High‐stakes species delimitation in eyeless cave spiders (Cicurina, Dictynidae, Araneae) from central Texas

Abstract

A remarkable radiation of completely eyeless, cave-obligate spider species (Cicurina) has been described from limestone caves of Texas. This radiation includes over 50 described species, with a large number of hypothesized single-cave endemics, and four species listed as US Federally Endangered. Because of this conservation importance, species delimitation in the group is 'high-stakes'- it is imperative that species hypotheses are data rich, objective, and robust. This study focuses on a complex of four cave-dwelling Cicurina distributed on the northwestern edge of Austin, Texas. Several of the existing species hypotheses in this complex are weak, based on morphological comparisons of small samples of adult female specimens; one species description (for C. wartoni) is based on a single adult specimen. Species limits in this group were newly assessed using morphological, mitochondrial and nuclear DNA sequence data evidence, analysed using a variety of approaches. All data support a clear lineage separation between C. buwata versus the C. travisae complex (including C. travisae, C. wartoni and C. reddelli). Observed congruence across multiple analyses indicate that the C. travisae complex represents a single species, and the formal species synonymy presented here has important conservation implications. The integrative framework utilized in this study serves as a potential model for other Texas cave Cicurina, including US Federally Endangered species. More generally, this study illustrates how and why taxon-focused conservation efforts must prioritize modern species delimitation research (if the existing taxonomy is weak), before devoting precious downstream resources to conservation efforts. The study also highlights the issue of taxonomic type II error that diversity biologists increasingly face as species delimitation moves into the genomics era.

Cryptic diversity in Tranzscheliella spp. (Ustilaginales) is driven by host switches

“…The GMYC and PTP analyses used in this study meet the basic requirements of these two methods. The GMYC method has a tendency to over-split and generate biologically unrealistic putative entities36. In this study, T. reverdattoana, T. schlechtendalii and Tranzscheliella sp., formed single PTP groups, although multiple-threshold analysis separated each of these species into two subclades (Fig.…”

Spiders in caves

“…Studies uncovered pronounced genetic structuring and low gene flow-if any-between cave populations, as found with Nesticidae [15,79,87,90], Linyphiidae [17] and Telemidae [91]. Although it is difficult to separate speciation from population structuring [92], the lack of gene flow supports the 'caves as islands' scenario sensu [90], in which dispersal is virtually absent.…”

“…Comparative studies supported by modern investigation tools-and accounting for phylogenetic effects-represent stimulating endeavours that would allow further light to be shed on this topic. (3) In the last 20 years, the use of a molecular approach to study subterranean spiders has proven to be a promising field of research, aiming to disclose biogeographic patterns of species diversification [16,17,79], delimit species boundaries [91,92] and unravel the role of dispersal in highly isolated populations [15,90].…”

“…Furthermore, the current species hypothesis regarding speciose taxa are often far for being solid [62,67,88,92,94], which is a crucial factor hindering the conservation of cryptic and restricted species [108].…”

Rapid dissemination of taxonomic discoveries based on DNA barcoding and morphology

“…For example, the combination of COI and ITS2 proved useful in barcoding of Collembola35. DNA barcoding can become more powerful when combined with classical morphological diagnoses and dissemination of standard taxonomical information, using a variety of analytical approaches4142434445.…”