Atsushi Fukui

Phylogenetic analysis of host–symbiont specificity and codivergence in bioluminescent symbioses

Several groups of marine fishes and squids form mutualistic bioluminescent symbioses with luminous bacteria. The dependence of the animal on its symbiont for light production, the animals specialized anatomical adaptations for harboring bacteria and controlling light emission, and the host family bacterial species specificity characteristic of these associations suggest that bioluminescent symbioses are tightly coupled associations that might involve coevolutionary interactions. Consistent with this possibility, evidence of parallel cladogenesis has been reported for squid–bacterial associations. However, genetic adaptations in the bacteria necessary for and specific to symbiosis have not been identified, and unlike obligate endosymbiotic associations in which the bacteria are transferred vertically, bacterially bioluminescent hosts acquire their light‐organ symbionts from the environment with each new host generation. These contrasting observations led us to test the hypotheses of species specificity and codivergence in bioluminescent symbioses, using an extensive sampling of naturally formed associations. Thirty‐five species of fish in seven teleost families (Chlorophthalmidae, Macrouridae, Moridae, Trachichthyidae, Monocentridae, Acropomatidae, Leiognathidae) and their light‐organ bacteria were examined. Phylogenetic analysis of a taxonomically broad sampling of associations was based on mitochondrial 16S rRNA and cytochrome oxidase I gene sequences for the fish and on recA, gyrB and luxA sequences for bacteria isolated from the light organs of these specimens. In a fine‐scale test focused on Leiognathidae, phylogenetic analysis was based also on histone H3 subunit and 28S rRNA gene sequences for the fish and on gyrB, luxA, luxB, luxF and luxE sequences for the bacteria. Deep divergences were revealed among the fishes, and clear resolution was obtained between clades of the bacteria. In several associations, bacterial species identities contradicted strict host family bacterial species specificity. Furthermore, the fish and bacterial phylogenies exhibited no meaningful topological congruence; evolutionary divergence of host fishes was not matched by a similar pattern of diversification in the symbiotic bacteria. Re‐analysis of data reported for squids and their luminous bacteria also revealed no convincing evidence of codivergence. These results refute the hypothesis of strict host family bacterial species specificity and the hypothesis of codivergence in bioluminescent symbioses.

Developmental and Microbiological Analysis of the Inception of Bioluminescent Symbiosis in the Marine Fish Nuchequula nuchalis (Perciformes: Leiognathidae)

ABSTRACT Many marine fish harbor luminous bacteria as bioluminescent symbionts. Despite the diversity, abundance, and ecological importance of these fish and their apparent dependence on luminous bacteria for survival and reproduction, little is known about developmental and microbiological events surrounding the inception of their symbioses. To gain insight on these issues, we examined wild-caught larvae of the leiognathid fish Nuchequula nuchalis, a species that harbors Photobacterium leiognathi as its symbiont, for the presence, developmental state, and microbiological status of the fishs internal, supraesophageal light organ. Nascent light organs were evident in the smallest specimens obtained, flexion larvae of 6.0 to 6.5 mm in notochord length (NL), a developmental stage at which the stomach had not yet differentiated and the nascent gasbladder had not established an interface with the light organ. Light organs of certain of the specimens in this size range apparently lacked bacteria, whereas light organs of other specimens of 6.5 mm in NL and of all larger specimens harbored large populations of bacteria, representatives of which were identified as P. leiognathi. Bacteria identified as Vibrio harveyi were also present in the light organ of one larval specimen. Light organ populations were composed typically of two or three genetically distinct strain types of P. leiognathi, similar to the situation in adult fish, and the same strain type was only rarely found in light organs of different larval, juvenile, or adult specimens. Light organs of larvae carried a smaller proportion of strains merodiploid for the lux-rib operon, 79 of 249 strains, than those of adults (75 of 91 strains). These results indicate that light organs of N. nuchalis flexion and postflexion larvae of 6.0 to 6.7 mm in NL are at an early stage of development and that inception of the symbiosis apparently occurs in flexion larvae of 6.0 to 6.5 mm in NL. Ontogeny of the light organ therefore apparently precedes acquisition of the symbiotic bacteria. Furthermore, bacterial populations in larval light organs near inception of the symbiosis are genetically diverse, like those of adult fish.

Pelagic larvae of Ventrifossa garmani (Gadiformes: Macrouridae) from Suruga Bay and offshore waters of Japan

Three pelagic larvae [5.1–5.9 mm in head length (80+ to 101+ mm in total length)] of a macrourid fish, Ventrifossa garmani, from Suruga Bay and offshore waters of central Japan are described. The specimens were characterized by a remarkably elongate caudal region (caudal region length >15.6 times head length), the longest known to date among macrourid larvae and juveniles. Other characteristics included a short snout, first dorsal and pelvic fin rays not elongated, external melanophores on most of the body and posteriorly on the anal fin membrane, and six or seven rectangular clusters of internal melanophores laterally on the anterior caudal region.

Dolichopteryx minuscula, a new species of spookfish (Argentinoidei: Opisthoproctidae) from the Indo-West Pacific

A new species Dolichopteryx minuscula is described on the basis of three specimens [49.4–59.6 mm in standard length (SL)] collected from the Indo-West Pacific. The new species is characterized by pouchlike eyes with a small lens (lens diameter 2.2% SL), an adipose fin, the anal fin base originating posterior to the dorsal fin base, and 16–17 (= 5–6 + 1 + 10–11) gill rakers. Total fecundity was relatively low, only 658 ova being obtained from one specimen, despite the ovary being mature. Ovarian eggs were clearly subdivided into “undeveloped” (0.1–0.7 mm diameter classes, n = 561) and “developed” (1.0–1.3 mm classes, n = 97) groups, based on their frequency distribution. Such relatively low fecundity and frequency distributions of ovarian eggs suggest that Dolichopteryx species spawn iteratively during spawning season.

Uncisudis posteropelvis, a new species of barracudina (Aulopiformes: Paralepididae) from the western North Pacific Ocean

Six specimens (2 flexion larvae: 9.5–10.4 mm in notochord length; 4 postflexion larvae: 12.3–18.2 mm in standard length) collected from the western North Pacific are tentatively ascribed to the genus Uncisudis of the tribe Lestidiini of the subfamily Paralepidinae (Paralepididae) in sharing remarkably elongate and filamentous pelvic fin rays, their tips reaching the origin of the anal fin. They are described as Uncisudis posteropelvis sp. nov. in uniquely having the insertion of pelvic fins closer to the origin of anal fin than to the posterior end of dorsal fin base among lestidiine species. Addition to this character, the new species has remarkably elongate and filamentous dorsal fin rays, the short distance between anus and origin of anal fin (4.2–6.1% of standard length, SL), the posteriorly located pelvic fins (prepelvic length 69.4–71.5% SL), dorsal fin rays 10, anal fin rays 28–29, myomeres 41–42 + 38–40 = 80–81 (vertebrae 38 + 41 = 79), and peritoneal pigment spots 11–12. The occurrence of larvae differing in pigment pattern from the present new species suggests another undescribed species of Uncisudis in the western South Pacific.

Larva of Chascanopsetta lugubris lugubris (Bothidae) disgorged by a lancetfish (Alepisaurus sp.)

Chascanopsetta lugubris lugubris Alcock of the family Bothidae occurs on the sea bottom at depths of 270–595 m in the western Pacific and Indian Ocean (Amaoka and Yamamoto 1984). Bruun (1937), Nielsen (1961), Amaoka (1971), and Ozawa and Fukui (1986) described the larva of this subspecies, which is known to attain 120 mm SL (Amaoka 1971), the largest size known among pleuronectoid larvae. Such large larvae are rarely collected, and their morphological development is not sufficiently understood. Interestingly, gut contents have not been reported from any bothid larvae inclusive of this subspecies. A large larva of this subspecies, 108mm SL, was disgorged on deck by a lancetfish (Alepisaurus sp.) caught in Tasman Sea. The larva was fresh and excellent in condition when it was delivered frozen to the Australian Museum, by officers of NSW Fisheries. It contained many food organisms in its gut. This article describes the larva and the gut contents. The measurement methods followed Ozawa and Fukui (1986), the clearing and staining techniques those of Potthoff (1984), and the institutional abbreviations those of Leviton et al. (1985). The gut contents were found to be a copepod, Scolecithrix danae. The copepods were slightly damaged; therefore, their body lengths were estimated as follows. The length of intact part from the anterior tip of head to the posterior tip of fourth thoracic segment was measured on the specimens from the gut and used to calculate the total body length from the proportions given by Mori (1964). The metasoma of all the contents was intact, and its maximum width was also measured. Chascanopsetta lugubris lugubris Alcock (Figs. 1, 2)

Larvae ofArnoglossus debilis (Bothidae) from Hawaii

T he genus Arnoglossus (Family Bothidae) is distributed worldwide in tropical and temperate waters. Among the approximately 33 species presently recognized in the genus, the larvae or 9 species and 3 unidentified types are known (Kyte, t913; PertsevaOstroumova, t 965: Amaoka, t 973, 1974; Ahlstrom et al., 1984; Ozawa and Fukui, 1986; Fukui, 1997). Exanaination of bothid larvae collected from around the Hawaiian Islands and deposited in the Australian Museum, Sydney, disclosed three larval specimens of Arnoglossus debilis (Gilbert), a species fbr which the larval stages are poorly known. Accordingly, the specimens are described below. Methods for measurements followed Ozawa and Fukui (1986: 328). Institutional abbreviations follow Leviton et al. (1985).

Early ontogeny of two bothid species, Psettina iijimae and Laeops kitaharae

From specimens collected in the western North Pacific, the early ontogeny ofPsettina iijimae andLaeops kitaharae is described. Diagnostic characters of the genera throughout larval stages are also provided. It is suggested that these species are distributed on continental shelf or at the edge, and that they spawn between July and September.

Larval and juvenile Polymetme elongata (Stomiiformes : Phosichthyidae) collected from Suruga Bay and offshore waters, Japan

Two larvae [17.4 mm standard length: SL (postflexion stage)] and 26.1 mm SL (transformation stage)] and a juvenile (31.7 mm SL) of a phosichthyid, Polymetme elongata, from Suruga Bay and offshore waters, central Japan, are described. These specimens had an elongate body with relatively short preanal length (53–63% SL), long anal fin base (2.6–3.4 times dorsal fin base length), and anal fin origin below dorsal fin base, and were further characterized by a blackish flap on each eye and internal clusters of melanophores (e.g., along caudal myosepta around midlateral line and on ventral margin of caudal peduncle). The short preanal length and larval melanophore pattern were very similar to those of another phosichthyid, Yarrella blackfordi, from the Atlantic Ocean.

Pelagic juvenile of Halargyreus johnsonii (Gadiformes: Moridae) from Suruga Bay, Japan

Abstract A pelagic juvenile (43.0 mm standard length) of the deep-sea gadiform fish Halargyreus johnsonii was collected by a larva net towed at depths from 200 m to 90 m at Suruga Bay, Japan. The specimen had an elongate body, eyes located dorsally on the head, a depressed anal fin, small bony tubercles on the lower jaw symphysis, elongate pelvic fin rays, and a pointed caudal fin. The body was silver with numerous small black spots. The gut was filled with a copepod, Pareuchaeta russelli, that is characterized by a surface to mesopelagic distribution.