PMC

(a) Frequency of infanticidal individuals in populations at the end of the breeding season. Closed circles show the mean number of voles in populations where infanticidal individuals were initially rare (and non-infanticidal individuals common); and open circles indicate the populations where infanticidal individuals were initially common (and non-infanticidal individuals rare) in founder populations. Dashed lines show the initial frequency of infanticidal tactics in each treatment. (b) Frequency change in infanticidal tactics with different food manipulations (for statistics see ). Asterisks indicate a significant difference (** P<0.01, * P<0.05) from the zero line. Infanticidal individuals can invade both food treatments when they are initially rare (closed circles; t=11.14, df=3, P=0.002; t=5.41, df=4, P=0.006; respectively), but more easily invade populations when food is limited (comparison between the food treatments: t=3.86, df=7, P=0.006). Instead, the rare non-infanticidal tactic (open circles) was significantly favoured only in the populations with supplemented food (t=5.41, df=4, P=0.012). (c) Population size increased with supplemental food (F=28.35, P<0.001), but was not affected by the initial frequency of infanticidal individuals in the population (F=0.018, P=0.895). NS, not significant.

(A) Schematic of viral injection and fiber implantation strategy for ChR2 stimulation.
(B) Example image of injection site and viral expression. Scale bar = 200 µm.
(C) Representative raster plots of control and ChR2 animals illustrating promotion of infanticidal behavior during photostimulation. * indicates when the pup was removed.
(D) Distribution of infanticidal behavior episodes in ChR2 animals (percentage of trials showing infanticide at different time points) with respect to stimulation onset.
(E) Percentage of animals showing infanticidal behavior.
(F) Average latency until infanticidal behavior onset following stimulation initiation.
(G) Latency distribution of infanticidal behavior onset following stimulation initiation.
ChR2, n = 22 trials (5 mice); control, n = 26 trials (4 mice). Mean ± SEM. Wilcoxon rank-sum test. ***p < 0.001.
See also .

Percentage of animals displaying maternal or infanticidal behavior during the second of two tests. During the first test, all animals were virgins and were found to be maternal (left panel) or infanticidal (right panel). During the second test, females were pregnant (black bars) or remained virgins (gray bars) and displayed maternal (M), unresponsive (U), or infanticidal (I) behavior. Numbers above bars indicate number of animals per group. Note that a large percentage of initially maternal voles were infanticidal while pregnant whereas initially infanticidal voles were likely to remain so whether pregnant or not.

AC3 or miR-200b/a in the MOE is crucial for infanticidal behavior
(A) No significant difference in the latency to investigate the pups was found between the AC3^−/− male mice and WT mice (n = 12 per group).
(B) The evaluation of infanticidal behavior showed that the AC3^−/− male mice exhibited significantly longer infanticide latencies than the WT mice. The duration of the infanticidal behavior assay was 300 s (n = 12 mice per group).
(C) IF analysis of AC3 in the MOE of MOE-specific AC3-KD mice and NC mice. Scale bars, 20 μm.
(D) WB analysis showing AC3 protein expression in the MOE of MOE-specific AC3-KD mice and NC mice. Actin served as a loading control.
(E) Spontaneous locomotor activity did not differ between the MOE-specific AC3-KD mice and NC mice (n = 7 mice per group).
(F and G) An analysis of aggressive male behaviors showed that the attack frequency (F) and duration (G) of the MOE-specific AC3-KD mice were significantly reduced compared with those of the NC mice (n = 12 mice per group).
(H and I) The male mating behavior test showed that the mating frequency (H) and duration (I) of the MOE-specific AC3-KD mice were significantly reduced compared with those of the NC mice (n = 12 mice per group).
(J) No significant difference in the latency to investigate the pups was found between MOE-specific AC3-KD mice and their controls (NC group: n = 14 mice, AC3-KD group: n = 16 mice).
(K) An evaluation of the infanticidal behavior showed that the infanticide latency of the MOE-specific AC3-KD mice was significantly longer than that of the NC mice. The duration of the infanticidal behavior assay was 300 s (NC group: n = 14 mice, AC3-KD group: n = 16 mice).
(L) A qPCR analysis revealed that the expression of miR-200a and miR-200b in the MOE was significantly decreased in the miR-200b/a-KD mice compared with that of the NC mice (n = 4 mice per group).
(M) No significant difference in the latency to investigate the pups was found between the MOE-specific miR-200b/a-KD mice and their controls (n = 15 mice per group).
(N) An evaluation of infanticidal behavior showed that the infanticidal latency of the miR-200b/a-KD mice was significantly longer than that of the NC mice. The duration of the infanticidal behavior assay was 300 s (n = 15 mice per group). The data are the mean values ± SEMs; ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001, and ∗∗∗∗p < 0.0001, as determined by unpaired two-tailed Student’s t-test. See also and .