Further evidence for the capacity of mirror self-recognition in cleaner fish and the significance of ecologically relevant marks.

Masanori Kohda,Satoshi Awata,Redouan Bshary,Akane Fujita,Shumpei Sogawa,Taiga Kobayashi,Naoki Kubo,Alex L. Jordan,Shun Satoh,Frans B. M. de Waal

doi:10.1371/journal.pbio.3001529

Masanori Kohda, Satoshi Awata + Show 8 more

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https://doi.org/10.1371/journal.pbio.3001529

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Abstract

An animal that tries to remove a mark from its body that is only visible when looking into a mirror displays the capacity for mirror self-recognition (MSR), which has been interpreted as evidence for self-awareness. Conservative interpretations of existing data conclude that convincing evidence for MSR is currently restricted to great apes. Here, we address proposed shortcomings of a previous study on MSR in the cleaner wrasse Labroides dimidiatus, by varying preexposure to mirrors and by marking individuals with different colors. We found that (1) 14/14 new individuals scraped their throat when a brown mark had been provisioned, but only in the presence of a mirror; (2) blue and green color marks did not elicit scraping; (3) intentionally injecting the mark deeper beneath the skin reliably elicited spontaneous scraping in the absence of a mirror; (4) mirror-naive individuals injected with a brown mark scraped their throat with lower probability and/or lower frequency compared to mirror-experienced individuals; (5) in contrast to the mirror images, seeing another fish with the same marking did not induce throat scraping; and (6) moving the mirror to another location did not elicit renewed aggression in mirror-experienced individuals. Taken together, these results increase our confidence that cleaner fish indeed pass the mark test, although only if it is presented in ecologically relevant contexts. Therefore, we reiterate the conclusion of the previous study that either self-awareness in animals or the validity of the mirror test needs to be revised.

Highlights

Passing the mark test, in which subject animals touch or scrape a mark placed on their body in a location that can only be indirectly viewed in mirror, demonstrates the capacity for mirror self-recognition (MSR), which has been interpreted as evidence for self-awareness (e.g., [1–7])
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In which subject animals touch or scrape a mark placed on their body in a location that can only be indirectly viewed in mirror, demonstrates the capacity for mirror self-recognition (MSR), which has been interpreted as evidence for self-awareness (e.g., [1–7])

Summary

Introduction

In which subject animals touch or scrape a mark placed on their body in a location that can only be indirectly viewed in mirror, demonstrates the capacity for mirror self-recognition (MSR), which has been interpreted as evidence for self-awareness (e.g., [1–7]). Variations of this test have been applied to many species of vertebrates. The results are clearly negative, including studies on lesser apes, monkeys, pig, dog, cat, panda, crows, and parrots (e.g., [1–2,5,8–16]). A small number of socially intelligent species including.

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