Primary processing neuropils associated with the malleoli of camel spiders (Arachnida, Solifugae): a re-evaluation of axonal pathways.

BACKGROUND: Arachnids possess highly specialized and unorthodox sense organs, such as the unique pectines of Scorpiones and the malleoli of Solifugae. While the external morphology, numbers, and shapes of sensory organs are widely used in taxonomic studies, little is known about the internal anatomy of these organs and their associated processing neuropils in the central nervous system. Camel spiders (Solifugae) possess pedipalps and first walking legs heavily endowed with sensory structures, as well as conspicuous malleoli located ventrally on the proximal fourth walking legs. Malleoli are fan-shaped organs that contain tens of thousands of presumptive chemoreceptor neurons, but mechanoreceptive structures are absent. RESULTS: Here, we examine the organization of the synganglion based on microCT analysis, 3D reconstruction of serial paraffin sections, and backfill preparations to trace the malleolar pathway. The projection area of malleolar afferents is intriguingly located in the most anterior ventral nerve cord, located in between the pedipalpal neuromere hemispheres. However, malleolar axon bundles are separated by a thin soma layer that points to an anteriad projection of the fourth walking leg neuromere. A conspicuous projection neuron tract that may receive additional input from pedipalpal sensory organs connects the malleolar neuropil with the mushroom bodies in the protocerebrum. CONCLUSION: Arthropod chemosensory appendages or organs and primary processing neuropils are typically located in the same segment, which also holds true in Solifugae, although the malleolar neuropil is partially shifted towards the pedipalpal neuromere. A comparison of the malleoli in Solifugae and the pectines in Scorpiones, and of their primary processing neuropils, reveals certain similarities, while striking differences are also evident. Similarities include the ventral arrangement of peg-shaped sensory structures on the respective segmental appendage, exposing dense arrays of chemoreceptive sensilla, and projections to a primary processing neuropil with glomerular subdivision. Differences are, e.g., the lack of mechanoreceptive afferents and an associated processing neuropil.

Effects of starvation on reproduction of the predacious mite Neoseiulus californicus (Acari: Phytoseiidae).

Effects of starvation on gravid females of Neoseiulus californicus were investigated at 20 degrees C and 85% RH. When females that had been reared with abundant prey were swapped, just after laying their first egg, to conditions without any prey and water, they laid 1.8 eggs and survived for 4.3 days. In the body of well-fed females, an egg with eggshell and/or two oocytes were observed in the ventral and dorsal regions, respectively. The larger oocyte had two roundish nuclei and abundant yolk granules, and was enveloped with a vitelline membrane. These two nuclei were not fused but were just close to each other. The smaller oocyte had a nucleus, but had not yet formed yolk granules and vitelline membrane. Females after 12 h starvation had an egg in the ventral region and an oocyte in the dorsal region of the body. After more than 24 h starvation females maintained an oocyte in the dorsal region of the body, but had no egg in the ventral region. The oocyte was filled with abundant yolk granules and contained two irregular nuclei when females were starved for 24 h, but when starved for more than 36 h it contained one irregular nucleus. These findings suggest that (1) gravid females maintained an oocyte in the dorsal region after laying two eggs during starvation, (2) the oocyte was not absorbed during starvation, (3) the oocyte advanced vitellogenesis and the fusion of two nuclei, and (4) the vitellogenic oocyte was not enveloped with an eggshell and had not started embryogenesis.

A comparison of the mitochondrial genomes from two families of Solifugae (Arthropoda: Chelicerata): Eremobatidae and Ammotrechidae.

Arachnids are an ancient and diverse group of arthropods, yet few representative mitochondrial genomes have been published for most of the 11 orders. Here, we present and compare sequence and genomic data from two complete mitochondrial genomes from the arachnid order Solifugae (the camel spiders or wind scorpions), representing two families, Ammotrechidae and Eremobatidae. We also make genome-level and sequence comparisons between these taxa and the horseshoe crab, a chelicerate from the sister group to arachnids. In their organization, the two solifuge mitochondrial genomes are similar to that of the horseshoe crab, although both of the solifuges possess a region of repeated sequence. All 13 protein-coding genes and the two ribosomal RNA genes are of similar sizes to those found in the horseshoe crab. The ammotrechid and the eremobatid each have one tRNA gene that differs in location from those of other chelicerates, suggesting that these translocations occurred after the divergence of Solifugae from other arachnid lineages. All 22 tRNA genes in both solifuges are inferred to form secondary structures that are typical of those found in other metazoan mt genomes. However, in the eremobatid, the tRNA(Ser(UCN)) gene in the repeat region appears to have undergone partial duplication and loss of function, and a new tRNA(Ser(UCN)) gene has been created de novo. Our divergence data, in conjunction with the fossil record, indicate that these two solifuge families diverged more than 230 million years ago. Thus, despite several gene rearrangements and duplications, these data indicate a remarkable degree of evolutionary stasis.