Data from: Invasion and high-elevation acclimation of the red imported fire ant, Solenopsis invicta, in the southern Blue Ridge escarpment region

The red imported fire ant (Solenopsis invicta) is a non-native invasive species that rapidly spread northward in the United States after its introduction from South America to the southern coast in the 1930s. Researchers predicted that the northward spread of this invasive ant would be limited by minimum temperatures with increased latitude and elevation in the Southern Appalachian Mountains. The presence of S. invicta at relatively high elevations north of their projected limits suggests greater cold tolerance than previously predicted; however, these populations might be ephemeral indications of strong dispersal abilities. In this study we investigated potential physiological and behavioral adaptations of S. invicta that would indicate acclimation to high elevation environments. We hypothesized that if S. invicta colonies can persist in colder climates than where they originated, we would find gradients in S. invicta worker cold tolerance along a montane elevational gradient. We also predicted that higher elevation S. invicta ants might require greater physiological costs to persist in the colder climate, so we measured colony lipid content to assess health status. Finally, we predicted that the ants might compensate for colder climates by adjusting microscale colony locations (e.g., nearer to radiant heat masses). For comparison, we also collected physiological temperature tolerance data for the co-occurring dominant native woodland ant Aphaenogaster picea. We found that S. invicta occurring at higher elevations exhibited greater physiological tolerance for cold temperatures as compared to lower-elevation conspecifics – a cold tolerance pattern that paralleled of the native A. picea ants along the same gradient. Whereas S. invicta had a higher tolerance for heat compared to A. picea, both exhibited a similar downward shift in thermal tolerances when moving up the elevational gradient. There was no change in S. invicta colony lipid content with elevation, suggesting that greater metabolic rates were not needed to sustain these ants through high-elevation winter dormancy. In addition, S. invicta ants at high elevations did not appear to offset the colder high-elevation temperatures by selecting nest sites proximate to thermal masses.

红火蚁（Solenopsis invicta）为非本土入侵物种，于1930年代从南美洲引入美国南部沿海后，迅速向北扩散。研究人员曾预测，在阿巴拉契亚山脉南部，该入侵蚁的向北扩散会随纬度与海拔升高而受到低温限制。在预测分布范围以北的较高海拔区域发现红火蚁，说明其耐寒性较此前预测更强；不过这些种群或仅为其强大扩散能力的短暂显现。本研究针对红火蚁适应高海拔环境的潜在生理与行为适应性展开调查。我们提出假说：若红火蚁群落能够在较其原生栖息地更寒冷的气候中存续，则沿山地海拔梯度，工蚁的耐寒性应呈现梯度变化。我们同时预测，高海拔红火蚁为在寒冷气候中存续，可能需要付出更高的生理代价，因此我们通过检测群落脂质含量来评估其健康状态。最后，我们推测红火蚁可能通过调整巢穴的微尺度位置（例如更靠近辐射热源）来弥补低温环境带来的不利影响。为便于对照，我们同时采集了同域分布的本土优势林地蚁（Aphaenogaster picea）的生理温度耐受性数据。研究结果显示，相较于低海拔的同种个体，高海拔红火蚁的低温生理耐受性更强——这一耐寒性梯度模式与同梯度下本土A. picea的模式一致。尽管红火蚁的耐热性强于A. picea，但随着海拔升高，二者的热耐受性均呈现相似的下降趋势。红火蚁群落的脂质含量未随海拔发生变化，说明这些蚂蚁无需通过提升代谢率来度过高海拔地区的冬季休眠期。此外，高海拔红火蚁并未通过选择靠近热源的巢穴来抵消高海拔的低温环境影响。