How labile are the egg‐laying preferences of seed beetles?

Abstract

Abstract. 1. Previous studies have produced conflicting results with respect to the genetic lability of host preference in the seed beetle Callosobruchus maculatus. 2. In this study, replicate lines of an Asian population were kept on an ancestral host (mung bean) or switched to a novel host (cowpea). After 40+ generations, lines were assayed for host preference (in choice tests) and host acceptance (under no‐choice conditions), and were compared to African lines chronically associated with cowpea. 3. Host preference diverged in the expected direction. When presented a mixture of cowpeas and mung beans, females from the cowpea lines laid a greater fraction of their eggs on cowpea than did females from the mung bean lines. Preference for cowpea was nearly as strong in the cowpea lines as it was in the cowpea‐adapted African lines. 4. In contrast, the experimental host shift did not affect long‐term host acceptance. African females laid more eggs if given cowpeas than if given mung beans, but realised fecundities in the cowpea and mung bean lines were similar on the two hosts. Females from all lines laid more eggs if they were reared on cowpea than on mung bean, but rearing host had no effect on either relative host acceptance or host preference. 5. Comparisons with earlier studies suggest that the lability of host preference varies among beetle populations, which precludes generalisation at the species level. Because lines were maintained under no‐choice conditions, modification of host preference probably occurred via a lower acceptance threshold for the novel host, without a concomitant change in the long‐term acceptance of the ancestral host.

Female Oviposition Decisions and Their Impact on Progeny Life-History Traits

“…In the experiment on oviposition preference we found that females laid more eggs and more often on black-eye beans than on mung beans. Earlier choice experiments between bean species have found similar results showing that C. maculatus females usually prefer larger beans within bean species (Cope and Fox 2003) as well as between species (Kawecki and Mery 2003; but see also Messina 2004), even if host preference and population may have some influence on a female's decisions (Wasserman 1981;Kawecki and Mery 2003;Messina 2004). Population may also influence on female egg dispersion and lifespan differences (Messina and Karren 2003;Fox et al 2004).…”

“…In addition to the type of the bean, we, unlike many other earlier studies of host preference (e.g. Guedes et al 2003;Kawecki and Mery 2003;but see: Messina and Mitchell 1989;Messina 2004) also considered that the beans of different types have a different surface area. This is important as surface area of the bean has an influence on the null hypothesis against which female oviposition preferences should be tested.…”

Genetic architecture of differences in oviposition preference between ancestral and derived populations of the seed beetle Acanthoscelides obtectus

“…This finding is consistent with our previous results, which showed a divergence of host preference between the same ancestral and derived populations (Tucić et al, 1995(Tucić et al, , 1997. Our studies of A. obtectus accord with those of Calosobruchus maculatus (Wasserman and Futuyma, 1981;Credland, 1987;Fox, 1993;Messina, 2004; but see Kawecki and Mery, 2003 for contrasting results) in demonstrating a divergence of host preference between populations maintained on different host species. Figure 2 The mean oviposition preference (7s.e.)…”

Warp-speed adaptation to novel hosts after 300 generations of enforced dietary specialisation in the seed beetle Callosobruchus maculatus (Coleoptera: Chrysomelidae: Bruchinae)

“…maculatus has become a model system for using experimental evolution to identify the fi tness consequences and genetics associated with host plant shifts in herbivorous insects (Fricke & Arnqvist, 2007, Gompert & Messina, 2016. However, previous studies in this system have focused on relatively long-term changes in host use, of at least 10 generations (Messina & Karren, 2003;Messina, 2004a). In the current study, under no-choice conditions, we evaluated the ability of C. maculatus populations to adapt to novel bean types over each of 5 generations fol-mey, Niger, where they also primarily targeted cowpeas in the wild.…”