Brachycybe
Genus of millipedes
From Wikipedia, the free encyclopedia
Brachycybe (Greek for "short head") is a genus of social millipedes found in temperate forests of North America and East Asia. In North America they are found in the Pacific coastal region from Oregon to southern California and in eastern regions including the southern Appalachian Mountains, the Cumberland Plateau, the Ozark Mountains, and parts of the Gulf Coastal Plain.[1] Species in this genus are often referred to as "feather millipedes" due to their shape.[2]
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| Brachycybe | |
|---|---|
| |
| Brachycybe lecontii | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Myriapoda |
| Class: | Diplopoda |
| Order: | Platydesmida |
| Family: | Andrognathidae |
| Genus: | Brachycybe Wood, 1864 |
| Type species | |
| Brachycybe lecontii Wood, 1864 | |
| Species | |
| |
| Synonyms | |
In a rare example of paternal care in invertebrates, males of most species guard the eggs until they hatch.[2]
Description
All species in the genus lack eyes.[2] Individuals attain lengths up to 1 inch (25 mm) and range in color from orange to tan to pink. B. picta is uniquely patterned with 5 brown spots.[3]
Brachycybe species are rather similar in appearance, varying in subtle features of the collum (first body segment) and paranota (lateral “keels” extending off of body segments).[3]
The 9th and 10th pair of legs in mature males are modified into gonopods (reproductive appendages). Unlike many millipede groups, species of Brachycybe exhibit relatively simple male gonopods that provide few diagnostic characters for species identification. As a result, species have historically been diagnosed primarily using somatic characters such as the shape of the collum and paranota.[1]
Integrative approaches combining morphology, molecular data, and biogeography are necessary to accurately differentiate species. [1]
Diet
Species of Brachycybe are primarily fungivorous and are typically found feeding on fungal growth on decaying wood. Colonies are often observed with individuals clustered on fungal mats growing on rotting logs, where they feed with their heads inserted into the fungal tissue.[4]
Studies of Brachycybe lecontii have revealed that these millipedes are associated with a highly diverse assemblage of fungi, including representatives of at least 176 genera across 39 orders and four fungal phyla. Twelve fungal genera were consistently found across multiple geographic populations and wood substrates and are considered part of a core fungal community associated with the species. Wood-decay fungi in the order Polyporales, long suspected to be the primary food source of Brachycybe, were found to be rare among fungi consistently associated with the millipede. Experimental assays indicated that some of these fungi were pathogenic and lethal to the millipedes rather than serving as food.[4]
Behaviour
Parental care
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Male egg brooding (care of eggs) has been extensively studied in B. nodulosa, a species found in Japan and South Korea. After the female lays eggs, the male coils his body around the mass, and guards them until hatching, a behaviour thought to protect the eggs from soil-dwelling fungi or predators such as ants.[5]
Paternal care has also been studied in B. lecontii, showing that although parental care may last through the 3-4 week incubation period, this does not extend to juveniles they have hatched. It appears that the survival of eggs is completely dependent on the presence of paternal care, as all eggs become unviable after being separated from the brooding male, perhaps because the brooding male is needed to clean the eggs and ward of fungal infections. Males will seek out and collect eggs if they have been separated from their clutch. Similarly, males will collect the eggs of other males if they have been abandoned, adding them to their own clutch.[2]
Sociality
Brachycybe are social millipede that form colonies. Sociality is uncommon amongst millipedes; outside of this genus, social behaviour has evolved in only a few other groups.[2]
Brachycybe species are known to form "pinwheel" shaped groups of individuals, where the millipedes form a circle, their heads pointing inwards and their bodies pointing outwards. Females are more likely to form such "pinwheels". The precise purpose of this "pinwheeling" behaviour is uncertain, but it is known to be a feeding behaviour, seen when feeding on fungi.[2]
Species
At least ten species have been named, and at least two undescribed species have been identified by genetic analysis. Molecular species delimitation analyses suggest that the genus may contain cryptic species that are not distinguishable using traditional morphological characters alone. Studies of genetic differences suggest the genus originated in California around 50 million years ago.[1]
Species list based on Shelley et al. (2005)[6]
- B. cooki (Loomis, 1942) – Jiangxi Province, China
- B. disticha Mikhaljova, Golovatch, Korsós, Chen & Chang, 2010 – Taiwan
- B. lecontii Wood, 1864 – Southeastern United States, from Virginia to Illinois and Kansas, south to Louisiana and southern Alabama.
- B. nodulosa (Verhoeff, 1935) – Central and Southern Japan, southern South Korea.
- B. petasata Loomis, 1936 – Southern Appalachians: in adjacent parts of North Carolina, Georgia, Alabama, and Tennessee.
- B. picta Gardner, 1975 – Northern California: Marin County and Mendocino County.
- B. producta Loomis, 1936 – Northern California
- B. rosea Murray, 1877 – Northern California
Phylogeny and Evolution
Molecular phylogenetic analyses have been used to reconstruct the evolutionary history of Brachycybe. These analyses recovered eight species-level lineages and suggested the presence of cryptic diversity within the genus.[1] Molecular dating analyses indicate that the genus originated more than 50 million years ago, making it an evolutionarily ancient lineage of millipedes.[1]
Ancestral range reconstruction suggests that the genus likely originated in western North America, particularly in the Sierra Nevada and coastal ranges of California, before dispersing eastward across North America and independently colonizing East Asia.[1]
