Phylogeography and cohesion species delimitation of California endemic trapdoor spiders within the Aptostichus icenoglei sibling species complex (Araneae: Mygalomorphae: Euctenizidae)

Abstract

Species delimitation is an imperative first step toward understanding Earth's biodiversity, yet what constitutes a species and the relative importance of the various processes by which new species arise continue to be debatable. Species delimitation in spiders has traditionally used morphological characters; however, certain mygalomorph spiders exhibit morphological homogeneity despite long periods of population-level isolation, absence of gene flow, and consequent high degrees of molecular divergence.Studies have shown strong geographic structuring and significant genetic divergence among several species complexes within the trapdoor spider genus Aptostichus, most of which are restricted to the California Floristic Province (CAFP) biodiversity hotspot. Specifically, the Aptostichus icenoglei complex, which comprises the three sibling species, A. barackobamai, A. isabella, and A. icenoglei, exhibits evidence of cryptic mitochondrial DNA diversity throughout their ranges in Northern, Central, and Southern California. Our study aimed to explicitly test species hypotheses within this assemblage by implementing a cohesion species-based approach. We used genomic-scale data (ultraconserved elements, UCEs) to first evaluate genetic exchangeability and then assessed ecological interchangeability of genetic lineages. Biogeographical analysis was used to assess the likelihood of dispersal versus vicariance events that may have influenced speciation pattern and process across the CAFP's complex geologic and topographic landscape. Considering the lack of congruence across data types and analyses, we take a more conservative approach by retaining species boundaries within A. icenoglei.

Microgeographic population structuring in a genus of California trapdoor spiders and discovery of an enigmatic new species (Euctenizidae: Promyrmekiaphila korematsui sp. nov.)

“…Phylogenetic analyses revealed a divergent lineage that is sister to the P. winnemem plus P. clathrata lineage (Figure 1; Figures S1 and S2). Discovery of cryptic genetic lineages in mygalomorph species has been well‐documented (e.g., Bond et al., 2001; Brandt et al., 2023; Castalanelli et al., 2014; Hamilton et al., 2014; Hendrixson & Bond, 2005a; Monjaraz‐Ruedas et al., 2023; Newton et al., 2023; Starrett & Hedin, 2007). However, P. korematsui sp.…”

“…from burrows occurring at the same collection site), we predict that denser sampling of localities and individuals will reveal areas where these species overlap given their proximity and the absence of obvious barriers to migration. making analyses of ecological differentiation unreliable (e.g., niche model analyses, see Newton et al, 2023). Yet, P. korematsui sp.…”

“…Yet, these groups do not consistently separate in the clustering and ancestry coefficient analyses with different SNP sets (Figure 3). Species delimitation assessments using SNP data within P. clathrata were sen- population-species boundaries (Battey et al, 2021;Derkarabetian et al, 2019;Newton et al, 2020Newton et al, , 2023 Abdomen. Moderately setose; apical segment of PLS short, triangular in shape.…”

“…Species Concept, seeNewton et al, 2023), we determine through a process of reciprocal illumination that the lineage comprising P. korematsui sp. nov. populations is genetically divergent and isolated, although infrequent gene flow may occur.…”

“…into distinct species. Expansion of the default training model to include more low-vagility species, or development of a new training model based on taxa more closely related and ecologically similarto Promyrmekiaphila, could make this delimitation method more informative for mygalomorph spiders(Derkarabetian et al, 2022;Newton et al, 2023).Despite extensive genomic and population level sampling, ques-tions regarding cryptic species delimitation in Promyrmekiaphila remain unresolved. Using an integrative approach that evaluates both genetic and demographic exchangeability (i.e., the Cohesion…”