Youtz Joseph, Miller Kelly D, Bowers Emerson K, Rogers Samantha L, Bulluck Lesley P, Johnson Matthew, Peer Brian D, Percy Katie L, Johnson Erik I, Ames Elizabeth M, Tonra Christopher M, Boves Than J
Department of Biological Sciences Arkansas State University State University Arkansas USA.
Department of Biological Sciences and Center for Biodiversity Research University of Memphis Memphis Tennessee USA.
Ecol Evol. 2020 Sep 1;10(19):10672-10686. doi: 10.1002/ece3.6721. eCollection 2020 Oct.
Bergmann's rule is a well-established, ecogeographical principle that states that body size varies positively with latitude, reflecting the thermoregulatory benefits of larger bodies as temperatures decline. However, this principle does not seem to easily apply to migratory species that are able to avoid the extreme temperatures during winter at higher latitudes. Further, little is known about the ontogeny of this relationship across life stages or how it is influenced by ongoing global climate change. To address these knowledge gaps, we assessed the contemporary relationship between latitude and body size in a long-distance migratory species, the prothonotary warbler (Protonotaria citrea) across life stages (egg to adult) on their breeding grounds. We also measured historic eggs (1865-1961) to assess if the relationship between latitude and size during this life stage has changed over time. In accordance with Bergmann's rule, we found a positive relationship between latitude and body mass during all post-embryonic life stages, from early nestling stage through adulthood. We observed this same predicted pattern with historic eggs, but contemporary eggs exhibited the reverse (negative) relationship. We suggest that these results indicate a genetic component to this pattern and speculate that selection for larger body size in altricial nestlings as latitude increases may possibly drive the pattern in migratory species as even rare extreme cold weather events may cause mortality during early life stages. Furthermore, the opposite relationships observed in eggs, dependent on time period, may be related to the rapidly warming environments of higher latitudes that is associated with climate change. Although it is unclear what mechanism(s) would allow for this recent reversal in eggs (but still allow for its maintenance in later life stages). This evidence of a reversal suggests that anthropogenic climate change may be in the process of altering one of the longest-standing principles in ecology.
伯格曼法则是一项已被充分确立的生态地理原则，该原则指出，身体大小与纬度呈正相关，这反映出随着气温下降，较大体型在体温调节方面的优势。然而，这一原则似乎并不容易适用于那些能够在冬季避开高纬度地区极端温度的迁徙物种。此外，对于这种关系在不同生命阶段的个体发育过程，或者它如何受到当前全球气候变化的影响，我们知之甚少。为了填补这些知识空白，我们评估了一种长距离迁徙物种——橙胸林莺（Protonotaria citrea）在其繁殖地从卵到成鸟的各个生命阶段中，纬度与身体大小之间的当代关系。我们还测量了历史上的卵（1865年至1961年），以评估在这个生命阶段，纬度与体型之间 的关系是否随时间发生了变化。根据伯格曼法则，我们发现从雏鸟早期到成年的所有胚胎后生命阶段中，纬度与体重之间存在正相关关系。我们在历史上的卵中也观察到了同样的预测模式，但当代的卵呈现出相反的（负）关系。我们认为，这些结果表明这种模式存在遗传成分，并推测随着纬度增加，对晚成雏较大体型的选择可能会推动迁徙物种呈现这种模式，因为即使是罕见的极端寒冷天气事件也可能在生命早期阶段导致死亡。此外，根据时间段不同，在卵中观察到的相反关系可能与高纬度地区与气候变化相关的快速变暖环境有关。尽管尚不清楚是什么机制导致了卵中这种近期的逆转（但仍使其在后期生命阶段得以维持）。这种逆转的证据表明，人为气候变化可能正在改变生态学中最长期存在的原则之一。
