Historical biogeography of scarabaeine dung beetles

Abstract Aim (1) To review briefly global biogeographical patterns in dung beetles (Coleoptera: Scarabaeidae: Scarabaeinae), a group whose evolutionary history has been dominated by ecological specialization to vertebrate dung in warmer climates. (2) To develop hypotheses accounting for the evolution of these patterns. Location Six principal biogeographical regions: Palaearctic, Oriental, Afrotropical, Australasia, Neotropical, Nearctic and five outlying islands or island groups harbouring endemic genera: Caribbean, Madagascar, Mauritius, New Caledonia, New Zealand. Methods Major patterns of tribal, generic and species distribution are investigated using cluster analysis, ordination, parsimony analysis of endemism and track analysis. Attempts are made to resolve biogeographical patterns with findings in the fields of plate tectonics, fossil and evolutionary history, plus phylogeny of both mammals and dung beetles. Results Because of conflict between published findings, it is uncertain at what point in time density of dinosaur dung, mammal dung or both became sufficiently great to select for specialized habits in dung beetles. However, biogeographical evidence would suggest a Mesozoic origin followed by further taxonomic radiation during the Cenozoic, possibly in response to the increasing size and diversity of mammalian dung types in South America and Afro‐Eurasia. Proportional generic distribution in fourteen tribes and subtribes showed four principal biogeographical patterns: (1) southerly biased Gondwanaland distribution, (2) Americas or (3) Madagascar endemism, and (4) northerly biased, Afro‐Eurasian‐centred distribution with limited numbers of genera also widespread in other regions. Proportional composition of faunas in eleven geographical regions indicated three principal distributional centres, East Gondwanaland fragments, Afro‐Eurasia and the Americas. These patterns probably result from three principal long‐term range expansion and vicariance events (Mesozoic: Gondwanaland interchange and fragmentation, Cenozoic: Afro‐Eurasian/Nearctic interchange and the Great American interchange). It is suggested that old vicariance caused by the Mesozoic fragmentation of Gondwanaland leads to a high degree of regional endemism at generic or tribal level across one or more Gondwanaland tracks. In contrast, it is suggested that the more recent Cenozoic range expansions occurred primarily towards northern regions leading to endemism primarily at species level. These Cenozoic radiations were facilitated by the re‐linking of continents, either because of tectonic plate movements (Africa to Eurasia in Miocene), climatically induced sea‐level change (Afro‐Eurasia to Nearctic in Miocene and Pleistocene), or similar coupled with orogenics (Nearctic to Neotropical in Pliocene). Speciation has followed vicariance either because of climatic change or physical barrier development. These recent range expansions probably occurred principally along an Afro‐Eurasian land track to the Nearctic and Neotropical and an Americas land track northwards from the Neotropics to the Nearctic, with limited dispersal from Eurasia to Australia, probably across a sea barrier. This accounts for the overall, spatially constrained, biogeographical pattern comprising large numbers of species‐poor genera endemic to a single biogeographical region and fewer more species‐rich genera, many of which show wider biogeographical distributions. In most southerly regions (Australasia, Madagascar, Neotropical), faunal composition and generic endemism is primarily dominated by elements with Gondwanaland ancestry, which is consistent with the Gondwanaland origin claimed for Scarabaeinae. In Afro‐Eurasia (Palaearctic, Oriental, Afrotropical), generic endemism of monophyletically derived Afro‐Eurasian and widespread lineages is centred in the Afrotropical region and faunal composition is numerically dominated by Afro‐Eurasian and widespread elements. In the Nearctic region, the fauna is jointly dominated by widespread elements, derived from Afro‐Eurasia, and Gondwanaland and Americas elements derived from the Neotropical region. Main conclusions Global biogeographical patterns in scarabaeine dung beetles primarily result from Mesozoic and Cenozoic range expansion events followed by vicariance, although recent dispersal to Australia may have occurred across sea barriers. Detailed phylogenetics research is required to provide data to support dispersal/vicariance hypotheses.     

A specialized dorsal rim area for polarized light detection in the compound eye of the scarab beetle Pachysoma striatum

Many animals have been shown to use the pattern of polarized light in the sky as an optical compass. Specialised photoreceptors are used to analyse this pattern. We here present evidence for an eye design suitable for polarized skylight navigation in the flightless desert scarab Pachysoma striatum. Morphological and electrophysiological studies show that an extensive part of the dorsal eye is equivalent to the dorsal rim area used for polarized light navigation in other insects. A polarization-sensitivity of 12.8 (average) can be recorded from cells sensitive to the ultraviolet spectrum of light. Features commonly known to increase the visual fields of polarization-sensitive photoreceptors, or to decrease their spatial resolution, are not found in the eye of this beetle. We argue that in this insect an optically unspecialised area for polarized light detection allows it not be used exclusively for polarized light navigation.     

Transformation of tetrachloromethane to dichloromethane and carbon dioxide by Acetobacterium woodii

Five anaerobic bacteria were tested for their abilities to transform tetrachloromethane so that information about enzymes involved in reductive dehalogenations of polychloromethanes could be obtained. Cultures of the sulfate reducer Desulfobacterium autotrophicum transformed some 80 microM tetrachloromethane to trichloromethane and a small amount of dichloromethane in 18 days under conditions of heterotrophic growth. The acetogens Acetobacterium woodii and Clostridium thermoaceticum in fructose-salts and glucose-salts media, respectively, degraded some 80 microM tetrachloromethane completely within 3 days. Trichloromethane accumulated as a transient intermediate, but the only chlorinated methanes recovered at the end of the incubation were 8 microM dichloromethane and traces of chloromethane. Desulfobacter hydrogenophilus and an autotrophic, nitrate-reducing bacterium were unable to transform tetrachloromethane. Reduction of chlorinated methanes was thus observed only in the organisms with the acetyl-coenzyme A pathway. Experiments with [14C]tetrachloromethane were done to determine the fate of this compound in the acetogen A. woodii. Radioactivity in an 11-day heterotrophic culture was largely (67%) recovered in CO2, acetate, pyruvate, and cell material. In experiments with cell suspensions to which [14C]tetrachloromethane was added, 14CO2 appeared within 20 s as the major transformation product. A. woodii thus catalyzes reductive dechlorinations and transforms tetrachloromethane to CO2 by a series of unknown reactions.     

The persistent microbicidal effect in water exposed to the corona discharge

This article describes and particularly explains a new phenomenon of persistent microbicidal effect of water previously exposed to the low-temperature plasma, which cannot be attributed to the acidification only. The direct microbicidal action of plasma is well documented, being mediated by number of reactive particles with a short lifetime. However, we observed the microbicidal effect also in exposed water stored for a month, where it must be mediated by stable particles. In water and in phosphate-buffered saline, the formation of NO_x and corresponding acids, H₂O₂ and O₃ was confirmed after exposition to the low-temperature plasma generated in air by DC negative glow corona and positive streamer discharge. The time course of acidification, H₂O₂ and O₃ formation were deremined. Except uncertain traces of HCN, SIFT-MS analysis of exposed liquids reveals no additional reactive compounds. The microbicidal effect persists almost unchanged during 4 weeks of storage, although O₃ completely and H₂O₂ almost disappears. Staphylococcus epidermidis and Escherichia coli were inactivated within 10 min of incubation in exposed liquids, Candida albicans needs at least 1 h. The solutions prepared by artificial mixing of reactive compounds mimic the action of exposed water, but in lesser extent. The acid milieu is the main cause of the microbicidal effect, but the possibility of still unidentified additional compound remains open.     

Elongated hindguts in desert‐living dung beetles (Scarabaeidae: Scarabaeinae) feeding on dry dung pellets or plant litter

Most adult dung beetles (Scarabaeidae: Scarabaeinae) feed on fresh, wet dung of larger herbivorous or omnivorous mammals. As refractory plant fragments are selected out before ingestion, the food is presumed easily digestible. However, members of the desert‐living scarabaeine genus Pachysoma (probably evolved from an ancestor closely related to the wet‐dung feeding genus Scarabaeus) select dry dung pellets and/or plant litter. Thus, they ingest a much higher proportion of structural plant material, which nevertheless appears to be digested rather efficiently. This study investigates morphological modifications of the gut for this digestion in adults of eight Pachysoma species, both pellet and litter feeders. To ascertain hypothesized ancestral conditions, four fresh‐dung feeding Scarabaeus species were also examined. The latter have the usual dung beetle gut consisting of a long, simple midgut, followed by an equally simple, much shorter hindgut of the same width. Lengths of midguts (M) and hindguts (H) divided by body length (B) for comparison between species of different size are: 4.9–6.3 (M/B) and 0.7–0.8 (H/B), which is normal for dung feeders. In Pachysoma, lengths are 6.3–6.5 (M/B) and 1.0–1.4 (H/B) in pellet feeders, and 4.4–5.0 (M/B) and 2.0–2.5 (H/B) for litter feeders. Hindguts are still morphologically undifferentiated and of midgut width, but clearly longer, particularly in litter feeders. Presumably, plant fragments in the food are digested, at least partly, in the hindgut. If so, the morphological adaptation is unusual: simple elongation rather than the expansion of part of the hindgut, as found in several other plant‐ or detritus‐feeding scarabaeids. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

Further Contribution to the Chemistry of Plasma-Activated Water: Influence on Bacteria in Planktonic and Biofilm Forms

This article is a continuation of the authors’ previous contribution. Plasma-activated water (PAW) prepared by exposure to the point-to-plane dc corona discharge was analyzed, and its biological effect tested on bacteria in planktonic and biofilm forms. Hydrogen peroxide and nitric acid were found as active components of PAW, although the presence of another unknown compound cannot be excluded unambiguously. PAW inhibits rapidly planktonic Gram-positive bacteria, whereas the inhibition of Gram-negative ones is somewhat slower. In biofilm form, this activity was not observed, so that PAW is not able to disinfect bacterial biofilms.