The Sensory Reactions of Amphioxus

Amphioxus photoreceptors - insights into the evolution of vertebrate opsins, vision and circadian rhythmicity

“…Parker (1908) described sensory reactions of amphioxus to various physical and chemical stimuli, including light. Parker´s observation about amphioxus photoresponses were in agreement with previous studies (Hesse, 1898;Willey, 1894), showing negative phototactic responses in adult amphioxus (Parker, 1908). Moreover, it was shown that amphioxus adults evince higher burrowing activity during the night (Schomerus et al, 2008).…”

“…Early studies dealing with photoreception of amphioxus, nevertheless, pushed the FE to the sidelines, showing, that the DO are more important for adult amphioxus light-guided behavior (Hesse, 1898;Parker, 1908). Parker (1908) (and later more precisely Crozier (1917)) confirmed an observation made by Hesse (1898), that the adult amphioxus photoresponse is connected with the presence of DO and he rejected the proposal of Krause (1888) that amphioxus can sense light with the whole neural tube. Parker also repeated experiments done by Nagel and Hesse, showing that upon removal of the anterior body end with the frontal eye, the rest of the body of the amphioxus still responded to the light in the same way as in intact animals (Hesse, 1898;Nagel, 1896).…”

“…Moreover no trace of optic nerve projecting from the FE posteriorly to the CV was observed at that time, which also questioned FE functionality as a possible photoreceptive organ. Yet Parker (1908) showed that when adult amphioxus was transversely cut in two parts, the anterior half was able to react to light, while the posterior half lost its light sensitivity, retaining its ability to be stimulated with addition of weak acid to the water. His results thus showed, that the anterior part of the neural tube (and probably also the FE) must be necessary for processing the photo-response, and that there is probably no direct connection between the dorsal ocelli and motor neurons.…”

“…The first obvious difference between the JCs and the DO is that each dorsal ocellus consists of one photoreceptor cell and one pigment cell, and is thus directional photoreceptor, while the JCs lack pigment and are thus non-directional photoreceptors. Due to the presence of pigment, the DO were already connected with photoreceptive behavior at the turn of 20 th century (Hesse, 1898;Parker, 1908). Boveri (1904) even proposed a scenario, saying that DO were evolutionary precursors of vertebrate lateral eyes, which would arise from DO by their aggregation into complex organ.…”

The opsin repertoire of the European lancelet: a window into light detection in a basal chordate

“…Photoreceptors located in the tail mediate light avoidance in larval lampreys (Binder and McDonald, 2008). Light sensitivity in the tail of amphioxus has been reported as early as 1908 (Parker, 1908), yet no study so far has documented any photoreceptor cells there. In regard to opsin expression in gonads, it has also been observed in the gonads of the cnidarian species Cladonema radiatum (Suga et al, 2008) and Tripedalia cystophora (Liegertova et al, 2015), and the oyster Crassostrea gigas (Porath-Krause et al, 2016).…”