Cleaner wrasse indirectly affect the cognitive performance of a damselfish through ectoparasite removal

Abstract

Cleaning organisms play a fundamental ecological role by removing ectoparasites and infected tissue from client surfaces. We used the well-studied cleaning mutualisms involving the cleaner wrasse, to test how client cognition is affected by ectoparasites and whether these effects are mitigated by cleaners. Ambon damselfish ( collected from experimental reef patches without cleaner wrasse performed worse in a visual discrimination test than conspecifics from patches with cleaners. Endoparasite abundance also negatively influenced success in this test. Visual discrimination performance was also impaired in damselfish experimentally infected with gnathiid (Crustacea: Isopoda) ectoparasites. Neither cleaner absence nor gnathiid infection affected performance in spatial recognition or reversal learning tests. Injection with immune-stimulating lipopolysaccharide did not affect visual discrimination performance relative to saline-injected controls, suggesting that cognitive impairments are not due to an innate immune response. Our results highlight the complex, indirect role of cleaning organisms in promoting the health of their clients via ectoparasite removal and emphasize the negative impact of parasites on host's cognitive abilities.

Host Cognition and Parasitism in Birds: A Review of the Main Mechanisms

“…In line with the idea that host behavior can be altered by pathogen infection, especially via a change in the host state (e.g., body condition), pathogen infection may cause a decrease in cognitive performance. For example, in the Ambon damselfish (Pomacentrus amboinensis), experimental infection with gnathiid parasites decreased individual performance at a visual discrimination test (Binning et al, 2018). To our knowledge, there is no direct evidence of a change in cognition after a pathogen infection in wild birds.…”

“…Developing such a framework has been particularly challenging because the causality of associations between parasites and cognition takes a variety of forms and can even change direction depending on the scenario, making it difficult to make unique, falsifiable predictions. Cognition can be affected by parasites: for example, most infections by pathogens can directly impair animal cognitive performance (Binning et al, 2018). However, cognition can also affect parasitism, e.g., by allowing a host to learn to avoid being exposed to pathogens (Zhang et al, 2005).…”

“…(2017) for more information. Research on other vertebrate taxa, including mammals (particularly primates and rodents, e.g., see McCabe et al, 2014;Kavaliers and Choleris, 2018) and fish (e.g., Kotrschal et al, 2016;Binning et al, 2018), have also been conducted, providing insights into the mechanisms that may also be at play in birds, and we discuss key results stemming from studies on other taxa when relevant. Our literature review (summarized in Table 1) shows that the association between host cognition and the richness, prevalence and intensity of parasites has rarely been investigated in wild birds.…”

Aquatic Parasite Cultures and Their Applications

“…Clients exposed to gnathiids spent more time seeking cleaners, showing parasite infection is a proximate cause of cleaning [110]. Client visual discrimination was reduced in gnathiid-exposed fish, providing a mechanism for how long-term cleaner presence in the wild similarly affected clients [9]. [13,143]…”

“…The current impetus to culture parasites is driven by the need for fundamental and applied research to support human and animal health agendas. Successful, continuous aquatic parasite cultures can be maintained for years or even decades [6][7][8][9][10][11], yet short term cultures may also be valuable for targeted experiments or the production of parasite tissues free of host contaminants. Indeed, many successful helminth culture media were developed from short-term maintenance media used in biochemical experiments.…”