Long-term genetic monitoring of a riverine dragonfly, Orthetrum coerulescens (Odonata: Libellulidae]: Direct anthropogenic impact versus climate change effects

Modern conservationists call for long term genetic monitoring datasets to evaluate and understand the impact of human activities on natural ecosystems and species on a global but also local scale. However, long-term monitoring datasets are still rare but in high demand to correctly identify, evaluate and respond to environmental changes. In the presented study, a population of the riverine dragonfly, Orthetrum coerulescens (Odonata: Libellulidae), was monitored over a time period from 1989 to 2013. Study site was an artificial irrigation ditch in one of the last European stone steppes and “nature heritage”, the Crau in Southern France. This artificial riverine habitat has an unusual high diversity of odonate species, prominent indicators for evaluating freshwater habitats. A clearing of the canal and destruction of the bank vegetation in 1996 was assumed to have great negative impact on the odonate larval and adult populations. Two mitochondrial markers (CO1 & ND1) and a panel of nuclear microsatellite loci were used to assess the genetic diversity. Over time they revealed a dramatic decline in diversity parameters between the years 2004 and 2007, however not between 1996 and 1997. From 2007 onwards the population shows a stabilizing trend but has not reached the amount of genetic variation found at the beginning of this survey. This decline cannot be referred to the clearing of the canal or any other direct anthropogenic impact. Instead, it is most likely that the populations’ decay was due to by extreme weather conditions during the specific years. A severe drought was recorded for the summer months of these years, leading to reduced water levels in the canal causing also other water parameters to change, and therefore impacting temperature sensitive riverine habitat specialists like the O. coerulescens in a significant way. The data provide important insights into population genetic dynamics and metrics not always congruent with traditional monitoring data (e.g. abundance); a fact that should be regarded with caution when management plans for developed landscapes are designed.当代保护生物学者呼吁构建长期遗传监测数据集，以在全球及区域尺度上评估并解析人类活动对自然生态系统与物种的影响。然而，当前能够精准识别、评估并响应环境变化的长期监测数据集仍较为稀缺，但相关需求却极为迫切。本研究针对河栖蜻蜓物种蓝额疏脉蜻（Orthetrum coerulescens，蜻蜓目：蜻科）的种群开展了1989年至2013年的长期监测。监测样地位于法国南部的克劳区域，该区域是欧洲仅剩的石质草原与"自然遗产"地之一，样地为一处人工灌溉渠。该人工河溪生境拥有异常丰富的蜻蜓目物种多样性，而蜻蜓类群是评估淡水生境质量的核心指示类群。1996年该渠道的清淤作业与岸带植被破坏曾被认为会对蜻蜓的幼虫与成虫种群造成严重负面影响。研究采用2种线粒体分子标记（CO1与ND1）以及一组核微卫星位点对种群遗传多样性进行评估。监测结果显示，遗传多样性参数在2004年至2007年间出现显著下降，但1996年至1997年间并未出现类似变化。2007年之后，该种群的遗传多样性呈现稳定趋势，但仍未恢复至本研究初始阶段的遗传变异水平。此次多样性下降并非由1996年的渠道清淤作业或其他直接人为活动所致，相反，该种群的衰退极有可能是由特定年份的极端天气事件引发的。上述年份夏季曾记录到严重干旱，导致渠道水位下降及其他水环境参数改变，进而对依赖河溪生境、对温度敏感的蓝额疏脉蜻种群造成了显著影响。本数据集为种群遗传动态与相关指标的研究提供了重要参考——这些遗传指标往往与传统监测数据（如种群丰度）并不一致，因此在制定开发型景观的管理规划时，需审慎考量这一特性。