Scotti Melissa-Ann L, Place Ned J, Demas Gregory E
Department of Biology, Center for Integrative Study of Animal Behavior and Program in Neuroscience, Indiana University, Bloomington, IN 47405, USA.
Horm Behav. 2007 Aug;52(2):183-90. doi: 10.1016/j.yhbeh.2007.03.029. Epub 2007 Apr 6.
Among the suite of adaptations displayed by seasonally-breeding rodents, individuals of most species display reproductive regression and concomitant decreases in gonadal steroids during the winter. In addition, some species display increased aggression in short "winter-like" days compared with long "summer-like" day lengths. For example, male Syrian and Siberian hamsters held in short days express heightened levels of aggression that are independent of gonadal steroids. Virtually nothing is known, however, regarding seasonal aggression in female Siberian hamsters (Phodopus sungorus). Studies were undertaken to determine female levels of aggression in long and short days as well as the role of gonadal steroids in mediating this behavior. In Experiment 1, females were housed in long or short days for 10 weeks and resident-intruder aggression was assessed. Prior to testing, estrous cycle stages were determined by vaginal cytology and females were tested during both Diestrus I and Proestrus. In Experiment 2, hormone levels were experimentally manipulated; long-day females were ovariectomized (OVx) or given sham surgeries whereas short-day females were implanted with capsules containing 17beta-estradiol (E(2)) or Progesterone (P). In Experiment 3, both long- and short-day females were ovariectomized and implanted with either an exogenous E(2) or blank capsule, or given a sham surgery. Short-day hamsters displayed increased aggression relative to long-day females. Aggression was not affected by estrous stage. There was no difference in aggression between long-day OVx and sham animals. Furthermore, neither exogenous E(2) nor P had any significant effect on aggression. These results support previous findings of increased non-breeding aggression and suggest that short-day aggression is not likely mediated by circulating levels of gonadal steroids. These results also suggest that the endocrine regulation of seasonal aggression may be similar between the sexes.
在季节性繁殖的啮齿动物所表现出的一系列适应性变化中，大多数物种的个体在冬季会出现生殖衰退以及性腺类固醇水平随之下降的情况。此外，与较长的“类似夏季”的日照时长相比，一些物种在较短的“类似冬季”的日照时长下会表现出更强的攻击性。例如，处于短日照条件下的雄性叙利亚仓鼠和西伯利亚仓鼠表现出更高水平的攻击性，且这种攻击性与性腺类固醇无关。然而，关于雌性西伯利亚仓鼠（Phodopus sungorus）的季节性攻击行为，我们几乎一无所知。因此开展了多项研究，以确定雌性在长日照和短日照条件下的攻击水平，以及性腺类固醇在介导这种行为中所起的作用。在实验1中，将雌性仓鼠置于长日照或短日照环境中10周，然后评估其领地入侵攻击行为。在测试前，通过阴道细胞学确定发情周期阶段，并在间情期I和动情前期对雌性进行测试。在实验2中，对激素水平进行实验性操控；长日照雌性仓鼠接受卵巢切除术（OVx）或假手术，而短日照雌性仓鼠则植入含有17β-雌二醇（E(2)）或孕酮（P）的胶囊。在实验3中，长日照和短日照雌性仓鼠均接受卵巢切除术，并植入外源性E(2)或空白胶囊，或接受假手术。与长日照雌性相比，短日照仓鼠表现出更强的攻击性。攻击行为不受发情阶段的影响。长日照OVx组和假手术组动物在攻击性上没有差异。此外，外源性E(2)和P对攻击性均无显著影响。这些结果支持了之前关于非繁殖期攻击性增加的研究发现，并表明短日照条件下的攻击性不太可能由性腺类固醇的循环水平介导。这些结果还表明两性之间季节性攻击行为的内分泌调节可能相似。
