scholarly journals Ignoring the challenge? Male black redstarts ( Phoenicurus ochruros ) do not increase testosterone levels during territorial conflicts but they do so in response to gonadotropin-releasing hormone

2011 ◽  
Vol 278 (1722) ◽  
pp. 3233-3242 ◽  
Author(s):  
Beate Apfelbeck ◽  
Wolfgang Goymann
Keyword(s):  
Breeding Season ◽  
Gonadotropin Releasing Hormone ◽  
Plasma Testosterone ◽  
Releasing Hormone ◽  
Social Challenges ◽  
Testosterone Levels ◽  
Territorial Conflicts ◽  
Territory Defence ◽  
Simulated Territorial Intrusion ◽  
Territorial Intrusion

Competition elevates plasma testosterone in a wide variety of vertebrates, including humans. The ‘challenge hypothesis’ proposes that seasonal peaks in testosterone during breeding are caused by social challenges from other males. However, during experimentally induced male–male conflicts, testosterone increases only in a minority of songbird species tested so far. Why is this so? Comparative evidence suggests that species with a short breeding season may not elevate testosterone levels during territory defence. These species may even be limited in their physiological capability to increase testosterone levels, which can be tested by injecting birds with gonadotropin-releasing hormone (GnRH). We studied two populations of black redstarts that differ in breeding altitude, morphology and the length of their breeding season. Unexpectedly, males of neither population increased testosterone in response to a simulated territorial intrusion, but injections with GnRH resulted in a major elevation of testosterone. Thus, black redstarts would have been capable of mounting a testosterone response during the male–male challenge. Our data show, for the first time, that the absence of an androgen response to male–male challenges is not owing to physiological limitations to increase testosterone. Furthermore, in contrast to comparative evidence between species, populations of black redstarts with a long breeding season do not show the expected elevation in testosterone during male–male challenges.

Opposite Changes in Plasma Testosterone and Corticosterone Levels Following a Simulated Territorial Challenge in Male Great Tits

Behaviour ◽  
2004 ◽  
Vol 141 (4) ◽  
pp. 451-467 ◽  
Author(s):  
Rianne Pinxten ◽  
Lutgarde Arckens ◽  
Els van Duyse ◽  
Marcel Eens ◽  
Veerle Darras
Keyword(s):  
Parus Major ◽  
Time Of Day ◽  
Behavioural Response ◽  
Egg Laying ◽  
Plasma Testosterone ◽  
Breeding Cycle ◽  
Territorial Defence ◽  
Breeding Stage ◽  
Simulated Territorial Intrusion ◽  
Territorial Intrusion

AbstractThe apparent ability of plasma testosterone (T) and corticosterone (B) levels to fluctuate rapidly in response to agonistic interactions, suggests that these hormones may play an important role in an animal's acute behavioural response during such interactions. In the present study, free-living male great tits, Parus major, were subjected to a simulated territorial intrusion (STI) during the egg laying, incubation and nestling stage of first broods. Plasma T and B levels of challenged males were compared to those of control males matched for breeding stage, day in breeding stage, and time of day. Plasma B levels were significantly higher in challenged males compared to control males during the egg laying and incubation stage but not during the nestling stage. On the other hand, challenged males had significantly lower plasma T levels than control males throughout the breeding cycle. While having low plasma T and elevated plasma B levels, challenged males showed a vigorous and unrelenting territorial response to the STI. Plasma T and B levels of challenged males did not correlate with the intensity of the behavioural response to the STI. These findings do not agree with the predictions of the 'challenge hypothesis' that males exposed to a territorial challenge while having breeding baseline T levels will respond with an increase in T or that T correlates with the intensity of aggression during a challenge. Together, our findings suggest a role for B rather than T in the regulation of territorial defence in male great tits.

scholarly journals Testosterone is associated with harem maintenance ability in free-ranging grey-headed flying-foxes, Pteropus poliocephalus

2009 ◽  
Vol 5 (6) ◽  
pp. 758-761 ◽  
Author(s):  
Stefan M. Klose ◽  
Justin A. Welbergen ◽  
Elisabeth K. V. Kalko
Keyword(s):  
Plasma Testosterone ◽  
Flying Foxes ◽  
Mating Period ◽  
Social Challenges ◽  
Testosterone Levels ◽  
Harem Size ◽  
Pteropus Poliocephalus ◽  
Original Size ◽  
Complex Forms ◽  
Free Ranging

Males of many vertebrate species aggressively defend their reproductive interests by monopolizing females, and the ‘challenge hypothesis’ predicts that testosterone levels in reproductive contexts rise to facilitate males' competitive behaviours necessary for meeting social challenges. The hypothesis is successful in explaining patterns of testosterone secretion in many avian species, but remains comparatively unexplored in mammals. ‘Circulating plasma testosterone levels (T)’ were studied in relation to harem maintenance in grey-headed flying-foxes, Pteropus poliocephalus . In this species, harems provide mating opportunities and so a male's ability to maintain a harem is likely to correlate with his fitness. We hypothesized that if T reflect a male's ability to withstand challenges from competitors, then T should be linked to successful harem maintenance. To test this, we temporarily removed males from their territories prior to and during the short mating period, recording their harem sizes both before removal and after reintroduction. Most males successfully reclaimed their territory and a harem, but during the mating period, males with higher T had harems closer to their original size, and males with lower T suffered reduction in harem size. Our findings highlight the role of T in harem maintenance in a major mammalian taxon with complex forms of social organization.

A neuroendocrine model for prolactin as the key mediator of seasonal breeding in birds under long- and short-day photoperiods

2003 ◽  
Vol 81 (4) ◽  
pp. 350-358 ◽  
Author(s):  
Peter J Sharp ◽  
Dominique Blache
Keyword(s):  
Breeding Season ◽  
Plasma Concentrations ◽  
Prolactin Secretion ◽  
Gonadotropin Releasing Hormone ◽  
Critical Threshold ◽  
Plasma Prolactin ◽  
Seasonal Breeding ◽  
Releasing Hormone ◽  
Short Day ◽  
Long Day

Seasonal breeding is associated with sequential increases in plasma luteinizing hormone (LH) and prolactin in the short-day breeding emu, and in long-day breeding birds that terminate breeding by the development of reproductive photorefractoriness. A model of the avian neuroendocrine photoperiodic reproductive response is proposed, incorporating a role for prolactin, to account for neuroendocrine mechanisms controlling both long- and short-day breeding. The breeding season terminates after circulating concentrations of prolactin increase above a critical threshold to depress gonadotropin releasing hormone (GnRH) neuronal and gonadotrope (LH) activity. Subsequently, photorefractoriness develops for prolactin secretion and for LH secretion, independently of high plasma prolactin. The breeding season in the emu is advanced compared with long-day breeders, because after photorefractiness for both LH and prolactin secretion is dissipated, plasma concentrations of both hormones increase to maximum values while days are still short.Key words: seasonal breeding, prolactin, gonadotropin releasing hormone, photorefactoriness.

Seasonal variation in plasma testosterone and the testis in captive male dingoes, Canis familiaries dingo

1979 ◽  
Vol 27 (6) ◽  
pp. 939 ◽  
Author(s):  
PC Catling
Keyword(s):  
Seasonal Variation ◽  
Breeding Season ◽  
Plasma Testosterone ◽  
Testosterone Levels ◽  
Central Australia ◽  
Eastern Highlands

Eastern Highlands and Central Australian dingoes housed in Canberra do not have a testicular cycle. They are spermatogenically active and capable of mating with oestrous females and fathering young all year. They do exhibit a breeding season (April-June) but this is entirely governed by the female. During the breeding season testosterone levels rise; this is thought to be influenced by the presence of an oestrous female and copulation. There are indications that captive dingoes in Central Australia may have a testicular cycle. Colony dingoes showed little interest in and do not mate with an oestrous domestic female at times other than January-July. They also become almost aspermous outside the breeding season. In contrast, Central Australian dingoes housed in Canberra are spermatogenically active and capable of successful matings all year.

scholarly journals Male White-shouldered Fairywrens (Malurus alboscapulatus) elevate testosterone when courting females but not during territorial challenges

2021 ◽  
Author(s):  
Jordan Boersma ◽  
John Anothny Jones ◽  
Erik D Enbody ◽  
Joseph F Welklin ◽  
Serena Ketaloya ◽  
...  
Keyword(s):  
Bird Species ◽  
Plasma Testosterone ◽  
Network Approach ◽  
Challenge Hypothesis ◽  
Agonistic Interactions ◽  
Causal Factors ◽  
Behavioral Traits ◽  
Social Network Approach ◽  
Simulated Territorial Intrusion ◽  
Territorial Intrusion

Testosterone mediates suites of physical and behavioral traits across vertebrates, and circulation varies considerably across and within taxa. However, an understanding of the causal factors of variation in circulating testosterone has proven difficult despite decades of research. According to the challenge hypothesis, agonistic interactions between males immediately prior to the breeding season produce the highest levels of testosterone measured during this period. While many studies have provided support for this hypothesis, most species do not respond to male-male competition by elevating testosterone. As a result, a recent revision of the hypothesis (challenge hypothesis 2.0) places male-female interactions as the primary cause of rapid elevations in testosterone circulation in male vertebrates. Here, we offer a test of both iterations of the challenge hypothesis in a tropical bird species. We first illustrate that male White-shouldered Fairywrens (Malurus alboscapulatus) differ by subspecies in plasma testosterone concentrations. Then we use a social network approach to find that males of the subspecies with higher testosterone are characterized by greater social interaction scores, including more time aggregating to perform sexual displays. Next, we use a controlled experiment to test whether males respond to simulated territorial intrusion or courtship interaction contexts by elevating testosterone. Males sampled during courtship had greater plasma testosterone both relative to flushed controls and males sampled during simulated intrusion. Ultimately, our results are consistent with challenge hypothesis 2.0, as males rapidly elevated testosterone following interactions with females, but not during territorial challenges.

scholarly journals Testosterone Does not Increase in Response to Conspecific Challenges in the White-Bellied Antbird (Myrmeciza Longipes), A Resident Tropical Passerine

The Auk ◽  
2006 ◽  
Vol 123 (1) ◽  
pp. 61-66
Author(s):  
Bradley C. Fedy ◽  
Bridget J. M. Stutchbury
Keyword(s):  
Breeding Season ◽  
Temperate Zone ◽  
Plasma Testosterone ◽  
Tropical Species ◽  
Zone Model ◽  
Territorial Aggression ◽  
Social Instability ◽  
Testosterone Levels ◽  
Testosterone Secretion ◽  
Removal Experiments

Abstract Resident tropical passerines that exhibit year-round territorial aggression do not fit well into the temperate-zone model, because testosterone does not increase substantially during the breeding season. We studied patterns of testosterone secretion in the White-bellied Antbird (Myrmeciza longipes), a resident tropical species in Panama that maintains territories year-round and is capable of aggression throughout the year, regardless of its stage of reproduction. Levels of plasma testosterone were low (mean = 0.30 ng mL−1) throughout the breeding and nonbreeding seasons and did not differ between them. Testosterone also did not increase in response to simulated conspecific intrusions. When we used temporary removal experiments to induce natural, extended conflict between males, testosterone levels did not increase in response to the extended social instability that resulted. White-bellied Antbirds demonstrate an apparent uncoupling of testosterone and territorial aggression throughout the year. La Testosterona no Aumenta como Respuesta a Desafíos de Individuos Coespecíficos en Myrmeciza longipes, un Paserino Residente de la Zona Tropical

Relugolix, an oral gonadotropin-releasing hormone antagonist for the treatment of prostate cancer

2021 ◽  
Author(s):  
Daniel J George ◽  
David P Dearnaley
Keyword(s):  
Prostate Cancer ◽  
Advanced Prostate Cancer ◽  
Gnrh Antagonist ◽  
Gonadotropin Releasing Hormone ◽  
Leuprolide Acetate ◽  
Phase Iii ◽  
Major Adverse Cardiovascular Events ◽  
Gnrh Analogues ◽  
Releasing Hormone ◽  
Testosterone Levels

Androgen deprivation therapy using gonadotropin-releasing hormone (GnRH) analogues is standard treatment for intermediate and advanced prostate cancer. GnRH agonist therapy results in an initial testosterone flare, and increased metabolic and cardiovascular risks. The GnRH antagonist relugolix is able to reduce serum testosterone levels in men with prostate cancer without inducing testosterone flare. In the HERO Phase III trial, relugolix was superior to leuprolide acetate at rapidly reducing testosterone and continuously suppressing testosterone, with faster post-treatment recovery of testosterone levels. Relugolix was associated with a 54% lower incidence of major adverse cardiovascular events than leuprolide acetate. As the first oral GnRH antagonist approved for the treatment of advanced prostate cancer, relugolix offers a new treatment option.

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