Cohabitation promotes high diversity of clownfishes in the Coral Triangle

Abstract

Global marine biodiversity peaks within the Coral Triangle, and understanding how such high diversity is maintained is a central question in marine ecology. We investigated broad-scale patterns in the diversity of clownfishes and their host sea anemones by conducting 981 belt-transects at 20 locations throughout the Indo-Pacific. Of the 1508 clownfishes encountered, 377 fish occurred in interspecific cohabiting groups and cohabitation was almost entirely restricted to the Coral Triangle. Neither the diversity nor density of host anemone or clownfish species alone influenced rates of interspecific cohabitation. Rather cohabitation occurred in areas where the number of clownfish species exceeds the number of host anemone species. In the Coral Triangle, cohabiting individuals were observed to finely partition their host anemone, with the subordinate species inhabiting the periphery. Furthermore, aggression did not increase in interspecific cohabiting groups, instead dominant species were accepting of subordinate species. Various combinations of clownfish species were observed cohabiting (independent of body size, phylogenetic relatedness, evolutionary age, dentition, level of specialization) in a range of anemone species, thereby ensuring that each clownfish species had dominant reproductive individuals in some cohabiting groups. Clownfishes are obligate commensals, thus cohabitation is an important process in maintaining biodiversity in high diversity systems because it supports the persistence of many species when host availability is limiting. Cohabitation is a likely explanation for high species richness in other obligate commensals within the Coral Triangle, and highlights the importance of protecting these habitats in order to conserve unique marine biodiversity.

Host identity and symbiotic association affects the taxonomic and functional diversity of the clownfish-hosting sea anemone microbiome

“…The clownfish-sea anemone symbiosis is found across a range of reef habitats and involves many combinations of sea anemoneclownfish associations [21,[23][24][25][26][27]. Clownfishes are considered obligate symbionts of sea anemones, have evolved a range of host specificities, and are never found solitarily [21,27]. Anemones in contrast, while receiving substantial benefits from hosting clownfishes [28,29], can be found solitarily [25].…”

Host identity and symbiotic association affects the genetic and functional diversity of the clownfish-hosting sea anemone microbiome

“…Within sea anemones (Order Actiniaria), symbiosis with clownfishes has evolved independently at least three times [24]. The clownfish-sea anemone symbiosis is found across a range of coral reef habitats and involves many combinations of sea anemone-clownfish associations that are co-distributed [21, 23-27]. Clownfishes are considered obligate symbionts of sea anemones, have evolved a range of host specificities, and are never found solitarily [21, 27].…”

“…The clownfish-sea anemone symbiosis is found across a range of coral reef habitats and involves many combinations of sea anemone-clownfish associations that are co-distributed [21, 23-27]. Clownfishes are considered obligate symbionts of sea anemones, have evolved a range of host specificities, and are never found solitarily [21, 27]. Anemones in contrast, while receiving substantial benefits from hosting clownfishes [28, 29], can be found solitarily [25].…”

Scary clowns: adaptive function of anemonefish coloration

“…Only the two largest individuals reproduce, the largest dominant individual being the female and the second largest individual the male (Fricke & Fricke 1977). In regions where the number of anemonefish species exceeds the number of anemone species, more than one group of different anemonefish species often share an individual host, in which case there is a dominance hierarchy between the species (Camp et al, 2016). Yet, cohabitation does not increase the amount of aggressive interactions, which are hence more likely to occur between individuals of the same species (Camp et al, 2016).…”

“…In regions where the number of anemonefish species exceeds the number of anemone species, more than one group of different anemonefish species often share an individual host, in which case there is a dominance hierarchy between the species (Camp et al, 2016). Yet, cohabitation does not increase the amount of aggressive interactions, which are hence more likely to occur between individuals of the same species (Camp et al, 2016). Because behavioural conflicts among individuals are costly (Mitchell & Dill, 2005), one possibility is that interspecific aggressive interactions are avoided using body coloration as a signal for species recognition.…”