EMBRYO STRUCTURE AND STORAGE RESERVE HISTOCHEMISTRY IN THE PALM WASHINGTONIA FILIFERA

The seed of Washingtonia filifera (Lindl.) Wendl. is hemispherical and has a smooth testa. The embryo is located on the rounded side of the seed near the raphe. The embryo consists of a prominent single cotyledon, an epicotyl, and a small root apex. The shoot apex is oriented at a right angle to the long axis of the embryo and possesses 2 to 3 leaf primordia. The cotyledon functions as a storage organ and is composed of three cell types with similar ultrastructure. These three types—the parenchyma, protoderm, and procambium—can be distinguished on the basis of position, size, and shape. The procambial strands in the cotyledon consist of a ring of bundles grouped into two distinct sympodia and extend from beneath the shoot apical meristem to the tip of the cotyledon where they are situated very close to the surface. The most prominent organelles within all cell types are protein bodies, lipid bodies, and crystalline protein fibers. The protein bodies contain small crystalline inclusions which are presumed to be phytin. Protein bodies in the protoderm were smaller, denser-staining, and contained fewer crystalline inclusions than those in the parenchyma or procambium. On a volume basis, the parenchyma was shown to be 43% protein bodies, 25% lipid bodies, 15% cytoplasm, 7% cell wall, 4% intercellular space, 2% nuclei, and 4% other organelles (mitochondria and plastids).     

ENDOSPERM STRUCTURE AND STORAGE RESERVE HISTOCHEMISTRY IN THE PALM,WASHINGTONIA FILIFERA

The endosperm of Washingtonia filifera consists of living cells with the same general cellular structure throughout the seed. The major storage reserves are carbohydrate, stored in the form of thickened walls; lipid, stored as numerous small lipid bodies which fill the cytoplasm; and protein, stored as large, but variably-sized, protein bodies. The protein bodies contain two types of inclusions: prismatically-shaped denser protein crystalloids and small crystalline deposits presumed to be phytic acid. The X-ray microanalysis shows these crystalline inclusions do contain P, Ca, Mg, and Fe. Protein bodies are positively stained with PAS. Nuclei are present in all cells, but stain very palely. Plastids and mitochondria are present, but infrequently seen. The plastids have few, poorly developed membranes. Endoplsasmic reticulum and dictyosomes are lacking. The cell wall is thick except in areas of pit fields and consists of three layers which differ in their staining with toluidine blue and in their ultrastructural characteristics: middle lamella, thickened outer wall, and thin inner wall. All wall layers are positively stained with PAS and calcofluor. Although general structural features of the endosperm in Washingtonia filifera are similar to those in date seeds, the composition of the wall polysaccharides and protein bodies appear to differ somewhat.     

GENETIC DIFFERENTIATION AMONG HOST-ASSOCIATED POPULATIONS OF THE GALLMAKER EUROSTA SOLIDAGINIS (DIPTERA: TEPHRITIDAE)

Eurosta solidaginis, a gallmaking tephritid (Diptera), infests at least two species of Solidago in the eastern United States. We used horizontal starch gel electrophoresis of enzymes to examine whether populations on the two principal host plant species, Solidago altissima and S. gigantea, have diverged genetically. At the d -β-hydroxybutyrate dehydrogenase (HBDH) locus, the predominant allele in all nine populations from S. altissima (HBDH^1.00) was absent or uncommon in all but 1 of the 12 populations from S. gigantea. At the phosphoglucomutase locus (PGM), the most common allele in all populations was PGM^1.00, but the frequency of this allele was, with one exception, higher in populations from S. gigantea than in populations from S. altissima. Genetic heterozygosity was usually greater in populations from S. altissima (H? = 0.028) than in populations from S. gigantea (H? = 0.009). A phylogenetic tree derived from a genetic distance matrix clustered gallmaker populations from the same host plant together.     

THE DIVERGENCE OF NEUTRAL QUANTITATIVE CHARACTERS AMONG PARTIALLY ISOLATED POPULATIONS

The neutral model of phenotypic evolution has yielded several simple predictions about the long-term rates of between-population divergence of polygenic traits and about the equilibrium level of within-population variance when mutation and random genetic drift are the sole evolutionary forces. These conclusions must be modified if populations are only partially isolated. A quantitative model is presented for the development of within- and between-population variance for neutral quantitative characters in pairs of populations with arbitrary effective sizes and migration rates. Both the variance in the base population and subsequent variance generated by mutation are considered, and several dynamical and equilibrium properties are shown to be adequately described by simple approximations. The resultant formulations provide some insight into the sensitivity of measures of morphological distance to gene flow, the necessity of isolation for the accumulation of variation between incipient species, and the consequences of gene flow into captive populations of endangered species.     

DIFFERENTIATION AMONG POPULATIONS OF TETRAPLOID GRINDELIA CAMPORUM

Ten populations of 4N Grindelia camporum (Asteraceae) were investigated in a common-garden study of phenotypic and genetic variability. This species is a long-lived perennial herb and an obligate outcrosser which would be expected to display considerable gene flow among populations based on its life-history traits. Each of the 17 morphological, phenological, and physiological traits examined showed significant differences between populations. Average within-population heritability was 0.39. The variation between populations averaged 3.3 times the variation within populations, indicating that the populations are well-differentiated for each of the 17 traits. Two possible explanations for the differentiation are given: populations may have diverged from a common ancestor in very little geologic time, or the species may have a polytopic origin.     

GENETIC DIFFERENTIATION AMONG POPULATIONS OF THE PLANKTONIC MARINE DIATOM DITYLUM BRIGHTWELLII (BACILLARIOPHYCEAE)1

Population genetic structure was determined for the planktonic diatom Ditylum brightwellii (West) Grunow in two connected estuaries—Puget Sound and the Strait of Juan de Fuca (WA, USA). Three genetically distinct populations were detected that were characterized by different microsatellite allele distributions and unique alleles. Isolates from the two most genetically diverged populations displayed identical full‐length 18S rDNA sequences suggesting that either a single or two recently diverged species were sampled. The extent of genetic differentiation between populations was not correlated with distance between water samples or time between sampling. Instead, distinct populations were associated with different estuaries. In Puget Sound waters, one population was detected three times over the course of 28 months. Cells from this population were likely maintained inside Puget Sound over long periods through water recirculation within the Sound. In Strait of Juan de Fuca waters, two additional populations were detected. Maximum growth rates of Puget Sound isolates were significantly different from Strait of Juan de Fuca isolates, indicating that populations were composed of cells with different physiological capabilities. The genetic and physiological differentiation observed between populations from intermixing estuaries suggested that genetic exchange between populations was restricted through differential selection. Despite the potential for widespread dispersal in planktonic organisms, it appears that populations with distinct genetic and physiological characteristics can be maintained over long time periods through a combination of hydrology and differential selection.     

GENETIC DIFFERENTIATION AMONG ANCESTRAL AND INTRODUCED POPULATIONS OF THE EURASIAN TREE SPARROW (PASSER MONTANUS)

We compared genetic variation in three introduced North American populations of Passer montanus with an ancestral German population, a native Swedish population, and an introduced Australian population. The North American P. montanus were less variable genetically than the ancestral German birds, presumably a result of the founding event. The genetic structure of all six populations of P. montanus can be explained in terms of interaction among mutation, genetic drift, effective population size, and unknown selective factors. Cluster analyses and an ordination of distance measures derived from electrophoretic data generally showed relationships in phenetic space among populations consistent with the magnitude of their geographic separation. An exception occurred with the Swedish population, which was closer in the ordination to a North American population than to the geographically neighboring German population. This seemingly anomolous juxtaposition was attributed to the relative abundance of alleles present in the Swedish birds. Populations of P. montanus seem to have diverged in a manner similar to that seen in conspecific disjunct populations, i.e., at present showing no trenchant indication of genetic speciation.     

GENETIC DIFFERENTIATION OF FITNESS-ASSOCIATED TRAITS AMONG RAPIDLY EVOLVING POPULATIONS OF THE SOAPBERRY BUG

In this study we used reciprocal rearing experiments to test the hypothesis that there is a genetic basis for the adaptive differences in host-use traits among host-associated soapberry bug populations (described in Carroll and Boyd 1992). These experiments were conducted on two host races from Florida, in which differences in beak length and development were found between natural populations on a native host plant species and those on a recently introduced plant species (colonized mainly post-1950). Performance was generally superior on the host species from which each lab population originated (i.e., on the “Home” host species): in analysis of variance, there was significant population-by-host interaction for size, development time, and growth rate. These results indicate that the population differences in nature are evolved rather than host induced. Increased performance on the introduced host was accompanied by reduced performance on the native host, a pattern that could theoretically promote further differentiation between the host races.     

鹅掌楸种群间光生态适应性的分化

通过对鹅掌楸７个不同种群幼苗的光合生长年进程、光合速率、光饱和点和光补偿点,以及不同光生境条件下的叶绿素含量和叶绿素ａ／ｂ比值的实验测定和生长量的统计,结果表明,种群间存在明显的光生态适应性分化。该物种地理分布上的西部亚区种群的光合适应能力和生长势总体上强于东部亚区的种群。而在西部亚区中又以金平、盐津种群的适应力和生存力更强。本研究支持该物种种群的生存能力由西向东逐渐下降,居于东部亚区中的种群其濒危程度更为严重的观点。这种濒危过程中的生态适应性的分化,说明该物种的濒危,在很大程度上是“致危生境”造成的。     

INTRASPECIFIC GENETIC DIFFERENTIATION IN CALIFORNIA SEA LIONS (ZALOPHUS CALIFORNIANUS) FROM SOUTHERN CALIFORNIA AND THE GULF OF CALIFORNIA

Intraspecific patterns of mitochondrial DNA sequence variation were determined among California sea lions ( Zalophus califomianus californianus ) from three colonies along the Pacific coast of southern and Baja California and one colony in the Gulf of California. We found no variation in 368 base pairs (bp) of cytochrome b sequence among 40 sea lions from these localities, but analysis of 360 base pairs of control region revealed eleven genotypes. The four genotypes found in the Gulf of California population were unique and phylogenetically distinct from those found in sea lions along the Pacific coast. The average sequence divergence between Gulf and Southern California genotypes was 4.3%, suggesting a relatively long period of isolation. However, colonies along the Pacific coast, which are less than 200 km apart, shared mtDNA genotypes, indicating that recent genetic exchange has occurred between them. Therefore, we suggest that regional female philopatry exists in California sea lions. Regional boundaries may be related to oceanic currents or patchiness in the distribution of resources. Further research is needed to better understand the underlying causes of genetic differentiation in the California sea lion.     

PATTERNS OF REPRODUCTION,GENETIC DIVERSITY,AND GENETIC DIFFERENTIATION IN CALIFORNIA POPULATIONS OF THE GENICULATE CORALLINE ALGA LITHOTHRIX ASPERGILLUM (RHODOPHYTA)1

The reproductive composition and genetic diversity of populations of the red seaweed Lithothrix aspergillum Gray (O. Corallinales) were studied at three southern California sites (Shaw's Cove and Treasure Island, Laguna Beach; Indian Rock, Santa Catalina Island) and at a fourth site (Bodega Bay) located in northern California. Sexually reproducing populations were confined to southern California. Diploid individuals were numerically dominant over haploid (gametophytic) individuals at all sites. Intertidal and subtidal subpopulations from Shaw's Cove differed in their reproductive profiles. Most intertidal specimens found on emersed surfaces were densely branched, turf-forming, and bore tetrasporangial (68.6%), carposporangial (11.4%), or spermatangial (5.7%) conceptacles, reflecting a sexual life history; none produced asexual bispores. In contrast, 74.3% of the larger, loosely branched subtidal specimens bore bisporangial conceptacles indicative of asexual reproduction. Nearly 70% of the Indian Rock thalli showed no evidence of conceptacle formation. Only asexual, diploid bispore-producing thalli were obtained from the Bodega Bay site. Genetic diversity (mean number of alleles per locus, percent of polymorphic loci, and average expected heterozygosity) of diploid L. aspergillum populations varied with life-history characteristics and geographic location. A total of 30 alleles was inferred from zymograms of 16 loci examined by starch-gel electrophoresis; of these loci, 11 were polymorphic. The genetic diversity of sexual, diploid populations of L. aspergillum (alleles per locus [A/L] = 1.4-1.5; percent polymorphic loci [%P] = 37.5-50.0) was relatively high compared with other red seaweeds. Lowest diversity (A/L = 1.0; %P = 0.0) occurred in the exclusively asexual Bodega Bay population which consisted of genetic clones. All sexual L. aspergillum populations deviated significantly from Hardy-Wein-berg expectations due to lower than expected heterozygosity. Genetic differentiation (Wright's F_statistic [F_ST]; Nei's Genetic Distance [D]) among sexually reproducing southern California populations was low (F_ST= 0.030) on a local scale (ca. 5 km), suggesting high levels of gene flow, but high genetic differention (F_ST= 0.390 and 0.406) occurred among southern California populations separated by ca. 70 km. Very high genetic differentiation (F_ST= 0.583–0.683) was obtained between northern and southern California populations separated by 700–760 km. Our genetic and reproductive data suggest that the L. aspergillum population from Bodega Bay is sustained by perennation, vegetative propagation, or asexual reproduction by bispores and may represent an isolated remnant or a population established by a founder event.     

VARIATION IN NITROGEN PHYSIOLOGY AND GROWTH AMONG GEOGRAPHICALLY ISOLATED POPULATIONS OF THE GIANT KELP,MACROCYSTIS PYRIFERA (PHAEOPHYTA)1

Three geographically isolated populations of the giant kelp, Macrocystis pyrifera (L.) C. Ag., were examined for responses to nitrate availability in batch culture experiments using juvenile sporophytes reared from spores in the laboratory. Although maximum rates of nitrate-saturated growth were similar among groups, there were significant quantitative differences in the response to nitrate limitation that can be related to natural patterns of nutrient availability at these sites. Plants from Santa Catalina Island (most oligotrophic) achieved maximum growth rates at ambient nitrate concentrations that were lower than those for plants from Monterey Bay, California (most eutrophic), or Refugio State Beach (near Santa Barbara, California). Tissue nitrogen and amino acid concentrations were highest in plants cultured from Santa Catalina Island populations at all external nitrate concentrations, suggesting that differences in nitrate requirements for growth may reflect the efficiency of nitrate uptake and assimilation at subsaturating nitrate concentrations. Given the different physical environments from which these plants came, the data suggest that geographically isolated populations of M. pyrifera have undergone genetic divergence that can be explained by ecotypic adaptation to unique habitat conditions at these sites.     

ON THE ORIGIN OF DIVERGENCE OF LEARNED SIGNALS (SONGS) IN ISOLATED POPULATIONS

Short-toed Treecreepers Certhia brachydactyla in Morocco sing very differently from European Short-toed Treecreepers.
Short-toed Treecreepers from Central Europe do not react to the playback of songs of North African Short-toed Treecreepers. This result is statistically highly significant.
Treecreepers C. familiaris of Central Europe do not react to the playback of songs of North African Short-toed Treecreepers or (some males) react just as little as they do to songsof Central European Short-toed Treecreepers. This result is statistically highly significant.
Three hypotheses are examined as interpretations of these results: contrast reinforcement, loss of contrast and withdrawal of learning. The facts are best explained by withdrawal of learning. According to this hypothesis, Morocco was colonised by young European Short-toed Treecreepers with a song that had not yet been fixed by learning. The founders of the new population evolved a divergent song, which has been transmitted by tradition ever since.     

DIFFERENTIATION AMONG NINE POPULATIONS OF PHLOX. I. ELECTROPHORETIC AND QUANTITATIVE VARIATION

The organization of genetic variation in Phlox drummondii was investigated using both allozyme electrophoresis and quantitative genetics. Variation at five polymorphic enzyme loci was characterized in nine populations, and variation in 16 morphological and life-history characters was examined using an analysis of full- and half-sibs in seven populations. Significant levels of genetic variation were found at enzyme loci and for metric characters. Significant heritabilities were observed for 15 of the 16 characters examined. Genetic differences among populations were revealed both by Nei's genetic distance and by phenotypic differences, summarized by discriminant analysis. Partitioning variance in allozyme frequencies among hierarchical levels of genetic organization indicated that 94% of this variance lay within populations, 4% between populations within varieties, and 2% between varieties. Partitioning phenotypic variance for metric characters indicated that 73% lay within populations, 24% lay between populations within varieties, and 3% lay between varieties. Thus, both electrophoretic and metric characters indicated that despite extensive genetic differentiation among populations, most of the evolutionary potential of the species lies within populations.