Editing Red imported fire ant (section)

===Physiology===
[[File:Photomicrograph of sting apparatus components journal.pone.0050400.png|thumb|200px|Photomicrograph of sting apparatus components]]

Like other insects, the red imported fire ant breathes through a system of gas-filled tubes called [[Invertebrate trachea|tracheae]] connected to the external environment through spiracles. The terminal tracheal branches ([[tracheole]]s) make direct contact with internal organs and tissue. The transport of oxygen to cells (and carbon dioxide out of cells) occurs through [[diffusion]] of gases between the tracheoles and the surrounding tissue and is assisted by a [[discontinuous gas exchange]].<ref name="Vogt_Appel_2000">{{cite journal|last1=Vogt|first1=J.T.|last2=Appel|first2=A.G.|title=Discontinuous gas exchange in the fire ant, ''Solenopsis invicta'' Buren: Caste differences and temperature effects|url=https://archive.org/details/sim_journal-of-insect-physiology_2000-04_46_4/page/403|journal=Journal of Insect Physiology|date=2000|volume=46|issue=4|pages=403–416|doi=10.1016/S0022-1910(99)00123-7|pmid=12770204|bibcode=2000JInsP..46..403V }}</ref> As with other insects, the direct communication between the tracheal system and tissues eliminates the need for a circulating fluid network to transport O<sub>2</sub>.<ref name="Klowden_2007">{{cite book|last1=Klowden|first1=M.J.|title=Physiological Systems in Insects|url=https://archive.org/details/physiologicalsys00mjkl|date=2007|publisher=Elsevier/Academic Press|location=Amsterdam; Boston|isbn=978-0-12-369493-5|pages=[https://archive.org/details/physiologicalsys00mjkl/page/n367 357]–383, 433–449}}</ref> Thus, red imported fire ants and other arthropods can have a modest circulatory system though they have highly expensive metabolic demands.<ref>{{cite book|last1=Hill|first1=R.W.|last2=Wyse|first2=G.A.|last3=Anderson|first3=M.|title=Animal Physiology|url=https://archive.org/details/animalphysiology0000hill|date=2012|publisher=Sinauer Associates|location=Sunderland, Massachusetts|isbn=978-0-87893-662-5|pages=[https://archive.org/details/animalphysiology0000hill/page/612 612]–614|edition=3rd}}</ref>

The [[excretory system]] consists of three regions. The basal region has three cells found within the posterior portion of the midgut. The anterior and superior cavities are formed by the bases of four [[Malpighian tubule system|Malpighian tubule]]s.<ref name="Vinson_1983">{{cite journal|last1=Vinson|first1=S.B.|title=The physiology of the imported fire ant revisited|journal=The Florida Entomologist|date=1983|volume=66|issue=1|pages=126–139|doi=10.2307/3494559|jstor=3494559}}</ref> The superior cavity opens into the [[Lumen (anatomy)|lumen]] of the small intestine. The rectum is a large but thin-walled sac that occupies the posterior fifth of the larvae. The release of waste is controlled by the [[Transverse folds of rectum|rectal valves]] that lead to the anus.<ref name="Vinson_1983"/> Sometimes, the larvae secrete a liquid that consists of [[uric acid]], water and salts.<ref>{{cite journal|last1=Petralia|first1=R.S.|last2=Williams|first2=H.J.|last3=Vinson|first3=S.B.|title=The hindgut ultrastructure, and excretory products of larvae of the imported fire ant, ''Solenopsis invicta'' Buren|journal=Insectes Sociaux|date=1982|volume=29|issue=2|pages=332–345|doi=10.1007/BF02228760|s2cid=7324976}}</ref> These contents are often carried outside by workers and ejected, but colonies under water stress may consume the contents.<ref name="Vinson_1983"/> In the [[reproductive system]], queens release a [[pheromone]] that prevents dealation and [[oogenesis]] in virgin females; those tested in colonies without a queen begin [[oocyte]] development after dealation and take up the egg-laying role.<ref>{{cite journal|last1=Fletcher|first1=D.J.C.|last2=Blum|first2=M.S.|title=Pheromonal control of dealation and oogenesis in virgin queen fire ants|journal=Science|date=1981|volume=212|issue=4490|pages=73–75|doi=10.1126/science.212.4490.73|pmid=17747633|bibcode=1981Sci...212...73F}}</ref> Flight muscle degeneration is initiated by mating and juvenile hormones, and prevented by [[wikt:corpus allatum|corpus allatectomy]].<ref>{{cite journal|last1=Barker|first1=J.F.|title=Neuroendocrine regulation of oocyte maturation in the imported fire ant ''Solenopsis invicta''|journal=General and Comparative Endocrinology|date=1978|volume=35|issue=3|pages=234–237|doi=10.1016/0016-6480(78)90067-9|pmid=689357}}</ref><ref>{{cite journal|last1=Jones|first1=R.G.|last2=Davis|first2=W.L.|last3=Hung|first3=A.C.F.|last4=Vinson|first4=S.B.|title=Insemination-induced histolysis of the flight musculature in fire ants (''Solenopsis'', spp.): An ultrastructural study|journal=American Journal of Anatomy|date=1978|volume=151|issue=4|pages=603–610|doi=10.1002/aja.1001510411|pmid=645619}}</ref> [[Histolysis]] begins with the dissolution of the [[myofibril]] and the slow breakdown of the [[myofilament]]s. Such dissolution continues until it reaches the only free Z-line materials, which would also disappear; only the [[Nucleus (neuroanatomy)|nuclei]] and [[lamellar bodies]] remain.<ref name="Vinson_1983"/> In one study, the [[amino acid]]s increase in the [[hemolymph]] after insemination.<ref>{{cite journal|last1=Toom|first1=P.M.|last2=Johnson|first2=C.P.|last3=Cupp|first3=E.W.|title=Utilization of body reserves during preoviposition activity by ''Solenopsis invicta''|journal=Annals of the Entomological Society of America|date=1976|volume=69|issue=1|pages=145–148|doi=10.1093/aesa/69.1.145}}</ref>

The [[Endocrine system|glandular system]] contains four glands: the mandibular, maxillary, labial, and [[Pharynx|postpharyngeal]] glands.<ref name="Vinson_1983"/> The postpharyngeal is well developed in the queen, while the other glands are larger in workers. The postpharyngeal gland functions as a vacuum to absorb [[fatty acid]]s and [[triglyceride]]s, as well as a gastric [[Cecum|caecum]].<ref name="Vinson_1980">{{cite journal|last1=Vinson|first1=S.B.|last2=Phillips|first2=S.A.|last3=Williams|first3=H.J.|title=The function of the post-pharyngeal glands of the red imported fire ant, ''Solenopsis invicta'' buren|journal=Journal of Insect Physiology|date=1980|volume=26|issue=9|pages=645–650|doi=10.1016/0022-1910(80)90035-9|bibcode=1980JInsP..26..645V }}</ref> The functions of the other glands remain poorly understood. In one study discussing the enzymes of the digestion system of adult ants, [[lipase]] activity was found in the mandibular and labial glands, as well as [[invertase]] activity. The [[Dufour's gland]] found in the ant acts as a source of [[trail pheromone]]s, although scientists believed the poison gland was the source of the queen pheromone.<ref name="Vinson_1983"/><ref>{{cite journal|last1=Vander Meer|first1=R.K.|last2=Lofgren|first2=C.S.|title=Biochemical and behavioral evidence foe hybridization between fire ants, ''Solenopsis invicta'' and ''Solenopsis richteri'' (Hymenoptera: Formicidae)|journal=Journal of Chemical Ecology|date=1989|volume=15|issue=6|pages=1757–1765|doi=10.1007/BF01012263|pmid=24272179|bibcode=1989JCEco..15.1757V |s2cid=23144401}}</ref><ref name="Vander">{{cite journal|last1=Vander Meer|first1=R.K.|last2=Glancey|first2=B.M.|last3=Lofgren|first3=C.S.|last4=Glover|first4=A.|last5=Tumlinson|first5=J.H.|last6=Rocca|first6=J.|title=The poison sac of red imported fire ant queens: source of a pheromone attractant|journal=Annals of the Entomological Society of America|date=1980|volume=73|issue=5|pages=609–612|doi=10.1093/aesa/73.5.609}}</ref> The neurohormone [[pheromone biosynthesis activating neuropeptide]] is found in the ant that activates the biosynthesis of pheromones from the Dufour's gland.<ref>{{cite journal|last1=Choi|first1=M.Y.|last2=Vander Meer|first2=R.K.|last3=Renou|first3=M.|title=Ant trail pheromone biosynthesis is triggered by a neuropeptide hormone|journal=PLOS ONE|date=2012|volume=7|issue=11|pages=e50400|doi=10.1371/journal.pone.0050400|pmid=23226278|pmc=3511524|bibcode=2012PLoSO...750400C|doi-access=free}}</ref> The [[spermatheca]] gland is found in queens, which functions in sperm maintenance. Males appear to lack these glands, but those associated with its head are morphologically similar to those found in workers, but these glands may act differently.<ref name="Vinson_1980"/>

[[File:A Comparative Study between Solenopsis invicta and Solenopsis richteri on Tolerance to Heat and Desiccation Stresses journal.pone.0096842.png|thumb|left|200px|Water loss rates of workers and female [[alate]]s in ''S. invicta'' and ''S. richteri'']]

The ant faces many respiratory challenges due to its highly variable environment, which can cause increased [[desiccation]], [[Hypoxia (medical)|hypoxia]], and [[hypercapnia]]. Hot, humid climates cause an increase in heart rate and respiration which increases energy and water loss.<ref name="Klowden_2007"/><ref>{{cite journal|last1=Elzen|first1=G.W|title=Oxygen consumption and water loss in the imported fire ant ''Solenopsis invicta'' Buren|journal=Comparative Biochemistry and Physiology A|date=1986|volume=84|issue=1|pages=13–17|doi=10.1016/0300-9629(86)90035-6}}</ref> Hypoxia and hypercapnia can result from red imported fire ant colonies living in poorly ventilated [[Thermoregulation|thermoregulatory]] mounds and underground nests. Discontinuous gas exchange (DGE) may allow ants to survive the hypercapnic and hypoxic conditions frequently found in their burrows;<ref name="Vogt_Appel_2000"/> it is ideal for adapting to these conditions because it allows the ants to increase the period of O<sub>2</sub> intake and CO<sub>2</sub> expulsion independently through spiracle manipulation. The invasion success of the red imported fire ant may possibly be related to its physiological tolerance to [[abiotic stress]], being more heat tolerant and more adaptable to desiccation stress than ''S. richteri''. This means that the ant is less vulnerable to heat and desiccation stress. Although ''S. richteri'' has higher water body content than the red imported fire ant, ''S. richteri'' was more vulnerable to desiccation stress. The lower sensitivity to desiccation is due to a lower water loss rate.<ref>{{cite journal|last1=Chen|first1=J.|last2=Rashid|first2=T.|last3=Feng|first3=G.|last4=Hughes|first4=W.|title=A comparative study between ''Solenopsis invicta'' and ''Solenopsis richteri'' on tolerance to heat and desiccation stresses|journal=PLOS ONE|date=2014|volume=9|issue=6|pages=e96842|doi=10.1371/journal.pone.0096842|pmid=24915009|pmc=4051589|bibcode=2014PLoSO...996842C|doi-access=free}}</ref> Colonies living in unshaded and warmer sites tend to have a higher heat tolerance than those living in shaded and cooler sites.<ref>{{cite journal|last1=Boyles|first1=J.G.|last2=Aubrey|first2=D.P.|last3=Hickman|first3=C.R.|last4=Murray|first4=K.L.|last5=Timpone|first5=J.C.|last6=Ops|first6=C.H.|title=Variation in physiological response of red imported fire ants (''Solenopsis invicta'') to small-scale thermal heterogeneity|journal=Journal of Thermal Biology|date=2009|volume=34|issue=2|pages=81–84|doi=10.1016/j.jtherbio.2008.10.005|bibcode=2009JTBio..34...81B }}</ref>

Metabolic rate, which indirectly affects respiration, is also influenced by environmental temperature. Peak [[metabolism]] occurs at about 32&nbsp;°C.<ref name="Poter_Tschinkel_1993">{{cite journal|last1=Porter|first1=S.D.|last2=Tschinkel|first2=W.R.|title=Fire ant thermal preferences: behavioral control of growth and metabolism|journal=Behavioral Ecology and Sociobiology|date=1993|volume=32|issue=5|page=321 |doi=10.1007/BF00183787|bibcode=1993BEcoS..32..321P |s2cid=9840395}}</ref> Metabolism, and therefore respiration rate, increases consistently as temperature increases. DGE stops above 25&nbsp;°C, although the reason for this is currently unknown.<ref name="Vogt_Appel_1999">{{cite journal|last1=Vogt|first1=J.T.|last2=Appel|first2=A.G.|title=Standard metabolic rate of the fire ant, ''Solenopsis invicta'' Buren: effects of temperature, mass, and caste|url=https://archive.org/details/sim_journal-of-insect-physiology_1999-07_45_7/page/655|journal=Journal of Insect Physiology|date=1999|volume=45|issue=7|pages=655–666|doi=10.1016/S0022-1910(99)00036-0|pmid=12770351|bibcode=1999JInsP..45..655V }}</ref>

Respiration rate also appears to be influenced significantly by caste. Males show a considerably higher rate of respiration than females and workers, due, in part, to their capability for flight and higher muscle mass. In general, males have more muscle and less fat, resulting in a higher metabolic O<sub>2</sub> demand.<ref name="Vogt_Appel_1999"/>
While the metabolic rate is highest at 32&nbsp;°C, colonies often thrive at slightly cooler temperatures (around 25&nbsp;°C). The high rate of metabolic activity associated with warmer temperatures is a limiting factor on colony growth because the need for food consumption is also increased. As a result, larger colonies tend to be found in cooler conditions because the metabolic demands required to sustain a colony are decreased.<ref name="Poter_Tschinkel_1993"/>