Entomophaga

, Volume 42, Issue 1–2, pp 13–20

Ladybirds as a model system for the study of male-killing symbionts

  • M. E. N. Majerus
  • G. D. D. Hurst
Article

Abstract

Maternally inherited bacteria that kill male but not female hosts during embryogenesis occur in a number of aphidophagous coccinellids. Work on EnglishAdalia bipunctata (L.), has shown the causative agent of male-killing to be a member of the bacterial genusRickettsia. In coccinellids, the primary advantage of male-killing behaviour to the bacterium has been identified. Following male death, resource reallocation occurs through sibling egg cannibalism: female neonate larvae of infected mothers gain a significant survival advantage by eating the soma of their dead male siblings. In addition, daughters of infected females suffer a reduced risk of cannibalism as a result of the lower egg hatch rate in infected clutches.

Predictions as to which species of coccinellid are liable to harbour male-killers may be made on the basis of the selective advantages of male-killing identified inA. bipunctata. Species which may harbour male-killers are likely to lay eggs in clutches, show sibling egg cannibalism, and exhibit high neonate mortality.

Recent work has shown male-killing to occur in a number of other aphidophagous coccinellids with the predicted characteristics. Molecular genetic analysis has putatively identified three bacterial symbionts associated with male-killing, coming from three phylogenetically distant bacterial taxa. We therefore suggest that within coccinellids that possess these features, male-killing may evolve in a taxonomically diverse range of inherited bacteria.

The implications of the presence of male-killing bacteria on the population demography of host coccinellids, and on host mitochondrial DNA variability are discussed. The aphidophagous coccinellids are proposed as a model system for studying the evolution and consequences of infection with male-killers.

Key-words

Coccinellidae female-biased sex ratio cytoplasmic bacteria male killing sibling egg cannibalism mitochondrial DNA 

Les coccinelles en tant que modèle de l’étude des symbiontes tueurs de mâles

Résumé

Il existe des bactéries transmises maternellement et qui tuent leurs hôtes mâles mais pas leurs hôtes femelles au cours de l’embryogénèse dans de nombreuses coccinelles aphidiphages. Un travail surAdalia bipunctata (L.) a montré que l’agent responsable de cette élimination des mâles était unRickettsia. Chez les coccinelles, on a trouvé l’avantage de base de l’élimination des mâles par les bactéries. Suite à la mort du mâle, la redistribution des ressources a lieu par le cannibalisme des œufs entre membres d’une même ponte : les larves femelles nouvellement écloses des mères infestées obtiennent un avantage significatif en terme de survie en dévorant leurs congénères mâles. En outre, les filles de femelles infestées souffrent d’un risque de cannibalisme réduit, résultat d’un taux d’éclosion des œufs plus bas dans les pontes infestées. La prédiction des espèces de coccinellides susceptibles de comporter des tueuses de mâles peut être faite sur la base des avantages sélectifs d’éliminer le mâle chezA. bipunctata. Les espèces susceptibles de comporter des tueuses de mâles pondent probablement leurs œufs groupés, présentent un cannibalisme entre œufs d’une même ponte et une forte mortalité néonate.

Un travail récent a montré que le comportement d’élimination des mâles existe chez de nombreuses autres coccinelles aphidiphages présentant les caractéristiques que l’on attendait. L’analyse génétique moléculaire a permis de distinguer trois symbiontes bactériens associés à ce phénomène, provenant de trois taxa de bactéries phylogénétiquement éloignés. Nous suggérons donc que parmi les coccinelles qui possèdent ces caractéristiques, l’élimination des mâles peut évoluer dans une gamme taxonomiquement diverse de bactéries transmises maternellement.

Les implications de la présence de bactéries tueuses sur la démographie des coccinelles hôtes et sur la variabilité de l’ADN mitochondrial de l’hôte sont discutées. Les coccinelles aphidiphages sont proposées comme modèle pour l’étude de l’évolution et les conséquences de l’infection par des bactéries tueuses de mâles.

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Copyright information

© Lavoisier Abonnements 1997

Authors and Affiliations

  • M. E. N. Majerus
    • 1
  • G. D. D. Hurst
    • 1
  1. 1.Department of GeneticsUniversity of CambridgeCambridgeU.K.

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