Specialized and generalized dispersal systems: where does ‘the paradigm’ stand?

I explore the specialization versus generalization paradigm in frugivory and seed dispersal. This view predicts that some tropical trees produce nutritious fruits adapted for use by a small coterie of specialized frugivores that provide reliable seed dissemination. Other tree species are expected to offer superabundant fruits of lower nutritional reward, relying instead on common opportunistic frugivores that are individually less reliable, but collectively disperse seeds effectively. Though widely referenced, many aspects of the paradigm are untested with tropical trees and avian frugivores, primarily because plant ecologists rarely determine whether specialist or generalist foragers are responsible for different patterns of seed distribution, while students of foraging behavior rarely determine the effects seed dispersal by different animals for survival of seeds or seedlings of specialist or generalist trees.Ecological paradigms provide alternative hypotheses, without evolutionary arguments. Keystone species have ecological effects disproportionate to their abundance; it is important for management considerations to know whether fruiting trees or frugivores serve as keystone mutualists in tropical forests. Alternatively, the extent to which vertebrate seed dispersers influence density-dependent seed, seedling, sapling, or adult mortality may have important consequences for spatial dispersion and population dynamics of tree species in tropical forests.     

The influence of seed dispersal mechanisms on the genetic structure of tropical tree populations

Seed dispersal mechanisms should have a direct impact on the genetic structure of populations. Species whose seeds are dispersed near the maternal plant (e.g. gravity or wind dispersal) or species whose seeds are deposited in clumps or patches should have more fine-scale genetic structure than species whose seeds are dispersed singly by mobile animals. Furthermore, due to the overlap of seed shadows, species with high adult densities should have less genetic structure than species with lower densities. Allozyme analyses of three tropical tree species belonging to the moist tropical forest of Barro Colorado Island, Republic of Panama, were used to describe variation in the scale and intensity of genetic structure within their populations. The genetic structure of seedlings and immature trees in the low-density, wind-dispersed species (Platypodium elegans) was the coarsest and strongest whereas genetic structure in a population of Swartzia simplex var. ochnacea (high density, bird-dispersed) was both the finest and the weakest. The genetic structure of Alseis blackiana, a high-density, wind-dispersed species was intermediate in both degree and scale. In P. elegans and A. blackiana, which had J shaped size distributions, the significant genetic structure seen in the smaller and intermediate diameter classes disappeared in the largest diameter class. The loss of genetic structure was not observed in S. simplex, a species with a more even size distribution.     

Estimation of the retention times and distances of seed dispersed by two monkey species, Alouatta seniculus and Lagothrix lagotricha, in a Colombian forest

Isolated-bout method to estimate the retention times and dispersal distances was applied to the seed dispersal by red howler monkeys (Alouatta seniculus) and Humboldts woolly monkeys (Lagothrix lagotricha) in a lowland tropical forest at La Macarena, on the border of the Macarena and Tinigua National Parks, the Department of Meta, Colombia. Continuous observations were made on the feeding and ranging behavior of well-habituated troops of howler monkeys and woolly monkeys as well as continuous collection of monkeys feces. We selected out the isolated-bout as a feeding bout on the specific species that was only once recorded within 48 h before the seeds of that species appeared in the feces of monkeys. In that case, the seeds were strongly suggested to come from that isolated bout. Then retention times, route seed dispersal distances and direct seed dispersal distances were estimated. Howler monkeys, which are regarded as generalist herbivores, showed longer retention times and dispersal distances along monkeys route than did woolly monkeys, which are specialist frugivores. However, the direct distances that seeds were carried from the mother tree were not significantly greater for howler monkeys than for woolly monkeys. This shows that both retention time and movement patterns by the monkeys, especially the total ranging area, influence the direct distance that seeds are carried from the mother tree.     

Seed dispersal curves: Behavior of the tail of the distribution

Summary Seed dispersal is important both to plant fitness and to plant population structure. We suggest that the tail of the seed dispersal curve is at least as important biologically as the modal portion of the curve, and we present a relatively simple, four-parameter model, based on diffusion principles, for the tail of the seed distribution. This model includes two types of qualitative behavior: algebraic tails (which tend to be longer and have greater reach) and exponential tails (which are shorter and have less reach). We have selected 68 data sets from the literature, each giving a seed shadow that could be categorized statistically as (1) exponential, (2) algebraic, (3) neither, or (4) both models fit adequately. Algebraic shapes for seed-shadow tails were common in this sample, and tail behavior was not generally specific to a particular dispersal mode. This result may suggest that algebraic tails are generally favored by selection and can be achieved by several means, but limitations of existing data sets and of statistical methodology preclude final judgement. Smaller complete samples of seed distances would provide a better basis for the analysis of tails than do the present form of data sets (consisting of counts of seeds in discrete distance categories).     

Isoform-Specific Membrane Translocation of Protein Kinase C After Ischemic Preconditioning

Mild cerebral anoxic/ischemic/stress insults promote tolerance and thereby protect the brain from subsequent lethal anoxic/ischemic insults. We examined whether specific activation of PKC , , , or isoforms is associated with ischemic preconditioning (IPC) in rat brain. IPC was produced by a 2-minute global cerebral ischemia. Membrane and cytosolic fractions of the hippocampi were immunoblotted using specific antibodies for PKC, , , and . PKC showed a significant translocation to the membrane fraction from 30 min to 4 h and PKC at 4 h following IPC. In contrast, the membrane/cytosol ratio of PKC showed a tendency to decrease at 30 min and 8 h, and the membrane/cytosol ratio of PKC was significantly decreased from 30 min to 24 h following IPC. These findings indicate PKC isoform-specific membrane translocations in the hippocampus after brief global brain ischemia and suggest that activation of PKC and PKC may be associated with IPC-induced tolerance in the rat hippocampus.     

Nuclear and cytoplasmic gene control of resistance to loose smut (Ustilago tritici (Pers.) Rostr.) in wheat (Triticum aestivum L.)

Summary Using disomic chromosome substitution lines based on the susceptible wheat cultivar Chinese Spring, loose smut resistance of wheat cultivars Hope and Thatcher was shown to be conferred in each case by a single dominant major gene carried on chromosome 7 A (Hope) or 7 B (Thatcher). Partial resistance was determined by genes on an additional eight Hope or seven Thatcher chromosomes, and similarities were evident between the partial resistance genotypes ofHope and Thatcher. Chinese Spring exhibited a mean infection value of approximately 50%, indicating a significant level of partial resistance, which was found to be due, in part, to genes on the homoeologous chromosome arms 1 As, 1 Es and 1 Ds, and to cytoplasmic genes. Substitution of the Chinese Spring nucleus into the cytoplasm of Aegilops squarrosa, Ae. variabilis or Ae. mutica resulted in increased susceptibility to Ustilago tritici. Several alloplasmic lines of the resistant wheat cultivars Selkirk and Chris exhibited race-specific susceptibility to U. tritici.     

The α2 cDNA sequence of human haptoglobin carries a bacterial promoter functionalin vivo

Various constructions of human haptoglobin (Hp) cDNA coding either for the complete ^2FS precursor protein or only for the subunit have been placed under the control of the P_R promoter in the bacterial expression vector pCQV2 (Queen, 1983). In addition to the expected 45,000 dalton polypeptide synthesized after induction of the P_R promoter, the complete ^2FS constructions constitutively express a smaller polypeptide of 30,000 dalton corresponding to a truncated Hp protein. Computer analysis of the HpcDNA revealed the presence of two strong potential bacterial promoters (²P_F and ²P_S) located in the duplicated ^2FS sequence. Both Hp promoter signals are followed by potential mRNA start sites and ribosome binding sites at a compatible distance from initiation codons. In addition, the Hp² cDNA sequence, when fused upstream to the cDNA coding for ¹-antitrypsin, constitutively promotesin vivo the efficient expression of an hybrid protein specifically recognized by antibodies raised against ¹-antitrypsin or haptoglobin.     

Triple hybridization with cultivated barley (Hordeum vulgare L.)

Summary A crossing programme for trispecific hybridization including cultivated barley (Hordeum vulgare L.) as the third parent was carried out. The primary hybrids comprised 11 interspecific combinations, each of which had either H. jubatum or H. lechleri as one of the parents. The second parent represented species closely or distantly related to H. jubatum and H. lechleri. In trispecific crosses with diploid barley, the seed set was 5.7%. Crosses with tetraploid barley were highly unsuccessful (0.2% seed set). Three lines of diploid barley were used in the crosses, i.e. Gull, Golden Promise and Vada. Generally, cv Gull had high crossability in crosses with related species in the primary hybrid. It is suggested that Gull has a genetic factor for crossability not present in cv Vada and cv Golden Promise. One accession of H. brachyantherum used in the primary hybrid had a very high crossability (seed set 54.7%) in combination with cv Vada but no viable offspring was produced. In all, two trispecific hybrids were raised, viz. (H. lechleri x H. brevisubulatum) x Gull (2n=7–30) and (H. jubatum x H. lechleri) x Gull (2n=20–22). The first combination invariably had a full complement of seven barley chromosomes plus an additional chromosome no. 7, but a varying number of chromosomes (19–22) of the wild-species hybrid. The second combination had a full set of barley chromosomes. The meiotic pairing was low in both combinations.     

Simulated effects of fire,dispersal and spatial pattern on competition within forest mosaics

Simulations representing tree locations on a rectangular grid (cellular automaton) imply that spatial patterns associated with fire, seed dispersal, and the distributions of plants and resources affect forest dynamics profoundly. Simulated fires ignited at random locations in a uniform environment create non-uniform habitats and lead to patches dominated by different vegetation types. Short-range seed dispersal promotes vegetation clumping; fires cause these clumps to coalesce into vegetation zones separated by sharp borders, especially across an environmental gradient. In simulation of competition within vegetation mosaics, tree populations with a competitive advantage still require the intervention of fire to eliminate rivals. Also, the availability of local seed sources enables established tree populations to exclude invaders, but fires can trigger sudden changes in the composition of such systems. In models of simple succession systems, climax vegetation tends to displace pioneer vegetation, even under harsh fire regimes.     

The effect of a seed source on primary succession in a forest ecosystem

An analysis of the Relative Importance Value Index (RIVI) of later successional tree species and the Shannon diversity indexH of all tree and shrub species was undertaken on previously mined sites within a sparsely forested area in central Florida, USA. A comparative analysis of the distance to a seed source and the age of a site suggested that the distance to a seed source was the best predictor (R ²=0.85) of the regeneration of the later successional species and a good predictor of species diversity. Both theRIVI of the later successional species and the diversity index decreased with the distance from the seed source. The lack of a seed source containing climax species resulted in arrested succession at some sites. It is suggested that biological information is the causative means of succession and the dispersal of this information entails spatial dependency while its introduction and development are time dependent processes.Research was part of a project of the Center for Wetlands, University of Florida, Gainesville under contract with the Florida Institute of Phosphate Research. Interactions of Wetlands with Phosphate Mining, H. T. Odum and G. R. Best, principal investigators. B. T. Rushton, J. Butner, G. R. Best, R. S. Schnoes and S. R. Humphrey are thanked for the use of their data.     

Molecular screening and fetal diagnosis of β-thalassemia in the Italian population

Summary This paper reports our experience of molecular screening and fetal diagnosis of -thalassemia in 457 at risk couples of Italian descent. Molecular screening was carried out by dot blot analysis on amplified DNA with oligonucleotide probes complementary to the eight most common mutations in Italians [39 (CT); 6 (-A); ⁺-87 (CG); ⁺ IVSI nt 110 (GA); IVSI nt 1 (GA); ⁺ IVSI nt 6 (TC); IVSII nt 1 (GA); ⁺ IVSII nt 745 (CG)]. By using this approach, we have been able to define the mutation in 92.8% of cases. The rest (all but four) were defined by direct sequencing and this led to the detection of nine rare mutations [76 (-C); ⁺ IVSI nt 5 (GA); ⁺ IVSI nt 5 (GC); ⁺ IVSI -1 (cod 30) (GC); ⁺-87 (CT), -290 bp del.; ⁺-101 (CT)], and to the characterization of a novel mutation consisting of the deletion of the G at the invariant AG of the IVSII splice acceptor site of the -globin gene ( IVSII nt 850-1 bp). In the remaining four cases, the -globin gene showed entirely normal sequences and the -globin gene cluster was intact, as indicated by Southern blot analysis. Fetal diagnosis was carried out by dot blot analysis with the oligonucleotide probes defined in the parents. The procedure is simple and reliable, and the results can be obtained within 1 week of sampling. No misdiagnosis has so far occurred. The results indicate that fetal diagnosis of -thalassemia by DNA analysis may be obtained in practically all cases (even in a population showing marked heterogeneity of -thalassemia) by the combination of dot blot analysis for detecting common mutations, and direct sequencing for defining those that are uncommon.     

Visual and lenticular pigments in the eyes of demersal deep-sea fishes

We report on the lens pigmentation and visual pigments of 52 species of demersal deep-sea fishes caught at depths ranging from 480 m to 4110 m in the Porcupine Seabight and Goban Spur area of the North-eastern Atlantic. Only one species, caught between 480 and 840 m, had a lens with large amounts of pigment, consistent with the hypothesis that heavily pigmented lenses in deep-sea fish serve to enhance the contrast of bioluminescent signals by removing much of the background radiance, which is only visible to fish living shallower than 1000 m. Low concentrations of lens pigmentation were also observed in a further two species (Rouleina attrita and Micromesisteus poutassou). The retinae of all species except five, contained only a single visual pigment, as determined by microspectrophotometry of individual rods, and/or spectrophotometry of retinal wholemounts and retinal extracts. Those fishes caught between 500 m and 1100 m had wavelengths of peak sensitivity (_max) ranging from 476 nm to 494 nm, while most fish living below 1100 m tended to be more conservative with (_max) values ranging from 475 nm to 485 nm. The only exceptions to this were three deep-living species caught between 1600 m and 2000 m whose retinae contain abnormally short-wave sensitive visual pigments (Cataetyx laticeps — _max 468 nm; Alepocephalus bairdii — _max 467 nm; Narcetes stomias _max 472 nm), suggesting adaptation for the detection of short-wave bioluminescence.     

Abiotrophic gene action inHomo sapiens: Potential mechanisms and significance for the pathobiology of aging

A subset of genetic loci ofHomo sapiens are reviewed that: 1) have the potential for allelic variation (either mutation or polymorphism) such that degenerative and/or proliferative phenotypic aberrations may be of relatively late onset (abiotrophic); 2) have phenotypic features which overlap, to some extent, with those of important age-related disorders of man (many of which are systematically tabulated in this review); 3) have had significant characterization at the biochemical genetic level. The ascertainment bias of physicians to discover strong phenotypic effects (non-leaky mutations) obscures the fact that, for many such instances, there exist numerous other alleles of lesser effects, including those whose gene actions probably escape the force of natural selection.The patterns of normal aging inHomo sapiens are quite variable and, hence, difficult to define. It seems likely that the wild-type alleles of a number of loci will also be found to have antagonistic pleiotropic effects that contribute to the syndromology of senescence in our species.     

Evolution of a unique seed maturity pattern in Croton bonplandianum Baill strengthens ant-plant mutualism for seed dispersal

Summary The female flowers of Croton bonplandianum bear nectar glands which become active during fruit maturation and attain peak activity just prior to the splitting of fruits. This temporal specificity of nectar gland activity is shown to facilitate seed dispersal by ants, which are attracted to the plant only during the fruit maturation period. The nectar glands establish a nectar influence zone with a radius of 60 cm around the plant within which seed dispersal by ants is effective. Seed dispersal by ants is facilitated only if the seeds are placed within this nectar influence zone. This is accomplished by an intriguing evolutionary shift in the maturation pattern of the fruits. Unlike the usual acropetal development, fruit maturation in Croton is temporally asymmetrical, with the fruits nearer the parental axis maturing early. This unique pattern of fruit development together with the polychasial branching system leads to a concentration of seeds within the nectar influence zone and enhances seed dispersal by ants. The proximate factors responsible for this asynchronous fruit maturity were investigated.     

Identification and confirmation of three neutral alleles conferring wide compatibility in inter-subspecific hybrids of rice (Oryza sativa L.) using near-isogenic lines

Wide-compatibility varieties (WCVs) are a special class of rice germplasm that is able to produce fertile hybrids when crossed to both indica and japonica subspecies. Previous studies determined Dular and 02428 as two WCVs and identified a number of QTLs as having large effects on fertility of inter-subspecific hybrids. In this study, we developed five near-isogenic lines (NILs) for three of the QTLs, f5, f6 and S5, by backcrossing and marker-assisted selection, using Dular and 02428 as the donors and Zhenshan 97 as the recipient. Three of the NILs each carried one introgressed allele, and two NILs each carried two introgressed alleles in combinations. The NILs were testcrossed to an indica tester Nanjing 11 and a japonica tester Balilla. The results showed that the f5 allele from Dular (f5-Du) is a neutral allele conferring wide compatibility, with a large effect on both pollen and spikelet fertility, and the f6 allele from Dular (f6-Du) is a neutral allele for spikelet fertility with smaller effect. The S5 allele from 02428 (S5-08) was confirmed to be a neutral allele for spikelet fertility. It is likely that f6 and S5 are the same locus as deduced by their genomic locations and effects. The results also showed that even in combination, two neutral alleles of different loci were not able to produce normal fertility hybrids in typical indica–japonica crosses. The implications of the findings in rice breeding programs are discussed.     

The endomembrane system and mechanism of membrane flow in the green alga,Gloeomonas kupfferi (Volvocales,Chlorophyta) II. A cytochemical analysis

Summary Cytochemical analysis of the endomembrane system of the chlamydomonad flagellate,Gloeomonas kupfferi (Chlorophyta), reveals distinct compartmentalization. Phosphatase localization shows that: IDPase is located throughout all cisternae of the dictyosome and vesicles associated with the contractile vacuole. Other alkaline phosphatases like TPPase, ATPase and ITPase were localized within the trans-face cisternae and vesicles of the contractile vacuole. IMPase was localized at the plasmamembrane and not within the endomembrane system. Acid phosphatases, incl. CMPase, NADPase and -glycerophosphatase, were localized in vesicles emerging from the central terminus of the trans-face of the dictyosome and in the peripheral vacuolar network. Silver proteinate labeling was noted in the dictyosome, contractile vacuole and on the anterior plasmamembrane. A summary of endomembrane compartmentalization and a putative interpretation of membrane flow and economy are presented.Abbreviations ER endoplasmic reticulum - IDPase inosine 5-diphosphatase - ITPase inosine 5-triphosphatase - ATPase adenosine 5-triphosphatase - TPPase thiamine pyrophosphatase - CMPase cytidine 5-monophosphatase - NADPase -nicotinamide adenine diphosphatase - AcPase acid phosphatase     

Proteins main-chain atomic displacements and density of stabilizing interactions

The assumption that interactions like hydrogen bonds, that establish the secondary structure of proteins, modulate the local flexibility of the polypeptide chain suggests a phenomenological relation between ²-the X-ray determined variance of the thermally-distributed location of a main-chain atom and the value of — a properly-defined linear density of stabilizing interactions at that location. The functional relation ² 1/ is verified from the data of lysozyme. is constructed from first principles after assuming that the thermal motions of an unstabilized polypeptide chain resemble those of a random chain. Taking the locations and the identity of the stabilizing interactions from literature, the predicted 1/g9 for lysozyme and metmyoglobin is compared with the observed ² along the proteins main-chain. The satisfactory results are discussed in the light of the possible role that hydrogen bonding plays in determining the equilibrium and the dynamic properties of the main-chain structural fluctuations in proteins, and its modelling by using a simplified mechanistic approach.     

Translational arrest in hypoxic potato tubers is correlated with the aberrant association of elongation factor EF-1α with polysomes

Translation elongation factor EF-1 became stably associated with potato tuber polysomes at the onset of hypoxia, coincident with a sharp rise in lactate and decrease in tissue pH. This aberrant association of EF-1 with polysomes also occurred when aerobic tuber extracts were acidified in vitro. Upon resumption of protein synthesis, an increase in the steady-state levels of EF-1, and expression of an EF-1/GUS transgene was observed. These results indicate that translational arrest results from to the failure of EF-1 to dissociate from ribosomes during the elongation cycle, and that restoration of protein synthesis is coordinated with expression of EF-1.     

On the significance of dispersal power for populations of carabid-beetles (Coleoptera,Carabidae)

Summary By various observations on carabid populations the author attempts to give an impression of the quantitative occurrence of dispersal and of the relation between dispersal and the chance of founding populations (dispersal power). Pitfall-catches in the recently reclamed Zuiderzee-polder E-Flevoland demonstrate that within seven years individuals of a number of monomorphic macropterous and dimorphic species had founded populations there. From the very high frequency of full-winged individuals within the latter populations it follows that full-winged carabid individuals generally must have a much greater power of dispersal than flightless ones. Therefore, winged individuals of dimorphic species were about equally able to reach E-Flevoland as were those of monomorphic macropterous ones, whereas individuals of monomorphic brachypterous species obviously are seriously hampered. The early appearance of individuals of riparian species on the shores of an artificial lake in the dune area Meijendel suggests that particularly populations living in unstable environments extensively invest in dispersal. It appears, however, that an important investment in dispersal apparently is not restricted to species from unstable environments; at least some sparse populations living in more stable environments also sacrifice relatively great numbers of individuals for dispersal (Pterostichus strenuus). The hypothesis is proposed, that populations facing a high risk of extinction generally will have a sufficient chance of founding populations (high turnover) when investing extensively in dispersal. Not only macropterous but — at least in some populations — also brachypterous individuals participate in migration, although in the populations studied the dispersal power of flightless individuals is found to be very small (Carabus problematicus). Under certain conditions the dispersal of full-winged individuals from wing-dimorphic populations may ultimately lead to a decrease or even a loss of dispersal power by a decrease of the frequency of macropterous individuals. It is assumed, however, that under certain natural conditions also brachypterous individuals may contribute to the spreading of risk within and between populations. The dispersal power of monomorphic macropterous, dimorphic and monomorphic brachypterous populations in a cultivated countryside like Drenthe is discussed. The connection between the dispersal power of different kinds of carabid populations and the resulting chance of survival under different conditions is discussed. Some suggestions for nature preservation management are given.Communication No. 144     

Seed set in Phormium: interactive effects of pollinator behaviour,pollen carryover and pollen source

Summary Fruit and seed set was studied in New Zealand flax (Phormium tenax Phormiaceae) a large monocot that preferentially sets outcrossed seeds. Fruit set was low and in particular situations could result from insufficient pollinator visitation. Observations of pollinator (Meliphagidae) movements showed that birds preferentially visited male phase flowers and predominantly moved pollen within inflorescences of the same plant. More dominant resident birds moved more between plants that subordinate non-resident birds. Combination of results of fluorescent dye carryover with known bird movements allowed predictions of fruit set and seed size that closely approximated observed levels. Resident birds account for almost half the observed foraging bouts but are predicted to be responsible for the vast majority of the viable seeds.