Three primary hypotheses currently prevail for correlations between heterozygosity at a set of molecular markers and fitness in natural populations. First, multilocus heterozygosityfitness correlations might result from selection acting directly on the scored loci, such as at particular allozyme loci. Second, significant levels of linkage disequilibrium, as in recently bottlenecked-and-expanded populations, might cause associations between the markers and fitness loci in the local chromosomal vicinity. Third, in partially inbred populations, heterozygosity at the markers might reflect variation in the inbreeding coefficient and might associate with fitness as a result of effects of homozygosity at genome-wide distributed loci. Despite years of research, the relative importance of these hypotheses remains unclear. The screening of heterozygosity at polymorphic DNA markers offers an opportunity to resolve this issue, and relevant empirical studies have now emerged. We provide an account of the recent progress on the subject, and give suggestions on how to distinguish between the three hypotheses in future studies.

A fragment of the mitochondrial cytochrome b gene of avian malaria (genera Haemoproteus and Plasmodium) was ampli¢ed from blood samples of 12 species of passerine birds from the genera Acrocephalus, Phylloscopus and Parus. By sequencing 478 nucleotides of the obtained fragments, we found 17 di¡erent mitochondrial haplotypes of Haemoproteus or Plasmodium among the 12 bird species investigated. Only one out of the 17 haplotypes was found in more than one host species, this exception being a haplotype detected in both blue tits (Parus caeruleus) and great tits (Parus major). The phylogenetic tree which was constructed grouped the sequences into two clades, most probably representing Haemoproteus and Plasmodium, respectively. We found two to four di¡erent parasite mitochondrial DNA (mtDNA) haplotypes in four bird species. The phylogenetic tree obtained from the mtDNA of the parasites matched the phylogenetic tree of the bird hosts poorly. For example, the two tit species and the willow warbler (Phylloscopus trochilus) carried parasites di¡ering by only 0.6% sequence divergence, suggesting that Haemoproteus shift both between species within the same genus and also between species in di¡erent families. Hence, host shifts seem to have occurred repeatedly in this parasite^host system. We discuss this in terms of the possible evolutionary consequences for these bird species.

A pair of degenerate PCR primers (FAP59/64) was designed from two relatively conserved regions of the L1 open reading frame of most human papillomaviruses (HPV). The size of the generated amplicon was about 480 bp. PCR using these primers was found capable of amplifying DNA from 87 % (65/75) of the HPV types tested, its sensitivity being 1-10 copies for HPV-5, -20 and -30 clones. HPV was found in 63 % (5/8) of tumour samples and in 63 % (5/8) of normal skin biopsies from patients with various cutaneous tumours. HPV-5, HPV-8, HPV-12, HPVvs20-4 and six putatively novel HPV types were identified. No correlation was found to exist between specific HPV and tumour types. Skin surface swab samples from one or more sites on three of four healthy volunteers were found to contain HPV, types 12 and 49 being identified, as well as eight novel HPV types, two of which were also found among the patients. In all, HPV was detected in 75 % (9/12) of those tested, five HPV types and 12 novel candidate types being identified, and 37 % (7/19) of HPV-positive samples were found to manifest more than one HPV type. All the HPV detected manifested high degrees of nucleotide sequence similarity with HPV types associated with skin lesions and epidermodysplasia verruciformis. The overall HPV finding in the skin samples was 50 % (20/40) using the FAP primers as compared to 18 % (7/40) using another PCR test designed for skin types. The results thus suggest the new method to be sensitive and generally applicable for detecting cutaneous HPV.

Recovery from infection is not always complete, and mild chronic infection may persist. Although the direct costs of such infections are apparently small, the potential for any long-term effects on Darwinian fitness is poorly understood. In a wild population of great reed warblers, we found that low-level chronic malaria infection reduced life span as well as the lifetime number and quality of offspring. These delayed fitness effects of malaria appear to be mediated by telomere degradation, a result supported by controlled infection experiments on birds in captivity. The results of this study imply that chronic infection may be causing a series of small adverse effects that accumulate and eventually impair phenotypic quality and Darwinian fitness.

Human papillomaviruses (HPV) are epitheliotropic viruses, with some types suggested to be associated with skin cancer. In this study, swab samples collected from five different sites on the skin of renal transplant recipients, dialysis patients, and age-and sex-matched healthy controls were analyzed for HPV DNA by a newly designed PCR test. Most individuals were found to have asymptomatic HPV infections; more specifically, 94% of the renal transplant patients, 82% of the dialysis patients, and 80% of the healthy controls were positive for HPV DNA. The multiplicity of the HPVs detected was astounding: 20 previously described and 30 putatively new types were identified by cloning and sequencing of 33 samples from 13 individuals. These results demonstrate that normal human skin harbors an array of papillomaviruses, most of them previously unknown.To date, 85 different genotypes of the human papillomaviruses (HPV) have been fully characterized. In addition to being the causative agents of common skin warts, there is evidence that certain types of HPV play a role in the pathogenesis of skin cancer associated with the rare hereditary disease epidermodysplasia verruciformis (EV) (22, 27), and they are therefore designated EV-associated HPV.Renal transplant recipients given immunosuppressive therapy for long periods of time have an increased incidence of cutaneous neoplasia (2,10,29). Also, more than 90% of kidney recipients develop skin warts and 40% develop skin cancer within 15 years of transplantation, a 50-to 100-fold increase compared to the general population (7), and EV-associated HPV types have been found in skin tumors from such patients (5,12,16,21,28). Interestingly, EV HPV types have also been detected in hairs plucked from normal skin of 94% of renal transplant recipients (8) and 67% of healthy controls (9), and in another study (1), 35% of biopsy specimens of normal skin obtained during cosmetic surgery were positive for HPV DNA.In a recent report (20), we presented a PCR test that holds promise as a potent tool for exploring HPV both in skin tumors and in normal skin. In the present investigation, we used the test to study the presence of HPV at various sites on normal skin of both renal patients who were or were not on immunosuppression and matched healthy controls, and there is a serendipitous aspect to the results. MATERIALS AND METHODSSubjects. We studied 52 of about 130 renal transplant recipients being followed up at the outpatient clinic of nephrology of Malmö University Hospital, Malmö, Sweden. The median time since transplantation was 5 years and 2 months, and the range was 2 months to 26 years. Also included in the study were 28 of the 67 patients being treated at the Dialysis Unit; the median length of dialysis treatment was 2 years and 5 months (range, 1 month to 14 years). All of the transplant and dialysis patients were randomly selected, and a sex-and age-matched healthy control was recruited for each of the patients. The age range of the individuals in the three groups was 21 to 80 years,...