Population Genetic Structure of Neotropical Mangrove Species on the Colombian Pacific Coast: Avicennia germinans (Avicenniaceae)1

We investigated the genetic variation of Avicennia germinans using 172 AFLP (Amplified Fragment Length Polymorphism) bands of 45 plants from four localities on the Colombian Pacific coast: 11 from Virudó (Chocó), 10 from La Plata (Valle), 12 from Tumaco (Nariño), and 12 from Chontal (Nariño). AFLP variation among localities (16.2%) was highly significant (AMOVA; P < 0.0001). All the analyses showed that Tumaco was the most genetically distinct locality of the four under study. The other three localities, La Plata, Virudó, and Chontal, apparently form a large single subpopulation with high‐to‐moderate gene flow among localities. We also found the genetic diversity of A. germinans on the Colombian Pacific coast (H_E= 0.251) higher than that estimated by others over the broad geographic range of A. germinans. All these results together show that mangroves on the Colombian Pacific coast deserve a strong investigative effort to improve our ecological, evolutionary, and biogeographic knowledge of this important tropical forest type.     

Characterization of microsatellite markers for the mangrove tree Avicennia germinans L. (Avicenniaceae)

We describe 10 primers for amplification of microsatellite loci for the mangrove, Avicennia germinans. Eight loci were isolated from a DNA sample from the Pacific coast of Baja California, Mexico and two loci were isolated from a DNA sample from the Atlantic coast of Bermuda. Polymorphism was investigated in a population from the Mexican Pacific coast (n = 15) and in four samples scattered throughout the range of the species. Total number of alleles for the species ranged from two to 10. Observed heterozygosity in the Mexican Pacific coast population ranged from 0.27 to 0.60, with two loci having fixed alleles.     

Ultrastructural features associated with secretion in the salt glands of Frankenia grandifolia (Frankeniaceae) and Avicennia germinans (Avicenniaceae)

Using stereological procedures, a detailed analysis was made from thin section electron micrographs of secreting and nonsecreting salt glands of Frankenia grandifolia (Cham. and Schlecht) and Avicennia germinans (L.) Stem. In F. grandifolia secretory cells, vacuolar volume significantly decreased, while the volume of endoplasmic reticulum increased in secreting glands. Numerous minivacuoles were predominantly located along the periphery of secreting secretory cells, some in apparent fusion with the plasma membrane. No difference was found in mitochondrial volume in the secretory cells between secreting and nonsecreting glands. In A. germinans, there was a significant decrease in vacuolar volume in secreting secretory cells. The volume of the endoplasmic reticulum and mitochondria also increased in these cells. However, no evidence of mini-vacuolar fusion with the plasma membrane was observed. These results indicate that the physical process of secretion may differ between F. grandifolia and A. germinans; in both, however, the ultrastructural observations support the contention that specific structural parameters are correlated with the process of secretion.     

Salt effects on membranes of the hypodermis and mesophyll cells of Avicennia germinans (Avicenniaceae): a freeze-fracture study

Freeze-fracture electron microscopy was used to investigate intramembranous particle (IMP) densities and particle distributions in the plasma membrane and tonoplast of the cells of secreting and nonsecreting leaves of Avicennia germinans (L.) Steam. Intramembranous particle densities of the protoplasmic (P) and exoplasmic (E) face of the plasma membrane and tonoplast were significantly higher in hypodermal cells of secreting leaves than of nonsecreting leaves. In contrast, no significant differences in the frequency of intramembranous particles were found in any membrane faces of secreting or nonsecreting mesophyll cells. However, particle densities were higher in the plasma membrane and tonoplast of the mesophyll cells, compared to the hypodermal cells, with the exception of the P-face of hypodermal plasma membranes of secreting tissue, which had the highest particle density measured. Particle distributions were dispersed and no discernible patterns such as paracrystalline arrays or other multi-IMP structures were observed. Results support the hypothesis that secretion is coupled to changes in membrane ultrastructure, and the possibility that salt secretion is an active process driven by integral membrane proteins such as the H⁺/ATPase. Additionally, the hypodermal cells of the leaf may function as storage reservoirs for salt as well as water, suggesting a regulatory role in salt secretion.     

冠层位置对5种阔叶树叶片解剖结构与氮含量的影响

不同树冠位置的叶片为了达到功能的最大化,形成了不同的结构与功能的特征。然而,在相同的环境条件下,不同树种之间叶片对环境的反应是否存在一致规律,我们仍然缺乏了解。本研究采用石蜡切片和化学分析方法,对东北林区5个常见阔叶树种（蒙古栎、白桦、水曲柳、胡桃楸和黄波罗）不同树冠位置叶片的形态（叶厚度）、解剖（气孔密度、保卫细胞长度、栅栏和海绵组织厚度）和氮（N）含量特征进行了研究。结果表明：叶片的特征在种间和种内不同树冠位置均存在明显差异,并存在较强的规律性。在种内,5个树种的叶片和栅栏组织厚度均是上层外部最大,而保卫细胞和海绵组织的变化不明显,N含量的变异与树种有关。叶片所处的树冠高度和暴露程度对叶片的结构与N含量变异有重要影响。树种之间,蒙古栎的气孔密度最大,叶片厚度和海绵组织厚度最小,保卫细胞最短,黄波罗恰恰相反。结果表明,为了更好地执行整个树冠的功能,不同树种叶片均出现了与冠层位置有关的结构特征适应。     

Land barriers and open oceans: effects on gene diversity and population structure in Avicennia germinans L. (Avicenniaceae)

Avicennia germinans L. is a widespread mangrove species occupying the west coast of Africa and the Atlantic and Pacific coasts of the Americas from the Bahamas to Brazil and Baja California to Peru. An amplified fragment length polymorphism (AFLP) molecular analysis was carried out to assess genetic architecture within this species and to evaluate the effects of the Atlantic Ocean and the Central American Isthmus (CAI) on population and regional genetic diversity and differentiation. In total, 349 polymorphic AFLP fragments were identified among 144 individuals from 14 populations from the east Atlantic, west Atlantic and east Pacific. Levels of genetic diversity varied considerably among populations, but were generally higher in populations from the east Atlantic. Regional differentiation between the Pacific coast and Atlantic populations was greater than between east and west Atlantic populations, suggesting that the CAI has had an important influence on population genetic structure in this species. The lower level of divergence of east Atlantic from west Atlantic populations suggests some dispersal across the Atlantic Ocean, although migration rates are probably low; Nm from GST equal to 0.41 and accumulation of private and rare alleles in the east Atlantic. Population differentiation did not appear to follow an isolation by distance model and has probably resulted from complex patterns of population bottlenecks, and founder events due to landscape changes during the Pleistocene, particularly in the west Atlantic. The molecular data provide no support for the treatment of east Atlantic populations as a separate species A. africana.     

Nutrients of the Saronikos Gulf in relation to environmental characteristics (1973–1976)

The nutrient distribution in relation to environmental characteristics of the Saronikos Gulf was studied at two stations for the period 1973–1976. The distribution of measured values and their spatiotemporal variations were compared with previous data for the same area. Winter convection resulted in a very weak gradient of temperature, salinity, oxygen and nutrients. Stratification started to develop in May and persisted. for about six months. Little seasonal variation of nutrients appeared to occur, with higher values generally in winter. It was found that the station in the vicinity of the outfall contained more phosphate and ammonia than the station in the source water. Their levels of nutrients were similar in both years, except in the case of phosphate and nitrite, which were double at the station near the outfall in 1975. Of the nutrients controlling productivity in the photic layer of the examined stations in the Saronikos Gulf, phosphate had a stronger limiting effect on plant growth than inorganic nitrogen.     

Tree diversity,tree height and environmental harshness in eastern and western North America

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co‐varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.     

Leaf water storage increases with salinity and aridity in the mangrove Avicennia marina: integration of leaf structure,osmotic adjustment and access to multiple water sources

Leaf structure and water relations were studied in a temperate population of Avicennia marina subsp. australasica along a natural salinity gradient [28 to 49 parts per thousand (ppt)] and compared with two subspecies grown naturally in similar soil salinities to those of subsp. australasica but under different climates: subsp. eucalyptifolia (salinity 30 ppt, wet tropics) and subsp. marina (salinity 46 ppt, arid tropics). Leaf thickness, leaf dry mass per area and water content increased with salinity and aridity. Turgor loss point declined with increase in soil salinity, driven mainly by differences in osmotic potential at full turgor. Nevertheless, a high modulus of elasticity (ε) contributed to maintenance of high cell hydration at turgor loss point. Despite similarity among leaves in leaf water storage capacitance, total leaf water storage increased with increasing salinity and aridity. The time that stored water alone could sustain an evaporation rate of 1 mmol m^?2 s^?1 ranged from 77 to 126 min from subspecies eucalyptifolia to ssp. marina, respectively. Achieving full leaf hydration or turgor would require water from sources other than the roots, emphasizing the importance of multiple water sources to growth and survival of Avicennia marina across gradients in salinity and aridity.     

Latitudinal gradients in the species richness of Australian termites (Isoptera)

Abstract Using data on the geographic range of 260 described species in the Atlas of Australian Termites, seven ‘regions’ with more complete data, across a wide range of latitudes were selected for further analysis. For these regions, mean species richness (± SE) was calculated for (i) all species from all families, (ii) Termitidae (197 spp.), (iii) Amitermes spp. (Termitidae, 58 spp.), (iv) all families excluding Amitermes spp. (139 spp.), (v) Termopsidae (5 spp.), (vi) Kalotermitidae (32 spp.) and (vii) Rhinotermitidae (25 spp.). In addition, we compared the Atlas data with species richness for five regions, across a comparable range of latitudes, based on the pooled species richness of described and un-described species given in community studies. No group of termites showed a consistent decline in species richness from tropical to temperate latitudes for either data set. The Atlas data showed similar total species richness from the tropics to the mediterranean southwest, before declining to lowest species richness at the highest latitudes. Species richness of Amitermes spp. and Rhinotermitidae was highest in the southwest. Termopsidae and Kalotermitidae showed no latitudinal pattern in species richness. Community studies showed highest and lowest total species richness in the southwest and at the highest latitudes (south-coastal Western Australia), respectively, and similar species richness from the tropics to arid central Australia. Species richness of. Amitermes spp. was highest in the southwest (31 spp.). Kalotermitidae and Rhinotermitidae showed no clear latitudinal pattern. The latitudinal patterns of species richness for the Australian termites is consistent with that for the Australian vertebrates and ants in that they differ from patterns established for these taxa on other continents.     

Elevational Variation of Leaf Traits in Montane Rain Forest Tree Species at La Chinantla, Southern México1

Variation in leaf traits of dominant tree species in six montane rain forest communities was analyzed along an elevational gradient ranging from 1220 to 2560 m within a single basin at La Chinantla, Oaxaca, México. Three groups of characters were used: morphological (leaf shape, margin, blade configuration, and phyllotaxy), morphometric (leaf area, leaf mass per area, stomatal density, and blade length/width ratio), and anatomical (thicknesses of blade, palisade [PP], and spongy [SP] parenchymae, PP/SP ratio, and epidermis and cuticle thicknesses). The variation of morphological characteristics was only evident at the highest elevations; in contrast, thickness of leaf blade, PP, SP, as well as leaf mass per area clearly increased along the gradient, whereas leaf area was the only variable that significantly decreased with elevation. Thicknesses of epidermis and of the two cuticles were not significantly correlated with elevation. A classification analysis based on a leaf trait matrix led to the distinction between low and high elevation communities, with an approximate limit between them at ca 2300 to 2400 m. The results are discussed in light of environmental changes occurring along elevational gradients. Leaf characteristics of montane rain forest plants offer important insights about the complex roles of abiotic factors operating in these environments and supplement the traditional physiognomic classification schemes for these communities.     

Revisiting Patterns of Tree Species Composition and their Driving Forces in the Atlantic Forests of Southeastern Brazil

The elucidation of phytogeographic patterns and their drivers in biodiversity hotspots is essential to the study of ecology and the conservation of these areas. In 2000, an important study by Oliveira‐Filho and Fontes led to changes in the paradigms that define our understanding of the Atlantic Forest (Brazil). Here, our aim was to revisit this study using a more comprehensive set of environmental predictors, an updated and much larger tree species dataset and checklist, and more refined data analyses. We performed exploratory and confirmatory analyses, including the modeling of the spatial components with Moran's Eigenvector Maps, using data from 483 sites in southeastern Brazil, which encompass a total of 3546 species and 33 geo‐climatic variables. We observed strong floristic similarities between rain‐ and seasonal forests and a species distribution continuum across the main gradients. The environmental and spatial variables were significantly correlated with floristic patterns, and we demonstrated that the tree flora of the seasonal forests should no longer be considered a simple subset of the rain forest flora. The findings of the original paper were not only confirmed but we also unveiled additional, important phytogeographic patterns. We also reinforced the main conclusion of the paper that the Atlantic Forest concept must encompass all of the forest types east of the dry corridor in South America, a designation of utmost importance for the conservation of this biodiversity hotspot.     

Microsatellite analysis of genetic structure in the mangrove species Avicennia marina (Forsk.) Vierh. (Avicenniaceae)

The level of genetic variation throughout the entire worldwide range of the mangrove species Avicennia marina (Forsk.) Vierh. was examined using microsatellite markers. Three microsatellite loci detected high levels of allelic diversity (70 alleles in total), essential for an accurate estimation of population genetic parameters. The informativeness of the microsatellite loci tended to increase with increasing average number of repeats. The levels of heterozygosity detected for each population, over all loci, ranged from 0.0 to 0.8, with an average of 0.407, indicating that some populations had little or no genetic variation, whereas others had a large amount. Populations at the extremes of the distribution range showed reduced levels of heterozygosity, and significant levels of inbreeding. This is not unexpected as these populations may be subject to founder effects and environmental constraints. The presence of genetic structure was tested in A. marina populations using three models: (i) a single panmictic model; (ii) the discrete subpopulation model; and (iii) the isolation by distance model. The discrete subpopulations model was supported by the overall measures of population differentiation based on the infinite alleles model (F-statistics), and the stepwise mutation model (R statistics). In addition, an analysis of molecular variance (AMOVA), using both theoretical models, found that most of the variation was between populations (41-71%), and within individuals in the total population (31-49%). There was little variation among individuals within populations (0-10%). There was no significant isolation by distance. The high levels of genetic differentiation observed among populations of A. marina may be due to environmental and ecological factors, particularly past sea level and climatic changes.     

Allometry of axis length, diameter, and taper in the devil's walking stick (Aralia spinosa; Araliaceae)

The allometry of axis length, diameter, and taper is described for the trunk, rachis, and rachilla of nonbranching ramets of Aralia spinosa. Significant log-linear relationships were found between length and diameter for all axis categories, and in all cases, scaling was negatively allometric. Linear models best described the relationship between length and diameter for the rachis and rachilla, while a quadratic model best described this relationship for the trunk. During the trunk-building stage, the safety factors for trunk height were size dependent, with larger trunks exceeding their predicted critical buckling height. Taper was described by a linear relationship between diameter and position along the axis for all axis categories. All rachises and rachillas sampled exhibited taper along the length of the axis, however, only 51% of the trunks showed continuous taper. The trunk was less tapered than the rachis, but no differences in taper were found between the trunk and the rachilla, or the rachis and the rachilla. In unbranched ramets the large bipinnately compound leaves occupy the space normally occupied by lateral branches. We suggest that the rachis and rachilla are functionally equivalent to branches, that is, acting as axes of exploration and exploitation of the environment.     

Microsatellite Variation Among Red Snapper (Lutjanus campechanus) from the Gulf of Mexico

Allelic variation at a total of 20 nuclear-encoded microsatellites was examined among adult red snapper (Lutjanus campechanus) sampled from 4 offshore localities in the Gulf of Mexico. The number of alleles at the 20 microsatellites ranged from 5 to 20; average (± SE) direct count heterozygosity values ranged from 0.148 ± 0.025 to 0.902 ± 0.008. No significant departures from expectations of Hardy-Weinberg equilibrium were found for any locus within samples, and genotypes at pairs of microsatellites appeared to be randomly associated, i.e., in genotypic equilibrium. Tests of homogeneity in allele distributions among the 4 localities were nonsignificant for 19 of the microsatellites. Allele distribution at microsatellite Lca 43 was heterogeneous among localities before (but not after) Bonferroni corrections for multiple tests executed simultaneously. Tests of homogeneity in the distribution of individual alleles at Lca 43 gave similar results: one low frequency allele was distributed heterogeneously among samples before, but not after, Bonferroni correction. Molecular analysis of variance indicated that more than 99% of variation at each microsatellite was distributed within sample localities. These results generally are consistent with the hypothesis of a single population (stock) of red snapper in the northern Gulf of Mexico. Received September 25, 2000; accepted January 16, 2001     

Cuticle micromorphology of leaves of Pinus (Pinaceae) from Mexico and Central America

Cuticle micromorphology of 34 taxa of Pinus from Mexico and Central America was studied with scanning electron microscopy, and leaf morphology was described. In total, 29 characters, 22 from the inner cuticular surfaces and seven from the outer, were described in detail. These characters have value either for testing infragenerie classifications or for identifying individual taxa. Characters relating to the periclinal wall texture of the epidermal cells, the shape and degree of development of the anticlinal walls of the epidermal cells, the basal and apical shapes of anticlinal epidermal cell walls, the continuity of the epidermal cells, the size ratio of the polar to lateral subsidiary cells, the grooves on subsidiary cells, the cuticular flanges between guard and subsidiary cells, the groove near the bristles and the elevation of the Florin ring ridge and striations on the Florin ring are particularly useful for infrageneric classification. The agreement between these characters and infrageneric classifications is discussed. Characters relating to the end wall shapes of the epidermal cells, the relative length of epidermal cells, the shape of the stomatal apparatus, the texture of guard and lateral subsidiary cell surfaces, the polar extensions, the number of subsidiary cells and epidermal cell layers between stomatal rows, the integrity of stomatal rows, cell numbers between stomata in a row, cuticular flanges between guard cells, bristle flanges and surface textures, epicuticular waxes, striations on Florin rings and stomatal shapes, contain some important information for identifying Mexican pines. The distribution of the states of each character is compared with that of the Asian pines. Cuticular characters are used to help determine the affinities of taxonomically difficult taxa.     

Characterisation and analysis of microsatellite loci in a mangrove species, Avicennia marina (Forsk.) Vierh. (Avicenniaceae)

An enriched microsatellite library of the mangrove species Avicennia marina was constructed, in which 85.8% of the clones contained microsatellite sequences. Of the microsatellite repeat sequences isolated, 55.0% were di-nucleotides, 34.2% were tri-nucleotides, 50.0% were perfect, 24.2% were imperfect, and 15.0% were compound. Four different di-nucleotide repeats were isolated with repeat lengths ranging from 5 to 33; ten different tri-nucleotide repeats were isolated with repeat lengths ranging from 3 to 25. The most common di-nucleotide was the AC/TG repeat; the most common tri-nucleotide was the CCG/GGC repeat. Sixteen microsatellite sequences were selected for primer design, and 6 primers were selected to investigate the polymorphism detected among 15 individuals of A. marina from three natural populations in Australia. A total of 40 alleles were detected at 6 microsatellite loci. The number of alleles per microsatellite locus ranged from 5 to 13. On average, 7 alleles were detected per locus. All microsatellite loci showed high levels of gene diversity (heterozygosity), with values ranging from 0.53 to 0.88; the mean value of gene diversity was 0.70. Microsatellite loci were also tested for conservation across Avicennia species. There was a decline in amplification success with increasing divergence between Avicennia species. The results indicate that microsatellites are abundant in the Avicennia genome and can be valuable genetic markers for assessing the effects of deforestation and forest fragmentation in mangrove communities, which is an important issue for mangrove conservation and afforestation schemes. Received: 8 June 1999 / Accepted: 21 September 1999     

Comparative analysis of genetic diversity in the mangrove species Avicennia marina (Forsk.) Vierh. (Avicenniaceae) detected by AFLPs and SSRs

Avicennia marina is an important mangrove species with a wide geographical and climatic distribution which suggests that large amounts of genetic diversity are available for conservation and breeding programs. In this study we compare the informativeness of AFLPs and SSRs for assessing genetic diversity within and among individuals, populations and subspecies of A. marina in Australia. Our comparison utilized three SSR loci and three AFLP primer sets that were known to be polymorphic, and could be run in a single analysis on a capillary electrophoresis system, using different- colored fluorescent dyes. A total of 120 individuals representing six populations and three subspecies were sampled. At the locus level, SSRs were considerably more variable than AFLPs, with a total of 52 alleles and an average heterozygosity of 0.78. Average heterozygosity for AFLPs was 0.193, but all of the 918 bands scored were polymorphic. Thus, AFLPs were considerably more efficient at revealing polymorphic loci than SSRs despite lower average heterozygosities. SSRs detected more genetic differentiation between populations (19 vs 9%) and subspecies (35 vs 11%) than AFLPs. Principal co-ordinate analysis revealed congruent patterns of genetic relationships at the individual, population and subspecific levels for both data sets. Mantel testing confirmed congruence between AFLP and SSR genetic distances among, but not within, population comparisons, indicating that the markers were segregating independently but that evolutionary groups (populations and subspecies) were similar. Three genetic criteria of importance for defining priorities for ex situ collections or in situ conservation programs (number of alleles, number of locally common alleles and number of private alleles) were correlated between the AFLP and SSR data sets. The congruence between AFLP and SSR data sets suggest that either method, or a combination, is applicable to expanded genetic studies of mangroves. The codominant nature of SSRs makes them ideal for further population-based investigations, such as mating-system analyses, for which the dominant AFLP markers are less well suited. AFLPs may be particularly useful for monitoring propagation programs and identifying duplicates within collections, since a single PCR assay can reveal many loci at once. Received: 3 October 2000 / Accepted: 19 February 2001     

Impact of introduced carp (Cyprinus carpio)in subtropical shallow ponds in Central Mexico

In Mexico, as in many other subtropical and tropical countries, there has been a recent trend towards stocking non-native carp (Cyprinus carpio) in lakes and ponds as a source of food in rural areas. However, the results of a study in a series of small(1–8 ha.), shallow (<2 m), semi-natural ponds in Acambay, a high altitude valley in the basin of the Lerma river in the volcanic belt in central west Mexico, illustrate that the stocking of carp over a threshold value may have a detrimental ecological impact at several trophic levels. Ponds with carp tended to be turbid with high levels of suspended solids, and with few rooted macrophytes and epibenthic invertebrates. In contrast, ponds without carp had clear water and abundant rooted macrophytes and associated invertebrates, particularly gastropod molluscs. The direct uprooting of macrophytes by benthic foraging carp appeared to be the most important mechanism in switching the ponds from a clear macrophyte-dominated to a turbid state. The subtropical study ponds thus appear to confirm the alternative stable-state hypothesis developed intemperate lakes, although the importance of benthic rather than pelagic interactions was emphasised. The implications of stocking carp for native fauna of high intrinsic conservation value and as a food supply for local people are outlined. This revised version was published online in July 2006 with corrections to the Cover Date.