Effects of light heterogeneity on growth of a submerged clonal macrophyte

Many studies have examined the effects of spatial heterogeneity in light supply on clonal plants in terrestrial environments, but few have examined those in aquatic conditions. In a greenhouse experiment, we grew the rhizomatous submerged macrophyte Vallisneria spiralis L. in containers in three homogeneous light treatments (100%, 65%, and 30% of ambient light coded as high, medium, and low light, respectively) and two heterogeneous ones differing in patch scale (small and large patch). The growth of V. spiralis decreased significantly with decreasing light availability. In the low light conditions, V. spiralis allocated greater biomass to shoots and developed elongated leaves. In the patchy treatments, ramets distributed in the light‐rich patches had significant costs in the large patch treatment, but not in the small patch treatment, while both small and large patch treatments had no significant benefits in the light‐poor patches. We conclude that V. spiralis could escape from adverse habitats and occupy the favorable habitats. Providing the same amount of light, responses of V. spiralis to different patch scales were different at the patch level, but not at the whole clone level. Together, growth of V. spiralis could not benefit from different patch scales in heterogeneous environments at the patch as well as the whole clone level.     

To share or not to share: Incentivizing data sharing in life science communities

Most scientists recognize the importance of sharing data online in an open fashion. Nonetheless, many studies have documented the concerns that accompany data sharing activities, including loss of credit or IP, misuse and the time needed to curate interoperable data. To this end, discussions around data sharing often identify incentives that could potentially ameliorate these disincentivising concerns. Nonetheless, current Open Data discussions often rely on evidence‐based studies to identify the disincentives to overcome. This results in highly specific and directed interventions. In contrast, this paper offers a different interpretation of these concerns. To do so, it makes use of the Thomas Theorem which suggests that: “If men define situations as real, they are real in their consequences”. Using empirical evidence from sub‐Saharan African (bio)chemistry laboratories, this paper illustrates how individual perceptions of research environments – whether associated with evidence or not – are highly influential in shaping data sharing practices. It concludes with the suggestion that discussion on incentivising data sharing amongst scientific communities need to take a broader set of concerns into account and offer a more creative approach to ameliorating environmental disincentives.     

Dynamics of submerged macrophyte populations in response to biomanipulation

1. A 6‐year study (1992–97) of changes in submerged vegetation after biomanipulation was carried out in the eutrophicated Lake Finjasjön, Southern Sweden. Ten sites around the lake were revisited each year. At each site five samples of above‐ground biomass were taken at 10 cm water depth intervals. An investigation of the seed bank at the 10 sites, and a grazing experiment where birds and large fish were excluded was also conducted. 2. Between 1992 and 1996, in shallow areas (water depth < 3 m), vegetation cover increased from < 3 to 75% and above‐ground biomass from < 1 to 100 g DW m^–2. Mean outer water depth increased from 0.3 to 2.5 m. Elodea canadensis and Myriophyllum spicatum accounted for > 95% of the increase in biomass and plant cover. The following year (1997), however, cover and above‐ground biomass decreased, mainly attributable to the total disappearance of E. canadensis. Secchi depth increased after biomanipulation until 1996, but decreased again in 1997. 3. Total and mean number of submerged species increased after biomanipulation, probably as a result of the improved light climate. However, after the initial increase in species number there was a decrease during the following years, possibly attributed to competition from the rapidly expanding E. canadensis and M. spicatum. The lack of increase in species number after the disappearance of E. canadensis in 1997 implies that other factors also affected species richness. 4. A viable seed bank was not necessary for a rapid recolonization of submerged macrophytes, nor did grazing by waterfowl or fish delay the re‐colonization of submerged macrophytes. 5. Submerged macrophytes are capable of rapid recolonization if conditions improve, even in large lakes such as Finjasjön (11 km²). Species that spread by fragments will increase rapidly and probably outcompete other species. 6. The results indicate that after the initial Secchi depth increase, probably caused by high zooplankton densities, submerged vegetation further improved the light climate. The decrease in macrophyte biomass in 1997 may have caused the observed increase in phosphorus and chlorophyll a, and the decrease in Secchi depth. We suggest that nutrient competition from periphyton, attached to the macrophytes, may be an important factor in limiting phytoplankton production, although other factors (e.g. zooplankton grazing) are also of importance, especially as triggers for the shift to a clear‐water state.     

To breed or not to breed: a seabird's response to extreme climatic events

Intermittent breeding is an important life-history strategy that has rarely been quantified in the wild and for which drivers remain unclear. It may be the result of a trade-off between survival and reproduction, with individuals skipping breeding when breeding conditions are below a certain threshold. Heterogeneity in individual quality can also lead to heterogeneity in intermittent breeding. We modelled survival, recruitment and breeding probability of the red-footed booby (Sula sula), using a 19 year mark–recapture dataset involving more than 11 000 birds. We showed that skipping breeding was more likely in El-Niño years, correlated with an increase in the local sea surface temperature, supporting the hypothesis that it may be partly an adaptive strategy of birds to face the trade-off between survival and reproduction owing to environmental constraints. We also showed that the age-specific probability of first breeding attempt was synchronized among different age-classes and higher in El-Niño years. This result suggested that pre-breeders may benefit from lowered competition with experienced breeders in years of high skipping probabilities.     

Morphological responses of a submerged macrophyte to epiphyton

Epiphyton might have distinctive influence on the morphology of substrate macrophyte. In this article, we evaluate the influence of epiphyton on the morphological characteristics of their substrate submerged macrophyte, Potamogeton perfoliatus under two light intensities. The experiment was carried out for a period of 84 days in 12 glass aquaria under laboratory conditions. It was based on a 2 × 2 factorial design with epiphyton status (present or absent) and light intensity (200 or 80 μE m⁻² s⁻¹). Both epiphyton and light intensity had significant effects on the morphology and biomass allocation of the experimental plants. The average number of leaves, total length of newly recruited shoots and diameter of stems were greater in the epiphyton-free control plants than in the epiphyton-colonized plants under low light conditions. The plants with epiphyton allocated more biomass in their rhizomes and roots (% relative to total biomass basis) when compared to the control plants in both light intensities. There were also significant epiphyton–light interactions. The control plants under low light intensity showed higher internodal elongation in their main shoots when compared to the plants under high light intensity as an adaptation mechanism. Whereas the plants with epiphyton did not show such an adaptation. The new shoots of the control plants under low light intensity did not show any internodal elongation as observed in the main shoots. Furthermore, the length of the leaves of main shoots was larger in control plants with epiphyton and high light intensity than in plants with epiphyton and low light intensity, but such a variation was absent in the new shoots. We conclude that the long-term colonization by epiphyton and their shading effects induced the observed morphological changes in plants.     

Habitat selection in spatially heterogeneous environments: a test of foraging behaviour in the clonal submerged macrophyte Vallisneria spiralis

1. To test whether clonal macrophytes can select favourable habitats in heterogeneous environments, clonal fragments of the stoloniferous submerged macrophyte Vallisneria spiralis were subjected to conditions in which light intensity and substratum nutrients were patchily distributed. The allocation of biomass accumulation and ramet production of clones to the different patches was examined. 2. The proportion of both biomass and ramet number of clones allocated to rich patches was significantly higher than in poor patches. The greatest values of both clone and leaf biomass were produced in the heterogeneous light treatment, in which clones originally grew from light‐rich to light‐poor patches, while clones produced the most offspring ramets in the treatments with heterogeneous substratum nutrients. Similarly, root biomass had the highest values in nutrient‐rich patches when clones grew from nutrient‐rich to nutrient‐poor patches. 3. The quality of patches in which parent ramets established significantly influenced the foraging pattern. When previously established in rich patches, a higher proportion of biomass was allocated to rich patches, whereas a higher proportion of ramet number was allocated to rich patches when previously established in poor patches. 4. Results demonstrate that the clonal macrophyte V. spiralis can exhibit foraging in submerged heterogeneous environments: when established under resource‐rich conditions V. spiralis remained in favourable patches, whereas if established in adverse conditions it could escape by allocating more ramets to favourable patches.     

Physiological integration helps a clonal macrophyte spread into competitive environments and coexist with other species

Physiological integration may help clonal macrophytes invade or escape from existing communities. No studies have tested the above hypothesis in aquatic plants. In an outdoor pond experiment, we subjected clonal fragments of the submerged macrophyte Vallisneria spiralis L. to heterogeneous environments in which V. spiralis spread from bare habitats towards vegetated habitats occupied by Myriophyllum spicatum L. or V. spiralis spread from vegetated habitats towards bare habitats. V. spiralis stolons between ramets in bare habitats and in vegetated habitats were either intact or severed. We investigated the habitat selection of V. spiralis by examining the allocation of biomass and ramets to heterogeneous habitats during its vegetative spread phase. Results showed that the stolon connection had different effects on the habitat selection of V. spiralis with regard to invasion and escape. When V. spiralis spread from bare to vegetated habitats, in comparison to severing the stolon, the stolon connection eventually facilitated a 49% increase in biomass and a 27% increase in number of ramets allocated to vegetated habitats. However, when V. spiralis spread from vegetated to bare habitats, biomass and ramets allocated to bare habitats were not significantly changed by the stolon connection (only a 5% increase in biomass and a 6% increase in number of ramets). These results indicate that clonal integration facilitated V. spiralis not to escape from but invade into vegetated habitats. The study provides evidence that physiological integration is important for survival and tolerance of ramets in competitively stressful environments and can help clonal macrophytes coexist with other species.     

Stress response and tolerance of the submerged macrophyte Elodea nuttallii (Planch) St. John to heat stress: a comparative study of shock heat stress and gradual heat stress

Sudden and gradual increases of temperature in aquatic environments play important roles in determining growth and physiological dynamics of aquatic macrophytes. However, a lesser attention has been paid to identify the effects of different temperature regimes on aquatic macrophytes. Therefore, the present study is focused on comparing the effects of shock and gradual heat stresses (SHS and GHS) on growth, photosynthetic attributes, and oxidative damage on Elodea nuttallii as a model plant. Laboratory-oriented two experimental setups were maintained to induce the SHS and GHS. A significant decline in shoot elongation coupled with a decline in endogenous indoleacetic acid (IAA) and an increase in hydrogen peroxide (H₂O₂) was observed in both temperature treatments. These effects were further accompanied by oxidative damage to photosynthetic pigments and cell membrane structures in E. nuttallii. Temperature-mediated oxidative stress was significantly pronounced under SHS, which induced the activation of different defensive mechanisms against reactive oxygen species, including antioxidant enzymes, secondary metabolites, and osmoprotectants. The present study revealed that temperature-induced oxidative damage was more severe when the temperature increased suddenly. Further, heat acclimation was observed when the plant was exposed to 30 °C under GHS, although this treatment induces significant oxidative stress under 35 °C.     

To fly or not to fly: response of water striders to drying out of habitat

Abstract .1. Adults of Aquarius paludum inhabit both temporary and permanent water surfaces; Gerris latiabdominis lives only in temporary habitats. To clarify whether adults of both species stay in position or fly when habitats dry up, overwintered adults of A. paludum and G. latiabdominis collected in spring were reared under one of the following four conditions: (A) on water with sufficient food, (B) on water, starved, (C) on wet paper with sufficient food, (D) on wet paper, starved. All rearings were at LD 15.5:8.5 h, 20 ± 2 °C, resembling natural conditions for April to June.
2. Females of A. paludum in group C had lower fecundity than the control group A and some stopped laying eggs. When a water surface was restored, females that had entered reproductive diapause began to lay eggs again. In contrast, females of G. latiabdominis continued to lay eggs even when reared on damp paper.
3. Adults of A. paludum lived longer and adopted diapause posture with high frequency when starved and reared without a water surface. There were, however, no significant differences in the longevity or in the number of adults showing diapause posture between groups A and D of G. latiabdominis.
4. Females of A. paludum collected in the middle of May had more mature oocytes (mean: 20.8) than females of G. latiabdominis (mean: 8.0), and most had histolysed their indirect flight muscles; most females of G. latiabdominis had retained their flight muscles and flew readily.
5. When water surfaces dry, with food shortage, adults of A. paludum may survive in place for a relatively long time until the water surface returns. Adults of G. latiabdominis may fly to other water surfaces and reproduce without delay.     

To tree or not to tree

The practice of tracking geographical divergence along a phylogenetic tree has added an evolutionary perspective to biogeographic analysis within single species. In spite of the popularity of phylogeography, there is an emerging problem. Recurrent mutation and recombination both create homoplasy, multiple evolutionary occurrences of the same character that are identical in state but not identical by descent. Homoplasic molecular data are phylogenetically ambiguous. Converting homoplasic molecular data into a tree represents an extrapolation, and there can be myriad candidate trees among which to choose. Derivative biogeographic analyses of 'the tree' are analyses of that extrapolation, and the results depend on the tree chosen. I explore the informational aspects of converting a multicharacter data set into a phylogenetic tree, and then explore what happens when that tree is used for population analysis. Three conclusions follow: (i) some trees are better than others; good trees are true to the data, whereas bad trees are not; (ii) for biogeographic analysis, we should use only good trees, which yield the same biogeographic inference as the phenetic data, but little more; and (iii) the reliable biogeographic inference is inherent in the phenetic data, not the trees.     

To permute or not to permute

Permutation test is a popular technique for testing a hypothesis of no effect, when the distribution of the test statistic is unknown. To test the equality of two means, a permutation test might use a test statistic which is the difference of the two sample means in the univariate case. In the multivariate case, it might use a test statistic which is the maximum of the univariate test statistics. A permutation test then estimates the null distribution of the test statistic by permuting the observations between the two samples. We will show that, for such tests, if the two distributions are not identical (as for example when they have unequal variances, correlations or skewness), then a permutation test for equality of means based on difference of sample means can have an inflated Type I error rate even when the means are equal. Our results illustrate permutation testing should be confined to testing for non-identical distributions. CONTACT: calian@raunvis.hi.is.     

To model or not to model

Summary Self-improving control systems may belong to either of two categories, according to whether or not they embody an explicit model of the part of their environment with which they interact. The two forms of operation are discussed and compared, and it is shown that the two may be mathematically equivalent. The treatment also gives theoretical justification for a particular mode of operation for nonmodel-forming controllers.