Data from: Phenological, but not social, variation associated with climate differences in a eusocial sweat bee, Halictus ligatus, nesting in southern Ontario

Studies of annual and geographic variation in eusocial bee populations suggest that more stringent environmental conditions result in stronger reproductive skew favouring queens, while moderate conditions favour increasing worker reproduction. To test these predictions, we compared the phenology and colony development of H. ligatus nesting in St. Catharines, Ontario, Canada to a previously studied aggregation 90 km north of St. Catharines, in Victoria, Ontario. Despite the close proximity of these two locations, St. Catharines has markedly shorter winters and longer summers. Comparisons between St. Catharines in 2006 and Victoria in the 1980s and 1990s incorporate both geographic differences in climate and temporal differences due to climate change. We predicted that St. Catharines foundress queens should emerge from hibernation and initiate nests earlier in spring, giving them time to produce more workers. Since earlier studies indicated that queens have difficulty suppressing worker reproduction in larger colonies, we also predicted higher rates of worker ovarian development in St. Catharines. In spring and summer 2006, we excavated 65 H. ligatus nests, comparing their contents to 713 specimens collected in pan traps. As predicted, nests were initiated about a month earlier in St. Catharines than in Victoria, but contrary to prediction, fewer workers were produced in St. Catharines. St. Catharines workers were just as likely to have developed ovaries as Victoria workers. About 40% of St. Catharines workers were classified as reproductive, and larger reproductive workers tended to have higher ovarian scores. Early queen mortality in the longer nest cycle of St. Catharines bees may have enhanced opportunities for worker reproduction despite their smaller numbers. Novel features of H. ligatus sociobiology in St. Catharines included evidence that queens can initiate new nests following the loss of their first brood, overlap between worker and gyne production within some nests, and high rates of independent nest founding by worker-sized females, suggesting that many worker-brood females overwinter. Overall, the distinctly warmer climate of St. Catharines compared to Victoria led to earlier nest initiation and lengthening of the flight season, but not to the predicted differences in colony social organisation or queen-worker reproductive skew. A second objective of our study was to assess how well pan trap collections capture important information about demographic and social parameters important in assessing social variability in sweat bees. Nest excavations and pan traps produced similar results, suggesting that pan traps are a good alternative when nest excavations are impossible.针对真社会性蜜蜂（eusocial bee）种群的年度与地理变异研究显示，环境条件越严苛，繁殖偏倚（reproductive skew）程度越高，更有利于蜂后；而环境条件适中时，则会促进工蜂的繁殖行为。为验证上述预测，我们对比了加拿大安大略省圣凯瑟琳斯（St. Catharines）筑巢的H. ligatus蜂群，与位于圣凯瑟琳斯以北90公里处、此前已被研究的安大略省维多利亚（Victoria）种群的物候特征与蜂群发育情况。尽管两地地理位置邻近，但圣凯瑟琳斯的冬季显著更短、夏季更长。本次研究对比了2006年圣凯瑟琳斯的种群与1980至1990年代维多利亚的种群，既纳入了气候的地理差异，也涵盖了因气候变化产生的时间维度差异。我们预测，圣凯瑟琳斯的建巢蜂后（foundress queen）会更早结束冬眠、于春季启动筑巢，从而获得更长时间培育更多工蜂。既往研究表明，蜂后难以在大型蜂群中抑制工蜂的繁殖活动，因此我们同时预测，圣凯瑟琳斯种群的工蜂卵巢发育比例会更高。2006年春夏季，我们共挖掘了65个H. ligatus蜂群的巢穴，并将其巢内内容与713份通过色盘诱捕器（pan trap）采集的标本进行对比。正如预测，圣凯瑟琳斯的筑巢启动时间比维多利亚早约1个月，但与预期相悖的是，其培育的工蜂数量更少。圣凯瑟琳斯的工蜂卵巢发育概率与维多利亚种群并无显著差异：约40%的圣凯瑟琳斯工蜂被归类为具有繁殖能力，且体型更大的繁殖型工蜂往往拥有更高的卵巢发育评分。圣凯瑟琳斯种群更长的巢周期中出现的蜂后早期死亡现象，或许为工蜂繁殖提供了更多机会，即便其工蜂总数较少。圣凯瑟琳斯种群中H. ligatus的社会生物学新特征包括：蜂后可在首批幼蜂群（brood）损失后重新启动筑巢；部分巢穴中存在工蜂与处女蜂王（gyne）培育的重叠期；以及工蜂体型的雌性个体独立筑巢的比例极高，这表明大量工蜂后代的雌性个体可顺利越冬。总体而言，相较于维多利亚种群，圣凯瑟琳斯明显更温暖的气候使得筑巢启动时间更早、成虫飞行季延长，但并未出现预测中的蜂群社会组织或蜂后-工蜂繁殖偏倚差异。本研究的第二项目标是评估色盘诱捕器（pan trap）采集能否有效获取评估汗蜂（sweat bee）社会变异性所需的关键种群参数与社会参数。挖掘巢穴与色盘诱捕器采集得到了相似的结果，这表明当无法开展巢穴挖掘时，色盘诱捕器是一种可靠的替代采样方法。