Spatial sorting promotes rapid (mal)adaptation in the red-shouldered soapberry bug after hurricane-driven local extinctions

Field sampling soapberry bug populations Our study was conducted as a long-term natural experiment in a 1,200 km2 region in the Houston area that spanned the year prior to and the three years after the 2017 flooding event caused by Hurricane Harvey. In doing so, we monitored soapberry bug populations that inhabit three locally available host plant species, balloon vine (Cardiospermum halicacabum), western soapberry (Sapindus v. drummondii), and goldenrain tree (Koelreuteria elegans), (Fig. 2d-f). Our study included 15 sites (three C. halicacabum, three S. drummondii, and nine K. elegans; Extended Figure 1) sampled 72 times over the three-year period after the hurricane (September 2017 to September 2020). Sampling was performed on days without precipitation and was conducted between the hours of 10:00 and 15:00. Each site was sampled once every 14 days. Of the 15 monitored sites, nine sites flooded (three S. drummondii, six K. elegans, two C. halicacabum), while four sites did not flood and serve as our controls (three K. elegans and one C. halicacabum; Supplemental Table 1). Flooded sites in this study were inundated with standing water from 7 days to 90+ days. No S. drummondii sites were included in our control as this natural experiment relied on the serendipitous overlap of flood patterns with our previous history of insect sampling. Taking advantage of haphazard flooding also created discrepancies in host plant abundance, which varied between sampling site with Koelreuteria- and Sapindus-associated sites consisting of anywhere from one to seven trees and Cardiospermum-associated sites consisting of five to twenty herbaceous plants. For each sampling effort, insects were collected by hand over a period of 30 minutes from a 50 m2 region around the base of the host plant. Captured insects were temporarily stored in a plastic container lined with Insect-a-Slip (polytetrafluoroethylene coating, Bio Quip Products, Inc., Rancho Dominguez, CA). For each individual soapberry bug, insect beak-length was measured in the field using a digital caliper (Stainless Steel iGaging ABSOLUTE ORIGIN 0–6ʺ Digital LCD Electronic Caliper-IP54; iGaging, Los Angeles, Calif.), and wing morphology (macropterous = full flight wings; brachypterous = reduced wings) was visually assessed by the presence of developed corium of the distal membrane of the insect’s forewing (Fig. 2b). Captured insects were immediately returned to their habitat after morphological measurements to avoid artificial selection on any population. Given that some flooded sites were colonized earlier than others, we limited our data analysis to individuals collected in the first year (26 sampling periods) after colonization at flooded sites and after the hurricane at control sites to avoid overrepresentation of any one individual site. Field measurements of soapberry bug morphology The morphological measurements of the focal insect traits included beak length, wing-form, and insect forewing length. We measured beak length as the distance from the clypeus margin of the insect's lower sclerites to the most distal point of the labium. The categorical variable wing-form was determined to be either “brachypterous” or “macropterous” based on visual inspection. An individual was classified as brachypterous when the medio-cubital and apical folding fields of the hind wing were underdeveloped and a developed distal membrane on forewing was absent; an individual was classified to be “macropterous” if the medio-cubital and apical folding fields of the hindwing were fully developed and the distal membrane of the forewing was present (Fig. 2b,c). Forewing length was measured as the distance from the proximal margin of the scutellum to the distal edge of the forewing membrane. Individuals where trait measurements were obscured by damage were excluded.皂荚蝽（soapberry bug）种群野外采样研究。本研究以长期野外自然实验形式开展，实验区域覆盖休斯顿地区1200平方千米的范围，实验周期涵盖飓风哈维（Hurricane Harvey）引发2017年洪涝灾害的前一年，以及灾后的三年时间。研究期间，我们对栖息于当地三种常见寄主植物的皂荚蝽种群进行监测，三种寄主分别为：倒地铃（balloon vine，*Cardiospermum halicacabum*）、西部皂荚（western soapberry，*Sapindus v. drummondii*）与栾树（goldenrain tree，*Koelreuteria elegans*），详见图2d-f。本研究共设置15个采样点（其中3个为倒地铃寄主点、3个为西部皂荚寄主点、9个为栾树寄主点；扩展图1），在飓风灾后的三年周期（2017年9月至2020年9月）内共完成72次采样。采样均选择无降水日期，且时段限定为每日10:00至15:00，每个采样点每14天采样一次。在15个监测采样点中，9个采样点发生洪涝（含3个西部皂荚寄主点、6个栾树寄主点、2个倒地铃寄主点），剩余4个采样点未发生洪涝，作为本研究的对照组（3个栾树寄主点与1个倒地铃寄主点；补充表1）。本研究中洪涝采样点的积水时长为7天至90天以上。本研究未将西部皂荚寄主点纳入对照组，原因在于该野外自然实验依赖于洪涝发生模式与我们此前昆虫采样历史的偶然重合。由于洪涝的随机发生特性，各采样点的寄主植物丰度存在差异：栾树与西部皂荚寄主点的寄主树木数量为1至7株不等，倒地铃寄主点的草本寄主植物数量则为5至20株。每次采样时，研究人员均在寄主植物基部周围50平方米的区域内，以手捕方式采集昆虫，采集时长为30分钟。捕获的昆虫将被暂时存放于内衬有Insect-a-Slip（聚四氟乙烯涂层，Bio Quip Products, Inc.，加利福尼亚州兰乔多明格斯）的塑料容器中。针对每头皂荚蝽，研究人员在野外使用数显卡尺（不锈钢iGaging ABSOLUTE ORIGIN 0–6英寸数显电子卡尺-IP54；iGaging，洛杉矶，加利福尼亚州）测量其喙长，并通过观察昆虫前翅远端膜片的革片（corium）发育情况，对翅型进行目视评估：长翅型（macropterous，即拥有完整飞行翅）与短翅型（brachypterous，即翅部退化），详见图2b。完成形态学测量后，捕获的昆虫会被立即放回原生栖息地，以避免对任何种群造成人工选择压力。考虑到部分洪涝采样点的种群定殖时间早于其他位点，我们将数据分析限定为：洪涝位点在定殖后第一年（共26次采样）、以及对照组在飓风灾后第一年采集的个体，以避免单一采样点的数据被过度代表。 皂荚蝽形态学野外测量。本研究聚焦的昆虫形态学测量性状包括喙长、翅型与前翅长度。喙长的测量方式为：从昆虫下唇骨片的唇基（clypeus）边缘至下唇（labium）最远端的距离。翅型作为分类变量，通过目视观察划分为“短翅型”与“长翅型”两类。当昆虫后翅的中肘区与顶端折叠区发育不良，且前翅无发达的远端膜片时，将其归类为短翅型；若后翅中肘区与顶端折叠区发育完全，且前翅存在远端膜片，则将其归类为长翅型，详见图2b、c。前翅长度的测量方式为：从小盾片（scutellum）的近端边缘至前翅膜片远端边缘的距离。因虫体受损导致性状测量无法准确进行的个体将被排除在分析之外。