Males’ strategies towards unweaned infant and its benefit
After male replacement, new males showed two strategies, either
aggression or tolerance, which would bring different reproductive
success. When males adopted a strategy of aggression, they obtained
increased reproductive success from killing infants because they sired
the next offspring of victims’ mother sooner (Case #2, #8 and #11).
However, they completely lost benefits as lactating females emigrated if
the first set of attack did not kill the offspring (#4, #6 and #17).
Although infanticide might be expected to be favoured by older males,
who might rely more on immediate fitness benefits, aggressive males are
not older than tolerant males (t = 1.93, df = 14, p= 0.0738). On the other side, when males adopted a strategy of
tolerance, which means they tolerated unweaned infant without any attack
(#10, #12 and #13) or when lactating female transferred the males
refrain from further attacks (#5, #9 and # 14-16), they needed to
wait longer until siring the next offspring of these females, but are
likely to gain increased future reproductive benefits with those females
who did not emigrate: (i) male tenures after take-over lasted on average
39.4 months, longer than the (on average) 23.5 months it takes a female
to successfully wean her current offspring (t = 3.55, df =
62, p < 0.001, Fig 4a ), and,
(ii) tenures of tolerant males are
significant longer than those of
aggressive males
(t= 2.31, df = 9, p < 0.05, Fig 4b ).