Do females invest more into eggs when males sing more attractively? Postmating sexual selection strategies in a monogamous reed passerine

Abstract

Maternal investment can play an important role for offspring fitness, especially in birds, as females have to provide their eggs with all the necessary nutrients for the development of the embryo. It is known that this type of maternal investment can be influenced by the quality of the male partner. In this study, we first verify that male song is important in the mate choice of female Eurasian reed warblers, as males mate faster when their singing is more complex. Furthermore, female egg investment varies in relation to male song characteristics. Interestingly, clutch size, egg weight, or size, which can be considered as an high-cost investment, is not influenced by male song characteristics, whereas comparably low-cost investment types like investment into diverse egg components are adjusted to male song characteristics. In line with this, our results suggest that female allocation rules depend on investment type as well as song characteristics. For example, egg white lysozyme is positively correlated with male song complexity. In contrast, a negative correlation exists between-song speed and syllable repetitiveness and egg yolk weight as well as egg yolk testosterone concentration. Thus, our results suggest that female egg investment is related to male song performance in several aspects, but female investment patterns regarding various egg compounds are not simply correlated.

Eggshell coloration and its importance in postmating sexual selection

“…According to the “differential allocation” hypothesis, females should adjust their investment into offspring in relation to the attractiveness of their partner (Burley, ; Sheldon, ). In line with this, it has been already shown that female maternal investment depends on male attractiveness (Gil, Graves, Hazon, & Wells, ; Horváthová, Nakagawa, & Uller, ; Krištofík et al., ; Williamson, Surai, & Graves, ) and eggshell coloration on maternal investment for both protoporphyrin‐based eggshell coloration (Holveck et al., ) and biliverdin‐based (Morales et al., ; Navarro et al., ) eggshell coloration. In support of that, we found that in pairs where the male showed comparatively bigger melanin‐based ornaments, the female laid darker eggs and melanin‐based ornaments are in fact known to signal quality, for example, social status and/or body condition (Hoi & Griggio, ; Nakagawa, Ockendon, Gillespie, Hatchwell, & Burke, ).…”

Traffic noise affects embryo mortality and nestling growth rates in captive zebra finches

“…However, high levels of egg failure in our experimental noise treatment group meant that entire nests were unsuccessful and pairs needed to re‐nest several times before successfully fledging a brood—the size of which was eventually equal to those in the quiet conditions. These entire initial nest failures were predominantly caused by high levels of embryo mortality, which in captive breeding birds is likely due to parental incubation failure (Birkhead et al, ), but may also be due to the quality of resources in the egg itself—a variable that might be affected by maternal condition (Hayward and Wingfield, ), investment (Krištofík et al, ) or simply due to a clutch size—egg size trade‐off (Williams, ). Since all environmental conditions other than noise were consistent between treatment groups, this alteration in incubating behaviour, and possibly in feeding behaviour (resulting in the lagging growth rates of nestlings in the noise treatment) is possibly due to increased vigilance by parents in a noisy environment.…”

“…We have categorized these hypotheses as follows: Parental investment is lower in noisy areas . Because females in some species alter parental investment according to the attractiveness of a male's song (Garcia‐Fernandez et al, 2013; Soma and Okanoya, ; Krištofík et al, ), song changes made to overcome masking noise may be considered less attractive and therefore affect female reproductive allocation (Habib et al, ; Halfwerk and Slabbekoorn, ), resulting in lower reproductive success in urban areas. Noisy territories are lower quality / are held by lower quality males . Both territory quality and male quality can affect reproductive success, and are often correlated (reviewed in Andersson, ).…”

Intraclutch eggshell colour variation in birds: are females able to identify their eggs individually?

“…Here we suggest that if eggs are of different value, eggshell colour can signal information about the quality of an egg ( Krištofík et al, 2013 ; Krištofík et al, 2014 ), which may allow the female to treat eggs accordingly.…”