High Inter-population Differentiation Research Articles

Allozyme diversity in three endemic species ofCistus(Cistaceae) from the Canary Islands: intraspecific and interspecific comparisons and implications for genetic conservation

Patterns of variation at 13 isozyme loci were examined in 11 populations in three Cistus species strictly endemic to the Canary Islands. Cistus osbaeckiaefolius and C. chinamadensis display low levels of isozyme variation associated with moderate to high interpopulation differentiation, which probably arose through historical bottlenecks in a landscape of habitat fragmentation, grazing, and human influence. By contrast, C. symphytifolius ranks among the subset of narrow endemics with high levels of isozyme variation and features different degrees of genetic structuring that are closely associated with taxonomic ascription. Low interpopulation differentiation in var. leucophyllus is possibly a reflection of its recent origin or of moderate levels of gene flow between its populations. High interpopulation differentiation in var. symphytifolius probably arose due to slight ecological differences between populations coupled with low levels of gene flow. Interpretation of neighbor-joining trees in the light of geological data substantiates the hypothesis that C. symphytifolius (or a very close relative) might be the ancestor of the other stands of Cistus in the islands. Conservation implications of our survey are the identification of the two populations of C. chinamadensis with the highest allele and genotype richness for preservation on genetic grounds and advice to prevent artificial gene flow in this taxon lest it might disrupt locally adapted gene combinations. All populations of C. osbaeckiaefolius should be given conservation priority on ecological grounds despite their genetic depauperation.

Low neighbourhood size and high interpopulation differentiation in the endangered shrub Grevillea iaspicula McGill (Proteaceae).

Mating system parameters and genetic diversity were examined for five populations of the endangered shrub Grevillea iaspicula (Proteaceae). Controlled pollinations show that G. iaspicula has an effective self-incompatibility system and little potential for agamospermy. This is reflected in uniformly high multilocus outcrossing rates (tm=0.96-1.00). However, average paternal diversity within open-pollinated sibships is low (rp=0.31-0.54), suggesting that mating within populations is quite restricted. Despite the small size of most populations (four of the five populations studied have fewer than 20 reproductive individuals) the species still possesses moderate to high allelic richness (A=1.6-2.5). Interpopulation genetic differentiation is high (D=0.04-0.32), suggesting that gene flow is limited, even among populations separated by only a few kilometres.

Genetic Diversities of Four Little-Known Species of Malesherbia (Malesherbiaceae) Endemic to the Arid Inter-Andean Valleys of Peru

Few studies of genetic variation have been conducted on plants of the Pacific coastal desert and neighboring Andes of Peru, although the region has many endemic taxa. Enzyme electrophoresis was employed to examine allozyme diversities of four species of the family Malesher-biaceae, an endemic to the arid Andes and coastal desert. One population ofMalesherbia splendens and two ofM. tubulosa, both endemics of the department of Lima, one population ofM. weberbaueri var.weberbaueri, an endemic of the Andean department Huancavelica, and the two Lima populations ofM. scarlatiflora were studied. Fifteen loci were examined for all populations and an additional seven loci were resolved forM. weberbaueri andM. splendens. Malesherbia splendens, which is known from three populations, has a low mean number of alleles per locus (A), proportion of polymorphic loci (P), and expected heterozygosity (Hs) (A=1.214, P=0.214, Hs=0.057).Malesherbia weberbaueri (A=1.231, P=0.154, Hs=0.079) andM. scarlatiflora (A=1.364, P=0.273, Ht=0.083) both have average expected heterozygosities and relatively low mean numbers of alleles per locus and proportions of polymorphic loci. InM. tubulosa, all measures of genetic diversity are high in comparison with other endemics (A=1.818, P=0.364, Ht=0.206).Malesherbia tubulosa has high interpopulation differentiation, whereasM. scarlatiflora has low among-population diversity. The relatively low allozyme diversities, restricted habitats, narrow ranges ofM. splendens andM. weberbaueri, and the morphological similarities of all four species suggest that they evolved recently by founder events. Greater allozyme diversities inM. tubulosa could be attributable to its maintenance of larger populations in a greater variety of habitats.

RECOMBINATION SYSTEM AND POPULATION STRUCTURE IN OENOTHERA.

Reproduction involves one of three recombination systems-outcrossing, selfing, or cloning-or some combination of the three (Fryxell, 1957). How these reproductive modes affect the population structure of a species has been the subject of considerable discussion (Fryxell, 1957; Grant, 1958, 1971; Baker, 1959; Wright, 1969; Levin and Kerster, 1971; Jain, 1976). The theory generated by this discussion predicts that different recombination systems ought to strongly influence how the genetic variation of a species is organized. Patterns of heterozygosity and population differentiation may be influenced by the recombination system (Baker, 1959; Wright, 1969; Levin and Kerster, 1971; Jain, 1976; Lokki, 1976; Brown, 1979). Populations of predominant selfers are expected to have lower levels of heterozygosity and intrapopulation polymorphism, but higher levels of interpopulation differentiation than obligate outcrossers (Wright, 1969; Jain, 1976). Selfing species as a whole are expected to be less heterozygous and polymorphic than outcrossers (Jain, 1976). On the other hand, clonal species should have higher levels of heterozygosity than outcrossing species, both within populations and species-wide, since they can retain mutant alleles by sheltering them from segregation (Lokki, 1976). But, like selfers, clonal species are expected to have low levels of within-population polymorphism and high interpopulation differentiation (Baker, 1959; Levin and Kerster, 1971). The ideal test of these hypotheses would be to compare population structure of three closely related, sympatric species: an obligate outcrosser, a selfer, and a clonal species. However, studies attempting to determine the influence of recombination system on population structure have compared related taxa representing only two reproductive modes; in most cases, the related taxa were allopatric. Comparisons among animals have been those of obligate outcrossing to unisexual species (Parker and Selander, 1976; Atchley, 1977; Parker et al., 1977; Schultz, 1977; Suomalinen et al., 1977). Conversely, students of plant population structure have concentrated mainly on comparing outcrossers with selfers (Solbrig, 1972; Gottlieb, 1973, 1977; Levy and Levin, 1975; Levin, 1978; Brown and Jain, 1979). But no one has yet investigated sympatric congeners, each with one of the three different reproductive modes. A model system for the study of how reproductive mode affects population genetic structure is provided by three closely related, geographically and ecologically sympatric species of Oenothera subsection Raimannia (Stubbe and Raven, 1979): Oenothera grandis Smyth, 0. mexicana Spach, and 0. laciniata Hill. Each of these annuals utilizes a different recombination system: Oenothera grandis is a self-incompatible outcrosser (Cleland, 1968); Oenothera mexicana exhibits a high degree of selfing (Ellstrand, 1978); and Oenothera laciniata is a permanent translocation heterozygote (Cleland, 1968), functionally a clonal species (see Cleland, 1972, for a detailed description of this unusual syndrome). These three species cooccur in disturbed areas of south and central Texas, often in mixed populations (see Ellstrand, 1978 for distribution). The purpose of this study is to determine the population genetic correlates of different re-