Millipedes in the tribe Apheloriini compose mimicry rings where unrelated species share an aposematic signal where they co-occur. 


These Müllerian mimicry rings in Appalachian millipedes parallel those in the Amazon, for example in nymphalid butterflies and poison dart frogs, and represent an independently-evolved instance of this biological phenomenon in the United States.


Many of these mimic species have highly variable color patterns, some with up to six unique color morphs.  Although species display highly variable color, other unrelated species appear exactly alike where they co-occur.


To study mimicry in Appalachian millipedes, I investigated 7 species as a model system, and integrated molecular systematics and spectral color measurements to test key predictions of Müllerian systems: (1) species share the same aposematic signal, (2) the signal is not a result of close evolutionary relationship.



Molecular phylogenetics of mimic millipedes (Xystodesmidae)


^ Molecular phylogenies of the Müllerian mimic species, Apheloria “clade A” (6) and Brachoria dentata (7) and their locations in a molecular phylogeny of Apheloriini (circle tree, bottom left). [click to enlarge]


Colored circles indicate unique color morphs, indicated by a drawing of the millipede’s dorsal plate (legend, bottom right). Although substantial color variation exists within each species, and across their phylogenies, individuals look almost identical at 6 of the 7 locations where the two species co-occur (shown in the center of the figure). This geographical synchrony in aposematic signal between unrelated species is a strong indication of mimicry.




Measuring color in millipedes


^ Color spectrum measured from the yellow patch on a millipede, in blue, and the dirt background upon which it crawls, in red.


By comparing the physical properties of color between mimic species, a less subjective assessment of color (i.e., one that does not rely on the human eye), I demonstrated that  species share an aposematic signal.


Groups of species from an area that have converged on the same warning color pattern is known as a “mimicry ring.” The phenomenon of color mimicry between millipede species occurs at many locations in the Appalachian Mountains, many of which with a different colored ring at each location. In the mountainous borderlands between Virginia and Kentucky, I observed seven unique mimicry rings which represented a complex mimicry system in Appalachia that is much more diverse and colorful than was previously thought.



Figures adapted from Marek & Bond (2009) A Müllerian mimicry ring in Appalachian millipedes, Proceedings of the National Academy of Sciences, U.S.A., 106, 9755-9760.   [Open access]


Molecular phylogeny of Apheloriini from Marek & Bond (2007) A reassessment of apheloriine millipede phylogeny: additional taxa, Bayesian inference, and direct optimization. Zootaxa, 1610, 27-39.

 

Müllerian mimicry