Supplementary Testosterone Inhibits Paternal Care in a Tropically Breeding Sparrow, Zonotrichia capensis

Abstract

In most male birds that exhibit paternal care, elevation in testosterone above the breeding baseline reduces nestling provisioning, which can be detrimental to offspring survival. Mechanisms that may allow some males to avoid this detrimental effect of elevated testosterone include (1) decreased sensitivity to testosterone's effects on behavior and (2) uncoupling of testosterone secretion from territorial challenges (thus reducing the number of transient elevations in testosterone above the breeding baseline). Both of these "cost-avoidance" mechanisms have been documented, but whether selection for these mechanisms is correlated or independent is unknown. We investigated the relationship between elevated testosterone and paternal care in a tropical bird, the rufous-collared sparrow (Zonotrichia capensis). Zonotrichia capensis males exhibit an uncoupling of testosterone secretion from territorial aggression, and this species has a flexible breeding season and a clutch size smaller than those of temperate congeners. We implanted males with testosterone or empty implants and observed paternal behavior 2-3 and 6-7 d posthatch. During both observation periods, 100% of control males fed chicks, whereas 22% and 0% of testosterone-implanted males fed chicks on days 2-3 and 6-7, respectively. Chicks of testosterone-implanted males weighed less than control chicks, but tarsus growth, wing growth, and fledging success did not differ. Thus, we demonstrate a robust negative effect of testosterone on nestling provisioning that may not ultimately affect reproductive success. We suggest that these results relate to extreme flexibility in breeding schedule and the small clutch size in this tropical species. Our data also suggest that selection for the two mechanisms to avoid deleterious effects of elevations in testosterone above the breeding baseline likely occurs independently.

Estrogen receptor α polymorphism in a species with alternative behavioral phenotypes

“…This life-history tradeoff is believed to be mediated in part by T, which increases singing and mate-finding and decreases parental behavior in many seasonally breeding sparrows (27)(28)(29)(30). In free-living populations of white-throated sparrows, plasma T levels are higher in WS birds (7,8), which have the ZAL2 m rearrangement, than in TS birds, which do not (2,31).…”

Endogenous testosterone is not associated with the trade-off between paternal and mating effort

“…This trade-off will be more pronounced when there are many opportunities for extrapair matings during the provisioning stage, which may occur when breeding synchrony in the population is low or when females reproduce more than once during a single breeding season. The parental effortmating effort trade-off has received considerable attention (e.g., De Ridder et al 2000;Trainor and Marler 2001;Van Roo et al 2004;Lynn et al 2005Lynn et al , 2009, particularly since the finding that extrapair fertilizations are common in most bird species (Griffith et al 2002). Hormones are a likely candidate as proximate mediators of life-history trade-offs because hormones typically influence many behaviors simultaneously .…”

“…Firstly, in socially monogamous birds, male testosterone concentrations are typically much higher around territory establishment and the female fertile period than during the paternal care phase (e.g., Wingfield et al 1990;Pinxten et al 2007;Sasvári et al 2009). Secondly, testosterone implant experiments generally find that males with artificially elevated testosterone concentration during provisioning feed their young at a lower rate than control males (e.g., Saino and Møller 1995;De Ridder et al 2000;Van Roo et al 2004;Lynn et al 2009; but see Van Duyse et al 2000;Lynn et al 2005). In other vertebrates, the role of testosterone in the paternal and mating effort tradeoff is less clear.…”

European robins (Erithacus rubecula) lack an increase in testosterone during simulated territorial intrusions

“…Furthermore, the male feeds both the female and young for at least 2-3 days after hatching (Pätzold 1995;Grajetzky 2000). Thus, it is possible that robins belong to the set of species in which male parental care is essential, and the lack of an increase in testosterone during STIs is consistent with the essential paternal care hypothesis Lynn et al 2002Lynn et al , 2005Lynn 2008; but see Lynn et al 2009). …”

“…In particular, high levels of testosterone may increase the risk of injury and exposure to predators, its anabolic properties may reduce fat stores, and it may impair the function of the immune system (Dufty 1989;Ketterson et al 1992Ketterson et al , 1996Folstad and Karter 1992;Wedekind and Folstad 1994;Hillgarth and Wingfield 1997;Duffy et al 2000;Wingfield et al 2001). Furthermore, testosterone has been reported to reduce male parental care in various bird species (Wingfield et al 1990), although this does not seem to be the case in species for which paternal care is essential (Lynn et al 2002(Lynn et al , 2005; but see Lynn et al 2009). …”