Aptostichus

Abstract: This systematic study documents the taxonomy, diversity, and distribution of 40 species of the predominately Californian trapdoor spider genus Aptostichus Simon, 1891. Thirty-three of these species are newly described: Aptostichus dantrippi, Aptostichus cabrillo, Aptostichus pennjillettei, Aptostichus asmodaeus, Aptostichus nateevansi, Aptostichus chiricahua, Aptostichus icenoglei, Aptostichus isabella, Aptostichus muiri, Aptostichus barackobamai, Aptostichus sinnombre, Aptostichus hedinorum, Aptostichus aguacaliente, Aptostichus chemehuevi, Aptostichus sarlacc, Aptostichus derhamgiulianii, Aptostichus anzaborrego, Aptostichus serrano, Aptostichus mikeradtkei, Aptostichus edwardabbeyi, Aptostichus killerdana, Aptostichus cahuilla, Aptostichus satleri, Aptostichus elisabethae, Aptostichus fornax, Aptostichus lucerne, Aptostichus fisheri, Aptostichus bonoi, Aptostichus cajalco, Aptostichus sierra, Aptostichus huntington, Aptostichus dorothealangeae, and Aptostichus chavezi. Most of these species are restricted to the California Floristic Province, a known biodiversity hotspot. Of the 40 recognized species, over half are considered to be imperiled or vulnerable and two have likely gone extinct over the past half-century; the conservation status of only 11 species is considered to be secure. Using 73 quantitative and qualitative morphological characters I propose a preliminary phylogeny for the genus that recognizes four major lineages: the Atomarius, Simus, Hesperus, and Sierra species groups. Additionally, the phylogenetic analysis indicates that adaptations favoring the invasion of the arid desert habitats of southern California have evolved multiple times across the group. The existence of both desert and non - desert species in three of the four species groups makes this genus an ideal candidate for the study of the evolutionary ecology of desert arthropods. A set of molecular characters based on the contiguous mitochondrial DNA genes 16S-tRNA valine-12S is used in an independent analysis to assist in placement of specimens into species. The taxonomy section explicitly identifies the concept employed in species delimitation. Niche based distribution models are constructed to predict the ranges of species for which an adequate number of sampling sites were known.

Abstract: We investigated the pattern of molecular variation with respect to secondary structure in the 16S ribosomal RNA gene and its phylogenetic implications for arachnids with a focus on spiders. Based on a model by Gutell et al. (1996), secondary structures were proposed for the 3′ half of 16S in the mygalomorph spider Aptostichus atomarius. Models were also constructed for a hypervariable length of the 16S in three other arachnids, which revealed a trend of stem and loop reduction in more advanced arachnids. Using a simple statistical approach to compare functional regions, we found that internal and external loops are more variable than stems or connection regions. Down-weighting or excluding regions which code for the more variable loops improved tree topologies by restoring the monophyly of the genus Aptostichus, a group supported by combined 16S, COI, and morphological data in other analyses. This study demonstrated the utility of considering secondary structure for DNA sequence alignment and phy...