Editing Termite (section)

===Caste system===
Due to termites being [[Hemimetabolism|hemimetabolous insects]], where the young go through multiple and gradual [[wikt:adultoid|adultoid]] molts before maturing, the advent of eusociality has significantly altered the developmental patterns of this group of insects of which, although similar, is not homologous to that of the eusocial [[Hymenoptera]]. Unlike ants, bees, and wasps which undergo a [[Holometabolism|complete metamorphosis]] and as a result only exhibit developmental plasticity at the [[Larva|larval stage]], the mobile [[Instar|adultoid instars]] of termites remain developmentally flexible throughout all life stages up to the [[Imago|final molt]], which has uniquely allowed for the evolution of distinct yet flexible castes amongst the immatures. As a result the caste system of termites consists mostly of [[Neoteny|neotenous]] or juvenile individuals that undertake the most labor in the colony, which is in contrast to the eusocial Hymenoptera where work is strictly undertaken by the adults.

The developmental plasticity in termites can be described similarly to [[cell potency]], where each molt offers a varying level of phenotypic potency. Early instars typically exhibit the highest phenotypic potency and can be described as totipotent, able to molt into all alternative phenotypes. Following instars can be pluripotent, being able to molt into reproductives and non-reproductives but cannot molt into at least one phenotype. Multipotent instars are able to molt into either reproductive or non-reproductive phenotypes. Unipotent instars are able to molt into developmentally close phenotypes, and then the final instar is committed, being no longer able to change phenotype and so are functionally an adult.<ref name=":4" /> In most termites, phenotypic potency decreases with every successive molt. Notable exceptions are basal taxa such as the [[Archotermopsidae]], which are able to retain high developmental plasticity even up to the late instars. In these basal taxa, the immatures are able to go through ''progressive'' (''nymph-to-imago''), ''regressive'' (''winged-to-wingless'') and ''stationary'' (''size increase, remains wingless'') molts, which typically indicates the developmental trajectory an individual follows.<ref name=":5" /><ref name=":2" />

There is significant variation of the developmental patterns in termites even across closely related taxa, but can typically be generalized into the following two patterns: The first is the ''linear developmental pathway'', where all immatures are capable of developing into winged adults (''[[Alate]]s''), exhibit high phenotypic potency, and where there exists no true sterile caste other than the soldier. The second is the ''bifurcated developmental pathway'', where immatures diverge into two distinct developmental lineages known as the ''<u>nymphal</u>'' (winged) and ''<u>apterous</u>'' (wingless) lines. The bifurcation occurs early, either at the egg or the first two instars, and represents an irreversible and committed development to either the reproductive or non-reproductive lifestyles. As such, the apterous lineage consists mostly of wingless and truly [[Altruism (biology)|altruistic]] sterile individuals (true workers, soldiers), whereas the nymphal lineage consists mainly of fertile individuals destined to become winged reproductives. The bifurcated developmental pathway is found mainly in the derived taxa (i.e. [[Neoisoptera]]), and is believed to have evolved in tandem with the sterile worker caste as species moved to foraging for food beyond their nests, as opposed to the nest also being the food (such as in obligate wood-dwellers).<ref name=":6" /><ref name=":5" />

There are three main castes which are discussed below:
[[File:Termite vs Ant Developmental biology.png|thumb|Developmental biology of ants versus termites. As opposed to ants which have a linear and irreversible development from larval instars to adult (imago), termites exhibit a more complex and often bifurcated development which allows for more flexible caste pathways. Although in most termites, caste development is restricted to closely related pathways dependent on a variety of factors such as pheromonal cues, sex and size of an individual.]]
''Worker'' termites undertake the most labor within the colony, being responsible for foraging, food storage, and brood and nest maintenance.{{sfn|Bignell|Roisin|Lo|2010|p=13}}<ref name="aus" /> Workers are tasked with the digestion of [[cellulose]] in food and are thus the most likely caste to be found in infested wood. The process of worker termites feeding other nestmates is known as [[trophallaxis]]. Trophallaxis is an effective nutritional tactic to convert and recycle nitrogenous components.<ref name="trophal">{{cite journal|last1=Machida|first1=M.|last2=Kitade|first2=O.|last3=Miura|first3=T.|last4=Matsumoto|first4=T.|title=Nitrogen recycling through proctodeal trophallaxis in the Japanese damp-wood termite ''Hodotermopsis japonica'' (Isoptera, Termopsidae)|journal=Insectes Sociaux|date=2001|volume=48|issue=1|pages=52–56|doi=10.1007/PL00001745|s2cid=21310420|issn=1420-9098}}</ref> It frees the parents from feeding all but the first generation of offspring, allowing for the group to grow much larger and ensuring that the necessary gut symbionts are transferred from one generation to another. Workers are believed to have evolved from older wingless immatures (''Larvae'') that evolved cooperative behaviors; and indeed in some basal [[Taxon|taxa]] the late instar larvae are known to undertake the role of workers without differentiating as a true separate caste.<ref name="aus" /><ref name=":4">{{Cite journal |last1=Revely |first1=Lewis |last2=Sumner |first2=Seirian |last3=Eggleton |first3=Paul |date=2021-02-18 |title=The Plasticity and Developmental Potential of Termites |journal=Frontiers in Ecology and Evolution |volume=9 |doi=10.3389/fevo.2021.552624 |issn=2296-701X|doi-access=free |bibcode=2021FrEEv...952624R }}</ref> Workers can either be male or female, although in some species with [[Polymorphism (biology)|polymorphic]] workers either sex may be restricted to a certain developmental path. Workers may also be fertile or sterile, however the term "worker" is normally reserved for the latter, having evolved in taxa that exhibit a bifurcated developmental pathway.<ref name=":6">{{Cite journal |last1=Higashi |first1=Masahiko |last2=Yamamura |first2=Norio |last3=Abe |first3=Takuya |last4=Burns |first4=Thomas P. |date=1991-10-22 |title=Why don't all termite species have a sterile worker caste? |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=246 |issue=1315 |pages=25–29 |doi=10.1098/rspb.1991.0120 |issn=0962-8452 |pmid=1684665 |s2cid=23067349}}</ref> As a result, sterile workers like in the family [[Termitidae]] are termed ''true workers'' and are the most derived, while those that are undifferentiated and fertile as in the wood-nesting [[Archotermopsidae]] are termed ''pseudergates'', which are the most basal.<ref name=":2" /> ''True workers'' are individuals which irreversibly develop from the ''apterous lineage and'' have completely forgone development into a winged adult. They display altruistic behaviors and either have terminal molts or exhibit a low level of phenotypical potency. True workers across different termite taxa (''Mastotermitidae'', ''Hodotermitidae'', ''Rhinotermitidae'' & ''Termitidae)'' can widely vary in the level of developmental plasticity even between closely related taxa, with many species having true workers that can molt into the other apterous castes such as ''[[ergatoid]]s'' (worker reproductive; apterous neotenics), soldiers, or the other worker castes. ''Pseudergates sensu stricto'' are individuals which arise from the linear developmental pathway that have regressively molted and lost their wing buds, and are regarded as totipotent immatures. They are capable of performing work but are overall less involved in labor and considered more cooperative than truly altruistic. ''Pseudergates sensu lato'', otherwise known as ''false workers'', are most represented in basal lineages (''Kalotermitidae'', ''Archotermopsidae'', ''Hodotermopsidae'', ''Serritermitidae'') and closely resemble true workers in which they also perform most of the work and are similarly altruistic, however differ in developing from the linear developmental pathway where they exist in a stationary molt; i.e they have halted development before the growth of wing buds, and are regarded as pluripotent immatures.<ref name=":2">{{Cite book |last=Jürgen |first=Korb, Judith Thomas-Poulsen, Michael Hu, Haofu Li, Cai Boomsma, Jacobus Jan Zhang, Guojie Liebig |url=http://worldcat.org/oclc/937913325 |title=A genomic comparison of two termites with different social complexity |date=2015 |oclc=937913325}}</ref><ref name=":5">{{Cite book |url=https://link.springer.com/book/10.1007/978-90-481-3977-4 |title=Biology of Termites: a Modern Synthesis |year=2011 |language=en |doi=10.1007/978-90-481-3977-4|isbn=978-90-481-3976-7 |editor-last1=Bignell |editor-last2=Roisin |editor-last3=Lo |editor-first1=David Edward |editor-first2=Yves |editor-first3=Nathan }}</ref>

The ''soldier'' caste is the most anatomically and behaviorally specialized, and their sole purpose is to defend the colony.{{sfn|Bignell|Roisin|Lo|2010|p=18}} Many soldiers have large heads with highly modified powerful jaws so enlarged that they cannot feed themselves. Instead, like juveniles, they are fed by workers.{{sfn|Bignell|Roisin|Lo|2010|p=18}}<ref name="Britannica" /> [[Fontanelle]]s, simple holes in the forehead that lead to a gland which exudes defensive secretions, are a feature of the clade [[Neoisoptera]] and are present in all extant taxa such as Rhinotermitidae.<ref>{{cite book|last1=Busvine|first1=J.R.|title=Insects and Hygiene The biology and control of insect pests of medical and domestic importance|date=2013|publisher=Springer US|location=Boston, MA|isbn=978-1-4899-3198-6|page=545|edition=3rd}}</ref> The majority of termite species have mandibulate soldiers which are easily identified by the disproportionately large sclerotized head and mandibles.<ref name="aus" />{{sfn|Bignell|Roisin|Lo|2010|p=18}} Among certain termites, the soldier caste has evolved globular (phragmotic) heads to block their narrow tunnels such as seen in [[Cryptotermes]].<ref>{{cite book|last1=Meek|first1=S.P.|title=Termite Control at an Ordnance Storage Depot|date=1934|publisher=American Defense Preparedness Association|page=159}}</ref> Amongst mandibulate soldiers, the mandibles have been adapted for a variety of defensive strategies: Biting/crushing (''[[Incisitermes]]''), slashing (''[[Cubitermes]]''), slashing/snapping (''[[Dentispicotermes]]''), symmetrical snapping (''[[Termes (insect)|Termes]]''), asymmetrical snapping (''[[Neocapritermes]]''), and piercing (''[[Armitermes]]'').<ref>{{Cite web|url=https://www.researchgate.net/publication/237089558|title=Worker mandible shape and feeding groups in termites}}</ref> In the more derived termite taxa, the soldier caste can be polymorphic and include minor and major forms. Other morphologically specialized soldiers includes the [[Nasutitermitinae|Nasutes]], which have a horn-like nozzle projection ([[Fontanellar gun|nasus]]) on the head.<ref name="aus" /> These unique soldiers are able to spray noxious, sticky secretions containing [[diterpene]]s at their enemies.<ref name="biosyn">{{cite journal|last1=Prestwich|first1=G.D.|title=From tetracycles to macrocycles|journal=Tetrahedron|date=1982|volume=38|issue=13|pages=1911–1919|doi=10.1016/0040-4020(82)80040-9}}</ref> [[Nitrogen fixation]] plays an important role in Nasute nutrition.<ref>{{cite journal|last1=Prestwich|first1=G. D.|last2=Bentley|first2=B.L.|last3=Carpenter|first3=E.J.|title=Nitrogen sources for neotropical nasute termites: Fixation and selective foraging|journal=Oecologia|date=1980|volume=46|issue=3|pages=397–401|doi=10.1007/BF00346270|pmid=28310050|issn=1432-1939|bibcode=1980Oecol..46..397P|s2cid=6134800}}</ref> Soldiers are normally a committed sterile caste and so do not molt into anything else, but in certain basal taxa like the Archotermopsidae they are known to rarely molt into neotenic forms that develop functional sexual organs.<ref name=":3">{{Cite journal|last1=Thorne|first1=B. L.|last2=Breisch|first2=N. L.|last3=Muscedere|first3=M. L.|date=2003-10-28|title=Evolution of eusociality and the soldier caste in termites: Influence of intraspecific competition and accelerated inheritance|journal=Proceedings of the National Academy of Sciences|language=en|volume=100|issue=22|pages=12808–12813|doi=10.1073/pnas.2133530100|issn=0027-8424|pmc=240700|pmid=14555764|bibcode=2003PNAS..10012808T|doi-access=free}}</ref> In species with the linear developmental pathway, soldiers develop from apterous immatures and constitute the only true sterile caste in these taxa.<ref name=":3" />

The primary reproductive caste of a colony consists of the fertile adult (''imago'') female and male individuals, colloquially known as the queen and king.<ref name=techreport>{{cite tech report |first1=M.A.|last1=Horwood|first2=R.H.|last2=Eldridge|title=Termites in New South Wales Part 1. Termite biology |number=96-38 |institution=Forest Resources Research |year=2005|url=http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0016/252007/Termites-Part-1--Termite-biology.pdf|issn=0155-7548}}</ref> The queen of the colony is responsible for egg production of the colony. Unlike in ants, the male and female reproductives form lifelong pairs where the king will continue to mate with the queen throughout their lives.<ref name=Keller1998/> In some species, the abdomen of the queen swells up dramatically to increase [[fecundity]], a characteristic known as [[physogastrism]].{{sfn|Bignell|Roisin|Lo|2010|p=13}}<ref name=techreport/> Depending on the species, the queen starts producing reproductive alates at a certain time of the year, and huge swarms emerge from the colony when [[nuptial flight]] begins. These swarms attract a wide variety of predators.<ref name=techreport/> The queens can be particularly long-lived for insects, with some reportedly living as long as 30 or 50 years. In both the linear and bifurcated developmental pathways, the primary reproductives only develop from winged immatures (nymphs). These winged immatures are capable of regressively molting into a form known as ''brachypterous neotenics'' (''nymphoids''), which retain juvenile and adult characteristics. ''BN''<nowiki/>'s can be found in both the derived and basal termite taxa, and generally serve as supplementary reproductives.<ref name=":4" /><ref name=":5" />