Hřbetní mícha letounů (Chiroptera): využitelnost znaků míšní morfologie v systematice [Spinal Cord of Chiroptera: Implications for the Phylogenetic Studies]
Pavel Němec, Hana Koudelková, Rastislav Druga, Ivan Horáček
|NĚMEC, Pavel, KOUDELKOVÁ, Hana, DRUGA, Rastislav a HORÁČEK, Ivan. Hřbetní mícha letounů (Chiroptera): využitelnost znaků míšní morfologie v systematice [Spinal Cord of Chiroptera: Implications for the Phylogenetic Studies]. Lynx, new series. Prague: National Museum, 2000, 31(1), 81–111. ISSN 0024-7774 (print), 1804-6460 (online). Also available from: https://publikace.nm.cz/en/periodicals/lns/31-1/hrbetni-micha-letounu-chiroptera-vyuzitelnost-znaku-misni-morfologie-v-systematice-spinal-cord-of-chiroptera-implications-for-the-phylogenetic-studies
Gross morphology and cyto-, myelo- and chemoarchitectonic (distribution of acetylcholinesterase and cytochrome oxidase activity) organization of the spinal cord were studied in five chiropteran taxa (representing both suborders of bats: Rousettus aegyptiacus, Cynopterus sphinx, Myotis myotis, Plecotus auritus and Nyctalus noctula) and four non-chiropteran taxa (Insectivora: Crocidura suaveolens, Neomys fodiens and Sorex araneus and Rodentia: Mus musculus) to reveal actual variation in state of individual characters, their taxonomic distribution and their possible significance for phylogenetic studies. Surprisingly, we found that microchiropterans share more traits of the spinal cord organization (often mentioned as unique for them: viz, extensive and wide dorsal horns with prominent substantia gelatinosa; well developed reticular formation; poorly developed ascending and descending pathways including the dorsal column pathways; high ratio of gray to white matter) with shrews, i. e. the basal insectivores corresponding to bats in a small body and brain size. The respective traits can thus be considered plesiomorphic. Alternatively, at least some of them might also be a direct consequence of a small body size. Perhaps the most important finding of this study is that the spinal cord of the small megachiropteran Cynopterus sphinx resembles (both in gross morphology and architecture) that of microchiropteran bats rather than that of large-sized megachiropterans (the only which were examined until now). This fact suggests that the commonly discussed differences between Mega- and Microchiroptera in spinal cord morphology need not to refer to any disparate qualities or characters with discrete states but to continuous quantitative variables supposedly scaled by body size and the degree of the neocortex development. Correspondingly, the spinal cord characters traditionally looked upon as unique to the Microchiroptera (as frequently reminded both in primary and secondary literature) represent, in fact, a complex mosaic of (a) the characters shared with at least some of the therian orders, i. e. supposedly, the symplesiomorphies of Theria, and (b) the derived characters which are apparently related to the musculoskeletal adaptations associated with flight (well developed cervical and poorly developed lumbar enlargements, abridged thoracic spinal segments) and to the enlarged body surface by presence of the patagial membrane (enlarged dorsal spinal roots and spinal ganglia, expanded dorsal horns). Our results provided evidence that most of the derived characters (b) are actually shared with Megachiroptera, and should then be looked upon as synapomorphies that, in any way, do not support a different ancestry of Micro- and Megachiroptera. The observed differences among individual microchiropteran taxa in relative sizes of their cervical and lumbar enlargements and in the segmental composition of the respective plexuses seem to be in good correspondence with the differences among them in flight style, foraging strategy and motor flexibility of the limbs. In general, for most of the spinal cord characters, the critical revision revealed a serious doubt upon actual relevancy of them for use in the phylogenetic studies. In full, it concerns those spinal characters which were believed to provide a strong indisputable support against monophyly of bats (cf. Pettigrew et al. 1989). Until now, however, only very few species were studied and only little information is available on taxonomic distribution of the particular traits. A broad comparative analysis operating with appropriate quantification techniques is urgently needed to clarify this issue.