Bailey Allison M, Rendon Nikki M, O'Malley Kyle J, Demas Gregory E
Department of Biology, Indiana University, 1001 E 3rd St., Bloomington, IN, USA.
Physiol Behav. 2016 Dec 1;167:298-308. doi: 10.1016/j.physbeh.2016.09.023. Epub 2016 Sep 28.
Animals living in temperate regions prepare for harsh winter conditions by responding to environmental cues that signal resource availability (e.g., food, day length). Siberian hamsters (Phodopus sungorus) breed in long, summer-like days (LD, >14h light), i.e., photoperiods, and undergo robust gonadal regression and become more aggressive when exposed to short, winter-like photoperiods that signal impending limited resources (SD, <10h light). When hamsters are reared within an intermediate photoperiod (ID, 13.5h light), they are reproductively active, but undergo gonadal regression in response to mild food restriction (FR) over 6-12weeks. We hypothesized that short-term (1-2weeks) FR in an ID photoperiod would provide a signal of impending limited resources and initiate the seasonal increase in aggression typical of SD photoperiods, as well as alter reproductive behaviors in advance of gonadal regression. To test this, we housed male and female hamsters in LD or ID photoperiods, with ad libitum (AL) access to food or a 90%-AL ration. We tested aggressive behavior after one week and reproductive behavior after two weeks, and subsequently monitored females for pregnancy and litter production. Both sexes displayed increased aggression in the ID-FR treatment. Untreated male intruders were less likely to ejaculate when paired with ID females during reproductive encounters. ID-FR males were undergoing gonadal regression after two weeks, but were more likely to have ejaculated. Female pregnancy and litter characteristics were unaltered by treatment: females were equally likely to achieve pregnancy and produce comparable litters across treatment groups. Collectively, we demonstrate that a signal of diminishing resources in an ID photoperiod is sufficient to trigger seasonal aggression, but that hamsters are reproductively resilient to inhibitory environmental cues in the short term. Broadly, our findings provide an important context for exploring seasonal changes in behavior and physiology from an ultimate perspective.
生活在温带地区的动物会通过对环境线索做出反应来为严酷的冬季条件做准备，这些线索能表明资源的可获得性（如食物、日照长度）。西伯利亚仓鼠（Phodopus sungorus）在长日照、类似夏季的日照时长（LD，光照时长>14小时），即光周期下繁殖，而当暴露于短日照、类似冬季的光周期时，它们的性腺会发生显著退化，并变得更具攻击性，这种短日照光周期预示着即将出现资源有限的情况（SD，光照时长<10小时）。当仓鼠在中间光周期（ID，光照时长13.5小时）下饲养时，它们具有生殖活性，但在6至12周内受到轻度食物限制（FR）时会发生性腺退化。我们推测，在ID光周期下的短期（1至2周）FR会提供即将出现资源有限的信号，并引发SD光周期典型的季节性攻击行为增加，同时在性腺退化之前改变生殖行为。为了验证这一点，我们将雄性和雌性仓鼠饲养在LD或ID光周期下，提供自由采食（AL）或90%AL的食物配给。我们在一周后测试攻击行为，两周后测试生殖行为，随后监测雌性仓鼠的怀孕和产仔情况。在ID-FR处理中，两性的攻击性都有所增加。在生殖相遇时，未处理的雄性入侵者与ID雌性配对时射精的可能性较小。ID-FR雄性在两周后性腺正在退化，但射精的可能性更大。处理对雌性仓鼠的怀孕和产仔特征没有影响：各处理组的雌性仓鼠怀孕和产仔的可能性相同。总体而言，我们证明了ID光周期下资源减少的信号足以引发季节性攻击行为，但仓鼠在短期内对抑制性环境线索具有生殖弹性。广泛地说，我们的研究结果为从最终角度探索行为和生理的季节性变化提供了重要背景。
