Abstracts (first author)
The fate of seasonal plasticity under relaxed selection
Phenotypic plasticity of wing patterns is a widespread phenomenon among butterflies. Species occurring in seasonal habitats, where larval food plants dry out for an extended part of the year, often have a distinct dry season morph that is sedentary and delay reproduction until fresh plants are available. The dry season morph has a cryptic wing pattern to avoid detection by predators, while the wet season morph instead have conspicuous eyespots to deflect predator attacks.
The butterfly Bicyclus anynana is a model system for studies of phenotypic plasticity. In this species the plasticity affects more than just wing pattern so that the wet season morph allocates more of its available resources for quick reproduction. Wing pattern polyphenism is found in most Bicyclus species, but has not been well studied in species from less seasonal habitats.
We studied the phenotypic responses to different rearing conditions in the rainforest species B. martius and compared them to B. anayana. The wing pattern responses were similar despite the fact that true dry season conditions never occur in the forest habitat. Other traits showed limited response, suggesting that B. martius is adapted for continuous breeding. Surprisingly, the relative reproductive investment from the larval resources was smaller than in wet season morphs of B. anynana. Knowing that B. martius is a long-lived butterfly this can be seen as an adaption for spreading investments over time while maintaining an optimal fat load for flight performance.
Phenotypic responses are known to be under developmental hormonal control and it is thought that changes in hormone levels control a whole suite of correlated traits. In B. martius the life history traits seem uncoupled from the wing pattern polyphenism that still remains despite the presumed relaxed selection. This might be due to a relatively low fitness cost of expressing the wrong phenotype in a constant wet season environment.