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S Creel

Publications and source records attributed to S Creel.

10 recordsLinked to original sources
PubMed2006

Estimating relatedness and relationships using microsatellite loci with null alleles.

Relatedness is often estimated from microsatellite genotypes that include null alleles. When null alleles are present, observed genotypes represent one of several possible true genotypes. If null alleles are detected, but analyses do not adjust for their presence (ie, observed genotypes are treated as true genotypes), then estimates of relatedness and relationship can be incorrect. The number of loci available in many wildlife studies is limited, and loci with null alleles are commonly a large proportion of data that cannot be discarded without substantial loss of power. To resolve this problem, we present a new approach for estimating relatedness and relationships from data sets that include null alleles. Once it is recognized that the probability of the observed genotypes is dependent on the probabilities of a limited number of possible true genotypes, the required adjustments are straightforward. The concept can be applied to any existing estimators of relatedness and relationships. We review established maximum likelihood estimators and apply the correction in that setting. In an application of the corrected method to data from striped hyenas, we demonstrate that correcting for the presence of null alleles affect results substantially. Finally, we use simulated data to confirm that this method works better than two common approaches, namely ignoring the presence of null alleles or discarding affected loci.

Alleles↗
PubMed2001

Deriving dispersal distances from genetic data.

Dispersal is one of the most important factors determining the genetic structure of a population, but good data on dispersal distances are rare because it is difficult to observe a large sample of dispersal events. However, genetic data contain unbiased information about the average dispersal distances in species with a strong sex bias in their dispersal rates. By plotting the genetic similarity between members of the philopatric sex against some measure of the distance between them, the resulting regression line can be used for estimating how far dispersing individuals of the opposite sex have moved before settling. Dispersers showing low genetic similarity to members of the opposite sex will on average have originated from further away. Applying this method to a microsatellite dataset from lions (Panthera leo) shows that their average dispersal distance is 1.3 home ranges with a 95% confidence interval of 0.4-3.0 home ranges. These results are consistent with direct observations of dispersal from our study population and others. In this case, direct observations of dispersal distance were not detectably biased by a failure to detect long-range dispersal, which is thought to be a common problem in the estimation of dispersal distance.

Animal Migration↗
PubMed2001

Patterns of population subdivision, gene flow and genetic variability in the African wild dog (Lycaon pictus).

African wild dogs are large, highly mobile carnivores that are known to disperse over considerable distances and are rare throughout much of their geographical range. Consequently, genetic variation within and differentiation between geographically separated populations is predicted to be minimal. We determined the genetic diversity of mitochondrial DNA (mtDNA) control region sequences and microsatellite loci in seven populations of African wild dogs. Analysis of mtDNA nucleotide diversity suggests that, historically, wild dog populations have been small relative to other large carnivores. However, population declines due to recent habitat loss have not caused a dramatic reduction in genetic diversity. We found one historical and eight recent mtDNA genotypes in 280 individuals that defined two highly divergent clades. In contrast to a previous, more limited, mtDNA analysis, sequences from these clades are not geographically restricted to eastern or southern African populations. Rather, we found a large admixture zone spanning populations from Botswana, Zimbabwe and south-eastern Tanzania. Mitochondrial and microsatellite differentiation between populations was significant and unique mtDNA genotypes and alleles characterized the populations. However, gene flow estimates (Nm) based on microsatellite data were generally greater than one migrant per generation. In contrast, gene flow estimates based on the mtDNA control region were lower than expected given differences in the mode of inheritance of mitochondrial and nuclear markers which suggests a male bias in long-distance dispersal.

Africa↗
PubMed1998

Birth order, estrogens and sex-ratio adaptation in African wild dogs (Lycaon pictus).

Because the sex of mammals is chromosomally determined, populations generally produce a similar proportion of males and females. However, it has been recognized for more than century that individuals might increase their fitness by over-producing offspring of one sex, under certain conditions. Small biases in the secondary sex ratio are seen in many vertebrates. Here, we report that the sex ratio of primiparous African wild dogs (Lycaon pictus) is strongly biased in favor of sons (63%), while multiparous females produce an excess of daughters (64%). The direction of these biases is predicted by individual females' need for subordinate helpers. For humans, elevated estrogens have been hypothesized to bias the secondary sex ratio toward males. Consistent with this hypothesis, primiparous female wild dogs had basal estrogen levels double those of multiparous females.

Animals↗
PubMed1997

Serosurvey for selected viral diseases and demography of African wild dogs in Tanzania.

African wild dogs (Lycaon pictus) are endangered, with only 3,000-5,000 remaining in the wild. It is believed that wild dogs are unusually vulnerable to viral diseases, particularly rabies and canine distemper (CDV). However, canine distemper has been confirmed by laboratory diagnosis in only one free-living wild dog. The 43,000 km2 Selous Game Reserve (SGR; Tanzania) holds approximately 900 adult wild dogs. In a study area of 2,600 km2, the population maintained high density (> or = 1 dog/20.5 km2) from 1991 to 1996. The population was stable, varying 18% below and 9% above the mean density over the 6-yr period. Serum samples (n = 22) collected over 3 yr showed that most individuals were exposed to CDV (59%:95% confidence interval = 43-76% seropositive) and canine parvovirus (68%:95% CI = 54-81% seropositive), although none were seropositive for rabies (0%:95% CI = 0-17%). CDV titers were positively related to age, with no seropositive dogs younger than 1.9 yr. At least five of 13 dogs positive for CDV seroconverted during the study. Dogs with high CDV titers did not survive better in the years after sampling (mean survival +/- SE for those that died = 638 +/- 92 days,). Variation in mean litter size was inversely related to CPV exposure in the SGR and elsewhere. Annual mortality rates were low in comparison to other populations for all age classes (pups: 31 +/- 8%, n = 127, yearlings: 22 +/- 10%, n = 93, adults: 20 +/- 6%, n = 235). Annual mortality rates fluctuated little between 1992 and 1996. These data show that wild dog populations, like those of other canids, can remain stable and demographically healthy despite exposure to CDV and CPV.

Animals↗
PubMed1990

How to measure inclusive fitness.

Although inclusive fitness (Hamilton 1964) is regarded as the basic currency of natural selection, difficulty in applying inclusive fitness theory to field studies persists, a quarter-century after its introduction (Grafen 1982, 1984; Brown 1987). For instance, strict application of the original (and currently accepted) definition of inclusive fitness predicts that no one should ever attempt to breed among obligately cooperative breeders. Much of this confusion may have arisen because Hamilton's (1964) original verbal definition of inclusive fitness was not in complete accord with his justifying model. By re-examining Hamilton's original model, a modified verbal definition of inclusive fitness can be justified.

Animals↗