Male and female helper effects on maternal investment and adult survival in red-winged fairy-wrens

TY - JOUR

T1 - Male and female helper effects on maternal investment and adult survival in red-winged fairy-wrens

AU - Lejeune, Léa

AU - van de Pol, Martijn

AU - Cockburn, Andrew

AU - Louter, Marina

AU - Brouwer, Lyanne

N1 - 6169, AnE; Data Archiving: Data archived at Dryad

PY - 2016

Y1 - 2016

N2 - Despite its importance for the evolution of cooperative breeding, it has proven difficult to determine whether helpers improve their recipients’ fitness. Helpers affect fitness in multiple ways, both positive and negative, but their effects can also be concealed through reduced maternal investment. Furthermore, determining the direction of causation is difficult, as helper presence may indicate a productive territory, rather than high productivity indicating an effect of help. In cooperatively breeding red-winged fairy-wrens (Malurus elegans) groups reduce care when they have male helpers, but groups with female helpers do not, so nestlings receive more food. Thus our predictions vary with helper sex rather than helper number, and by studying within-group changes with regard to group composition we separate phenotypically plastic responses from among-group correlations. Females did not reduce egg size in response to an increasing number of female helpers. However, more male or female helpers allowed females to lay larger clutches and more female helpers reduced re-nesting intervals. There was mixed support for a benefit of load lightening: Helpers, but not breeders, gained survival benefits with increasing number of male helpers. However, helper survival decreased with the number of female helpers, suggesting that increased competition counterbalanced these male helper benefits. We also found consistent among-group differences, which would have erroneously been interpreted as helper effects had we not disentangled the within-group changes with regard to group composition. This study highlights the importance of assessing carers’ benefits in relation to both group composition and size, and of investigating the within-individual plastic response of helper effects.

AB - Despite its importance for the evolution of cooperative breeding, it has proven difficult to determine whether helpers improve their recipients’ fitness. Helpers affect fitness in multiple ways, both positive and negative, but their effects can also be concealed through reduced maternal investment. Furthermore, determining the direction of causation is difficult, as helper presence may indicate a productive territory, rather than high productivity indicating an effect of help. In cooperatively breeding red-winged fairy-wrens (Malurus elegans) groups reduce care when they have male helpers, but groups with female helpers do not, so nestlings receive more food. Thus our predictions vary with helper sex rather than helper number, and by studying within-group changes with regard to group composition we separate phenotypically plastic responses from among-group correlations. Females did not reduce egg size in response to an increasing number of female helpers. However, more male or female helpers allowed females to lay larger clutches and more female helpers reduced re-nesting intervals. There was mixed support for a benefit of load lightening: Helpers, but not breeders, gained survival benefits with increasing number of male helpers. However, helper survival decreased with the number of female helpers, suggesting that increased competition counterbalanced these male helper benefits. We also found consistent among-group differences, which would have erroneously been interpreted as helper effects had we not disentangled the within-group changes with regard to group composition. This study highlights the importance of assessing carers’ benefits in relation to both group composition and size, and of investigating the within-individual plastic response of helper effects.

KW - international

UR - http://dx.doi.org/10.5061/dryad.rt3f3

U2 - 10.1093/beheco/arw121

DO - 10.1093/beheco/arw121

M3 - Article

SN - 1045-2249

VL - 27

SP - 1841

EP - 1850

JO - Behavioral Ecology

JF - Behavioral Ecology

IS - 6

ER -