Utility of the nuclear protein-coding gene, elongation factor-1 gamma (EF-1gamma), for spider systematics, emphasizing family level relationships of tarantulas and their kin (Araneae: Mygalomorphae)

Spider systematics has overwhelmingly relied on morphological characters to resolve higher-level phylogenetic questions. Molecular phylogenetic studies of spiders above the genus level have been rare, partly because of a paucity of characterized genes available for amplification and sequencing. Here we show the phylogenetic utility of a new molecular marker, elongation factor-1 gamma (EF-1gamma) for discerning family level relationships in the spider infraorder, Mygalomorphae. We included genomic sequences from 26 mygalomorph genera in 14 families as well as cDNA sequences from 10 families in the infraorder Araneomorphae. We found strong support for the traditional split of mygalomorphs into atypoids (Antrodiaetidae, Atypidae, and Mecicobothriidae) and non-atypoids (all other families). Some families with multiple generic representatives were found to be polyphyletic or paraphyletic, such as the Nemesiidae, Ctenizidae, and Hexathelidae. A small portion of genomic EF-1gamma that could be amplified from araneomorphs contained a short intron, suggesting that longer genomic sequences could not be amplified due to the presence of introns. This intron may be useful for intra-familial araneomorph relationships. A tentative timeline for spider evolution is proposed using the evolutionary rate of EF-1gamma, estimated to be approximately 0.22% pairwise divergence per million years based on a non-parametric smoothing method (NPRS) and fossil constraints.     

A total evidence assessment of the phylogeny of North American euctenizine trapdoor spiders (Araneae, Mygalomorphae, Cyrtaucheniidae) using Bayesian inference

North American trapdoor spiders of the subfamily Euctenizinae (Cyrtaucheniidae) are among the most diverse mygalomorph spiders (trapdoor spiders, tarantulas, and their relatives) on the continent in terms of species numbers and ecological habits. We present a generic level phylogenetic study of the subfamily based on a total evidence approach. Our dataset comprises approximately 3.7 kb of molecular characters (18S and 28S rRNA gene sequences) and 71 morphological characters scored for 32 taxa. When analyzed independently, these data sets, particularly the morphology, depict very different views of mygalomorph and euctenizine relationships, albeit with weak support. However, when these data are combined we recover a tree topology that is supported by high posterior probability for most nodes. The combined data recover a phylogenetic pattern for euctenizines different than previously published and indicate the presence of a narrowly endemic new genus from central California. While euctenizine monophyly is unequivocal, the monophyly of a number of other mygalomorph groups is questionable (e.g., Cyrtaucheniidae, Mecicobothriodina, Rastelloidina). This non-monophyly is noteworthy, as our analysis represents the first employing a total evidence approach for mygalomorphs, a group known to be morphologically conservative.     

Dye coupling and connexin expression by cortical radial glia in the early postnatal subventricular zone

In this study, we have analyzed the specific contribution of the cortical radial glia (RG) for gap junctional communication (GJC) within the postnatal subventricular zone (SVZ). To specifically target RG as source of dye‐coupling in situ, we have developed a new technique that involves direct cell loading through the processes that reach the pial surface, with a mix of gap junction permeant (Lucifer yellow, LY) and nonpermeant (rhodamine‐conjugated dextran 3 KDa, RD) fluorochromes, the latter used as a marker for direct loaded cells. Tissue sections were analyzed for identification of directly loaded (LY+RD+) and coupled cells (LY+RD–) in the SVZ. Directly loaded cells were restricted to the region underlying the pial loading surface area. Coupled cells were distributed in a bistratified manner, along the outer dorsal surface of the SVZ and aligning the ventricle, leaving the SVZ core relatively free. Blocking GJC prior to pial loading greatly reduced dye coupling. Phenotypic analysis indicated that coupling by RG excludes neuroblasts and is mostly restricted to cells of glial lineage. Notwithstanding, no corresponding restriction to specific cell phenotype was found for two connexin isotypes, Cx43 and Cx45, in the postnatal SVZ. The extensive homocellular cell coupling by RG suggests an important role in the regulation of neurogenesis and functional compartmentalization of the postnatal SVZ. © 2012 Wiley Periodicals, Inc. Develop Neurobiol 2012     

Reshaping of sandstone surfaces by cryptoendolithic cyanobacteria: bioalkalization causes chemical weathering in arid landscapes

We report a novel weathering mechanism in South African sandstone formations, where cryptoendolithic cyanobacteria induce weathering by substrate alkalization during photosynthesis. As a result, the upper rock part is loosened and then eroded away by physical forces such as wind, water, trampling. This special type of ‘exfoliation’ is widely distributed and affects the geomorphology of whole sandstone mountain ranges and outcrops across several biomes. We show, that this weathering type is initiated by bioalkalization because of the photosynthesis of cryptoendolithic (i.e. those organisms living in small tight open spaces between the sand grains) cyanobacteria causing pH values high enough to enhance silica solution in the cryptoendolithic zone. As modern cyanobacteria are the initial photoautotrophic colonizers of bare rocks in arid and semiarid landscapes, it is possible that they may also have played a significant role in shaping sandstone landscapes in the geological past.     

Linear and threshold-dependent expression of secondary sexual traits in the same individual: insights from a horned beetle (Coleoptera: Scarabaeidae)

Elaborate horns or horn‐like structures in male scarab beetles commonly scale with body size either (a) in a linear fashion with horn size increasing relatively faster than body size or (b) in a threshold‐dependent, sigmoid fashion; that is, males smaller than a certain critical body size develop no or only rudimentary horns, whereas males larger than the threshold size express fully developed horns. The development of linear vs. sigmoid scaling relationships is thought to require fundamentally different regulatory mechanisms. Here we show that such disparate regulatory mechanisms may co‐occur in the same individual. Large males of the south‐east Asian Onthophagus (Proagoderus) watanabei (Ochi & Kon) (Scarabaeidae, Onthophagini) develop a pair of long, curved head horns as well as a single thoracic horn. We show that unlike paired head horns in a large number of Onthophagus species, in O. watanabei the relationship between head horns and body size is best explained by a linear model. Large males develop disproportionately longer horns than small males, but the difference in relative horn sizes across the range of body sizes is small compared to other Onthophagus species. However, the scaling relationship between the thoracic horn and body size is best explained by a strongly sigmoid model. Only males above a certain body size threshold express a thoracic horn and males smaller than this threshold express no horn at all. We found a significant positive correlation between head and thoracic horn length residuals, contrary to what would be expected if a resource allocation tradeoff during larval development would influence the length of both horn types. Our results suggest that the scaling relationship between body size and horn length, and the developmental regulation underlying these scaling relationships, may be quite different for different horns, even though these horns may develop in the same individual. We discuss our results in the context of the developmental biology of secondary sexual traits in beetles. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83 , 473–480.     

SPECIATIONAL HISTORY IN A DIVERSE CLADE OF HABITAT-SPECIALIZED SPIDERS (ARANEAE: NESTICIDAE: NESTICUS): INFERENCES FROM GEOGRAPHIC-BASED SAMPLING

This paper summarizes the results of an initial effort to reconstruct the speciational history of cave spiders (Nesticus) from the southern Appalachian Mountains of eastern North America. The Appalachian Nesticus fauna includes a large series of about 30 species distributed across islandlike cave and montane habitats. Many of the species are geographically restricted; all of the species are found in allopatry. Observed patterns of morphological variation and biogeographic evidence suggest that species diversification in this lineage may have occurred recently, perhaps in response to Pleistocene climatic fluctuations. To address questions about the spatial and temporal dynamics of Nesticus speciation, while accounting for potential phylogenetic difficulties, I have gathered nuclear and mitochondrial DNA sequences for a sample of individuals from 81 populations representing 28 Nesticus species. Analyses of these data indicate that considerable genetic divergence exists within and among currently recognized morphological species. Consistent with relatively deep species divergences, most of which likely predate the Pleistocene, is a prevailing pattern of phylogenetic concordance between taxonomic species and monophyletic gene tree lineages. The few deviations from monophyly detected can be tentatively attributed to a peripatric mode of speciation. Although species limits as inferred by the molecular data are generally concordant with patterns of morphological continuity and discontinuity in genitalia, there is evidence to suggest that cryptic phylogenetic lineages exist within some morphologically continuous units. This observation, in combination with the general depth of species lineages, makes any argument about rapid evolution in Nesticus genitalic characteristics unnecessary.