Males of a Strongly Polygynous Species Consume More Poisonous Food than Females

Abstract

We present evidence of a possible case of self-medication in a lekking bird, the great bustard Otis tarda. Great bustards consumed blister beetles (Meloidae), in spite of the fact that they contain cantharidin, a highly toxic compound that is lethal in moderate doses. In addition to anthelminthic properties, cantharidin was effective against gastrointestinal bacteria that cause sexually-transmitted diseases. Although both sexes consumed blister beetles during the mating season, only males selected them among all available insects, and ingested more and larger beetles than females. The male-biased consumption suggests that males could use cantharidin to reduce their parasite load and increase their sexual attractiveness. This plausibly explains the intense cloaca display males perform to approaching females, and the meticulous inspection females conduct of the male's cloaca, a behaviour only observed in this and another similar species of the bustard family. A white, clean cloaca with no infection symptoms (e.g., diarrhoea) is an honest signal of both, resistance to cantharidin and absence of parasites, and represents a reliable indicator of the male quality to the extremely choosy females. Our results do not definitely prove, but certainly strongly suggest that cantharidin, obtained by consumption of blister beetles, acts in great bustards as an oral anti-microbial and pathogen-limiting compound, and that males ingest these poisonous insects to increase their mating success, pointing out that self-medication might have been overlooked as a sexually-selected mechanism enhancing male fitness.

Cantharidin is conserved across phylogeographic lineages and present in both morphs of Iberian Berberomeloe blister beetles (Coleoptera, Meloidae)

“…The existence of toxic populations composed of entirely black specimens within the red-striped lineages suggests that the selective pressures that maintained the red-striped coloration were either not related to visual predation, or alternatively, selective pressures became relaxed in recent times, when entirely black populations appeared. Although a few predators tolerate cantharidin toxicity (Eisner et al, 1990;Bartram & Boland, 2001;Bravo et al, 2014Bravo et al, , 2016, reports on blister beetle predation are very scarce (see Bologna, 1991).…”

“…The efficiency of cantharidin as a deterrent for predators (Carrel & Eisner, 1974) and its poisoning effects on livestock have been widely reported (Bahme, 1968;Ray et al, 1980;Beasley et al, 1983). In fact, only a few species consume blister beetles (Eisner et al, 1990;Bartram & Boland, 2001;Bravo et al, 2014Bravo et al, , 2016. A second function of cantharidin could also be to help blister beetles avoid internal parasites, due to its fungicidal, nematocidal, and bactericidal properties (Carrel & Eisner, 1974;Bravo et al, 2014).…”

“…In fact, only a few species consume blister beetles (Eisner et al, 1990;Bartram & Boland, 2001;Bravo et al, 2014Bravo et al, , 2016. A second function of cantharidin could also be to help blister beetles avoid internal parasites, due to its fungicidal, nematocidal, and bactericidal properties (Carrel & Eisner, 1974;Bravo et al, 2014). Among blister beetles, males usually have more cantharidin than females (Capinera, Gardner & Stermitz, 1985;Blodgett, Carrel & Higgins, 1991;Carrel et al, 1993;Carrel, 1999;Nikbakhtzadeh & Tirgari, 2002;Mebs et al, 2009;Nikbakhtzadeh et al, 2012), and apparently only males are able to synthesize this toxin (Sierra, Woggon & Schmid, 1976;Holz et al, 1994).…”

Using dietary analysis and habitat selection to inform conservation management of reintroduced Great BustardsOtis tardain an agricultural landscape

“…We found that emergent mustard leaves were consumed in large quantities in July only; high in fat and protein, the glucosinolate levels in the very young leaves may have been initially low enough to be considered palatable (Bellostas et al 2004). Alternatively, in some populations toxic compounds Great Bustard diet and habitat 9 may be ingested in larger quantities by males to selfmedicate and reduce their parasite load, increasing their breeding success (Bravo et al 2014). However, we consider this to be an unlikely function of mustard consumption in the UK bustards, because it took place at the end of the breeding season.…”

Auf Exkursion in Südmähren

“…Neuerdings weiß man, dass Ölkäfer von Großtrappen ( Otis tarda ) gezielt gefressen werden, um mit der so eingeschleusten Giftdosis Darmparasiten abzutöten. Dieses Verhalten wurde vor allem bei den Trapphähnen registriert, die damit augenscheinlich ihre Attraktivität für die Weibchen erhöhen . Die Hähne präsentieren während der Balz ihre Kloaken: Bei unparasitierten sind diese sauber, bei belasteten aber verschmutzt – ein schönes Beispiel für Selbstmedikation im Tierreich.…”