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bioRxiv · 10.1101/2023.09.08.556834

Investigating the role of non-helpers in group-living thrips

Gilbert, J. D.
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Abstract

O_LIBehavioural variation among individuals is a hallmark of cooperative societies, which commonly contain breeders and non-breeders, helpers and non-helpers. In some cases labour is divided, with non-breeders "helping". Conversely, in some societies subordinate non-breeders often do not help. These individuals may be (i) an insurance workforce to ensure continuity of help for breeders when other helpers are lost, (ii) conserving energy while waiting to breed themselves, or (iii) simply of too poor physiological quality either to help or breed. C_LIO_LIIn the Australian Outback, Acacia thrips Dunatothrips aneurae (Thysanoptera) glue Acacia phyllodes into "domiciles" using silk-like secretions, either alone or cooperatively. Domicile maintenance is important for humidity, so repair can be interpreted as helping. I found that not all females helped to repair experimental damage; some repaired partially or not at all ("non-helpers"). At the same time, some co-foundresses are non- or only partially reproductive, and their role is currently unknown. C_LIO_LII first tested the possibility that helping and breeding are divided, with non-helping females breeding, and non-breeders helping. In a lab experiment, I rejected this idea. Experimentally damaged domiciles were typically repaired by reproductive females, and not by non- or partially reproductive individuals. C_LIO_LITo test whether non-helpers are an insurance workforce, I successively removed repairing females and found that non-helping females did not increase effort as a result. Then, in a field experiment, I tested whether non-helping females were conserving energy while waiting to breed by removing all other females, allowing either a helpful female or a non-helping female to "inherit" her domicile. Isolated like this, non-helpers laid very few eggs compared to helpers or naturally occurring single foundresses, despite having similar ovarian development. C_LIO_LIMy findings show that labour was not divided: reproduction and helping covaried positively, probably depending on individual variation in female quality and intra-domicile competition. Non-helping females were neither an insurance workforce nor conserving energy waiting to breed themselves. They are likely simply of poor quality, freeloading by benefiting from domicile maintenance by others. I hypothesize they are tolerated because of selection for indiscriminate communal brood care in the form of domicile repair. C_LI

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Gilbert, J. D.. 2023-09-08. Investigating the role of non-helpers in group-living thrips. https://doi.org/10.1101/2023.09.08.556834

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