Saturday, April 28, 2012

Mutualism: Women and L. acidophilus


As human beings, we have thousands of different species of bacteria on our bodies, not including the other types of microorganisms. With all the different bacterial species, it would seem that no single bacteria is an indispensable member of our microbiome, however this is not the case. Lactobacillus acidophilus is a species of bacteria that women rely on just as much as the bacteria do. The L. acidophilus reside (among other places in the body) on the human vagina and use the woman as a resource host in exchange for protection from other potentially more harmful micro-organisms.

Description of the Relationship:

The presence of bacteria on the vagina was discovered over 100 years ago and is now one of the most well known examples of mutualism between humans and bacteria that there is. It is considered mutualistic because both the woman and the bacteria necessarily rely on one another. The L. acidophilus, once introduced to the vagina,  begins to adhere to the vaginal epithelial cells and colonize. The bacterial colony consumes the natural sugars excreted by the skin and ferments them into lactic acid. This product lowers the pH to a level intolerable by most bacteria not of the Lactobacillus genus. During menstruation, many of the bacteria are killed, reducing them to an appropriate level.

Cost/Benefit Analysis:

The woman benefits from this mutualistic relationship by gaining protection from more harmful organisms that could potential cause a yeast, bladder, or urinary tract infection. This is at the cost of a slight decrease in reproductive fitness. L. acidophilus taking glucose molecules that the woman worked to obtain might not have a large negative affect on the woman by itself, but there are thousands of micro-organisms on and inside the human body that all contribute to a somewhat heavy, yet necessary burden. The bacteria (L. acidophilus) benefit from the relationship by gaining a steady food supply, and a habitable living place. This is at the cost a attack by the woman's defense system (daily hygiene, monthly menstruation, and immune response if levels get too high)


  1. "Lactobacillus acidophilus" University of Maryland Medical Center.
  2. "Methods for Quantitative and Qualitative Evaluation of Vaginal Microflora During Menstruation" Pub Med Central.
  4. "Bugs Inside: What Happens When the Microbes That Keep Us Healthy Dissapear?" Scientific American.

Friday, April 27, 2012

Orchids and Orchid mycorrhiza

            Orchids are widely distributed across the world with 25,000 to 35,000 species except for Antarctica [1].  Orchid’s lifecyle begins after pollination with the shivering of its petal and sepals. Then, it begins to form a seed; The maturation period of the seed is unique to each orchid species.  Next, the seed germinates into a seedling resulting in the flowering of orchid and the process begins again.  Since orchids’ seeds lack endosperm, they use resources from fungus to complete the germination process [2]

Description of the Relationship
Intracellular hyphal peloton [7]
            Basidiomycetes fungi provide energy and nutrients to orchids, from family Orchidaceae.  The fungi in the orchid mycorrhiza fulfill the role of endosperm in orchid seed [3].   During the non-photosythentic phase of the orchid’s lifecycle, the fungi provide the orchid with energy and carbon compounds [4].  After the non-photosynthetic phase, the fungi can also increase the nutrients and mineral intake of the orchid through the roots.   The fungi form pelotons that are like the host cell. These pelotons are surrounded by a membrane similar to plasma membrane. An infect orchid has altered microtubules and cell wall microfibrils [3].  All these alterations caused by the fungi help the orchid to absorb inorganic nutrients and trace elements from the soil.  The fungi also benefits from these interactions by receiving some of the photosynthesized carbohydrates [5]. Thus, the relationship between orchid and orchid mycorrhiza is mutualistic.  Some orchid mycorrhiza have evolved to be specific based on the species of the orchid therefore, can serve to be pathogenic to other orchid species [3].

Cost and Benefit Analysis
            As stated above, both the orchid and fungi benefit from this relationship.  The fungi gains carbohydrates from the orchid while the orchid receives nutrients and energy.  

The orchid does not spend a lot of energy in developing its roots in order to increase its volume of nutrients and minerals absorption from the soil.  Instead, the fungi fulfill that role.  The fungi are not limited to the roots alone.  They can explore other cavities and compounds that are not near the roots[5]
            Even though fungal infection can be pathogenic to the orchid, the orchid is able to control the infection.  The orchid has defense genes and compounds such as orchinol that can control the fungal infection [3].  These defense mechanisms does not significantly affect the reproductive success of the fungus.


Wednesday, April 25, 2012

Mighty Mitochondria and the Endosymbiosis Theory


         Scientists approximate that bacteria first appeared on Earth around 3.5 billion years ago, while the first eukaryotes were not thought to inhabit Earth until approximately 1.5 billion years ago. What happened in this time gap of 2 billion years? Well, scientists can only make an educational guess, considering that primates likely did not come to be until approximately 65 million years ago (1). The endosymbiosis theory points to perhaps the earliest known form of mutualism in which bacteria are thought to have inhabited a “primordial eukaryotic cell” (2). The presence of a bacterial organism inside the larger cell allowed cellular life to adapt to the harsh conditions of the time. Scientists believe that photosynthetic bacteria appeared 3.2 million years ago, thereby releasing oxygen into the atmosphere. Oxygen can actually be a toxic substance, but the first aerobic bacteria lived about 2.5 billion years ago, very shortly before the first aerobic eukaryotes. These inferences, among many other observations, point to the endosymbiosis theory as a plausible explanation for adaption to an environment abundant in oxygen (1).

                                                                      Endosymbiosis Theory: 

Cost/Benefit Analysis          

          Why would we think that bacteria would crawl inside of another cell? Well, we assume that in a mutualistic relationship, both parties benefit due to the relationship. Additionally, the endosymbiosis theory suggests that mitochondria and chloroplasts’ lineages can be traced back to ancient bacteria. Not only are these structures about the size of a bacterium (70S), but these organelles also contain their own DNA in the form of one circular chromosome like bacteria (3). Both bacteria and the organelles replicate via binary fission (1).
Rickettsia prowazekki

         Although this background information is necessary in understanding the basic evolution of the eukaryotic cell, I would like to specifically examine the relationship between mitochondria (derived from ancient bacteria) and the primitive eukaryotic cell. As previously stated, at the time of the initial endosymbiotic encounter, few species were equipped to convert oxygen into another substance to avoid oxidation. Therefore, the host cell greatly benefitted from its smaller counterpart because mitochondria convert oxygen to ATP via substrate-level phosphorylation. Today, researchers have evidence to suggest the mitochondria are related to the proteobacterium Rickettsia prowazekii, “an obligate intracellular parasite” (3) due to its similarity in genomic sequence. Although it is not exactly clear why the bacterium benefitted from the relationship, it can be inferred that the bacterium was provided a “safe” environment to reside in a chemically stable environment. This idea applies to chloroplasts as well.

Mitochondria and the Cell
         To understand the role of early bacteria in the cell, let us look at the function of a mitochondrion. Ultimately converting oxygen to ATP, mitochondria are the powerhouses of a cell through their production of energy. Mitochondria have two membranes, of which the outer membrane, containing porins, resembles Gram-negative bacteria. The inner membrane contains cristae, infoldings that greatly increase surface area. The inside of the mitochondria, the mitochondrial matrix, contains ribosomes (similar to size of those of bacteria), DNA, and calcium phosphate granules. The DNA and ribosomes are used to synthesize some of its proteins (3).

        The mitochondrion is the location of the tricarboxylic acid cycle (TCA), production of ATP, and oxidative phosphorylation.  In the TCA cycle, pyruvate is oxidized and cleaved to form CO2 and acetyl-coenzyme A (acetyl-CoA), an energy-rich molecule. After a series of reactions on acetyl-CoA, NADH and FADH2 are formed, which are both electron carriers. This reaction also yields four ATP molecules. The electron carriers formed in the TCA cycle are active players in the electron transport chain, as electrons are transferred to acceptors such as oxygen. The electron transport chain involves an energy gradient within the inner membrane of the mitochondria in eukaryotes and in the plasma membrane in prokaryotes. In this process, NADH is oxidized to NAD+, while the electrons are transferred to other molecules (such as oxgygen) with more positive reduction potentials. Oxidative phosphorylation is the result of the electron transport chain, in which protons move across the mitochondrial membrane and ultimately produce a maximum of 34 ATPs. These processes are very simplified, as more complex explanations involve in-depth biochemistry (3).

         Through these complicated processes in the mitochondria, eukaryotic cells are able to reap the benefits of an abundant amount of energy to sustain more complex forms of life. Although the TCA cycle and electron transport chain produce small amounts of ATP, oxidative phosphorylation allows for 34 molecules of ATP to be produced.

Mitochondria and the Body

An eye that has been affected by optic neuropathy.
          We already have an idea of how beneficial mitochondria are to sustaining life, but what happens when mitochondria start to malfunction? As already mentioned, mitochondria contain their own DNA. Mitochondria are passed from mother to offspring in the cytoplasm of the egg. Over 200 human diseases are caused by mutations in DNA due to mitochondrial DNA’s inability to repair, unlike nuclear DNA. Most of these diseases come about in cells that require an abundance of ATP, such as muscle and nerve cells. Several examples of dysfunctional mitochondria-caused diseases are the following: optic neuropathy, often resulting in blindness; neurogenic muscle weakness; maternal and cardiomyopathy; and myoclonic epilepsy (2). Regardless of the primitive bacteria-eukaryotic cell relationship, it is apparent that eukaryotic cells have become very dependent on mitochondria to sustain life. 


    (1) The Endosymbiotic Theory. (2004, February 18). Retrieved from
    (2)    Brooker, R. J. (2009). Genetics: Analysis & Principles. (4 ed., pp. 119-120). New York: McGraw Hill. Print.
    (3)  Willey, Sherwood, and Woolverton. (2008).  Microbiology.  (7 ed., pp. 88 and 476-478). New York: McGraw Hill. Print.

Sunday, April 22, 2012

Farming beetles: Ambrosia beetles and their fungus

Different ambrosia beetles from tropical rainforests.
As we have seen with the Attine ant and Leucoprini fungus, animals have beaten humans to the act of farming. Another example of this would be the ambrosia beetles and ambrosia fungi. Ambrosia beetle is a general term used to describe several species of beetles from the two weevil subfamilies Scolytinae and Platypodinae [1]. One of the most rapidly diversifying, most widely distributed, and probably most ecologically and economically important group of ambrosia beetles is the tribe Xyleborini [1]. Ambrosia beetles can be found in all regions with tropical vegetation and even in some temperate areas [1].

Beautiful pink Fusarium repeatedly isolated from mycangia of Xylosandrus crassiusculus.

Since there are several species of ambrosia beetles, it comes with no surprise that there are many species of fungi that have a long established relationship with these beetles. The most common are polymorphic asexual anamorphs from the general Ambrosiella, Raffaelea, Ambrosiozyma and Dryadomyces [1]. Most ambrosia fungi are not capable of living independently of the beetles [1].

Description of the relationship:
The relationship between the beetles and the fungus has been describes as one of the most successful and widespread cases of insect-fungus symbiosis, ambrosia beetles are the product of sixty million years of intricate mutualism between the faster evolving beetles and some of the most bizarre fungi [2].

Surface pit mycangia. Left: Female of Treptolatypus solidus with glandular pit mycangia on top of the pronotum. Right: Simple nonglandular pit mycangium on the head of Scolytodes unipunctatus. Arrow on the right points to a fungus spore.
Ambrosia beetles have evolved a variety of morphological structures to carry their fungal symbionts from tree to tree. These structures are generally called mycangia [1]. As the beetles leave their initial home, they carry spores of the fungus in their mycangia. Once they find a suitable tree, they then create tunnels (galleries)  inside the wood which will make small strings of compacted sawdust protrude from the tree [3].

Sawdust stacks on a dead tree - typical sign of ambrosia beetles at work.
The beetles will then cultivate the fungi inside the galleries within dead or decaying wood and feed on their mycelium. Once the "fungus farming" has started, the beetles can lay their eggs that will produce larva. The beetles will care for their young larva in the trees where they will become beetles and carry fungal spores to their next habitat.

Cost/benefit analysis:
     The beetles are dependent upon the fungi, from which they require amino acids, vitamins, and sterols [5]. Certain immature stages of the beetles are unable to complete development in the absence of the fungus [6], At the same time, the activities of female beetles have been hypothesized to control the growth of composition of ambrosial gardens. If the female dies, the garden is quickly overgrown by contaminating fungi and bacteria, which ultimately results in the death of the brood [5].
     The interaction is clearly mutualistic. The symbiosis allows the beetles to exploit a nutritionally poor resource (wood) and reduce interspecific competition, while providing the fungi consistent transport to a relatively rare and ephemeral resource (a new host of the appropriate condition and successional stage) [5].
     Although both the beetle and the fungi are benefited by this relationship, there are also cost to pay. The beetle could die if the fungus is suddenly removed from its habitat as the beetles are too specialized to be able to use another species of fungus. The fungus has also evolved to where it does not reproduce sexually, thus reducing genetic diversity and ability to explore different niches without the help of the beetle.


Saturday, April 21, 2012

Living Easy: Podarcis lilfordi and Daphne rodriguezii



The lizard, Podarcis lilfordi, is found on the Balearic Islands off the coast of Spain [1]. However, unlike other lizards, this species shares a mutualistic relationship with the shrub Daphne rodriquezii [2]. D. rodriquezii is characterized from its beautiful white flowers and it also contains many fruits that the lizards like to consume [3]. The lizards consume and disperse the seeds of the plant by eating the fruits that grow from the shrubs [4].

 P. lilfordi is a medium sized lizard that grows to a maximum of 80mm. Its body mass can be anywhere between 4.2 to 9.5 grams. The females reproduce cyclically, producing 2-4 eggs per clutch. They can lay multiple clutches in one season [3]. However, as new predators and lizards show up to the islands and compete for resources, the population of P. lilfordi has slowly started to decline [1]. The shrub, D. rodriguezii, starts to grow during the early spring season. They contain very small, white flowers. The sepals and petals unite, forming a tube called the hypanthium that usually has purple dyes and is 7 to 11 mm in length. During the summer, the shrubs mature and produce red-orange, fleshy globose fruits. The shrubs rarely grows above 50 centimeters in height [2].

Description of the Relationship:
P. lilfordi are very productive seed-dispersers for the shrubs. It is a mutualistic relationship, in which the lizards use the shrubs not only as a food source, but also as a second home [1]. The lizard eats the fruits that D. rodriguezii produces, and it also uses the shrub as a home, keeping it out of sight from other predators and the hot sun [2]. In return, the shrub gets the benefit of having the lizards disperse their seeds for them. They are then better able to spread their offspring to other areas [3].
However, P. lilfordi also has other priorities and responsibilities on the ecosystem found on the Balearic Islands. It is also a pollinator of the aroid Dracunculus muscivorus, and a seed disperser for Withania frutescens and Phillyrea media [1].

Cost Benefit Analysis:

As mentioned before, the mutualistic association between P. lilfordi and D. rodriguezii is very straightforward. D. rodriguezii serves as both a food source and a shelter for P. lilfordi, and in return P. lilfordi disperses the seeds of the shrub through fecal defecation. Without D. rodriguezii being present in nature, P. lilfordi would still be able to survive and reproduce in nature. However, it would have a better chance to pass its progeny if D. rodriguezii was present, as it would have an extra food source and shelter [1]. D. rodriguezii, however, would have a much harder time reproducing in nature as their seeds would not get dispersed if P. lilfordi was not present in the environment.  


Relaxing in the Rectum

Many organisms living in the sea benefit from a symbiotic relationship with other organisms around them. One example of this is the relationship between the sea cucumber and the pearl fish. Sea cucumbers are echinoderms that have a shape very similar to soft cucumbers (1). They have “leathery skin” and their body is essentially one long digestive tube. These invertebrates crawl along the floor of the ocean and can reside in both shallow and deep areas of the ocean. They are omnivorous and usually eat small particles and detritus they find on the ocean floor. The sea cucumber can grow between 2 to 200 cm and can live to be between 5 and ten years old (2). Spawning for the sea cucumber usually occurs between June and August. The sea cucumbers release their sperm and eggs in the water and allow fertilization to take place. These fertilized eggs continue to develop into larvae, which become suspended in the water column for up to 70 days. Eventually, these planktonic forms settle on the ocean floor, where they change into tiny little juvenile sea cucumbers. Growth is slow for these invertebrates, and it can take up to 4 years for the cucumber to reach adult size (3).

The symbiont of the sea cucumber is the pearl fish. Pearl fish are “eel-shaped” fish that are found worldwide, but primarily in tropical, shallow areas around coral reefs. They have long, slender bodies that lack scales and they usually have transparent skin. The tail of the pearl fish is long and pointed, and the anus of this fish is located close to its neck. Pearl fish typically grow to be about 15 cm long (4). The female pearl fish releases clumps of eggs late in the summer to begin the life cycle. These eggs rise to the surface and hatch, turning into a specific type of larvae called vexillifers. These larvae live among the plankton until reaching a length of about 7 to 8 cm. At this point, the larvae develop into tenuis. These forms descend to the ocean floor and begin their search for food and a host (5). The pearl fish will constantly be on the lookout for sea cucumbers to create a symbiotic relationship.

Description of Relationship:
Once a pearl fish (Onuxodon or Carapus) finds a sea cucumber (Holothuroidea), it immediately begins to smell around to distinguish between the head and the anus of the cucumber (6). Once it finds the anus, the pearl fish works its way into the rectum of the sea cucumber, eventually being completely engulfed in the digestive canal of its host. There it will spend the day inside, using its host as a form of protection. At night, the pearl fish comes out to feed on small crustaceans, but it doesn’t go too far from its host (7). After feeding, the pearl fish returns to its host and waits for the sea cucumber to take a breath. When the anus opens for respiration, the pearl fish simply swims back inside, seeking shelter in the rectum of its host (8). The pearl fish and the sea cucumber have evolved a symbiotic relationship know as commensalism. In this relationship, the pearl fish benefits because it gains a place to live that is cozy and protected from predators as well as any nutrients that can be absorbed as they flow out of the cucumber’s anus. Meanwhile, the sea cucumber appears to be unaffected by this relationship. It doesn’t even seem to notice the pearl fish entering its anus. As far as we know, the pearl fish is not taking anything from the sea cucumber. The reproductive success of the cucumber remains the same. Therefore, since the pearl fish benefits and the sea cucumber is neither helped nor harmed, one can argue that this relationship is one of commensalism. Many other organisms have benefitted from relationships similar to that of the sea cucumber and the pearl fish. The pearl fish have also learned to penetrate the bodies of other invertebrates such a starfish, sea squirts, and clams. A number of crabs and polychaete worms have also evolved to live inside sea cucumbers and have become specialized for gaining protection from the cloaca of that host (9).

Cost/Benefit Analysis:
The relationship between the pearl fish and the sea cucumber is not obligatory, but the pearl fish benefits from its symbiosis with the sea cucumber. The costs for the pearl fish in this relationship are very small. They must expend energy searching for a sea cucumber and for wiggling their way into the anus of the host. On the other hand, the benefits for the pearl fish are immense. The fish is provided protection from predators when it resides within the rectum of the cucumber. They also can take up any nutrients found in the waste products being excreted from the rectum of the sea cucumber. Another benefit for certain species of pearl fish is that they can use the rectum of the sea cucumber as a place to develop into their adult forms and complete their life cycle (9). While the pearl fish is provided with shelter, the sea cucumber has nothing to gain from this relationship. Nor does it have anything to lose. Both the cost and benefit for the sea cucumber is nothing. The reproductive success of the sea cucumber is not affected and the pearl fish benefits, it is likely that this relationship will persist as commensalism. Eventually, there may even be an adaptation that would benefit the sea cucumber, creating a relationship that is more like mutualism.

8. echinoderms/sea_cucumbers

Thursday, April 19, 2012

Friends or Foes? Kennethiella tristosa Mites


(Image from a scanning electron microscope of
the phoretic mite Kennethiella tristosa) [7]
The phoretic mite Kennethiella tristosa attaches itself to the wasp Ancistrocerus antilope. This pair exhibits both vertical and horizontal transmission. Vertical transmission occurs when a female wasp lays an egg and the larva, or deutonymphs, leave the wasp and transmit to the egg. Horizontal transmission happens during mating from wasp to wasp [1]. Kennethiella tristosa gains a mode of transmission and housing, from a special cavity solely developed for housing mites, from the wasps without harming it.  However, it has been shown that large numbers of Kenethiella tristosa can actually become parasitic and harm the wasp.  It was observed that when large number of mites was present, juvenile wasp’s mortality rate increased by 30% [2].  According to the distribution map (from the encyclopedia of life) these mites are only found in two select areas [3]. Since the distribution is so small, these mites are rarely researched. The life cycle of these mites includes a deutonymph stage where the mites attach themselves to the propodeum of the female wasp after she has mated with an infected male. After they have attached to the wasp, they travel to a new nesting site via the females and feed in order to complete their life cycle. After reproduction, the cycle starts all over again [1] [4].

(Distribution Map for Kennethiella tristosa)[3]

Description of the Relationship:

(Life cycle of K. tristosa compared to the life cycle of A. antilope) [8]
This species of phoretic mites comes from the genus Kennethiella and the species is tristosa [1]. The second partner in this relationship comes from the genus Ancistrocerus and the species antilope. These tiny mites gain a mode of protection and transportation during their non-feeding stage of a deutonymph.  The wasps are not harmed in the process if the number of mites is kept at a manageable rate [2].  These two species exhibit commensalism where the mite obtains transportation, protection, and food while the wasp is not harmed [5].

Cost/Benefit Analysis:

Benefit for Kennethiella tristosa: The mites gain protection from the propodeum in the wasp. This area only has one function and that is to provide protection for the mites.  It also gains transportation and food.  These mites feed on the larva of the wasp and in order to finish their life cycle they must transfer to new nests with fresh larva. [1] [2]

Benefit for Ancistrocerus antilope: There is no recorded benefit thus far for the wasp in the relationship. [2]

(K. tristosa on the propodeum of the A. antilope) [6] 
Cost for Kennethiella tristosa: If there are too many mites on a single wasp, the host is killed and there are no more resources for the mites.  Therefore, they cannot finish their life cycle and produce the next generation.

Cost for Ancistrocerus antilope: If the wasp becomes too heavily parasitized, it will die.
There are no specific strategies employed by either partner in order to make contact easier.  Researchers are still uncertain as to why this commensalism relationship continues, but they have notices that the only function of this cavity in the wasp is to protect and house the phoretic mites [2].

1. Cowan, D. P. (2002, January 24). Symbiosis and mode of transfer between hosts. Retrieved from

2. Okabe, K. (2010, April). Conditional mutualism Retrieved from

3. (2010). Collection sites: world map showing specimen collection locations for kennethiella trisotosa. (2010). [Web Map]. Retrieved from

4.Gasperin, O. (2012). Behavioral ecology group. Retrieved from

5. commensalism. (2012). In Encyclopædia Britannica. Retrieved from

6.Cowan, D. P. (Photographer). (2002). A male a. antilope wasp with a large cluster of k. trisetosa deutonymphs clustered on the right side of the propodeum and thorax. [Web Photo]. Retrieved from

7.Eversol, R. (Photographer). (2002). Scanning electron micrographs of k. trisetosa on a. antilope.. [Web Photo]. Retrieved from

8.Cowan, D. P. (Designer). (2002). Life cycle of k. tristosa compared to a. antilope. [Web Drawing]. Retrieved from

Wednesday, April 18, 2012

Workin' Over Time: Rhizobium and Legumes

Introduction: Rhizobium are motile, rod shaped, gram negative bacteria.  They are particularly interesting because of their ability to form nodules with the roots of leguminous plants.  Legumes are herbaceous plants that produce seeds in pods.  Examples include peas, beans, trefoils, and mimosa.
This relationship is common in nitrogen limited environments.  [1]This relationship occurs hen the rhizobium responds chemotactically to flavonoids produced by the plant.
The rhizobium cause conformational changes in the root itself, asides from the nodule.  It causes the root hairs to change the direction of their growth, which ultimately plays a large role in infection.  The root hair curls around the bacterium and traps it and brings it into the root [2, 3].
Rhizobium are able to fix nitrogen with the aid of the enzyme nitrogenase.  The presence of oxygen would decrease the efficiency of the nitrogenase.  Leghemoglobin protects the nitrogenase from oxygen.  There is dispute as to the leghemoglobin's origin.  In the school of thought we will follow, the protein portion is contributed by the plant and the heme group is contributed by the bacteria. [3].
It should be noted that rhizobium has been shown to be an enivronmentally friendly and effective fertilizer and has great potential for the agricultural industry [5].

Cost Benefit:  Both species benefit from this relationship, but they can exist independently of each other as well.  The roots of the legume plants provide energy to the rhizobium in the form of nutrients and carbohydrates [4].  While the plant gives energy to the rhizobium, it does not give so much so that the plant itself suffers. The rhizobium benefit the plant by fixing nitrogen to ammonia. Some species on fix up to 220 lbs of N2 per agricultural acre per year [1].  The lack of negative aspects of this relationship leads me to conclude that this non-obligatory relationship should continue.

2.) Bisseling, T; Geurts, R. Rhizobium Nod Factor Perception and Signalling. The Plant Cell, Vol. 14, 239-249. May 2002.
3.) Van Rhijn, P; Vanderleyden, J. The Rhizobium-Plant Symbiosis. MICROBIOLOGICAL REVIEWS. Vol 59(1). 124–142.  Mar. 1995.
4.) Combes, C. Parasitism: The Ecology and Evolution of Intimate Interactions.
5.) Mia, M; Shamsuddin, Z.  African Journal of Biotechnology Vol. 9 (37), pp. 6001-6009, 13 September, 2010


Libinia emarginata: Spider or Crab?


Spider Crabs, Libinia emarginata, are from the species of crab, stenohaline. They live in the Atlantic Ocean on the coast of North America, but can be found from Nova Scotia to the Florida Keys, and the Gulf of Mexico. 


They have long legs, round spiny bodies, and 9 spines down their back. They live at depths up to 150 feet Females can only reproduce after molting. The young hatch from eggs as zoea larvae [5]. Since predation is a concern for these crustaceans, these crabs will attach pieces of shell, seaweed, and algae to the sticky hairs on their bodies for camouflage [1]. The crabs also use the greenish-brown algae on their back to help hide it from predators [2].


Spider crabs come from the genus and species Libinia emarginata. These crabs can grow to be up to 12 inches from claw to claw [5]. They have different claws than other crabs do in order for them to scoop up algae [3]. Spider crabs and algae share a mutualistic relationship. “A mutualistic relationship is when two organisms of different species ‘work together,’ each benefiting from the relationship” [2]. Even though this is a mutualistic relationship, it is a facultative relationship for both meaning it is not obligatory for either organism. Both organisms benefit from the relationship with the other: the crab gets to blend in with its surroundings and the algae get a place to live [2]. The relationship is established when L. emarginata scoops up the algae. This relationship is not unique to spider crabs. Spider crabs are not the only animals that use algae for camouflage. Devil scorpionfish are camouflaged to their environment because they allow algae to grow on them. Also, other types of crabs use this camouflage technique by allowing algae and dirt to stick to hairs on their body [4].


Benefit for spider crabs: As previously stated, the spider crabs benefit from the relationship with algae by using it as camouflage. Because of this, the crabs have a better chance of surviving predators.

Benefit for algae: Since the crabs pick up the algae, they get a permanent place to live. It is also protected from predators now because it has a permanent home on the crab [2].

Cost for spider crab: The spider crab spends energy to find, collect, and scoop algae onto its back.

Cost for algae: Even though the algae get a place to live, the crabs possibly could take them into a new, unfamiliar environment. Therefore, it might not be as successful there.

Since this is a mutualistic relationship, there is not a great amount of cost for either the spider crab or the algae. Any “cost” is outweighed by the benefits. Even though the crab spends energy recruiting the algae, it pays off since it can hide from predators.

Since this symbiotic relationship shows strong, beneficial qualities for both organisms, it seems like this relationship will proceed.