Demography and blood genetics of Argentinian Mapuche Indians

The whole Mapuche Indian community of Blancura Centro was covered by a demographic census, with special attention given to variables of genetic interest. Afterwards a sample of it was investigated in relation to 22 genetic systems. The community can be characterized as a young group, with high fertility, but moderate mortality and endogamy. The index of opportunity for selection is relatively low (0.46). The presence of variation at the ABO and Lutheran loci suggests some non-Indian admixture, calculated as 7% in the sample studied. Unusual findings were the absence of L^*NS, low frequency (7%) of L^*MS and high frequency (37%) of L^*Ns. They also showed low frequencies of P^*1 (28%) and DI^*a (3%), but high of HP^*1 (74%). Similarities, but also differences, were noted with previous results obtained in this tribe in Argentina and Chile.     

Demography in stochastic environments. I. Exact distributions of age structure

The steady state distribution of age structure is studied for populations with two age classes and stochastic vital rates. For a serially uncorrelated dichotomic vital rate the distribution of age structure is found analytically to be a singular steplike function; outside a specific region of vital rate values the singular function crosses a threshold to a smooth function. For a vital rate following a correlated two state Markov process the joint distributions of age structure and environment are found analytically to be singular steplike functions; again a threshold marks a transition to a smooth function. For fecundities which are serially uncorrelated but continuously distributed the age structure distribution is obtained as a smooth analytic function for all parameter values. These explicit results have applications to studies of age structure and average growth rate.     

Assessing minimum viable population size: Demography meets population genetics

The discussion of a population's minimum viable size provides a focus for the study of ecological and genetic factors that influence the persistence of a threatened population. There are many causes of extinction and the fate of a specific population cannot generally be predicted. This uncertainty has been dealt with in two ways: through stochastic demographic models to determine how to minimize extinction probabilities; and through population genetic theory to determine how best to maintain genetic variation, in the belief that the ability to evolve helps buffer a population against the unknown. Recent work suggests that these two very different approaches lead to very similar conclusions, at least under panmictic conditions. However, defining the ideal spatial distribution for an endangered species remains an important challenge.     

Demography and genetics of the Krahó and Gorotire Indians of Brazil

Three populations of two Brazilian Ge-speaking groups, the Krahó and Gorotire, have been studied demographically and the results compared with previous investigations on their genetic polymorphisms. The Krahó population is older, more acculturated, and has a smaller sex ratio than the Gorotire. It may also have derived from a larger number of founders. Intertribal marriages occurred with relative frequency among the Krahó, but in the Gorotire the predominant picture is one of exchange with other Cayapo subgroups. The latter have a distribution range roughly 9 × larger than the Krahó. The reproductive histories of the Krahó and Gorotire are similar, leading to equivalent estimates of selection potential. But mortality may have been selectively more important among the Krahó. Wright's fixation index F is of the same order of magnitude in the two groups and intermediate between values obtained among the North American Indian Zuni and the East Indian Bhil. Despite considerable exogamy it showed positive values.     

Levodopa in Huntingtons chorea.

Sixteen patients with Huntington''s chorea were treated for periods as long as 8 months with levodopa. The condition of none of the patients improved; in fact, there appeared to be an exacerbation of chorea and dementia in addition to undesirable behavioural changes. Therefore, future use of levodopa in these patients is not warranted. The postulated association of low homovanillic acid values in cerebrospinal fluid and favourable response to levodopa therapy was not borne out.     

The genetics of phenotypic plasticity I. Heritability

Methods for estimating the genetic component of phenotypic plasticity are presented. In the general case of clonal replicates or full-sibs raised in several environments, the heritability of plasticity can be measured as the ratio of the genotype-environment interaction variance to the total phenotypic variance. In the special case of only two environments plasticity also can be measured as the difference among environments in genotype or family means. In that case, the heritability of plasticity can be measured as either a ratio of variance components or as the slope of a parent-offspring regression. The general measure suffers because no least-square standard errors have been developed, although they can be calculated by maximum-likelihood or bootstrapping techniques. For the other two methods least-square standard errors can be calculated but require very large experiments for statistical significance to be achieved. The heritability measures are compared using data on plasticity of thorax size in response to temperature in Drosophila melanogaster. The heritability estimates are all in close agreement. Models of the evolution of phenotypic plasticity have treated it as a trait in its own right and as a cross-environment genetic correlation. Although the first approach is the one used here, neither one is preferred.     

The genetics of Otosclerosis. I. Distorted sex ratio.

The offspring of 214 otosclerotic x normal couples were investigated, and within these sibships, the segregation of otosclerosis is compatible with autosomal dominant inheritance. However, the overall sex ratio is approximately 0.73, with otosclerosis being approximately 1.8 times more frequent in female offspring. These observations are interpreted as the consequence of selection against males carrying the otosclerosis gene. Elimination of such males occurs only in certain sibships. The remaining families demonstrate a sex ratio approximating unity with similar rates of otosclerosis in both sexes. This selection operates mainly, and possibly only, prenatally.     

Chloroplast genetics of chlamydomonas. I. Allelic segregation ratios

This paper presents allelic segregation data from a series of 16 crosses segregated for nuclear and chloroplast genes. By means of pedigree analysis, segregants of chloroplast markers occurring in the zygote have been distinguished from those occurring in zoospore clones. The genes ac1, ac2, and tm1 showed little if any deviation from 1:1 either in zygotic segregation or in zoospore clones. The genes sm2, ery, and spc showed a significant excess of the allele from the mt (+) parent in zygotes. However, in zoospores, mt( +) excess was seen only when that allele was the mutant (resistant) form but not when it was wild type (sensitive).These results show that the extent of preferential segregation differs in zygotes and in zoospores, and that preferential segregation is influenced by map location and by allele specificity. A comparison of progeny from zygotes mated after 0, 15', 30', and 50' UV irradiation of the mt(+) gametes demonstrated the lack of an effect of UV upon allelic segregation ratios. In total, these results exclude the multi-copy model of chloroplast genome segregation suggested by Gillham, Boynton and Lee (1974) and support the diploid model we have previously proposed (Sager and Ramanis 1968, 1970; Sager 1972).     

Social organization of the spotted hyaena (Crocuta crocuta). I. Demography

A 4-year field study of one group of 60–80 spotted hyaenas (Crocuta crocuta) in Kenya's Masai Mara National Reserve has revealed a form of social system undescribed among carnivores but common among primates. Male juveniles disperse from the natal group around puberty and join a population of nomadic males, wandering widely before settling in a new clan. Adult males frequently leave their adopted clan after a variable period of residence. Females remain in their natal group for life. Thus, the clan comprises several matrilines of related females, while resident adult males originate outside the group. Clans in the Mara tend to be separated by wide buffer zones where prey is scarce and boundary maintenance behaviours are relatively uncommon. Transients are subordinate to residents, but are tolerated by them, in contrast to the more territorial clan system that has been described in Ngorongoro Crater.