Data from: Crop domestication facilitated rapid geographic expansion of a specialist pollinator, the squash bee Peponapis pruinosa

Squash was first domesticated in Mexico and is now found throughout North America along with Peponapis pruinosa, a pollen specialist bee species of the squash genus Cucurbita. The origin and spread of squash cultivation is well-studied archeologically and phylogenetically; however, no study has documented how cultivation of this or any other crop has influenced species in mutualistic interactions. We used molecular markers to reconstruct the demographic range expansion and colonization routes of P. pruinosa from its native range into temperate North America. Populations east of the Rocky Mountains expanded from the wild host plant’s range in Mexico and were established by a series of founder events. Eastern North America was most likely colonized from squash bee populations in present-day continental Midwest US and not from routes that followed the Gulf and Atlantic coasts from Mexico. Populations of P. pruinosa west of the Rockies spread north from the warm deserts much more recently, showing two genetically differentiated populations with no admixture: one in California and the other one in eastern Great Basin. These bees have repeatedly endured severe bottlenecks as they colonized North America, following human spread of their Cucurbita pollen hosts during the Holocene.

南瓜属作物最早于墨西哥被驯化，如今与南瓜蜂（Peponapis pruinosa）——一种南瓜属（Cucurbita）花粉专性传粉蜂类——一同分布于整个北美地区。南瓜栽培的起源与传播路径已在考古学（archaeology）与系统发育学（phylogenetics）层面得到充分研究，但尚无研究阐明该作物或其他作物的种植如何影响其所在互惠共生互作中的物种。本研究利用分子标记（molecular markers）重建了P. pruinosa从原生分布区向温带北美扩张的种群分布范围动态与定殖路线。落基山脉以东的种群源自墨西哥境内的野生寄主植物分布区，并通过一系列奠基者事件（founder events）形成。北美东部的种群最有可能源自现今美国大陆中西部的南瓜蜂种群，而非沿墨西哥湾与大西洋沿岸从墨西哥出发的定殖路径。落基山脉以西的P. pruinosa种群则是较晚近地从暖荒漠向北扩散，形成两个遗传分化且无基因交流的种群：一个分布于加利福尼亚地区，另一个分布于大盆地东部。在全新世（Holocene）期间，随着人类将其南瓜属花粉寄主的分布范围扩散，这些蜂类在定殖北美过程中反复经历了严重的种群瓶颈效应（population bottlenecks）。