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  -