Kareklas Kyriacos, Kunc Hansjoerg P, Arnott Gareth
Integrative Behavioural Biology Group, Instituto Gulbenkian de Ciência, Rua da Quinta Grande 6, 2780-156, Oeiras, Portugal.
School of Biological Sciences, Queen's University Belfast, 19 Chlorine Gardens, Belfast, BT9 5DL, Northern Ireland, UK.
Front Zool. 2021 Mar 20;18(1):12. doi: 10.1186/s12983-021-00397-x.
Competition is considered to rely on the value attributed to resources by animals, but the influence of extrinsic stressors on this value remains unexplored. Although natural or anthropogenic environmental stress often drives decreased competition, assumptions that this relies on resource devaluation are without formal evidence. According to theory, physiological or perceptual effects may influence contest behaviour directly, but motivational changes due to resource value are expected to manifest as behavioural adjustments only in interaction with attainment costs and resource benefits. Thus, we hypothesise that stressor-induced resource devaluations will impose greater effects when attainment costs are high, but not when resource benefits are higher. Noise may elicit such effects because it impacts the acoustic environment and imposes physiological and behavioural costs to animals. Therefore, we manipulated the acoustic environment using playbacks of artificial noise to test our hypotheses in the territorial male Siamese fighting fish, Betta splendens.
Compared to a no-playback control, noise reduced defense motivation only when territory owners faced comparatively bigger opponents that impose greater injury costs, but not when territories also contained bubble nests that offer reproductive benefits. In turn, nest-size decreases were noted only after contests under noise treatment, but temporal nest-size changes relied on cross-contest variation in noise and comparative opponent size. Thus, the combined effects of noise are conditional on added attainment costs and offset by exceeding resource benefits.
Our findings provide support for the hypothesised modulation of resource value under extrinsic stress and suggest implications for competition under increasing anthropogenic activity.
竞争被认为依赖于动物赋予资源的价值，但外在压力源对这种价值的影响仍未得到探索。尽管自然或人为环境压力通常会导致竞争减少，但认为这依赖于资源贬值的假设却缺乏正式证据。根据理论，生理或感知效应可能直接影响竞争行为，但由于资源价值导致的动机变化预计仅在与获取成本和资源收益相互作用时才表现为行为调整。因此，我们假设当获取成本高时，压力源引起的资源贬值会产生更大影响，但当资源收益更高时则不会。噪音可能会引发此类效应，因为它会影响声学环境并给动物带来生理和行为成本。因此，我们使用人工噪音回放来操纵声学环境，以在领地性雄性暹罗斗鱼（Betta splendens）中检验我们的假设。
与无回放对照组相比，只有当领地所有者面对体型相对较大、会带来更大伤害成本的对手时，噪音才会降低防御动机，而当领地中也有提供繁殖益处的泡泡巢时则不会。反过来，只有在噪音处理下的争斗之后才注意到巢大小的减小，但巢大小的时间变化依赖于噪音和相对对手大小的跨争斗变化。因此，噪音的综合影响取决于额外的获取成本，并会被超过资源收益所抵消。
我们的研究结果为外在压力下资源价值的假设调节提供了支持，并暗示了在人为活动增加情况下竞争的影响。
