How Attractive Is the Girl Next Door? An Assessment of Spatial Mate Acquisition and Paternity in the Solitary Cape Dune Mole-Rat, Bathyergus suillus

Behavioural observations of reproduction and mate choice in wild fossorial rodents are extremely limited and consequently indirect methods are typically used to infer mating strategies. We use a combination of morphological, reproductive, spatial, and genetic data to investigate the reproductive strategy of a solitary endemic species, the Cape dune mole-rat Bathyergus suillus. These data provide the first account on the population dynamics of this species. Marked sexual dimorphism was apparent with males being both significantly larger and heavier than females. Of all females sampled 36% had previously reproduced and 12% were pregnant at the time of capture. Post-partum sex ratio was found to be significantly skewed in favour of females. The paternity of fifteen litters (n = 37) was calculated, with sires assigned to progeny using both categorical and full probability methods, and including a distance function. The maximum distance between progeny and a putative sire was determined as 2149 m with males moving between sub-populations. We suggest that above-ground movement should not be ignored in the consideration of mate acquisition behaviour of subterranean mammals. Estimated levels of multiple paternity were shown to be potentially as high as 26%, as determined using sibship and sire assignment methods. Such high levels of multiple paternity have not been found in other solitary mole-rat species. The data therefore suggest polyandry with no evidence as yet for polygyny

Temperature-sensitive mutants of physarum polycephalum: A search for cell cycle mutants.

Physarum polycephalum is a Myxomycete which grows as uninucleate amoebae or multinucleate plasmodia. The aim of this work was to isolate mitotic cycle mutants in an apogamic strain (CLd) of P. polycephalum and to exploit the natural mitotic synchrony of plasmodia for their analysis. The first stage (Chapter 3) involved isolation of temperature-sensitive growth mutants. Such mutants can be isolated by testing amoebal clones or plasmodia derived from amoebal clones. Testing amoebae is much easier, but previous work indicated that most mutations expressed in the plasmodial phase could only be isolated by testing plasmodia. The evidence, however, was equivocal, so both methods were used to isolate mutants, and their merits compared. It was concluded that over 70% of mutants isolated were expressed in both amoebae and plasmodia. Thus, mutations expressed in plasmodia can be isolated by testing amoebae. The second stage (Chapter 4) involved identification of mitotic cycle mutants amongst the temperature-sensitive mutants. Asynchronous cultures of amoebae or plasmodia of the mutants were transferred from permissive to nonpermissive temperature and observed microscopically. Of more than 100 mutants screened, three had altered mitotic indices and one was defective in cell division. The third stage (Chapter 5) involved preliminary characterization of these putative cell cycle mutants. Synthesis of macromolecules in plasmodia, and the DNA contents of plasmodial and amoebal nuclei were measured. These measurements were complemented by time-lapse cinematography of amoebal cultures (Chapter 6). It was concluded that none of the four mutants was completely blocked in cell cycle progression Despite limited success, the results indicated that future attempts to isolate cell cycle mutants of P. polycephalum should be more successful

Genetic Analysis of Resistance to Benzimidazoles in Physarum: Differential Expression of β-Tubulin Genes

Physarum displays two vegetative cell types, uninucleate myxamoebae and multinucleate plasmodia. Mutant myxamoebae of Physarum resistant to the antitubulin drug methylbenzimidazole-2-yl-carbamate (MBC) were isolated. All mutants tested were cross-resistant to other benzimidazoles but not to cycloheximide or emetine. Genetic analysis showed that mutation to MBC resistance can occur at any one of four unlinked loci, benA, benB, benC or benD. MBC resistance of benB and benD mutants was expressed in plasmodia, but benA and benC mutant plasmodia were MBC sensitive, suggesting that benA and benC encode myxamoeba-specific products. Myxamoebae carrying the recessive benD210 mutation express a β-tubulin with noval electrophoretic mobility, in addition to a β-tubulin with wild-type mobility. This and other evidence indicates that benD is a structural gene for β-tubulin, and that at least two β-tubulin genes are expressed in myxamoebae. Comparisons of the β-tubulins of wildtype and benD210 strains by gel electrophoresis revealed that, of the three (or more) β-tubulin genes expressed in Physarum, one, benD, is expressed in both myxamoebae and plasmodia, one is expressed specifically in myxamoebae and one is expressed specifically in plasmodia. However, mutation in only one gene, benD, is sufficient to confer MBC resistance on both myxamoebae and plasmodia

Cell cycle regulation of tubulin RNA level, tubulin protein synthesis, and assembly of microtubules in Physarum. ,L Cell Biol

ABSTRACT The temporal relationship between tubulin expression and the assembly of the mitotic spindle microtubules has been investigated during the naturally synchronous cell cycle of the Physarum plasmodium. The cell cycle behavior of the tubulin isoforms was examined by two-dimensional gel electrophoresis of proteins labeled in vivo and by translation of RNA in vitro. al-, a2-, ß1-, and ß2-tubulin synthesis increases coordinately until metaphase, and then falls, with 02 falling more rapidly than 01. Nucleic acid hybridization demonstrated that a- and ß-tubulin RNAs accumulate coordinately during G2, peaking at metaphase. Quantitative analysis demonstrated that a-tubulin RNA increases with apparent exponential kinetics, peaking with an increase over the basal level of>40-fold. After metaphase, tubulin RNA levels fall exponentially, with a short half-life (19 min). Electron microscopic analysis of the plasmodium showed that the accumulation of tubulin RNA begins long before the polymerization of mitotic spindle microtubules. By contrast, the decay of tubulin RNA after metaphase coincides with the depolymerization of the spindle microtubules