Larval burrow morphology and groundwater dependence in a mire-dwelling dragonfly, Petalura gigantea (Odonata: Petaluridae)

Most species of petalurid dragonflies have a fossorial larval stage, which is unique in the Odonata. Larvae typically excavate burrows in soft peaty soils in mires, seepages or along stream margins, which are occupied by a single larva throughout the long larval stage. This paper reports on a study of burrow morphology in Petalura gigantea, with the objectives of describing their burrows, documenting any variability in burrow morphology across the hydrogeomorphic range of habitats used by the species, identifying factors contributing to any such variability, resolving questions in relation to the single previous illustration of a burrow system and identifying the level of groundwater dependence of larvae. The species was found to be an obligate, groundwater dependent, mire-dwelling species with well-maintained and sometimes complex burrows. Burrow complexity and morphological variation are inferred to be a response by larvae to the hydrogeomorphic characteristics of the habitat and substrate attributes. All burrows were occupied by a single larva, consistent with previous observations of other fossorial petalurids, but in contrast to the previous description of a P. gigantea burrow complex occupied by multiple larvae. The functional role of identified burrow features is discussed. Although the fossorial larval habit confers ecological benefits, the species' groundwater dependence and restriction to mire habitats places it at increased risk in the event of any reduction in groundwater availability, more intense fire regimes, and the potential compounding effects of rapid climate change.