Data used in Manuscript from Carrying eggs uphill: are costs of reproduction stronger on steeper slopes?

Locomotor impairment during pregnancy is a well-documented cost of reproduction, but most empirical studies have not incorporated ecological complexity, such as locomotion on sloping inclines rather than horizontal surfaces. Biomechanical factors suggest that carrying a heavy burden—including shifts in the body's centre of mass—may impair locomotor ability even more when an animal is running uphill. If so, then measuring costs of reproduction on horizontal racetracks may underestimate these costs in nature for arboreal species. To evaluate this prediction, we measured the pregnancy-induced reduction in speed for jacky dragons (<i>Amphibolurus muricatus</i>) at inclines ranging from 0 to 45°. Both pregnancy and steeper slopes reduced lizard performance, but pregnancy did not exacerbate the locomotor decrement on steeper racetracks. An ability to maintain mobility on steep slopes during pregnancy may be a target of selection in arboreal taxa. To understand the evolutionary context of locomotion-based costs of reproduction, we also need studies on the relationship between organismal performance and ecologically relevant measures such as predation risk.

妊娠期间的运动机能损伤是繁殖过程中已有充分文献记录的繁殖代价，但多数实证研究未纳入生态复杂性因素，例如动物在倾斜坡面而非水平表面的运动模式。生物力学研究表明，当动物上坡奔跑时，背负较重负荷（包括身体重心偏移）可能会进一步削弱其运动能力。若此推论成立，那么在水平实验跑道上测量繁殖代价，可能会低估自然环境中树栖物种所承受的此类代价。为验证该预测，我们对杰克龙蜥（Amphibolurus muricatus）在坡度0°至45°条件下的妊娠诱导速度下降情况进行了测量。妊娠与更陡峭的坡面均会降低蜥蜴的运动表现，但妊娠并未在坡度更陡的实验跑道上加剧运动机能的下降。妊娠期间仍能在陡峭坡面上维持运动能力的特性，可能是树栖类群自然选择的作用靶点。为阐明基于运动能力的繁殖代价的演化背景，我们还需要开展关于个体运动表现与生态相关指标（如捕食风险）之间关联的研究。