Convergent evolution of alternative developmental trajectories associated with diapause in African and South American killifish

Annual killifish adapted to life in seasonally ephemeral water-bodies exhibit desiccation resistant eggs that can undergo diapause, a period of developmental arrest, enabling them to traverse the otherwise inhospitable dry season. Environmental cues that potentially indicate the season can govern whether eggs enter a stage of diapause mid-way through development or skip this diapause and instead undergo direct development. We report, based on construction of a supermatrix phylogenetic tree of the order Cyprinodontiformes and a battery of comparative analyses, that the ability to produce diapause eggs evolved independently at least six times within African and South American killifish. We then show in species representative of these lineages that embryos entering diapause display significant reduction in development of the cranial region and circulatory system relative to direct-developing embryos. This divergence along alternative developmental pathways begins mid-way through development, well before diapause is entered, during a period of purported maximum developmental constraint (the phylotypic period). Finally, we show that entering diapause is accompanied by a dramatic reduction in metabolic rate and concomitant increase in long-term embryo survival. Morphological divergence during the phylotypic period thus allows embryos undergoing diapause to conserve energy by shunting resources away from energetically costly organs thereby increasing survival chances in an environment that necessitates remaining dormant, buried in the soil and surrounded by an eggshell for much of the year. Our results indicate that adaptation to seasonal aquatic environments in annual killifish imposes strong selection during the embryo stage leading to marked diversification during this otherwise conserved period of vertebrate development.     

Profundulus kreiseri,a new species of Profundulidae (Teleostei,Cyprinodontiformes) from northwestern?Honduras

A new species of Profundulus, Profundulus kreiseri (Cyprinodontiformes: Profundulidae), is described from the Chamelecón and Ulúa Rivers in the northwestern Honduran highlands. Based on a phylogenetic analysis using cytochrome b and the presence of synapomorphic characters (dark humeral spot, a scaled preorbital region and between 32-34 vertebrae), this new species is placed in the subgenus Profundulus, which also includes Profundulus (Profundulus) oaxacae, Profundulus (Profundulus) punctatus and Profundulus (Profundulus) guatemalensis. Profundulus kreiseri can be distinguished from other members of the subgenus Profundulus by having less than half of its caudal fin densely scaled. Profundulus kreiseri can further be differentiated from Profundulus (Profundulus) oaxacae and Profundulus (Profundulus) punctatus by the absence of rows of dark spots on its flanks. The new species can further be differentiated from Profundulus (Profundulus) guatemalensis by the presence of fewer caudal- and pectoral-fin rays. The new species is distinguished from congeners of the profundulid subgenus Tlaloc (viz., Profundulus (Tlaloc) hildebrandi, Profundulus (Tlaloc) labialis, Profundulus (Tlaloc) candalarius and Profundulus (Tlaloc) portillorum) by having a scaled preorbital region and a dark humeral spot. Profundulus kreiseri and Profundulus portillorum are the only two species of Profundulus that are endemic to the region south of the Motagua River drainage in southern Guatemala and northwestern Honduras.     

云南青鳉鱼类的分类和分布(鳉形目:青鳉科)

经研究,云南的青鳉鱼类有2种:(1)分布于西双版纳的小青鏘 Oryzias minutillus Smith为中国境内首次记录;(2)另一种是新亚种,定名中华青鳉 Oryzias latipes sinentis subsp.nov.广泛分布于云南及中国其他地区。本新亚种与产自日本的指名亚种日本青鳉 Oryzias latipes latipes Temminck et Schlegel的主要区别在于:本新亚种的第一肋骨连接第二而不是第三脊椎骨上;平均脊椎骨数为29.2±0.6而不是30.3±0.5;胸鳍条多数为9而不是多数为10枚;染色体数目2n=46而不是2n=48。这些差异,明显地表示了由于地理隔离而引起的亚种分化。     

Historical biogeography of cynolebiasine annual killifishes inferred from dispersal–vicariance analysis

Aim To analyse the biogeographical events responsible for the present distribution of cynolebiasine killifishes (Teleostei: Rivulidae: Cynolebiasini), a diversified and widespread Neotropical group of annual fishes threatened with extinction. Location South America, focusing on the main river basins draining the Brazilian Shield and adjacent zones. Methods Phylogenetic analysis of 214 morphological characters of 102 cynolebiasine species using tnt , in conjunction with dispersal–vicariance analysis (diva ) based on the distribution of cynolebiasine species among 16 areas of endemism. Results The basal cynolebiasine node is hypothesized to be derived from an old vicariance event occurring just after the separation of South America from Africa, when the terrains at the passive margin of the South American plate were isolated from the remaining interior areas. This would have been followed by geodispersal events caused by river‐capturing episodes from the adjacent upland river basins to the coastal region. Optimal ancestral reconstructions suggest that the diversification of the tribe Cynolebiasini in north‐eastern South America was first caused by vicariance events in the Paranã–Urucuia–São Francisco area, followed by dispersal from the São Francisco to the Northeastern Brazil area. The latter dispersal event occurred simultaneously in two different cynolebiasine clades, possibly as a result of a temporary connection of the São Francisco area before the uplift of the Borborema Plateau during the Miocene. The diversity of cynolebiasines inhabiting the Paraguay area is hypothesized to be derived from two processes: an older vicariance event (about 30 Ma) separating Paraguay from southern Amazonian areas (Guaporé–Xingu–Araguaia–Tocantins), and a series of more recent dispersal and vicariance events (about 15–11 Ma) caused by successive marine transgressions, which permitted alternating biotic exchange and isolation in the Paraguay, La Plata, Negro and Patos areas. Main conclusions diva indicates there to have been a series of vicariance events congruent with tectonic episodes in South America, but the present distribution of cynolebiasines has also been shaped by a series of dispersal events. The effects of the combined action of dispersal and vicariance events were more conspicuous in the Eastern Brazil and Paraguay areas, thus generating reticulate biogeographical scenarios.     

The vertical distributions and spawning site choices of red and yellow bluefin killifish Lucania goodei colour morphs

A genetic colour polymorphism is present in bluefin killifish Lucania goodei, where red and yellow anal‐fin morphs coexist in clear springs, but the source of balancing selection is unknown. In a field study, vertical distributions did not differ between the morphs and there was little evidence that light environments differed qualitatively over the 200 cm at which fish were collected. A greenhouse study showed that both morphs preferred to spawn at shallow depths and hence vertical distribution and spawning site choice are unlikely to explain the maintenance of the colour polymorphism.     

A test for negative frequency-dependent mating success as a function of male colour pattern in the bluefin killifish

Rare male mating advantage (a form of negative frequency dependence) is frequently proposed as a mechanism for the maintenance of genetic variation within populations. This hypothesis is attractive for systems with pronounced male colour polymorphism because it can maintain particularly high levels of variation. We tested for negative frequency-dependent mating success between yellow and red male colour patterns in bluefin killifish, Lucania goodei . Lucania goodei populations harbour substantial colour pattern polymorphism, and a large proportion of this variation has a genetic basis. We established outdoor mesocosms with red and yellow males in three different ratios: yellow rare (one yellow ♂ : five red ♂), even (three yellow ♂ : three red ♂), and red rare (five yellow ♂ : one red ♂). We obtained eggs and used microsatellites to determine paternity. By contrast to expectations, we found no support for a rare male mating advantage. Red males had slightly higher spawning success than yellow males, particularly in replicates with large clutches and when red males were rare. However, yellow males did not have higher mating success when rare. We discuss alternative mechanisms for the maintenance of the polymorphism as well as the potential reasons for the lack of a rare male mating advantage.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 489–500.     

Patterns and drivers of Nothobranchius killifish diversity in lowland Tanzania

Temporary pools are seasonal wetland habitats with specifically adapted biota, including annual Nothobranchius killifishes that survive habitat desiccation as diapausing eggs encased in dry sediment. To understand the patterns in the structure of Nothobranchius assemblages and their potential in wetland conservation, we compared biodiversity components (alpha, beta, and gamma) between regions and estimated the role and sources of nestedness and turnover on their diversity. We sampled Nothobranchius assemblages from 127 pools across seven local regions in lowland Eastern Tanzania over 2 years, using dip net and seine nets. We estimated species composition and richness for each pool, and beta and gamma diversity for each region. We decomposed beta diversity into nestedness and turnover components. We tested nestedness in three main regions (Ruvu, Rufiji, and Mbezi) using the number of decreasing fills metric and compared the roles of pool area, isolation, and altitude on nestedness. A total of 15 species formed assemblages containing 1–6 species. Most Nothobranchius species were endemic to one or two adjacent regions. Regional diversity was highest in the Ruvu, Rufiji, and Mbezi regions. Nestedness was significant in Ruvu and Rufiji, with shared core (N. melanospilus, N. eggersi, and N. janpapi) and common (N. ocellatus and N. annectens) species, and distinctive rare species. Nestedness apparently resulted from selective colonization rather than selective extinction, and local species richness was negatively associated with altitude. The Nothobranchius assemblages in the Mbezi region were not nested, and had many endemic species and the highest beta diversity driven by species turnover. Overall, we found unexpected local variation in the sources of beta diversity (nestedness and turnover) within the study area. The Mbezi region contained the highest diversity and many endemic species, apparently due to repeated colonizations of the region rather than local diversification. We suggest that annual killifish can serve as a flagship taxon for small wetland conservation.     

Functional significance of intramandibular bending in Poeciliid fishes

Substrate-feeding teleosts show multiple, independent evolutionary acquisitions of intramandibular bending (bending within the lower jaw)—a behavior that likely enhances performance when feeding on attached or encrusting food items. However, intramandibular bending has only been quantified for marine teleosts. Here, we examine substrate feeding in eight species from the order Cyprinodontiformes and quantify movements produced by the anterior jaws of four target species selected from the family Poeciliidae to represent a variety of trophic strategies. Intramandibular bending, defined here as bending between the dentary and angular–articular bones of the lower jaw, is not present in some poeciliids (i.e. Gambusia affinis), nor is it present in outgroup cyprinodontiforms (i.e. Fundulus rubrifrons). However, intramandibular bending is present in certain poeciliids (i.e. Poecilia sphenops), and can exceed 90°. Such jaw bending enables the production of a gape angle that approaches 120°, which likely allows the fish to maximize contact between the toothed tips of the jaws and the substrate during the bite. Intramandibular bending in poeciliid species is associated with specific trophic shifts: the greater the intramandibular bending in a given species, the more attached algae (periphyton) reported in its diet. This result supports the hypothesis that intramandibular bending enhances performance when feeding on encrusting food items. We predict that additional examples of functional convergence are likely to be documented in freshwater teleosts as more herbivorous species are examined, and we propose that intramandibular bending represents an excellent model system in which to examine the functional processes that underlie convergent evolution. An erratum to this article can be found at