Caught between two worlds: genes and environment influence behaviour of plains × Grevy's zebra hybrids in central Kenya

Hybridization between related species has been documented in many animal groups, but little work has been done on the behaviour of hybrids relative to the parental species. Hybrid individuals generally possess physical characteristics of both parents, but behaviour may vary depending on complexity of gene interaction and the extent to which behaviours are learned from one species or the other. Studying hybrid behaviour can be an opportunity to separate environmental or learned traits from genetic ones. Here we report on the behaviour and sociality of natural plains-Grevy's zebra hybrids (Equus quagga × Equus grevyi) from central Kenya. All hybrids were born to plains zebra mothers and raised exclusively in the plains zebra society. When leaving natal groups, hybrids showed no interest in and did not interact with Grevy's zebras. Therefore, any behavioural differences between hybrids and plains zebra may result from genetic influences of their Grevy's zebra fathers. We found several significant behavioural differences between hybrids and plains zebra. Hybrid females were more vigilant than plains zebra females and showed equivalent levels of vigilance to Grevy's zebra females. Male hybrids were seen alone more often (a Grevy's zebra trait) and in a greater diversity of behavioural states (bachelor, satellite, challenger, stallion, alone), and changed state more often than plains zebra males, indicating conflicting environmental and genetic cues. Adult hybrid males appear to show a divergence in behavioural paths, with some behaving like plains zebra males challenging for harems and others setting up territories as Grevy's males do. Both male and female hybrids stayed with their natal harems longer than either plains or Grevy's juveniles.