Immunoreactivity of the Serotonin-Like and FMRF-Amide-Like Nervous Systems of Four Gnesiotrochan Rotifers
Reorganization of the nervous system during metamorphosis is a common phenomenon across taxa (species through phyla). In phylum Rotifera, sessile species belonging to the superorder Gnesiotrocha metamorphose from free-swimming larvae into sessile adults. Once mature, gnesiotrochan rotifers display an intricate corona or infundibulum associated with lifestyle modalities and feeding behaviors. Here, I examine serotonin-like immunoreactivity (SLIR) and FMRF-amide-like immunoreactivity (FLIR) of the gnesiotrochans Lacinularia flosculosa, Collotheca ferox, and Acyclus inquietus with a focus on life stage and sex. Based on previous research, I hypothesize that 1) innervation of the larval nervous system will vary according to the lifestyle constraints observed in each species, and 2) innervation of the nervous system in male rotifers will vary from the adult female and will be similar to the female larvae. Neural features were observed using immunohistochemistry and confocal laser scanning microscopy to provide renditions of SLIR and FMRF-amide-like structures. The SLIR and FLIR nervous systems of L. flosculosa larvae showed a reduction of brain perikarya as larvae mature into adults. The nervous system of adult A. inquietus showed an absence of two SLIR varicosities, and the absence of two FLIR longitudinal neurites extending posteriorly into the larval foot. Contrastingly, the number FLIR brain perikarya increased in the nervous system of adult C. ferox. This may result from species-specific lifestyle adaptations (i.e., coloniality (L. flosculosa) versus feeding behaviors exhibited by predatory rotifers (C. ferox)), or lifestyle constraints associated with sessility. To further understand if the variation of SLIR/FLIR nervous system elements occurred because of metamorphosis, the direct developing gnesiotrochan rotifer Filinia longiseta was observed (neonate/adult and male/female). As expected, the reorganization of nervous system elements was not observed. However, similarities between the nervous system of males and females were observed. Similar to results of previous studies, SLIR structures comprising the nervous system are species-specific. The nervous system of male L. flosculosa, C. ferox, and A. inquietus was comparable to the larval stage, while the nervous system of male F. longiseta was comparable to the female. This may correlate with their morphologies or behaviors associated with motility. This phenomenon aligns with the concept of progenesis and suggests that the lifestyle constraints associated with the male life history may influence the development and evolution of their nervous system. This study represents the first examination of the relationships between sexual dimorphism and the nervous system in gnesiotrochan rotifers. The knowledge collected here enhances our comprehension of specific nervous system characteristics that may be essential to the diverse lifestyle demands associated with adulthood and sexes within Gnesiotrocha.
Walsmith, Robert Neil, "Immunoreactivity of the Serotonin-Like and FMRF-Amide-Like Nervous Systems of Four Gnesiotrochan Rotifers" (2023). ETD Collection for University of Texas, El Paso. AAI30634627.