Extremely early maturity found in Okinawan gobioid fishes

 Extremely small animals including fishes have been reported with discussion of the causes and consequences of their miniaturization. Here we demonstrate, for the first time, very early (i.e., 23–60 days old and 42–67 days old) sexual maturity in two groups of gobioid fishes (Schindleria and Paedogobius, respectively) in warm water, based on the otolith increments. The generation time of Schindleria is the shortest known among vertebrates under natural conditions. We discuss the occurrence and evolutionary significance of the progenesis found in gobioid fishes. Received: September 27, 2001 / Revised: January 26, 2002 / Accepted: February 20, 2002     

Phylogeny of cardinalfishes (Teleostei: Gobiiformes: Apogonidae) and the evolution of visceral bioluminescence

The cardinalfishes (Apogonidae) are a diverse clade of small, mostly reef-dwelling fishes, for which a variety of morphological data have not yielded a consistent phylogeny. We use DNA sequence to hypothesize phylogenetic relationships within Apogonidae and among apogonids and other acanthomorph families, to examine patterns of evolution including the distribution of a visceral bioluminescence system. In conformance with previous studies, Apogonidae is placed in a clade with Pempheridae, Kurtidae, Leiognathidae, and Gobioidei. The apogonid genus Pseudamia is recovered outside the remainder of the family, not as sister to the superficially similar genus Gymnapogon. Species sampled from the Caribbean and Western Atlantic (Phaeoptyx, Astrapogon, and some Apogon species) form a clade, as do the larger-bodied Glossamia and Cheilodipterus. Incidence of visceral bioluminescence is found scattered throughout the phylogeny, independently for each group in which it is present. Examination of the fine structure of the visceral bioluminescence system through histology shows that light organs exhibit a range of morphologies, with some composed of complex masses of tubules (Siphamia, Pempheris, Parapriacanthus) and others lacking tubules but containing chambers formed by folds of the visceral epithelium (Acropoma, Archamia, Jaydia, and Rhabdamia). Light organs in Siphamia, Acropoma, Pempheris and Parapriacanthus are distinct from but connected to the gut; those in Archamia, Jaydia, and Rhabdamia are simply portions of the intestinal tract, and are little differentiated from the surrounding tissues. The presence or absence of symbiotic luminescent bacteria does not correlate with light organ structure; the tubular light organs of Siphamia and chambered tubes of Acropoma house bacteria, those in Pempheridae and the other Apogonidae do not.     

A standardized reanalysis of molecular phylogenetic hypotheses of Gobioidei

Gobioidei is a suborder of perciform fishes with about 2000 species distributed worldwide. Despite the evolutionary and ecological importance of gobioids, their phylogenetic inter- and intrarelationships are still poorly understood. Only a few studies (either morphological or molecular) have tackled the phylogeny of Gobioidei as a whole. Of these, only six studies thus far have addressed gobioid intrarelationships based on molecular data (each using different taxon sampling, genes, outgroups and method of phylogenetic inference), yielding contrasting results regarding the phylogenetic relationships among major lineages. In this study, we have reanalysed data from four of these molecular phylogenetic studies of Gobioidei under standardization criteria (same outgroup and methods of phylogenetic inference) in order to assess the robustness of their results, as well as to identify which parts of the gobioid tree are least resolved. Results from all datasets reanalysed in this study are generally similar to those of the respective original studies, and suggest broad patterns of phylogenetic relationships among gobioid lineages. However, there are numerous topological discrepancies among the four studies, support is low for many phylogenetic relationships and topology tests are unable to reject the vast majority of alternative topologies tested. The concatenation of datasets yields a relatively robust phylogeny of major lineages of Gobioidei, but there are some issues of overlap and missing data, which are ameliorated with the inclusion of additional homologous sequences from GenBank that increase dataset completeness. Because both monophyly of major gobioid groups and phylogenetic relationships among them cannot be fully resolved, it is clear that further phylogenetic research is needed, and this should be accompanied by a major taxonomic revision of the Gobioidei. Nevertheless, even with the relatively unstable nature of the available molecular phylogenies, there are some monophyletic units that can be identified, and a basic structure of the gobioid tree appears evident.     

Molecular phylogeny of the gobioid fishes (Teleostei: Perciformes: Gobioidei)

The phylogeny of groups within Gobioidei is examined with molecular sequence data. Gobioidei is a speciose, morphologically diverse group of teleost fishes, most of which are small, benthic, and marine. Efforts to hypothesize relationships among the gobioid groups have been hampered by the prevalence of reductive evolution among goby species; such reduction can make identification of informative morphological characters particularly difficult. Gobies have been variously grouped into two to nine families, several with included subfamilies, but most existing taxonomies are not phylogenetic and few cladistic hypotheses of relationships among goby groups have been advanced. In this study, representatives of eight of the nine gobioid familes (Eleotridae, Odontobutidae, Xenisthmidae, Gobiidae, Kraemeriidae, Schindleriidae, Microdesmidae, and Ptereleotridae), selected to sample broadly from the range of goby diversity, were examined. Complete sequence from the mitochondrial ND1, ND2, and COI genes (3573 bp) was used in a cladistic parsimony analysis to hypothesize relationships among the gobioid groups. A single most parsimonious topology was obtained, with decay indices indicating strong support for most nodes. Major phylogenetic conclusions include that Xenisthmidae is part of Eleotridae, and Eleotridae is paraphyletic with respect to a clade composed of Gobiidae, Microdesmidae, Ptereleotridae, Kraemeriidae, and Schindleriidae. Within this five-family clade, two clades are recovered. One includes Gobionellinae, which is paraphyletic with respect to Kraemeriidae, Sicydiinae, Oxudercinae, and Amblyopinae. The other contains Gobiinae, also paraphyletic, and including Microdesmidae, Ptereleotridae, and Schindleriidae. Previous morphological evidence for goby groupings is discussed; the phylogenetic hypothesis indicates that the morphological reduction observed in many goby species has been derived several times independently.     

Comparative phylogeography of five sympatric Hypseleotris species (Teleostei: Eleotridae) in south-eastern Australia reveals a complex pattern of drainage basin exchanges with little congruence across species

Aim To determine biogeographical patterns in five closely related species in the fish genus Hypseleotris, and to investigate the relative roles of drainage divide crossings and movement during lowered sea levels between drainage basins and biogeographical provinces based on the phylogeographical patterns within the group. The high degree of overlap in the distributions and ecology of these species makes them ideal candidates for comparative phylogeographical study. Location Eastern, central and south‐eastern Australia. Methods A total of 179 Hypseleotris individuals were sequenced from 45 localities for the complete mitochondrial cytochrome b gene and the first 30 base pairs of the threonine transfer RNA for a total of 1170 bp. Phylogenetic relationships were hypothesized using parsimony and Bayesian analyses. Results Phylogenetic analysis resolves the five species into three clades. The first corresponds to the species Hypseleotris klunzingeri ( Ogilby, 1898 ); within it two clades are resolved, one consisting of individuals from the Eastern Province (EP), plus two eastern Murray‐Darling Province (MDP) localities, and the other including the remainder of the MDP localities, along with the Lake Eyre Basin (Central Australian Province, CAP) individuals. The other two clades include a mixed Hypseleotris galii ( Ogilby, 1898 )/Hypseleotris sp. 3 Murray‐Darling clade, with EP and MDP lineages mostly segregated and differentiations in populations spread along the EP, and a mixed Hypseleotris sp. 4 Lake's and Hypseleotris sp. 5 Midgley's clade, with two groups of MDP localities and two CAP lineages indicated, interspersed with EP lineages as well as those from the Northern Province. Main conclusions This study is broadly congruent with a previous analysis of Hypseleotris phylogeny, but the previously observed overall relationship of south‐eastern Australian provinces [EP(MDP+CAP)] was not confirmed and is more complicated than hitherto thought. This highlights the necessity of obtaining a sufficient number of sampling localities to identify potential connectivity between populations in order to demonstrate congruent biogeographical patterns. We identified many instances of drainage divide crossings, which were the major means of movement between provinces. Despite the commonness of movement across drainage divides, very few of these were found to be exactly congruent among the species. Most occurred in different places, or if in the same location, apparently at different times, or in at least one case, in opposite directions. Patterns of movement between adjacent coastal drainages were also found to be largely incongruent; when congruence was found the populations involved had quite different genetic divergences.     

Molecular phylogeny of gobioid fishes (Perciformes: Gobioidei) based on mitochondrial 12S rRNA sequences

The molecular phylogeny of the gobioid fishes, comprising 33 genera and 43 valid species, was examined by use of complete mitochondrial 12S rRNA and tRNA(VAL)genes. Both parsimony and neighbor-joining analyses revealed comparable results and are generally congruent with those of morphological studies. The Odontobutis, which was always placed at the base of the phylogenetic trees, can be treated as a sister group of all other nonrhyacichthyid gobioids. Within eleotrid fishes, the monophyly of the Eleotrinae is strongly supported by molecular data. The Butinae is closer to fishes with five branchiostegal rays and should be treated as a sister group of the latter. The group with five branchiostegal rays, except for sicydiines, can be divided into two groups according to their epural counts. Fish with one epural, the Gobiinae of Pezold plus Microdesmidae, form a monophyletic group which is sister to those with two epurals, the Oxudercinae and Gobionellinae of Pezold. However, Sicydiinae, which have one epural, are closer to the Oxudercinae and Gobionellinae rather than to the Gobiinae. Since progressive reduction in epural number has been observed along this lineage, the sicydiines should be treated as a derived group within the groups with two epurals.     

Dynamics of demographically open mutualists: immigration, intraspecific competition, and predation impact goby populations

Although it is now recognized that mutualistic species are common and can have stable populations, the forces controlling their persistence are poorly understood. To better understand the mechanisms that impact the stability of obligate mutualists, I conducted several field experiments within a sandy coral reef lagoon in Moorea, French Polynesia that manipulated densities of fish (gobies) that interact mutualistically with shrimp. Obligate, mutualistic partnerships of gobies and shrimp are common on Indo-Pacific coral reefs and have been shown previously to interact as follows: shrimp construct burrows in which both species reside, and gobies warn shrimp of predators through tactile communication. Augmentation of gobies by up to 100% above ambient densities within 9 m² plots produced no change in overall density of gobies or shrimp because gobies competed intraspecifically for a limited number of shrimp burrows and smaller gobies were outcompeted by larger individuals. I used predators to assess the impact of goby removal on the stability of goby and shrimp populations. First, although surveys taken throughout the lagoon revealed no relationship between goby and predator densities, predators correlated negatively with the proportion of adult gobies and positively with the proportion of small gobies paired with large shrimp. Second, experimental augmentation of predators resulted in a dramatic reduction of adult gobies within predator-addition plots, but had no impact on overall densities as immigrants rapidly replaced the missing adult gobies. Furthermore, goby turnover resulted in an increase in the proportion of small gobies paired with large shrimp because body sizes of gobies and shrimp in a burrow were similar prior to predator introduction, and predators apparently had a greater impact on gobies than shrimp. The mechanisms that prevent expansion (intraspecific competition) and collapse (immigration) of goby-shrimp populations likely contribute to local-scale stability of mutualistic populations in other terrestrial and aquatic environments.     

Molecular phylogeny of basal gobioid fishes: Rhyacichthyidae, Odontobutidae, Xenisthmidae, Eleotridae (Teleostei: Perciformes: Gobioidei)

Morphological character analyses indicate that Rhyacichthyidae, Odontobutidae, Eleotridae, and Xenisthmidae are the basal families within the perciform suborder Gobioidei. This study uses DNA sequence data to infer the relationships of genera within these families, as well as determine the placement of more derived gobioids (family Gobiidae) and the identity of the outgroup to Gobioidei. Complete sequences of the mitochondrial ND1, ND2, COI, and cyt b genes (4397 base pairs) are analyzed for representatives of 27 gobioid genera and a variety of perciform and scorpaeniform outgroup candidates; the phylogeny is rooted with a beryciform as a distal outgroup. The single most parsimonious tree that results indicates that, of the outgroups sampled, the perciform family Apogonidae is most closely related to Gobioidei. Gobioidei is monophyletic, and Rhyacichthys aspro is the most basal taxon. The remainder of Gobioidei is resolved into clades corresponding to the families Odontobutidae (plus Milyeringa) and Eleotridae+Xenisthmidae+Gobiidae. Within Eleotridae, the subfamily Butinae (minus Milyeringa) is paraphyletic with respect to Gobiidae, and Eleotrinae is paraphyletic with respect to Xenisthmidae. Other than these groupings, the primary disagreement with the current morphology-based classification is that the molecular data indicate that the troglodytic Milyeringa should be placed in Odontobutidae, not Butinae, although support for this placement is weak. The most basal lineage of Gobioidei is known from the freshwaters of the Indo-Pacific, with marine-dwelling lineages arising several times independently in the group. The phylogeny also indicates that different gobioid lineages are distributed in Asia, Africa, Madagascar and the Neotropics. Five sister pairs of basal gobioid species inhabit Atlantic and Pacific drainages of Panama, with widely varying divergences.     

Unusual gonad structure in the paedomorphic teleost Schindleria praematura(Teleostei: Gobioidei): a comparison with other gobioid fishes

The gonads of eight gobioid species were examined histologically, including Pandaka pygmaea and Schindleria praematura , in order to investigate the manifestations of miniaturization and paedomorphosis in the gonads. Rearrangements of reproductive structures were found only in S. praematura , and included only the gonad tissues, not the gametes. Both sexes of S. praematura maintain basic germinal components: the spermatocyst composed of Sertoli cells and spermatogonia in the testis and the follicle and oocyte complex in the ovary. The stromal ovarian tissue and testicular interstitial tissue, however, is reduced compared to other gobies, and the number and location of gonial cells is restricted. This sequestered pattern of gonial cells is known as a restricted spermatogonial type in the testis, and has been reported only in atherinomorphs. The restriction of gonial cells in the ovary is extremely rare among teleosts, known only from one other species. These restricted gonial patterns in S. praematura are probably related to the overall reduction of morphological complexity in this genus, due to its extreme paedomorphosis.     

Four new species of dwarfgobies (Teleostei: Gobiidae: Eviota) from the Austral,Gambier, Marquesas and Society Archipelagos,French Polynesia

Four new species of Eviota (Teleostei: Gobiidae) are described from French Polynesia. Eviota hinanoae occurs from the Gambier, Austral and Society Archipelagos and differs from its closest relatives primarily in sensory pore pattern, having cuplike male urogenital papilla, and in lacking prominent dark pigmentation on the base of the pectoral fin. Three other new species, E. dorsimaculata, E. lacrimosa and E. deminuta, are known only from the Marquesas Islands and are distinguished from congeners by differences in pigmentation, sensory pore pattern, urogenital papilla shape, the number of rays in the dorsal and anal fins, and the length of the fifth pelvic-fin ray. Eviota deminuta represents one of the smallest known species of Eviota and features reductions in several morphological characters, including the loss of all head pores. Three of the new species are included in a phylogenetic analysis based on mitochondrial cytochrome c oxidase-I, along with 21 additional species of Eviota.