Overview on the diversity of sounds produced by clownfishes (Pomacentridae): importance of acoustic signals in their peculiar way of life.

Background: Clownfishes (Pomacentridae) are brightly colored coral reef fishes well known for their mutualistic symbiosis with tropical sea anemones. These fishes live in social groups in which there is a size-based dominance hierarchy. In this structure where sex is socially controlled, agonistic interactions are numerous and serve to maintain size differences between individuals adjacent in rank. Clownfishes are also prolific callers whose sounds seem to play an important role in the social hierarchy. Here, we aim to review and to synthesize the diversity of sounds produced by clownfishes in order to emphasize the importance of acoustic signals in their way of life. Methodology/Principal Findings: Recording the different acoustic behaviors indicated that sounds are divided into two main categories: aggressive sounds produced in conjunction with threat postures (charge and chase), and submissive sounds always emitted when fish exhibited head shaking movements (i.e. a submissive posture). Both types of sounds showed size-related intraspecific variation in dominant frequency and pulse duration: smaller individuals produce higher frequency and shorter duration pulses than larger ones, and inversely. Consequently, these sonic features might be useful cues for individual recognition within the group. This observation is of significant importance due to the size-based hierarchy in clownfish group. On the other hand, no acoustic signal was associated with the different reproductive activities. Conclusions/Significance: Unlike other pomacentrids, sounds are not produced for mate attraction in clownfishes but to reach and to defend the competition for breeding status, which explains why constraints are not important enough for promoting call diversification in this group

Predation risk assessment by larval reef fishes during settlement-site selection

Predation rates of marine species are often highest during the transition from the pelagic to the benthic life stage. Consequently, the ability to assess predation risk when selecting a settlement site can be critical to survival. In this study, pairwise choice trials were used to determine whether larvae of three species of anemonefish (Amphiprion melanopus, A. percula and Premnas biaculeatus) are able to (1) assess the predation risk of potential anemone settlement sites through olfactory cues alone and (2) alter their settlement choices depending on the options available (host or non-host anemone). When predation risk was assessed with host and non-host anemone species independently, all species of anemonefish significantly chose the odor associated with the low-risk settlement option over the high-risk site. Most importantly, all species of anemonefish selected water with olfactory cues from their host anemone regardless of predation risk when paired against non-host anemone odor. These results demonstrate that larval reef fishes can use olfactory cues for complex risk assessment during settlement-site selection; however, locating the correct habitat is the most important factor when selecting a settlement site

Intrasexual competition and sexual selection in cooperative mammals

In most animals, the sex that invests least in its offspring competes more intensely for access to the opposite sex and shows greater development of secondary sexual characters than the sex that invests most1,2. However, in some mammals where females are the primary care-givers, females compete more frequently or intensely with each other than males3–5. A possible explanation is that, in these species, the resources necessary for successful female reproduction are heavily concentrated and intrasexual competition for breeding opportunities is more intense among females than among males. Intrasexual competition between females is likely to be particularly intense in cooperative breeders where a single female monopolizes reproduction in each group6. Here, we use data from a twelve-year study of wild meerkats (Suricata suricatta), where females show high levels of reproductive skew, to show that females gain greater benefits from acquiring dominant status than males and traits that increase competitive ability exert a stronger influence on their breeding success. Females that acquire dominant status also develop a suite of morphological, physiological and behavioural characteristics that help them to control other group members. Our results show that sex differences in parental investment are not the only mechanism capable of generating sex differences in reproductive competition and emphasize the extent to which competition for breeding opportunities between females can affect the evolution of sex differences and the operation of sexual selection