Effects of Ultraviolet Irradiation on the Cell Cycle

Cultured mouse Cloudman melanoma cells, EMT6 breast carcinoma cells, and 3T3 fibroblasts all accumulated in the G2/M phase of the cell cycle when exposed to UVB radiation. The effects of UVB were maximal at 20–30 mJ/cm² for all three cell lines, and could be observed by flow cytometry as early as 12 hr post irradiation. It has been known since the mid-1970s that MSH receptor binding activity is highest on Cloudman melanoma cells when they are in the G2/M phase of their cycle. Here we show that either UVB irradiation or synchronization of Cloudman cells with colchicine results in a stimulation of MSH binding within 24 hr following treatment, a time when both treatments have resulted in accumulation of cells in the G2/M phase of the cycle. Furthermore, the two treatments performed together on the melanoma cells stimulated MSH receptor activity to the same extent as either treatment performed separately, suggesting that each may be influencing MSH receptor activity solely through a G2/M accumulation of cells. Together, these results raise the possibility that an increase in the number of cells in the G2 phase of the cell cycle is a generalized cellular response to injury, such as UV irradiation. However, in the case of pigment cells this response includes a mechanism for increasing melanin formation, i.e., increased MSH receptor activity. Should this be the case, similar G2/M “injury responses” of other cell types might be expected, consistent with their differentiated phenotypes.     

Strong genetic cohesiveness between Italy and North Africa in four butterfly species

The sea acts as an effective dispersal barrier for most terrestrial animal species. Narrow sea straits, therefore, often represent areas where species are able to disperse from one land mass to another. In the Mediterranean Sea, the narrowest connecting points between North Africa and Europe are the Strait of Gibraltar and the Strait of Sicily. In the past, climatic oscillations caused changing sea levels and thus influenced the permeability of these sea straits. We analysed the genetic structure of four butterfly species that all occur on both sides of the Strait of Sicily. In all four species, we observed a lack of genetic differentiation between the populations of North Africa and those of Italy. Species distribution models support the strong cohesiveness in that they show a largely continuous glacial distribution over Italy and North Africa. The data obtained reveal that there was a large exchange of individuals between Italy and the eastern Maghreb during the last ice age. This might not only be the case for the species under investigation in the present study, but also might represent a more general pattern for mobile thermophilic western Palearctic species. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 818–830.     

Pliensbachian gastropods from Venetian Southern Alps (Italy) and their palaeobiogeographical significance

Abstract: The Pliensbachian gastropods described by De Toni in 1912, coming from an isolated boulder at the foot of Mt Vedana (eastern margin of Trento Platform, Venetian Southern Alps, Italy) are revised. The fauna consists of 13 species representing nine families and eight superfamilies. Despite the low number of species, the assemblage represents the most diverse Early Jurassic gastropod fauna known for the Venetian Southern Alps. The boulder yielding the material was thought to derive from the upper part of the Early Jurassic Calcari Grigi Group, a carbonate platform unit extensively cropping out in the Mt Vedana area. The sedimentological analysis indicates a prevalently bioclastic wackstone‐floatstone, reflecting a lime‐muddy deposit undergone to an early consolidation. This and the high content of ammonoids, which is unusual for the Calcari Grigi Group, are typical aspects of a condensed pelagic sediment, presumably a fissure filling at the top of the carbonate platform succession. Palaeobiogeographical comparisons show that the fauna is composed of species occurring exclusively in pelagic limestones of the western Tethys. By contrast, it shows no relationships with the coeval faunas of the adjacent Trento platform and of the other western Tethyan carbonate platforms. These lines of evidence and the facies analysis would testify to the Pliensbachian drowning of the eastern margin of the Trento platform. In the wider context of the palaeobiogeographical history of Early Jurassic western Tethyan gastropods, the species from Vedana belong to a faunal stock which is typical for pelagic, mainly postdrowning sediments. Thus, appearance and diffusion in space and time of this stock were probably regulated by the direction, rate and pattern of the Neotethyan rifting. A new subgenus, Proarcirsa (Schafbergia) subgen. nov., and three new species, namely Ataphrus (Ataphrus) cordevolensis sp. nov., Guidonia pseudorotula sp. nov. and Proarcirsa (Schafbergia) zirettoensis sp. nov. are erected.     

Fire,landscape change and models of small mammal habitat suitability at multiple spatial scales

Fire is an important process in many ecosystems, but inappropriate fire regimes can adversely affect biodiversity. We identified a naturally flammable heathy woodland ecosystem where the use of planned fire had increased the extent of older vegetation, and quantified the abundance of two small native mammals in this landscape (silky mouse Pseudomys apodemoides and heath rat P. shortridgei). We defined four time‐since‐fire (TSF) categories representing a 2‐ to 55‐year post‐fire sequence and, on the basis of a habitat accommodation model, predicted that both species would select younger age‐classes over older ones. We also predicted that (i) much of the variance in vegetation structure would remain unexplained by TSF and (ii) statistical models of mammal abundance and occupancy including structural variables as predictors would be better than models including TSF. Pseudomys apodemoides selected 17‐ to 23‐year‐old sites, while there was no evidence that P. shortridgei selected a particular TSF category, findings that were inconsistent with our predictions. In line with our predictions, relatively large portions of the variance in vegetation structure remained unexplained by TSF (adjustedr² for four structural variables: 0.24, 0.29, 0.35 and 0.57), and in three of four cases there was strong evidence that statistical models of mammal abundance and occupancy including structural variables were better than those including TSF. At the site scale (hectares), P. shortridgei abundance was positively related to the cover of dead material at the base of Xanthorrhoea plants and at the trap scale (metres), the trapability of both species was significantly related to vegetation volume at 0–20 cm. Our findings suggest that TSF may not be a good proxy for either vegetation structure or species abundance/occupancy.