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in Beasley‐Hall, Rose, ... et Lo, 2021. DOI: 10.1111/syen.12487 |
ABSTRACT
Soil‐burrowing cockroaches (Blaberidae: Geoscapheinae) are large insects endemic to Australia. Originally thought to represent a monophyletic group, these enigmatic species have in fact evolved burrowing behaviour, associated fossorial morphological modifications, and dietary transitions to dry leaf litter feeding multiple times from the wood‐feeding Panesthiinae in a striking example of parallel evolution. However, various relationships within these two subfamilies remain unresolved or poorly understood, notably the apparent paraphyly of Panesthiinae with respect to Geoscapheinae, the position and diversification of certain species within major clades, and several aspects of the overall group's biogeography and morphological evolution. Here, we investigate the phylogeny of Australian members of these two subfamilies using whole mitochondrial genomes paired with nuclear ribosomal markers and highly conserved genes from the bacterial endosymbiont Blattabacterium. Using the resulting robust, fossil‐calibrated phylogeny from these three sources we confirm the nonmonophyly of both subfamilies and recover Geoscapheinae as polyphyletic within a paraphyletic Panesthiinae. The nonmonophyly of natural groups, at all levels from subfamily to species, has been driven by repeated, independent acquisitions of burrowing forms in Geoscapheinae from panesthiine ancestors that colonized the continent on two separate occasions during the Miocene. We additionally find morphological variation within Geoscapheinae itself is correlated with species distributions. Older soil‐burrowing clades living in comparatively arid environments have additional morphological reductions beyond obvious fossorial adaptations compared to those in younger burrowing clades from more temperate habitats. Ultimately, the results presented here demonstrate connections among phylogeny, biogeography and morphology throughout Australian representatives of these two subfamilies, factors that could not be previously consolidated using existing phylogenetic frameworks. Given the discordance between molecular data implemented here and the existing taxonomic classification, we find no support for retaining Geoscapheinae as a discrete taxonomic grouping. In closing, we discuss the taxonomic implications of these results and present a roadmap for future research on Geoscapheinae and their panesthiine relatives.
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| Macropanesthia mutica Rose, Walker & Woodward, a geoscapheine, surrounded by leaf litter in captivity. Macropanesthia displays morphology common to all geoscapheines, including the loss of wings and ocellar spots, reduced compound eyes, ‘shovel‐like’ protibiotarsi for digging and a generally ovoid body shape. Photograph by Braxton Jones. |
Conclusions:
The results of this study are consistent with ancestral Asian wood‐feeding lineages of Panesthiinae dispersing to Australia at least twice, with one of those colonization events giving rise to soil‐burrowing cockroaches presently classified as Geoscapheinae. We find that soil‐burrowing has evolved at least seven times from this ancestral state and that the diversification of burrowing forms was ongoing from approximately 17–3 Mya. These transitions were likely driven by bursts of aridification the Australian continent experienced beginning ∼25 Mya, and this parallel evolution of burrowing traits in geoscapheines has rendered soil‐burrowing associated morphology alone phylogenetically misleading. Within Geoscapheinae, we demonstrate additional character reductions have occurred related to reproductive and tergite morphology in clades that diverged from their panesthiine ancestors earlier and inhabit more arid biomes compared to younger burrowing clades found in more temperate environments. We also identify a distinction between panesthiines with putatively plesiomorphic traits that have close soil‐burrowing relatives compared to those with more ‘geoscapheinae’‐like morphology that are nested within, or gave rise to, geoscapheine clades.
Ultimately, our revised phylogenetic framework is reflective of both biogeography and morphology of these species, and this is the first time such factors have been unified in the context of the evolutionary history of these insects. Given this new phylogenetic evidence, we propose the morphology and habitat preferences of Geoscapheinae no longer warrant subfamilial status for the group.
Perry G. Beasley‐Hall, Harley A. Rose, James Walker, Yukihiro Kinjo, Thomas Bourguignon and Nathan Lo. 2021. Digging Deep: A revised Phylogeny of Australian Burrowing Cockroaches (Blaberidae: Panesthiinae, Geoscapheinae) Confirms Extensive Nonmonophyly and Provides insights into Biogeography and Evolution of Burrowing. Systematic Entomology. DOI: 10.1111/syen.12487
