation population. This may be due to sexual selection in which male become larger to increase competition for mating with more females. Thus, Xinzheng population showed characteristics of polygyny.2. In the open field, we found that F1 generation Chengcun mandarin voles spent more time in the central area than did Xinzheng voles. In addition, the percentage of time in the central area in Chengcun females was significantly larger than males. These data are consistent with that from wild population and suggest that Chengcun mandarin voles are less anxious than Xinzheng voles in novel environment. The total transitions of F1 generation Chengcun voles were significantly higher than Xinzheng voles. This result suggests that Xinzheng voles displayed less locomotor activity in a novel environment.3. In social interaction test, wild Xinzheng voles engaged in more aggression and less affiliation than wild Chengcun mandarin voles. However, we did not find these differences between two populations of mandarin voles in F1 generation population. The consistency as wild populations was that Chengcun males spent more time in investigating novel same-sex individuals, and less time in staring than Xinzheng voles. These results indicated that under laboratory conditions, sociability of F1 Xinzheng voles was significantly increased.In partner preference test, we found that Chengcun males showed significant preferences to familiar partners, but female voles did not display partner preference whether in wild or F1 generation population. In addition. Chengcun voles exhibited significantly more aggressive behavior toward strangers than toward familiar partner. It is inferred that Chengcun mandarin voles reliably display behaviors that are indicative of pair bond formation. There was an interesting finding that wild Xinzheng voles showed a significant preference for strangers, while F1 generation voles displayed an opposite preference. These indicated that F1 generation Xinzheng voles might be able to form preference, whereas wild voles did not after 72h of cohabitation.In parental care test, male mandarin voles from both two populations display paternal care, it is suggested that the social system of this species is a type of social monogamy characterized by different levels of paternal care across different populations. Chengcuan voles display significant high levels of nesting than Xinzheng voles in wild population, but levels of licking behavior were higher in Fl generation population at PND 0 of their pups. In addition, Chengcuan voles display significant high levels of hover-crouching than Xinzheng voles whether in wild or Fl population at PND 13 of their pups. Therefore, it could be suggested that Chengcun voles showed significant more parental investment than Xinzheng populations.4. In our results, F1 generation Xinzheng males expressed significantly more ERa in the MPOA and BNST than Chengcun males. The only difference in females is in the MPOA with Xinzheng expressing more than Chengcun females. In addition, numbers of ERa-IR was sexually different in Chengcun with males expressing less in the MPOA and BNST. There was no sexually dimorphic in Xinzheng voles. We therefore infer that the distribution patterns of ERa in the F1 generation Chengcun population are charactersitc of monogamous traits, the distribution patterns of ERa in F1 generation Xinzheng voles are characteristic of a polygamous social system.5. No significant sexual difference in OT-IR neurons, but Chengcun voles displayed significantly more OT-IR neurons than Xinzheng voles. The same as OT expression, F1 generation Chengcun voles possess more AVP-IR neurons than that of Xinzheng population. The above results suggest that Fl generation Xinzheng possess polygamous traits in the expression of neuropeptide OT and AVP.From the above results, the present study concludes that from the levels of anxiety, locomotor activity, parental care, the patterns of ERa. and the expression of OT and AVP. we can inferred that F1 generation Xinzheng voles still exhibited polygamous traits. However, they tend to be monogamy in sociability and parental care. This is in part due to rearing environment which is changed under laboratory conditions. In order to adapt this change, mandarin voles need to change their related behaviors. |
PDF Full Text Request