Testosterone Affects Song Modulation during Simulated Territorial Intrusions in Male Black Redstarts (Phoenicurus ochruros)

Abstract

Although it has been suggested that testosterone plays an important role in resource allocation for competitive behavior, details of the interplay between testosterone, territorial aggression and signal plasticity are largely unknown. Therefore, we investigated if testosterone acts specifically on signals that communicate the motivation or ability of individuals to engage in competitive situations in a natural context. We studied the black redstart, a territorial songbird species, during two different life-cycle stages, the early breeding phase in spring and the non-breeding phase in fall. Male territory holders were implanted with the androgen receptor blocker flutamide (Flut) and the aromatase inhibitor letrozole (Let) to inhibit the action of testosterone and its estrogenic metabolites. Controls received a placebo treatment. Three days after implantation birds were challenged with a simulated territorial intrusion (STI). Song was recorded before, during and after the challenge. In spring, both treatment groups increased the number of elements sung in parts of their song in response to the STI. However, Flut/Let-implanted males reacted to the STI with a decreased maximum acoustic frequency of one song part, while placebo-implanted males did not. Instead, placebo-implanted males sang the atonal part of their song with a broader frequency range. Furthermore, placebo-, but not Flut/Let-implanted males, sang shorter songs with shorter pauses between parts in the STIs. During simulated intrusions in fall, when testosterone levels are naturally low in this species, males of both treatment groups sang similar to Flut/Let-implanted males during breeding. The results suggest that song sung during a territorial encounter is of higher competitive value than song sung in an undisturbed situation and may, therefore, convey information about the motivation or quality of the territory holder. We conclude that testosterone facilitates context-dependent changes in song structures that may be honest signals of male quality in black redstarts.

Does a short-term increase in testosterone affect the intensity or persistence of territorial aggression? — An approach using an individual's hormonal reactive scope to study hormonal effects on behavior

“…In contrast, no such increase is observed in black redstarts [15][16][17]. Furthermore, blocking of testosterone and estrogen action within a breeding and outside a breeding context did not alter territorial aggression in male black redstarts [48,57,65]. In this study, we show that a short-term rise in testosterone would be ineffective in increasing the intensity or persistence of territorial aggression in a species that otherwise lacks a testosterone response during male-male interactions.…”

Vocal behaviour during aggressive encounters between Siberian hamsters, Phodopus sungorus

“…For example, castrated Alston's singing mice, Scotinomys teguina, show higher levels of subordination accompanied by songs that have higher dominant frequencies (Pasch et al, 2011). However, across a wide range of mammal and bird species that use agonistic vocalizations, many call qualities other than tonality and frequency are associated with increased aggression; these qualities include bandwidth, intensity and call rate or number (Apfelbeck, Kiefer, Mortega, Goymann, & Kipper, 2012;DuBois, Nowicki, & Searcy, 2008;Harding, Walters, Collado, & Sheridan, 1988;Pasch et al, 2011). Moreover, exceptions to the motivational-structural rules hypothesis exist in species such as ocellated antbirds, Phaenostictus mcleannani, which produce higher-pitched syllables that may signal better condition or greater genetic diversity during maleemale aggression (Araya-Ajoy, Chaves-Campos, Kalko, & DeWoody, 2009).…”

Peripheral androgen action helps modulate vocal production in a suboscine passerine

“…These findings are consistent with other work that similarly shows androgen-dependent changes in the acoustic “content” of vocal production. In male Black Redstarts ( Phoenicurus ochruros ), for instance, inhibition of androgenic and estrogenic action induced shifts of ~300 Hz in frequency parameters of aggressive song (Apfelbeck et al 2012). Likewise, in male Zebra Finches ( Taeniopygia guttata ), long-term testosterone implantation caused a ~100 Hz decrease in the F 0 of directed sexual song (Cynx et al 2005).…”

“…In passerine birds, for example, males sing and/or call to attract mates (Catchpole and Slater 2008), and research has shown that androgens influence such behavior by changing the number of times that individuals sing and/or call (Silverin 1980, Nowicki and Ball 1989, Ketterson et al 1992, P. G. McDonald et al 2001, Kurvers et al 2008), as well as the acoustic structure or makeup of these songs and/or calls (Deviche and Schumacher 1982, Groothuis and Meeuwissen 1992, Fusani et al 1994, Galeotti et al 1997, Cynx et al 2005, Apfelbeck et al 2012). However, in general, we know relatively little about where and how androgens act within the body to mediate acoustic parameters of bird songs and calls.…”