Neuromuscular organization of the freshwater colonial rotifer, Sinantherina socialis, and its implications for understanding the evolution of coloniality in Rotifera |
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Authors: | Rick Hochberg Graham Lilley |
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Institution: | (1) Department of Biological Sciences, University of Massachusetts Lowell, Lowell, MA 01854, USA;(2) Department of Cellular and Molecular Biology, University of Vermont, Burlington, VT 05405, USA |
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Abstract: | Coloniality among rotifers is rare, and while the adaptive significance of the lifestyle has been explored previously, there
are few details about how it may have influenced the morphology of colony members. In this study, we use confocal laser scanning
microscopy combined with cyto- and immunohistochemistry to determine if the colonial rotifer, Sinantherina socialis, differs in neuromuscular organization relative to other colonial and solitary forms. Our observations indicate that the
patterns of serotonergic neurons and somatic muscles in S. socialis are broadly similar to other rotifers. At the neuronal level, the distribution of serotonergic (5HT-IR) neurons in S. socialis is most similar to colony-forming species of Conochilus: (1) paired nerve cords extend the length of the body; (2) the cerebral ganglion innervates the corona with paired neurites
that form a neuronal ring; and (3) a single pair of neurites innervates the ventral sensory antennae. Unique to S. socialis is the presence of two additional neuronal rings that supply the corona and may function to modulate ciliary beat. At the
muscular level, S. socialis displays a typical pattern of somatic muscle organization similar to other rotifers, but diverges from the pattern in three
significant ways: (1) somatic circular muscles form complete rings; (2) circular muscles are distinguishable based on their
size and position in the body; and (3) transverse muscles are present within the corona and presumably function to modify
its shape for feeding and defensive purposes. These differences in neuromuscular organization may be adaptations to the colonial
and/or sessile lifestyle, both of which are characteristic of S. socialis. |
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