Biomedical subjects

S D Albon

Publications and source records attributed to S D Albon.

At least 19 recordsLinked to original sources

PubMed2006

Low-level parasitic worm burdens may reduce body condition in free-ranging red deer (Cervus elaphus).

Regulation of ungulate populations by parasites relies on establishing a density-dependent relationship between infection and vital demographic rates which may act through the effect of parasites on body condition. We examine evidence for parasite impacts in 285 red deer (Cervus elaphus) harvested during 1991 and 1992 on the Isle of Rum. In the abomasa, prevalence of nematodes was 100% and the most abundant genus observed were Ostertagia species, however, mean intensity of infection was low (less than 1000) relative to other studies. Additional species, also present in low numbers, included Nematodirus spp., Capillaria spp., Cooperia spp., Monieza expanza, Oesophagostomum venulosum and Trichuris ovis. Lungworm (Dictyocaulus spp.) and tissue worm (Elaphostronygylus cervi) larvae were also observed in faecal samples. There was no evidence for acquired immunity to abomasal nematodes. Despite low levels of infection, both adult male and female deer showed significant negative correlation between indices of condition (kidney fat index, dressed carcass weight and larder weight) and intensity of Ostertagia spp. infection. However, there was no evidence that pregnancy rate in females was related to intensity of infection. For calves, there was no relationship between body condition and intensity of infection. The apparent subclinical effects of low-level parasite infection on red deer performance could alternatively be due to animals in poorer nutritional state being more susceptible to infection. Either way the results suggest that further studies of wild populations are justified, in particular where high local host densities exist or alternative ungulate hosts are present, and, where experimental treatments are tractable.

Abomasum↗

PubMed2005

Sex ratio variation in gastrointestinal nematodes of Svalbard reindeer; density dependence and implications for estimates of species composition.

Estimates of the intensity and abundance of species provide essential data for ecological, evolutionary and epidemiological studies of gastrointestinal nematode communities. These estimates are typically derived from the species composition of adult males when only males have readily scorable species-specific morphological traits. Such estimation assumes that all species in the community have the same adult sex ratio. We evaluated this assumption for the trichostrongyle nematodes Ostertagia gruehneri and Marshallagia marshalli in infracommunities in Svalbard reindeer by identifying to species adult females using a polymerase chain reaction assay. The proportion of males was found to be slightly higher in O. gruehneri than in M. marshalli. Evidence for seasonal variation and density dependence in the adult sex ratio was only found for O. gruehneri. Possible demographic mechanisms for such sex ratio variation are discussed, and stochastic models that generate density-dependent sex ratios proposed. Sex ratio variation caused substantial bias in some male-based estimates of intensity of infection, while substantial and consistent bias in estimates of abundances was only evident in late winter samples. Our results suggest that estimating sex ratios can be particularly important in individual host level studies of nematode species of low abundance.

Animals↗

PubMed2002

The role of parasites in the dynamics of a reindeer population.

Even though theoretical models show that parasites may regulate host population densities, few empirical studies have given support to this hypothesis. We present experimental and observational evidence for a host-parasite interaction where the parasite has sufficient impact on host population dynamics for regulation to occur. During a six year study of the Svalbard reindeer and its parasitic gastrointestinal nematode Ostertagia gruehneri we found that anthelminthic treatment in April-May increased the probability of a reindeer having a calf in the next year, compared with untreated controls. However, treatment did not influence the over-winter survival of the reindeer. The annual variation in the degree to which parasites depressed fecundity was positively related to the abundance of O. gruehneri infection the previous October, which in turn was related to host density two years earlier. In addition to the treatment effect, there was a strong negative effect of winter precipitation on the probability of female reindeer having a calf. A simple matrix model was parameterized using estimates from our experimental and observational data. This model shows that the parasite-mediated effect on fecundity was sufficient to regulate reindeer densities around observed host densities.

Animal Diseases↗

PubMed2002

The population dynamics of Ostertagia gruehneri in reindeer: a model for the seasonal and intensity dependent variation in nematode fecundity.

The gastrointestinal nematode Ostertagia gruehneri is a parasite of reindeer that can have a significant impact on host population dynamics. To gain a better understanding of the population dynamics of O. gruehneri, we parameterise a model for its fecundity that describes the observed seasonal and intensity dependent pattern of faecal egg counts well. The faecal egg count model is combined with a model for the seasonal faecal production rate of Svalbard reindeer to obtain quantitative estimates of the fecundity of O. gruehneri. The model is used to evaluate the relative contribution to pasture contamination of variation in the abundance of O. gruehneri and variation in reindeer densities. It is concluded that due to the intensity dependence in nematode fecundity, variation in reindeer population densities is likely to be the most important of these factors for pasture contamination.

Animals↗

PubMed2002

Microsatellite DNA evidence for genetic drift and philopatry in Svalbard reindeer.

Mainland populations of Arctic reindeer and caribou Rangifer tarandus often undergo extensive movements, whereas populations on islands tend to be isolated and sedentary. To characterize the genetic consequences of this difference, levels of genetic diversity and subdivision of Svalbard reindeer (R. t. platyrhynchus) from two adjacent areas on Nordenskjiöldland, Spitsbergen were estimated using data from up to 14 microsatellites. The mean number of alleles per locus in Svalbard reindeer was 2.4 and mean expected heterozygosity per locus was 0.36. The latter value was significantly lower than in Canadian caribou and Norwegian reindeer but higher than in some other cervid species. Large samples of females (n = 743) and small samples of males (n = 38) from two sites approximately 45 km apart showed genetic subdivision, which could be due to local population fluctuations or limited gene flow. To our knowledge, this is the first study to report significant differentiation at microsatellite loci in Rangifer at such short geographical distances. Neither population showed genetic evidence for recent population bottlenecks when loci unbiased with respect to heterozygosity were analysed. In contrast, false signals of a recent bottleneck were detected when loci upwardly biased with respect to heterozygosity were analysed. Thus, Svalbard reindeer appeared to conform to the paradigm of island populations made genetically depauperate by genetic drift.

Alleles↗

PubMed2001

Age, sex, density, winter weather, and population crashes in Soay sheep.

Quantifying the impact of density, extrinsic climatic fluctuations, and demography on population fluctuations is a persistent challenge in ecology. We analyzed the effect of these processes on the irregular pattern of population crashes of Soay sheep on the St. Kilda archipelago, United Kingdom. Because the age and sex structure of the population fluctuates independently of population size, and because animals of different age and sex respond in different ways to density and weather, identical weather conditions can result in different dynamics in populations of equal size. In addition, the strength of density-dependent processes is a function of the distribution of weather events. Incorporating demographic heterogeneities into population models can influence dynamics and their response to climate change.

Aging↗

PubMed2001

Contrasting regulation of fecundity in two abomasal nematodes of Svalbard reindeer (Rangifer tarandus platyrhynchus).

Stability of trichostrogylid populations indicates that some form of density-dependent regulation occurs which could act through fecundity. We present evidence for intraspecific density-dependent effects in 1 of 2, dominant, abomasal nematodes species (Ostertagia gruehneri) of Svalbard reindeer (Rangifer tarandus platyrhynchus). We found evidence in O. gruehneri, for density-dependent regulation of female worm length in April, July and October 1999. However, it is only in July that female worm length explains the variation in the number of eggs in utero which is also related to egg production per female worm only in this month and not at other times of the year. The seasonal pattern in faecal egg output in this species focuses egg production in the summer months when conditions are favourable to transmission. In contrast, we found no evidence in the other common species (Marshallagia marshalli) for density-dependent regulation of female worm length during or the number of eggs in utero. Faecal egg output in M. marshalli was positively related to worm burden but not to the mean number of eggs in utero. Neither inter-specific interactions nor host body condition appeared to influence worm fecundity. The contrasting patterns of density-dependent regulation of fecundity provides further evidence for divergent life-histories in this nematode community.

Abomasum↗

PubMed2000

Identification by polymerase chain reaction (PCR) of Marshallagia marshalli and Ostertagia gruehneri from Svalbard reindeer.

A polymerase chain reaction (PCR) assay to identify two common abomasal nematodes Marshallagia marshalli and Ostertagia gruehneri of Svalbard reindeer was developed. Species-specific PCR primers were designed from internal transcribed spacer (ITS)-2 sequences of rDNA and validated using morphologically identified adult male and female nematodes. Using the species-specific primers, a 110 bp fragment was amplified from M. marshalli and its minor morph Marshallagia occidentalis and a 149 bp fragment was amplified from Ostertagia gruehneri and its minor morph Ostertagia arctica. No PCR products were amplified from the third rare species, Teladorsagia circumcincta, or DNA from the reindeer host. The assay provides a useful tool to estimate species composition for both sexes in this nematode community.

Abomasum↗

PubMed2000

Life-history strategies and population dynamics of abomasal nematodes in Svalbard reindeer (Rangifer tarandus platyrhynchus).

The observation that the total abundance of adult nematodes in the abomasum of Svalbard reindeer increases between October and April suggests adaptation to cope with the Arctic winter. Here we investigate the extent to which selection has led to similar life-history strategies in the 3 most numerous trichostrongyle species. The life-histories are found to differ markedly. We use flexible statistical models for the abundance and dispersion of parasites in the host population. One of the taxa, Marshallagia marshalli, was most abundant and had its highest egg output in the winter. In contrast, the abundance of the most common taxa, Ostertagia gruehneri, m. gruehneri was stable or declined from autumn to late winter, and the closely related taxa, O. gruehneri, m. arcticus, showed a similar over winter drop. The faecal egg output of these 2 taxa was highest in summer, as found in temperate trichostrongyle species. Despite the apparent contamination of summer pastures with O. gruehneri, calves showed negligible burdens until their second summer and the abundance of infection reached an asymptote within their third year. In contrast, the abundance of M. marshalli in calves showed a rapid increase over the first summer and by late winter was similar to peak levels found in adults (8000 worms). This increase could not be accounted for by the developing abomasum larvae population and is therefore evidence for transmission over the winter for this taxa. While M. marshalli showed little between-year variation, O. gruehneri showed 2-fold fluctuation in the abundance of infection. O. gruehneri may therefore play a role in the fluctuating population dynamics of the host. Since there was no apparent decline in abundance with host age in any of the 3 taxa there was no evidence of reindeer mounting an immune response.

Abomasum↗

PubMed1999

Population density affects sex ratio variation in red deer.

Many mammal populations show significant deviations from an equal sex ratio at birth, but these effects are notoriously inconsistent. This may be because more than one mechanism affects the sex ratio and the action of these mechanisms depends on environmental conditions. Here we show that the adaptive relationship between maternal dominance and offspring sex ratio previously demonstrated in red deer (Cervus elaphus), where dominant females produced more males, disappeared at high population density. The proportion of males born each year declined with increasing population density and with winter rainfall, both of which are environmental variables associated with nutritional stress during pregnancy. These changes in the sex ratio corresponded to reductions in fecundity, suggesting that they were caused by differential fetal loss. In contrast, the earlier association with maternal dominance is presumed to have been generated pre-implantation. The effects of one source of variation superseded the other within about two generations. Comparison with other ungulate studies indicates that positive associations between maternal quality and the proportion of male offspring born have only been documented in populations below carrying capacity.

Adaptation, Physiological↗

PubMed1999

Comparison of plasma progesterone, transrectal ultrasound and pregnancy specific proteins (PSPB) used for pregnancy diagnosis in reindeer.

The study aimed to compare plasma progesterone concentrations, rectal ultrasonography and plasma concentrations of pregnancy-specific protein B (PSPB) used for pregnancy diagnosis in reindeer. A total of 1,595 blood plasma samples were collected between 1991 and 1996 from 3 semidomestic reindeer (Rangifer tarandus tarandus) herds on the Norwegian mainland (Magerøy, Sørøy, Filefjell) and from 92 wild Svalbard reindeer (Rangifer tarandus platyrhynchus). Samples were collected between January and late April. Plasma levels of progesterone and PSPB were measured and used as indicators of pregnancy. In addition, animals from the Filefjell herd and the Svalbard reindeer were investigated using transrectal ultrasound. The results showed that plasma progesterone lower than 7 nmol l-1 rarely occurs in females diagnosed pregnant either by ultrasound or by observing a calf at foot 7 months after blood sampling. A very good agreement was found between plasma progesterone and PSPB when used for pregnancy diagnosis. On the Norwegian mainland, but not to the same extent on Svalbard, a high proportion of females with a high progesterone concentration was diagnosed not pregnant by ultrasound. This probably reflects a high rate of false negative diagnoses by the ultrasound method rather than false positives in the progesterone analysis.

Animals↗

PubMed1998

Microsatellites reveal heterosis in red deer.

The fitness consequences of inbreeding and outbreeding are poorly understood in natural populations. We explore two microsatellite-based variables, individual heterozygosity (likely to correlate with recent inbreeding) and a new individual-specific internal distance measure, mean d2 (focusing on events deeper in the pedigree), in relation to two measures of fitness expressed early in life, birth weight and neonatal survival, in 670 red deer calves (Cervus elaphus) born on the Isle of Rum between 1982 and 1996. For comparison, we also analyse inbreeding coefficients derived from pedigrees in which paternity was inferred by molecular methods. Only 14 out of 231 calves (6.1%) had non-zero inbreeding coefficients, and neither inbreeding coefficient nor individual heterozygosity was consistently related to birth weight or neonatal survival. However, mean d2 was consistently related to both fitness measures. Low mean d2 was associated with low birth weight, especially following cold Aprils, in which foetal growth is reduced. Low mean d2 was also associated with low neonatal survival, but this effect was probably mediated by birth weight because fitting birth weight to the neonatal survival model displaced mean d2 as an explanatory variable. We conclude that in the deer population fitness measures expressed early in life do not show evidence of inbreeding depression, but they do show evidence of heterosis, possibly as a result of population mixing. We also demonstrate the practical problems of estimating inbreeding via pedigrees compared with a direct marker-based estimate of individual heterozygosity. We suggest that, together, individual heterozygosity and mean d2, estimated using microsatellites, are useful tools for exploring inbreeding and outbreeding in natural population.

Age Factors↗

PubMed1997

Blastocyst development and conceptus sex selection in red deer Cervus elaphus: studies of a free-living population on the Isle of Rum.

Skewing of the sex ratio at birth occurs in red deer in response to dominance status, with dominant hinds giving birth to a higher proportion of male calves than subordinates. To investigate the physiological basis for this phenomenon, reproductive tracts were collected from red deer during a cull for management purposes carried out on the Island of Rum, Scotland. Blastocysts were flushed from the uterus and sexed by polymerase chain reaction using Y chromosome-specific primers. Concentrations of interferon (measured as antiviral activity) in uterine flushings, of oxytocin receptors in endometrium, and of progesterone in jugular venous blood were measured, and ovarian morphology was recorded. Times of mating were determined retrospectively from calving dates observed during the following spring. Changes in uterine and fetal weights and sizes confirmed the degree of reproductive synchrony. Intervals between stages of blastocyst development (spherical, tubular, filamentous, and attached) derived from the observed incidence of each form showed that approximate times of blastocyst elongation and attachment were 13 and 30 days after conception, respectively. Hinds carrying male blastocysts were in better body condition (higher kidney fat weights, P = 0.025) than those carrying females. Interferon was detectable in uterine flushings from 1 of 7 hinds carrying early filamentous blastocysts and 5 of 12 hinds carrying late filamentous blastocysts, but in no case where the blastocysts were male (P = 0.035). Oxytocin receptor concentrations in caruncular endometrium (but not in intercaruncular endometrium) were lower in pregnant than in nonpregnant hinds (P < 0.05), but there was no correlation with interferon concentrations in flushings. Corpora luteal concentrations of oxytocin ranged from 1.8 to 51.2 micrograms/g tissue and declined with advancing blastocyst development. The data are consistent with the hypothesis that sexual dimorphism in trophoblast interferon production leads to differential blastocyst loss and hence to sex ratio skewing on the basis of dominance status.

Animals↗

PubMed1997

Behavioral dominance and corpus luteum function in red deer Cervus elaphus.

Times of the ovulatory LH surge and characteristics of the rise in circulating progesterone concentrations after ovulation in red deer hinds were investigated in relation to each animal's dominance status. Observations were made during the 1992 (experiment 1) and 1993 (experiment 2) breeding seasons, while the same 12 hinds were held in a pen in the absence of a stag. Ovulation was synchronized by administration of progesterone followed by luteolytic prostaglandin F2 alpha analogue. Social status was determined for each hind by noting dyadic agonistic interactions during the period of progesterone treatment. Hinds were weighed before and after the experiments. Time of onset of estrus (lordosis) was recorded while handling at 3-hr intervals (for 81 hr in experiment 1; 96 hr in experiment 2) after progesterone withdrawal, and blood samples were collected at these times to characterize the preovulatory LH surge. Subsequently, daily blood samples were collected for up to 11 days for measurement of progesterone concentrations. There was a tendency for weight change to be related to dominance status in experiment 1 and this was significant in experiment 2 (p < 0.01). The rate of increase in circulating progesterone concentration after ovulation was related to status (data of experiments 1 and 2 combined; p < 0.02), but was not correlated with the time of estrus or with the time or height of the LH surge. A third experiment (carried out in 1993), when the same hinds were kept with a stag after induced ovulation, showed that time of estrus (mating) was not related to dominance status. The data suggest that corpus luteum function is affected by social status. The results are discussed in the context of mechanisms by which dominance status influences the sex of a hind's calves.

Animals↗

PubMed1996

The maintenance of genetic polymorphism in small island populations: large mammals in the Hebrides.

Conventionally, small populations living on islands are expected to lose genetic variation by drift. Fluctuations in population size, combined with polygynous mating systems, are expected to contribute to the process by increasing sampling effects on genetic variation. However, in individually monitored populations of Red deer on Rum and Soay sheep on St. Kilda, which experience fluctuations in population size, two processes have been identified which mitigate loss of genetic variation. First, in a number of examples, population reductions are associated with selection. Selection may be in favour of heterozygotes, or, as we have documented in several cases, it may fluctuate in direction temporally. Second, in Soay sheep, in which mortality over population crashes is male-biased, ostensibly leading to low effective numbers of males, molecular studies show that there are systematic changes in the reproductive success of young males, and in variance in male success, that broaden genetic representation compared with expectation.

Adenosine Deaminase↗

PubMed1996

Density-dependent selection in a fluctuating ungulate population.

Despite considerable theoretical interest no direct examples of density-dependent natural selection acting on simple polymorphic variation have been documented in a natural population. Here we show that the magnitude of selective differences in survival between phenotypes in two conspicuous polymorphisms of coat colour and horn type in Soay sheep Ovis aries living on St Kilda, Scotland are associated with marked changes in population density. Selection is strongest in years of high density but weak in years of low density. In addition to direct observations of density-dependent 'soft' selection in a natural population, the analysis revealed that the level of overcompensatory mortality (responsible for promoting population instability) was higher after accounting for genetic variation in the coat and horn morph traits. The results emphasize the importance of understanding the interaction between selection and population demography for both genetic and ecological studies of natural populations.

Animals↗

PubMed1995

Molecular genetic variation and individual survival during population crashes of an unmanaged ungulate population.

Theoretical models of the effect of population bottlenecks on genetic variation assume that individuals are removed at random from the population. We investigated this assumption in a naturally regulated, unstable population of Soay sheep (Ovis aries). During rapid population declines or 'crashes', individuals were not removed at random with respect to genotype: we found associations between individual survival and certain genotypes at five polymorphic protein or microsatellite DNA loci (Ada, Got, Tf, MAF18 and OPACAP). Some loci appeared to show simple associations with survival whereas others had more complex interactions with crash year or age: all displayed different patterns of association between the sexes. Simple overdominance was not a general feature of our data; it seems likely that fluctuating selecting, countervailing selection in different fitness components or frequency-dependent selection may explain the pattern and complexity of the associations shown at different loci. Our study cannot distinguish between selection acting at these loci or at other, closely linked loci. However, our empirical study implies that the molecular genetic outcome of population bottlenecks in natural populations does not always follow theoretical expectations based on the random removal of genotypes. Bottlenecks in which individuals are removed at random are distinct from bottlenecks in which there is scope for selection via non-random survival of individuals.

Alleles↗

PubMed1993

Parasite-associated polymorphism in a cyclic ungulate population.

An unmanaged population of Soay sheep living on Hirta, St Kilda, Scotland is persistently unstable, fluctuating between about 600 and 1600 individuals. Population crashes occurring approximately every 3 years are primarily due to winter food shortage. In this paper we show that sheep experimentally relieved of their gastrointestinal nematodes (predominantly Teladorsagia spp.) survived a crash better than matched controls, showing that nematode parasites contribute to the probability that a sheep dies in a crash. We also show that over three successive crashes mortality was significantly different between individuals of the three different genotypes at the diallelic adenosine deaminase locus (Ada). FF animals were most likely to die, SS animals had an intermediate probability of dying, and FS animals were least likely to die. Finally, three independent lines of evidence suggest that nematode burdens differ between the three Ada genotypes. First, in August, heterozygous females are less likely to have nematode eggs in their faeces than homozygous females. Second, at lambing, the periparturient rise in faecal egg count was highest in homozygous FF individuals. Finally, during the Autumn mating season, heterozygous males has lower faecal egg counts than homozygotes, although this relation was complicated by interactions with year and age of male. These results are consistent with the idea that Ada allele frequencies are maintained in the sheep population by parasite-associated selection.

Adenosine Deaminase↗