Incomplete offspring sex bias in Australian populations of the butterfly Eurema hecabe

Kemp, D.J., Thomson, F.E., Edwards, W., and Iturbe-Ormaetxe, I. (2017) Incomplete offspring sex bias in Australian populations of the butterfly Eurema hecabe. Heredity, 118. pp. 284-292.

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Theory predicts unified sex ratios for most organisms, yet biases may be engendered by selfish genetic elements such as endosymbionts that kill or feminize individuals with male genotypes. Although rare, feminization is established for Wolbachia-infected Eurema butterflies. This paradigm is presently confined to islands in the southern Japanese archipelago, where feminized phenotypes produce viable all-daughter broods. Here, we characterize sex bias for E. hecabe in continental Australia. Starting with 186 wild-caught females, we reared >6000 F1–F3 progeny in pedigree designs that incorporated selective antibiotic treatments. F1 generations expressed a consistent bias across 2 years and populations that was driven by an ~5% incidence of broods comprising greater than or equal to 80% daughters. Females from biased lineages continued to overproduce daughters over two generations of outcrossing to wild males. Treatment with antibiotics of differential strength influenced sex ratio only in biased lineages by inducing an equivalent incomplete degree of son overproduction. Brood sex ratios were nevertheless highly variable within lineages and across generations. Intriguingly, the cytogenetic signature of female karyotype was uniformly absent, even among phenotypic females in unbiased lineages. Molecular evidence supported the existence of a single Wolbachia strain at high prevalence, yet this was not clearly linked to brood sex bias. In sum, we establish an inherited, experimentally reversible tendency for incomplete offspring bias. Key features of our findings clearly depart from the Japanese feminization paradigm and highlight the potential for more subtle degrees of sex distortion in arthropods.

Item ID: 46891
Item Type: Article (Research - C1)
ISSN: 1365-2540
Keywords: wolbachia, sex ratio, Eurema
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Funders: Australian Research Council (ARC), Australia-Pacific Science Foundation (APSF), James Cook University
Projects and Grants: ARC DP0557190, ARC DP140104107, APSF 10-09
Research Data:
Date Deposited: 22 Jan 2017 23:16
FoR Codes: 31 BIOLOGICAL SCIENCES > 3104 Evolutionary biology > 310407 Host-parasite interactions @ 50%
31 BIOLOGICAL SCIENCES > 3104 Evolutionary biology > 310408 Life histories @ 50%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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