The interaction between inbreeding and high-temperature stress was examined in the cactophilic fruit fly, Drosophila buzzatii. Embryos of four inbreeding levels (F =0, F = 0.25, F = 0.375, F = 0.5) were either maintained at 25°C throughout egg-to-adult development or were exposed to 41.5°C for 110 mm at an age of 20 h. Hatching, larva-to-pupa survival, pupato-adult survival, and egg-to-adult survival were estimated. Heat shock reduced hatching rates, but survival to adulthood for individuals that hatched was unaffected by the heat shock. Inbreeding reduced the proportion of eggs hatching in the 25°C control group only. For larvato-pupa and pupa-to-adult survival there was no interaction between inbreeding and stress. The effect of inbreeding on egg-to-adult survival was stronger in the 25°C control group compared with the group exposed to heat shock. The results imply environmental dependency of inbreeding depression and suggest that stress tolerance may not always be reduced by inbreeding. The thermal microenvironment of cactus rots in the field was assessed by measuring temperatures inside 17 rots. Internal rot temperatures varied with a maximum temperature of 48°C during the day. Selection for temperature tolerance in nature may have depleted genetic variation for this trait limiting the effect of inbreeding on thermal resistance.

Stress tolerance is often measured as a threshold trait, the proportion of a group that survives a defined stress regime. Requirements of large offspring numbers coupled with fitness variation in the surviving cohort limit the use of some standard genetic analyses for estimating heritability. Therefore, we present an isofemale line analysis, which is a modified full-sib design, to estimate heritability of tolerance to heat shock in pretreated Drosophila buzzatii adults. Highly significant levels of genetic variation were found in males and females at the third generation of laboratory rearing, and the intraclass correlations were estimated to be about 0.2 for four independent sets of 25 isofemale lines. The proportion of the variance explained within lines among same-sex replicates, however, was larger than that between replicates of males and females. Because genetic variation was estimated from groups, the error variation required factoring by the group size to estimate heritability, which averaged 0.03. The four most tolerant, four least tolerant and four lines of average tolerance to heat stress in each set were reanalysed after 10-11 generations of rearing at 25°C. Survival in the l3th-l4th generations was positively and significantly associated with survival at generation 3. These comparisons indicate the high repeatability of measurements of heat-shock tolerance.

One hundred and twenty-four specimens of the harbour porpoise, Phocoena phocoena, occurring in inner Danish waters (IDW), the North Sea and West Greenland were analysed to study subdivision into genetically differentiated subpopulations using PCR-amplifled DNA-microsatellites and isozyme markers. Three polymorphic microsatellites, 415/416, 41 7/418 and Igf-I (insulin-like growth factor I) were detected with nine, eight and 15 alleles, respectively, and from a former study two polymorphic isozymes, Mpi-1 and Pgm, with three and two alleles, respectively, were used in the analysis. Overall deviations from the expected Hardy-Weinberg distribution were only observed in the total sample and at a single locus in the North Sea-summer sample and at two loci in the West Greenland sample. Whenever this occurred a surplus of homozygotes was observed, suggesting a Wahlund effect, a null allele or nonrandom mating. The analysis of the genetical population structure showed that harbour porpoises from West Greenland, the North Sea and IDW were three geographically, genetically differentiated populations even though connected through some degree of gene flow. A tendency for females to be more stationary than males was suggested. Furthermore, the population structure suggested a closer relationship between IDW and the North Sea.

No abstract

No abstract