Single-locus complementary sex determination in the inbreeding wasp Euodynerus foraminatus Saussure (Hymenoptera: Vespidae).

The Hymenoptera have arrhenotokous haplodiploidy in which males normally develop from unfertilized eggs and are haploid, while females develop from fertilized eggs and are diploid. Multiple sex determination systems are known to underlie haplodiploidy, and the best understood is single-locus complementary sex determination (sl-CSD) in which sex is determined at a single polymorphic locus. Individuals heterozygous at the sex locus develop as females; individuals that are hemizygous (haploid) or homozygous (diploid) at the sex locus develop as males. sl-CSD can be detected with inbreeding experiments that produce diploid males in predictable proportions as well as sex ratio shifts due to diploid male production. This sex determination system is considered incompatible with inbreeding because the ensuing increase in homozygosity increases the production of diploid males that are inviable or infertile, imposing a high cost on matings between close relatives. However, in the solitary hunting wasp Euodynerus foraminatus, a species suspected of having sl-CSD, inbreeding may be common due to a high incidence of sibling matings at natal nests. In laboratory crosses with E. foraminatus, we find that sex ratios and diploid male production (detected as microsatellite heterozygosity) are consistent with sl-CSD, but not with other sex determination systems. This is the first documented example of sl-CSD in a hymenopteran with an apparent natural history of inbreeding, and thus presents a paradox for our understanding of hymenopteran genetics.

Artificially increasing scent mark rate increases urogenital gland size in mice Mus musculus.

Male mice produce scent marks by depositing urine throughout their territory. The scent marks contain a number of pheromones and contain major urinary proteins (MUPs). Up to 1 g of these MUPs may be produced everyday. It is therefore likely that scent marking is costly and as such will impact on male fitness. In order to investigate the costs of scent marking, we conducted an experiment where scent marking rate was increased artificially, without changing the social environment (which may have an independent and different effect on both scent marking and physiology), or changing travelling time (such as would occur in a larger territory). Novel objects were introduced every other day (Replace); objects were introduced on day 1 and moved on alternate days (Move); or the mice were left undisturbed (Control). Introducing new objects daily caused a significant increase in scent marking rate, and an increase in the size of both the coagulating gland and the testes compared to the other two conditions. This is likely to be due to increased hormonal activity, which is known to affect these gland sizes. Interestingly, the preputial gland, which produces a number of pheromones, did not differ between the three conditions. There were no differences in male weight, growth rate or condition, indicating that the effect of an increase in scent marking of this magnitude does not have measurable fitness effects.

The Norway rat as a reservoir host of Cryptosporidium parvum.

The potential of Norway rats (Rattus norvegicus) to spread the parasite Cryptosporidium parvum was investigated by examining parasite prevalence in relation to the structure and movements of three permanent rat populations living on farmland in Warwickshire (UK) from October 1994 to March 1997. One population lived among a group of farm buildings housing cattle, while the other two had no contact with livestock, one living around a pond and its outflowing stream and the other on a rubbish tip. Overall, parasite occurrence was 24% (n = 438), but it varied according to body weight (age) with 40% of juveniles (< or =100 g) infected decreasing to 12% for adults >400 g, suggesting that actively breeding populations are potentially more likely to spread the parasite than non-breeding populations. There was no difference in prevalence between the three populations. The parasite was detected in more males (29%) than females (19%). Seasonally, on the livestock farm, prevalence was significantly lower in autumn (10%), but varied little (31-36%) from winter to summer. In contrast, on the arable farm, prevalence peaked in summer (50%) with a trough in winter (6%). Infection in rats appeared to last <67 days. Rats living on the livestock farm had home ranges largely confined to the cattle sheds, thereby maintaining a potential source of infection for livestock if rodent control was not part of a decontamination program. Equally, rats living around the pond on the arable farm provided a source of oocysts to contaminate the pond water, as well as being able to carry the parasite to nearby farm buildings or even to neighboring farms.

Symptom-dependent taste aversion induced by an anticoagulant rodenticide in the brown rat (Rattus norvegicus).

In a series of 3 experiments with different experimental paradigms, feeding patterns of laboratory rats (Rattus norvegicus) were monitored in 2-choice feeding tests after intubation with a sublethal dose of an anticoagulant rodenticide. We report for the first time that contrary to accepted wisdom, anticoagulants can induce taste aversions. Furthermore, we report behavioral symptoms within the 1st day after dosing. Our data suggest that the taste aversion is induced through an inhibition of the vitamin K cycle and is transient, attenuating over the same period as the levels of vitamin K-dependent proteins return to normal. Because the taste aversion is expressed most strongly when symptoms are most pronounced and is not expressed after symptoms have disappeared, we term this novel form of control symptom-dependent taste aversion.

Sibling matings in a hunting wasp: adaptive inbreeding?

Upon emergence as adults, brothers of Euodynerus foraminatus compete among themselves for the microterritory around their natal nest. The winning male inseminates his sisters as they emerge several days later. Unlike most species that inbreed in a similar fashion, both sexes of this common wasp are strong fliers. The possibility is raised that siblings may be preferred as mates even when out-breeding is possible.