Posts

Cleaner fishes and shrimp diversity and a re-evaluation of cleaning symbioses

/0 Comments/in , /by

By Shannon Moorhead, SRC Masters Student

If you’ve ever gone diving on a tropical coral reef, you may have noticed some of the fish seemed to be behaving rather strangely: a solitary fish hovering just above the reef while smaller fish pick at its skin and mouth. While this may appear bizarre compared to the other creatures zipping about the reef, this is a common behavior in the animal kingdom known as cleaning symbiosis. Cleaning symbiosis occurs when, after brief communication between the animals involved, a cleaner animal removes harmful materials from a client animal of a different species. This is a mutually beneficial act for both the cleaner and the client: the client is ridded of parasites and dead skin while the cleaner gets an easy meal! 

A pair of Hawaiian cleaner wrasse clean a dragon wrasse. [Source: Wikimedia Commons, photo by Brocken Inaglory (https://commons.wikimedia.org/wiki/File:Cleaning_station_konan.jpg)]

A pair of Hawaiian cleaner wrasse clean a dragon wrasse. [Source: Wikimedia Commons, photo by Brocken Inaglory (https://commons.wikimedia.org/wiki/File:Cleaning_station_konan.jpg)]

Many water-dwelling organisms have been observed cleaning others. Currently, researchers estimate there are about 208 species of marine and freshwater cleaner fish and 51 species of marine cleaner shrimp known to the scientific community. Some of these species are considered “dedicated cleaners”; for these fish and shrimp, cleaning is a major aspect of their lifestyle once they grow past the larval stage. Other, less committed cleaners, are designated as “facultative cleaners”. There are various levels of facultative cleaning. Some facultative cleaners are opportunistic, only partaking in cleaning when the opportunity presents itself. Others may be temporary, acting as cleaners during only a portion of their life cycle.

Interspecific communication between cleaner and client is a key aspect of cleaning symbiosis. Acts of assertion or submission, by client or cleaner or both, are the catalysts that initiate the cleaning process. Often, cleaners will perform a “dance” or touch the client to signal their intention to clean; the willing client then submits and poses itself in a way that indicates its acceptance of the cleaning. While visual cues are important to this process, in some cases tactile stimulation is just as, if not more important. By approaching and touching the client, cleaner fish make it clear that they are not prey items, as prey would not directly approach a potential predator. Cleaning interactions between cleaner shrimp and moray eels, who have poor vision and are primarily nocturnal, are most likely initiated solely by tactile stimulation. Shrimp have been observed touching eels with their antennae and legs, followed by morays submitting and opening their mouth, allowing the shrimp to begin cleaning.

A shrimp cleans inside the mouth of a moray eel.[Source: Wikimedia Commons, photo by Steve Childs (https://commons.wikimedia.org/wiki/File:Moray_Eel_and_Cleaner_Shrimp.jpg)]

A shrimp cleans inside the mouth of a moray eel.[Source: Wikimedia Commons, photo by Steve Childs (https://commons.wikimedia.org/wiki/File:Moray_Eel_and_Cleaner_Shrimp.jpg)]

Though the cleaning relationship is usually mutually beneficial, sometimes the cleaner or client may take advantage of the other’s trust, referred to as “cheating”. Cheating occurs when the symbiotic relationship is disturbed by one of the partakers. For example, clients have been known to eat their cleaners and cleaners have been reported choosing to eat the mucus or healthy scales of their client fish instead of ectoparasites or dead or diseased tissue. Despite the threat this breach of contract poses to the health of cheated participants, it does not occur often enough to outweigh the benefits of cleaning symbiosis.

Though it is well known that the removal of ectoparasites is beneficial for the health of fishes, the ecological balance maintained by cleaner organisms is poorly understood. Many studies have attempted to quantify loss of reef fish abundance and diversity after the removal of one or multiple species of cleaners from a reef, with varying results. Some studies reported little change in the number of fish, while others reported drastic differences in the number and diversity of fish observed, as well as increases in the number of lesions on remaining fish. The large diversity and abundance of cleaners in marine ecosystems suggest they perform a critical ecological function; the discrepancies among study results make it clear that more research must be done to fully understand the intricacies and significance of cleaning symbiosis.

Works cited

Vaughn DB, Grutter AS, Costello MJ, Hutson KS (2016). Cleaner fishes and shrimp diversity and a re-evaluation of cleaning symbiosis. Fish and Fisheries: 1-19. Doi: 10.1111/faf.12198

 

A novel aspect of goby–shrimp symbiosis: gobies provide droppings in their burrows as vital food for their partner shrimps

/0 Comments/in , /by

By SRC intern, Andriana Fragola

The goby A. japonica and shrimp A. bellulus symbiosis are a perfect example of a mutualistic relationship between two marine animals. The goby lives in the shrimp’s burrow, which lends it shelter, and the goby warns the shrimp if there is a predatory threat nearby (Kohda et al. 2017). It has been hypothesized that the shrimp actually eats the goby’s droppings as its primary food source (Kohda et al. 2017). Kohda and colleagues conducted a laboratory experiment to replicate this relationship, and examine if this feeding behavior is actually occurring.

Figure1 

Field studies were conducted to examine the goby and shrimp interactive behavior. Between the shrimps, A. bellulus and the gobies A. japonica it was observed that the shrimps were not foraging much outside of their burrow, and the gobies were never really observed defecating outside of their burrow (Kohda et al. 2017). Most burrowing organisms do not defecate inside of their burrows – likely to be an act to keep it cleaner (Kohda et al. 2017). If the shrimp is using the goby’s droppings as a nutritional supplementation, then it would not be an issue of keeping the burrow clean because the droppings would still be removed via consumption by the shrimp (Kohda et al. 2017). The animals were collected at Morote Beach, Ehime Prefecture, Japan and were then studied in a laboratory setting.

The gobies and shrimps were kept in tanks with the burrow being a vinyl tube with one open side up against the glass wall of the tank for visual observation (Kohda et al. 2017). This experiment took place over a 2 week period. The shrimp were weighed prior to and after the experiment to determine if they had lost weight when they had no access to food other than the goby droppings (Kohda et al. 2017). In treatment 1, in order to make the goby feed inaccessible to the shrimp, it was placed on a suspended board away from the entrances of the burrows (Kohda et al. 2017). This way the goby could reach the food by swimming, but the shrimp could not and had to rely entirely on the goby droppings for nutrition. In treatment 2, the gobies and shrimp were kept in different tanks, and the researchers collected the goby faeces and then placed them up at the top of the shrimp’s burrow (Kohda et al. 2017). The shrimps were noted to come to the entrance and collect the faeces and bring them back down into the burrow and eat them (Kohda et al. 2017). A control tank was set up where the shrimp were isolated from the gobies, and were not fed during the entirety of the experiment (Kohda et al. 2017).

Final observations noted that the gobies stayed very close to the burrow unless they were feeding, and were never observed defecating outside of the burrow (Kohda et al. 2017). The shrimp were never noted to forage outside of the burrow unless they were taking algae off of the rocks near the burrow entrance (Kohda et al. 2017). Between the two treatments, there was not a significant difference between body weight of shrimps prior and after the experiment (Kohda et al. 2017). But there was a significant decrease in shrimp body weight in the control groups where they were isolated from the gobies (Kohda et al. 2017). Meaning that the shrimp were able to maintain a stable body weight with only the goby faeces as food (Kohda et al. 2017).

 

Figure2
Understanding behavioral relationships between species is incredibly important for conservation initiatives. Learning that two species heavily rely on each other to thrive is vital in establishing protection for them. In a mutualistic relationship similar to this, both species need to be protected because if one is missing, they cannot perform their usual behaviors, and do not have that resources they typically rely on. For example, the droppings of the goby being a primary food source by the shrimp. This study demonstrated that solely having goby droppings as food is enough to maintain the shrimp’s weight even without other nutritional sources available (Kohda et al. 2017). Therefore the goby is a very beneficial to the shrimp as a partner, and without these mutualistic relationship the shrimp would have a much more limited food supply, and the goby would not have a burrow to reside in.

Works cited
Kohda, M., Yamanouchi, H., Hirata, T., Satoh, S., & Ota, K. (2017). A novel aspect of goby–shrimp symbiosis: gobies provide droppings in their burrows as vital food for their partner shrimps. Marine Biology, 164(1). doi:10.1007/s00227-016-3060-2

Living on the Edge: Settlement Patterns by the Symbiotic Barnacle Xenobalanus globicipitis on Small Cetaceans

/0 Comments/in , /by

 

By Rachel Skubel, RJD Intern

If you were a barnacle, how would you choose your home? For X. globicipitis barnacles residing on striped dolphins, this question was ‘put under the microscope’ by Juan Carillo and colleagues at the University of Southern Mississippi and Cavanilles Institute of Biodiversity and Evolutionary Biology (Valencia, Spain).

Of all obligate barnacles studied, X. globicipitis has been found on animals that experience the most intense currents (Bearzi and Patonai, 2010). These organisms will settle on dolphins to optimize for (a) availability of passing current, to provide food, and (b) low drag from said current, to reduce physical degradation of the animal. Here, the investigators asked the following questions:

  1. Where do these barnacles choose to settle?
  2. How does this choice affect the barnacles’ recruitment (define), survival, and growth?

The researchers examined stranded striped dolphins (Stenella coerleoalba) along 556 km of the spanish mediterranean coastline (map), from 1979 to 2009. In 1990 and 2007, many of the dolphins examined had been killed by the morbillivirus (link to http://www.nmfs.noaa.gov/pr/health/mmume/midatlantic2013/morbillivirus_factsheet2013.pdf) – infected animals would have swam slower and had weaker immune systems than otherwise, making them more likely to be colonized by the barnacles. For each animal, the researchers looked at the abundance (i.e. amount), location, and size of the barnacles. Then, they used a model to investigate why barnacles were colonizing certain locations of the dolphins.

Figure 1: Barnacles were mainly found on the trailing edges of dorsal fins, flippers, and flukes, over an area ~2cm wide (Dr. Mariano Domingo, Autonomous University of Barcelona, Spain)

Figure 1: Barnacles were mainly found on the trailing edges of dorsal fins, flippers, and flukes, over an area ~2cm wide (Dr. Mariano Domingo, Autonomous University of Barcelona, Spain)

Results

Out of 242 dolphins examined, 104 had the X. globicipitis barnacles – on either their dorsal fins, flippers, and tail flukes. Of these locations, the tail flukes were by far the most common. Even if the dolphins had barnacles in multiple locations, linear density (barnacles/cm) was significantly higher on the tail. Also, the shell size of barnacles on the flukes was higher than on the flippers and dorsal fins. For these dolphins with barnacles on their tail flukes, it was more common to find them on the dorsal (top) than ventral (bottom) size of the tail.

Figure 2: When dolphins were found with X. globicipitis barnacles, they were most likely on the caudal fin.

Figure 2: When dolphins were found with X. globicipitis barnacles, they were most likely on the caudal fin.

Dolphins thought to have died from the morbillivirus did not have any significant differences in where the barnacles were located, or their size, compared to the unaffected animals.

Explaining the trends

When interpreting these results, it was important to consider that these were all pre-deceased study subjects, and the barnacles might have even settled on the carcasses. However, the finding of tail flukes being a popular settlement area for these barnacles matches with observations in the wild (see video below).

https://www.youtube.com/watch?v=8aJdW5IRZSs

 Beginning around 0:13, you can see barnacles are common on the tails of wild dolphins, supporting the findings of the present study by Carillo et al.

How do the barnacles choose where to dig in? The researchers propose that once they’ve used chemical cues to recognize the dolphins as proper hosts, a two-pronged mechanism follows.

  • First, attachment success: those that choose the tail to latch onto will be less likely to fall off in the process because there is some shelter from strong currents. And once one barnacle settles, it actually becomes easier for more to do the same because they will be ‘sheltered’ by this first individual.
  • Second, there is less early cyprid mortality, which means that once fully attached, it is easier to stay attached.

Lastly, the authors considered why there were more barnacles on the dorsal sides of the tails. This could be due to an asymmetrical swimming style by the dolphins, which means that their ‘downstroke’ is stronger than their ‘upstroke’, so there is less force on the settled barnacles if they settle on the top of the tail. However, whether the swimming style of these dolphins is symmetrical or assymetrical is not conclusively known.

 

References

Bearzi M, Patonai K (2010). Occurrence of the barnacle (Xenobalanus globicipitis) on coastal and offshore common bottlenose dolphins (Tursiops truncatus) in Santa Monica Bay and adjacent areas, California. Bull South Calif Acad Sci. 109: 37–44. DOI: 10.3160/0038-3872-109.2.37

Carrillo JM, Overstreet RM, Raga JA, Aznar FJ (2015) Living on the Edge: Settlement Patterns by the Symbiotic Barnacle Xenobalanus globicipitis on Small Cetaceans. PLoS ONE 10(6): e0127367. DOI: 10.1371/journal.pone.0127367