Molecular phylogeography of the troglobiotic millipede Tetracion Hoffman, 1956 (Diplopoda, Callipodida, Abacionidae)

Kirk Zigler,Julian Lewis,Stephanie Loria

doi:10.3897/ijm.5.1891

Abstract

More than 85 species of cave-obligate (troglobiotic) millipede have been described from North America. Understanding the patterns and processes that determine their distribution in this region is an area of recent research. Here, we present the first molecular phylogeographic study of troglobiotic millipedes. Millipedes of the genus Tetracion Hoffman, 1956 (Callipodida: Abacionidae) inhabit caves on the Cumberland Plateau in Tennessee and Alabama, a global hotspot for cave biodiversity. Three species have been described: T. jonesi Hoffman, 1956, T. antraeum Hoffman, 1956, and T. tennesseensis Causey, 1959. To examine genetic divergence within and between species of Tetracion we sequenced part of the mitochondrial cytochrome oxidase 1 gene from 53 individuals from eleven caves across the range of T. tennesseensis and in the northern part of the range of T. jonesi. We found: (1) little variation within species (six haplotypes in T. tennesseensis and four haplotypes in T. jonesi, with a maximum of 1.4% intraspecific divergence between haplotypes), (2) that gene flow between caves is limited (7 of 10 haplotypes were restricted to a single cave, and F ST > 0.80 and P < 0.05 for fifteen of eighteen comparisons between caves), and (3) significant genetic divergence between species (8.8% between T. tennesseensis and T. jonesi). Our results are consistent with previous morphology-based species definitions showing T. tennesseensis and T. jonesi belonging to distinct taxa. Our research contributes to the growing body of phylogeographic information about cave species on the Cumberland Plateau, and provides a point of comparison for future studies of troglobionts and millipedes.

Highlights

Millipedes (Diplopoda) are a large, understudied group
Due to the uncertain status of T. antraeum, we refer to our specimens from Jackson County, Alabama and Franklin County, Tennessee as T. jonesi
Our sampling covered the full range of T. tennesseensis and the northern portion of the range of T. jonesi (Figure 1)

Summary

Introduction

Millipedes (Diplopoda) are a large, understudied group. Twelve thousand species belonging to sixteen orders have been described and it is estimated that as many as 80,000 species exist. Laing et al (1976) used isozymes to study two populations of Scoterpes in Kentucky and found high genetic diversity between populations but low genetic diversity within each population These populations were later described as belonging to different species (Shear 2010). Three species have been described: T. jonesi Hoffman, 1956, T. antraeum Hoffman, 1956 and T. tennesseensis Causey, 1959 They are relatively large (up to 8 cm in length) and exhibit troglomorphic characters including lack of pigmentation, reduced ocelli and elongated appendages (Peck 1989; Figure 1). This is the first molecular phylogeographic study of troglobiotic millipedes

Materials and Methods

Results

Discussion