DISSERTATION RESEARCH: Molecular Systematics of Needlefishes: Interpreting Heterochrony and Biogeography

针鱼（针鱼科），因其长长的针状下颚而得名，是一种快速的掠食性鱼类，主要生活在热带海水中。在过去的一个世纪里，生物学家一直对针鱼一生中身体形状的惊人变化很感兴趣：幼鱼有一个长长的下颚，但后来发育成有长长的上下颚的成年鱼。奇怪的是，成年的近亲半嘴鱼（半嘴鱼科）有一个长长的下颚，但从未发育出长长的上颚，因此类似于幼年的针鱼。半喙可能起源于类似针鱼的祖先，反之亦然，这是由于上颚和下颚发育时间（异时性）的变化。几种针鱼栖息在南美洲的淡水河中。这些鱼可能是从大西洋、太平洋或两者都入侵的淡水——针鱼的生物地理模式也可能适用于该地区发现的其他生物。对这些发育和生物地理模式的解释依赖于对针鱼物种如何相互关联（物种谱系）的基本知识，而这方面的知识目前是不足的。在这项研究中，内森·洛夫乔伊将在艾米·麦库恩和理查德·哈里森的指导下，通过比较不同物种的DNA序列来研究针鱼之间的关系。大多数物种的标本都有；一次南美的收藏之旅将完成这个清单。利用聚合酶链反应从鱼组织样本中扩增线粒体和核基因，并利用这些基因的DNA序列构建系统发育树。由此产生的对针鱼生物学的见解将阐明热带水生物种非凡多样性的起源，以及这些物种之间产生巨大不同体型的机制。

9622827 McCUNE The needlefishes (family Belonidae), so-named because of their long needle-like jaws, are fast, predatory fishes found mainly in tropical marine waters. Over the past century, biologists have been intrigued by striking changes of body shape that needlefishes undergo during their life span: juveniles have a long lower jaw, but later develop into adults with long upper and lower jaws. Curiously, adults of the closely-related halfbeak fishes (family Hemiramphidae), have a long lower jaw but never develop the long upper jaw, and thus resemble juvenile needlefishes. Halfbeaks may have arisen from needlefish-like ancestors, or vice versa, through changes in developmental timing (heterochrony) of upper and lower jaw growth. Several needlefish species inhabit South American freshwater rivers. These fish may have invaded freshwater from the Atlantic Ocean, the Pacific Ocean, or both - and the biogeographic patterns among needlefish may also apply to other organisms found in this region. Interpretations of these developmental and biogeographic patterns depends on basic knowledge of how needlefish species are related to one another (a genealogy of species), and this knowledge currently is inadequate. In this study, Nathan Lovejoy, under the supervision of Amy McCune and Richard Harrison, will investigate the relationships of needlefishes by comparing DNA sequences from different species. Specimens of most species are available; a South American collecting trip will complete the list. Mitochondrial and nuclear genes will be amplified from fish tissue samples using the Polymerase Chain Reaction, and the DNA sequences of these genes will be used to construct phylogenetic trees. The resulting insights into needlefish biology will illuminate both the origins of the extraordinary diversity of aquatic species in the tropics, and the mechanisms producing dramatically different body-shapes among these species.