Reproductive control via the threat of eviction in the clown anemonefish

Abstract

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.

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

“…Such individuals were classified as disappearances if they could not be found in any of the other anemones on the reef after careful inspection 35 . If introducees were still present, they were considered evicted if they spent more than 3 min out of 5 outside the anemone (i.e., with their full body length outside of the range of anemone tentacles) and considered tolerated if they were still present and spent less than 3 min outside of the anemone 48 . When the introduced non-breeder was less than 80% of the size of breeding male (rank 3’), it contested for a breeding position and was evicted in only 3/16 cases and it was tolerated in 13/16 cases.…”

Substantial plasticity of reproduction and parental care in response to local resource availability in a wild clownfish population

“…Fieldwork was conducted on ten discrete platform reefs near Mahonia Na Dari Research and Education Center in Kimbe Bay, Papua New Guinea (5°16'66.667''S 150° 5'E) using SCUBA. These nearshore reefs were located approximately 0.2–1.4 km from the shoreline and support a population of over 100 groups of Amphipirion percula living within magnificent sea anemones, Heteractis magnifica (Chausson et al 2018, Rueger et al 2018). In the two weeks prior to the start of the experiment, 117 groups were located and marked with numbered tags for identification.…”

Cooperative and aggressive behaviours vary between ranks in anemonefish social hierarchies

“…Our findings contribute to the growing body of literature disentangling the causes of sociality in groups of unrelated vertebrates. For anemonefishes, the reasons for subordinates to stay in groups of non-relatives and forego reproduction have been found to range from future fitness benefits through territory inheritance (Buston, 2004a), to the presence of social constraints (Buston, 2003c;Rueger et al, 2018) and environmental constraints (Branconi et al, 2020). However, why dominants tolerate unrelated, non-breeding subordinates has remained unclear, since subordinates have not been shown to directly increase dominant reproductive output, at least in the short term (Buston, 2004b).…”

“…While the two species both primarily inhabit the same anemone species, Heteractis magnifica, and are otherwise ecologically similar, differences in their behaviours have recently been reported. A. perideraion, particularly individuals at the top of the dominance hierarchy, have been observed leaving their anemone and forcefully taking over groups of A. percula (Rueger et al, 2018). In contrast, A. percula has been shown to not leave the confines of their host, even to bridge small distances (Branconi et al, in press).…”