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''Synalpheus regalis'' is a
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
of snapping shrimp that commonly live in
sponge Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...
s in the coral reefs along the tropical West Atlantic. They form a prominent component of the diverse marine cryptofauna of the region. For the span of their entire lives, they live in the internal canals of the host sponge, using it as a food resource and shelter. It has been shown that colonies contain over 300 individuals, but only one reproductive female. Also, larger colony members, most of which apparently never breed, defend the colony against
heterospecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
intruders. This evidence points towards the first known case of
eusociality Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...
in a marine animal. The species name "regalis" comes from the Latin ''regalis'' which means royal. This likely stems from the structural hierarchy of the colonies in which only a single female produces all of the offspring.


Taxonomy

''Synalpheus regalis'' is a member of the
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomencla ...
''
Synalpheus ''Synalpheus'' is a genus of snapping shrimp of the family Alpheidae, presently containing more than 100 species; new ones are described on a regular basis, and the exact number even of described species is disputed. ''Zuzalpheus'' The genus ''Z ...
'', the second largest genus in the snapping shrimp
family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...
(
Alpheidae Alpheidae is a family of caridean snapping shrimp, characterized by having asymmetrical claws, the larger of which is typically capable of producing a loud snapping sound. Other common names for animals in the group are pistol shrimp or alpheid s ...
), with over 150 species worldwide. The species was discovered by J. Emmet Duffy in 1996 on the
Belize Barrier Reef The Belize Barrier Reef is a series of coral reefs straddling the coast of Belize, roughly offshore in the north and in the south within the country limits. The Belize Barrier Reef is a long section of the Mesoamerican Barrier Reef System, ...
. As of 2013, ''S. regalis'' is one of at least seven recognized species of eusocial shrimp. The other six are ''
Synalpheus brooksi ''Synalpheus'' is a genus of snapping shrimp of the family Alpheidae, presently containing more than 100 species; new ones are described on a regular basis, and the exact number even of described species is disputed. ''Zuzalpheus'' The genus ''Z ...
'', ''
Synalpheus chacei ''Synalpheus'' is a genus of snapping shrimp of the family Alpheidae, presently containing more than 100 species; new ones are described on a regular basis, and the exact number even of described species is disputed. ''Zuzalpheus'' The genus '' ...
'', '' Synalpheus elizabethae'', ''
Synalpheus filidigitus ''Synalpheus'' is a genus of snapping shrimp of the family Alpheidae, presently containing more than 100 species; new ones are described on a regular basis, and the exact number even of described species is disputed. ''Zuzalpheus'' The genus ''Z ...
'', '' Synalpheus microneptunus'' and ''
Synalpheus rathbunae ''Synalpheus'' is a genus of snapping shrimp of the family Alpheidae, presently containing more than 100 species; new ones are described on a regular basis, and the exact number even of described species is disputed. ''Zuzalpheus'' The genus '' ...
''.


Appearance

''Synalpheus regalis'' is a translucent orange. The
distal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
portion of its major
chela Chela may refer to: * ''Chela'' (fish), a genus of small minnow-type fish in the Cyprinid family * Chela (organ), a pincer-like organ terminating certain limbs of some arthropods such as crabs * Chela (meteorite), a meteorite fall of 1988 in Tan ...
(the
pincer Pincer may refer to: * Pincers (tool) *Pincer (biology), part of an animal *Pincer ligand, a terdentate, often planar molecule that tightly binds a variety of metal ions *The Pincer move in the game of Go See also *Pincer movement The pince ...
) is brighter orange than the rest of its body and its
embryos An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm c ...
and
ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
are pale green. Scattered red
chromatophores Chromatophores are cells that produce color, of which many types are pigment-containing cells, or groups of cells, found in a wide range of animals including amphibians, fish, reptiles, crustaceans and cephalopods. Mammals and birds, in contrast, ...
decorate the facial region of its
carapace A carapace is a dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the under ...
(the region between and lateral to the eyes). Its
rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * R ...
(forward extension of the carapace) is thin and is about the same length as the triangular ocular hood, which covers the
shrimps Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are referre ...
’ eyestalks. Ovigerous females are generally 2.6–3.7 mm in length and males and juveniles are approximately 2.8 mm. Externally, the females can be distinguished from the males by their ovaries; however, males and juveniles cannot be distinguished from each other. ''S. regalis'' is morphologically similar to several other species of Synalpheus including ''S. elizabethae'', ''S. rathbunae'', and ''S. filidigitus''. It is distinguishable from its close relative, the ''S. elizabethae'', as its non-ovigerous colony members have rounded
abdominal The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips be ...
compared to the ''S. elizabethae'' that have pointed abdominal pleura. ''S. regalis'', however, has a more acute abdominal pleura, less fixed
teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tea ...
, and lacks a secondary armature on its major chela compared to the ''S. rathbunae''. The ''S. filidigitus'' males have much more rounded abdominal pleura and longer scaphocerites (
lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction *Lateral cricoarytenoid muscle *Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral cons ...
stabilizing
fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fin ...
) compared to the ''S. regalis''.


Habitat

''S. regalis'' lives exclusively in association with
sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...
; however, it has only been found to associate with three sponge species: '' Neopetrosia proxima'', '' Neopetrosia subtriangularis'', and '' Hyatella intestinalis''. In
Jamaica Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of Hispanio ...
, they are found in ''H. intestinalis'', in depths of over six meters. In
Belize Belize (; bzj, Bileez) is a Caribbean and Central American country on the northeastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a wate ...
, the only other known locality of the ''S. regalis'', they are more commonly found in ''N. proxima'' and ''N. subtriangularis'' in addition to ''H. intestinalis''. They rarely cohabit sponges with other shrimps, suggesting that competition in the
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
is fierce and would explain why they are found associated exclusively with only two species of sponges. For co-inhabitance situations, ''S. regalis'' appeared to dominate the sponge, leaving the other species severely under-represented compared to cases in which ''S. regalis'' was not present. In some places such as the
Bocas del Toro Archipelago The Bocas del Toro Archipelago is a group of islands in the Caribbean Sea in the northwest of Panama. The archipelago separates Almirante Bay and Chiriquí Lagoon from the open Caribbean Sea. The archipelago is part of the Bocas del Toro Distric ...
, ''S. regalis'' co-occurs with close relative ''S. elizabethae''. The shrimp feed on the host tissues as well as on the detritus, which includes bodies of dead organisms or fecal material.


Life cycle

''Synalpheus regalis'' exhibits
eusocial Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...
organization like many other species in the genus. There is one breeding female and members of the colony defend, forage, and take care of the colony. The young hatches from the eggs as a crawling larva and undergoes direct development. ''S. regalis'' goes through outbreeding, where at least one of its sexes leaves to find mates, but the details of this process are yet unknown.


Behavior and ecology


Eusociality

J. Emmett Duffy, a primary investigator of ''S. regalis'', uses the term "
eusociality Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...
" to refer to the syndrome of multigenerational, cooperative colonies with strong reproductive skew (usually a single breeding female) and cooperative defense of the host sponge found in several ''
Synalpheus ''Synalpheus'' is a genus of snapping shrimp of the family Alpheidae, presently containing more than 100 species; new ones are described on a regular basis, and the exact number even of described species is disputed. ''Zuzalpheus'' The genus ''Z ...
'' species. Eusociality requires that generations overlap, allowing close contact between individuals such that altruistic behaviors can be favored by
kin selection Kin selection is the evolutionary strategy that favours the reproductive success of an organism's relatives, even when at a cost to the organism's own survival and reproduction. Kin altruism can look like altruistic behaviour whose evolution i ...
. The populations that live in sponges contain a few hundred individuals, each with two generations of kin. Also, by having just one reproductive female, colonies clearly fit the first criterion of reproductive division of labor. Most hypotheses that explain eusociality entail some form of adaptive
division of labor The division of labour is the separation of the tasks in any economic system or organisation so that participants may specialise (specialisation). Individuals, organizations, and nations are endowed with, or acquire specialised capabilities, and ...
, which results in enhanced reproductive output of the breeders and inclusive fitness benefits for the nonbreeding helpers.


Colony organization

''S. regalis'' has the largest colonies and the largest
reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are al ...
skew of all
eusocial Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...
shrimp. Its colonies can consist of up to 350 organisms, who are related to each other with an average of r=0.50, with one queen. Furthermore, many colonies show
heterozygote Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...
excesses. This led researchers to conclude that
outbreeding Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity. Outcrossing can be a usefu ...
is common in the ''S. regalis'', and at least one of the sexes leaves its natal home to find mates. The queen is the sole breeder of the colony. Studies show that there is a strong correlation between the size of the queen and the size of the colony, which implies that there is a parallel between growth of the breeding female and her colony. Furthermore, the queen is not as
aggressive Aggression is overt or covert, often harmful, social interaction with the intention of inflicting damage or other harm upon another individual; although it can be channeled into creative and practical outlets for some. It may occur either reacti ...
or active as the other adults in the colony, suggesting that she does not dominate other individuals and instead looks to them for protection. The reason behind the reproductive skew in ''S. regalis'' is currently unknown, but a theory that explains this phenomenon in other organisms, the “majority rules” model by Reeve and Jeanne, could explain the reproductive skew in ''S. regalis''. In this theory, the queen dominates the colony’s
reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual or ...
by being the individual that each of the other colony members are most genetically related to. The non-breeding workers are more closely related to the queen’s offspring (siblings; r=0.50) than they are to offspring of another worker (nieces/nephews; r=0.25). Therefore, it will be in the best interest of their genes to prevent each other from reproducing in favor of their queen.


Fortress defense

Fortress defense is one of two modes of
eusociality Eusociality (from Greek εὖ ''eu'' "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generat ...
. Queller and Strassmann (1998) distinguished between "life insurers", which include most
Hymenoptera Hymenoptera is a large order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are parasitic. Females typic ...
, where cooperation reduces the risk of total reproductive failure, and "fortress defenders", where cooperation enhances the defense of a commonly held, valuable resource. Crespi (1994) argued that three conditions must be met to explain most cases of fortress defense: a coincidence of food and shelter in an enclosed habitat, a high value of food-habitat resources that renders inhabitants vulnerable to predatory attacks, and the ability to defend the resource effectively. The strong selective pressures of enemies on kin-structured aggregations may promote evolution of specialized defenders that raise their own and the breeders' inclusive fitness by defending the colony. Because few predators can enter the narrow canals of the sponges, the greatest competition comes from enemies that are of the same or closely related species. ''S. regalis'' lives and feeds exclusively within their hosts, therefore meeting the first condition. Also, data shows that fewer than 5% of sponges sampled were unoccupied by shrimp, which means that sponges are in short supply and subject to strong competition. Finally, the large non-breeding defenders utilize the snapping claw, a potent weapon that produces a water jet intense enough to stun small animals. ''S. regalis'' appears to reach Crespi's (1994) three criteria. A study was conducted to observe the responses of colonies by introducing heterospecific intruders. The results were dramatic: contact between a resident and an intruder generally resulted in an intense battle, with both individuals snapping at each other with their powerful major chelae. However, contacts between residents and 'natives' were quite peaceful. ''S. regalis'' will give warnings to the intruders in the form of single snaps with their chelae. If these single snaps do not succeed in driving away the intruder, a coordinated snapping event will occur in which either a localized group or the entire colony will snap in unison. At this point the intruder will usually leave, but if it does not, for example getting stuck in the canal of a sponge, it will be killed. The larger residents were the most active and aggressive, contacting foreign intruders more than twice as often as did smaller residents, and engaging intruders in combat (snapping) ten times more often than did juveniles. The larger shrimp tend to be older than the rest of the colony, and thus they allocate their energy to defending rather than breeding. Such size- or age-related polyethism is a common aspect of labor specialization among social insects. Since most of the defenders do not breed, the only way to secure their genes in future generations is to protect their juvenile siblings, allowing them to grow to adulthood free from predation and survive long enough to reproduce. This nest defense amounts to cooperative brood care and establishes ''S. regalis'' as a eusocial species. If fortress defense plays an important role in favoring cooperation among sponge-dwelling shrimps, it can be predicted that eusociality would enhance the ability to acquire, defend, and retain limited host resources compared to less social species. Duffy and Macdonald (2010) tested this prediction in
Belize Belize (; bzj, Bileez) is a Caribbean and Central American country on the northeastern coast of Central America. It is bordered by Mexico to the north, the Caribbean Sea to the east, and Guatemala to the west and south. It also shares a wate ...
by examining how shrimp abundance correlated with sociality among species. They discovered that eusocial species are more abundant, occupy more sponges and have broader host ranges than non-social sister species.


Nestmate recognition

''S. regalis'' are exceptionally tolerant of
conspecifics Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
within their colonies, and aggressive towards
conspecifics Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organis ...
not of their own colony. These peaceful interactions are attributable to close genetic relatedness among nestmates.
Allozyme Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. These are opposed to isozymes, which are enzymes that perf ...
data revealed that
relatedness The coefficient of relationship is a measure of the degree of consanguinity (or biological relationship) between two individuals. The term coefficient of relationship was defined by Sewall Wright in 1922, and was derived from his definition of t ...
within colonies is high, averaging 0.50, indicating that colonies in this species represent close kin groups. The existence of such groups is an important prerequisite of explanations of social evolution based on kin selection. During the intruder experiment, resident shrimp contacted foreign conspecifics less and snapped more frequently than they did when faced with a nestmate. Because nestmates are generally close kin in ''S. regalis'', this discrimination may reflect kin recognition and may help maintain the integrity of kin-structured social colonies. Nestmate discrimination likely involves both waterborne and contact chemical signals which have been shown to mediate sex recognition in other alpheids. The high frequency of intruder contacts with the queen may suggest that she produces
pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavi ...
s like in social insects.


See also

*''
Austroplatypus incompertus ''Austroplatypus incompertus'' is a species of ambrosia beetle belonging to the true weevil family, native to Australia, with a verified distribution in New South Wales and Victoria. It forms colonies in the heartwood of ''Eucalyptus'' trees a ...
''


References


External links

* {{Taxonbar, from=Q7661956 Alpheidae Crustaceans of the Atlantic Ocean Crustaceans described in 1996