Maternal allocation in eggs when counting on helpers in a cooperatively breeding bird

Abstract

For cooperatively breeding birds, it has been proposed that breeders should reduce their investment in eggs when they count on helpers, because this can be compensated for by helpers provisioning of nestlings. Data from some species have supported this prediction, but this is not the case in others. It has also been proposed that mothers should not reduce but rather increase investment if the presence of helpers enhances the reproductive value of offspring, a pattern that might also influence egg production as long as helpers are predictable for laying females. Here, we studied maternal expenditure in eggs and clutches in the Iberian magpie, to see whether mothers reduce their expenditure at the egg stage in the presence of helpers. Our results show that investment in clutches varied depending on the year, date in the season and age of the mother, but there were no reductions in maternal expenditure per individual egg when they counted on helpers. On the contrary, a pattern emerged in the opposite direction of more investment in eggs associated with the future presence of helpers at the nestling stage. Our data suggest that the predictability of helpers, along with the type of benefits accrued from the contribution of helpers, may be crucial to understanding the reaction of mothers at egg production.

The relationship between egg size and helper number in cooperative breeders: a meta-analysis across species

“…Six relevant papers ( Legge, 2000 ; Taborsky, Skubic & Bruintjes, 2007 ; Koenig, Walters & Haydock, 2009 ; Canestrari, Marcos & Baglione, 2011 ; Santos & Macedo, 2011 ; Lejeune et al, 2016 ) were located using keyword searches on Google Scholar with the search terms ‘egg size’ and ‘helpers’, on 30th October 2016 (search carried out by TD and confirmed by DL; search criteria were specific and hence disagreements were solved easily by discussion). Forward and backward citation searches were then performed to find five further relevant studies ( Russell et al, 2007 ; Paquet et al, 2013 ; Santos & Nakagawa, 2013 ; Santos, 2016 ; Valencia et al, 2016 ). One study ( Langmore et al, 2016 ) was identified as an ‘online-early’ abstract during the literature search, and was included as full publication occurred during the course of our study.…”

Egg investment in response to helper presence in cooperatively breeding Tibetan ground tits

“…Female apostlebirds Struthidea cinerea and chestnut-crowned babblers Pomatostomus reficeps also increase clutch size with helper assistance, but whether they adjust egg size is not known (Woxvold and Magrath 2005, Russell and Lummaa 2009, Liebl et al 2016. Finally, female Iberian magpie Cyanopica cooki do not adjust their clutch size but produce larger eggs in response to helper presence (Valencia et al 2017). Similar to what was found in the acorn woodpecker Melanerpes formicivorus, both egg size and clutch size were not associated with helper presence in female ground tits (Koenig et al 2009).…”

“…In some studies, a load-lightening strategy has been shown in response to helper presence (Russell et al 2007, Canestrari et al 2011, Santos and Macedo 2011. In contrast, other studies have shown that females may increase their investment in eggs when they are assisted by helpers (Woxvold and Magrath 2005, Russell and Lummaa 2009, Liebl et al 2016, Lejeune et al 2016, Valencia et al 2017 or show no response (Koenig et al 2009). Although a change in egg investment in relation to helper presence is expected to affect survival and reproductive success, few studies have investigated this (Russell et al 2007).…”

Peer Review #1 of "The relationship between egg size and helper number in cooperative breeders: a meta-analysis across species (v0.1)"

“…Six relevant papers (Legge, 2000;Taborsky, Skubic & Bruintjes, 2007;Koenig, Walters & Haydock, 2009;Canestrari, Marcos & Baglione, 2011;Santos & Macedo, 2011;Lejeune et al, 2016) were located using keyword searches on Google Scholar with the search terms 'egg size' and 'helpers', on 30th October 2016 (search carried out by TD and confirmed by DL; search criteria were specific and hence disagreements were solved easily by discussion). Forward and backward citation searches were then performed to find five further relevant studies (Russell et al, 2007;Paquet et al, 2013;Santos & Nakagawa, 2013;Santos, 2016;Valencia et al, 2016).…”

“…In good conditions, the impact of small amounts of additional care is low, and hence mothers would be selected to reduce care in the current generation (Hatchwell, 1999). Furthermore, when helpers provide assistance which increases the survival of offspring or reproductive success beyond that which would be expected from provisioning alone (for example by reducing predation risk), breeders may be selected to increase investment in the presence of helpers (Carranza et al, 2008), due to the high reproductive value of the current brood in comparison with potential future broods (Valencia et al, 2006;Carranza et al, 2008;Russell et al, 2010;Valencia et al, 2016). These predictions primarily apply when variation in maternal pre-natal investment is in the size of each offspring, Manuscript to be reviewed small offspring rather than the same number of larger offspring, more help is likely to be beneficial (e.g.…”