Male infanticide and paternity analyses in a socially natural herd of Przewalski’s horses: sexual selection?

The research article analyses male infanticide behaviour and its relationship with paternity among Przewalski’s horses, a wild horse species. The researchers found scant support for the theory that sexual selection drives infanticide. Infanticidal attacks weren’t necessarily linked to herd takeovers and didn’t happen often. Stallions at births did not tend to kill unrelated foals and infanticide didn’t always lead to shorter birth intervals. A potential link was seen between such behaviour and horses reared in unnatural social groups like zoos.

Understanding the Study

• The researchers of this study followed a herd of Przewalksi’s horses over an 11-year period. Their focus was on understanding the patterns of infanticide by males and its relationship with paternity, primarily testing the sexual selection hypothesis. This theory suggests that infanticide is a tactic used by males to increase their chances of reproducing, as females may come into estrus or breeding condition sooner after losing a foal.
• The cases of infanticide observed in this study were not directly linked to herd takeovers. The researchers noted infanticidal attacks in only five out of 39 cases following a takeover, demonstrating that such events weren’t a consistent trigger for infanticide.
• With the help of DNA paternity tests, the study further scrutinized the relationship between the paternity of foals and occurrences of infanticide. The results revealed that stallions committing infanticide were typically not the biological fathers of the foals. At the same time, the researchers found that the stallions present at foaling did not significantly attempt to kill unrelated offspring. This contradicts the sexual selection hypothesis, which would predict that stallions would aim to eliminate potential competition by killing unrelated foals.

Additional Findings and Conclusions

• Another component of the sexual selection hypothesis suggests that infanticide can shorten the time interval between births, as it induces earlier estrus in females. Observations from this study did not support this theory, providing another blow to the sexual selection hypothesis.
• Researchers also found behavioural changes in the mares whose offsprings were victim to infanticide. These mothers tended to avoid associating with stallions that exhibited infanticidal behaviour. This behaviour presents a significant challenge to the sexual selection argument, implying that infanticide does not necessarily increase mating opportunities for the stallions.
• The authors instead suggested the ‘human disturbance’ hypothesis as an alternative explanation for the observed infanticide. This theory received some support from the study’s findings, as it was noted that only stallions born and raised in unnatural social groups, such as zoos, showed infanticidal behaviour towards foals of mares who were pregnant during herd takeovers. This highlights the potential influence of rearing environment and social structures on aggressive behaviours in male horses.