Abstract
Chemical detection is key to various behaviours in both marine and terrestrial animals. Marine species, though highly diverse, have been underrepresented so far in studies on chemosensory systems, and our knowledge mostly concerns the detection of airborne cues. A broader comparative approach is therefore desirable. Marine annelid worms with their rich behavioural repertoire represent attractive models for chemosensory studies. Here, we study the marine worm Platynereis dumerilii to provide the first comprehensive study of head chemosensory organ physiology in an annelid. By combining microfluidics and calcium imaging, we record neuronal activity in the entire head of early juveniles upon chemical stimulation. We find that Platynereis uses four types of organs to detect stimuli such as alcohols, esters, amino acids and sugars. Antennae, but not nuchal organs or palps as generally hypothesised in annelids, are the main chemosensory organs. We report chemically-evoked activity in possible downstream brain regions including the mushroom bodies, which are anatomically and molecularly similar to insect mushroom bodies. We conclude that chemosensation is a major sensory modality for marine annelids, and propose early Platynereis juveniles as a model to study annelid chemosensory systems.
Abbreviations list
- ac
- anal cirrus;
- adc
- anterior dorsal tentacular cirrus;
- an
- antennal nerve;
- ant, a
- antenna;
- at
- akrotroch;
- avc
- anterior ventral tentacular cirrus;
- bv
- blood vessel;
- cc
- circum-oesophageal connectives;
- ch
- chaetae;
- cn
- cirral nerve;
- cp
- ciliary photoreceptor;
- csc
- cilia of the nuchal organ supporting cells;
- dcp
- dorsal ciliated pit;
- dp
- dorsal peduncle of the mushroom bodies;
- drcc
- dorsal root of the circum-oesophageal connectives;
- ec
- pigmented eye cup;
- g
- gut;
- gc
- glandular cell;
- j
- jaw;
- ld
- lipid droplet;
- mo
- mechanosensory organ;
- mt
- metatroch;
- nc
- nuchal cavity;
- nco
- nuchal commissure;
- nn
- nuchal nerve;
- np
- main neuropil;
- nsn
- neurosecretory neuropil;
- pa, p
- palp;
- pcc
- palpal coelomic cavity;
- pdc
- posterior dorsal tentacular cirrus;
- pm
- palpal muscle;
- pp
- parapodia;
- prc
- photo-receptor cells;
- pvc
- posterior ventral tentacular cirrus;
- rpn
- roots of the palpal nerve;
- sog
- sub-oesophageal ganglion;
- st
- stomodeum;
- stn
- stomodeal nerve;
- tc, c
- tentacular cirrus;
- vp
- ventral peduncle of the mushroom bodies;
- vrcc
- ventral root of the circum-oesophageal connectives.