Abstract
An ovipositing insect experiences many sensory challenges during her search for a suitable host plant. These sensory challenges become exceedingly pronounced when host range increases, as larger varieties of sensory inputs have to be perceived and processed in the brain. Neural capacities can be exceeded upon information overload, inflicting costs on oviposition accuracy. One presumed generalist strategy to diminish information overload is the acquisition of a focused search during its lifetime based on experiences within the current environment, a strategy opposed to a more genetically determined focus expected to be seen in relative specialists. We hypothesized that a broader host range is positively correlated with mushroom body (MB) plasticity, a brain structure related to learning and memory. To test this hypothesis, butterflies with diverging host ranges (Polygonia c-album, Aglais io and Aglais urticae) were subjected to differential environmental complexities for oviposition, after which ontogenetic MB calyx volume differences were compared among species. We found that the relative generalist species exhibited remarkable plasticity in ontogenetic MB volumes; MB growth was differentially stimulated based on the complexity of the experienced environment. For relative specialists, MB volume was more canalized. All in all, this study strongly suggests an impact of host range on brain plasticity in Nymphalid butterflies.
Highlights
The search for a suitable host plant to lay eggs on has proved to be a challenging task for an insect
The results confirmed our hypothesis and showed that the generalist species P. c-album exhibited higher neural plasticity compared with the specialist species Ag. io and Ag. urticae
The results further showed a significant correlation between relative antennal lobe (rAL) and relative MB calyx (rCA) volumes among treatments, where the generalist species exhibited the largest overall volumes of both neuropils
Summary
The search for a suitable host plant to lay eggs on has proved to be a challenging task for an insect. Included relative specialist species were Aglais io and Aglais urticae, which were compared with the relative generalist Polygonia c-album For the latter species, two distinct populations (English and Swedish) were investigated with diverging degrees of specialization, allowing intraspecific comparisons. English P. c-album is specialized on U. dioica to a relatively high degree [26] Both host-plant and non-host-plant species were used for oviposition experiments. The plants Al. petiolata, B. pendula, L. album, Ae. podagraria and C. arvense were only temporarily present in the complex environment (1 – 2 days) These plants are non-host plants for all used butterfly species and naturally grow interspersed in the host-plant habitat; these plants were included to make the environment more complex and to potentially confuse the ovipositing butterfly. Linear regression analyses were performed to identify potential correlations between brain structure volumes among treatments and species
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