Evolution of flatworm central nervous systems: Insights from polyclads.
The nervous systems of flatworms have diversified extensively as a consequence of the broad range of adaptations in the group. Here we examined the central nervous system (CNS) of 12 species of polyclad flatworms belonging to 11 different families by morphological and histological studies. These comparisons revealed that the overall organization and architecture of polyclad central nervous systems can be classified into three categories (I, II, and III) based on the presence of globuli cell masses -ganglion cells of granular appearance-, the cross-sectional shape of the main nerve cords, and the tissue type surrounding the nerve cords. In addition, four different cell types were identified in polyclad brains based on location and size. We also characterize the serotonergic and FMRFamidergic nervous systems in the cotylean Boninia divae by immunocytochemistry. Although both neurotransmitters were broadly expressed, expression of serotonin was particularly strong in the sucker, whereas FMRFamide was particularly strong in the pharynx. Finally, we test some of the major hypothesized trends during the evolution of the CNS in the phylum by a character state reconstruction based on current understanding of the nervous system across different species of Platyhelminthes and on up-to-date molecular phylogenies.
Programa de Biología, Facultad de Ciencias Básicas, Universidad del Magdalena, Santa Marta, Colombia.
Sigmer Y
SY
Quiroga
Laboratorio de Biología del Desarrollo, Departamento de Ciencias Biológicas, Universidad de los Andes, Bogotá, Colombia.
E
E
Carolina Bonilla
Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH, USA. ; Laboratorio de Biología del Desarrollo, Departamento de Ciencias Biológicas, Universidad de los Andes, Bogotá, Colombia.
D
D
Marcela Bolaños
Laboratório de Ecologia e Evolução, Escola de Artes, Ciências e Humanidades, Universidade de São Paulo, São Paulo, SP, Brazil. ; Programa de Pós-Graduação em Zoologia, Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil.
Fernando
F
Carbayo
Department of Natural Resources and the Environment, University of New Hampshire, Durham, NH, USA.
Marian K
MK
Litvaitis
Laboratorio de Biología del Desarrollo, Departamento de Ciencias Biológicas, Universidad de los Andes, Bogotá, Colombia. ; Programa de Pós-Graduação em Zoologia, Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, SP, Brazil. ; Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil. ; Centro de Biologia Marinha, Universidade de São Paulo, São Sebastião, Brazil.
Federico D
FD
Brown
FMRFamide; brain; globuli cell masses; orthogon; serotonin