Female collared flycatchers adjust yolk testosterone to male age, but not to attractiveness

Abstract

The differential allocation hypothesis predicts that females invest more resources into reproduction when mating with attractive males. In oviparous animals this can include prefertilization decisions such as the production of larger eggs and the deposition of hormones, such as the steroid testosterone, into yolks. On the other hand, a compensatory hypothesis posits that females allocate more resources into the eggs when mated with males of inferior quality. In the present study, we show that free-living females of the collared flycatcher (Ficedula albicollis), a small passerine bird, do not produce larger eggs or deposit more testosterone into eggs when mating with attractive males reflected by a large forehead patch size, which is contrary to the prediction of the differential allocation hypothesis. However, we found higher yolk testosterone concentrations in eggs laid for young than older males. Because in young males genetic quality, parental experience, or willingness to invest into paternal care is likely to be low, high yolk testosterone level in their clutches may indicate that their females follow a compensatory tactic. They may elicit more paternal care from young, inexperienced males by hormonally increasing nestling begging. Laying date was also correlated with yolk testosterone level; however, when we controlled for it, male age still remained a strong determinant of testosterone allocation.

Differential allocation in relation to mate song quality in the Bengalese finch

“…In addition, it has been revealed that the attractiveness of mates affects the concentration of egg yolk components thought to contribute to the early physical development of offspring, such as testosterone (Gil et al, 1999;Gil et al, 2004; but see Mazuc et al, 2003;Michl et al, 2005) and immune factors (Saino et al, 2002b). These findings confirm that females invest more in reproduction when the prospective fitness return is high.…”

Yolk androgens do not appear to mediate sexual conflict over parental investment in the collared flycatcher Ficedula albicollis

“…data). No within-clutch pattern of yolk androgens was found in a Hungarian population of the collared flycatchers (Michl et al, 2005), thus yolk androgen concentration in the middle egg should be a good proxy for the mean hormone level of a clutch. Even if within-clutch variation in hormone deposition would have occurred in some individuals of our study population, the third egg would still represent the medium concentration of the whole clutch, as long as the pattern of within-clutch variation is linear (as found in many studied species with significant within-clutch variation, e.g.…”

“…In most species studied so far, including the collared flycatcher and its sister species the pied flycatcher (Ficedula hypoleuca), the between-clutch variation in yolk androgen levels is higher than the within-clutch variation (e.g. Reed and Vleck, 2001;Groothuis and Schwabl, 2002;Pilz et al, 2003;Tschirren et al, 2004;Michl et al, 2005;Müller et al, 2007b, Tobler et al, 2007T. Laaksonen, unpubl.…”

“…The effects of yolk androgens thus seem to vary, but there is evidence that they can affect offspring traits. It has therefore been proposed that by allocating more yolk androgens into the egg, a female could affect offspring trait(s) to which males respond, and this way increase the relative feeding effort of the male to her benefit (Groothuis et al, 2005a;Michl et al, 2005;Gil et al, 2006;Lessells, 2006;Moreno-Rueda, 2007;Müller et al, 2007a).…”

Females allocate differentially to offspring size and number in response to male effects on female and offspring fitness

“…In some cases, female effort has also been found to increase when females mate with a male that offers fewer benefits to offspring fitness. This phenomenon has been termed 'reproductive compensation' [2,[17][18][19][20][21][22][23] and has recently been suggested to be a special case of differential allocation, as female allocation is likely to fall on a continuum between positive and negative responses to male phenotype (e.g. attractiveness) [2,10,20].…”