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Cichlids do not adjust reproductive skew to the availability of independent breeding options
Authors:Heg  Dik; Bergmuller  Ralph; Bonfils  Danielle; Otti  Oliver; Bachar  Zina; Burri  Reto; Heckel  Gerald; Taborsky  Michael
Institution:a Department of Behavioural Ecology, Zoological Institute, University of Bern, Wohlenstrasse 50a, CH-3032 Hinterkappelen, Switzerland and b Computational and Molecular Population Genetics Lab, Zoological Institute, University of Bern, CH-3012 Bern, Switzerland
Abstract:Helpers in cooperatively breeding species forego all or partof their reproduction when remaining at home and assisting breedersto raise offspring. Different models of reproductive skew generatealternative predictions about the share of reproduction unrelatedsubordinates will get depending on the degree of ecologicalconstraints. Concession models predict a larger share when independentbreeding options are good, whereas restraint and tug-of-warmodels predict no effects on reproductive skew. We tested thesepredictions by determining the share of reproduction by unrelatedmale and female helpers in the Lake Tanganyika cichlid Neolamprologuspulcher depending on experimentally manipulated possibilitiesfor helper dispersal and independent breeding and dependingon helper size and sex. We created 32 breeding groups in thelaboratory, consisting of two breeders and two helpers each,where only the helpers had access to a nearby dispersal compartmentwith (treatment) or without (control) breeding substrate, usinga repeated measures design. We determined the paternity andmaternity of 1185 offspring from 47 broods using five to nineDNA microsatellite loci and found that: (1) helpers participatedin reproduction equally across the treatments, (2) large malehelpers were significantly more likely to reproduce than smallhelpers, and (3) male helpers engaged in significantly morereproduction than female helpers. Interestingly, in four broods,extragroup helper males had fertilized part of the brood. Nohelper evictions from the group after helper reproduction wereobserved. Our results suggest that tug-of-war models based oncompetition over reproduction within groups describe best thereproductive skew observed in our study system. Female breedersproduced larger clutches in the treatment compared to the controlsituation when the large helpers were males. This suggests thatmale breeder-male helper reproductive conflicts may be alleviatedby females producing larger clutches with helpers around.
Keywords:Cichlidae  clutch size adjustment  cooperative breeding  ecological constraints  reproductive partitioning  
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