FUNCTIONAL MORPHOLOGY AND FEEDING OF DONAX SERRA ROODING AND DONAX SORDIDUS HANLEY (BIVALVIA: DONACIDAE)

The functional morphology of Donax serra and D. sordidus fromSouth African beaches was examined, and comparative measurementsmade of the rate of water filtration. The two species differin the structure and ciliation of the ctenidia, the number andspacing of the ridges on the labial palps, the direction ofciliary currents on the surface of the mantle and visceral mass,and the length and coiling of the mid-gut. The maximum ratesof water filtration recorded showed similar relationships tosize for the two species, but in D. sordidus the rate declinedrapidly with time during the observations. These differencesindicate differences in feeding strategy related to differencesin distribution and behaviour of the two species on beaches.     

PRELIMINARY ANALYSIS OF QUANTITATIVE GENETICS AND PHENOTYPIC PLASTICITY IN AULACOSEIRA SUBARCTICA (BACILLAR-IOPHYTA)

Several clones of Aulacoseira subarctica were isolated from Yellowstone, Lewis, and East Rosebud Lakes (Montana, Wyoming). Two to four clones from each lake were grown in batch cultures under three light intensities, 2, 11.4 and 115 μE m⁻² s⁻¹. Clones were conditioned to their light environment for a three-week period. Inoculants from the conditioned clones taken during log phase of growth, were grown until in log phase, then samples were collected. Five randomly chosen valves for 2 replicates of each clone were examined using a scanning electron microscope and captured on film at a magnification of 20,000x. Each image was digitized and quantitative morphometric characters were measured. A preliminary quantitative genetic analysis was performed on selected characters within each light environment. Plasticity of characters within clones across the three light regimes were also examined. The amount of variability found within characters in A. subarctica will be discussed in terms of environmental, genetic, and microenvironmental sources.     

AN INTERPRETATION OF PHENOTYPIC PLASTICITY IN AGROPYRON REPENS (GRAMINAE)

Phenotypic plasticity and genotypic variation were studied in Agropyron repens L. (Beauv.) collected from populations in two grassland communities which differed in the length of time since the last major disturbance. Twenty genotypes were collected from each population. Each genotype was vegetatively propagated, and subjected to six different treatments in a greenhouse. Phenotypic plasticity and genotypic variability were measured as across- and within-treatment standardized variances respectively. Patterns of plasticity were measured by genotype correlations across treatments. The results were presented graphically by the regression method of Garbutt and Zangerl (1983). Analysis of variance revealed significant population, genotype and treatment effects. Significant positive correlations between magnitude and variability of performance were found for all characters. Phenotypic plasticity and magnitude of performance were generally greater in plants collected from the older established field. Evidence for greater specialization in the older population was suggested by negative correlations between performance in the most favorable and least favorable treatments and by greater dissimilarity of genotype response across treatments. A more variable phenotypic response across treatments (i.e., higher plasticity) for plants from the older population may therefore be a consequence of specialization and not an adaptive trait per se.     

POPULATION STRUCTURE,BIOMASS ALLOCATION,AND PHENOTYPIC PLASTICITY IN MURDANNIA KEISAK (COMMELINACEAE)

Field and glasshouse studies were used to explain differences in plant biomass, shoot length, and reproductive effort in four populations of a wetland annual herb, Murdannia keisak. Populations were chosen from continually thermally disturbed, intermittently thermally disturbed, revegetating, and undisturbed portions of a floodplain forest in South Carolina, USA. Plants in the two thermally disturbed areas were shorter, flowered earlier in the autumn, and produced more and smaller seeds than plants in revegetating and undisturbed sites. Reproductive effort was higher in populations from undisturbed and revegetating sites than in the two thermally disturbed sites. Generally, differences observed in the field were not expressed in the glasshouse plants. Glasshouse experiments suggested that most of the observed among-population differences in size and reproductive effort in the field study were a result of a plastic response to water depth and light. The combination of field and glasshouse data showed that this wetland weed adjusts readily to newly disturbed habitats, thus spreading rapidly and maintaining local dominance.     

PHENOTYPIC PLASTICITY OF BRANCHING PATTERN IN SUGAR MAPLE (ACER SACCHARUM)

Branching patterns of leader shoots and lower branches were compared in 15 sugar maple trees. The number of first-order branches per second-order branch (R_1:2) differed very significantly between leader shoots and lower branches. Values of R_1:2 averaged 6.47 for leaders and 4.06 for lower branches. Stepwise bifurcation ratios between successive higher orders did not differ significantly. The difference in R_1:2 between leader shoots and lower branches within individual trees is the result of developmental-phenotypic interactions, such that the number of leaf-bearing shoots per support shoot decreases over time. These results indicate that branching patterns within individual trees are not stationary, as has commonly been claimed.     

PHENOTYPIC PLASTICITY AND HETEROCHRONY IN CICHLASOMA MANAGUENSE (PISCES,CICHLIDAE) AND THEIR IMPLICATIONS FOR SPECIATION IN CICHLID FISHES

Cichlid fishes in African rift lakes have undergone rapid speciation, resulting in “species flocks” with more than 300 endemic species in some of the lakes. Most researchers assume that there is little phenotypic variation in cichlid fishes. I report here extensive phenotypic plasticity in a Neotropical cichlid species. I examined the influence of diet on trophic morphology during ontogeny in Cichlasoma managuense. Two groups of full siblings were fed two different diets for eight months after the onset of feeding; thereafter both groups were fed a common diet. Phenotypes that differed significantly at 8.5 months converged almost completely at 16.5 months. If feeding on two different diets is continued after 8.5 months, the phenotypes remain distinct. Differences in diet and possibly in feeding mode are believed to have caused these phenotypic changes. Phenotypic plasticity is described in terms of a qualitative model of heterochrony in which phenotypic change in morphology is explained as retardation of the normal developmental rate. If phenotypic expression of morphology is equally plastic in African cichlid species as it may be in the American cichlids, as exemplified by C. managuense, then taxonomic, ecological, and evolutionary analyses of “species flocks” may be in need of revision. However, Old World cichlids may be less phenotypically plastic than New World cichlids, and this may contribute to the observed differences in speciation rate and degree of endemism.     

PHENOTYPIC PLASTICITY IN DRAPARNALDIA (CHAETOPHORACEAE). II. THE PHYSICAL ENVIRONMENT AND CONCLUSIONS

Eight isolates of Draparnaldia from a variety of freshwater habitats were grown in unialgal, defined culture. The morphological responses of these isolates to different daylengths, light intensities and temperatures are described. The phenotypic expression of Draparnaldia is markedly modified by all three factors. The interaction of these environmental variables was highly significant, and it is not possible, in most cases, to describe or predict the morphological appearance of Draparnaldia by referring to one of these parameters in isolation. The adaptive significance of phenotypic plasticity in Draparnaldia is discussed.     

PHENOTYPIC PLASTICITY IN CHRYSOPERLA: GENETIC VARIATION IN THE SENSORY MECHANISM AND IN CORRELATED REPRODUCTIVE TRAITS

A genetically variable sensory mechanism provides phenotypic plasticity in the seasonal cycle of the Chrysoperla carnea species-complex of green lacewings. The mechanism functions as a switch during the pupal and early imaginal stages to determine aestival reproduction versus aestival dormancy, and it has two major components: (1) response to photoperiod and (2) response to a stimulus(i) associated with the prey of the larvae. Ultimately, the switch is based on the response to photoperiod—an all-or-nothing trait whose variation (long-day reproduction versus a short-day/long-day requirement for reproduction) is determined by alleles at two unlinked autosomal loci. In eastern North America, variation in this component of the switch differentiates two reproductively isolated “species” that are sympatric throughout the region: Chrysoperla carnea, in which both loci are homozygous for the dominant alleles that determine long-day, spring and summer reproduction and thus multivoltinism, and C. downesi, which has a very high incidence of the recessive alleles for the short-day/long-day requirement, and thus univoltine spring breeding. In contrast, geographical populations in western North America harbor variable amounts of within-and among-family genetic variation for the photoperiodic responses and also for the switch's second component—adult responsiveness to the prey of the larvae. The geographic pattern of genetic variation in the two components of the switch indicates that it is a highly integrated adaptation to environmental heterogeneity. Expression of among-family variation in the prey component of the switch is highly dependent on photoperiodic conditions and genotype (it requires a constant long daylength and the recessive short-day/long-day genotype). Thus, we infer that responsiveness to prey evolved as a modifier of the photoperiodic trait. The switch has a significant negative effect on a major determinant of fitness; it lengthens the preoviposition period in nondiapausing reproductives. This negative effect may result in temporal variation in the direction of selection, which helps maintain genetic variability in the switch mechanisms of western populations. Also, the photoperiodic and prey components of the switch are positively correlated with fecundity in nondiapausing reproductives; however, the strong influence of environmental factors—presence or absence of prey—leaves open the question whether the correlated effects on fecundity are expressed in nature.     

PHENOTYPIC PLASTICITY IN SCENEDESMUS COMMUNIS HEGEW. (CHLOROPHYCEAE). II. EXAMPLES OF ALGAL CYCLO- AND NONCYCLOMORPHOSIS

A new dimension to the well-known phenotypic plasticity in Scenedesmus is presented. Large colony type Scenedesmus communis Hegew. reproduced in a typical fashion in batch culture in standard media but produced small colonies (SCT) resembling S. komarekii Hegew. and S. subspicatus Chod. at low cell densities in dilute media. Highest frequency of production occurred after cells had been pretreated in a concentrated (inorganic nutrients) medium. Examples of both cyclic and noncyclic behavior in the life history of Scenedesmus are presented. The noncyclic behavior resembles previous reports on induced heritable changes in flax and tobacco due to different treatment applications of fertilizers. An analysis of gross morphological features using scanning electron microscopy showed that isolated strain SCT1 was similar to S. komarekii (strain UTEX 1236) and isolated strain SCT2 was similar to S. subspicatus (strain UTEX 1358). Growth and morphological expression of the induced SCT strains were highly similar to those of the respective UTEX species. The current state of taxonomy and the implications of phenotypic plasticity on taxonomy in Scenedesmus are discussed.     

INTRASPECIFIC LIFE HISTORY VARIATION IN A POND SNAIL: THE ROLES OF POPULATION DIVERGENCE AND PHENOTYPIC PLASTICITY

Two approaches were used to determine the degree of divergence in life histories among populations of the pond snail, Lymnaea elodes. Juvenile snails were reciprocally transferred between ponds differing in permanence and productivity, and the resulting variation in life history traits was recorded. In a second experiment, parents and their offspring from both a vernal and a permanent pond population were reared in the same pond. Proximal factors had by far the greatest effects on life history traits in the transfer experiment, with snails reared in a more productive pond showing earlier reproduction at a larger size, higher fecundity, and longer life cycle length. Snails from the more uncertain pond in terms of drying date did reproduce at an earlier age and smaller size and grew less in each pond. However, these population differences, for the most part, disappeared when snails were reared for two generations in the same environment. Much of the intraspecific variation in life histories seen in this species must therefore be considered the result of phenotypic plasticity. I argue that the plasticity in life histories itself may be adaptive to this inhabitant of unpredictable, vernal ponds.     

鼠肝线粒体呼吸链质子泵高能质子流向膜表面及其在能量偶联中的作用

利用△ψ敏感的荧光探针Ｒｈｏｄａｍｉｎｅ１２３,测定了琥珀酸脉冲引起的鼠肝线粒体内膜体△ψ时相的变化,同时用高精度ｐＨ电极测定相应体系介质ｐＨ时相的变化,结果表明,线粒体跨膜电位的变化速率,快于介质ｐＨ的变化速率,并发现琥珀酸氧化时建立△ψ所维持的时间,短于介质酸化所维持的时间,后者是个缓慢的回复过程,这两者之间存在时间差,随着温度,Ｋ＾＋浓度和线粒体蛋白浓度的降低及琥珀酸浓度的增加,此两者的时间     

高温强光环境条件下3种沙地灌木的光合生理特点

比较研究了3种沙地灌木羊紫（Hedysarum fruticosum var.mongloicum）、油蒿（Artemisia ordosia)和沙柳（Salix pasmmophylla)在适宜光照和温度（春季）以及高温强光（炎热的夏季）的光合气体交换特点。前两种灌木为自然分布的种类,后一种为人工插条栽植的种类,瞬时光合有效辐射（PPFD）、叶面温度（Tleaf)、净光合速率（PN）、光系统Ⅱ最大量子产率（Fv/Fm)等参数每隔2h进行1次测量,羊柴和油蒿分别比沙柳具有高的净光合速率（PN）和气孔导度（gs),在高叶温（＞46℃）和强日辐射光（PPFD＞2100μmol.m^-2.s^-1)下这种差异更明显。在光合作用日进程中,净光合速率的下降主要受气孔开度的影响。沙柳的光合作用在高温条件下受到严重的抑制,表现在光合产物的负积累（以呼吸消耗为主）,炎热夏季沙柳的光合净积累仅在早上进行,沙柳的最大量子产率在16：00左右最低,表明这一阶段光系统Ⅱ受到抑制,但这种作用至晚间消失。在炎热夏季,荒漠灌木的光合作用日动态曲线表现出典型的双峰型,而在春季则为单峰型,且夏季的第一个峰值比春季的峰值早2h左右。实验表明高温造成了沙柳光合作用的严重抑制,而天然种类羊柴和油蒿则在相同的环境下更抗高温与强光辐射。沙柳在春季适宜的环境下积累光合产物,而大炎热夏季则以维持其生长为主,光合生理特征表明柳不适合在强光与高温等严酷环境下生存,毛乌素沙地沙柳群落经一定时间后开始腿可能与此有关。     

PHENOTYPIC PLASTICITY IN DRAPARNALDIA (CHLOROPHYTA: CHAETOPHORACEAE). I. EFFECTS OF THE CHEMICAL ENVIRONMENT1

Eight axenic isolates of Draparnaldia spp. were in defined media under controlled condidom of day length, light intensity and temperature to study effects of the nutrientions on genera; pheuotype and development of main text cells. Phosphate (0–6,8 mg/l P), magnesium (0-9.6 mg/l Mg), sulfate (1.2 –14.0 mg/l S) and chloride (0.2-48.2mg/l Cl) had no effect. Small, but significant, concentration-independent, isolate-specific differences due to sodium and patassium (as the phosphate salt) occured in main axis cell length. The presence of calcium (>1.7 mg/l) was required by all isolates for main axis differentiation. In the absence of calcium, only zoospores and stunted Stigeoclonium- like plants were produced. Nitrate (>5 mg/l N) depressed main axis cell size;at higher levels (> 15 mg/l N) hair prooduction was depressed and several isolates developed a very typical Cloniophora appearance, Several of the isolates did not produce typical Draparnaldia- like phenotypes under any of the chemical formulations tried; therefore, it is suggested that chemical factors alone do not account for either the phemotypec plasticity of Draparnaldia in the field or the failure of others to grow typical plants in culture.     

THE EVOLUTION OF PHENOTYPIC PLASTICITY IN LIFE-HISTORY TRAITS: PREDICTIONS OF REACTION NORMS FOR AGE AND SIZE AT MATURITY

We used life-history theory to predict reaction norms for age and size at maturation. We assumed that fecundity increases with size and that juvenile mortality rates of offspring decrease as ages-at-maturity of parents increase, then calculated the reaction norm by varying growth rate and calculating an optimal age at maturity for each growth rate. The reaction norm for maturation should take one of at least four shapes that depend on specific relations between changes in growth rates and changes in adult mortality rates, juvenile mortality rates, or both. Most organisms should mature neither at a fixed size nor at a fixed age, but along an age-size trajectory. The model makes possible a clear distinction between the genetic and phenotypic components of variation. The evolved response to selection is reflected in the shape and position of the reaction norm. The phenotypic response of a single organism to rapid or slow growth is defined by the location of its maturation event as a point on the reaction norm. A quantitative test with data from 19 populations and species of fish showed that predictions were in good agreement with observations (r = 0.93, P < 0.0001). The predictions of the model also agreed qualitatively with observed phenotypic variation in age and size at maturity in humans, platyfish, fruit flies, and red deer. This preliminary success suggests that experiments designed to test the predictions directly will be worthwhile.     

REMOTE BIOMINERALIZATION IN DIVARICATE RIBS OF STRIGILLA AND SOLECURTUS (TELLINOIDEA: BIVALVIA)

Deposits composed of aragonite prisms, which were formed aftertheouter shell layer, have been found at the posterior steepslopes ofdivaricate ribs in two species of Strigilla and anothertwo ofSolecurtus. These prisms have their axes oriented perpendicularto theouter shell surface and differ in morphology from fibresof thesurface-parallel composite prisms forming the outer shell.Theydisplay crystalline features indicating that, unlike crystalsformingthe outer shell surface, their growth front was free,unconstrained bythe mantle or periostracum. These particulardeposits are calledfree-growing prisms (FGPs). In these generathe periostracum isclearly not the substrate for biomineralizationand, upon formation,does not adhere to the steep slope of ribs,but detaches at the ribpeak and reattaches towards the posterior,just beyond the foot of theposterior scarps of ribs. In thisway, a sinus or open space developedbetween the internal surfaceof the periostracum and the outer shellsurface along each steeprib slope. These spaces could remain filledwith extrapallialfluid after the mantle advances beyond that pointduring shellsecretion. FGPs grow within this microenvironment, out ofcontactwith the mantle. Other species with divaricate ribs do notdevelopFGPs simply because the periostracum adheres tightly to bothribslopes (which are never so steep as in Solecurtus andStrigilla).FGPs constitute one of the rare cases of remotebiomineralizationin which aragonite is produced and direct contactwith the mantlenever takes place. (Received 22 November 1999; accepted 20 February 2000)     

PHENOTYPIC PLASTICITY IN THE SAILFIN MOLLY,POECILIA LATIPINNA (PISCES: POECILIIDAE). II. LABORATORY EXPERIMENT

Field studies indicate that the influence of environmental factors on growth rate and size and age at maturity in sailfin mollies (Poecilia latipinna) is inconsistent over time and suggest that the marked interdemic variation in male body size in this species is the result of genetic variation. However, the role of specific environmental factors in generating phenotypic variation must be studied under controlled conditions unattainable in nature. We raised newborn sailfin mollies from four populations in laboratory aquaria under all possible combinations of two temperatures, three salinities, and two food levels to examine explicitly the influence of these environmental factors. Males were much less susceptible than females to temperature variation and were generally less plastic than females in terms of all three traits. Members of both sexes matured at larger sizes and at later ages in less saline and in cooler environments. Food levels were not sufficiently different to affect the traits we studied. The effects of temperature and salinity were not synergistic. Males from different populations exhibited different average ages and sizes at maturity, but females did not. The magnitudes of the effects we found were not substantial enough to account for the consistent interdemic differences in male and female body size that have been observed previously. Our results also indicate that no single environmental factor is solely responsible for the environmental effects observed in field experiments on growth and development. These studies, together with other work, indicate that the strongest sources of interdemic variation are genetic differences in males and differences in postmaturation growth and survivorship in females.