Systematic Studies on the Lanternfishes (Myctophiformes)

Autor:	John Ta-Ming Wamg, 王大明
Rok vydání:	2001
Druh dokumentu:	學位論文 ; thesis
Popis:	90 Lanternfishes which include the Myctophidae and Neoscopelidae are ubiquitous and speciose, with approximately 250 species in 36 genera. Until 1996, only 17 species in 6 genera had been recorded in the waters around Taiwan. This study aims to better elucidate the distribution of lanternfish around Taiwan and the Tungsha Islands, and to resolve the phylogenetic relationships of the genera in their 2 families. The area sampled for lanternfishes lies between 19°N and 25°N and 114°E and 123°E; lanternfish specimens were collected during 9 cruises from 1991 to 1997. They comprised 53 species belonging to 16 genera. Among these, 23 species are new to this area. These newly recorded species include: Benthosema fibulatum, Bolinichthys supralateralis, Diaphus fulgens, D. fragilis, D. kuroshio, D. problematicus, D. perspicillatus, D. phillipsi, Electrona risso, Hygophum proximum, H. reinhardtii, Lampadena anomala, Lobianchia gemellarii, Lampanyctus niger, L. turneri, L. tenuiformis, Myctophum asperum, M. aurolaternatum, M. nitidulum, M. spinosum, Notolychnus valdiviae, Notoscopelus caudispinosus, and N. resplendens. Among these, 6 species, including Bolinichthys supralateralis, Electrona risso, Lampanyctus turneri, Lampadena anomala, Notolychnus valdiviae, and Notoscopelus caudispinosus, are first records for the South China Sea, and the species, Lampadena anomala is a new record for Asian oceans. The similarity indexes (SI) of lanternfish composition among the 3 areas were very close to one another. The SI between the southwestern and eastern waters of Taiwan was 0.78; it was 0.76 between southwestern waters and the Tungsha Islands. The SI between the Tungsha Islands and eastern Taiwan was 0.70, whereas the SI (0.78) between southwestern and eastern Taiwan showed the highest similarity among these 3 regions; this may be caused by the Kuroshio Current which passes along the east coast of Taiwan and its branch which passes off the southwestern coast. The characters used in this study were composed of both external and internal characters. The external characters included mainly those from teeth, maxillary shape, olfactory shape, numbers of procurrent rays or spines, location of fins, comparison between dorsal and anal fin bases, and patterns of photophores and luminous tissue. The internal characters were comprised mainly of the vertebrae number, number of gill rakers, and information on the soft organs from the following parts: types of rete mirabile and oval in the swimbladder, shape of the stomach, number of pyloric caeca, and relative size of the brain. Many soft organ characters mentioned above help resolve the interrelationships of most myctophid genera. In the Neoscopelidae, the data matrix is composed of 15 characters of 4 species (in 3 genera) with Aulops japonicus (Family: Aulopidae) as the outgroup. After the analysis using MacClade 4.0, by sharing the same apomorphic character of pterygoid teeth, the genus Neoscopelus was determined to be closer to the genus Solivomer than to the genus Scopelengys. In the Myctophidae, the data matrix was composed of 56 characters of 129 taxa (in 33 genera). Scopelengys (Family: Neoscopelidae) was the outgroup. An analysis shows that Scopelopsis is the sister group of a large clade formed by 2 main monophyletic subgroups (the Myctophinae and Lampanyctinae). The latter clade is supported by 10 synapomorphic characters. Three tribes, the Gonichthyini, Gymnoscopelini, and Lampanyctini, are in the subfamily Lampanyctinae. However, Paxton and Stiassny put the tribe Gonichthyini in the Myctophinae. The Gonichthyini was placed in the Lampanyctinae in the present study, because it shares 3 apomorphic characters with other lampanyctines. The Gonichthyini includes Loweina, Tarletonbeania, Gonichthys, Centrobranchus, and Krefftichthys. The genus Krefftichthys is now placed in the tribe Gonichthyini, which was allocated to the subfamily Myctophinae by Paxton and Stiassny. My treatment was based on the reasoning that this species shares the same apomorphic characters (e.g., olfactory organ almost equal with eye lens, pyloric caeca very close to cardiac region, the number of precaudal vertebrae less than 12, and 2 optic lobes parallel) with other Gonichthyini members (Loweina, Gonichthys, and Centrobranchus). There are many polytomous states in the phylogenetic trees of Paxton's and Stiassny’s phylogenetic proposals which were derived from osteological and muscular characters. Such a polytomous phenomenon means that the relationships among genera of the Myctophidae remain unsettled. Unresolved interrelationships remain among genera of the Myctophidae in Paxton's analysis, and more polytomous states occurred in Stiassny's tree such as: Hygophum, Myctophum, and Metelectrona; Hintonia, Gymnoscopelus, and Lampichthys; Lampanyctodes, Idiolychnus, Lobianchia, and Diaphus; and Bolinichthys, Triphoturus, Stenobrachius, and Parvilux. Because of sharing 5 apomorphic characters, the genera Lampanyctus and Naanobrachium are in 1 clade. Despite many scientists placing Naanobrachium in the genus Lampanyctus, synapomorphic characters for each of these 2 genera support their having valid generic status. The genus Diaphus, the most speciose genus of the Myctophidae, can be divided into 2 groups by analysis of 41 characters in 46 taxa through MacClade 4.0. Among 46 species examined, 1 group possesses the apomorphic character of the photophore So, while the other group possesses the apomorphic character of the maxillary exceeding the eye orbital. Much evidence supports lanternfish monophyly, such as structures of the swimbladder and photophores. The “unipolar” rete mirabile of the swimbladder in lanternfishes greatly differs from the “bipolar” rete mirabile of the swimbladder in Stomiiformes. The 3-strand unipolar rete mirabile of the swimbladder in the Myctophidae and the 5-strand unipolar rete mirabile of the swimbladder in the Neoscopelidae represent derived character states as the bipolar rete mirabile of the swimbladder in the Stomiiformes. Ovals of swimbladders are present in lanternfishes but are absent from the Stomiiformes. Photophores in the Myctophidae are covered by scales, but no scales cover the photophores in the Neoscopelidae. Furthermore, the “open-circle”shaped photophores in the Neoscopelidae differ from the “closed-circle”-type found only in the Myctophidae; however many differences exist with the Stomiiformes such as deciduous photophores in the family Phosichthyidae. Fifty-three species of 16 genera in the families Myctophidae and Neoscopelidae were collected from waters surrounding Taiwan, including the Tungsha Islands. Among these, 23 species are new records to these areas. A key to the species is provided. And a key also to 36 genera, recorded from all over the world, in the 2 families is established in the present study. In phylogenetic relationships, the Myctophidae is comprised of 2 subfamilies: the Myctophinae and Lampanyctinae. We hypothesize about the generic interrelationships among the Myctophidae and Neoscopelidae. And Lampanyctus and Naanobrachium are valid genera. The genus Diaphus can be divided into 2 subgroups. Characters analyzed in this study provide additional evidence to support the monophyly of the Myctophiformes.
Databáze:	Networked Digital Library of Theses & Dissertations
Externí odkaz:	http://ndltd.ncl.edu.tw/handle/76324134577858203632 Zobrazit plný text záznamu