DOI: 10.5061/dryad.prr4xgxk5
title: Complex effects of helper relatedness on female extra-pair reproduction in a cooperative breeder

description: In cooperatively-breeding species, the presence of male helpers in a group
 often reduces the breeding female’s fidelity to her social partner,
 possibly because there is more than one potential sire in the group. Using
 a long-term study of cooperatively-breeding superb fairy-wrens (Malurus
 cyaneus) and records of paternity in 1936 broods, we show that the effect
 of helpers on rates of extra-pair paternity varied according to the
 helpers’ relatedness to the breeding female. The presence of unrelated
 male helpers in a group increased average rates of extra-pair paternity,
 from 57% for groups with no unrelated helpers, to 74% with one unrelated
 helper, to 86% with 2+ unrelated helpers. However, this increase was due
 in equal part to helpers within the group and males in other groups
 achieving increased paternity. In contrast, helpers who were sons of the
 breeding female did not gain paternity, nor did they affect the level of
 extra-group paternity (which occurred at rates of 60%, 58%, 61% in the
 presence of 0, 1, 2+ helper-sons respectively). There was no evidence of
 effects of helpers’ relatedness to the female on nest productivity or
 nestling performance. Because the presence of helpers per se did not
 elevate extra-pair reproduction rates, our results undermine the
 ‘constrained female hypothesis’ explanation for an increase in extra-pair
 paternity with helper number in cooperative breeders. However, they
 indicate that dominant males are disadvantaged by breeding in
 ‘cooperative’ groups. The reasons why the presence of unrelated helpers,
 but not of helper-sons, results in higher rates of extra-group
 reproduction are not clear.
description: Please see associated publication and publications cited therein
 for details of data collection for this long-term study.
 For convenience, here is an excerpt of the Methods from the
 associated publication: The study population consisted
 of a color-banded population of superb fairy-wrens living in a ~60 ha area
 located in and around the Australian National Botanic Gardens, Canberra,
 Australia (35 ◦ 16 S, 149 ◦ 06 E). The study population was censused all
 52 weeks of the year (Cockburn et al. 2003), and census records included
 details of the presence and identity of helpers on each territory. During
 the breeding season the progress of all nests was monitored, with
 nestlings banded 5-8 days post-hatching, at which point blood samples were
 taken for parentage analysis using microsatellite genotypes (see methods
 in Hajduk et al. (2018)). Fairy-wrens are multi-brooded: due to heavy nest
 predation, a female may initiate up to eight clutches in a given year, but
 will only ever raise a maximum of three broods to ﬂedging. Clutches may
 contain 1-5 eggs, with a strong mode at 3 eggs (Cockburn et al.
 2008b).[...] We categorized all offspring in a brood as to whether they
 were the result of within-pair, within-group extra-pair, or extra-group
 paternity: see Box 1 for definitions. [...] data spanned 26 years
 (1988-2013) and contained a total of 1936 broods and 5485
 nestlings. [...]
description: Please see
 the Hajduk-etal-2020_hlpr-rltdnss-fmle-EP-rprdctn_README.md
 file.