Does the hygiene hypothesis apply to COVID-19 susceptibility?

In this commentary we argue that the hygiene hypothesis may apply to COVID-19 susceptibility and also that residence in low hygienic conditions acts to train innate immune defenses to minimize the severity of infection. We advocate that approaches, which elevate innate immune functions, should be used to minimize the consequences of COVID-19 infection at least until effective vaccines and antiviral therapies are developed.     

Does Bertrand's rule apply to macronutrients?

It has been known for over a century that the dose-response curve for many micronutrients is non-monotonic, having an initial stage of increasing benefits with increased intake, followed by increasing costs as excesses become toxic. This phenomenon, termed Bertrand's rule, is widely assumed not to apply to caloric macronutrients. To date this assumption has been safe, owing to the considerable methodological challenges involved in coaxing animals to over-ingest macronutrients in a way that enables the effects of specific food components to be isolated. Here we report an experiment which overcomes these difficulties, to test whether the second phase (incurring costs with excessive intake) applies to carbohydrate intake by the generalist-feeding caterpillar Spodoptera littoralis. The results showed that excess carbohydrate intake caused increased mortality, thus extending Bertrand's rule to macronutrients.     

Does the Animal Welfare Act apply to free-ranging animals?

Despite the long-standing role that institutional animal care and use committees (IACUCs) have played in reviewing and approving studies at academic institutions, compliance with the Animal Welfare Act (AWA) is not always complete for government natural resource agencies that use free-ranging animals in research and management studies. Even at universities, IACUCs face uncertainties about what activities are covered and about how to judge proposed research on free-ranging animals. One reason for much of the confusion is the AWA vaguely worded exemption for "field studies." In particular, fish are problematic because of the AWA exclusion of poikilothermic animals. However, most university IACUCs review studies on all animals, and the Interagency Research Animal Committee (IRAC) has published the "IRAC Principles," which extend coverage to all vertebrates used by federal researchers. Despite this extended coverage, many scientists working on wild animals continue to view compliance with the AWA with little enthusiasm. IACUCs, IACUC veterinarians, wildlife veterinarians, and fish and wildlife biologists must learn to work together to comply with the law and to protect the privilege of using free-ranging animals in research.     

Extending the growth rate hypothesis to species development: Can stoichiometric traits help to explain the composition of macroinvertebrate communities?

Ecological stoichiometry seeks to understand the ecological consequences of elemental imbalances between consumers and their resources. Therein, the well-accepted growth rate hypothesis (GRH) states that organisms exhibiting rapid growth have higher phosphorus (P) demand – and thus lower C:P and N:P ratios – than slow growing ones, due to a higher allocation to P-rich rRNA. However, GRH has rarely been extended to other biological traits than growth, especially at the community level. In this study, we investigated whether macroinvertebrate stoichiometric traits (e.g. C:P and N:P ratios) can be linked to their development traits, and whether these stoichiometric traits are related to macroinvertebrate community assemblage under different nutrient conditions. We allocated more than 400 European taxa to different groups, defined using available information about three development-related traits: ‘life span', ‘voltinism' and ‘number of reproductive cycles per individual'. We sampled 18 invertebrate taxa in six streams exhibiting different levels of nutrient concentration and measured their stoichiometric traits. Further, we quantified invertebrate taxon abundances in these streams during an annual survey. Based on these data, we tested whether community composition regarding the developmental groups differs, depending on nutrient concentration. We found significant differences in the proportions of the developmental groups along a gradient of water N:P, in relation to their stoichiometric traits. Taxa with low C:P and N:P ratios were generally associated with faster development groups, and these taxa tended to occur at higher proportions in streams exhibiting low dissolved N:P ratios. In contrast, communities from P-poor, high dissolved N:P streams, were dominated by slowly developing taxa with high N:P ratios. Our results highlight that extending the GRH to species development rate might give some insights about the mechanisms by which nutrient concentrations in ecosystems influence consumers' community composition.     

Does the energy equivalence rule apply to intertidal macrobenthic communities?

Energy equivalence assumes equal contribution of large and small species to production and energy flow in communities. As in a double logarithmic plot, physiological rates decline with body weight by –0.25, log biomass should increase by 0.25 and log abundance decline by –0.75 with log species weight, when this concept is valid. This was tested with annual data sets of the macrobenthos of 4 intertidal sites in the German Wadden Sea (Königshafen) and 3 sites in a south Portuguese lagoon (Ria Formosa). Only abundance data from two of these sites displayed significantly negative slopes with mean body size of the species. Biomass and secondary production data were significantly positively correlated with mean body size for all Ria Formosa sites and also for the biomass of a mussel bed in Königshafen. However, high variation in body size of the individuals of a species limits interpretation of these plots.It is preferable to test this concept by body weight classes regardless of its species composition. At Königshafen, biomass and production displayed two distinct peaks. One peak at small body size was caused by browsing species. The other peak at larger body size was caused by animals which potentially extract their food from the water column. This bimodality was only vaguely reflected at one station in the Ria Formosa, possibly because of a dominance of detritus feeding species. In a normalized form (log biomass or production / width of size classvs. log size class), these spectra imply a dominance of small individuals in biomass and production at all sites (except for a mussel bank at Königshafen). This is interpreted as a consequence of permanent disturbances.     

Does growth rate determine the rate of metabolism in shorebird chicks living in the Arctic?

We measured resting and peak metabolic rates (RMR and PMR, respectively) during development of chicks of seven species of shorebirds: least sandpiper (Calidris minutilla; adult mass 20-22 g), dunlin (Calidris alpina; 56-62 g), lesser yellowlegs (Tringa flavipes; 88-92 g), short-billed dowitcher (Limnodromus griseus; 85-112 g), lesser golden plover (Pluvialis dominicana; 150-156 g), Hudsonian godwit (Limosa haemastica; 205-274 g), and whimbrel (Numenius phaeopus; 380 g). We tested two opposing hypotheses: the growth rate-maturity hypothesis, which posits that growth rate in chicks is inversely related to functional maturity of tissues, and the fast growth rate-high metabolism hypothesis, which suggests that rapid growth is possible only with a concomitant increase in either RMR or PMR. We have found no evidence that chicks of shorebirds with fast growth rates have lower RMRs or lower PMRs, as would be predicted by the growth rate-maturity hypothesis, but our data suggested that faster-growing chest muscles resulted in increased thermogenic capacity, consistent with the fast growth-high metabolism hypothesis. The development of homeothermy in smaller species is a consequence primarily of greater metabolic intensities of heat-generating tissues. The maximum temperature gradient between a chick's body and environment that can be maintained in the absence of a net radiative load increased rapidly with body mass during development and was highest in least sandpipers and lowest among godwits. Chicks of smaller species could maintain a greater temperature gradient at a particular body mass because of their higher mass-specific maximum metabolic rates.     

Does seed mass drive the differences in relative growth rate between growth forms?

The idea that herbaceous plants have higher relative growth rates (RGRs) compared with woody plants is fundamental to many of the most influential theories in plant ecology. This difference in growth rate is thought to reflect systematic variation in physiology, allocation and leaf construction. Previous studies documenting this effect have, however, ignored differences in seed mass. As woody species often have larger seeds and RGR is negatively correlated with seed mass, it is entirely possible the lower RGRs observed in woody species is a consequence of having larger seeds rather than different growth strategies. Using a synthesis of the published literature, we explored the relationship between RGR and growth form, accounting for the effects of seed mass and study-specific effects (e.g. duration of study and pot volume), using a mixed-effects model. The model showed that herbaceous species do indeed have higher RGRs than woody species, and that the difference was independent of seed mass, thus at all seed masses, herbaceous species on average grow faster than woody ones.     

Does the rate of German chamomile growth and development influence the response of plants to soil drought?

The response of the wild type (WT) and a strain C6/2 of German chamomile to 7-d soil drought and subsequent 7-day rehydration was studied. Shoot and leaf growth, vegetative development, water and protein contents, ascorbate peroxidase activity and gas exchange were compared. At the stress stage, water content of WT plants was slightly influenced and the effect was ceased after rehydration. Also the decrease in gas exchange was temporary. New leaves were formed, although their area was diminished. On the contrary, leaves of C6/2 plants were more desiccated and the durable decrease in water content was accompanied by the impairment in gas exchange also at the recovery stage (20–40% loss when compared to the control). At both stages of the experiment the growth of the long shoots of this genotype was drastically decreased, as well as leaf formation. Ascorbate peroxidase activity was increased by drought in leaves of both genotypes, but the pattern of changes in WT plants reflected the enhancement of metabolism resulting from proper water content and gas exchange at the recovery stage. Different pattern of changes in the protein content during drought was also noticed: a slight increase in WT, while the decrease by ¼ in C6/2 leaves. The response of WT plants to desiccation and rewatering was found to be more elastic than that of C6/2.     

Does the management of surrounding terrestrial habitats increase the tendency of odonates to leave aquatic habitats?

Generally, dragonflies and damselflies (odonates) are considered aquatic invertebrates. However, the ecological requirements of their adults are not different from those of fully, terrestrial insects. Surprisingly, there is a very little information on whether the management and structure of surrounding habitats has any influence on the diversity and seasonal dynamics of odonates. This is important to know because recently, a large proportion of freshwater habitats in Central Europe have becomes surrounded by intensively managed habitats. The aim of this study was to investigate the effects of different types of terrestrial habitats on their long-term utilization by dragonflies and damselflies. I assumed that this pattern varied over time; therefore, I used generalized additive mixed models to analyze the effects of management on seasonal changes in the abundance of individuals in terrestrial environments. From my results, it was evident that the management practices of surrounding terrestrial habitats had a significant impact on the population dynamics of dragonflies. The abundance of dragonfly adults in surrounding terrestrial habitats increased toward the end of the season. However, this was only, when the natal aquatic habitat was not affected by fish farming and was able to supply surrounding terrestrial habitats with offspring. This was evidenced by the fact that, compared to areas with extensive water management, in sites with fish farming, seasonal increases in abundance was negligible. There is no doubt that the structure of surrounding terrestrial habitats has a significant influence on the diversity of terrestrial invertebrates. However, we must not forget that terrestrial habitats, regardless of their management, are not able to replace the poor quality of the aquatic (natal) habitat. Interestingly, the abundance of damselflies decreased toward the end of the season, regardless of the management practices of the surrounding areas. This indicates that their dynamics is more controlled by time stress or other similar mechanisms than that of dragonflies.     

Does Rubisco control the rate of photosynthesis and plant growth? An exercise in molecular ecophysiology

Experiments are described in which tobacco (Nicotiana tabacum L.) transformed with antisense rbcS to decrease expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) was used to evaluate the contribution of Rubisco to the control of photosynthetic rate, and the impact of a changed rate of photosynthesis on whole plant composition, allocation and growth. (1) The concept of flux control coefficients is introduced. It is discussed how, with adequate precautions, a set of wild-type and transgenic plants with varying expression of an enzyme can be used to obtain experimental values for its flux control coefficient. (2) The flux control coefficient of Rubisco for photosynthesis depends on the short-term conditions. It increases in high light, or low CO₂. (3) When plants are grown under constant irradiance, the flux control coefficient in the growth conditions is low (<0.2) at irradiances of up to 1000μmol quanta m⁻² s⁻¹. In a natural irradiance regime exceeding 1500μmol quanta m⁻² s⁻² over several hours the flux coefficient rose to 0.8–0.9. It is concluded that plants are able to adjust the balance between Rubisco and the remainder of the photosynthetic machinery, and thereby avoid a one-sided limitation of photosynthesis by Rubisco over a wide range of ambient growth irradiance regimes. (4) When the plants were grown on limiting inorganic nitrogen, Rubisco had a higher flux control coefficient (0.5). It is proposed that, in many growth conditions, part of the investment in Rubisco may be viewed as a nitrogen store, albeit bringing additional marginal advantages with respect to photosynthetic rate and water use efficiency. (5) A change in the rate of photosynthesis did not automatically translate into a change in growth rate. Several factors are identified which contribute to this buffering of growth against a changed photosynthetic rate. (6) There is an alteration in whole plant allocation, resulting in an increase in the leaf area ratio. The increase is mainly due to a higher leaf water content, and not to changes in shoot/root allocation. This increased investment in whole plant leaf area partly counteracts the decreased efficiency of photosynthesis at the biochemical level. (7) Plants with decreased Rubisco have a lower intrinsic water use efficiency and contain high levels of inorganic cations and anions. It is proposed that these are a consequence of the increased rate of transpiration, and that the resulting osmotic potential might be a contributory factor to the increased water content and expansion of the leaves. (8) Starch accumulation in source leaves is decreased when unit leaf photosynthesis is reduced, allowing a more efficient use of the fixed carbon. (9) Decreased availability of carbohydrates leads to a down-regulation of nitrate assimilation, acting via a decrease in nitrate reductase activity.     

Does the temporal mismatch hypothesis match in boreal populations?

The temporal mismatch hypothesis suggests that fitness is related to the degree of temporal synchrony between the energetic needs of the offspring and their food supply. The hypothesis has been a basis in studying the influence of climate warming on nature. This study enhances the knowledge on prevalence of temporal mismatches and their consequences in boreal populations, and questions the role of the temporal mismatch hypothesis as the principal explanation for the evolution of timing of breeding. To test this, we examined if synchrony with caterpillar prey or timing of breeding per se better explains reproductive output in North European parid populations. We compared responses of temperate-origin species, the great tit (Parus major) and the blue tit (Cyanistes caeruleus), and a boreal species, the willow tit (Poecile montanus). We found that phenologies of caterpillars and great tits, but not of blue tits, have advanced during the past decades. Phenologies correlated with spring temperatures that may function as cues about the timing of the food peak for great and blue tits. The breeding of great and blue tits and their caterpillar food remained synchronous. Synchrony explained breeding success better than timing of breeding alone. However, the synchrony effect arose only in certain conditions, such as with high caterpillar abundances or high breeding densities. Breeding before good synchrony seems advantageous at high latitudes, especially in the willow tit. Thus, the temporal mismatch hypothesis appears insufficient in explaining the evolution of timing of breeding.     

Does the response of the intestinal epithelium to keratinocyte growth factor vary according to the method of administration?

BACKGROUND: Keratinocyte growth factor (KGF) is a potent mitogen and may be of value for the treatment of conditions such as short bowel syndrome and chemotherapy-induced mucositis. However the most efficacious route and method of administration is unclear. METHODS: Rats maintained by total parenteral nutrition (TPN) were given KGF (1 mg/kg/rat/day, i.v.) infused continuously or as a once-daily injection. The same dose was also given s.c. to chow-fed rats. Changes in gut growth were assessed by measurement of wet weight, proliferation (vincristine induced metaphase arrest) and crypt branching index. Changes in gut hormone profile were also determined to examine if any trophic effects were mediated via this mechanism. RESULTS: KGF caused a 70-100% increase in wet weight of the stomach, small and large intestine of TPN-fed rats (P < 0.01) with no significant differences seen between the two methods of administration. The increase in metaphase counts was greatest in the stomach (about seven-fold P < 0.01), but was less pronounced in the distal small intestine and colon (about 50% increase). The trophic effect of KGF was much less prominent in orally-fed rats. Crypt branching index was significantly reduced by KGF in the proximal small intestine of TPN, but not orally-fed rats. Plasma gastrin, PYY, total glucagon, enteroglucagon and GLP-1 all increased by two-three-fold (all P < 0.01) in response to KGF whereas insulin levels fell by about 25% in the TPN group. CONCLUSIONS: The mitogenic action of KGF occurred predominantly in the stomach and proximal small intestine. Its efficacy was less pronounced in orally-fed animals, suggesting KGF may be of greatest benefit in conditions associated with lowered intestinal proliferation. Clinical trials of KGF can probably use single daily i.v. injections without reduction in efficacy.     

The plant vigour hypothesis revisited – how is browsing by ungulates and elephant related to woody species growth rate?

The way herbivores select what to eat is of considerable practical and theoretical interest, and has given rise to different theories and hypotheses. The plant vigour hypothesis predicts that herbivores feed preferentially on vigorous, i.e., large and/or fast-growing plants or plant parts. These predictions have previously primarily been tested on variation within plant species. Here we test whether differences in vigour among plant species in the same environment can explain differences in herbivore attack. We studied variation in browsing pressure by a guild of large herbivores on different woody species in an African savanna ecosystem. Shoot growth rate, annual shoot length, basal shoot diameter and annual shoot volume of 14 woody plant species were measured in the field. Plant species’ shoot vigour represented by the first PCA axis scores generated from the four shoot variables were then related to browsing pressure (% utilisation) on each of the species by native ungulates and elephant. Nutrient and fibre concentrations and tannin activity were also determined for the 14 woody plant species. We found ungulate browsing pressure to show a unimodal relationship with plant species’ shoot vigour. The heaviest browsing pressure was on plant species with shoots of intermediate vigour. We suggest that species with less vigorous shoots had low nutrient and high fibre concentrations and offered small bite sizes, whereas species with vigorous shoots had high nutrient concentrations but larger shoot diameters than the bite diameters of browsing ungulates. Elephant browsing pressure was not related to plant species’ shoot vigour.     

Do submerged aquatic plants influence their periphyton to enhance the growth and reproduction of invertebrate mutualists?

It has been suggested that submerged aquatic plants can influence the nutritional quality of the periphyton which grows on their surfaces, making it more nutritious for grazing invertebrates, particularly snails. In return, these grazers might preferentially feed on the periphyton and clear the plants of a potential competitor, with the plants and grazers both gaining from this mutualistic relationship. A highly replicated experiment was conducted, in which the nature of the plant (isoetid and elodeid types compared with similar-shaped inert substrata), the nutrient loading, and the influence of periphyton grazers (the bladder snail, Physa fontinalis) of similar size and history were controlled. Plant growth and survival significantly increased in the presence of the periphyton grazer. Whilst the presence of the grazers had the largest influence on periphyton abundance, nutrient availability and plant type also had effects. Plant type had little influence on the nutritional quality of the periphyton measured as carbohydrate, protein and C:N. Effects of treatment on snail growth, and the timing and extent of snail reproduction disappeared when they were compared with the quantity of periphyton available. There was no evidence of enhanced grazer success in the presence of the live plants compared with inert substrata. Although submerged plants affect the growth and reproduction of the grazers which feed on their surfaces, through differences in the amount of periphyton which grows there, we found no evidence that they manipulate the periphyton to encourage such grazers. Received: 1 September 1998 / Accepted: 12 May 1999     

Does the universality of the species–area relationship apply to smaller scales and across taxonomic groups?

The universality of the shape of the species–area relationship (SAR) is subject to regular debate. Recently, Storch et al. (2012) argued that species–area relationships collapse into a single curve at continental scales after the axes are rescaled adjusting the area‐axis being to the mean range size of species and the species‐axis to the species richness of an area equal to mean range size. It has been claimed that this rescaling generates a universal model, invariant of taxon and continent, and that it is driven by differences in range sizes. Here, we test the universality of the rescaled SAR across scales smaller than the continental level, using presence data for plants, birds and butterflies. We also test an alternative rescaling approach, by using the total extent of the study area and total species richness. At the scales analysed here, we found that the proposed rescaling by Storch et al. adjusts for differences in the extent of the study area and for variation in gamma diversity. Consequently, while the rescaled curves were closely aligned, they did not converge into a single curve. The observed remaining variation is independent of scale and biogeographical region, and is correlated with beta diversity; thus, it reflects the differentiation of species composition in space.     

Hypoxia and temperature: Does hypoxia affect caiman embryo differentiation rate or rate of growth only?

In crocodilians, the rate of embryonic development and consequently many posthatch attributes are affected by temperature. Since temperature exhibits strong influences on fitness (embryo survivorship and phenotype) by shaping development, we manipulated oxygen concentration in order to uncouple the effects of developmental rate from the direct effects of temperature. Here we consider whether oxygen constrains either differentiation rate (progression from one stage to the next) or embryonic growth (size). Thus, we incubated Caiman latirostris eggs at various oxygen concentrations, and at two temperatures (31 °C, 100% female-producing temperature, and 33 °C, 100% male-producing temperature). We monitored the developmental stages of these embryos within the thermosensitive period (stages 20–24), and assessed several physiological and morphological hatchling traits. While embryonic size was strongly influenced by oxygen, differentiation rate did not seem to be affected. Very low oxygen concentrations and high temperatures inhibited embryo survival. In addition, oxygen availability affected incubation period and hatchling size, whereas temperature did not cause a significant variation in hatchling size. By investing energy in differentiation hypoxic embryos decreased their size.     

Sinuses and flotation: Does the aquatic ape theory hold water?

The idea that people went through an aquatic phase at some time in their evolutionary past is currently undergoing a popular resurgence (see Foley & Lahr 1 ). This idea has even started to gain some traction in more learned circles; the late paleoanthropologist Phillip Tobias wrote in support of aspects of it in an edited e‐book 2 and a conference on the topic held recently in London was endorsed by celebrities such as the television presenter Sir David Attenborough. 3 Despite (or perhaps because of) the lack of interest within the academic community, advocates of the concept continue to fill the media (and blogosphere) with challenges to the “savannah hypothesis” of the origins of people and to bemoan the fact that their views are not taken seriously by mainstream academia.     

How does the 50/500 rule apply to MVPs?

The 50/500 rule has been used as a guiding principle in conservation for assessing minimum viable effective population size (N(e)). There is much confusion in the recent literature about how the 500 value should be applied to assess extinction risk and set priorities in conservation biology. Here, we argue that the confusion arises when the genetic basis for a short-term N(e) of 50 to avoid inbreeding depression is used to justify a long-term N(e) of 500 to maintain evolutionary potential. This confusion can result in misleading conclusions about how genetic arguments alone are sufficient to set minimum viable population (MVP) thresholds for assessing the extinction risk of threatened species, especially those that emphasize that MVPs should be in the thousands to maintain evolutionary potential.