Early environmental enrichment protects captive-born striped mice against the later development of stereotypic behaviour

Understanding how birth origin (whether born in the wild or captivity) influences behavioural development is important for fundamental and applied ethology, especially when captive-bred (CB) individuals from wild species are used in research or conservation. CB animals are typically much more prone to stereotypic behaviour (SB) than are wild caught (WC) conspecifics, an effect which in striped mice is accompanied by increased tendencies to form behavioural routines. However, WC mice, if stereotypic, are far more severely affected than CB mice and are also more physiologically stressed and inactive than CB mice, regardless of their stereotypy status. Capturing subjects from the wild to further study these latter effects raises serious practical, ethical and potentially conservation concerns. Here, we therefore tested whether rearing CB striped mice in enriched conditions and then placing them in standard cages could provide a more suitable model for investigating how wild-caught (WC) conspecifics respond to the reduced environmental complexity they experience after capture. Compared with striped mice which were always standard-housed (n = 36), enriched striped mice (n = 24) were four times less likely to develop SB and, similarly to the benefits of being wild born, early environmental enrichment (30–170 days) successfully protected CB striped mice from the emergence of SB after transfer to standard caging (171–240 days). However, unlike WC mice, previously enriched CB striped mice which then became stereotypic did not develop markedly more severe SBs; they showed diverse forms, unlike stereotypic WC mice which exclusively circuit ran; and they were not more inactive once SB levels were controlled for. These findings thus show that early environmental complexity can have lasting suppressive effects on SB, suggesting that early enrichment protocols could indeed provide a practicable, potentially more ethical model for investigating the causal mechanisms underpinning birth origin effects on SB. Furthermore, they add to a corpus of data for this species showing that more naturalistic early experiences, both social and physical, lastingly protect against SB development. These results also highlight how unpredictable and poorly understood early enrichment effects are (since in some species early enrichment exacerbates later SB); and moreover reveal that early environmental complexity is not the sole factor shaping behavioural phenotypes in WC animals, with differential social experience and human contact being other likely causes of developmental divergence.