Explore the vast range of titles available.

The turquoise killifish, Nothobranchius furzeri, is a promising vertebrate model in ageing research and an emerging model organism in genomics, regenerative medicine, developmental biology and ecotoxicology. Its lifestyle is adapted to the ephemeral nature of shallow pools on the African savannah. Its rapid and short active life commences when rains fill the pool: fish hatch, grow rapidly and mature in as few as two weeks, and then reproduce daily until the pool dries out. Its embryos then become inactive, encased in the dry sediment and protected from the harsh environment until the rains return. This invertebrate-like life cycle (short active phase and long developmental arrest) combined with a vertebrate body plan provide the ideal attributes for a laboratory animal.

Nothobranchius furzeri is an important new model organism. This Protocol aims to help laboratories establish healthy breeding colonies of this species and to standardize husbandry methods, which differ from those for other model fish because of dry incubation of the eggs. Turquoise killifish, Nothobranchius furzeri , have an intrinsically short life span, with a median life span of <6 months and a maximum (90%) life span of 9 months. This short life span, which is unique among vertebrates, evolved naturally and has resulted in N. furzeri becoming a widely used laboratory model species in aging research and other disciplines. Here, we describe a protocol for the maintenance and breeding of the species under laboratory conditions. We provide details for egg incubation, hatching, everyday care of juvenile and adult fish, breeding and treatment of most common diseases. Emphasis is given to the fact that the requirements of N. furzeri substantially differ from those of other fish model taxa; N. furzeri live brief lives and in nature undergo nonaquatic embryo development, with consequences for their laboratory culture.

Brood parasites are involved in coevolutionary arms races with their hosts, whereby adaptations of one partner elicit the rapid evolution of counter-adaptations in the other partner. Hosts can also mitigate fitness costs of brood parasitism by learning from individual or social experience. In brood parasites, however, the role of learning can be obscured by their stealthy behaviour. Cuckoo catfish ( Synodontis multipunctatus ) parasitise clutches of mouthbrooding cichlids in Lake Tanganyika and are the only non-avian obligate brood parasites among vertebrates. We experimentally demonstrate that cuckoo catfish greatly enhance their efficiency in parasitising their hosts as they learn to overcome host defences. With increasing experience, cuckoo catfish increased their parasitism success by greater efficiency through improved timing and coordination of intrusions of host spawnings. Hence, within the coevolutionary arms races, brood parasites learn to overcome host defences during their lifetime. The importance of learning for brood parasites is explored using cuckoo catfish. The catfish increase their parasitism success as they gain experience, mainly by improving their social coordination and timing of intrusions to cichlid host spawnings.

Aim: We compared the genetic variability and phylogeographical structure of three sympatric clades of annual killifishes (the Nothobranchius furzeri complex, N. orthonotus complex and N. rachovii complex) inhabiting annually desiccating savanna pools. Hypotheses on the mechanisms affecting intraspecific structure and speciation were tested. Location: Temporary pools in Mozambique (Africa). Methods: The study is based on spatially detailed samples covering the entire range of all three species complexes. A set of 12-13 microsatellites (1638 individuals, 96 populations) and cytochrome b sequences (463 fish, 152 populations) were used as genetic markers. Phylogenetic and population genetic approaches were used to describe the spatial genetic structure and to test the respective roles of river channels and river basins on diversification. Results: Profound genetic differentiation among populations was evident; some populations located only a few kilometres apart were genetically very distinct, suggesting a significant role of genetic drift and low dispersal ability. Large rivers (Zambezi, Save, Limpopo) formed major barriers to gene flow, with minor differences among the three complexes. Further, the demographic expansion of previously isolated lineages was often limited by the river channel, and rivers were also confirmed as factors affecting speciation events. River basins and elevational gradient had a smaller, but non-negligible, role in population structuring. Main conclusions: River channels are the main barriers to gene flow in Nothobranchius fishes. The study demonstrated low dispersal ability and congruence in the phylogeographical pattern of all three complexes. Cases where Nothobranchius appear to have crossed river channels result from the dynamics of river morphology rather than from rare dispersal events. This conclusion is supported by simultaneous crossing events across lineages. A further division, also consistent among the three complexes, was detected between drier inland and wetter coastal areas. The phylogeographical pattern of Nothobranchius is unique in that it combines features of both aquatic and terrestrial taxa.

The natural history of model organisms is often overlooked despite its importance to correctly interpret the outcome of laboratory studies. Ageing is particularly understudied in natural populations. To address this gap, we present lifetime demographic data from wild populations of an annual species, the turquoise killifish, Nothobranchius furzeri , a model species in ageing research, and two other species of coexisting annual killifishes. Annual killifish hatch synchronously, have non-overlapping generations, and reproduce daily after reaching sexual maturity. Data from 13 isolated savanna pools in southern Mozambique demonstrate that the pools supporting killifish populations desiccated 1–4 months after their filling, though some pools persisted longer. Declines in population size over the season were stronger than predicted, because they exceeded the effect of steady habitat shrinking on population density that, contrary to the prediction, decreased. Populations of N. furzeri also became more female-biased with progressing season suggesting that males had lower survival. Nothobranchius community composition did not significantly vary across the season. Our data clearly demonstrate that natural populations of N. furzeri and its congeners suffer strong mortality throughout their lives, with apparent selective disappearance (condition-dependent mortality) at the individual level. This represents selective force that can shape the evolution of lifespan, and its variation across populations, beyond the effects of the gradient in habitat persistence.

Embryo–environment interactions are of paramount importance during the development of all organisms, and impacts during this period can echo far into later stages of ontogeny. African annual fish of the genus Nothobranchius live in temporary pools and their eggs survive the dry season in the dry bottom substrate of the pools by entering a facultative developmental arrest termed diapause. Uniquely among animals, the embryos (encased in eggs) may enter diapause at three different developmental stages. Such a system allows for the potential to employ different regulation mechanisms for each diapause. We sampled multiple Nothobranchius embryo banks across the progressing season, species, and populations. We present important baseline field data and examine the role of environmental regulation in the embryonic development of this unique system. We describe the course of embryo development in the wild and find it to be very different from the typical development under laboratory conditions. Development across the embryo banks was synchronized within and across the sampled populations with all embryos entering diapause I during the rainy season and diapause II during the dry season. Asynchrony occurred at transient phases of the habitat, during the process of habitat desiccation, and at the end of the dry season. Our findings reveal the significance of environmental conditions in the serial character of the annual fish diapauses. Annual killifish of the African genus Nothobranchius are being widely used as laboratory model organisms. Nothing was known on their embryonic development under natural conditions. We bring first complete data on the natural course of embryonic development of the fish.

As invaders of European and North American aquatic systems, Ponto–Caspian gobiids are believed to represent a significant negative threat to native fish assemblages and cottid species in particular. To date, relatively few studies have tried to document actual impacts, most being short-term and/or laboratory based. Here, we examine 8 years (2008–2015) of electrofishing data from a 1200-m stretch of rip-rap along the Austrian Danube, initiated following establishment of four non-native gobiids: tubenose goby Proterorhinus semilunaris, bighead goby Ponticola kessleri, racer goby Babka gymnotrachelus and round goby Neogobius melanostomus. While we registered 26 fish species in total, most native species were caught along the rip-rap only occasionally. Only native bullhead Cottus gobio and the four non-native gobiids were caught regularly. Although cottids are presently believed to be most vulnerable to gobiid invasion, we observed no negative trend in bullhead abundance over the 8-year dataset, the population remaining stable and at similar abundances to gobiids. While we observed no significant trend in round, racer or tubenose goby abundance, bighead goby showed a continuous decline. Our data contradict previous reports of drastic impacts on cottid abundance by gobiids (mainly round goby), suggesting potential region-specific effects following invasion.

Interspecific reproductive isolation is typically achieved by a combination of intrinsic and extrinsic barriers. Behavioural isolating barriers between sympatric, closely related species are often of primary importance and frequently aided by extrinsic factors causing spatial and temporal interspecific separation. Study systems with a severely limited role of extrinsic factors on reproductive isolation may provide valuable insights into how reproductive isolation between sympatric species is maintained. We used no-choice experimental set-up to study reproductive barriers between two closely related sympatric African killifish species, Nothobranchius furzeri and Nothobranchius orthonotus. These fish live in small temporary savannah pools and have complete spatial and temporal overlap in reproductive activities and share a similar ecology. We found that the two species display largely incomplete and asymmetric reproductive isolation. Mating between N. furzeri males and N. orthonotus females was absent under standard experimental conditions and eggs were not viable when fish were forced to mate in a modified experimental setup. In contrast, male N. orthonotus indiscriminately mated with N. furzeri females, the eggs were viable, and offspring successfully hatched. Most spawnings, however, were achieved by male coercion and egg production and embryo survival were low. Behavioural asymmetry was likely facilitated by mating coercion from larger males of N. orthonotus and at relatively low cost to females. Interestingly, the direction of asymmetry was positively associated with asymmetry in post-mating reproductive barriers. We showed that, in fish species with a promiscuous mating system and multiple matings each day, selection for strong mate preferences was relaxed. This effect was likely due to the small proportion of resources allocated to each single mating and the high potential cost to females from mating refusal. We highlight and discuss the fact that males of rarer species may often coercively mate with females of a related, more abundant species.

Background African annual killifishes ( Nothobranchius spp.) are adapted to seasonally desiccating habitats (ephemeral pools), surviving dry periods as dormant eggs. Given their peculiar life history, geographic aspects of their diversity uniquely combine patterns typical for freshwater taxa (river basin structure and elevation gradient) and terrestrial animals (rivers acting as major dispersal barriers). However, our current knowledge on fine-scale inter-specific and intra-specific genetic diversity of African annual fish is limited to a single, particularly dry region of their distribution (subtropical Mozambique). Using a widespread annual killifish from coastal Tanzania and Kenya, we tested whether the same pattern of genetic divergence pertains to a wet equatorial region in the centre of Nothobranchius distribution. Results In populations of Nothobranchius melanospilus species group across its range, we genotyped a part of mitochondrial cytochrome oxidase subunit 1 ( COI ) gene (83 individuals from 22 populations) and 10 nuclear microsatellite markers (251 individuals from 16 populations). We found five lineages with a clear phylogeographic structure but frequent secondary contact. Mitochondrial lineages were largely congruent with main population genetic clusters identified on microsatellite markers. In the upper Wami basin, populations are isolated as a putative Nothobranchius prognathus , but include also a population from a periphery of the middle Ruvu basin. Other four lineages (including putative Nothobranchius kwalensis ) coexisted in secondary contact zones, but possessed clear spatial pattern. Main river channels did not form apparent barriers to dispersal. The most widespread lineage had strong signal of recent population expansion. Conclusions We conclude that dispersal of a Nothobranchius species from a wet part of the genus distribution (tropical lowland) is not constrained by main river channels and closely related lineages frequently coexist in secondary contact zones. We also demonstrate contemporary connection between the Ruvu and Rufiji river basins. Our data do not provide genetic support for existence of recently described cryptic species from N. melanospilus complex, but cannot resolve this issue.

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. We compared biodiversity components (alpha, beta, and gamma) of Nothobranchius killifish in coastal Tanzanian ecoregions and decomposed beta diversity to nestedness and turnover components. We found unexpected local variation in the sources of beta diversity (nestedness and turnover) within the study area and identified a region that contained the highest diversity and endemism.