TY - JOUR A1 - Eccard, Jana A1 - Dammhahn, Melanie A1 - Ylonen, Hannu T1 - The Bruce effect revisited: is pregnancy termination in female rodents an adaptation to ensure breeding success after male turnover in low densities? JF - Oecologia N2 - Pregnancy termination after encountering a strange male, the Bruce effect, is regarded as a counterstrategy of female mammals towards anticipated infanticide. While confirmed in caged rodent pairs, no verification for the Bruce effect existed from experimental field populations of small rodents. We suggest that the effect may be adaptive for breeding rodent females only under specific conditions related to populations with cyclically fluctuating densities. We investigated the occurrence of delay in birth date after experimental turnover of the breeding male under different population composition in bank voles (Myodes glareolus) in large outdoor enclosures: one-male-multiple-females (n = 6 populations/18 females), multiple-males-multiplefemales (n = 15/45), and single-male-single-female (MF treatment, n = 74/74). Most delays were observed in the MF treatment after turnover. Parallel we showed in a laboratory experiment (n = 205 females) that overwintered and primiparous females, the most abundant cohort during population lows in the increase phase of cyclic rodent populations, were more likely to delay births after turnover of the male than year-born and multiparous females. Taken together, our results suggest that the Bruce effect may be an adaptive breeding strategy for rodent females in cyclic populations specifically at low densities in the increase phase, when isolated, overwintered animals associate in MF pairs. During population lows infanticide risk and inbreeding risk may then be higher than during population highs, while also the fitness value of a litter in an increasing population is higher. Therefore, the Bruce effect may be adaptive for females during annual population lows in the increase phases, even at the costs of delaying reproduction. KW - Breeding strategies KW - Dip test KW - Infanticide KW - Myodes voles KW - Sexual conflict KW - Sexual selection Y1 - 2017 U6 - https://doi.org/10.1007/s00442-017-3904-6 SN - 0029-8549 SN - 1432-1939 VL - 185 SP - 81 EP - 94 PB - Springer CY - New York ER - TY - JOUR A1 - Eccard, Jana A1 - Reil, Daniela A1 - Folkertsma, Remco A1 - Schirmer, Annika T1 - The scent of infanticide risk? BT - Behavioural allocation to current and future reproduction in response to mating opportunity and familiarity with intruder JF - Behavioral ecology and sociobiology N2 - The killing of young by unrelated males is widespread in the animal kingdom. In short-lived small rodents, females can mate immediately after delivery (post-partum oestrus) and invest in future reproduction, but infanticide may put the nestlings, their current reproductive investment, at risk. Here, we investigated the behavioural trade-offs between mating interest and nest protection in an arena experiment with bank voles (Myodes glareolus). Non-gravid females (n=33) were housed at one end of a large structured arena with their nestlings. Different scents (cage bedding) were presented to each female in a replicated design. Three combinations of mating opportunities and male-female familiarity were simulated using different scent donors: mating opportunity with the sire of the nestlings with whom the female was familiar; mating opportunity with a male unrelated to the offspring and unfamiliar to the female, thus posing a higher risk to the offspring; and neither risk nor mating opportunity (clean control). Most females investigated male scents, regardless of familiarity, leaving their litter unprotected. During control treatment, females with larger litters spent less time at the scent area, indicating increasing nursing demands or better protection. Females with older litters visited scents more often, suggesting an increased interest in reproduction while they are non-gravid alongside the decreased risk of infanticide for older young. In the presence of unfamiliar scents, females spent more time protecting their nests, supporting the perceived association of unfamiliarity with infanticide risk. Thus, rodent females flexibly allocate time spent between searching for a mate and protecting their nest, which is modulated by their familiarity with a potential intruder.Significance statementInfanticide by conspecific males is an extreme form of sexual conflict and has large costs on females, abolishing their investment into current offspring. In an experimental approach, we exposed lactating female bank voles to different combinations of mating opportunity and familiarity to a (simulated) intruder: (1) the sire of the nestlings with whom the female was familiar and, therefore, potentially less risky in terms of infanticide; (2) a male which was unrelated and unfamiliar to the female and thus posed a higher risk to the offspring; or (3) as a control, cage bedding, which posed neither risk of infanticide nor a mating opportunity. We show that females flexibly allocated pup protection and mating interest based on their familiarity with the male, indicating that the unfamiliar males pose a threat to offspring, which is perceived by the females. Females further adjusted their behaviour to the size and/or age of their current litter, investing more time in male scents when offspring were older, thus balancing future and current investments into reproduction. KW - Reproductive strategy KW - Infanticide risk KW - Odour recognition KW - Familiarity KW - Counterstrategy KW - Sexual conflict Y1 - 2018 U6 - https://doi.org/10.1007/s00265-018-2585-4 SN - 0340-5443 SN - 1432-0762 VL - 72 IS - 175 PB - Springer Nature Switzerland AG CY - New York ER -