Reproductive control via the threat of eviction in the clown anemonefish

Social regulation of reproduction: control or signal?

Traditionally, dominant breeders have been considered to be able to control the reproduction of other individuals in multimember groups that have high variance in reproductive success/reproductive skew (e.g., forced sterility/coercion of conspecifics in eusocial animals; sex-change suppression in sequential hermaphrodites). These actions are typically presented as active impositions by reproductively dominant individuals. However, how can individuals regulate the reproductive physiology of others? Alternatively, all contestants make reproductive decisions, and less successful individuals self-downregulate reproduction in the presence of dominant breeders. Shifting perspective from a top-down manipulation to a broader view, which includes all contenders, and using a multitaxon approach, we propose a unifying framework for the resolution of reproductive skew conflicts based on signalling rather than control, along a continuum of levels of strategic regulation of reproduction.

Review of housing and husbandry of anemonefishes for use in research

Anemonefishes of the genus Amphiprion are emerging as a model organism for marine science, so there is potentially a lot for the research community to gain by optimizing and standardizing housing and husbandry protocols. Here, we conducted a literature review and a questionnaire survey regarding the housing and husbandry of anemonefishes for use in research. The questionnaire survey was completed by 27 laboratories, with a 45% response rate, across 11 different countries in Europe, North America, Asia and Australia. Results from the literature review identified that housing and husbandry protocols varied widely in terms of tank volume, diet composition and lighting type for the housing of broodstock pairs. These results also emphasize the significant impacts that variation in housing and husbandry protocols have on fish. Results from the questionnaire survey confirmed this. We identified multiple opportunities for improvement of protocols, including the potential for exchange of larvae between laboratories to create strains and reduce pressure on natural populations. In conclusion, our research suggests that the anemonefish research community should be discussing the optimization and standardization of housing and husbandry or, minimally, recognizing that housing and husbandry influence a wide range of traits and will influence the results and conclusions drawn from experiments.

Higher ultraviolet skin reflectance signals submissiveness in the anemonefish, Amphiprion akindynos

Ultraviolet (UV) vision is widespread among teleost fishes, of which many exhibit UV skin colors for communication. However, aside from its role in mate selection, few studies have examined the information UV signaling conveys in other socio-behavioral contexts. Anemonefishes (subfamily, Amphiprioninae) live in a fascinating dominance hierarchy, in which a large female and male dominate over non-breeding subordinates, and body size is the primary cue for dominance. The iconic orange and white bars of anemonefishes are highly UV-reflective, and their color vision is well tuned to perceive the chromatic contrast of skin, which we show here decreases in the amount of UV reflectance with increasing social rank. To test the function of their UV-skin signals, we compared the outcomes of staged contests over dominance between size-matched Barrier Reef anemonefish (Amphiprion akindynos) in aquarium chambers viewed under different UV-absorbing filters. Fish under UV-blocking filters were more likely to win contests, where fish under no-filter or neutral-density filter were more likely to submit. For contests between fish in no-filter and neutral density filter treatments, light treatment had no effect on contest outcome (win/lose). We also show that sub-adults were more aggressive toward smaller juveniles placed under a UV filter than a neutral density filter. Taken together, our results show that UV reflectance or UV contrast in anemonefish can modulate aggression and encode dominant and submissive cues, when changes in overall intensity are controlled for.

Towards an absolute light pollution indicator

The growing concern about the negative impact of artificial light at night on biodiversity and human health increases the need of defining a general indicator that could be used for characterizing light pollution as well as performing both spatial and temporal comparisons. In this paper, we show that the traditional indicators based on direct numerical measurements of sky brightness suffer from significant limitation due to calibration bias and lack of reproducibility. Furthermore, these measures are most often performed in periods of clear sky. They do not reflect the wide variety of meteorological conditions that can produce highly inhomogeneous levels of light pollution on a given site. To overcome these issues, we propose a statistical indicator called NSB Dispersion Ratio. This indicator is derived from a statistically significant number of individual night sky brightness measurements, under various meteorological conditions. It is independent of any absolute photometer calibration. It only requires on-time precise corrections of the contribution of natural light sources such as the Galactic plane.

Negotiations over parental care: a test of alternative hypotheses in the clown anemonefish

In species with biparental care, conflict arises over how much each parent provides to their offspring because both parents benefit from shifting the burden of care to the other. Here, we tested alternative hypotheses for how parents will negotiate offspring care using a wild population of clownfish (Amphiprion percula). We experimentally handicapped parents by fin-clipping the female in 23 groups, the male in 23 groups, and neither parent in 23 groups and measured changes in indicators of female, male, and pair effort in response to handicapping. First, we found that handicapping resulted in a decrease in the number of eggs laid by fin-clipped females and a decrease in the amount of parental care by fin-clipped males. Second, contrary to predictions, female effort did not change in response to the male being handicapped, or vice versa. Finally, the number of embryos that matured to hatching, an indicator of pair effort, was not influenced by the manipulation, suggesting that although the handicap was effective, clownfish do not face the predicted “cost to conflict” when one parent is handicapped. Together, these results test the generality of theoretical predictions and uncover novel questions about whether and how negotiations operate in systems where interests are aligned.

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).

Anemonefish, a model for Eco-Evo-Devo

Anemonefish, are a group of about 30 species of damselfish (Pomacentridae) that have long aroused the interest of coral reef fish ecologists. Combining a series of original biological traits and practical features in their breeding that are described in this paper, anemonefish are now emerging as an experimental system of interest for developmental biology, ecology and evolutionary sciences. They are small sized and relatively easy to breed in specific husbandries, unlike the large-sized marine fish used for aquaculture. Because they live in highly structured social groups in sea anemones, anemonefish allow addressing a series of relevant scientific questions such as the social control of growth and sex change, the mechanisms controlling symbiosis, the establishment and variation of complex color patterns, and the regulation of aging. Combined with the use of behavioral experiments, that can be performed in the lab or directly in the wild, as well as functional genetics and genomics, anemonefish provide an attractive experimental system for Eco-Evo-Devo.

Reproductive control via the threat of eviction in the clown anemonefish

In social groups, high reproductive skew is predicted to arise when the reproductive output of a group is limited, and dominant individuals can suppress subordinate reproductive efforts. Reproductive suppression is often assumed to occur via overt aggression or the threat of eviction. It is unclear, however, whether the threat of eviction alone is sufficient to induce reproductive restraint by subordinates. Here, we test two assumptions of the restraint model of reproductive skew by investigating whether resource limitation generates reproductive competition and whether the threat of eviction leads to reproductive restraint in the clown anemonefish Amphiprion percula First, we use a feeding experiment to test whether reproduction is resource limited, which would create an incentive for the dominant pair to suppress subordinate reproduction. We show that the number of eggs laid increased in the population over the study period, but the per cent increase in fed groups was more than twice that in unfed groups (205% and 78%, respectively). Second, we use an eviction experiment to test whether the dominant pair evicts mature subordinates, which would create an incentive for the subordinates to forgo reproduction. We show that mature subordinates are seven times more likely to be evicted than immature subordinates of the same size. In summary, we provide experimental support for the assumptions of the restraint model by showing that resource limitation creates reproductive competition and a credible threat of eviction helps explain why subordinates forego reproduction. Transactional models of reproductive skew may apply well to this and other simple systems.