Understanding the ecological and environmental contexts in which eusociality can evolve is fundamental to elucidating its evolutionary origins. A sufficiently long active season is postulated to have been a key factor facilitating the transition to eusociality. Many primitively eusocial species exhibit an annual life cycle, which is thought to preclude the expression of eusociality where the active season is too short to produce successive worker and reproductive broods. However, few studies have attempted to test this idea experimentally. We investigated environmental constraints on the expression of eusociality in the obligate primitively eusocial sweat bee Lasioglossum malachurum, by transplanting nest foundresses from the south to the far north of the United Kingdom, far beyond the natural range of L. malachurum. We show that transplanted bees can exhibit eusociality, but that the short length of the season and harsher environmental conditions could preclude its successful expression. In one year, when foundresses were transplanted only after provisioning first brood (B1) offspring, workers emerged in the north and provisioned a second brood (B2) of reproductives. In another year, when foundresses were transplanted prior to B1 being provisioned, they were just as likely to initiate nesting and provisioned just as many B1 cells as foundresses in the south. However, the life cycle was delayed by approximately 7 weeks and nests suffered 100% B1 mortality. Our results suggest that short season length together with poor weather conditions represent an environmental barrier to the evolution and expression of eusociality in sweat bees.

中文翻译：

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专性社会性汗蜂社会性的环境障碍

了解真社会性可以进化的生态和环境背景是阐明其进化起源的基础。据推测，一个足够长的活跃季节是促进向真社会性过渡的关键因素。许多原始的真社会性物种表现出一年一度的生命周期，这被认为排除了在活跃季节太短而无法产生连续的工人和繁殖后代的情况下真社会性的表现。然而，很少有研究试图通过实验来测试这个想法。我们通过将巢穴从英国南部移植到远超出 L. malachurum 的自然范围的远北地区，调查了对专性原始真社会性汗蜂 Lasioglossum malachurum 中真社会性表达的环境限制。我们表明，移植的蜜蜂可以表现出真社会性，但季节短和更恶劣的环境条件可能会妨碍其成功表达。一年后，当母鸡仅在提供第一代 (B1) 后代后才移植时，工蜂出现在北方并提供第二代 (B2) 繁殖后代。再过一年，当在供应 B1 之前移植女工时，它们开始筑巢的可能性与南方的女工一样多的 B1 细胞。然而，生命周期延迟了大约 7 周，巢穴的 B1 死亡率为 100%。我们的结果表明，短暂的季节长度和恶劣的天气条件是汗蜂进化和表达社会性的环境障碍。但季节的短暂和更恶劣的环境条件可能会妨碍它的成功表达。一年后，当母鸡仅在提供第一代 (B1) 后代后才移植时，工蜂出现在北方并提供第二代 (B2) 繁殖后代。再过一年，当在供应 B1 之前移植女工时，它们开始筑巢的可能性与南方的女工一样多的 B1 细胞。然而，生命周期延迟了大约 7 周，巢穴的 B1 死亡率为 100%。我们的结果表明，短暂的季节长度和恶劣的天气条件是汗蜂进化和表达社会性的环境障碍。但季节的短暂和更恶劣的环境条件可能会妨碍它的成功表达。一年后，当母鸡仅在提供第一代 (B1) 后代后才移植时，工蜂出现在北方并提供第二代 (B2) 繁殖后代。再过一年，当在供应 B1 之前移植女工时，它们开始筑巢的可能性与南方的女工一样多的 B1 细胞。然而，生命周期延迟了大约 7 周，巢穴的 B1 死亡率为 100%。我们的结果表明，短暂的季节长度和恶劣的天气条件是汗蜂进化和表达社会性的环境障碍。