Temporal patterns of geographic parthenogenesis in a freshwater snail

Geographic parthenogenesis describes the observation that parthenogenetic organisms tend to occupy environments different from those of their close, sexually reproducing relatives. These environments are often described as extreme or disturbed habitats. We examined whether patterns of geographical parthenogenesis persist over time, by conducting a 3-year life-history survey and comparing two very proximate habitats of the freshwater snail Melanoides tuberculata : Nahal Arugot, a desert stream naturally disturbed by flash floods, and Or Ilan, a stable freshwater pond. Both sites occur in a xeric environment and are subject to otherwise similar biotic (e.g. parasites, predators) and climatic conditions. In the stable habitat, male frequencies and snail densities were significantly higher than in the disturbed one, whereas infection levels, mean embryo counts, and water temperatures were similar at both sites. Additionally, male frequencies declined after density decreased, thereby providing evidence for geographical parthenogenesis via reproductive assurance. Infection prevalence was very low regardless of reproduction mode. Although further genetic work is required, the apparent metapopulation structure of M. tuberculata in the Judean desert may be suitable for evaluating other possible explanations of geographical parthenogenesis.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 711–718.     

Land clearing reduces gene flow in the granite outcrop‐dwelling lizard,Ctenophorus ornatus

An important question for the conservation of species dwelling in fragmented habitats is whether changes to the intervening landscape create a barrier to gene flow. Here, we make use of the spatial distribution of the granite outcrop‐dwelling lizard, Ctenophorus ornatus, to compare inferred levels of gene flow between outcrops in a nature reserve with that between outcrops in the adjacent agricultural land. Genetic variation, relatedness and subdivision were compared within groups of individuals from different outcrops similar in size and distance apart at each site. In the agricultural land, we found significantly lower genetic variation within outcrops and greater genetic differentiation between outcrops than in the reserve. Further, the rate at which genetic divergence between outcrops increased over geographical distance was significantly greater in the agricultural land than in the reserve. We also found that individuals were more closely related within outcrops but more distantly related between outcrops in the cleared land. These effects occur over a small spatial scale with an average distance between outcrops of less than five kilometres. Thus, even though land clearing around the outcrops leaves outcrop size unchanged, it restricts gene flow, reducing genetic variation and increasing population structure, with potentially negative consequences for the long‐term persistence of the lizards on these outcrops.     

The beetle tree of life reveals that Coleoptera survived end‐Permian mass extinction to diversify during the Cretaceous terrestrial revolution

Here we present a phylogeny of beetles (Insecta: Coleoptera) based on DNA sequence data from eight nuclear genes, including six single‐copy nuclear protein‐coding genes, for 367 species representing 172 of 183 extant families. Our results refine existing knowledge of relationships among major groups of beetles. Strepsiptera was confirmed as sister to Coleoptera and each of the suborders of Coleoptera was recovered as monophyletic. Interrelationships among the suborders, namely Polyphaga (Adephaga (Archostemata, Myxophaga)), in our study differ from previous studies. Adephaga comprised two clades corresponding to Hydradephaga and Geadephaga. The series and superfamilies of Polyphaga were mostly monophyletic. The traditional Cucujoidea were recovered in three distantly related clades. Lymexyloidea was recovered within Tenebrionoidea. Several of the series and superfamilies of Polyphaga received moderate to maximal clade support in most analyses, for example Buprestoidea, Chrysomeloidea, Coccinelloidea, Cucujiformia, Curculionoidea, Dascilloidea, Elateroidea, Histeroidea and Hydrophiloidea. However, many of the relationships within Polyphaga lacked compatible resolution under maximum‐likelihood and Bayesian inference, and/or lacked consistently strong nodal support. Overall, we recovered slightly younger estimated divergence times than previous studies for most groups of beetles. The ordinal split between Coleoptera and Strepsiptera was estimated to have occurred in the Early Permian. Crown Coleoptera appeared in the Late Permian, and only one or two lineages survived the end‐Permian mass extinction, with stem group representatives of all four suborders appearing by the end of the Triassic. The basal split in Polyphaga was estimated to have occurred in the Triassic, with the stem groups of most series and superfamilies originating during the Triassic or Jurassic. Most extant families of beetles were estimated to have Cretaceous origins. Overall, Coleoptera experienced an increase in diversification rate compared to the rest of Neuropteroidea. Furthermore, 10 family‐level clades, all in suborder Polyphaga, were identified as having experienced significant increases in diversification rate. These include most beetle species with phytophagous habits, but also several groups not typically or primarily associated with plants. Most of these groups originated in the Cretaceous, which is also when a majority of the most species‐rich beetle families first appeared. An additional 12 clades showed evidence for significant decreases in diversification rate. These clades are species‐poor in the Modern fauna, but collectively exhibit diverse trophic habits. The apparent success of beetles, as measured by species numbers, may result from their associations with widespread and diverse substrates – especially plants, but also including fungi, wood and leaf litter – but what facilitated these associations in the first place or has allowed these associations to flourish likely varies within and between lineages. Our results provide a uniquely well‐resolved temporal and phylogenetic framework for studying patterns of innovation and diversification in Coleoptera, and a foundation for further sampling and resolution of the beetle tree of life.     

Changes in the Shape of Leishmania major Promastigotes in Response to Hexoses, Proline, and Hypo-osmotic Stress

Leishmania major promastigotes in late-log phase are generally long and slender, and remain so during a 1 h incubation in buffer without exogenous substrate. When glucose, 2-deoxyglucose, fructose, mannose, or proline are added, the cells become shorter and more rounded. The shape change in response to glucose is complete within 20 min and is reversible upon incubating the cells without substrate. Galactose, 3-O-methylglucose, 6-deoxyglucose, sucrose, maltose, ribose, glycerol, alanine, glutamate or aspartate do not cause the shape change. Decreasing the osmolarity of the medium causes a rounding of the cells similar to that observed in the presence of glucose, and increasing the osmolarity inhibits the shape change in response to glucose. Inhibitors of glucose transport and 2nd messenger analogs do not affect the shape change.     

Morphological and Developmental Studies of the Snake Trypanosome Trypanosoma hydrae Ayala, Atkinson, Vakalis, 1983 in Experimentally Infected Hosts and in Culture

Trypanosoma hydrae from the broad-banded watersnake, Nerodia fasciata confluens, underwent development in the freshwater leech, Placobdella parasitica. Epimastigotes and transitional stages were present only in the crop and gastric caecum. Only one metacyclic form was observed. The potential of leeches as vectors is discussed. Two broad-banded watersnakes were infected by inoculation with culture forms of T. hydrae maintained on NNN medium. Parasitemias varied from 10⁵/ml to 10⁶/ml with dividing forms seen only rarely. A broad and a slender form of T. hydrae are described from the peripheral blood of a watersnake 7 months after an experimental infection.     

The Effect of Dietary Sterol on the Activity of Fatty Acid Desaturases Isolated from Tetrahymena setosa

Tetrahymena setosa has a nutritional requirement for micro amounts of sterol, a requirement which is also satisfied by relatively large amounts of either intact phospholipids or a mixture of unsaturated fatty acids normally found in these ciliates. Three microsomal fatty acyl-CoA desaturases have been isolated from T. setosa and partially characterized. These enzymes which can account for the formation of the majority of the ciliate's unsaturated fatty acids, include: a Δ9, a Δ12 and a Δ6 desaturase which catalyze the transformation of stearoyl-CoA to oleic acid, of oleoyl-CoA to linoleic acid and of linoleoyl-CoA to ?-linolenic acid, respectively. The stearoyl CoA desaturase required NAD (or NADP), ATP and free CoA; the Δ6 and Δ12 desaturases required NADP, but not ATP or CoA. Cellular levels of the three desaturases were highest in mid-logarithmic phase cells and lowest in stationary phase cells. In order to determine if there was a relationship between the sterol requirement and the ability of the organism to desaturate, T. setosa was grown in a synthetic medium supplemented with either cholesterol or a phospholipid which permits growth in the absence of cholesterol, or with both phospholipid and cholesterol. Cells grown with phospholipid alone had only half as much stearoyl-CoA and oleoyl-CoA desaturase activity as cells of identical culture age grown either on cholesterol alone or on cholesterol plus phospholipid.