North American camel spiders (Arachnida, Solifugae, Eremobatidae): Systematic revision and biogeography of an understudied taxon

NSF ARTS PROPOSAL 1733117

Research and Mentoring Objectives.

 

The research and mentoring objectives of this proposal are intertwined since students and the postdoc will be involved in all aspects of the project. Research goals are to: 1) Continue to revise the taxonomy of Eremobatidae to reflect monophyletic groups (beginning with well-supported clades); 2) Use phylogenomic markers (Ultra-Conserved Elements, or UCEs), more thorough taxon sampling, and inclusion of novel morphological characters (chaetotaxy) to construct a more comprehensive phylogeny of Eremobatidae; 3) Examine the roles of Neogene tectonics and Pleisto/Holocene climate change on the biogeography of the Eremobates palpisetulosus species group; 4) Improve the online resources for this group of arachnids by: increasing digitization of eremobatid records in the NSF-funded SCAN (TCN) database portal; creating an online guide to camel spiders in the family Eremobatidae; and redesigning the current online site for this order (http://www.solpugid.com/) to make a new website (http://www.solifugae.info) a more inclusive resource for these enigmatic arachnids.

 

 

Taxonomic revision

 

Cushing, Brookhart, and Savary will mentor a team of students (high school and undergraduate REU students) in revising the taxonomy of monophyletic taxa including: Eremorhax (10 described species) and Eremothera (two described species and one undescribed)6. Both these genera are defined by clear morphological synapomorphies. Cushing & Brookhart (2016)6 revised the taxonomy of the Eremobates scaber species group (21 described species), which is geographically cohesive and defined by clear synapomorphies6, 26. Cushing & Brookhart also completed a taxonomic revision of the monophyletic genus Eremocosta (13 described and nine new species)41, another group well supported in the 2015 phylogeny that is united by clear synapomorphies. They will work with the students in their lab to explore the utility of morphological chaetotaxy characters as diagnostic synapomorphies for groups. Solifugae have unique setal structures not found in any other group of arachnids27, 28, 29, 30 (Fig. 2). However, the phylogenetic significance of these morphological characters has not been explored even though chaetotaxy is an important suite of characters for many other groups of arachnids31, 32, 33, 34.

 

The high school and undergraduate students working in Cushing’s lab will assist with field work, lab work, digitization, and data analysis involved in the taxonomic revisions. Cushing has had excellent success including high school and undergraduate students in past research projects and some have been co-authors on scientific publications27, 28, 35. Graham has also been successful including motivated undergraduates in research through Independent Study courses and Honors Theses at ECSU and will send students to DMNS for taxonomic training. Brookhart is a retired high school science teacher and also has extensive experience mentoring students. The MS and PhD students will be mentored in Cushing’s lab with Graham serving as committee member and Brookhart and Savary assisting in student training, mentoring, and taxonomic revisions. Cushing is an affiliated faculty at the University of Colorado, Denver. These students will take a lead on reassessing the phylogeny of the genera previously placed in the polyphyletic and artificial subfamily Therobatinae: Chanbria (four species), Hemerotrecha (33 species), Eremochelis (38 species), and the species groups in the latter two genera (see Table 1 on the Project Introduction page).

 

 

Figure 2. Specialized setae on the pedipalps
of solifuges.

 

Phylogenomics

 

In our 2015 multi-locus analysis of Eremobatidae using four gene markers, Chanbria was rendered paraphyletic in the BI and ML analyses but monophyletic with strong support in the BEAST analysis6. To resolve these contradictory results, more data are clearly needed. Therefore, we will pioneer the use of a recently developed phylogenomic toolkit for arachnids (UCEs) that allows targeted sequencing36 of hundreds of loci. Other phylogenomic techniques (i.e. transcriptomes) require highquality RNA, but the UCE approach only needs DNA and has been demonstrated to be effective even when starting concentrations are low. Excitingly, the UCE protocol should allow us to use both freshly caught and museum preserved specimens for analysis. DMNS currently houses 128 species of Eremobatidae (or 68% of the diversity) in the arachnology collection; about 2/3 of these specimens can be used for the UCE protocol. Additional material will be acquired through field collection as part of this grant. Additionally, UCEs are effective at resolving evolutionary relationships at both shallow (young) divergences and deep (ancient) timeframes37, 38, 39, enabling exploration of phylogenetic relationships along the family’s approximately 30 million year history6. A UCE probe set for arachnids has been developed that targets about 1000 loci resulting in over 40,000 parsimony-informative sites36.

 

Using UCE data in combination with morphological characters and additional samples, the MS student will conduct an additional, more extensive, test of the hypothesis that Chanbria is monophyletic. The PhD student will use the same approach to lead our effort to revise the more complicated genera Hemerotrecha and Eremochelis, both of which are polyphyletic (Fig. 1)6. No morphological characters used to diagnose Eremochelis or Hemerotrecha could be considered synapomorphic for these genera because they occur in various combinations throughout the family Eremobatidae. The PhD student will expand the sampling of species currently placed in these two genera as well as other species in the Eremobatidae through extensive fieldwork throughout the deserts of North America. Both students (MS and PhD) will use a combined analysis with UCEs and morphological characters, including the new chaetotaxic characters, to re-analyze the phylogeny of these polyphyletic clades and the overall phylogeny of Eremobatidae using this much larger dataset. The students will then revise the taxonomy of all species currently placed in the “Therobatinae” subfamily.

 

Biogeography of the Eremobates palpisetulosus species group

 

Components of the Eremobates palpisetulosus species group form well supported regional subgroups6; one from xeric habitats of Coast, Transverse, and Peninsular ranges of California with origins in the Pliocene and an older subgroup from Texas/Chihuahuan short grass prairie that probably originated in the Miocene. The postdoc (under the mentorship of Graham) will conduct population level sampling of the Eremobates palpisetulosus group throughout the Mojave, Sonoran, and Chihuahuan deserts. Again exploiting the UCE approach, the postdoc will conduct a comparative phylogeographic analysis. The utility of UCEs for population level analyses has recently been demonstrated, with authors suggesting that the approach is preferred for comparative phylogeography and shallow systematics due to higher comparability among data sets39, 40. The timing of diversification and cladogenesis in the E. palpisetulosus group is ideal for exploring how Neogene tectonics and Quaternary climatic changes have influenced camel spider diversity, distribution, and abundance in different deserts. UCEs have only been used in a phylogeographic context for vertebrates, so the postdoc will also evaluate the efficacy of the approach for arthropods by comparing the UCE results to those from the traditional (Sanger) DNA sequencing of a subset of the phylogeographic samples. For this, the postdoc will use the same four makers provided in Cushing et al. (2015)6. The postdoc will be based at ECSU, but will also conduct work in Cushing’s lab at DMNS to carry out a taxonomic revision of this large species group that includes over 40 species.

 

 

Online Resources for Camel Spiders

 

Data from the DMNS arachnology collection, where all voucher material from this project will be accessioned, is published online via the NSF-funded Symbiota Collections of Arthropods Network (SCAN). 95% of these DMNS data are geocoded and all type specimens contained in the DMNS arachnology collection have been imaged as part of these digitized records. The PhD student will be hired as a part-time Research Associate in the Arachnology collection to image and digitize diagnostic characters for the newly revised taxa using hardware and focus-stacking software purchased as part of the previous TCN grant. The goal will be to produce an online photographic guide, including a key, to Eremobatidae species of North America, similar to the existing SCAN guide to the Weevils of North America. When users click on a species name, a separate page will come up presenting diagnostic images of that species, a distribution map (based on SCAN database records), and a description of that species. In other words, we will synergistically build upon past NSF funding to create a definitive resource guide to an otherwise notoriously difficult to identify group of arachnids. Past NSF funding (DEB-0640245) also allowed us to further develop an online website devoted to the order Solifugae: http://www.solpugid.com/), originally registered and maintained by Savary. Content of that website has not been regularly updated due, in part, to changes in software and HTML standards. A duplicate website, http://www.solifugae.info has recently been created as a replacement to the older website (which will redirect users to the new site). The new website utilizes a well-established and responsive hosting service, up-to-date development software, and current coding standards (HTML5 and CSS). We will include funding to support the development of the new website. Savary will update and digitize the bibliographic resources, add images of eremobatid taxa, expand identification aids, and augment information on this group of arachnids.