Am Nat. 2019 Apr;193(4):560-574. doi: 10.1086/701826. Epub 2019 Feb 18.
Organisms must often make developmental decisions without complete information about future conditions. This uncertainty-for example, about the duration of conditions favorable for growth-can favor bet-hedging strategies. Here, we investigated the causes of life cycle variation in Osmia iridis, a bee exhibiting a possible bet-hedging strategy with co-occurring 1- and 2-year life cycles. One-year bees reach adulthood quickly but die if they fail to complete pupation before winter; 2-year bees adopt a low-risk, low-reward strategy of postponing pupation until the second summer. We reared larval bees in incubators in various experimental conditions and found that warmer-but not longer-summers and early birthdates increased the frequency of 1-year life cycles. Using in situ temperature measurements and developmental trajectories of laboratory- and field-reared bees, we estimated degree-days required to reach adulthood in a single year. Local long-term (1950-2015) climate records reveal that this heat requirement is met in only ∼7% of summers, suggesting that the observed distribution of life cycles is adaptive. Warming summers will likely decrease average generation times in these populations. Nevertheless, survival of bees attempting 1-year life cycles-particularly those developing from late-laid eggs-will be <100%; consequently, we expect the life cycle polymorphism to persist.
生物在做出发育决策时，往往无法完全了解未来的环境条件。这种不确定性——例如，关于有利于生长的条件持续时间的不确定性——有利于风险分散策略。在这里，我们研究了同时存在 1 年和 2 年生命周期的蜜蜂 Osmia iridis 生命周期变化的原因。1 年生的蜜蜂很快就能成年，但如果它们在冬季前不能完成蛹化，就会死亡；2 年生的蜜蜂则采取一种低风险、低回报的策略，将蛹化推迟到第二个夏天。我们在不同的实验条件下在孵化器中饲养幼虫蜜蜂，发现温暖但不是更长的夏季和更早的出生日期增加了 1 年生命周期的频率。使用原位温度测量和实验室和野外饲养的蜜蜂的发育轨迹，我们估计了在一年内达到成年所需的天数。当地长期（1950-2015 年）气候记录显示，这种热量需求仅在约 7%的夏季得到满足，这表明观察到的生命周期分布是适应性的。夏季变暖可能会降低这些种群的平均世代时间。然而，试图进行 1 年生命周期的蜜蜂的存活率——特别是那些从后期产卵中发育的蜜蜂——将<100%；因此，我们预计生命周期多态性将持续存在。
