[The evolution of the forms of hermaphroditism in Cyclophyllidea (Cestoda). 2. Morphofunctional causes of the formation of tapeworms having a protogynous type of the genital apparatus development].
Morpho-biological causes of the formation of protogynous forms of Anoplocephalidae (Cyclophyllidea) parasitizing rodents have been studied. The reduction in the number of segments in the strobila of anoplocephalideans (Anoplocephaloides, Paranoplocephaloides) in comparison with related polymeric species of the taxon (Paranoplocephala) suggests that protogyny is resulted from the secondary oligomerization of strobila in the phylogenesis of these cestodes. It is evident that the ecological cause of the selection for a small number of segments in the strobila is a tough competition among large polymeric cestodes that results in the formation of small anoplocephalideans located in the back part of the small intestine (Paranoplocephaloides) and in the blind gut (Anoplocephaloides) of rodents. There is slowing down of strobilation rates, acceleration of genital apparatus development and somatic proglottid morphogenesis during the change into protogyny. Due to an earlier, regarding testicle morphogenesis, formation of the ovary and uterus, uterus segments are developing most of the time in the strobila. Thus, proterogyny is one of the universal mechanisms to extend the terms of hexacanth embryogenesis in the second oligomeric strobila of tapeworms.
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D000222:Adaptation, Physiological; D000818:Animals; D005075:Biological Evolution; D002589:Cestoda / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D005835:Genitalia / Q000033:anatomy & histology / Q000254:growth & development; D057850:Hermaphroditic Organisms; D007422:Intestines / Q000469:parasitology; D012377:Rodentia / Q000469:parasitology*; D019849:Sex Determination Processes