Food as a supplementary cue triggers seasonal changes in aggression, but not reproduction, in Siberian hamsters

Abstract

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, >14 h 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, <10 h light). When hamsters are reared within an intermediate photoperiod (ID, 13.5 h light), they are re-productively active, but undergo gonadal regression in response to mild food restriction (FR) over 6–12 weeks. We hypothesized that short-term (1–2 weeks) FR inanID 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.

Overcoming neonatal sickness: Sex-specific effects of sickness on physiology and social behavior

“…We recorded and analyzed reproductive behavior, aggression, investigation, and scent-marking using the resident-intruder paradigm with opposite-sex social partners per previously outlined methods for this species [34]. All experimental trials were performed under low illumination (25W), red light conditions, with a video camera (Sony Handycam HD R-SR7) positioned in front of the cage with mirrors on either side, to ensure visibility of all cage corners.…”

“…Adult males ( n =7 saline-treated; n =12 LPS-treated) and females ( n =10 saline-treated; n =10 LPS-treated) were introduced to a novel individual of the opposite sex, and behavior was recorded within a 30-minute testing period. Each of the interactions took place on 5 consecutive nights with the same pairs in order to capture when females were receptive [34]. Although it is possible to identify changes in vaginal cytology, we are unable to determine a pattern between the estrous stage and the receptivity of the female during behavioral assessments in Siberian hamsters [35].…”

“…We analyzed female reproductive behaviors, including the occurrence of receptivity, frequency of lordosis, and lordosis quotient (LQ = number of lordoses/10 mounts × 100) [34,38–40]. Their male intruders were monitored for the occurrence of ejaculation, as determined by the male thrusting for a period of time followed by the male falling on its side while still intromitting.…”

Biological Clocks and Rhythms of Anger and Aggression

“…Significant work remains to be done to further elucidate these mechanisms. Furthermore, much remains unknown regarding the mechanisms by which non-photoperiod–based seasonal zeitgebers , such as food availability, influence circannual cycles of aggressive behavior (Bailey et al, 2016 ).…”

Aggressive behaviours track transitions in seasonal phenotypes of female Siberian hamsters

“…long days) (Jasnow et al 2000;Scotti, Place & Demas 2007;Bedrosian et al 2012;Rendon et al 2015b). From a functional perspective, shortday aggression might confer an evolutionary advantage for this solitary animal when food availability is relatively low and competition for limited resources is highfood restriction increases aggression in a photoperiod regime that mimics the transition between breeding and nonbreeding seasons (Bailey et al 2016). Aggression during the breeding season co-occurs with elevated testosterone concentrations in males and 17b-oestradiol (oestradiol) in females (Jasnow et al 2000;Scotti, Place & Demas 2007).…”