Rpirea puilor de pinguini imperiali un efect secundar al hormonilor

Rpirea puilor de pinguini imperiali un efect secundar al hormonilor

Kidnapping chicks of emperor penguins: a hormonal by-product?

Masterand:Iriza Elena Maria RezumatFuncia i cauzele rpirii juvenile sunt foarte puin nelese, deoarece indivizii ntmpin unele probleme n a crete puii altor pinguini . Acest studiu se axeaz asupra cauzelor proximale ale acestui comportament de a fura puii ntlnit la pinguinii care nu se pot nmuli . S-a testat experimental ipoteza conform creia acest comportament a fost rezultatul unor niveluri reziduale de prolactin (PRL) ridicate, un hormon implicat n comportamentul parental. Pinguinii cu niveluri de PRL sczute artificial prin administrarea de bromocriptin au rpit puii mai rar dect pinguinii de control.n grupul tratat cu bromociptin, comportamentul de rpire nu a fost complet suprimat i probabilitatea rpirii unui pui a fost corelat cu nivelurile de PRL msurate naintea tratamentului.n timpul reproducerii, pinguinii imperiali trebuie s caute hran n zone ndeprtate, pe mare, fr ghea.Summary The function and causes of kidnapping juveniles are little understood because individuals experience some breeding problems to grow offspring. Here we focus on the proximal causes of this behavior in emperor penguins (Aptenodytes forsteri), whose failed breeders often kidnap chicks. We experimentally tested the hypothesis that kidnapping behavior was the result of high residual levels of prolactin (PRL), a hormone involved in parental behavior.Penguins with artificially decreased PRL levels cased by bromocriptine administration have kidnapped chicks less often than control penguins. Within the treated group with bromocriptine , kidnapping behavior was not totally suppressed and the probability of kidnapping a chick was correlated to PRL levels measured before the treatment. During breeding, emperor penguins have to forage for food in remote ice-free areas. La aceste psri, secreia de PRL este slab influenat de stimulii puilor i a evoluat, probabil, pentru a menine dorina de a se ntoarce la colonie dup o lung absen pe mare.Astfel, pinguinii care i-au pierdut puii n timpul unei cltorii dup hran nc i pstreaz niveluri reziduale ridicate de PRL i acest lucru, combinat cu reproducerea colonial, probabil, faciliteaz rpirea.Studiul sugerez c rpirea n sisteme necooperante poate fi provocat de un efect secundar hormonal al unei adaptri reproductive la condiii extreme.

These birds, PRL secretion is poorly influenced by chick stimuli and has probably evolved to maintain a willingness to return to the colony after a long absence at sea. Therefore, penguins that have lost their chick during a foraging trip still maintain high residual PRL levels and this, combined with colonial breeding, probably facilitates kidnapping. We suggest that kidnapping in non-cooperative systems may result from a hormonal byproduct of a reproductive adaptation to extreme conditions.

Introducere n afar de cteva specii de animale care se reproduc n colonii, cauzele rpirii juvenile sunt puin nelese. De ce indivizii se lupt, hrnesc i ngrijesc puii altor indivizi nu este clar i astfel de rpiri par a fi n contradicie cu teoria evoluionist. Totui, unii factori receni au fost propui pentru a explica acest comportament ciudat. n primul rnd, rpirea altor pui ar putea intensifica experiena de reproducere a rpitorului i, prin urmare, ar promova succesul lor de reproducere pe viitor.n al doilea rnd, datorit aparentului lor succes de reproducere i, deci, a nivelullui ridicat de ncredere n sine, rpitorul i-ar putea mri posibilitatea de a gsi un partener pentru urmtoarea reproducere.n ultimul rnd, rpirea poate chiar s creeze o legtur cu puiul rpit i, astfel, s creasc probabilitatea ca rpitorul s fie ajutat n timpul urmtoarei perioade de reproducere.n ciuda acestor poteniale beneficii, acest comportament poate fi duntor, deoarece rpitorul se poate rni dac ncearc s fure puiul de lng prinii lui.

Introduction Apart from a few species of cooperatively breeding animals, the function and causes of kidnapping juveniles are little understood . Why individuals struggle, feed and provide care for the offspring is not clear, and such kidnapping appears to be inconsistent with evolutionary theory. However, some ultimate factors have been proposed to explain this strange behavior. Firstly, kidnapping offspring could increase the kidnapper's breeding experience and hence promote their future breeding sucess.Secondly, because of their apparent breeding success and thus high individual quality, kidnappers could also enhance their probability of finding a mate for the next breeding event. Finally, kidnapping can even create an association with the kidnapped offspring and thus enhance the probability of the kidnapper being helped during the subsequent breeding event. Despite these potential benefits, kidnapping behavior could also be costly because injuries may occur to the kidnapper if it tryes to take away the offspring from its parents.

n acest studiu a fost analizat mecanismul fiziologic al comportamentului rpirii. A fost testat, n mod special, efectul nivelurilor de PRL sczute artificial la o specie necooperant, pinguinul imperial Aptenodytes forsteriGray, la care rpirea puilor de ctre pinguinii ce nu se pot reproduce este des ntlnit.

In this study, we examined the physiological mechanism of kidnapping behavior. We tested specifically for the effect of artificially decreased PRL levels on kidnapping behavior in a non-cooperative species, the emperor penguinAptenodytes forsteriGray, where the kidnapping of chicks by failed breeders is commonly observed.

Materiale i metodeZona de studiu i speciile

Studiul a fost realizat din 20 August pn n 30 Septembrie 1999, n Antarctica, Terre Adlie, arhipelagul Pointe Gologie (6640S, 14001E) , asupra pinguinilor imperiali care se nmulesc ntr-o colonie aproape de Dumont d'Urville Station. Pinguinii imperiali se mperecheaz n timpul iernii antarctice, n colonii numeroase, pe gheaa mrii. Perechile monogame se formeaz n Mai i, dup o perioad de incubare de 65 de zile, efectuat doar de mascul, femelele se ntorc pentru a-i elibera de sarcin pe partenerii lor i pentru a aduce hran pentru puiul proaspt eclozat. Apoi, ambii prini hrnesc puiul pe rnd , ducndu-se pe mare, i stau cu ceilali pui ai lor, pn cnd acetia prsesc colonia, cnd gheaa mrii se rupe.Materials and methods We conducted our study from 20 August to 30 September, 1999, at Pointe Gologie archipelago, Terre Adlie, Antarctica (6640S, 14001E) on emperor penguins that breed in a colony near the Dumont d'Urville Station. Emperor penguins breed during the Antarctic winter in dense colonies on sea ice. Monogamous pairs form in May, and following a 65 day incubation shift undertaken by the male alone, females come back to relieve their partner and bring food to the newly hatched chick. Then, both parents take turns to feed at sea and to stay with their offspring, until the chicks leave the colony when the sea ice breaks up.

Comportamentul de rpireComportamentul de rpire este ntlnit mai mult la prinii euai, n special femelele care au pierdut un ou sau un pui tnr. n timpul rpirii, prinii biologici ncearc, ntotdeauna, s protejele puiul, luptndu-se cu intrusul (ciugulit, lovituri cu aripa, dar, uneori, rpitorii pot s i ndeprteze pe prini i s le ia puiul.Foarte rar se ntmpl ca procesul de rpire s se finalizeze cu rni fizice asupra printelui sau rpitorului. Puii rpii pot fi, uneori, rnii de printele rpitor, dar, n cele mai multe cazuri, acetia i neglijeaz puiul la doar cteva ore dup ce l-a rpit, iar puiul lsat nesupravegheat moare datorit hipotermiei sau prdtorilor.Readoptarea puilor de ctre prinii lor biologici este rar i se ntmpl doar cnd rpitorul abandoneaz rapid puiul, iar printele este nc aproape de acesta i i aude strigtele. Rpirea are loc, cu precdere, n lunile August i Septembrie. Prinii euai sunt foarte activi n sptmnile care urmeaz dup perioada de eclozare, cnd prezena puilor poate stimula comportamentul de rpire. Kidnapping behaviourKidnapping behavior is mostly exhibited by failed breeders, especially females, which have lost an egg or a young chick. During kidnapping, the biological parent always tries to protect the chick by fighting (pecking, stroke of flipper) the intruder but kidnappers are sometimes able to displace the parent and to get the chick. It is very rare that kidnapping episodes end in physical injury to the parent or to the kidnapper. Kidnapped chicks can sometimes benefit from being fed by the kidnapping parent, but in most cases kidnappers neglect the chick only a few hours after it was kidnapped, and the chick left unattended dies due to hypothermia or predation. `Readoptions' of chicks by their parents are rare and occur only when the kidnapper rapidly abandons the chick, when the parent is still close to the chick and when the abandoned chick calls its parent. Kidnapping mostly occurs during August and September. Failed breeders are very active during the weeks that follow the hatching period, when the presence of chicks may stimulate kidnapping behavior.

Manipularea i testarea nivelurilor de PRLn iarna anului 1999, 47 de prini euai au fost capturai, marcai individual, printr-un numr pictat pe pieptul lor i a fost colectat 1 ml de snge, important pentru tratamentul din vena marginal a aripii, introdus n tuburi cu hepalin i, apoi, imediat centrifugat.Plasma a fost depozitat la -20 grade Celsius, pn cnd a fost stabilit concentraia de PRL, prin radioimunoanaliz. Nivelurile de PRL din plasm au fost sczute experimental, prin tratarea pinguinului cu o injecie intramuscular de bromocriptin,Bromocriptina este un agonist dopaminergic care inhib secreia de PRL la mamifere i la psri. Un grup a fost tratat cu bromocriptin (N=23 psri), iar cellalt (N=24 psri) a fost tratat cu un solvent (soluie etanol 10%). Pimguinii au fost, apoi, eliberai aproape de colonie. Nu a fost observat niciun efect advers al bromocriptinei n comportamentul pinguinilor tratai i probabilitatea de reperare a fost similar ntre grupuri.n plus, toi pinguinii tratai au fost vzui mai trziu (la sfritul sezonului de mperechere n colonie).

Manipulation of prolactin levels and prolactin assay

In winter 1999, 47 failed breeders were captured, individually marked by a number painted on their chest and 1 ml of blood was collected, prior to treatment, from the marginal vein of the flipper into heparinized tubes and then immediately centrifuged. Plasmas were stored at 20C until measured for PRL concentration by radioimmunoassay. Plasma PRL levels were experimentally decreased by treating the penguin with an intramuscular injection of bromocriptine. Bromocriptine is a dopamine agonist that inhibits PRL secretion in mammals and in birds. One group (bromocriptine group,N=23 birds) was treated with bromocriptine; the other (control group,N=24 birds) was treated with a vehicle (10% ethanol solution).We did not observe any adverse effect of bromocriptine on the behavior of treated penguins and the sighting probability was similar between groups. Moreover, all treated penguins were seen later (at the end of the breeding season) in the colony.

Pentru a monitoriza efectul tratamentului, cu bromocriptin asupra nivelurilor de PRL, au fost pstrate n captivitate 2 psri (una injectat cu bromocriptin i cealalt injectat cu solvent) i sngele a fost recoltat la 3 i 8 zile dup capturare. Ulterior, au fost eliberate napoi n colonie.Nivelurile de prolactin au fost determinate prin radioimunoanaliz.To monitor the effect of bromocriptine treatment on PRL levels, we kept two additional birds (one injected with bromocriptine and one injected with a vehicle) in captivity and blood was sampled 3 days and 8 days after the capture.Afterwards, they were released back to the colony. PRL levels were determined by radioimmunoassay.

Monitorizarea comportamentului i analize statisticeS-a urmrit comportamentul de rpire al psrilor din cele dou grupuri timp de 3 ore n fiecare zi, n timpul sptmnii ulterioare tratamentului. Prin urmare, s-a putut atribui fiecrei zile i fiecrei psri monitorizate date exacte. O pasre a fost clasificat ca fiind rpitor cnd aceasta, indiferent de sex, a fost n contact fizic cu puiul. Pentru a determina comportamentul de rpire, datele colectate zilnic de la fiecare individ au fost analizate folosind modelele probabilistice de stare.Aceste modele includ 3 tipuri de parametri:Probabilitatea de reperare,Probabilitatea de supravieuire,Probabilitatea de tranziie de la o stare la alta.S-au folosit dou stri: (1) psri prezente, dar care nu au fost vzute rpind, (2) psri observate rpind (fig. 1).Studiul s-a axat, n principal, asupra probabilitii de tranziie de la prima stare la cea de prdtor de la prima zi dup tratament (t), pn la cea de-a doua zi (t+1).

Behavioral monitoring and statistical analysis

We followed the kidnapping behavior of the birds from the bromocriptine and control groups during a 3 h scan each day during the week following treatment. Hence we were able to attribute for each day and each monitored bird a categorical datum. A bird was classified as a kidnapper when he or she was in physical contact with the chick. To model the kidnapping behavior, daily collected data obtained for each individual were analyzed using multistate probabilistic models. These models include three kinds of parameters: sighting probability, survival probability and transition probabilities from one state to another. We used two states in our study: (1)birds present but not seen kidnapping, and (2) birds seen kidnapping (Fig. 1). We focused mainly on the probability of transition () from the non-kidnapping state to the kidnapping state over one post-treatment day (t) to the next (t+1).

Modeling kidnapping behavior with a multi-state approach in the emperor penguin. States 1 and 2 are, respectively, the non-kidnapping state and the kidnapping state. abis the transition probability from state a to state b over one post treatment day (t) to the next one (t+1). 12is the probability that a penguin will kidnap a chick fromttot+1. (1S) is the probability that a bird will leave the colony fromttot+1.Pand (1P) are, respectively, the probabilities that a bird present on the colony in one of the behavioral state was seen or not during the daily scan.Modelarea comportamentului de rpire cu o abordare a diferitelor stri ale pinguinului imerial. Starea 1i 2 sunt starea normal a pinguinului i, respectiv, starea de rpitor. abeste probabilitatea de tranziie de la starea a la starea b, de la o zi dup tratament (t) pn la a doua (t+1). 12 este probabilitatea ca pinguinul s rpeasc un pui din t pn n t+1. (1S) este probabilitatea ca o pasre s prseasc colonia din t pn n t+1. P i (1-P) sunt probabilitatea ca o pasre prezent n colonie , avnd una din cere dou stri, s fie sau nu vzut n timpul supravegherii zilnice.Acest lucru ne permite s estimm probabilitatea de rpire la prinii euai i s testm efectul tratamentului cu bromocriptin asupra comportamentului de rpire al acestor psri.This allowed us to estimate the kidnapping probability of failed breeders, and to test for an effect of bromocriptine treatment on the kidnapping behavior of these birds.Rezultate Efectele bromocriptinei asupra nivelului de prolactin

Ambele psri tratate i pstrate n captivitate au avut nivelul de PRL similar nainte de tratament, dar pasrea injectat cu bromocriptin a avut un nivel PRL mai sczut dect pasrea de control dup 3 i, respectiv 8 zile de la injecie.

Comportamentul de rpire i determinarea strii

S-a nregistrat un numr de 28 de rpiri n timpul monitorizrii comportamentului, 30,4% din pinguinii tratai cu bromocriptin i 54, 2% din pinguinii tratai cu solvent au fost cel puin o dat observai n prezena unui pui. ncepnd cu modelul general , s-a observat c probabilitatea de supravieuire nu a depins de tratament. Probabilitatea de reperare nu a depins de tratament, ci de tipul de comportament. Nu s-a observat niciun efect asupra nivelului de PRL din plasm, msurat naintea injectrii cu bromocriptin sau solvent asupra probabilitii de tranziie a grupului de control. Totui, acest efect a fost puternic la grupul cu bromocriptin.

Results Effect of bromocriptine on prolactin level

Both treated birds kept in captivity had similar PRL levels before the treatment, but the bird injected with bromocriptine had lower PRL level than the control bird 3 days and 8 days after the injection.

Kidnapping behavior and model selectionA total of 28 chick kidnappings were observed during the behavioral monitoring. 30.4% of the penguins treated with bromocriptine and 54.2% of the penguins treated with vehicle were sighted at least once with a chick. Starting with the general model we found that survival probability did not depend on treatment. Sighting probability did not depend on treatment, but on behavioral state. We also observed no effect of plasma PRL levels measured prior to the injection of bromocriptine or vehicle on this transition probability for the control group. This effect was, however, strong in the bromocriptine group.Estimrile paramentrilor au indicat probabilitatea tranziiei de la stadiul de simplu membru al coloniei (non-kidnapping) la cel de rpitor au fost mai ridicate n grupul de control dect n grupul de bromocriptin (fig. 2). n grupul de bromocriptin, comportamentul de rpire nu a fost total suprimat i probabilitatea de tranziie de la o stare la alta a fost corelat pozitiv cu nivelul PRL din plasm, msurat nainte de injecia cu bromocriptin. n grupul de bromocriptin, rpitorii au avut niveluri de PRL mai ridicate naintea tratamentului dect ceilali pinguini studiai, n timp ce acest lucru nu a fost observat n grupul de control.

Parameters estimates indicated that the transition probability from the non-kidnapping to the kidnapping state was higher in the control than in the bromocriptine group (Fig. 3). Within the bromocriptine group, kidnapping behavior was not totally suppressed and the transition probability from the non-kidnapping to the kidnapping state (12) was positively correlated to the plasma PRL level measured before injection of bromocriptine. Within the bromocriptine group, kidnappers had higher PRL levels prior to the bromocriptine treatment than non-kidnappers whereas this was not observed in the control group.

Estimates of the transition probability from the non-kidnapping to the kidnapping state for prolactin inhibited (bromocriptine,N=23) and control individuals (N=24), showing 95% confidence limits. Estimri ale probabilitii de tranziie de la o stare la alta pentru indivizii nivelul de prolactin inhibat (bromocriptin, N=23) i indivizii de control (N=24), evindeiind limitele de toleran de 95%Discuii n acest experiment s-a dovedit c pinguinii tratai cu bromocriptin au rpit pui mai rar. Dei statisticile nu au putut demonstra o diferen n scderea nivelului de PRL ntre cele dou grupuri, deoarece numai cte un anmal din fiecare grup a fost pstrat n captivitate i implicat n tratamente, studiul susine c tratamentul a sczut nivelul de PRL deoarece administrarea de bromocriptin suprim nivelurile de PRL la psri. n plus, bromocriptina este cunoscut, n mod special, ca un inhibator al secreiei de PRL la pinguini. Scderea nivelului de PRL , observat n urma tratamentului confirm eficiena bromocriptinei.Cnd pinguinii au fost injectai cu bromocriptin, probabilitatea ca ei s rpeasc un pui a fost , n medie, de 4,5 ori mai mic dect aceea a pinguinilor injectai cu solventul de control. Dei e probabil ca bromocriptina, un agonist dopaminergic, s fi redus probabilitatea de rpire prin alte mecanisme dect proprietile sale de inhibare a prolactinei, acest rezultat este n concordan cu ipoteza conform creia rpirea puilor de ctre cresctorii euai este rezultatul unui nivel ridicat de PRL.Discussions In this experiment, penguins treated with bromocriptine had kidnapped chicks less often. Although statistics cannot be run to test for a difference in the decrease in PRL levels between bromocriptine and control groups as only one animal was kept in captivity and involved in each treatment, we are confident that the treatment decreased PRL levels, as bromocriptine administration is known to suppress PRL levels in birds. The decrease that we observed in our bromocriptine treated penguin (i.e. 75%) confirms the efficiency of bromocriptine treatment in our study.When penguins were injected with bromocriptine, the probability that they kidnapped a chick was on average 4.5 times lower than that of penguins injected with a vehicle. Although bromocriptine, as a dopamine agonist, might have reduced the probability of kidnapping by other mechanisms that its prolactin-inhibiting properties , this result is consistent with the hypothesis that kidnapping of chicks by failed breeders is the result of high residual level of PRL.

Dei comportamentul de rpire a fost redus printr-o injecie cu bromocriptin, acesta nu a fost suprimat n totalitate. Acest lucru se poate datora unei absene temporare a efectului bromocriptinei asupra nivelului de PRL.n concluzie, aceste rezultate demonstreaz c bromocriptina a avut efect asupra probabilitii de rpire, ncepnd cu prima zi dup tratament.

Although kidnapping behavior was reduced by an injection of bromocriptine, it was not totally suppressed. This could be due to a temporary absence of effect of bromocriptine on PRL levels. These results demonstrate that bromocriptine had an effect on kidnapping probability since the day following the treatment.

Bibliografie http://jeb.biologists.org/content/209/8/1413.full