Natural history of the social millipede Brachycybe lecontii (Wood, 1864)
Wong, Victoria L.
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The millipede Brachycybe lecontii Wood, 1864 is a social millipede known for forming pinwheel-shaped groups and for paternal care of eggs. Brachycybe lecontii is endemic to the eastern U.S., and its distribution overlaps with another species within the genus, Brachycybe petasata, from the Southern Appalachian Mountains. Molecular data, however, show that the closest relative of B. lecontii is Brachycybe nodulosa from East Asia. Here, I investigated various aspects of the life history, paternal care, defense, feeding, and social behavior of B. lecontii, and provided morphological and anatomical descriptions using light and scanning electron microscopy. Based on detailed observations of millipedes from 14 localities in the distribution of B. lecontii, I found the following natural history aspects. The oviposition period of B. lecontii was from mid-April to late June and the incubation period lasted 3–4 weeks. Males exclusively cared for eggs, but care of juveniles was not observed. In one case, the clutches of two males became combined and they were later cared for by only one of the males. The defensive compound of B. lecontii consisted of two isomers of the alkaloid deoxybuzonamine. Defense glands were large, occupying up to a third of the paranotal volume, and were present on all but the first four body rings. Stadia I juveniles do not have defensive secretions and stadia II juveniles have defensive pores but do not secrete. Secretions were observed only in stadia III millipedes and older. I observed Brachycybe lecontii feeding on liquids from fungi of the order Polyporales, and describe a cuticular structure on the tip of the labrum that may relate to fungivory. I found that pinwheel-shaped aggregations do not form in the absence of fungus and suggested the aggregation is associated with feeding. I describe and illustrate a previously undescribed comb-like structure on the tibia and tarsi of the six foremost leg-pairs and measure and analyze the spectral reflectance of B. lecontii exoskeleton.
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