Odum School of Ecology, University of Georgia, Athens, GA 30602, USA.
Biol Lett. 2020 Apr;16(4):20190922. doi: 10.1098/rsbl.2019.0922. Epub 2020 Apr 8.
For many animals and insects that are experiencing dramatic population declines, the only recourse for conservationists is captive rearing. To ensure success, reared individuals should be biologically indistinct from those in the wild. We tested if this is true with monarch butterflies, , which are increasingly being reared for release by citizens and commercial breeders. Since late-summer monarchs should be as migration capable as possible for surviving the arduous long-distance migration, we evaluated four migration-relevant traits across two groups of captive-reared monarchs ( = 41 and 42) and one group of wild-caught migrants ( = 41). Monarchs (descendants of wild individuals) were reared from eggs to adulthood either in a warm indoor room next to a window, or in an incubator that mimicked late-summer conditions. Using an apparatus consisting of a perch mounted to an electronic force gauge, we assessed 'grip strength' of all groups, then used image analysis to measure forewing size, pigmentation and elongation. In three of the four traits, reared monarchs underperformed compared to wild ones, even those reared under conditions that should have produced migration-ready individuals. The average strength of reared monarchs combined was 56% less than the wild group, even when accounting for size. Their orange wing colour was paler (an indicator of poor condition and flight ability) and their forewings were less elongated (elongation is associated with migration propensity) than wild monarchs. The reason(s) behind these effects is unknown but could stem from the frequent disturbance and/or handling of reared monarchs, or the fact that rearing removes the element of natural selection from all stages. Regardless, these results explain prior tagging studies that showed reared monarchs have lower migratory success compared to wild.
对于许多正经历数量急剧下降的动物和昆虫来说，保护主义者唯一的办法就是圈养繁殖。为了确保成功，圈养个体应该在生物学上与野外个体没有区别。我们用黑脉金斑蝶（ monarch butterflies ）检验了这是否属实，黑脉金斑蝶越来越多地被公民和商业饲养者饲养以供放生。由于夏末的黑脉金斑蝶应该具备尽可能强的迁徙能力，以便在艰苦的长途迁徙中幸存下来，我们评估了两组圈养黑脉金斑蝶（每组 41 只和 42 只）和一组野外捕捉的迁徙黑脉金斑蝶（每组 41 只）的四个与迁徙相关的特征。黑脉金斑蝶（由野外个体的后代饲养）要么在靠近窗户的温暖室内房间里从卵中饲养到成年，要么在模仿夏末条件的孵化器中饲养。我们使用一个由安装在电子力计上的栖木组成的装置，评估了所有组的“握力”，然后使用图像分析来测量前翅的大小、色素沉着和伸长率。在四个特征中的三个中，圈养黑脉金斑蝶的表现不如野生黑脉金斑蝶，即使是在那些应该培养出适合迁徙的个体的条件下饲养的黑脉金斑蝶也是如此。即使考虑到体型大小，圈养黑脉金斑蝶的平均强度也比野生黑脉金斑蝶低 56%。它们橙色的翅膀颜色更浅（表明身体状况不佳和飞行能力差），前翅也较短（翅膀的伸长与迁徙倾向有关），与野生黑脉金斑蝶相比。这些影响的原因尚不清楚，但可能源于圈养黑脉金斑蝶经常受到干扰和/或处理，或者圈养过程从所有阶段都去除了自然选择的因素。无论如何，这些结果解释了之前的标记研究，即圈养黑脉金斑蝶的迁徙成功率比野生黑脉金斑蝶低。
