Michael Naegle and Dr. Michael Whiting, Department of Biology
Introduction
Dermaptera (earwigs) is a small order of insects, typically characterized by the presence of cerci on the abdomen that are modified into forceps-like appendages (Giles, 1963). Dermaptera includes approximately 2200 extant species comprising 11 families (Kocarek 2013). The majority of earwigs are free-living feeding on detritus and other plant material (Sakai 1987). Two families, Arixeniidae and Hemimeridae are ectoparasitic, associating with Malay Peninsula bats and giant murid rats of sub- Saharan Africa respectively (Jarvis 2005).
Hemimeridae is the most morphologically different from the other dermateran families. Hemimeridae are small (5mm to 15mm long) and contain eleven species. Adaptations to their life as external parasites (epizoic lifestyle) include: short broadened legs with grooves that allow them to cling to the host, loss of wings and eyes, straight narrowed cerci, and specialized mouthparts for scraping dead skin and fungus off their host (Nakata & Maa, 1974).
Arixeniidae contains five species and feeds on dead skin and skin gland secretions of their host. Arixeniidae can reach up to 25mm in length. They have similar adaptations to Hemimeridae, with loss of wings, reduced eyes and thin cerci (Jarvis 2005). Until recently the relationship between the ectoparasitic families, Arixeniidae and Hemimeridae, to the remaining free-living families was unknown. Jarvis in 2005 published his findings on the relationship existing between Hemimeridae and free-living Dermaptera. Kocarek in 2013 continued Jarvis’s work by adding Arixeniidae to Jarvis’s analysis. However only a portion of one ribosomal gene (18S) was used to decipher Hemimeridae’s relationship to the free-living Dermaptera (Jarvis 2005, Kocarek 2013) and only partial ribosomal genes (18S and 28S) were used to elucidate the relationships between Arixeniidae the other earwigs (Kocarek 2013). Lack of a mitochondrial gene, and only partial ribosomal genes cast doubt upon the relationships existing between dermapteran families. My research aimed to address two questions 1) Do Hemimeridae and Arixeniidae form a monophyletic group, or in other words has parasitism evolved once or more than once within Dermaptera? 2) What is the phylogenetic relationship existing between Hemimeridae, Arixeniidae, and the remaining dermapteran families?
Materials and Methods
Fifty-five species representing all three dermapteran suborders and 9 of 11 families (efforts are being made to include all 11 families) were selected for DNA sequencing. DNA was extracted using QIAGEN DNeasy Kit. Nuclear (18S, 28S, H3, and Tuba) and mitochondrial (Cox I) genes were amplified via PCR based on primers optimized for earwigs. PCR products were visualized on an agarose gel to determine specificity and potential contamination. Successful reactions were cleaned using a USB PrepEase PCR Purification plate. Products were sequenced using BigDye (Applied Biosystems Inc., version 3.1) chain terminating chemistry. Sequencing reactions were purified using sephadex, and submitted to the BYU DNA Sequencing Center. Sequences were then assembled and edited on Geneious 5.6.3. Protein-coding genes were translated into amino acid sequences using Mega 5.0 and aligned using MUSCLE and then were backtranslated into nucleotide sequences. Ribosomal RNA wias aligned using the E-INS-i strategy in MAFFT. Phylogenies were reconstructed in a maximum likelihood (RAxML) framework, and morphological characters associated with parasitism were mapped on the topology using Mesquite 2.75 (Madison, 2011).
Results/Discussion
Two terms are necessary for understanding discussions about relationships depicted in the accompanying trees:
Monophyletic- A group (clade) consisting of a common ancestor and all of its descendants
Paraphyletic- A group (clade) not consisting of a common ancestor and all of its descendants – typically paraphyletic groups include some but not all of the descendants from a common ancestor.
Sister taxa – closest relatives of a group within a phylogenetic tree.
Basal – earliest diverging group within a clade
We found four families were monophyletic: Hemimeridae, Arixeniidae, Chelisochidae, and Forficulidae. Four were not found to be monophyletic: Anisolabididae, Pygidicranidae, Spongiphoridae, and Labiduridae. Two of the monophyletic families (Arixeniidae and Hemimeridae) were recovered with high bootstrap support. Our findings agree with Koracek (2013) that Arixeniidae and Hemimeridae do not form a monophyletic clade of parasitic dermaterans. Our results indicate two separate and independent derivations of ectoparasitism in Dermpatera. At least twice within this order an organism has transitioned from a free-living lifestyle, to being dependent on a mammal to survive. However our analysis does not support the findings of Kocarek that Arixeniidae is sister to Chelisochidae and Hemimeridae is sister to Forficulidae (Kocarek 2013). Instead both groups are sister to different clades comprised of genera within the paraphyletic Spongiphoridae. These relationships were found under various phylogenetic reconstruction methods, though the support value at the nodes were weak.
The Anisolabididae were recovered as paraphyletic. One taxon was found to be sister to the remaining Dermaptera. The bulk of Anisolabididae were well supported as a sister clade to one of the Spongiphoridae clades. A final Anisolabididae (Parisolabis sp.) was recovered as sister to Sphingolabis sp. (Spongiphoridae) and was nested within the family Labiduridae.
The Spongiphoridae were recovered as paraphyletic with 5 clades (4 of which are listed above). One clade was isolated between two other Spongiphoridae clades, one of which is sister to Hemimeridae, and the other clade is sister to Arixeniidae. The Pygidicranidae were recovered as paraphyletic, and appear to be more basal lineages, excluding the Anisolabididae that was found to be sister to the remaining Dermaptera.
Conclusion
Not only has parasitism evolved twice independently within Dermaptera, but also the features shared between the two groups are examples of convergent evolution. Both groups have thin straight cerci, which is uncommon in the remaining dermapterans. These epozoic lineages are wingless and have either reduced eyes (Arixeniidae) or are eyeless altogether (Hemimeridae). Although size and body type differ greatly between the two families, these features appear closely associated with their ectoparasitic lifestyle. Our analysis also demonstrates that our current classification of Dermaptera is incorrect. Four paraphyletic families were recovered. The morphological character that were used to distinguish and classify these earwigs do not adequately inform us of the evolutionary relationships among these families. Additional genes and a broader taxon sampling should be used to confirm our results.
We are currently preparing a manuscript for submission to the journal Molecular Phylogenetics and Systematics.
References
- Giles, E. T. (1963) The comparative external morphology and affinities of the Dermaptera. Transactions of the Royal Entomological Society of London, 115, 95-164.
- Jarvis K.J., Haas F., Whiting M.F. (2004) Phylogeny of earwigs (Insecta: Dermaptera) based on molecular and morphological evidence: reconsidering the classification of Dermaptera. Systematic Entomology 30, 442-453
- Kocarek P. et al. (2013) When the Body Hides the Ancestry: Phylogeny of Morphologically Modified Epizoic Earwigs Based on Molecular Evidence. PLOS one, 8(6)
- Nakata, S. & Maa, T.C. (1974) A review of the parasitic earwigs (Dermpatera, Arixeniina; Hemimerina). Pacific Insects, 16, 307-374.
- Maddison W. P. and Maddison D. R. (2011) Mesquite: a modular system for evolutionary analysis. Version 2.75 http://mesquiteproject.org
- Rentz, D.C.F. & Kevan, D.K.M. (1991) Dermaptera. The Insects of Australia: a Textbook for Students and Research Workers (ed. By I. D. Naumann et al.), pp. 360-368. Cornell University Press, Ithaca.
- Sakai, S. (1982) A new proposed classification of the Dermpatera with special reference to the check list of the Dermpatera of the world. Bulletin of Daito Bunka University, 20, 1-108.