The control of metamorphosis in the pollution-indicating polychaete Capitella teleta
Abstract: The larvae of many marine invertebrates are planktonic and must
disperse within the tides and currents of the ocean. The adults of these invertebrate
species are often sessile and their planktonic larvae act as the dispersal mechanism for
their species. Several biological aspects of the larvae themselves can influence potential
dispersal distances and species distributions. One of th... read moree least understood aspects of
larval biology that can influence potential dispersal is the time until the ability to
metamorphose is gained. Another aspect of larval biology that can influence potential
species distributions is the settlement cue, which stimulates larvae to settle to the
benthic substrate and initiate metamorphosis. Settlement cues have not been characterized
for most species. Here, I used the salt-marsh deposit-feeding polychaete worm Capitella
teleta as a model organism to further our knowledge about these aspects of larval biology.
Larvae of C. teleta rapidly metamorphose in response to salt-marsh sediment; however, the
chemical settlement cue in this sediment was unknown at the start of my studies. Because it
would be advantageous for deposit-feeders to select substrates with adequate nutrients, I
focused on determining whether vitamins could act as settlement cues. Indeed, we found that
two B vitamins, nicotinamide and riboflavin rapidly stimulated larvae of C. teleta to
metamorphose at low concentrations. Because microbes living in salt-marsh sediments could
produce these vitamins, we then isolated Desulfovibrio oceani from salt-marsh sediment.
This bacterium rapidly stimulated larvae of C. teleta to metamorphose when grown as a
biofilm. Furthermore, we found that menaquione-6, a form of vitamin K, was synthesized by
D. oceani and rapidly stimulated larvae to metamorphose. Finally, we studied the
transcriptional changes that could underlie the onset of metamorphic competence. It appears
that once larvae of C. teleta have completed development of internal structures required
for juvenile life, competent larvae then up-regulate the expression of possible
chemosensory proteins and neurotransmitter receptors to make the detection and transduction
of a signal from external settlement cues possible. Overall, larvae of C. teleta likely
gain metamorphic competence once they increase expression of chemosensory receptors and
other components of the signal transduction cascade leading to metamorphosis. They then
could use this sensory system to assess the nutritional content of the environment around
them. By metamorphosing in nutrient-rich sediments, larvae could ensure that they could
successfully develop as juveniles and reach reproductive maturity.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Biology.
Advisor: Jan Pechenik.
Committee: Colin Orians, Harry Bernheim, Benjamin Wolfe, and Andreas Heyland.
Keyword: Biology.read less