Maternal Effects in Relation to Helper Presence in the Cooperatively Breeding Sociable Weaver

Abstract

In egg laying species, breeding females may adjust the allocation of nutrients or other substances into eggs in order to maximise offspring or maternal fitness. Cooperatively breeding species offer a particularly interesting context in which to study maternal allocation because helpers create predictably improved conditions during offspring development. Some recent studies on cooperative species showed that females assisted by helpers produced smaller eggs, as the additional food brought by the helpers appeared to compensate for this reduction in egg size. However, it remains unclear how common this effect might be. Also currently unknown is whether females change egg composition when assisted by helpers. This effect is predicted by current maternal allocation theory, but has not been previously investigated. We studied egg mass and contents in sociable weavers (Philetairus socius). We found that egg mass decreased with group size, while fledgling mass did not vary, suggesting that helpers may compensate for the reduced investment in eggs. We found no differences in eggs’ carotenoid contents, but females assisted by helpers produced eggs with lower hormonal content, specifically testosterone, androstenedione (A4) and corticosterone levels. Taken together, these results suggest that the environment created by helpers can influence maternal allocation and potentially offspring phenotypes.

Maternal allocation in cooperative breeders: should mothers match or compensate for expected helper contributions?

“…For example, in studies of cooperative meerkats, Suricata suricatta (Russell, Brotherton, McIlrath, Sharpe, & Clutton-Brock, 2003), increasing helper number indirectly increases pup mass at burrow emergence, as helpers boost maternal weight at conception, and heavier mothers produce heavier pups. By contrast, in fish species (Taborsky, Skubic, & Bruintjes, 2007) and a range of birds (Canestrari, Marcos, & Baglione, 2011;Paquet, Covas, Chastel, Parenteau, & Doutrelant, 2013;Russell, Langmore, et al, 2007;Santos & Macedo, 2011), studies have generally reported a reduction in prebirth investment with increasing group size (for an exception see Koenig, Walters, & Haydock, 2009), without a corresponding change in the number of offspring produced.…”

“…more helpers) should invest more to exploit current conditions, or save resources to increase their future survival probability. To this end, we explore two possible effects of increased maternal investment on outcomes for offspring: a 'head start' relationship under which greater prebirth investment leads to lower postbirth investment from the entire care group (Paquet et al, 2013;Russell, Langmore, et al, 2007), and a 'silver spoon' relationship under which prebirth investment has long-term effects on offspring phenotype (Eising, Müller, & Groothuis, 2006;Strasser & Schwabl, 2004), but may lead to greater demands during rearing, for example if larger offspring require more food (Clutton-Brock, Albon, & Guinness, 1985;Klaassen & Bech, 1992). This approach contrasts with previous theoretical work on parental care, which has focused on either postbirth investment in isolation (Houston & Davies, 1985;McNamara, Gasson, & Houston, 1999) or maternal control of offspring number rather than offspring 'quality' (Savage, Russell, & Johnstone, 2013a, 2013b.…”

Antagonistic effect of helpers on breeding male and female survival in a cooperatively breeding bird

“…2007; Taborsky, Skubic & Bruintjes 2007; Canestrari, Marcos & Baglione 2011; Santos & Macedo 2011; Paquet et al . 2013). Hence, in these species, a stronger effect of helpers might be expected on female survival compared to male survival.…”

“…Additionally, sociable weaver females lay lighter eggs when assisted by helpers (Paquet et al . 2013). Therefore, we predict a greater positive effect of the presence of helpers on female than on male survival probability.…”

A cross-fostering experiment reveals that prenatal environment affects begging behaviour in a cooperative breeder

“…Cooperative breeders are usually long-lived species (Arnold & Owens, 1998;Covas & Griesser, 2007) and females with good future reproductive prospects are expected to decrease their investment in eggs with an increasing number of helpers in order to maximize their lifetime reproductive success (Russell & Lummaa, 2009). Indeed, recent results have shown that females may invest less by producing smaller eggs when they have helpers, since the additional food brought by the helpers will compensate for this difference in egg size (Canestrari, Marcos, & Baglione, 2011;Paquet, Covas, Chastel, Parenteau, & Doutrelant, 2013;Russell, Langmore, Cockburn, Astheimer, & Kilner, 2007;Santos & Macedo, 2011). Additionally, in the presence of helpers, sociable weaver, Philetairus socius, females have been found to deposit less steroid hormones in eggs , which are potentially immunosuppressive (see Groothuis, Muller, von Engelhardt, Carere, & Eising, 2005 for a review).…”