Genetic evidence for a family structure in stable social aggregations of the Australian lizard Egernia stokesii.

In this study we used data from six unlinked microsatellite loci to examine stable aggregations of Egernia stokesii, from a population in the southern Flinders Ranges of South Australia. We show that these aggregations are comprised of breeding partners, their offspring from two or more cohorts, and related adults, providing the first genetic evidence of a family structure in any lizard species. Despite this high level of relatedness within aggregations, most breeding pairs were unrelated and partners were less closely related to each other than they were to other potential within-group partners. Where individuals dispersed, both sexes usually moved to social groups close to their natal group. Although both sexes showed natal philopatry, there was some evidence that females in groups were more related than males in groups. These data suggest that an active choice of unrelated partners and male-biased dispersal may be the mechanisms used by E. stokesii to avoid inbreeding within groups.

A low-affinity nucleobase transporter in the protozoan parasite Giardia intestinalis.

A membrane transporter with general affinity for purine and pyrimidine bases has been identified in Giardia intestinalis trophozoites by measuring cellular influx of [3H]adenine, [3H]guanine and [3H]thymine at 0 degrees C. The base transporter is distinct from the thymine/uracil-specific (type 1) and broad-specificity (type 2) nucleoside transporters of G. intestinalis. Influx of each labelled base was retarded by unlabelled bases, with inhibition in the order: hypoxanthine greater than adenine greater than thymine greater than uracil. The IC50 values for these bases (measured for [3H]adenine influx) were 0.46 mM, 1.15 mM, 1.52 mM and 2.28 mM, respectively. Nucleosides did not inhibit base influx (less than or equal to 15% inhibition at 2 mM, a 400-fold molar excess, at which concentration [3H]nucleoside influx was inhibited by greater than 95%). The Michaelis-Menten constant (Km), calculated for adenine and thymine influx at 0 degrees C, was 1.44 +/- 0.08 mM and 1.61 +/- 0.37 mM, respectively, with corresponding Vmax of 383 +/- 16 and 498 +/- 112 pmol min-1 (10(6) cells)-1. The data demonstrate the existence of a low-affinity, facilitative base transporter with no detectable affinity for nucleosides. The inability of uridine or thymidine to significantly reduce the rate of thymine influx indicates that the previously described thymine/uracil-specific (type 1) thymidine transporter cannot transport thymine, despite its affinity for the base.