Skew in ovarian activation depends on domicile size in phyllode-glueing thrips

J D J Gilbert,A Wells,S J Simpson

doi:10.1038/s41598-018-21635-z

J D J Gilbert, A Wells + Show 1 more

Open Access

https://doi.org/10.1038/s41598-018-21635-z

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Abstract

Costs and benefits of group living are a fundamental topic in behavioural ecology. Resource availability affects individuals’ breeding prospects alone and in groups, as well as how reproduction is distributed within groups (“reproductive skew”). Here, in facultatively social thrips, we provide correlational evidence that breeding resources are associated with (1) whether solitary or social living is favoured, and (2) the degree of ovarian skew. Dunatothrips aneurae (Thysanoptera, Phlaeothripidae) cooperatively build silk “domiciles” on Australian Acacias, feeding exclusively from internal phyllode surfaces. Per capita productivity scaled differently with group size depending on domicile volume — females in small domiciles did better alone than in groups, whereas in large domiciles single and group-nesting females did equally well. Ovarian dissections revealed that in small domiciles some females were nonreproductive, indicating ovarian (i.e. reproductive) skew. Skew increased as domicile size decreased and group size increased. Breeders had smaller oocyte volume in smaller domiciles, especially those containing nonreproductives. These findings suggest group formation and reproductive skew in D. aneurae may be influenced by reproductive competition for breeding resources. Nonreproductive females in small domiciles may be reproductively suppressed, subfertile, or accumulating resources to reproduce.

Highlights

Is it better for animals to breed alone, or in groups? The size of animal breeding groups represents the balance of multiple benefits and costs to individuals[1]
Over a substantial range of domicile sizes, single females had higher expected per capita reproduction than multiple females (Fig. 1)
In the smallest third of domiciles, per capita offspring decreased when multiple foundresses were present, whereas in medium-sized or large domiciles, per capita offspring did not change with foundress number (Fig. 2)

Summary

Introduction

Is it better for animals to breed alone, or in groups? The size of animal breeding groups represents the balance of multiple benefits and costs to individuals[1]. Acacia thrips present contrasts and comparisons with the better-studied social Hymenoptera, and are increasingly appreciated as a parallel model clade for social research[21] Both of the social thrips lineages are herbivorous, the group members living, feeding and reproducing entirely within their resource. The gall-inducing thrips, which are eusocial, a general evolutionary trend towards smaller galls (i.e. fewer resources) has been accompanied by more pronounced division of reproduction between foundress and soldiers (i.e. increasing reproductive skew)[22,23,24] This finding was interpreted as evidence that within-gall competition for resources may have helped to drive the evolution of the soldier caste[22]. Without a truly solitary option available, the effects of resource size upon the costs and benefits of social behaviour are hard to assess

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