Electronic Supplement 2
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Organisms
Diversity & Evolution 5 (2005) Electronic Supplement 2 |
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Thomas Stach:
Comparison of the serotonergic nervous system among
Tunicata: implications for its evolution within Chordata
print version: Org. Divers. Evol. 5(1): 15-24. 2005 (full
article)
electr. suppl.: Colour figures. pdf-format,
598 KB
| Video files | Ascidia interrupta Sections.
avi-format, 98 MB Animated sequence showing a z-series of individual confocal optical sections of serotonergic nervous system in the larva (21.5h post fertilization, ca. 20ºC) of the solitary ascidian Ascidia interrupta (Ascidiidae, Phlebobranchiata). Reduced from originally 93 confocal optical sections taken at 0.5µm intervals. |
| Clavelina oblonga Sections.
avi-format, 39 MB Animated sequence showing a z-series of individual confocal optical sections of serotonergic nervous system in the larva of the colonial ascidian Clavelina oblonga (Clavelinidae, Aplousobranchiata). Reduced from originally 93 confocal optical sections taken at 0.5µm intervals. |
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| Herdmania momus Rotation. avi-format, 83 MB Animated sequence showing rotation of serotonergic nervous system in the larva (21.5h post fertilization, ca. 20ºC) of the solitary ascidian Herdmania momus (Pyuridae, Stolidobranchiata). Reduced from originally 104 confocal optical sections taken at 0.5µm intervals. |
Abstract:
Using immunohistochemistry in combination with
confocal laser scanning microscopy, the serotonergic nervous systems of major
tunicate taxa were studied in three-dimensional detail. Organisms analyzed
included aplousobranchiate, phlebobranchiate, and stolidobranchiate ascidian
larvae, appendicularian juveniles and adults, and doliolid oozooids. Outgroup
comparisons to notochordates showed that the serotonergic nervous system of the
last common ancestor of Chordata consisted of two elements: (i) an anterior
concentration of serotonergic cell bodies, and (ii) a fiber network that
followed posteriorly and gave rise to fiber tracts that descended towards the
effective somatic lateral musculature. Within Tunicata, the nervous systems of
Appendicularia and Aplousobranchiata appear serotonin-reduced or negative. This
could be interpreted as a heterochronic reduction and a synapomorphy between
Appendicularia and Aplousobranchiata. In this hypothesis, free-living
Appendicularia are derived within Tunicata, and a biphasic life cycle with a
free-swimming larva and a sessile, ascidian-like adult is most parsimoniously
reconstructed for the last common ancestor of Tunicata. The close spatial
relation of the serotonergic cell cluster with the statocyte complex suggests a
function as an integrative control center for the coordination of locomotion. A
similar anterior concentration of serotonergic nerve cells is known from
tornaria larvae.
Key words: Chordata; Urochordata; Tunicata; Phylogeny; Serotonin; 5-HT
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