DISSERTATION RESEARCH: The Evolution of Diapause in Aplocheiloid Killifishes (Cyprinodontiformes)

滞育，定义为胚胎发育的可逆延迟，通常由不利条件引起。虽然在昆虫和其他在恶劣气候中越冬的无脊椎动物中很常见，但在脊椎动物中很少见。脊椎动物中最特殊的滞育形式之一发生在一年生的鳉鱼身上，它们在季节性干燥的短暂水体中完成生命周期。刀鱼是世界各地受欢迎的宠物鱼，启发了许多国家的水族馆组织，如美国刀鱼协会。水族学家早就知道，鳉鱼可以停止细胞生长，延缓发育，降低新陈代谢率。这使它们成为研究癌症、胚胎储存和动物发育的极好模式生物，但滞育的分子遗传基础和进化尚未得到研究。研究人员将参加水族馆会议，分享有关这些鱼类对科学研究的重要性的信息，突出这个项目的问题，方法和结果。许多一年生鳉鱼在野外濒临灭绝或灭绝，因为它们出现在孤立的池塘中，由于气候变化，地理范围和频率可能会发生变化，因此在生物多样性丧失之前研究这些鱼类非常重要。当它们短暂的池塘栖息地干涸时，它们会出现独特的滞育现象。所有的成虫都死了，留下了埋在土壤里的卵。发育中的胚胎通过进入独特的滞育阶段存活到下一个雨季，如果不利的条件持续存在，卵可能在土壤中保持这种休眠状态超过一年。系统发育研究表明，这种对极端环境的适应，可能已经进化了至少六次在鳉鱼。本研究的最终目的是了解鳉鱼滞育的遗传基础，并着重于其进化起源。将查明与滞育有关的基因，并将利用数学模型确定和分析这些滞育基因的DNA序列，这些数学模型估计自然选择在分子水平上发挥作用的强度。这些数据将表明这些鱼类滞育的进化祖先，这些鱼类的特征是如何进化的，并可能多次重新进化。该项目将使用比较转录组学来识别，测序和表征与胚胎滞育相关的候选基因。滞育相关基因的分子进化将模拟一年生和非一年生鱼类的发育，以测试滞育的进化起源的假设，并连接系统发育模式与支持这种复杂的生活史特征的进化的结构和调控基因的适应性遗传变化的签名。

Diapause, defined as a reversible delay in embryonic development, is often brought on by unfavorable conditions. While common among insects and other invertebrate animals that overwinter in harsh climates, it is rare in vertebrates. One of the most exceptional forms of diapause among vertebrate animals occurs in annual killifishes that complete their life cycle in ephemeral bodies of water subject to seasonal desiccation. Killifish are popular pet fishes around the world that have inspired aquarium organizations such as the American Killifish Association in many countries. Aquarists have long known that killifish can stop cellular growth, delay development, and lower their metabolic rate. This makes them excellent model organisms for studying cancer, storage of embryos, and development in animals, yet the molecular genetic basis and evolution of diapause has not yet been examined. The researchers will participate in Aquarists conventions, sharing information about the importance of these fish for scientific research, highlighting the questions, methods and results of this project. Many annual killifishes are endangered or extinct in the wild and because they occur in isolated pools, which will likely change in geographic range and frequency as a result of climate change, making it important to study these fishes before their biodiversity is lost. The unique diapause of killifish occurs when their ephemeral pool habitat dries up. All the adults die, leaving their eggs behind, buried in the soil. Developing embryos survive until the following wet season by entering unique diapause stages, and the eggs may remain in this dormant state in the soil for over a year if unfavorable conditions persist. Phylogenetic studies suggest that this adaptation to extreme environments;may have evolved at least six times among killifishes. The ultimate goal of this project is to understand the genetic basis of diapause among killifishes focusing on its evolutionary origin. Genes associated with diapause will be identified and the DNA sequence of these diapause genes will be determined and analyzed using mathematical models that estimate the strength of natural selection acting at the molecular level. These data will indicate the evolutionary ancestry of diapause in these fish, how the trait evolved and possibly re-evolved multiple times in these fishes. The project will use comparative transcriptomics to identify, sequence, and characterize candidate genes associated with embryonic diapause. Molecular evolution of diapause-associated genes will be modeled on a phylogeny of annual and non-annual fishes to test hypotheses of the evolutionary origin of diapause and to connect the phylogenetic pattern with signatures of adaptive genetic changes in structural and regulatory genes underpinning the evolution of this complex life history trait.