An experimental investigation of patch use by female monarch butterflies,Danaus plexippus (L.)

Monarch butterflies, which breed throughout the year in southeastern Queensland, Australia, were studied in four dense milkweed patches during the winter months (June-August) 1983. The percentage of marked females recaptured was measured in each of four 15-day sampling periods. In patches where males were experimentally removed, female recapture rate decreased compared with patches which had the same density reduction but no change in sex ratio. There was a significant correlation between female recapture rate and the proportion of males in samples, but female recapture rate was not correlated with population density, the number of males, the number of females or the proportion of young butterflies in the samples. We propose that females assessed patch quality by the sex ratios, and left a patch sooner if encounter rate with males was low. Since males provide a nutrient ‘reward’ during copulation, they may be a limited resource for females during winter. An alternative interpretation, that females left a patch sooner when female density was higher, was not supported as strongly by the data.     

Microhabitat choice and its role in determining the distribution of the reptile tick Amblyomma vikirri

Abstract A newly described tick species, Amblyomma vikirri, infests two lizard species in the Flinders Ranges of South Australia. Although one of the hosts, Tiliqua rugosa, has a wide distribution, the tick distribution is restricted to a subset of rocky habitats where the other host, Egernia stokesii, lives. Experiments were conducted with unfed ticks, the stage when the tick is waiting for a host and is susceptible to desiccation. Amblyomma vikirri had a significantly stronger preference for rock microhabitats than two other tick species (Aponomma hydrosauri and Amblyomma limbatum) that infest T. rugosa. Unfed Amb. vikirri were also more active than the other two species, and more likely to be in the upper pan of the substrate. At warm temperatures, larvae of Amb. vikirri survived for shorter periods under desiccation stress than larvae of the other two species, although as nymphs Amb. vikirri survived as well or better. The rock crevice microhabitat experienced lower maximum temperatures than other potential, non-rock refuge sites. The behaviour of Amb. vikirri, its susceptibility to desiccation in the larval stage and the relatively benign conditions in the rock crevices may act together to prevent Amb. vikirri establishing populations beyond rock habitat.     

INVESTIGATIONS OF THE ROLE OF MUCUS AND FAECES IN INTERSPECIFIC INTERACTIONS OF TWO LAND SNAILS

A previous report (Smallridge & Kirby, 1988) showed interspecificcompetition between the two land snails Theba pisana and Cernuellavirgata and suggested the mechanism of competition may be thatheterospecific mucus and excrement inhibits activity. We describea series of experiments in which we could find no consistentevidence for any short-term inhibition of activity in the presenceof heterospecific mucus. Furthermore snails did not consistentlyavoid mucus-treated surfaces or mucus-coated food. Cernuellastopped at and fed from snail faeces (both conspecific and heterospecific)more than did Theba. This suggests an alternate mechanism forinterspecific competition. (Received 9 April 1992; accepted 9 June 1992)     

Lack of reproductive isolation between populations of the grasshopper Myrmeleotettix maculatus across a steep cline in B-chromosome frequency

The rapid cline in B-chromosome frequency in populations of the grasshopper Myrmeleotettix maculatus in East Anglia, reported by Hewitt & Brown (1970), has not been satisfactorily explained. Test were made of the hypothesis that the cline represented the contact of two groups of populations with differently co-adapted genomes, between which there was reproductive isolation. There was no evidence that females in a cage discriminated between the courtship of males from the same or the opposite side of the cline. Progeny from crosses between populations on opposite sides of the cline showed no reduced survival to hatching, survived to adulthood and had normal meiosis. Thus the evidence available does not support the hypothesis that the cline is the interface of two incompatible genomes. The problems of other models accounting for the cline are discussed.     

Joint Report of the Third International Workshop on Lymphocyte Alloantigens of the Horse, Kennett Square, Pennsylvania, 25–27 April 1984

Summary. The Third International Workshop on Lymphocyte Alloantigens of the Horse was held on 25–27 April 1984 in Kennett Square, Pennsylvania. Twelve laboratories from five countries participated. The principal purpose of this Workshop was to determine the phenotypic and gene frequencies of the 10 equine lymphocyte antigens (ELA) and a non-ELA lymphocyte antigen, ELY-2.1, in several breeds of horse. A total of 86 alloantisera characterized in previous workshops were tested against lymphocytes from 1179 horses. In addition, several experimental antisera were also tested against the same panel of lymphocytes. As a result of analysis of these data, the Workshop recognized two new equine lymphocyte alloantigens: W11 of the ELA system, and ELY-1.1, an antigen not linked to the ELA system.