The distribution and biology of Sepsidae (Diptera) in upland regions of northern England

Abstract. 1. A survey of the distribution of Sepsidae was made over 2 years at forty-two sites in northern England. Material was collected by pitfall trapping and in sweep-net samples.
2. With the exception of a single specimen taken in a pasture, only members of the genus Sepsis were found and three species, S.cynipsea, S.orthocnemis and S.neocynipsea , occurred at most sites. The numbers of S.cynipsea were greater than S.orthocnemis at the great majority of sites. S.neocynipsea was the least abundant of the three species but occurred over the whole altitudinal range and formed a greater proportion of the catch at higher sites.
3. It is suggested that the three commonest species use sheep dung as their main larval habitat in upland areas. Cow dung (the commonest reported larval habitat of Sepsis spp.) did not occur on any of the main sites studied. No sepsids were reared from red grouse droppings.
4. There was no difference in the species composition on peat and grassland sites but almost 4 times as many sepsids were caught on the peat moor than on the neighbouring grasslands.
5. There was a marked bimodal distribution of adults with a trough of captures in June and July. This is in contrast to data from other studies, at low altitudes, and is probably the result of there being only two generations per year in upland areas rather than four (or more) in warmer conditions.     

Moisture relationships of the high arctic collembolan Onychiurus arcticus

Abstract. Rates of desiccation, rehydration and survival, under conditions of 0 and 100% relative humidity, were investigated in the high arctic collembolan Onychiurus arcticus (Tullberg) over a range of temperatures from -3 to 10C. Desiccation, measured over 4h in a dry environment, was rapid and highly significantly correlated with saturated vapour pressure deficit (SVPD). At 10C animals lost over 60% of body moisture in under 1h. Under moist conditions body weight remained constant. Survival, measured over 4h under dry conditions, showed a highly significant negative correlation with SVPD across the range of temperatures. Survival in moist controls was 100%. Partially desiccated animals were able to rehydrate using free water or moisture from a saturated atmosphere, but uptake of the former was faster. Rates of water uptake were around 30 times slower than rates of loss through desiccation. Animals given free water regained initial weights in 24-144h, dependent on temperature. Uptake rates of free water, measured over the time necessary fully to rehydrate, were highly significantly correlated with temperature, whereas those for atmospheric moisture were not. Over the time scales used in the experiments, three linear regression equations accurately predict rates of desiccation, rehydration and survival from SVPD or temperature. Ecological adaptation by O.arcticus to the highly contrasting climatic environments of the arctic summer and winter seasons is discussed in the context of climate change.     

Genotype by environment interactions in winter survival in red deer

1. The extent to which environmental heterogeneity interacts with genetic hetero geneity to affect individual fitness within populations has the potential to affect the dynamics of natural populations and the amount of genetic variation maintained in natural populations, yet is a relatively poorly investigated topic in either ecology or evolutionary biology.
2. Many individual-based studies are precluded from such investigations by the practical problems of measuring heritability of traits affecting fitness and the difficulties of experimental manipulation of the study population. One way of demonstrating how commonly genotype by environmental interactions affect fitness, though not their overall importance in determining fitness, is to investigate fitness in a population subdivided by genotype at one or more marker loci.
3. We analyse data on calf winter survival from a population of red deer from the Isle of Rum, Scotland. Data on individual survival, environmental fluctuations and genotype at 13 loci were collected from 1982 to 1994.
4. We found associations between survival over the first winter of life and calf genotype at two out of three allozyme loci and five out of 10 microsatellite loci. All of the results remained significant under randomization tests. Other genotypes that initially appeared to have an association with survival were rejected when bootstrapped, usually due to insufficient data or anomalies in the data.
5. Our results suggest that associations between fitness and genotype are common. Five out of the seven associations found involved interactions with environmental variables. Four of these showed density-dependent selection with different genotypes showing high survival at high population size compared to low population size and one interacted with autumn rainfall. In a sixth case, genotype interacted with sex.