Membrane lipids and maximum lifespan in clownfish

The longevity-homeoviscous adaptation (LHA) theory of ageing states that lipid composition of cell membranes is linked to metabolic rate and lifespan, which has been widely shown in mammals and birds but not sufficiently in fish. In this study, two species of the genus Amphiprion (Amphiprion percula and Amphiprion clarkii, with estimated maximum lifespan potentials [MLSP] of 30 and 9–16 years, respectively) and the damselfish Chromis viridis (estimated MLSP of 1–2 years) were chosen to test the LHA theory of ageing in a potential model of exceptional longevity. Brain, livers and samples of skeletal muscle were collected for lipid analyses and integral part in the computation of membrane peroxidation indexes (PIn) from phospholipid (PL) fractions and PL fatty acid composition. When only the two Amphiprion species were compared, results pointed to the existence of a negative correlation between membrane PIn value and maximum lifespan, well in line with the predictions from the LHA theory of ageing. Nevertheless, contradictory data were obtained when the two Amphiprion species were compared to the shorter-lived C. viridis. These results along with those obtained in previous studies on fish denote that the magnitude (and sometimes the direction) of the differences observed in membrane lipid composition and peroxidation index with MLSP cannot explain alone the diversity in longevity found among fishes.

Rank Change and Growth Within Social Hierarchies of the Orange Clownfish, Amphiprion Percula

Social hierarchies within groups define the distribution of resources and provide benefits that support the collective group or favor dominant members. The progression of individuals through social hierarchies is a valuable characteristic for quantifying population dynamics. On coral reefs, a number of small site-attached fish maintain size-based hierarchical communities where individuals queue through social ranks. The cost of waiting in a lower-ranked position is outweighed by the reduced risk of eviction and mortality. Clownfish exist in stable social groups with subordinate individuals queuing to be part of the dominant breeding pair. Site attachment to their host anemone, complex social interactions, and relatively low predation rates make them ideal model organisms to assess changes in group dynamics through time in their natural environment. Here, we investigate the rank changes, and isometric growth rates of individual orange clownfish, Amphiprion percula, from 247 naturally occurring social groups in Kimbe Island, Papua New Guinea (5°12’13.54” S, 150°22’32.69” E). We use DNA profiling to assign and track individuals over an eight-year time period in 2011 and 2019. Over half of the individuals survived alongside two or three members of their original social group, with twelve breeding pairs persisting over the study period. Half of the surviving individuals increased in rank and experienced double the growth rate of those that maintained their rank. Examining rank change over a long-term period in a wild fish population gives new insights and highlights the complexity and importance of rank and social hierarchy in communal site-attached reef fish.Subject Area: behavior, ecology, evolution

Thyroid hormones regulate the formation and environmental plasticity of white bars in clownfishes

Determining how plasticity of developmental traits responds to environmental conditions is a challenge that must combine evolutionary sciences, ecology, and developmental biology. During metamorphosis, fish alter their morphology and color pattern according to environmental cues. We observed that juvenile clownfish (Amphiprion percula) modulate the developmental timing of their adult white bar formation during metamorphosis depending on the sea anemone species in which they are recruited. We observed an earlier formation of white bars when clownfish developed with Stichodactyla gigantea (Sg) than with Heteractis magnifica (Hm). As these bars, composed of iridophores, form during metamorphosis, we hypothesized that timing of their development may be thyroid hormone (TH) dependent. We treated clownfish larvae with TH and found that white bars developed earlier than in control fish. We further observed higher TH levels, associated with rapid white bar formation, in juveniles recruited in Sg than in Hm, explaining the faster white bar formation. Transcriptomic analysis of Sg recruits revealed higher expression of duox, a dual oxidase implicated in TH production as compared to Hm recruits. Finally, we showed that duox is an essential regulator of iridophore pattern timing in zebrafish. Taken together, our results suggest that TH controls the timing of adult color pattern formation and that shifts in duox expression and TH levels are associated with ecological differences resulting in divergent ontogenetic trajectories in color pattern development.

Diel CO2 fluctuations alter the molecular response of coral reef fishes to ocean acidification conditions

Environmental CO2 variation can modify the responses of marine organisms to ocean acidification, yet the underlying mechanisms for this effect remain unclear. On coral reefs, environmental CO2 fluctuates on a regular day-night cycle. Effects of future ocean acidification on coral reef fishes might therefore depend on their response to this diel cycle of CO2. To evaluate the effects on the brain molecular response, we exposed two common reef fishes (Acanthochromis polyacanthus and Amphiprion percula) to two projected future CO2 levels (750 and 1,000 microatmospheres) under both stable and diel fluctuating conditions. We found a common signature to stable elevated pCO2 for both species, which included the downregulation of immediate early genes, indicating lower brain activity. The transcriptional program was more strongly affected by higher average CO2 in a stable treatment than for fluctuating treatments, however, the largest difference in molecular response was between stable and fluctuating CO2 treatments. This indicates that a response to a change in environmental CO2 conditions is different for organisms living in a fluctuating than in stable environments. The differential regulation was related to steroid hormones and circadian rhythm (CR). Both species exhibited a marked difference in the expression of CR genes among CO2 treatments, possibly accommodating a more flexible adaptive approach to acid-base control, which could explain reduced impairment. Our results suggest that environmental CO2 fluctuations might enable reef fishes to phase shift their clocks and anticipate CO2 changes, thereby avoiding impairments and more successfully adjust to ocean acidification conditions.

Assessing the impact of static and fluctuating ocean acidification on the behavior of Amphiprion percula

Coral reef organisms are exposed to both an increasing magnitude of pCO2, and natural fluctuations on a diel scale. For coral reef fishes, one of the most profound effects of ocean acidification is the impact on ecologically important behaviors. Previous behavioral research has primarily been conducted under static pCO2 conditions and have recently come under criticism. Recent studies have provided evidence that the negative impacts on behavior may be reduced under more environmentally realistic, fluctuating conditions. We investigated the impact of both present and future day, static (500 and 1000 μatm) and diel fluctuating (500 ± 200 and 1000 ± 200 μatm) pCO2 on the lateralization and chemosensory behavior of juvenile anemonefish, Amphiprion percula. Our static experimental comparisons support previous findings that under elevated pCO2, fish become un-lateralized and lose the ability to discriminate olfactory cues. Diel-fluctuating pCO2 may aid in mitigating the severity of some behavioral abnormalities such as the chemosensory response, where a preference for predator cues was significantly reduced under a future diel-fluctuating pCO2 regime. This research aids in ground truthing earlier findings and contributes to our growing knowledge of the role of fluctuating conditions.

Ecological and social constraints combine to promote evolution of non-breeding strategies in clownfish

Individuals that forgo their own reproduction in animal societies represent an evolutionary paradox because it is not immediately apparent how natural selection can preserve the genes that underlie non-breeding strategies. Cooperative breeding theory provides a solution to the paradox: non-breeders benefit by helping relatives and/or inheriting breeding positions; non-breeders do not disperse to breed elsewhere because of ecological constraints. However, the question of why non-breeders do not contest to breed within their group has rarely been addressed. Here, we use a wild population of clownfish (Amphiprion percula), where non-breeders wait peacefully for years to inherit breeding positions, to show non-breeders will disperse when ecological constraints (risk of mortality during dispersal) are experimentally weakened. In addition, we show non-breeders will contest when social constraints (risk of eviction during contest) are experimentally relaxed. Our results show it is the combination of ecological and social constraints that promote the evolution of non-breeding strategies. The findings highlight parallels between, and potential for fruitful exchange between, cooperative breeding theory and economic bargaining theory: individuals will forgo their own reproduction and wait peacefully to inherit breeding positions (engage in cooperative options) when there are harsh ecological constraints (poor outside options) and harsh social constraints (poor inside options).

Studi Awal: Persentase Penetasan dan Performa Pertumbuhan Benih Ikan Clown (Amphiprion percula)

AbstrakPermintaan ikan clown (Amphiprion percula) saat ini cukup tinggi, baik untuk pemenuhan pasar dalam negeri dan pengiriman ke luar negeri. Perkembangan kondisi pasar yang menggiurkan tersebut, tentu akan memacu para eksportir untuk mengeksploitasi sumber dialam secara tidak terkendali. Tujuan dari studi ini adalah untuk menghitung persentase penetasan dan performa pertumbuhan benih ikan clown. Studi ini dilaksanakan di Balai Perikanan Budidaya Laut (BPBL) Lombok, Nusa Tenggara Barat. Studi ini menggunakan metode observasi secara langsung pada wadah pembenihan dan pemeliharaan larva ikan clown. Induk ikan clown dipijahkan pada akuarium ukuran 0,4 m × 0,3 m × 0,5 m. Jumlah telur yang dihasilkan bervariasi sekitar 403-698 butir/induk dengan persentase fertilisasi dan penetasan, masing-masing sebesar 97,29 dan 82,87 %.. Selanjutnya larva dan benih ikan dipelihara di bak beton dengan ukuran 2 m × 2 m × 1 m. Persentase kelangsungan hidup benih mencapai 98,33 % dan peningkatan bobot tubuh rerata setiap minggu adalah 0,332 , 0,343, 0,388, dan 0,421 g. Budidaya ikan clown di darat dengan kelangsungan hidup tinggi dapat mengurangi tingkat eksploitasi ikan clown di alam dan kebutuhan akan ekspor ikan hias dapat terpenuhi.Kata kunci- Amphiprion percula, pembenihan, pembesaran benih, hatching rate, survival rate