Synalpheus regalis

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Synalpheus regalis
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Caridea
Family: Alpheidae
Genus: Synalpheus
Species:
S. regalis
Binomial name
Synalpheus regalis
Duffy, 1996 [1]
Synonyms[2]

Zuzalpheus regalis (Duffy, 1996)

External image
image icon Images and further information from 'ants', Thailand

Synalpheus regalis is a

heterospecific intruders.[5] This evidence points towards the first known case of eusociality
in a marine animal.

The species name "regalis" comes from the Latin regalis which means royal.[3] 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 Synalpheus, the second largest genus in the snapping shrimp family (Alpheidae), with over 150 species worldwide.[3] The species was discovered by J. Emmet Duffy in 1996 on the Belize Barrier Reef.[3] As of 2013, S. regalis is one of at least seven recognized species of eusocial shrimp. The other six are Synalpheus brooksi, Synalpheus chacei, Synalpheus elizabethae, Synalpheus filidigitus, Synalpheus microneptunus and Synalpheus rathbunae.[6][7]

Appearance

Synalpheus regalis is a translucent orange. The

shrimps
’ eyestalks.

Ovigerous females are generally 2.6–3.7 mm in length and males and juveniles are approximately 2.8 mm.[3] 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

lateral stabilizing fin) compared to the S. regalis.[3]

Habitat

S. regalis lives exclusively in association with

sponges; however, it has only been found to associate with three sponge species: Neopetrosia proxima, Neopetrosia subtriangularis, and Hyatella intestinalis. In Jamaica, they are found in H. intestinalis, in depths of over six meters. In Belize, 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.[6][8]

They rarely cohabit sponges with other shrimps, suggesting that competition in the habitat is fierce and would explain why they are found associated exclusively with only two species of sponges.[3] 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.[3] In some places such as the Bocas del Toro Archipelago, S. regalis co-occurs with close relative S. elizabethae.[9]

The shrimp feed on the host tissues as well as on the detritus, which includes bodies of dead organisms or fecal material.[3]

Life cycle

Synalpheus regalis exhibits

eusocial 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.[7] 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.[10]

Behavior and ecology

Eusociality

J. Emmett Duffy, a primary investigator of S. regalis, uses the term "

division of labor, which results in enhanced reproductive output of the breeders and inclusive fitness benefits for the nonbreeding helpers.[10]

Colony organization

S. regalis has the largest colonies and the largest reproductive

outbreeding
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

aggressive
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.[12]

In this theory, the queen dominates the colony’s reproduction 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. Queller and Strassmann (1998) distinguished between "life insurers", which include most Hymenoptera, where cooperation reduces the risk of total reproductive failure, and "fortress defenders", where cooperation enhances the defense of a commonly held, valuable resource.[11][13]

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.[11] 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.[14][15]

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.[11]

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.[10] 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.[15] 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.[5] The larger shrimp tend to be older than the rest of the colony, and thus they allocate their energy to defending rather than breeding.[4] Such size- or age-related polyethism is a common aspect of labor specialization among social insects.[10][16] 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.[4] This nest defense amounts to cooperative brood care and establishes S. regalis as a eusocial species.[5]

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 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.[14][17]

Nestmate recognition

S. regalis are exceptionally tolerant of

relatedness 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.[10][18][19] 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.[10]

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 pheromones like in social insects.[10]

See also

References

  1. ^ Sammy De Grave (2012). "Synalpheus regalis Duffy, 1996". WoRMS. World Register of Marine Species. Retrieved October 10, 2012.
  2. doi:10.1651/07-2969.1
    .
  3. ^
    JSTOR 1548748
    .
  4. ^ a b c d Esra Deniz Gumuser. "A marine dwelling eusocial organism: Synalpheus regalis". Connexions. Retrieved 9 October 2012.
  5. ^
    S2CID 33166806
    .
  6. ^
    PMID 23418429
    .
  7. ^
    doi:10.11646/zootaxa.2834.1.1
    .
  8. ^ a b c Kenneth MacDonald; Kristin Hultgren & J. Emmett Duffy (2009). "The sponge-dwelling snapping shrimps (Crustacea, Decapoda, Alpheidae, Synalpheus) of Discovery Bay, Jamaica, with descriptions of four new species" (PDF). Zootaxa. 2199: 42.
  9. ^ Rios, R.; J.E. Duffy (2007). "A review of the sponge-dwelling snapping shrimp from Carrie Bow Cay, Belize, with description of Zuzalpheus, new genus, and six new species". Zootaxa (1602): 3–89.
  10. ^
    S2CID 25384748. Archived from the original
    (PDF) on 2015-08-03.
  11. ^ a b c d J. Emmett Duffy (2002). "The ecology and evolution of eusociality in sponge-dwelling shrimp". In T. Kikuchi (ed.). Genes, Behavior, and Evolution in Social Insects (PDF). Sapporo, Japan: University of Hokkaido Press. pp. 1–38.
  12. ^
    ISBN 978-0-19-517992-7
    .
  13. JSTOR 1313262
    .
  14. ^
    ISBN 978-1-4051-1416-5
    .
  15. ^
    PMID 17148125
    .
  16. ISBN 978-0-674-45490-3
    .
  17. PMID 19889706
    .
  18. S2CID 5310280
    .
  19. PMID 5875340
    .

External links
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