# Phragmosis

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{{Short description|Animal method of defense}}
{{Multiple image
|image1=Cephalotes varians casent0103754 head 1.jpg
|image2=Cephalotes varians casent0103754 profile 2.jpg
|total_width=320
|footer=The phragmotic head of ''[Cephalotes varians](/source/Cephalotes_varians)''.
}}
'''Phragmosis''' is any method by which an animal defends itself in its [burrow](/source/burrow), by using its own body as a barrier.<ref name=":0">{{Cite journal|last1=Wheeler|first1=Diana E.|last2=Hölldobler|first2=Bert|title=Cryptic Phragmosis: The Structural Modifications|journal=Psyche: A Journal of Entomology|language=en|volume=92|issue=4|pages=337–353|doi=10.1155/1985/76848|issn=0033-2615|year=1985|doi-access=free}}</ref> This term was originally coined by W. M. Wheeler (1927), while describing the defensive technique exhibited by [insect](/source/insect)s.<ref name=":1">{{Cite journal|last1=Brandão|first1=C. R. F.|last2=Diniz|first2=J. L. M.|last3=Silva|first3=P. R.|last4=Albuquerque|first4=N. L.|last5=Silvestre|first5=R.|title=The first case of intranidal phragmosis in ants. The ergatoid queen of Blepharidatta conops (Formicidae, Myrmicinae) blocks the entrance of the brood chamber|journal=Insectes Sociaux|language=en|volume=48|issue=3|pages=251–258|doi=10.1007/pl00001774|issn=0020-1812|year=2001|s2cid=25923049}}</ref> Wheeler observed the positioning of specially modified body structures to block nest entrances, as exhibited in various [insect](/source/insect) species.<ref name=":1" /> The term phragmosis has since been further extended beyond just insects.

Examples of phragmosis are found in the order [Anura](/source/Frog) (frogs and toads). Some species, such as [''Pternohyla fodiens''](/source/Lowland_burrowing_tree_frog) and ''[Corythomantis greeningi](/source/Corythomantis_greeningi)'', have evolved a peculiarly casqued head adapted to protect the animal as it backs down a hole.<ref name=":2">{{Cite journal|last1=Jared|first1=C.|last2=Antoniazzi|first2=M. M.|last3=Navas|first3=C. A.|last4=Katchburian|first4=E.|last5=Freymüller|first5=E.|last6=Tambourgi|first6=D. V.|last7=Rodrigues|first7=M. T.|date=2005-01-01|title=Head co-ossification, phragmosis and defence in the casque-headed tree frog Corythomantis greeningi|journal=Journal of Zoology|language=en|volume=265|issue=1|pages=1–8|doi=10.1017/s0952836904005953|s2cid=59449901 |issn=1469-7998}}</ref> Another example is the head-plug defense used by the [aphid](/source/aphid) ''Astegopteryx'' sp., in which a banana-bunch shaped [gall](/source/gall) consisting of several subgalls is used as a barrier.<ref name=":4">{{Cite journal|last1=Kurosu|first1=U.|last2=Narukawa|first2=J.|last3=Buranapanichpan|first3=S.|last4=Aoki|first4=S.|date=2006-02-01|title=Head-plug defense in a gall aphid|journal=Insectes Sociaux|language=en|volume=53|issue=1|pages=86–91|doi=10.1007/s00040-005-0839-4|s2cid=2070334|issn=0020-1812}}</ref> Arguably, the most commonly observed phragmotic behaviour is within the [ant](/source/ant) family.<ref name=":1" /> The behaviour is displayed in numerous taxa such as ''[Camponotus](/source/Camponotus)'', ''[Colobostruma](/source/Colobostruma)'', ''[Crematogaster](/source/Crematogaster)'', ''[Pheidole](/source/Pheidole)'', ''[Blepharidatta](/source/Blepharidatta)'', ''[Cephalotes pusillus](/source/Cephalotes_pusillus)'', [''Carebara elmenteitae''](/source/Carebara), ''[Stenamma expolitum](/source/Stenamma_expolitum)'', in which the soldiers have unusually large, disc-shaped heads, which are used to block nest entrances against intruders.<ref name=":0" />

== In Anura ==
=== ''Corythomantis greeningi'' ===
[Anurans](/source/Frog) involve a diverse group of largely [carnivorous](/source/Carnivore), short-bodied, tailless [amphibian](/source/amphibian)s. Within this group, some [frog](/source/frog)s are characterized by a peculiar casqued head, with the skin [co-ossified](/source/Ossification) with the underlying bones. This type of [skull](/source/skull) is generally associated with phragmotic behaviour, where the animal will enter a hole and block the entrance with its head.<ref name=":2" />

Recent studies of ''[Corythomantis greeningi](/source/Corythomantis_greeningi)'', a casque-headed [tree frog](/source/tree_frog) from [semi-arid](/source/Semi-arid_climate) areas, have provided substantial information regarding the water economy associated with [co-ossification](/source/co-ossification) of the head.<ref name=":2" /> Due to the [arid](/source/arid) environments of most casque-headed [anurans](/source/anurans), it has been proposed that head co-ossification, together with phragmotic behaviour confer protection against [water loss](/source/Dehydration). Upon further investigation, it has been found that cranial co-ossification contributes little to conservation of water, but instead has a primary role of defence. This type of [skull morphology](/source/Skull) primarily acts to protect the animal against [predators](/source/Predation), and in doing so, leads to an indirect enhancement of water balance within the body.<ref name=":2" />

In the study conducted by Jared et al. (1999) and Navas, Jared & Antoniazzi (2002), ''[C. greeningi](/source/Corythomantis_greeningi)'' demonstrated the ability to enter [test tube](/source/test_tube)s backwards and close the entrance with their heads, a behaviour termed 'experimental phragmosis'. The study found that while phragmotic behaviour does not provide a significant reduction in water evaporation, it is important for preventing [desiccation](/source/desiccation).<ref name=":2" /> It was concluded that in ''[C. greeningi](/source/Corythomantis_greeningi)'', the co-ossified head likely [evolved](/source/evolved) originally as a protective lid for phragmotic individuals, but does aid in reducing water permeability through the head.<ref name=":2" />

=== ''Pternohyla fodiens'' ===
The Mexican hylid casque-headed frog, ''[Pternohyla fodiens](/source/Lowland_burrowing_tree_frog),'' utilizes the head casque to close the entrance of its refuge in a tree cavity by deflecting the head. Due to their frequent [foraging](/source/foraging) on the ground, this species often makes use of [vertical burrows](/source/Burrowing) already extant in the ground layer as well. Upon arrival of intruder, ''[P. fodiens](/source/Lowland_burrowing_tree_frog)'' assumes an immobile position – the head tipped back, with the entire body assumed in a gentle arch. The eyes close tightly, fore-legs are brought forward and upward, and hind-legs are flexed upward. By exhibiting the phragmotic habit during this interaction, it is more likely to effectively avoid [predation](/source/predation).<ref name=":3">{{Cite journal|last=Firschein|first=I. Lester|date=1951|title=Phragmosis and the "Unken Reflex" in a Mexican Hylid Frog, Pternohyla fodiens|journal=Copeia|volume=1951|issue=1|pages=74|doi=10.2307/1438060|jstor=1438060}}</ref>

== In gall-forming aphids ==
thumb|Aphid gall on ''Ulmus minor''The [aphid](/source/aphid) ''Astegopteryx'' sp. exhibits a head-plugging defense by forming a banana-bunch shaped [gall](/source/gall), consisting of several subgalls, on ''[Styrax benzoin](/source/Styrax_benzoin).'' The [soldier aphids](/source/Aphid) of ''Astegopteryx'' are characterized by their sclerotic, protruded heads, covered in many spine-like [seta](/source/seta)e. Several soldiers cooperate with one another to plug the [ostiole](/source/ostiole) of the subgall, utilizing their specialized morphology.<ref name=":4" />

In a study by Kurosu et al. (2005), of 173 [ostiole](/source/ostiole)s examined, 90.8% were plugged, with no space among the guarding soldiers.<ref name=":4" /> Of the 90.8% plugged [ostiole](/source/ostiole)s, several male intruders were found outside the phragmotic plug, attempting to enter.<ref name=":4" /> All intruders were blocked by the guarding soldiers, and it was nearly impossible to enter the subgall.<ref name=":4" />

''Astegopteryx'' soldiers effectively defend their subgall by plugging the [ostiole](/source/ostiole) nearly completely with their sclerotic, spiny heads, which are very likely to have [evolved](/source/evolved) for that purpose.<ref name=":4" />

== In ants ==
thumb|276x276px|Ant queen excavating hole
Phragmotic-headed [ant](/source/ant)s prevent intruders from entering nests by blocking the entrances, or by pushing them out of entrance galleries. 
Within the Neotropical species, ''[Blepharidatta conops](/source/Blepharidatta),'' queens are characterized by shield-like heads, and appear to secrete fibrous material. The material acts as a coating and eventually accumulates into a dense tangle of material, creating a disk over the head. When nests are visited, or inhabited by predators (especially [beetle](/source/beetle)s), the entrance is quickly blocked by the peculiar phragmotic disk of the queen. This modification of the body enables the queen to act as a living gate to the brood chamber.<ref name=":1" />

Phragmosis in ants has evolved independently in the diverse [ant](/source/ant) genera ''[Camponotus](/source/Carpenter_ant)'' Mayr (''Hypercolobopsis''), ''[Colobopsis](/source/Colobopsis)'' Mayr, ''[Cephalotes](/source/Cephalotes)'' Latreille,<ref>{{Cite journal|last=Urbani|first=C. Baroni|date=1998-08-01|title=The number of castes in ants, where major is smaller than minor and queens wear the shield of the soldiers|journal=Insectes Sociaux|language=en|volume=45|issue=3|pages=315–333|doi=10.1007/s000400050091|s2cid=34121973|issn=0020-1812}}</ref> ''[Colobostruma](/source/Colobostruma)'' Wheeler (''C. leae''), ''[Crematogaster](/source/Crematogaster)'' Lund (''Colobocrema''), ''[Pheidole](/source/Pheidole)'' Westwood (''P. colobopsis'', ''P. lamia''), but also in other genera, such as ''[Blepharidatta](/source/Blepharidatta)'' Smith, (''B''. ''conops''), ''[Tetraponera](/source/Tetraponera)'' Smith (''T. phrag- motica'') and ''[Carebara](/source/Carebara)'' Westwood.<ref name=":5">{{Cite journal|last1=Fischer|first1=Georg|last2=Azorsa|first2=Frank|last3=Garcia|first3=Francisco Hita|last4=Mikheyev|first4=Alexander|last5=Economo|first5=Evan|date=2015-05-10|title=Two new phragmotic ant species from Africa: morphology and next-generation sequencing solve a caste association problem in the genus Carebara Westwood|url=https://zookeys.pensoft.net/articles.php?id=6057|journal=ZooKeys|language=en|issue=525|pages=77–105|doi=10.3897/zookeys.525.6057|pmid=26487817|pmc=4607851|issn=1313-2970|doi-access=free|bibcode=2015ZooK..525...77F }}</ref> The behaviour is most developed in the genus ''[Cephalotes](/source/Cephalotes),'' where all castes (both [queens](/source/Queen_ant) and [workers](/source/Worker_ant)), have highly adapted head morphologies.<ref name=":5" /> The shield-like armor which characterizes this behaviour enables plugging of nest entrances, without exposing eyes, [antenna](/source/Antenna_(biology)) or [mandibles](/source/Mandible_(insect_mouthpart)) to any potential intruders.<ref name=":5" />

== In spiders ==

[[File:Cyclocosmia truncata.jpg|thumb|''[Cyclocosmia truncata](/source/Cyclocosmia_truncata)'']]
The trapdoor spider ''[Cyclocosmia](/source/Cyclocosmia)'' has an abdomen ending in a hardened disc that it uses to plug the entrance to its burrow.<ref>* {{aut|Zhu, M.S.}}, {{aut|Zhang, J.X}} & {{aut|Zhang, F.}} (2006): Rare spiders of the genus ''Cyclocosmia'' (Arachnida: Araneae: Ctenizidae) from tropical and subtropical China. ''The Raffles Bulletin of Zoology'' '''54'''(1): 119-124 [http://rmbr.nus.edu.sg/rbz/biblio/54/54rbz119-124.pdf PDF] {{Webarchive|url=https://web.archive.org/web/20070811074158/http://rmbr.nus.edu.sg/rbz/biblio/54/54rbz119-124.pdf |date=2007-08-11 }} (with pictures)</ref>

== References ==
<references />
Category:Ethology

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Adapted from the Wikipedia article [Phragmosis](https://en.wikipedia.org/wiki/Phragmosis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Phragmosis?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.