Competitive growth in a social fish

Abstract

Many animal societies have dominance hierarchies in which social rank is correlated with size. In such societies, the growth and size of individuals can be a strategic response to their social environment: in fishes, individuals may decrease their growth rate to remain small and retain a subordinate position; in mammals, individuals may increase their growth rate to become large and attain a dominant position—a strategy called competitive growth. Here, we investigate whether the clown anemonefish, Amphiprion percula , exhibits competitive growth also. We show that juvenile clownfish paired with a size-matched reproductive rival increase their growth rate and size relative to solitary controls. Remarkably, paired individuals achieved this, despite being provided with the same amount of food as solitary controls. Our results demonstrate that clownfish are able to increase their growth rate in response to social competition. This study adds to the growing body of evidence that the growth of social vertebrates can be a fine-tuned plastic response to their social environment.

Spontaneous alloparental care of unrelated offspring by non-breeding Amphiprion ocellaris in absence of the biological parents

“…Hence, the experience would be for nothing, as the females are not the primary care-givers 37 and with the male and female eliminated, the non-breeder would unlikely have an opportunity to mate in a male role. Under these conditions, to enhance individual fitness, a better strategy would seem to be for the non-breeder to consume the eggs and build somatic growth, especially since substantial growth is known to precede sex change in A. ocellaris 24,47 . Hence, the unconditional fathering behavior seems to, if anything, impair fitness slightly when the biological parents are displaced, which favors the spandrel hypothesis over adaptation.…”

Sensory cues underlying competitive growth in the clown anemonefish (Amphiprion percula)

“…In many of these societies, access to breeding positions is determined by individuals' social rank (Drummond 2006) which in turn, partially or fully depends on individual's size (Reeve et al 1998, Clutton-Brock et al 2006). In such societies, where breeding opportunities depends on individual's social rank and size, selection may favor growth and size modification strategies that maximize an individual's chances of maintaining their current rank or attaining a higher rank (Buston 2003, Wong et al 2007, Huchard et al 2016, Reed et al 2019. For example, in clown anemonefish (Amphiprion percula) and emerald coral gobies (Paragobiodon xanthosomus) in stable dominance hierarchies, individuals will reduce their growth rate to avoid coming into conflict with their immediate dominants and thereby maximize their chances of inheriting breeding positions (Buston 2003a, Buston 2004a, Wong et al 2007).…”

“…that lives in anemones on IndoPacific coral reefs. Amphiprion percula live in social groups composed of a breeding pair and zero to four nonbreeders, in which individuals adjust their growth and size in response to other group members (Buston 2003a, Buston and Cant 2006, Reed et al 2019.…”

“…At the initiation of size hierarchies, clownfish individuals increase their growth rate to outcompete their rivals and attain the highest dominance rank without conflict (Reed et al 2019). How clownfish are able to assess their own size, the size of others, and adjust their growth accordingly remains an open question.…”

“…Auditory sensory signals such as dominant frequency and pulse duration convey information regarding fish size and hypothetically could be used to assess size and recognize individuals within a group (Colleye and Parmentier 2012). Here, to assess the type of sensory cues required for clownfish individuals to engage in competitive growth [e.g., mechanosensory (pressure and/or touch), auditory, chemosensory, and/or visual] we use a suite of experiments, in which we size match individuals in an experimental design analogous to that of Reed et al (2019) but selectively block different types of cues across different treatments. We test four main hypotheses regarding the sensory cues required for size-matched individuals to engage in competitive growth: 1) they must have mechanosensory (pressure and/or touch) cues; 2) they must have auditory cues; 3) they must have chemical cues; 4) they must have visual cues.…”