Tuesday, June 14, 2016

Punishment in Cleaner Fish, by Saghar Qadir

How do male cleaner fish “punishing” female cleaner fish affect the symbiotic relationship between cleaner fish and other species?  What are the costs and rewards of this distinct behavior?  Punishment is a form of intricate interaction that was considered to be carried out solely by the human species to alter cooperation in one way or another. However, recent studies have proven this belief false by observing behavior of a fish underwater.  The fish, Bluestreak Cleaner Wrasse Labroides dimidiatus, has a significantly smaller brain than humans.  Labroides dimidiatus, more commonly referred to as the cleaner wrasse. This unique species of marine fish thrive off of a symbiotic relationship with their “clients” where they provide grooming services for other fish species in response to nutrients and evasion from predation. 
Cleaner fish with host damselfish.  Photo by Richard Smith Source
 Obstacles to this relationship created by outlaw Cleaner fish causing reduced fitness result in punishment. This species essentially runs its underwater ‘spa’ while attending to their customers in pairs of male and female. However, this business does not hold the best reputation in the ocean as often time, one fish in the pair will tend to cheat and bite off more than it is expected to. In other words, it takes a chunk off of the client’s mucus membrane in addition to the ectoparasites. This results in the client swimming away and reduced fitness for both of the fish, even though only one cheated. This reduction in fitness leads to punishment where a fish would chase the criminal aggressively, but strangely, only the female wrasses get punished. This may have been a result of various evolutionary processes but it leads to various situations and restrictions regarding fitness, with males ensuring their position as the reproductive competitors.
            Cleaner wrasses avoid predation by providing a service to several species of fish in the reef. This relationship is proven in results of several studies but one of the most significant was conducted by Karen Cheney of the University of Queensland in Australia. In the study, a mimic of the juvenile cleaner wrasse Labroides dimidiatus, also known by the name of the Bluestriped Fangblenny was observed. Even though Fangblennies attack reef fish, they use mimicry to wrasses to avoid predation. It was found that this species can change to the mimic coloration within 5-10 minutes depending on the presence of the wrasse (Cheney et al. 2013). It is definitely a possibility that this mimic species affects the fitness of the cleaner wrasse in a negative way by making potential clients wary of the actual cleaner wrasse itself. (Cheney et al. 2013).
              The primary and most significant factor affecting fitness comes from clients. Clients will tend to avoid stations at which they have not been treated well in the past. This will greatly reduce fitness of both the male and female since there will be less nutrients available to them. In a male dominated population, a smaller male resulting from less nutrients available will have significantly lower reproductive success when it comes to competition. In certain cases, cheating by female wrasses will lead to a point where they will get as big in size as the male wrasses and consequently, change their sex due to their hermaphroditic nature. Since this species relies on size-based dominance hierarchies, and this species is able to change sex if it reaches a certain size (With the exception of the Carribean cleaner), punishment is a crucial factor for males in the society. The male has to ensure that the female partner does not outgrow him and change its sex to become a reproductive competitor. In this situation, the female proceeds to become a competitor with the male wrasses for client territory. 
Bluestreak Cleaner Wrasse with Moray Eel host.
There have been several scientific experiments carried out on the behavior of wrasses with their client and how it affects the relationship between the competing male wrasses, and the wrasse couples that include the male and female. In one study, pairs of cleaners were exposed to a model client offering either prawn items which were more preferred, or flake items which were less preferred and used to imitate ecto-parasites. When the model client was removed as the consequence of the wrasse eating the prawn items (analogous to client mucus), the severity of male punishment was based on the actual pay-off reduction from the client lost. More severe punishments lead to higher female cooperation only until the female gains advantage in size through the foraging benefits obtained from cheating. In this inverse relationship, the bigger the female gets in size through foraging advantages derived from cheating, the smaller the male gets through two factors: Firstly, the male will be unable to obtain nutrition from the ecto-parasites and secondly, the male loses the client from his “spa” forever while the female has already benefited from cheating. Therefore, this dilemma eventually allows the female to surpass the male in size and become a reproductive competitor by changing her sex due to the hermaphroditic nature of the species. Hence, the male has to ensure that the cost the punishing has on his fitness is worth the punishment so the female is prevented from cheating again and getting larger in size. (Raihani et al. 2011) Other studies have demonstrated that this relationship is not only a simple all or none type of punishment cooperation relationship, but more of a carefully evolved relationship where the amount of punishment is elaborately calculated in response to the intensity of the payoff lost. Additionally, other methods of intricate control are also employed by male wrasses depending on the cheating which include sanctions and partner switching. Results showing different forms of punishment for different cheating behaviors prove that these punishment responsive cooperations have developed and adjusted over numerous amounts of years as a results of evolution when compared to a non-cleaning fish species Halichoeres melanurus, which showed no difference in foraging behavior under the same conditions. (Gingins et al. 2013)
When it comes to collateral effects of cleaner fish on other species and the coral reef habitat, it was found that cleaner fish are extremely beneficial to the coral reef habitat and species that it hosts. In a study carried out on the coral reef, patch reefs with and without cleaner fish were observed for populations and fitness of client fish. It was found that individuals in reef patches without the cleaner fish were smaller, 37% less abundant and 23% less species rich when compared to control reef patches with the cleaner fish. This demonstrates that cleaner fish behavior has community-wide effects and is beneficial to client fish. Additional evidence also suggested that juveniles were 65% less abundant which points to lower survivorship (Waldie et al. 2011).  This evidence proves that the cleaner wrasse qualifies as a keystone species in a coral reef and impacts the health of all fish species in the habitat by playing the role of the doctor.
Cheney, K.L. 2013.  Cleaner fish coloration decreases predation risk in aggressive fangblenny mimics.  Behavioral Ecology  doi: 10.1093/beheco/art043 

Gingins, S., J. Werminghausen, R.A. Johnstone, A.S. Grutter, and R. Bshary. 2013. Power and temptation cause shifts between exploitation and cooperation in a cleaner wrasse mutualism.  Proceedings of the Royal Society B. DOI: 10.1098/rspb.2013.0553    

Raihani, N J., A.I. Pinto, A.S. Grutter, S. Wismer, and R. Bshary. 2011.  Male cleaner wrasses adjust punishment of female partners according to the stakes.  Proceedings of the Royal Society B.  DOI: 10.1098/rspb.2011.0690        

Waldie, P.A., S.P. Blomberg, K.L. Cheney, A.W. Goldizen, and A.S. Grutter.  2011.  Long-term effects of the cleaner fish Labroides dimidiatus on coral reef fish communities.  PLOS ONE     http://dx.doi.org/10.1371/journal.pone.0021201         

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