Indian Journal of Geo Marine Sciences Vol. 46 (08), August 2017, pp. 1511-1518

Review article

Emergence of in aquatic environment: Synalpheid show the way!

T. Subramoniam

Centre for Climate Change Studies, Sathyabama University, Jeppiaar Nagar, Rajiv Gandhi Salai, Chennai – 600119. Tamil Nadu. India

[Email: [email protected] ]

Received 16 April 2015 ; revised 22 November 2016

Life history traits such as direct development and restricted dispersal, ecological specialization to live in the host , defending the valuable host resource, as well as selective breeding by one or more queens contribute to the in marine Crustacea, in particular, the synalpheid . This review critically examines the preconditions necessary for the evolution of complex social behaviours and structures including eusociality in these symbiotic shrimps and other .

[Key words: Eusociality, mating systems, , synalpheid shrimps, communal living]

Introduction Eusociality, the apex of social searching” to complex social monogamy with organization is defined by Wilson1 as the mate guarding practises, along with their condition of multiple generations organising into symbiotic mode of living with other marine groups by means of an altruistic division of invertebrate species, may be the harbinger of labour. The condition extends further into communal living and the evolutionary origin of cooperative care of offspring, and reproductive eusociality. The social Synapheus shrimps are skew, by which is relegated to a generally monogamous carideans, living as single mother queen. Such advanced social symbionts inside the marine , life-long, systems have been well recognised only among and produce crawling larvae that are retained in social insects and the African mole-rats2. Among the sponge colony, across generations4. The the aquatic organisms, crustaceans have the resulting kinship relationship among the offspring unique distinction of having evolved such plays a pivotal role in the progression towards complex social systems only in the coral reef- social behaviour, ultimately leading to associated caridean shrimps. Various sponge- eusociality. In addition, prolonged parental care dwelling snapping shrimp species, composing the of the young in a microhabitat has also bolstered taxonomic , developed well- social living and near-eusocial conditions in coordinated aggregations, which may seem to be certain crabs and peracarides5. This review on the cusp of eusociality. Sexual patterns and endeavours to analyse various preconditions that modes of development are the most important life promote evolutionary origin of social systems, history traits in the coral reef associated caridean which qualify crustacean species such as shrimps3. However, it is the diversified mating Synalpheid shrimps to eusocial conditions, strategies ranging from promiscuous “pure among aquatic organisms. 1512 INDIAN J. MAR. SCI., VOL. 46, NO. 08, AUGUST 2017

Social insects eusociality has evolved in mole-rats through kin Eusocial behaviour of social insects mainly selection and in response to constraints imposed depends on the ability of the group members to by ecological factors such as distribution of food develop different castes with their respective in the form of underground roots and tubers. By division of labour. As an example, the honeybees living in large social groups with cooperation and live in highly structured colonies. Reproduction is reproductive repression, eusocial mole-rats are by the queen and drones, and the infertile able to exploit an ecological niche where solitary females, the workers, perform all other duties to or small groups would be unlikely to support the colony. The young workers tend the survive. Incidentally, members of the burrowing larvae, and then switch functions to forage and rodent family, Bathyergidae, to which the mole- collect pollen or nectar6. Honeybee vitellogenin, rats also belong, exhibit varied social strategies besides its principal role of providing precursors that include solitary, social/colonial dwelling, to yolk formation, exerts an effect on division of and, at the extreme, the eusocial condition as seen labour, and reduces oxidative stress by in the mole-rat Heterocephalus glaber8. scavenging free radicals, thereby prolonging Correlatively, the caridean alpheid shrimps also lifespan in the facultative sterile workers and the represent a single taxonomic group in which an reproductive queen6. Sterile workers (genetic entire spectrum of is witnessed; with females) are capable of synthesizing vitellogenin, only sponge-dwelling synalpheids evolving into a but use it only for making the royal jelly to feed eusocial condition (see below). the larvae. Understandably, the social life history traits of hymenopteran insects are determined by Synalpheid shrimps vitellogenin, which in insects is synthesized under Recognition of eusociality in the control of juvenile hormone7. It can therefore crustaceans inhabiting the aquatic environment be presumed that this hormone could be the is rather recent with the lifestyle description of ultimate decider of caste differentiation in these sponge-dwelling alpheid shrimp species, eusocial insects. belonging to the Synalpheus9. These coral-reef dwelling caridean shrimps have African naked mole-rats adapted to these specialized niches, on which In another example, the extremely eusocial they have depended for both shelter and food. African naked mole-rats characteristically live in Naturally, these symbiotic synalpheid shrimps colonies containing overlapping generations that developed innovations in their social behaviour, cooperate in the rearing of their offspring8. with respect to defending their bio-shelters, as Reproduction is normally monopolized by a well as in life history strategies that will bolster single breeding queen, who mates with one to retention of successive generations in the same three breeding males. All other colony members colony. Since such elaborate and safe sponge either act as “workers”, maintaining the burrow hosts for colonization are hard to find in the system, or “soldiers”, defending the colony crowded coral reef environment, the shrimps against foreign mole-rats or snakes. Although guard their invertebrate hosts fiercely with they have enhanced longevity, they suffer from powerful weaponry such as their snapping chronic infertility and never reproduce. The claws. Arguably, the first step in the evolution of socially induced suppression of reproduction in social behaviour of these shrimps may be the male and female mole rats is mediated by a successful occupation and defence of their mechanism involving direct contact with the symbiotic invertebrate hosts. breeding queen, rather than by primer Furthermore, many of the marine shrimp . Subtle agonistic interactions belonging to the genus Synalpheus exhibit social between the queen and non-breeders cause a monogamy, in which adults live as heterosexual neuroendocrine response in the latter, the pairs in a burrow (Table 1). Since female physiological result of which is inhibition of receptivity is restricted to a brief period after gonadal function and infertility. The genetic moulting, as in many decapods, males practise relatedness is very high in these eusocial forms, precopulatory mate-guarding and do not allow due to high inbreeding and the absence of other males into their territory. Social dispersal of non-breeders. It is thought that monogamy in these pair-forming alpheids is also SUBRAMONIAM: EMERGENCE OF EUSOCIALITY IN AQUATIC ENVIRONMENT 1513 maintained by cooperative defending of the entire reproduction is carried out by the common burrow by the pair10. A more complex queen in a colony, thereby making a level of communal living is found in some resemblance between the social insects sponge-dwelling synalpheid species such as () and the synalphid social shrimps. Synalpheus longicarpus, in which hundreds of Evidently, social monogamy seems to be the heterosexual pairs cohabit in a host with forerunner of eusociality in the sponge-dwelling multiple breeding females11. A further road to Synapheus shrimp for the reason that there is eusociality is however witnessed in certain direct development (bypassing planktonic species such as S. regalis, S. filidigitus, and S. dispersive larval stages) and a long-term parent- rathbunae (Table 1). All these fully eusocial offspring association which fosters formation of species live in colonies of hundreds of close kin groups. Thus, in these caridean individuals inside the spongocoel, with only a shrimps, the defining eusocial characteristics single female, breeding, as in S. regalis. In include (1) symbiotic social living in sponges another eusocial species, S. chacei, the colonies which provides shelter and food, (2) mate- are much smaller, but genetically heterogeneous. guarding and shared resource defence, (3) non- This genetic heterogeneity in S. chacei is due to dispersive larvae, and (4) social monogamy. In the presence of multiple queens in the colony. the eusocial species such as S. regalis, there is a The females of this multi-queen colonies are not strong reproductive skew, brought about by only smaller, but also possess the snapping restriction of reproduction to a single queen and claws12. As suggested by Duffy4 this condition a few male partners11. In addition, genetic may enhance the chance of the subordinate relatedness among the colony members of S. females to breeder status, leading to weaker kin regalis, as revealed from allozyme data, together selection and weaker cooperative behaviour in S. with demographic evidence of natal philopatry chacei. would further indicate that colonies in this species represent close kin groups, as a Eusociality in Synalpheus regale necessary prerequisite for evolution into a is the only social eusocial condition13. In particular, pair-forming species in the family in which all the monogamy has not only given rise to many preconditions necessary for the evolution of intermediary stages in shrimp species, but has eusociality have been described9. The sponge also provided the spring – loading of their social colony of up to 350 individuals contains behaviour, which finally culminated in a invariably a single breeding female, the queen. eusocial condition in some species. S. regalis colonies consist largely of full-sib offspring of a single breeding pair, as Evolution of mating systems and eusociality determined by genetic data as well as Establishment of mating systems in reproductive allometry. Long-term reproductive various crustacean groups has a profound effect monopoly by a single female in S. regalis is also on the likelihood of progress towards communal reflected in the strong correlation between queen living and eusociality. Several mating body size and colony size. An interesting associations have developed in response to observation is that a large male, which ecological adaptiveness of protection to aggressively behaves with other approaching overcome predation as well as food security both males, guards the queen4. The queen apparently for the female and the young. In addition, loses the snapping claw which assumes a small continued somatic growth in adult females has size equivalent to that of the juveniles. This created a physiological necessity for the results in the reduced of the queen, moulting females to seek protection from male relegating the colony defence to the large males. partners during their moulting period, which is Whereas the juveniles in the colony are free to followed by obligatory mating and oviposition feed and grow, the queen is allowed to feed and in several decapods. Mate guarding of females reproduce. The restriction of reproduction to a prior to and after mating in several crustacean single queen in S. regalis colonies is akin to species is an example to illustrate adaptation to physogastric queen of termites in as much as the such ecological and physiological demands of 1514 INDIAN J. MAR. SCI., VOL. 46, NO. 08, AUGUST 2017

Table 1: Occurrence of eusocial developmental traits in the genus Synalpheus of Alpheidae

Criteria conferring eusociality S. No. Name of the species Single/multiple Larval development Location Host sponge species References queen colonies direct/dispersive Carrie Bow Xestospongia and 1. Synalpheus regalis Single Direct Duffy13; Duffy et al.14 cay, Hyattella sp. Carrie Bow Oceanapia sp. and Duffy and 2. S. filidigitus Single Direct cay, Belize Xestospongia sp. Macdonald15 Carrie Bow 3. S. chacei Multiple Direct Niphates amorpha Duffy12 cay, Belize Carribean 4. S. agelas Multiple Direct coast of Agelas clathrodes Duffy16 Panama Carribean Xestospongia 5. S. rathbunae Multiple Direct coast of Duffy16 rosariensis Panama Carribean Spheciospongia Duffy16; 6. S. brooksi Multiple Direct coast of vesparium Duffy17 Panama Florida, Belize and Xestospongia 7. S. paraneptunus Single Direct Duffy16; Duffy et al.18 Carribean rosariensis Panama

mating system has prevailed in fast swimming caridean shrimps in dense populations, in which mate finding is not a difficult proposition20. Hence prolonged mate guarding, typical of other free-living decapods such as brachyuran crabs, has also evolved in those shrimp species that display receptivity for mating during a restricted period in the post moult condition. In this context, it is easy to understand the transition from pure searching to monogamy via pre- copulatory mate guarding of females, ultimately ending in social monogamy, which necessitates co-habitation of the heterosexual pairs either in burrows or in bio-nests. As an instance, temporal extension of mate guarding to social monogamy has been suggested in the burrow-dwelling snapping shrimp Alpheus angulatus21. In many decapods, in which moulting alternates with the reproductive cycle, the female undergoes an obligatory moulting before mating, so as to Fig 1: Evolution of eusociality among coral reef caridean facilitate intromission in the fresh moult shrimps. (Adapted from 19Subramoniam, 2016) condition. Furthermore, many decapods brood

their eggs in the pleopodal region and the reproduction. These kinds of reproductive development of the brood interferes with the behaviours have become important moult cycle. Possibly, mate guarding in decapod preconditions for eusocial life in these aquatic crustaceans has originated in response to a crustaceans (Fig.1). situation in which the gullible moulting female To discuss further, evolution of social obtains physical protection from its mate monogamy itself has its origin from a primitive guarding males against predators. Alternatively, form of “pure search” mating system practiced the males also receive benefits by way of by many extant shrimp species. The pure search paternity assurances, especially when the male SUBRAMONIAM: EMERGENCE OF EUSOCIALITY IN AQUATIC ENVIRONMENT 1515 extends guarding of the female well beyond transforming phase. None of the synalpheid copulation and/or oviposition. Eventually, this eusocial shrimps is hermaphroditic, and hence kind of extended mate guarding of the females the suppression of vitellogenesis in the sub could lead to pair forming social monogamy, adults would either be by way of the suggesting a strong relationship of mate vitellogenesis inhibitory neuropeptide, or by guarding behaviour with the evolution of social other hormonal factors proposed in the control monogamy in decapod crustaceans5. of vitellogenin synthesis. Nevertheless, social An unresolved question in the evolution cues from the breeding queen may also exert of eusociality in the sponge-dwelling synalpheid influence on the sub-adults in the alpheid colony caridean shrimp is the suppression of to suppress reproductive function, as in the case reproduction in sub-adults of the colony. of the African mole rats. Further work in this Wilson22 stated that the primary organizing regard is warranted. principle in insect societies is the control of female reproduction, especially egg Other crustaceans with eusocial tendencies development. In the truly eusocial forms, only Life history traits such as direct the queen performs the reproductive function, development with non-dispersive larvae as well while her descendants in the colony have their as extended parental care have also been reproductive activity considerably suppressed. observed in other crustacean species. Although All the castes are genetically identical, and are the eusocial conditions found in the Synalpheid considered to be alternative adult forms. In the shrimps has not been reached in certain crabs, honey , a young larva is totipotent and has amphipods and terrestrial isopods, they the capacity to develop into any of the above nevertheless represent the evolutionary route castes. The choice to metamorphose into one or towards advanced social life, including other form depends on the nutritional or eusociality. pheromonal signals the larvae are exposed to, during the critical period in its development. Bromeliad crabs Recent studies however point to the possible role In the Bromeliad crabs, another decapod played by the vitellogenin gene that could affect crustacean group with the potential to become a these social life history traits in the eusocial species, only the colony mother is Apis mellifera6. Vitellogenin, in addition to reproductive, whereas other subordinate females being the major precursor yolk protein, appears with physical attributes to reproduce, will not to have evolved pleotropic functions in the carry eggs in the pleopod. However, the advanced eusocial honeybee. Variation in subordinate females that leave the colony, start vitellogenin gene expression early in the life of reproducing by becoming solitary breeding the honey bee is associated with a subsequent foundresses of new colonies24. Furthermore, behavioural specialization that gives rise to a subordinate females could refrain from early division of labour among colony members. dispersal and reproduction for the benefit of Interestingly, in the sterile worker honey bees, staying at home and taking over the colony, once which are genetic females, vitellogenin level in the colony mother dies, or acquiring a new the haemolymph is very low with a adjacent bromeliad clone. Apparently, the corresponding regression in the ovarian activity. subordinates are under reproductive suppression by social cues emanating from the breeding Decapod crustaceans also produce colony queen. Whether the suppression of vitellogenin as the main yolk precursor protein, reproduction in these sub-adults is caused by any but its synthesis in the ovary and hepatopancreas released by the mother crab of the is modulated by an inhibitory neuropeptide and a colony, or impacted by any social cues from the 23 host of stimulatory hormonal factors . breeding dominant, and in this case, the Suppression of vitellogenesis could also be aggressive female, is not known. Although the effected by the unique androgenic gland genetic relatedness of the siblings in the colony hormone in crustaceans, but this male hormone of this crab has not been determined with is known to inhibit vitellogenesis in sequential molecular methods, the retention of the hermaphroditic forms during the sex subordinate females in the colony may provide 1516 INDIAN J. MAR. SCI., VOL. 46, NO. 08, AUGUST 2017

some benefits by their altruistic system to discern the family members from behaviour and perhaps by improving survival aliens. The females are semelparous and the and growth of younger siblings. Strangely, offspring cohabit in the burrow, and the male unlike the synalpheid queens, which have lost participates in the brood care. The coexistence their fighting claws, the bromeliad queen crabs of individuals in the well-guarded burrows can attack and expel intruding adult females as forms ideal conditions for the evolution of well as smaller individuals. However, adult eusocial behaviours in Crustacea. female colony members are allowed to stay, probably because they may be the daughters of Conclusions the breeding queen. In the Bromeliad crabs, Preconditions set for evolving parental care for offspring is also a special case eusociality vary among different eusocial of , since a breeding female also organisms. In social insects, it is their vigorously protects the young with its powerful physiological ability that made it possible to chelae. differentiate into both reproductive and non- reproductive castes. Successful colonization of Amphipods and isopods social and hymenopterans has almost led to Parental care is also considered to be an a „social conquest on earth‟ among land important evolutionary precursor to eusocial invertebrates, according to Wilson1. Conversely, behaviour in crustaceans. As many in the African mole rats, risk of predation malacostracan crustaceans brood their eggs outside the burrows and the availability of attached the pleopods, extended parental care is subterranean food sources could have driven offered by the females. Even after the broods are them to choose community living underground released, the young ones are kept in the brood and the consequent development to eusociality. for a prolonged period. Both leucothoid and On the aquatic front, what could be the anamixid amphipods, like all other amphipods, conditions that set the tone for eusocial have direct development. That restricts dispersal evolution? Is it their symbiotic living with a live of their young ones outside their sponge or sponge in the coral niche that has driven ascidian hosts, found on the tropical coral synalpheid shrimps to choose group living and reefs25. The males have hypertrophied evolve eusociality? The coral reef environment gnathopods, presumably employed in abounds with diversified marine species, cooperative defence of the host. It has been offering innumerable habitat niches, resulting in suggested that their group living could not the adoption of various lifestyles, reproductive proceed further towards eusociality, as they had modes and behaviour. While the sponge- to compete with the more powerful and dwelling synalpheid shrimps could be credited dominant Synalpheus shrimps in the sponge with their successful adaptation to live and hosts4. reproduce in this microenvironment for their Isopods are known for their mate evolution into a eusocial group, it is the inherent guarding behaviour, which becomes crucial with capacity to form mating systems that paved the the advent of biphasic molting and the restricted way for communal living among these decapod female receptivity period26. Precopulatory crustaceans. guarding and copulation may be followed by Subramoniam19 reasoned in his recent postcopulatory guarding, as in review that evolution of social monogamy Thermosphaeroma baltica and T. among different alpheid caridean shrimps might thermophilum27. In the desert isopod, lead to complex social systems and living. This Hemilepstus reaumuri, the female prefers however is not a new tenet in the social sheltered copulation in burrows made by large evolution of marine crustaceans. But the males. Interestingly, the male and female form a ultimate basis for the development of mating sexually and socially monogamous cooperative systems in decapods could very well be the pair defending the burrow against intra-and peculiar mate guarding behaviour that originated interspecific competitors28. The families of H. in crustaceans. Origin of mate guarding among reaumuri are strictly closed units. They also use the marine crustaceans could be conveniently an extremely variable chemical recognition linked to the continued moulting in the adults, a SUBRAMONIAM: EMERGENCE OF EUSOCIALITY IN AQUATIC ENVIRONMENT 1517 developmental feature not existent in their shrimps) would shed light on the anthropogenic winged insect cousins. Furthermore, none of the impacts on this climate-sensitive marine other successful marine invertebrates such as ecosystem. In India, coral reef caridean shrimps molluscs and echinoderms practises mate have an important market value as ornamental guarding, as they do not undergo moulting. shrimps. Any unmindful collection and illegal Female mate guarding in decapods starts in the trading of them will adversely affect their premoult stage, and extends in many cases normal distribution and their specific symbiotic beyond intromission and sometimes oviposition. living with other marine invertebrate in the coral While guarding, the male gets the benefit of reef zones32. Therefore, any undertaking on the mating assurance, and the female gets additional life-history study of these commercially benefits of protection from predators during the significant coral reef organisms will benefit vulnerable period of ecdysis, which obligatorily vastly the governmental agencies concerned precedes mating and spawning in the majority of with the protection of these enchanting decapods. Post-copulatory extended mate ecosystems in the Indian waters. guarding by the males is also a form of paternal care of the offspring by way of protecting the References hapless brooding female. This condition is ideal 1. Wilson, E. O., The social conquest of earth (New for pair-forming monogamy, especially when York: Liveright Publishing Corporation), (2012). 2. Jarvis, J. U. M., Bennett, N. C., Eusociality has the pair chooses to live in burrows or other bio- evolved independently in two species of shelters, leading to social monogamy. 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