velikost textu

Biology of the soldier caste in the termite genus Prorhinoterme (Isoptera: Rhinotermitidae)

Upozornění: Informace získané z popisných dat či souborů uložených v Repozitáři závěrečných prací nemohou být použity k výdělečným účelům nebo vydávány za studijní, vědeckou nebo jinou tvůrčí činnost jiné osoby než autora.
Název:
Biology of the soldier caste in the termite genus Prorhinoterme (Isoptera: Rhinotermitidae)
Typ:
Disertační práce
Autor:
Mgr. Robert Hanus, Ph.D.
Školitel:
prof. RNDr. Pavel Štys, CSc.
Oponenti:
prof. RNDr. Jan Žďárek, DrSc.
prof. Judith Korb, Dr.
Id práce:
112472
Fakulta:
Přírodovědecká fakulta (PřF)
Pracoviště:
Katedra zoologie (31-170)
Program studia:
Zoologie (P1502)
Obor studia:
-
Přidělovaný titul:
Ph.D.
Datum obhajoby:
18. 6. 2008
Výsledek obhajoby:
Prospěl/a
Informace o neveřejnosti:
Příloha práce byla vyloučena ze zveřejnění.
Jazyk práce:
Angličtina
Abstrakt:
CíIe Hlavním cíIem mojí dofuorcké práce bý popis rozmaniýh aspeků biologie kosý vojóka u rodu Prorhinotermes Silvestri, 7909 (lsoptera: Rhinotermitidae). Můj zájem o tento rod je motivovón u.ýjimečnými rysy v jeho biologii a specifickou ýlogenetickou pozicí. Porozumnění biologii rodu Prorhinotermes je krokem k nalezení odpovědi na několik klíčoých otázek biologie termitťt,joko jsou: ,Je přítomnost kasý prauých dělníkú vskutku odvozeným jevem, jak bylo mnohoktút usuzováno? A uyvinula se tdto kasto v čeledi Rhinotermitidae z předkťt podobných rodu Prorhinotermes? Nebo existovola již u společných předků čeledi Rhinotermitidae o byla núsledně druhotně dmceno u rodu Prorhinotermes? A jaké vliuy zopříčinily tuto ztrátu?" Hledóní odpovědí no vo otózlgt spolu se zvědavostí povstóvající z mnoha dolších qýjimečných ryrsůbiologie rodu Prorhinotermes sfo./7 zrodu u velkého vědeckého zájmu o tento rod. liným zdrojem mojí motivace byl zdjem o foscinace kastou vojóka u termitů,jejížexistence je z mnoha pohledů unikótním jevem. Pod vlivem těchto inspimcí jsem se rozhodl zdměřit no vojólcy u rodu Prorhinotermes, kteří se zdojí hrót zásodní úlohu v jeho spoleěensfuích, Pokusil jsem se studovot úlohu vojóků s důrazem na ontogenezi a mortogenezi vojóků, populační dynamiku v raných koloniích, obranné schopnosti vojúků, jejich podíl na $zické obraně, no spuštění a šířenípoplašné komunikace a dolší behaviotúlní schopnosti, stejně jako chemii a onatomii hlavní obranné adoptoce vojákťt, tedy Írontólní žlózy. Představené ýsledlcy byý získány studiem tří druhťt rodu Prorhinotermes ze tří tlzójemně vzdólených zoogeografick.ých oblastí, t7i, P. simp|ex z Neotropické oblasti, P' cana|ifrons z Malgašské oblasti a P. inopinatus z Papuánské oblasti. Tam, kde to bylo žódoucí a možné,jsem ověřoval o/nebo srovnóval ýdedl<y no dvou nebo třech druzích s rozdílnou evoluční historií. Výsledlg jsou předloženy jako uýký pěti pťtvodních člónkú, jednoho přijatého rukopisu a jedné miniatury posteru' Shrnutí azávěr uýdedky představené vmojí dokorské próci opakovaně prokózoý zósadní podíl vojóků na mnoha aspektech biologie rodu Prorhinotermes. Tato klíčová role může bý popsóno nósledujícím shmutím nejdůležitějších charakeristik vojáků: Q) uysokó proporce vojóků, rod Prorhinotermes se tak řadí mezi termiý s nejuyšším podílem vojóků; Q) raný uývoj pruních vojóků v mlodých koloniích a brzké ustavení jejich uysokého podílu; (iii) specifická behaviorólní schopnost zóchrany vojíčekv reakci na porušení hnízda; (iu) iniciace a zprostředkovóní poplašné komunikace s pomocí vibračních, chemických a fyzických prostředkťl; (u) široký rejstřík obranného chovóní při konfrontaci s hmyzím vetřelcem či nepřítelem; (v) nezuykle objemnó obrannó frontólní žlóza, zabímjící ulznamnou část tělní dutiny; (vi) neobyčejně vysoké množstvíjedovaté obranné lótlg, které můžepředstavovat ož deset procent tělesné hmotnosti. Uvedené charafuertstiý kasý vojóka tak řadí rod Prorhinotermes po bok odvozených termitích linií z čeledíRhinotermitidae a Termitidoe, kde velmi početní, chemiclcy ozbrojení vojóci zastóvají širokou paletu úloh, včetně uyhledóvání a iniciace sběr potrauy mimo hnízdo a obrony během ýpmv za potrdvou. Vnedóvné době bylo tato schopnost popsóno také u rodu Prorhinotermes' l zde jsou uyhledóvóní a sběr koordinovóny vojól<y,keří v plné míře uplatňují vlostnosti, ježjsme mohli pozorovot u vojóků námi zkoumoných druhů. Odvozené schopnosti vojáků a ceých kolonií rodu Prorhinotermes kontrastují s jedním zósqdním rysem jeho biologie, ReÚ je všeobecně povožovón za primitivní: druhům tohoto rodu chybí kasto praých dělníků, charokteristickó pro termity, keří jsou schopni opatřovot potravu mimo hnízdo, Tento paradox, diskutovaný vzóvěrečné čósti mojÍ práce, zůstóvó i nodóIe n euysvětl en o u zúha do u.
Abstract v angličtině:
A pair of neotenic reproductives of P. simplex SUMMARY Ontogeny of soldiers in Prorhinotermes simplex The soldiers were found to develop from larvae of the second up to the eighth instar, via a short (13–17 days) presoldier stage. The early soldier instars were found exclusively in incipient colonies while the mature colony contained late instar soldiers only. The first soldiers occur early in the incipient colonies; as soon as one year aer the establishment of these colonies a high proportion of soldiers was observed, which is comparable to that in mature colonies. The abrupt change in the external anatomy occurs in two steps. During the larva-presoldier moult, the head increases in length but only slightly in width. During the presoldier-soldier moult, both the length and width of the head increase markedly and the typical cordate shape is attained; the relative size of the pronotum increases considerably. The long falcate mandibles develop mainly during the larva-presoldier moult. One antennal segment is added during these two moults. With increasing instar age of soldiers a relative increase of the pronotum and the head size in its posterior region was observed. No functional differences in external anatomy were found among the six soldier instars. The composition of the frontal gland secretion is similar in the six soldier instars, an extraordinarily high amount of the defensive substance, (E)-1-nitropentadec-1-ene, was detected together with (Z,E)-α-farnesene, presumably an alarm pheromone. P. simplex displays the typical mode of colony-age dependent strategy of soldier production. The observed patterns of soldier development and production in P. simplex well correspond to its ecological strategy of an advanced single-site nester able to migrate and form foraging groups. Egg care by soldiers in Prorhinotermes We observed an unusual non-combative mode of behaviour in soldiers of P. simplex and P. inopinatus, i.e. the handling and transportation of eggs aer a nest disturbance. The soldiers, apart from performing alarm and defensive activities, tried to handle the eggs on the open surface. They oen succeeded in liing an egg or even a group of eggs, and then searched for a nest entrance. They either entered the nest to come out without the egg(s) within a while, or they passed the egg(s) onto a pseudergate waiting in the opening. As a result, all eggs were rapidly evacuated. Laboratory experimentation showed that pseudergates and nymphs try to deposit the eggs in a dark shelter, whereas the soldiers tend to transfer the eggs to nestmates and drop them aer a while if no other termite accepts them. The described activity of Prorhinotermes spp. represents a behavioural ele- ment of great adaptive value: it enables the saving of eggs without exposing the pseudergates to the risk of predation in the open. The soldiers, on the other hand, are well adapted to perform open-air activities (they are sclerotized, armed, and toxic). Moreover, the observed cooperation of soldiers with pseudergates (waiting in the openings) proves that the soldier collecting behaviour is not a simplified “worker-like” activity, but a highly specialized behaviour. This is also evidenced by the elementary differences between pseudergates and soldiers in the mode of egg deposition (formation of egg clusters in the case of pseudergates and transmission of eggs to another individual in the case of soldiers). This observation changes our view of the soldier caste as an ex- clusively defensive caste. Alarm communication and alarm pheromone in Prorhinotermes canalifrons Behavioural experiments showed that both the frontal gland secretion and (E,E)-α-farnesene triggered alarm reactions in P. canalifrons, whereas (E)-1-nitropentadec-1-ene did not affect the behaviour of termite groups. The alarm reactions were characterised by rapid walking of activated termites and efforts to alert and activate other members of the group. Behavioural responses to alarm pheromone differed between homogeneous and mixed groups, suggesting complex interactions. Antennae of both soldiers and pseudergates were sensitive to the frontal gland secretion and to (E,E)-α-farnesene, but soldiers showed quantitatively stronger responses. The dose responses to (E,E)-α-farnesene were identical for both soldiers and pseudergates, suggesting that both castes use similar receptors to perceive (E,E)-α-farnesene. Our study confirmed the complementary role of compounds contained in the frontal gland secretion of P. canalifrons soldiers: the toxic (E)-1-nitropentadec- 1-ene is known to act as a contact poison, whereas the minor compound, the sesquiterpene (E,E)-α-farnesene, acts as an alarm pheromone. Agonistic behaviour in Prorhinotermes canalifrons Each of the three non-reproductive castes of Prorhinotermes canalifrons (pseudergates, presoldiers, soldiers of different ages) as well as artificial intercastes pseudergate-soldier displayed a specific behavioural repertoire when confronted with conspecific and heterospecific aliens. Pseudergates appeared to be non-negligible partici- pants in termite-termite agonistic interactions, though the principle element of the striking power of the colony defence is the soldier caste. The typical defensive activities of the soldier start to appear during the second day aer exuviation and the complete set of defensive behaviours can be observed on the third day, well before its defensive secretion is synthesized in the frontal gland. Reactions to heterospecific aliens were much faster and more violent than reactions to conspecifics, suggesting that individuals experience difficulties in identifying conspecific aliens. The behaviour of artificial intercastes induced by an analogue of JH is intermediate between that of pseudergates and soldiers presumably due to simultaneous expression of behavioural phenotypes of a pseudergate and a soldier in these individuals. Ultrastructure of the frontal gland in castes of Prorhinotermes simplex The frontal gland as a sac-like organ in Prorhinotermes simplex is present only in presoldiers, soldiers, and imagoes, but it develops also in nymph-soldier intercastes. The fully developed frontal gland of soldiers extends deep into the abdominal cavity. The secretory epithelium consists of a single type of secretory cells adhering directly to the cuticular intima. Secretory vacuoles originate in electron dense vesicles, which are transformed into large electron lucent vacuoles. Intermediate vacuoles frequently contain lipid droplets. The frontal gland cells in presoldiers reveal modifications connected with the production of a new cuticle; the new cuticle is thin and compact, whereas the old one is thick, porous, and wrinkled. None of these cuticles are present in soldiers. In soldiers, the cuticular intima is of endocuticular origin and is formed by dispersed dense material; the apical parts of secretory cells are formed by numerous irregular finger-like projections, true microvilli are completely lacking. In imagoes, the cuticle is composed of an epicuticle, a layer of epicuticular filaments, and one more basal layer; sexual differences were not observed. In nymph-soldier intercastes, the structure of the gland differs in the head and in the metathorax; the head part of the gland resembles the imaginal gland whereas the thoracic part resembles more that of the soldier; the development of secretory vacuoles stops at the stage of presence of lipid droplets. The frontal gland of Prorhinotermes soldiers belongs among the cases of the most pronounced development of these defensive weapons in termites. Defensive secretion of the frontal gland in Prorhinotermes soldiers Frontal gland contents of soldiers of three Prorhinotermes species, Prorhinotermes canalifrons, Prorhinotermes inopinatus, and Prorhinotermes simplex, consisted of two groups of compounds: nitroalkenes and sesquiter- pene hydrocarbons. Analysis by gas chromatography-mass spectrometry revealed (E)-1-nitropentadec-1-ene as the major component of the secretion with mean values of 152, 207, and 293 µg/individual for P. canalifrons, P. inopinatus, and P. simplex, respectively. Four other 1-nitroalkenes (C13, C14, C16, and C17), and two nitro- dienes (C15 and C17) were also detected in the three species. The C17:1 nitroalkene was identified as (E)-1- nitroheptadec-1-ene. The efficient protection of Prorhinotermes colonies provided by the nitroalkenes comes at a relatively high price: the use of large amounts of rare nitrogen. The sesquiterpene composition of the gland was species-specific: P. simplex contained (3Z,6E)-α-farnesene (mean of 39 µg/individual), while P. canalifrons and P. inopinatus contained the same compound (means of 0.5 and 1.5 µg/individual, respectively) as well as the (3E,6E) isomer (means of 1.8 and 0.7 µg/individual, respectively). Two other sesquiterpenes, trans-β-bergamotene and (Z)-γ-bisabolene, were also found in low quantities in the frontal gland of P. canalifrons. In light of our findings identifying (3E,6E)-α-farnesene as a component of alarm signalling in P. canalifrons, we can hypothesize that the sesquiterpenes also act as alarm substances in other Prorhinotermes species. At the same time we cannot exclude their simultaneous role as irritants, which adopted secondarily the information role. This would partially explain the observed interspecific chemical diversity of sesquiterpenes. Differential response of tissues and organs to JHA treatment in Prorhinotermes simplex The experiment has proved that the given JHA can be transmitted by contact (trophallaxis and/or grooming) from individuals held on a treated substrate to untreated individuals. The parallel expression of soldier and reproductive traits appears to be due to this specific mode of JHA intake. Aer ingestion or topical application the intercastes never display any reproductive features despite their orphaning: they are pseudergate-soldier intercastes; they usually moult for the second time within two weeks. The neotenic-soldier intercastes obtained in our treatment moulted only once and their anatomy undoubtedly showed that they were intermediate between neotenics and soldiers. The basic neotenic traits were: well-developed gonads and outer genitalia, epidermal glands composed of numerous class 1 and 3 secretory cells; principal soldier traits were: prolonged sharp man- dibles, and presence of developed frontal gland. In general, the response of tissues, and especially of the epidermis, to JHA proved to follow the all-or-none rule of JH action: the individual phenotype was intermediary between two castes whereas particular cells could always be attributed to one of the two castes; they were not „intercaste“. The variety of observed phenotypes can be explained by differential readiness and sensitivity of particular cells and tissues to JHA in the course of intermoult. The cells of the frontal gland epithelium, on the other hand, revealed a specific ultrastructure in the artificial intercastes, which cannot be compared to the ultrastructure of any of the described naturally occurring castes. This question is being addressed in our present-day research.
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