|
|
Mushroom Body Evolution - Figure 1 |
Click on inline image to retrieve larger version (approx. 128k)
Figure 1: Early theories about the evolution of mushroom bodies. The first was formulated by Nils Holmgren (1916), followed by his student Bertil Hanström (1926). Hanström's classic 1926 paper claimed arthropod monophyly on the basis of similarities amongst visual systems and mushroom bodies. To accommodate mushroom bodies (blue) into this view (lower illustration, from Hanström, 1928), Hanström accorded them a primary function in both olfactory (antennal/olfactory lobes colored red) and visual processing (neuropils colored green). This allowed their seamless demonstration across taxa, from annelids (A in his figure) through to the araneans (C, in lower illustration). Annelids, however, show no evidence of connections between visual neuropil and mushroom bodies. In Hanström's figure, the panel labeled "arthropods" (B) depicts only two optic neuropils suggesting either a brachiopod crustacean or a thysanuran, either one of which is equipped with an insect-like mushroom body. A serious objection to Hanström is that basal apterygotes, such as thysanurans, lack olfactory glomeruli and calyces and the even more primitive archaeognathan Machilis lacks a mushroom body entirely. Branchiopod crustaceans, such a Triops, lack antennule lobes and hemiellipsoid bodies, the supposed malacostracan equivalent of the insect mushroom body.
All contents are copyright © 2000 Evolbrain or their original publication (as noted).
AAxxxxx
Images or text may be used with proper acknowledgement.