Regulation of filter-feeding house components in response to varying food regimes in the appendicularian, Oikopleura dioica

The frequent repetitive secretion of filter-feeding houses of the tunicate, Oikopleura dioica represents investment of a substantial proportion of total body carbon. Despite this investment, the filter-feeding strategy of pelagic tunicates has been proposed as an adaptation to oligotrophic environments. Here, we examined the capacity of 0. dioica to modify its house renewal rate (HRR) and expression of component proteins, oikosins, as well as ingestion rates of different sized particles in response to varying food regimes. There were no significant changes in HRR (0.26 ± 0.07 SD house h -1 ) with age or food concentration throughout the life cycle. Our data suggest that the complex pattern of endoreduplicating cycles in the oikoplastic epithelium probably limits the capacity to reduce the energetic output of house replacement as a response to a limiting food environment. On the other hand, at the molecular level, there was differential regulation of component house proteins when animals were cultured in standard versus limiting food regimes. Animals pre-conditioned in each of these regimes and subsequently challenged with an identical mixture of large and small particles exhibited different retention efficiencies of larger food particles. Taken together, these results raise the possibility that a limited ability to modulate house architecture may underlie the differential particle retention efficiencies observed.