Male‐killer dynamics inDanaus chrysippus(L.) (Lepidoptera:Nymphalidae) inEastAfrica

Abstract

Within certain regions in East Africa, the butterfly Danaus chrysippus (L.) shows female‐biased population sex ratio, because of the production by some females of all‐female broods, as a result of infection by maternally inherited, male‐killing bacterium of the genus Spiroplasma. In this study, we describe a 3‐year field survey for the population dynamics of the male‐killing Spiroplasma in D. chrysippus in four independent localities, namely Uganda, Ghana, Sudan and Madagascar. The prevalence of the bacterium was found to show extensive variations at multiple scales among different sites, in various countries, seasons and years. A novel, selection‐based hypothesis was suggested to explain the high variability of male‐killer prevalence over space and time, based on the existence of an adaptive link between larval food‐plant density and the magnitude of resource reallocation fitness advantage for the male‐killer.

Biased sex ratios and aposematic polymorphism in African butterflies: A hypothesis

“…These expectations can serve as a base for testing this hypothesis against field data. In a thorough investigation for population sex ratios, male-killer prevalences and morph ratios in D. chrysippus, A. encedon and A. encedana conducted in Uganda (Hassan et al 2012a(Hassan et al , 2012b, two temporal patterns were found, which are highly consistent with theoretical predictions. Firstly, comparing the bacterial prevalences recorded during (2005)(2006)(2007) with those recorded a few years later (1998)(1999) (Jiggins et al 2000a(Jiggins et al , 2000b(Jiggins et al , 2000c for the three species has shown that the male killer undergoes extensive population dynamics.…”

Intragenomic conflict produces sex ratio dynamics that favor maternal sex ratio distorters

“…Genetic cytoplasmic distorters normally exhibit perfect maternal vertical transmission, and near-perfect or perfect transmission rates near have been documented in parasitic systems as well Jiggins, Randerson, Hurst, & Majerus, 2002). While some distorters are capable of completely feminizing broods, many distorters have more modest impacts, and distorter brood sex ratios frequently range from 60% to 80% female (Hassan, Idris, & Majerus, 2012;Mercot et al, 1995;Rigaud et al, 1999;Vala, Van Opijnen, Breeuwer, & Sabelis, 2003).…”

Male-killing in African butterflies

“…26,33,34 The extensive population dynamics experienced by the male-killing Spiroplasma is likely to underlay the substantial difference in the overall Spiroplasma prevalence at Uganda estimated by Jiggins et al 26 and Hassan et al (40% and 24.9%, respectively). It has been suggested 34 that the male-killer dynamics reflect fundamental differences in the equilibrium prevalence of Spiroplasma between populations, maintained by natural selection.…”

“…It has been suggested 34 that the male-killer dynamics reflect fundamental differences in the equilibrium prevalence of Spiroplasma between populations, maintained by natural selection. 34 According to this view, resource reallocation (i.e. the fitness advantage gained by infected females due to the death of their male siblings) does occur in D. chrysippus, not as a consequence of a genetically-determined life history trait, but, rather, as a response to an environmental limiting factor, which is the density of larval food-plants, the milkweeds; lower milkweed densities can enforce a modification of the innate oviposition behaviour so that females lay multiple eggs on a single plant.…”