No apparent cost of evolved immune response in Drosophila melanogaster

Maintenance and deployment of the immune system are costly and are hence predicted to trade‐off with other resource‐demanding traits, such as reproduction. We subjected this longstanding idea to test using laboratory experimental evolution approach. In the present study, replicate populations of Drosophila melanogaster were subjected to three selection regimes—I (Infection with Pseudomonas entomophila), S (Sham‐infection with MgSO₄), and U (Unhandled Control). After 30 generations of selection flies from the I regime had evolved better survivorship upon infection with P. entomophila compared to flies from U and S regimes. However, contrary to expectations and previous reports, we did not find any evidence of trade‐offs between immunity and other life history related traits, such as longevity, fecundity, egg hatchability, or development time. After 45 generations of selection, the selection was relaxed for a set of populations. Even after 15 generations, the postinfection survivorship of populations under relaxed selection regime did not decline. We speculate that either there is a negligible cost to the evolved immune response or that trade‐offs occur on traits such as reproductive behavior or other immune mechanisms that we have not investigated in this study. Our research suggests that at least under certain conditions, life‐history trade‐offs might play little role in maintaining variation in immunity.     

Life span and reproductive cost explain interspecific variation in the optimal onset of reproduction

Fitness can be profoundly influenced by the age at first reproduction (AFR), but to date the AFR–fitness relationship only has been investigated intraspecifically. Here, we investigated the relationship between AFR and average lifetime reproductive success (LRS) across 34 bird species. We assessed differences in the deviation of the Optimal AFR (i.e., the species‐specific AFR associated with the highest LRS) from the age at sexual maturity, considering potential effects of life history as well as social and ecological factors. Most individuals adopted the species‐specific Optimal AFR and both the mean and Optimal AFR of species correlated positively with life span. Interspecific deviations of the Optimal AFR were associated with indices reflecting a change in LRS or survival as a function of AFR: a delayed AFR was beneficial in species where early AFR was associated with a decrease in subsequent survival or reproductive output. Overall, our results suggest that a delayed onset of reproduction beyond maturity is an optimal strategy explained by a long life span and costs of early reproduction. By providing the first empirical confirmations of key predictions of life‐history theory across species, this study contributes to a better understanding of life‐history evolution.     

Histological and morphological aspects of reproduction in the sandbar shark Carcharhinus plumbeus in the U.S. south‐eastern Atlantic Ocean and Gulf of Mexico

The reproduction of the sandbar shark Carcharhinus plumbeus in the U.S. south‐eastern Atlantic Ocean including the Gulf of Mexico was examined using a combination of histological and morphological characteristics of C. plumbeus collected through fishery‐dependent and ‐independent sampling programmes (n = 1,567). Indices of maturity were constructed using measurements of gonads, reproductive tracts and claspers, and sandbar sharks exhibited 50% maturity sizes of 140 and 148 cm fork length for males and females respectively. Gonado‐somatic indices and variation in reproductive tract condition were used to determine seasonal trends in reproduction of mature C. plumbeus. Sandbar sharks have discrete seasonal reproductive cycles in which males produce sperm from January to May with a peak in May and females develop eggs from January to May with ovulation occurring in June. Females were shown to exhibit a >2 year reproductive cycle. Embryonic development was assessed through measurements of masses and lengths of uterine contents. Gestation was 12 months, from July to the following June, with parturition in late June. This research highlights a difference from previously reported data on the periodicity of female reproduction in C. plumbeus in the U.S. south‐eastern Atlantic Ocean and Gulf of Mexico, which may have major effects on future C. plumbeus stock management.     

Why grow up? A perspective on insect strategies to avoid metamorphosis

1. Insects with complete metamorphosis (holometaboly) are extremely successful, constituting over 60% of all described animal species. Complete metamorphosis confers significant advantages because it enables organisms to optimise life‐history components through temporal partitioning, and thereby to exploit multiple ecological niches. Yet holometaboly can also impose costs, and several lineages have evolved life cycle modifications to avoid complete metamorphosis. 2. In this review, we discuss different strategies that have evolved that result in the loss of complete metamorphosis (type I and type II paedomorphosis). In addition, the ecological pressures and developmental modifications that facilitate this avoidance are considered, as well as the importance of life cycle complexity in life‐history evolution. 3. Interestingly, only female holometabolous insects have entirely avoided complete metamorphosis, and it is always the ancestrally juvenile morphology that is retained. These findings point to a strong sex‐biased trade‐off between investment in reproduction and development. While the loss of complete metamorphosis in females has occurred independently on several occasions across holometabolous insects, only a small number of species possessing this ability have been described. 4. Thus, complete metamorphosis, which originated only once in insects, appears to have been almost fully retained. This indicates that significant modifications to the holometabolan metamorphic ground plan are highly constrained, and suggests that the transition to complete metamorphosis is evolutionarily irreversible.     

On the relevance of using laboratory selection to study the adaptive value of circadian clocks

The phrase ‘as sure as night comes after day’ highlights the most conspicuous phenomenon on earth (i.e. the daily cycling of geophysical factors). It is hypothesized that life‐forms on earth have evolved timekeeping mechanisms (circadian clocks) as adaptations to cope with such cyclic variations in their environment and, to test this hypothesis, diverse strategies have been employed. In this review, these different approaches, including comparative, clinal, ecology and/or trait manipulation and laboratory selection strategies are discussed, aiming to evaluate the adaptive value of circadian clocks. The limitations of each of these methods are assessed, and it is suggested that laboratory selection is an ideal, potent and suitable strategy for examining whether circadian clocks are indeed adaptations. In support of this, laboratory selection strategies are highlighted and critically reviewed in a discussion of studies that demonstrate the evolution of circadian clocks and life‐history traits in response to selection for the timing of rhythmic behaviours, as well as those studies that demonstrate the evolution of circadian clocks in response to selection for life‐history traits. Finally, newer approaches are proposed that involve the use of mutants, simultaneous manipulation of multiple environmental factors and genomic technologies in conjunction with laboratory selection to further explore the adaptive significance of circadian clocks.     

The logical priority of the tree over characters and some of its consequences for taxonomy

The aim of the present paper is to explore the role of the character in phylogenetic systematics. I argue that too much emphasis is put on particular characters rather than congruence both in the choice of phylogenetic hypotheses and in taxonomic decisions. This means that the logical priority of the tree over the characters is neglected. To a large extent, this is a result of not paying enough attention to the individuality thesis which states that clades are historical individuals and hence contingent in nature.     

Plant quality or quantity? Host exploitation strategies in three Chrysomelidae species associated with Asteraceae host plants

Phytophagous insects which feed on the leaves of herbaceous host plants have to adapt their life histories to the fact that protein nitrogen is usually highest in growing tissues in spring. We monitored field populations of larvae and adults of three chrysomelid species (Galeruca tanaceti (L.) (main host Achillea millefolium (L.) Yarrow), Cassida rubiginosa (Mueller) (main host Cirsium arvense (L.) Scop.) and Oreina luctuosa (Suffrian) (host Centaurea scabiosa (L.)) together with the amount of protein nitrogen of their food resources and host plant biomass. As expected, the development of host quality, measured as concentration of protein nitrogen, and host plant biomass showed inverse trends during the season. The euryphagous G. tanaceti attacks Achillea early and profits from high nitrogen concentrations in the leaves. Occasional overexploitations of local populations of Achillea are compensated by the capacity to move to other host species. In C. rubiginosa, a species with a host range restricted to the Cardueae, the main larval feeding activity is postponed to a period when the nitrogen content of the host leaves had dropped to 50% of its initial value, but when host plant biomass had increased by 30%. In the monophagous O. luctuosa the larval development is synchronized with a still later phase of host phenology, at which the nitrogen content is below 50% but plant biomass has reached its maximum. There seem to be selection factors, which oppose the use of high quality food in spring and which force the latter two species to postpone their larval development to a later time in the year. This could be caused by numerous factors like, for example, mean daytime temperature. Later in the season the larvae have to cope with the low quality of their host plants. They have, however, the advantage of large quantities of food available.A laboratory study with adults and mature larvae of O. luctuosa shows that this species can overcome low levels of protein nitrogen either by selecting younger leaves with higher nitrogen concentrations or by increasing the daily food consumption rate (RCR) on leaves with a low level of nitrogen and by a prolongation of the feeding period. In this way the larvae compensate the effect of lower daily growth rates (RGR) and a lower food conversion index (ECI) on poor food quality: Regardless of the level of protein nitrogen there was no statistically significant difference in total gain of weight during the third-instar feeding period and in the weight at the end of the third larval stage. The three investigated chrysomelids show that there exists a broad spectrum of adaptations to overcome the dilemma of variable food quality.     

Interpopulation variation of hibernal-aestival-diapause in the egg parasitoid wasp Anagrus takeyanus: adaptation to seasonal host-plant alternation of the tingid host, Stephanitis takeyai

The egg parasitoid wasp, Anagrus takeyanus Gordh & Dunbar (Hymenoptera: Mymaridae), is one of the few natural enemies of the andromeda lace bug, Stephanitis takeyai Drake & Maa (Heteroptera: Tingidae). Studying this wasp in two habitats, I found that at Kyoto, where the bug alternates its host plants seasonally, most wasp individuals in the overwintering eggs of the bug entered summer diapause immediately after winter diapause. However, at Nara, where the bug does not alternate its host plant, the wasp proved to have no summer diapause. Changes in the parasitization rate between generations differed at the two study sites. In Kyoto, the overwintered generation suffered the highest parasitism among the three generations of the year. In contrast, the first and second generations suffered higher parasitization rates in Nara. This difference in level of parasitization between the two study sites corresponded to the different diapause regime of the wasp and the seasonal population trends of the lace bug. Laboratory experiments showed that short photoperiod in combination with low temperature could terminate the long diapause at the time the non-aestivating individuals terminate winter diapause. As a life cycle without host plant alternation is likely to be an ancestral character of the bug, the aestivation of the wasp is thought to have been appended to overwintering as an adaptation to the evolution of seasonal host plant alternation in the lace bug.     

A comparison of thermal treatment processes for hazardous waste

This paper (the second in a series of three) compares incineration options for hazardous waste with LCA. Provided that acceptance criteria are met with regard to metals, PAHs and chlorine, Dutch Municipal Solid Waste Incinerators (MSWls) appeared to be preferable above rotary kilns since they have a better energy recovery and — unlike rotary kilns — produce reusable slags. The position of the cement kiln relative to the MSWI and rotary kiln depends on the allocation method chosen. System enlargement, which may be most highly defensible, tends to give cement kilns the advantage. Yet, two key concerns which are unsolvable by LCA make final conclusions impossible. First, an input of highly contaminated waste leads to an enrichment of cement with metals. Long-term consequences are not known, so the incineration of waste with a high metal content will inevitably be controversial. Second, no convincing proof was found that cement kilns would not produce additional hazardous process emissions (e.g. dioxins) when using waste instead of fuel. The precautionary principle demands that such proof be provided before cement kilns can be considered for the incineration of waste with a composition other than their regular fuel.     

Post-fire seedling establishment in Florida sand pine scrub

Abstract. This study deals with a quantification of pre- and post-fire seedling establishment and microsite characteristics in two Florida sand pine scrub sites burned in May 1993. In addition, life history characteristics related to seedling establishment are described for five perennial species –Calamintha ashei, Chapmannia floridana, Eriogonum floridanum, Garberia heterophylla and Palafoxia feayi. Post-fire seedling establishment in sand pine scrub was sparse (median = 1, 12 seedling/m²), with 17 of 35 species establishing seedlings. Chapmannia, Eriogonum, Garberia and Palafoxia resprouted and flowered after fire; Eriogonum and Garberia had strong post-fire seedling establishment responses within 19 months post-fire. Calamintha individuals were killed by fire, but this species had a strong post-fire seedling establishment response, presumably from seeds in a soil seed bank. Eriogonum and Calamintha seedlings established preferentially in plots centered on conspecific adults. For these species with poor seed dispersal, spatial patterns of seedling establishment may be influenced more by pre-fire adult plant location than by post-fire microsite conditions. Post-fire seedling density in sand pine scrub was much lower than in California chaparral and South African sand plain lowland fynbos.