Life history evolution in Asobara tabida: plasticity in allocation of fat reserves to survival and reproduction

Life history variation can be genetically based, or it may be due to environmental effects on the phenotype. In this paper we examine life history variation in relation to differences in habitat in the parasitoid Asobara tabida. Differences in the spatial distribution of host patches, the length of the season, host suitability, and competition between parasitoids all contribute to the selection for differences in life history between strains from northern and southern Europe. Strains were compared with respect to the allocation between reproduction and survival in experimental environments that varied with regard to the availability of food or to the number of hosts offered per day. Upon emergence parasitoids originating from southern Europe have higher egg loads and smaller fat reserves than parasitoids originating from northern Europe. Parasitoids from both southern and northern Europe show plasticity in allocation: food shortage causes a decrease in egg production, and rich breeding opportunities an increase in egg production. This plasticity is greater in the northern strain. Fat reserves play a central role in the physiology of this allocation. Fat can be used for both reproduction and survival. There is no oosorption, so once fat is allocated to reproduction it can no longer be used for survival. Differences in plasticity in allocation can therefore be considered as differences in the timing of egg production.     

Weak negative associations between avian influenza virus infection and movement behaviour in a key host species,the mallard Anas platyrhynchos

Animal movements may contribute to the spread of pathogens. In the case of avian influenza virus, [migratory] birds have been suggested to play a role in the spread of some highly pathogenic strains (e.g. H5N1, H5N8), as well as their low pathogenic precursors which circulate naturally in wild birds. For a better understanding of the emergence and spread of both highly pathogenic (HPAIV) and low pathogenic avian influenza virus (LPAIV), the potential effects of LPAIVs on bird movement need to be evaluated. In a key host species, the mallard Anas platyrhynchos, we tested whether LPAIV infection status affected daily local (< 100 m) and regional (> 100 m) movements by comparing movement behaviour 1) within individuals (captured and sampled at two time points) and 2) between individuals (captured and sampled at one time point). We fitted free‐living adult males with GPS loggers throughout the autumn LPAIV infection peak, and sampled them for LPAIV infection at logger deployment and at logger removal on recapture. Within individuals, we found no association between LPAIV infection and daily local and regional movements. Among individuals, daily regional movements of LPAIV infected mallards in the last days of tracking were lower than those of non‐infected birds. Moreover, these regional movements of LPAIV infected birds were additionally reduced by poor weather conditions (i.e. increased wind and/or precipitation and lower temperatures). Local movements of LPAIV infected birds in the first days of tracking were higher when temperature decreased. Our study thus demonstrates that bird‐assisted dispersal rate of LPAIV may be lower on a regional scale than expected on the basis of the movement behaviour of non‐infected birds. Our study underlines the importance of understanding the impact of pathogen infection on host movement in order to assess its potential role in the emergence and spread of infectious diseases.     

Effects of exposure to short-term heat stress on male reproductive fitness in a soil arthropod

Ambient temperature is a key environmental factor influencing a variety of aspects of the ecology and evolution of ectotherms. Reproductive traits have been suggested to be more sensitive to thermal stress than other life history traits. This study investigated the direct and indirect effects of heat shock on male reproductive success in the widespread springtail Orchesella cincta. Male springtails were exposed to four temperature treatments: heat hardening (35.2 °C for 1 h), heat shock (37.2 °C for 1 h), heat hardening + heat shock (35.2 °C for 1 h, followed 15 h later by 37.2 °C for 1 h), and control (20 °C). The heat shock gene Hsp70 showed high expression in all the heat treatments, indicating that the treatments indeed induced thermal stress. Significant mortality was only found in the treatment with heat shock, both with and without heat hardening. A direct effect of heat treatment was found on time to first reproduction, which was significantly longer after heat shock (with or without heat hardening) than in the control treatment. There was no difference among treatments in the number of spermatophores produced in the first reproductive instar. Heat treatment also had indirect effects on male reproductive success. Females chose significantly more spermatophores from control males than from males that received heat shock, heat hardening or both. A high percentage of spermatophores produced by heat shocked males caused reproductive failure in females, but no significant differences among treatments were found.Our results suggest that not all traits were equally affected by the heat stress. Heat hardening did not protect reproductive traits against the negative effects of heat shock. The indirect effects of heat shock on reproduction may be equally important as the direct effects.     

Maternal topoisomerase II alpha, not topoisomerase II beta, enables embryonic development of zebrafish top2a -/- mutants

Background

Determining the type and source of cells involved in regenerative processes has been one of the most important goals of researchers in the field of regeneration biology. We have previously used several cellular markers to characterize the cells involved in the regeneration of the intestine in the sea cucumber Holothuria glaberrima.

Results

We have now obtained a monoclonal antibody that labels the mesothelium; the outer layer of the gut wall composed of peritoneocytes and myocytes. Using this antibody we studied the role of this tissue layer in the early stages of intestinal regeneration. We have now shown that the mesothelial cells of the mesentery, specifically the muscle component, undergo dedifferentiation from very early on in the regeneration process. Cell proliferation, on the other hand, increases much later, and mainly takes place in the mesothelium or coelomic epithelium of the regenerating intestinal rudiment. Moreover, we have found that the formation of the intestinal rudiment involves a novel regenerative mechanism where epithelial cells ingress into the connective tissue and acquire mesenchymal phenotypes.

Conclusions

Our results strongly suggest that the dedifferentiating mesothelium provides the initial source of cells for the formation of the intestinal rudiment. At later stages, cell proliferation supplies additional cells necessary for the increase in size of the regenerate. Our data also shows that the mechanism of epithelial to mesenchymal transition provides many of the connective tissue cells found in the regenerating intestine. These results present some new and important information as to the cellular basis of organ regeneration and in particular to the process of regeneration of visceral organs.     

Traits underpinning desiccation resistance explain distribution patterns of terrestrial isopods

Predicted changes in soil water availability regimes with climate and land-use change will impact the community of functionally important soil organisms, such as macro-detritivores. Identifying and quantifying the functional traits that underlie interspecific differences in desiccation resistance will enhance our ability to predict both macro-detritivore community responses to changing water regimes and the consequences of the associated species shifts for organic matter turnover. Using path analysis, we tested (1) how interspecific differences in desiccation resistance among 22 northwestern European terrestrial isopod species could be explained by three underlying traits measured under standard laboratory conditions, namely, body ventral surface area, water loss rate and fatal water loss; (2) whether these relationships were robust to contrasting experimental conditions and to the phylogenetic relatedness effects being excluded; (3) whether desiccation resistance and hypothesized underlying traits could explain species distribution patterns in relation to site water availability. Water loss rate and (secondarily) fatal water loss together explained 90 % of the interspecific variation in desiccation resistance. Our path model indicated that body surface area affects desiccation resistance only indirectly via changes in water loss rate. Our results also show that soil moisture determines isopod species distributions by filtering them according to traits underpinning desiccation resistance. These findings reveal that it is possible to use functional traits measured under standard conditions to predict soil biota responses to water availability in the field over broad spatial scales. Taken together, our results demonstrate an increasing need to generate mechanistic models to predict the effect of global changes on functionally important organisms.     

Externally visible fluorochrome marks and allometries of growing sea urchins

Externally visible, growing calcitic structures can be marked using fluorochromes. Such marks are useful for field recapture studies in ecology, evolution, and aquaculture as well as for studies on mechanisms of growth and development. We marked 2‐month‐old sea urchins (Strongylocentrotus droebachiensis) with the fluorochromes calcein, calcein blue, and tetracycline by batch‐marking via immersion. Neither growth nor survival was affected by marking. Marks were externally visible on the skeletal plates, demipyramids, and spines of 100% of the marked sea urchins up to 63 d post‐marking. After 342 d, marks were still externally visible on 100% of calcein‐marked, 98% of calcein blue‐marked, and 22% of tetracycline‐marked sea urchins. Marks were brightest on calcein‐marked and faintest on tetracycline‐marked sea urchins, in correspondence to the fluorochrome dose. Growth marks in the aboral oculogenital ring, followed for 333 d, showed that genital plate growth in the hoop direction was greatest adjacent to the anal suture and that both the oculogenital ring and periproct grew less than isometrically. Internal marks (not externally visible) were subsequently seen on 99% of the demipyramids at 342 d post‐marking. Such fluorochrome marks on demipyramids have previously been used to measure aboral and oral‐end demipyramid growth to allometrically calibrate diametrical growth rates of field sea urchins. We found that although aboral demipyramid marks were always clear, 13% of marks on the oral end were obscured. However, we show that measuring only aboral end growth is sufficient for allometric calibration. In a separate experiment, multiple marks of the above three fluorochromes plus alizarin complexone, administered by injection to larger (12.9–37.1 mm diameter) sea urchins, persisted internally for at least 2 years. Multi‐color, internally and externally visible, persistent marks will enhance experimental designs in laboratory, field, and common garden experiments.     

A comparative analysis of clinging ability among pad-bearing lizards

We examined clinging ability, subdigital pad area and body mass in 14 pad-bearing lizard species from three families to test three predictions: (1) clinging ability and pad area should be tightly correlated among species; (2) pad area and clinging ability should scale similarly to body mass among 14 species; and (3) functional similarity in clinging capabilities should exist among species despite differences in body mass. Our results confirm two predictions; clinging ability is tightly correlated with pad area, even when the effects of body size are removed, and the lizards examined are approximately functionally similar in their clinging capabilities. Nevertheless, despite the tight correlation between pad area and clinging ability, pad area scales with body mass by a lower slope than clinging ability. Overall, these results indicate that although pad area is a strong determinant of clinging ability, other factors enable these lizards to maintain functional similarity.     

Interplay of robustness and plasticity of life‐history traits drives ecotypic differentiation in thermally distinct habitats

Phenotypic plasticity describes the ability of an individual to alter its phenotype in response to the environment and is potentially adaptive when dealing with environmental variation. However, robustness in the face of a changing environment may often be beneficial for traits that are tightly linked to fitness. We hypothesized that robustness of some traits may depend on specific patterns of plasticity within and among other traits. We used a reaction norm approach to study robustness and phenotypic plasticity of three life‐history traits of the collembolan Orchesella cincta in environments with different thermal regimes. We measured adult mass, age at maturity and growth rate of males and females from heath and forest habitats at two temperatures (12 and 22 °C). We found evidence for ecotype‐specific robustness of female adult mass to temperature, with a higher level of robustness in the heath ecotype. This robustness is facilitated by plastic adjustments of growth rate and age at maturity. Furthermore, female fecundity is strongly influenced by female adult mass, explaining the importance of realizing a high mass across temperatures for females. These findings indicate that different predicted outcomes of life‐history theory can be combined within one species' ontogeny and that models describing life‐history strategies should not assume that traits like growth rate are maximized under all conditions. On a methodological note, we report a systematic inflation of variation when standard deviations and correlation coefficients are calculated from family means as opposed to individual data within a family structure.     

Body size and the timing of egg production in parasitoid wasps

In insects several key fitness-related variables are positively correlated with intraspecific variation in body size, but little is known about size-related variation in the timing of egg production within species. Female insects are known to vary in the degree to which they concentrate egg production into the early part of life. This variation has been quantified as the ovigeny index, defined as the proportion of the maximum potential lifetime complement of eggs that is mature following emergence from the pupa. We tested the hypothesis that the timing of egg production depends both on body size and on host availability, by means of a dynamic programming model that predicted optimal resource allocation to reproduction and survival together with the resulting ovigeny index, in non-feeding synovigenic parasitoids of different sizes. As body size increases, the proportionate increase in resource allocation to initial egg load is less than the proportionate increase in allocation to lifetime fecundity and potential life span, leading to a deferred investment in reproduction as shown by a decrease in ovigeny index. High habitat quality and high habitat stochasticity in reproductive opportunities have a significant effect on the optimal allocation of resources to reproduction and survival, and thus select for early reproduction, i.e. an increased ovigeny index. The ovigeny concept – ovigeny index together with its life-history correlates – enables understanding of the general occurrence of size-related deferment of reproductive investment in parasitoid wasps and also helps explain a significant part of the considerable life-history variation found among such insects.     

Protein synthesis in trifluralin-treated corn root tips

The effect of trifluralin (,,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) on protein synthesis in corn (Zea mays) root tips was determined. ¹⁴C-leucine uptake and subsequent incorporation into protein in intact and excised root tips was measured. Root tips were treated with and without 15 µM trifluralin for 2 hr; incorporation of ¹⁴C-leucine was observed during a 20-min interval. Total amino acid content in the soluble pool and protein hydrolysate was reduced in the excised tissue by the herbicide. Kinetic analysis showed trifluralin had no effect on endogenous leucine pool size nor on the rate of protein synthesis in intact tissue. Uptake was unaffected; however, in excised tissue uptake increased 100% over the control. While ¹⁴C-leucine content was greater in both the soluble pool and protein in treated, excised root tips, analysis showed the apparent increase in protein synthesis was in response to increased pool size.