Abstract
Symbiosis can facilitate the development of specialized organs in the host body to maintain relationships with beneficial microorganisms. To understand the developmental and genetic mechanisms by which such organs develop, it is critical to first investigate the morphology and developmental timing of these structures during the onset of host development. We utilized micro-computed tomography (μCT) to describe the morphology and development of mycangia, a specialized organ, in the Asian ambrosia beetle species Euwallacea validus which maintains a mutualistic relationship with the Ascomycete fungus, Fusarium oligoseptatum. We scanned animals in larval, pupal and adult life stages and identified that mycangia develop during the late pupal stage. Here we reconcile preliminary evidence and provide additional morphological data for a second paired set of structures, including the superior, medial mycangia and an inferior, lateral pair of pouch-like structures, in both late-stage pupae and adult female beetles. Furthermore, we report the possible development of rudimentary, or partially developed pairs of medial mycangia in adult male beetles which has never been reported for any male Xyleborini. Our results illustrate the validity of μCT in observing soft tissues and the complex nature of mycangia morphology and development.
Highlights
Symbiotic relationships can affect the development of the host body
Persistent colonization of the bacterial symbiont is required to efficiently regress surface epithelia and maintain the mature interior organ cell types [1]. Another prominent model for symbiont-directed host morphogenesis can be found in the Rhizobia-legume symbiosis [2]
Similar columnar cells lining the lateral pouches along with peripheral duct-like and hair-like structures can be seen in the lateral mycangia of closely related beetle genera as well as more distantly related tribes (S2 Fig) [24, 35]
Summary
Symbiotic relationships can affect the development of the host body. Non-obligate two-partner systems have allowed for detailed examinations of how symbiotic partners may direct development in one another. Recent work in the Vibrio-Euprymna squid symbiosis has examined the role the bacterial symbiont V. fischeri plays in directing and maintaining “mature” morphology in the light organ of the squid [1]. Persistent colonization of the bacterial symbiont is required to efficiently regress surface epithelia and maintain the mature interior organ cell types [1]. Another prominent model for symbiont-directed host morphogenesis can be found in the Rhizobia-legume symbiosis (as reviewed by Gage 2004) [2]. Presence of the microbial symbiont triggers differentiation within the legume host root to begin the root nodulation process
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