Normal development of the tomato clownfish Amphiprion frenatus: live imaging and in situ hybridization analyses of mesodermal and neurectodermal development

The normal embryonic development of the tomato clownfish Amphiprion frenatus was analysed using live imaging and by in situ hybridization for detection of mesodermal and neurectodermal development. Both morphology of live embryos and tissue‐specific staining revealed significant differences in the gross developmental programme of A. frenatus compared with better‐known teleost fish models, in particular, initiation of somitogenesis before complete epiboly, initiation of narrowing of the neurectoderm (neurulation) before somitogenesis, relatively early pigmentation of melanophores at the 10–15 somite stage and a distinctive pattern of melanophore distribution. These results suggest evolutionary adaptability of the teleost developmental programme. The ease of obtaining eggs, in vitro culture of the embryo, in situ staining analyses and these reported characteristics make A. frenatus a potentially important model marine fish species for studying embryonic development, physiology, ecology and evolution.     

Mutualism can mediate competition and promote coexistence

Mutualistic interactions are not believed to promote coexistence of competitors because mutualisms produce positive feedbacks on abundances whereas coexistence requires negative feedbacks. Here we show that a mutualism between an anemonefish (Amphiprion) and its sea anemone host mediates the effect of asymmetrical competition for space between the anemonefish and another damselfish (Dascyllus) in a manner that fosters their coexistence. Amphiprion stimulates increases in host area, the shared resource, but social interactions cap the number of anemonefish to two adults per host. Space generated by the mutualism becomes differentially available to Dascyllus because the effectiveness of an anemonefish in excluding its competitor declines with increases in the area it defends. This alters Amphiprion's ratio of per capita intra‐ to interspecific effects and thus facilitates coexistence of the fishes. This mechanism may be prevalent in nature, adding another major pathway by which mutualism can enhance diversity.     

Response to underwater laser pointer in the Orange-finned Anemonefish Amphiprion chrysopterus and three-spot damselfish Dascyllus trimaculatus

Response of orange-finned anemonefish Amphiprion chrysopterus and three-spot damselfish Dascyllus trimaculatus to red laser-pointer light was studied in Mo'orea, French Polynesia. Four magnificent anemones Heteractis magnifica and their resident fish were observed for typical behaviours (biting, chasing, hiding, posing, lunging and retreating) with and without exposure to laser-pointer light. Lunging behaviour increased significantly for both fish species upon exposure to laser-pointer light; none of the other behaviours changed significantly. We advance the hypothesis that orange-finned anemonefish and three-spot damselfish interpret laser pointer stimulation as a territorial threat.     

Host specialist clownfishes are environmental niche generalists

Why generalist and specialist species coexist in nature is a question that has interested evolutionary biologists for a long time. While the coexistence of specialists and generalists exploiting resources on a single ecological dimension has been theoretically and empirically explored, biological systems with multiple resource dimensions (e.g. trophic, ecological) are less well understood. Yet, such systems may provide an alternative to the classical theory of stable evolutionary coexistence of generalist and specialist species on a single resource dimension. We explore such systems and the potential trade-offs between different resource dimensions in clownfishes. All species of this iconic clade are obligate mutualists with sea anemones yet show interspecific variation in anemone host specificity. Moreover, clownfishes developed variable environmental specialization across their distribution. In this study, we test for the existence of a relationship between host-specificity (number of anemones associated with a clownfish species) and environmental-specificity (expressed as the size of the ecological niche breadth across climatic gradients). We find a negative correlation between host range and environmental specificities in temperature, salinity and pH, probably indicating a trade-off between both types of specialization forcing species to specialize only in a single direction. Trade-offs in a multi-dimensional resource space could be a novel way of explaining the coexistence of generalist and specialists.     

First draft genome of an iconic clownfish species (Amphiprion frenatus)

Clownfishes (or anemonefishes) form an iconic group of coral reef fishes, principally known for their mutualistic interaction with sea anemones. They are characterized by particular life history traits, such as a complex social structure and mating system involving sequential hermaphroditism, coupled with an exceptionally long lifespan. Additionally, clownfishes are considered to be one of the rare groups to have experienced an adaptive radiation in the marine environment. Here, we assembled and annotated the first genome of a clownfish species, the tomato clownfish (Amphiprion frenatus). We obtained 17,801 assembled scaffolds, containing a total of 26,917 genes. The completeness of the assembly and annotation was satisfying, with 96.5% of the Actinopterygii Benchmarking Universal Single‐Copy Orthologs (BUSCOs) being retrieved in A. frenatus assembly. The quality of the resulting assembly is comparable to other bony fish assemblies. This resource is valuable for advancing studies of the particular life history traits of clownfishes, as well as being useful for population genetic studies and the development of new phylogenetic markers. It will also open the way to comparative genomics. Indeed, future genomic comparison among closely related fishes may provide means to identify genes related to the unique adaptations to different sea anemone hosts, as well as better characterize the genomic signatures of an adaptive radiation.     

Behavioural acclimation to cameras and observers in coral reef fishes

Observer presence can bias behavioural studies of animals in both the wild and the laboratory. Despite existing evidence for significant observer effects across several taxa, little is known about the minimum periods of acclimation that should precede behavioural observations. To date, most studies either do not report any acclimation periods or include a non‐specific period without empirically quantifying its appropriateness. Here, we conducted in situ behavioural observations of two species of demersal coral reef fishes using cameras and/or observers to examine the biases associated with either approach. For both treatments, we generated 25 min time series of a number of vigilance‐associated behaviours (i.e., distance from shelter and mate, time out of shelter, swimming activity) and estimated the point of acclimation using changepoint analysis. In the camera trials, acclimation in both species appeared to occur between 2 and 7 min for different behaviours. When an observer was present, however, no apparent acclimation occurred until the observer left the area. Overall, our findings demonstrate that (i) behavioural studies of wild fishes conducted by an observer may be biased due to permanent observer effects, and (ii) when using video equipment, a species‐ and behaviour‐specific acclimation period should precede behavioural scoring.     

Eight microsatellite loci in Clark's anemonefish,Amphiprion clarkii

To determine the genetic relationship between different colour morphs (orange and black morphs) of Clark's anemonefish (Amphiprion clarkii) in Taiwan, we isolated eight polymorphic microsatellite loci. A large number of alleles (range, 6–30), and high levels of observed heterozygosity (range, 0.1231–0.8358) were resolved in 71 individuals from two populations, indicating that these markers should be useful in assessing the relationship between the two colour morphs of A. clarkii.     

Scaring Nemo: Contrasting effects of observer presence on two anemonefish species

Behaviours of Clark's anemonefish Amphiprion clarkii and the dusky anemonefish Amphiprion melanopus were studied in Vanuatu. Six anemones and their resident fish were observed for typical behaviours (hiding, watching, roaming, inter-, and intraspecific behaviour) with and without the presence of a snorkelling observer. Observer presence had significant but contrasting effects on hiding behaviour in A. clarkii and A. melanopus. Bolder anemonefish species may be able to outcompete other species in areas with high human presence.     

Co-existence of subadult males and females as alternative tactics of breeding post acquisition in a monogamous and protandrous anemonefish

Summary The monogamous and protandrous anemonefish,Amphiprion clarkii, utilizes only large host sea anemones as breeding sites. Under conditions of breeding site shortage, an important strategy for unmated fish may be to prepare themselves to enter quickly a breeding site from which a breeding male or female has recently disappeared. There are two types of subadults. Some juveniles become subadult males, which can change either to male or female afterwards, but others become subadult females, which can change only to female. Subadult females seem to acquire female posts more easily than subadult males. We develop an ESS model which evaluates the future reproductive success of subadult females and subadult males and test whether coexistence of subadult males and females can be interpreted as adaptive alternative tactics, using field data from two populations. The model predicts that if mortality does not differ between adult males and females the frequency for juveniles to become subadult females should be equal to the proportion of breeding post acquisition by subadult females among that by all subadults. The model also predicts that if mortality does not differ between subadult males and females, nor in adults, the frequency of subadult females among all subadults should be equal to the proportion of post acquisition. The model, with data from two study sites, suggests that alternative life-history pathways found inA. clarkii have evolved through adaptive tactics of breeding post acquisition.