Elevation-related differences in the age structure of breeding birds suggest stronger selection at harsher elevations
Elevation-related differences in the age structure of breeding birds suggest stronger selection at harsher elevations
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DOI：
10.1007/s00265-019-2750-4
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发表时间：
2019-10-01
影响因子：
2.3
通讯作者：
Pravosudov, Vladimir V.
中科院分区：
文献类型：
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作者：
Branch, Carrie L.;Pitera, Angela M.;Pravosudov, Vladimir V.
环境变化如何影响选择的强度对于理解种群内的表型变异是很重要的。评价选择压力差异的一种间接方法是比较一个繁殖种群的年龄构成。较高的成虫/第一年繁殖比率，由于较高的幼虫死亡率，可能表明更强的选择。研究了不同海拔山地食藏山雀的成虫/第一年繁殖率。与低海拔地区的山雀相比，高海拔地区的山雀经历了更严酷的冬季条件，储存了更多的食物，并且具有更好的空间认知能力来恢复储存的食物。空间认知能力和贮藏空间恢复能力对越冬生存至关重要，空间认知能力越强的个体越容易存活；因此，这些差异可能是高海拔地区空间认知和缓存行为的选择压力更大的结果。为了支持这一假设，我们发现高海拔地区的成虫/第一年繁殖比明显高于低海拔地区。这可能表明，在高海拔地区，越冬幼鱼的死亡率更高，因此生存相关性状的选择压力更大，这与海拔相关的表型差异一致。在不同的异质环境中，生存相关性状的选择强度是不同的。评估选择强度的一种方法是测量能够在特定选择事件中生存下来的个体的特征。在这里，我们评估了经历不同严酷冬季气候的留鸟、食物贮藏鸟的成虫/第一年繁殖比率。这些鸟依靠空间认知来获取食物并度过冬天；年度最大的评选活动。在个体水平上，认知能力越强的个体越冬存活率越高。然而，在种群水平上，尚不清楚严酷和温和冬季气候的选择强度是否有所不同。通过对繁殖者年龄的评估，我们发现，与生活在温和的低海拔地区的鸟类相比，生活在恶劣的高海拔地区的鸟类的成虫/第一年繁殖率显著高于生活在温和的低海拔地区的鸟类。这表明，在高海拔地区，越冬幼鱼的死亡率更高，因此生存相关性状的选择压力更大。
How environmental variation affects the strength of selection is important for understanding phenotypic variation within a population. An indirect method to evaluate differences in selection pressures is to compare the age composition of a breeding population. A larger adult/first-year breeding ratio, due to higher juvenile mortality, may indicate stronger selection. We investigated the adult/first-year breeding ratios of food-caching mountain chickadees inhabiting different elevations. Chickadees at high elevations experience harsher winter conditions and cache more food items and have better spatial cognition to recover caches compared with their low-elevation counterparts. Cache recovery and spatial cognition are critical for overwinter survival and individuals with better spatial cognitive abilities are more likely to survive their first winter; therefore, these differences are likely a result of stronger selection pressures on spatial cognition and caching behavior at higher elevations. In support of this hypothesis, we found a significantly larger adult/first-year breeding ratio at high elevations compared with low elevations. This may suggest higher overwinter juvenile mortality and hence stronger selection pressures on survival-related traits at high elevations, consistent with elevation-related phenotypic differences.Significance statementThe strength of selection on survival-related traits varies across heterogenous environments. One way to assess the strength of selection is to measure the traits of individuals that are able to survive a particular selection event. Here we assessed the adult/first-year breeding ratios of resident, food-caching birds experiencing differentially harsh winter climates. These birds rely on spatial cognition to retrieve food caches and survive the winter; the largest annual selection event. At the individual level, those with better cognitive ability have demonstrated higher overwinter survival. However, at the population level, it remains unclear whether or not the strength of selection differs between harsh and mild winter climates. By assessing the age of breeders, we found a significantly larger adult/first-year breeding ratio in birds inhabiting harsher, high elevations compared with milder, low elevations. This suggests higher overwinter juvenile mortality and hence stronger selection pressures on survival-related traits at high elevations.