Longevity of clonal plants: why it matters and how to measure it

Background

Species'' life-history and population dynamics are strongly shaped by the longevity of individuals, but life span is one of the least accessible demographic traits, particularly in clonal plants. Continuous vegetative reproduction of genets enables persistence despite low or no sexual reproduction, affecting genet turnover rates and population stability. Therefore, the longevity of clonal plants is of considerable biological interest, but remains relatively poorly known.

Scope

Here, we critically review the present knowledge on the longevity of clonal plants and discuss its importance for population persistence. Direct life-span measurements such as growth-ring analysis in woody plants are relatively easy to take, although, for many clonal plants, these methods are not adequate due to the variable growth pattern of ramets and difficult genet identification. Recently, indirect methods have been introduced in which genet size and annual shoot increments are used to estimate genet age. These methods, often based on molecular techniques, allow the investigation of genet size and age structure of whole populations, a crucial issue for understanding their viability and persistence. However, indirect estimates of clonal longevity are impeded because the process of ageing in clonal plants is still poorly understood and because their size and age are not always well correlated. Alternative estimators for genet life span such as somatic mutations have recently been suggested.

Conclusions

Empirical knowledge on the longevity of clonal species has increased considerably in the last few years. Maximum age estimates are an indicator of population persistence, but are not sufficient to evaluate turnover rates and the ability of long-lived clonal plants to enhance community stability and ecosystem resilience. In order to understand the dynamics of populations it will be necessary to measure genet size and age structure, not only life spans of single individuals, and to use such data for modelling of genet dynamics.     

The size of the largest marsupial and why it matters

We show that at 2786 kg, the largest known marsupial, Diprotodon optatum, was much larger than has previously been suggested. Our results contradict the conclusion that the maximum attainable body mass of an Australian marsupial has been constrained by low productivity.     

Same river,different values and why it matters

Summary Examination of the values that people assign to specific natural places is likely to be useful for environmental decision‐making but is an underdeveloped area of socio‐psychological research. A mail survey was used to examine the differences and similarities in values assigned by people to the Loddon River in south‐eastern Australia. Environmental, social and economic values were explored across five different community types: urban residents, rural residents, natural resource management (NRM) professionals, environmental group members (EGM) and landholders. While urban residents, rural residents and landholders had similar responses, NRM professionals and EGM placed much stronger emphasis on environmental values derived from the river, and much less emphasis on economic values. Members of two community types (EGM and NRM professionals) responded in a relatively homogenous way, within a narrow range of response options. By contrast, three community types (urban residents, rural residents and landholders) responded in more diverse ways. There were similarities in the social values (historical and aesthetic) expressed by the different community types, suggesting common points for stakeholder engagement in the management of the river. Results point to the need for environmental managers to ensure that consultation is not limited to the most actively engaged sectors of the community, as their responses may not be representative of other groups.     

Pollination failure in plants: why it happens and when it matters

Pollination is the primary step in seed formation. Pollination biologists have shown that pollination failure can occur at all steps in the dispersal process and at several different levels. Increased risk of pollination failure is associated with pollen if it is delivered to a stigma too little, too much, too late, too mixed in composition or too poor in quality. It is associated with pollinators when they are too few or too inconstant, and with plants when they are too specialized or too selective. It is associated with populations when they are too sparse, too small in number or too uniform genetically, and with communities when they are too fragmented, genetically impoverished or under rapid modification. Understanding the causes of pollination failure in plants can aid the successful conservation and recovery of rare plants, maintenance of crop yields, and sustainable use of wild plant resources such as forest timber.     

The role of values in scientific theory selection and why it matters to medical education

In this paper, I argue that the role of values in theory selection is an important issue within medical education. I review the underdetermination argument, which is the idea within philosophy of science that the data serving as evidence for theories are by themselves not sufficient to support a theory to the exclusion of alternatives. There are always various explanations compatible with the data, and we ultimately appeal to certain values as our grounds for choosing one theory over another. I explore some of the ways contemporary feminist philosophers have chosen to grapple with the problem of underdetermination and proposed solutions to systematize how values might be incorporated into theory choice, drawing primarily from the work of Helen Longino and Elizabeth Anderson. I conclude by discussing how value‐laden inquiry should be incorporated within medical education to promote reflection towards medicine’s normative underpinnings.     

Linking exposure to environmental pollutants with biological effects

Exposure to ambient air pollution has been associated with cancer. Ambient air contains a complex mixture of toxics, including particulate matter (PM) and benzene. Carcinogenic effects of PM may relate both to the content of PAH and to oxidative DNA damage generated by transition metals, benzene, metabolism and inflammation. By means of personal monitoring and biomarkers of internal dose, biologically effective dose and susceptibility, it should be possible to characterize individual exposure and identify air pollution sources with relevant biological effects. In a series of studies, individual exposure to PM(2.5), nitrogen dioxide (NO(2)) and benzene has been measured in groups of 40-50 subjects. Measured biomarkers included 1-hydroxypyrene, benzene metabolites (phenylmercapturic acid (PMA) and trans-trans-muconic acid (ttMA)), 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in urine, DNA strand breaks, base oxidation, 8-oxodG and PAH bulky adducts in lymphocytes, markers of oxidative stress in plasma and genotypes of glutathione transferases (GSTs) and NADPH:quinone reductase (NQO1). With respect to benzene, the main result indicates that DNA base oxidation is correlated with PMA excretion. With respect to exposure to PM, biomarkers of oxidative damage showed significant positive association with the individual exposure. Thus, 8-oxodG in lymphocyte DNA and markers of oxidative damage to lipids and protein in plasma associated with PM(2.5) exposure. Several types of DNA damage showed seasonal variation. PAH adduct levels, DNA strand breaks and 8-oxodG in lymphocytes increased significantly in the summer period, requiring control of confounders. Similar seasonal effects on strand breaks and expression of the relevant DNA repair genes ERCC1 and OGG1 have been reported.In the present setting, biological effects of air pollutants appear mainly related to oxidative stress via personal exposure and not to urban background levels. Future developments include personal time-resolved monitors for exposure to ultrafine PM and PM(2.5,) use of GPS, as well as genomics and proteomics based biomarkers.     

Natural history of model organisms: The secret (group) life of Drosophila melanogaster larvae and why it matters to developmental ecology

1. Model organisms such as Drosophila melanogaster have been key tools for advancing our fundamental and applied knowledge in biological and biomedical sciences. However, model organisms have become intertwined with the idea of controlled and stable laboratory environments, and their natural history has been overlooked.
2. In holometabolous insects, lack of natural history information on larval ecology has precluded major advances in the field of developmental ecology, especially in terms of manipulations of population density early in life (i.e., larval density). This is because of relativistic and to some extent, arbitrary methodologies employed to manipulate larval densities in laboratory studies. As a result, these methodologies render comparisons between species impossible, precluding our understanding of macroevolutionary responses to population densities during development that can be derived from comparative studies.
3. We recently proposed a new conceptual framework to address this issue, and here, we provide the first natural history investigation of Drosophila melanogaster larval density under such framework. First, we characterized the distribution of larval densities in a wild population of D. melanogaster using rotting apples as breeding substrate in a suburban area in Sweden.
4. Next, we compiled the commonly used methodologies for manipulating larval densities in laboratory studies from the literature and found that the majority of laboratory studies identified did not manipulate larval densities below or above the densities observed in nature, suggesting that we have yet to study true life history and physiological responses to low and high population densities during D. melanogaster development.
5. This is, to our knowledge, the first direct natural history account of larval density in nature for this model organism. Our study paves the way for a more integrated view of organismal biology which re‐incorporates natural history of model organisms into hypothesis‐driven research in developmental ecology.

     

Linking dung beetle-mediated functions to interactions in the Atlantic Forest: Sampling design matters

Interactions between dung beetles and vertebrate dung are intimately linked to a suite of ecosystem functions in tropical forests. We show that the trapping method and the type of dung used affect the suite of beetles captured, with the potential to influence the outcome of experiments linking functions to interactions.     

Linking variability of tree water use and growth with species resilience to environmental changes

Tree growth is an indicator of tree vitality and its temporal variability is linked to species resilience to environmental changes. Second-order statistics that quantify the cross-scale temporal variability of ecophysiological time series (statistical memory) could provide novel insights into species resilience. Species with high statistical memory in their tree growth may be more affected by disturbances, resulting in lower overall resilience and higher vulnerability to environmental changes. Here, we assessed the statistical memory, as quantified with the decay in standard deviation with increasing time scale, in tree water use and growth of co-occurring European larch Larix decidua and Norway spruce Picea abies along an elevational gradient in the Swiss Alps using measurements of stem radius changes, sap flow and tree-ring widths. Local-scale interspecific differences between the two conifers were further explored at the European scale using data from the International Tree-Ring Data Bank. Across the analysed elevational gradient, tree water use showed steeper variability decay with increasing time scale than tree growth, with no significant interspecific differences, highlighting stronger statistical memory in tree growth processes. Moreover, Norway spruce displayed slower decay in growth variability with increasing time scale (higher statistical memory) than European larch; a pattern that was also consistent at the European scale. The higher statistical memory in tree growth of Norway spruce in comparison to European larch is indicative of lower resilience of the former in comparison to the latter, and could potentially explain the occurrence of European larch at higher elevations at the Alpine treeline. Single metrics of resilience cannot often summarize the multifaceted aspects of ecosystem functioning, thus, second-order statistics that quantify the strength of statistical memory in ecophysiological time series could complement existing resilience indicators, facilitating the assessment of how environmental changes impact forest growth trajectories and ecosystem services.     

Size matters when it comes to the survival of transplanted yellow gorgonian fragments

The yellow gorgonian Eunicella cavolini is a Mediterranean endemic coral. Mediterranean populations underwent sharp decreases in the last decades due to climatic anomalies. In the meanwhile, populations in the Sea of Marmara thrive under conditions exempted from significant thermal variations thanks to the peculiar oceanography of the basin. However, they are vulnerable to anthropogenic activities, such as fishing, coastal constructions, dredging and landfilling. Major infrastructure projects at two remote islands, Yassıada and Sivriada, put healthy gorgonian communities at risk. We observed many dead colonies when Yassıada was constructed and before operations commenced on Sivriada, we transplanted gorgonian fragments 13 km away to a site at lower risk from construction. The transplantation site already hosts yellow gorgonian as sparse colonies; but also, it sits within an important fishing area, and entangled nets over rocks are common. Therefore, together with a local NGO, we initiated conservation efforts simultaneously with the transplantation works. 300 gorgonian fragments in the 4.5–15.4 cm size range were transplanted in two years (2017 – 2019). At six months, the survival of the colonies was significantly size dependent. Fragments of 10 – 15.4 cm initial sizes had the highest survival rate (up to 90 %), while small fragments yielded substantially lower survival. Despite severe impacts from fishing nets and mucilaginous entanglement, 50 % of fragments larger than 10 cm survived after 4.5 years of plantation. Besides, several recruits were observed among 4.5 years old transplants. Therefore, when restoration by raw transplantation actions is planned for gorgonians with thin scleraxis, a minimum fragment size of 10 cm is recommended. The study was a notable example of science/NGO collaboration with substantial local conservation success by using extensive media coverage of conservation efforts as leverage to declare the recipient area as a Marine Protected Area.