Butterfly host plant range: an example of plasticity as a promoter of speciation?

Mary Jane West-Eberhard has suggested that plasticity may be of primary importance in promoting evolutionary innovation and diversification. Here, we explore the possibility that the diversification of phytophagous insects may have occurred through such a process, using examples from nymphalid butterflies. We discuss the ways in which host plant range is connected to plasticity and present our interpretation of how West-Eberhard’s scenario may result in speciation driven by plasticity in host utilization. We then review some of the evidence that diversity of plant utilization has driven the diversification of phytophagous insects and finally discuss whether this suggests a role for plasticity-driven speciation. We find a close conceptual connection between our theory that the diversification of phytophagous insects has been driven by oscillations in host range, and our personal interpretation of the most efficient way in which West-Eberhard’s theory could account for plasticity-driven speciation. A major unresolved issue is the extent to which a wide host plant range is due to adaptive plasticity with dedicated modules of genetic machinery for utilizing different plants.     

Phenolic contents of submerged,emergent and floating leaves of aquatic and semi‐aquatic macrophyte species: why do they differ?

The phenolic content of leaves of 40 aquatic and semi-aquatic plant species, collected from stands distributed over the Netherlands was investigated. Species with submerged leaves showed a significantly lower phenolic content than species with emergent or floating leaves; the latter two showing no significant differences. Possible explanations for the observed differences are discussed in relation to defence strategies.     

Canopy ergodicity: can a single leaf represent an entire plant canopy?

While leaves typically emerge near shoot apices around the outer surface of a plant canopy, their relative position “moves” deeper into the canopy as additional leaves emerge. The photosynthetic capacity (A _max) of a given leaf can be expected to decline over time as its relative position (P _r) in the canopy becomes progressively deeper; this can be observed as a spatial gradient with the A _max of leaves declining distally from the shoot apex. As a consequence, we propose that the photosynthetic capacity averaged over a single leaf’s lifespan is equivalent to the average photosynthetic capacity of the entire plant canopy at a given time; in other words, there is an ergodic time to space averaging in the organization and development of plant canopies. We tested this “canopy ergodic hypothesis” in two woody (Alnus sieboldiana and Mallotus japonica) and two herbaceous (Polygonum sachalinensis and Helianthus tuberosus) species by following the photosynthetic capacity in 100 individual leaves from the time of their emergence until their death. We compared the average photosynthetic capacity of individual leaves through time (time-average) to the average photosynthetic capacity of all the leaves along a shoot at the time of emergence of the focal leaf (space-average). We found that A _max and P _r were positively correlated and that the time-averages of three plant species (Alnus, Mallotus, and Helianthus) were not significantly different from the corresponding space-averages, although the averages differed among individual plants. Polygonum, however, did show significant differences between time and space averages. Ergodicity appears to apply to the leaf–canopy relationship, at least approximately—the average photosynthetic capacity of a single leaf through time (time-average) can represent the average photosynthetic capacity of the entire canopy.     

Changes in aquatic macrophyte communities in Loch Leven: evidence of recovery from eutrophication?

This article assesses changes in the macrophyte community of Loch Leven over a period of 100 years. Evidence is presented that shows that these changes are associated with eutrophication and with subsequent recovery from eutrophication when anthropogenic nutrient inputs to the loch were reduced. This study uses macrophyte survey data from 1905, 1966, 1972, 1975, 1986, 1993, 1999 and 2008. In each of the four most modern surveys, the loch was divided into 19 sectors, each with at least one transect ranging from the shallowest to the deepest occurrence of macrophytes. From these data, a range of indicators of recovery were derived at the whole lake scale: the relative abundance of taxa, taxon richness and evenness. All of these metrics showed an improvement since 1972. Species richness, measured at the scales of survey sector and individual samples, also appeared to have increased in recent years. All of these measures, coupled with ordination of the presence/absence composition data from all survey years, indicate that the macrophyte community in the loch is recovering towards the state that was recorded in 1905.     

Dissecting the epidemiology of a trinucleotide repeat disease – example of FRDA in Finland

Friedreich ataxia (FRDA) is associated with the expansion of a GAA trinucleotide repeat in the first intron of the frataxin (X25) gene. Worldwide it is considered to be the most common form of hereditary ataxia, but it is infrequently encountered in Finland. We have performed the first epidemiological study on the frequency of FRDA in Finland by combining results from a nationwide clinical survey and a molecular carrier testing study. Haplotype analysis was performed for the Finnish FRDA patients and the distribution of frataxin gene GAA repeats was analyzed in controls. In the general population of Finland, the carrier frequency was only 1 in 500, corresponding to a birth incidence of 1 in 10(6). In the more sparsely populated Northern Finland the carrier frequency was five times higher and also four out of the seven Finnish FRDA patients originated from this region. Haplotype analysis revealed the major universal risk haplotype in all the investigated patients. Alleles in the uppermost end of the normal variation (28-36 GAA) were totally missing in the Finnish population. The relative enrichment of the FRDA mutation in the north probably dates back to the internal migration movement and inhabitation of northern Finland in the 1500s. Breaking down the epidemiology of FRDA into clinical and molecular components brings along the possibility of providing more reliable and population-based genetic counseling and recurrence risk estimations.     

Vertical canopy gradients in δ13C correspond with leaf nitrogen content in a mixed-species conifer forest

Stable carbon isotope composition varies markedly between sun and shade leaves, with sun leaves being invariably more enriched (i.e., they contain more¹³C). Several hypotheses have emerged to explain this pattern, but controversy remains as to which mechanism is most general. We measured vertical gradients in stable carbon isotope composition (δ¹³C) in more than 200 trees of nine conifer species growing in mixed-species forests in the Northern Rocky Mountains, USA. For all species except western larch, δ¹³C decreased from top to bottom of the canopy. We found that δ¹³C was strongly correlated with nitrogen per unit leaf area (N _area), which is a measure of photosynthetic capacity. Usually weaker correlations were found between δ¹³C and leaf mass per area, nitrogen per unit leaf mass, height from the ground, or depth in the canopy, and these correlations were more variable between trees than for N _area. Gradients of δ¹³C (per meter canopy depth) were steeper in small trees than in tall trees, indicating that a recent explanation of δ¹³C gradients in terms of drought stress of upper canopy leaves is unlikely to apply in our study area. The strong relationship between N _area and δ¹³C here reported is consistent with the general finding that leaves or species with higher photosynthetic capacity tend to maintain lower CO₂ concentrations inside leaves. We conclude that photosynthetic capacity is a strong determinant of δ¹³C in vertical canopy profiles, and must be accounted for when interpreting δ¹³C values in conifer forests.     

Equilibrium freezing of leaf water and extracellular ice formation in Afroalpine ‘giant rosette’ plants

The water potentials of frozen leaves of Afroalpine plants were measured psychrometrically in the field. Comparison of these potentials with the osmotic potentials of an expressed cellular sap and the water potentials of ice indicated almost ideal freezing behaviour and suggested equilibrium freezing. On the basis of the osmotic potentials of expressed cellular sap, the fractions of frozen cellular water which correspond to the measured water potentials of the frozen leaves could be determined (e.g. 74% at -3.0° C). The freezing points of leaves were found to be in the range between 0° C and -0.5° C, rendering evidence for freezing of almost pure water and thus confirming the conclusions drawn from the water-potential measurements. The leaves proved to be frost resistant down to temperatures between -5° C and -15° C, as depending on the species. They tolerated short supercooling periods which were necessary in order to start ice nucleation. Extracellular ice caps and ice crystals in the intercellular space were observed when cross sections of frozen leaves were investigated microscopically at subfreezing temperatures.Symbols T temperature - water potential Dedicated to Professor Dr. Hubert Ziegler on the occasion of his 60th birthday     

Coexistence of behavioural types in an aquatic top predator: a response to resource limitation?

Intra-population variation in behaviour unrelated to sex, size or age exists in a variety of species. The mechanisms behind behavioural diversification have only been partly understood, but density-dependent resource availability may play a crucial role. To explore the potential coexistence of different behavioural types within a natural fish population, we conducted a radio telemetry study, measuring habitat use and swimming activity patterns of pike (Esox lucius), a sit-and-wait predatory fish. Three behavioural types co-occurred in the study lake. While two types of fish only selected vegetated littoral habitats, the third type opportunistically used all habitats and increased its pelagic occurrence in response to decreasing resource biomasses. There were no differences in size, age or lifetime growth between the three behavioural types. However, habitat-opportunistic pike were substantially more active than the other two behavioural types, which is energetically costly. The identical growth rates exhibited by all behavioural types indicate that these higher activity costs of opportunistic behaviour were compensated for by increased prey consumption in the less favourable pelagic habitat resulting in approximately equal fitness of all pike groups. We conclude that behavioural diversification in habitat use and activity reduces intraspecific competition in preferred littoral habitats. This may facilitate the emergence of an ideal free distribution of pike along resource gradients.     

Treacher Collins syndrome—an example of a craniofacial development defect

Treacher Collins syndrome is an autosomal dominant disorder of craniofacial development the features of which include conductive hearing loss and cleft palate; diagnosis is complicated by marked variability in expression. Whilst the underlying genetic defect is unknown it is thought to be due to an abnormality of neural crest cell migration. The mutated gene has been mapped to chromosome 5q32-33.1, a high resolution genetic and radiation hybrid map surrounding the locus created, and flanking markers identified. The critical region has subsequently been cloned in yeast artificial chromosome and attempts to isolate the mutated gene are in progress.     

Approaching the taxonomic affiliation of unidentified sequences in public databases – an example from the mycorrhizal fungi

Background  

During the last few years, DNA sequence analysis has become one of the primary means of taxonomic identification of species, particularly so for species that are minute or otherwise lack distinct, readily obtainable morphological characters. Although the number of sequences available for comparison in public databases such as GenBank increases exponentially, only a minuscule fraction of all organisms have been sequenced, leaving taxon sampling a momentous problem for sequence-based taxonomic identification. When querying GenBank with a set of unidentified sequences, a considerable proportion typically lack fully identified matches, forming an ever-mounting pile of sequences that the researcher will have to monitor manually in the hope that new, clarifying sequences have been submitted by other researchers. To alleviate these concerns, a project to automatically monitor select unidentified sequences in GenBank for taxonomic progress through repeated local BLAST searches was initiated. Mycorrhizal fungi – a field where species identification often is prohibitively complex – and the much usedITSlocus were chosen as test bed.     

Cell and leaf size plasticity in Arabidopsis: what is the role of endoreduplication?

Leaf area expansion is affected by environmental conditions because of differences in cell number and/or cell size. Increases in the DNA content (ploidy) of a cell by endoreduplication are related to its size. The aim of this work was to determine how cell ploidy interacts with the regulation of cell size and with leaf area expansion. The approach used was to grow Arabidopsis thaliana plants performing increased or decreased rounds of endoreduplication under shading and water deficit. The shading and water deficit treatments reduced final leaf area and cell number; however, cell area was increased and decreased, respectively. These differences in cell size were unrelated to alterations of the endocycle, which was reduced by these treatments. The genetic modification of the extent of endoreduplication altered leaf growth responses to shading and water deficit. An increase in the extent of endoreduplication in a leaf rendered it more sensitive to the shade treatment but less sensitive to water deficit conditions. The link between the control of whole organ and individual cell expansion under different environmental conditions was demonstrated by the correlation between the plasticity of cell size and the changes in the duration of leaf expansion.     

Food,microhabitat, or both? Macroinvertebrate use of leaf accumulations in a montane stream

1. Leaf packs in streams may serve as food and substrate to many macroinvertebrates, but the relative importance of these two functions has not been disentangled. To test the hypothesis that leaf packs are colonized primarily for their food value rather than as microhabitat, the colonization of leaf packs of red alder and of polyester cloth in a natural stream was compared. 2. Species of shredders showed large differences in the colonization of the two types of leaf pack with almost no use of artificial leaf packs. Non-shredders were also more abundant on natural leaf packs, however, they colonized artificial leaf packs six to eighty times proportionally more than shredders. 3. The effect of different leaf types was virtually eliminated for non-shredders when the amount of fine parriculate detritus (food for many non-shredders) trapped in the leaf pack was added to the analysis as a covariate. Therefore, to non-shredders, leaf types differed only in the retention of fine particulate organic matter. 4. Comparisons of the use of both kinds of leaf packs in riffles versus pools revealed that significantly fewer animals colonized pool leaf packs. 5. These results suggest that food value, and not microhabitat, is the primary determinant of leaf pack use for most shredders and non-shredders.     

Advances in management and utilization of invasive water hyacinth (Eichhornia crassipes) in aquatic ecosystems – a review

The objective of this review is to provide a concise summary of literature in the Chinese language since late 1970s and focuses on recent development in global scenarios. This work will replenish the FAO summary of water hyacinth utilization from 1917 to 1979 and review ecological and socioeconomic impacts of the water hyacinth from 1980 to 2010. This review also discusses the debate on whether the growth of the water hyacinth is a problem, a challenge or an opportunity. Literature suggested that integrated technologies and good management may be an effective solution and the perception of water hyacinth could change from that of a notorious aquatic weed to a valuable resource, including its utilization as a biological agent for the application in bioremediation for removing excess nutrients from eutrophic water bodies at low cost. Key aspects on system integration and innovation may focus on low-cost and efficient equipment and the creation of value-added goods from water hyacinth biomass. In the socioeconomic and ecological domain of global development, all the successful and sustainable management inputs for the water hyacinth must generate some sort of social and economic benefit simultaneously, as well as benefiting the ecosystem. Potential challenges exist in linkages between the management of water hyacinth on the large scale to the sustainable development of agriculture based on recycling nutrients, bio-energy production or silage and feed production. Further research and development may focus on more detailed biology of water hyacinth related with its utilization, cost–benefit analysis of middle to large-scale application of the technologies and innovation of the equipment used for harvesting and dehydrating the plant.     

Invasion strategies in clonal aquatic plants: are phenotypic differences caused by phenotypic plasticity or local adaptation?

Background and Aims

The successful spread of invasive plants in new environments is often linked to multiple introductions and a diverse gene pool that facilitates local adaptation to variable environmental conditions. For clonal plants, however, phenotypic plasticity may be equally important. Here the primary adaptive strategy in three non-native, clonally reproducing macrophytes (Egeria densa, Elodea canadensis and Lagarosiphon major) in New Zealand freshwaters were examined and an attempt was made to link observed differences in plant morphology to local variation in habitat conditions.

Methods

Field populations with a large phenotypic variety were sampled in a range of lakes and streams with different chemical and physical properties. The phenotypic plasticity of the species before and after cultivation was studied in a common garden growth experiment, and the genetic diversity of these same populations was also quantified.

Key Results

For all three species, greater variation in plant characteristics was found before they were grown in standardized conditions. Moreover, field populations displayed remarkably little genetic variation and there was little interaction between habitat conditions and plant morphological characteristics.

Conclusions

The results indicate that at the current stage of spread into New Zealand, the primary adaptive strategy of these three invasive macrophytes is phenotypic plasticity. However, while limited, the possibility that genetic diversity between populations may facilitate ecotypic differentiation in the future cannot be excluded. These results thus indicate that invasive clonal aquatic plants adapt to new introduced areas by phenotypic plasticity. Inorganic carbon, nitrogen and phosphorous were important in controlling plant size of E. canadensis and L. major, but no other relationships between plant characteristics and habitat conditions were apparent. This implies that within-species differences in plant size can be explained by local nutrient conditions. All together this strongly suggests that invasive clonal aquatic plants adapt to a wide range of habitats in introduced areas by phenotypic plasticity rather than local adaptation.