Energetics of reproduction: consequences of divergent selection on egg size, food limitation, and female age for egg composition and reproductive effort in a butterfly

Using lines artificially selected on egg size and being subjected to a restricted and an unrestricted feeding treatment, we examined the relationships between egg size, egg number, egg composition, and reproductive investment in the butterfly Bicyclus anynana . Despite a successful manipulation of egg size, correlated responses to selection in larval time, pupal mass, pupal time, longevity, fecundity, or the amount of energy allocated to reproduction were virtually absent. Thus, there was no indication for an evolutionary link between offspring size and reproductive investment. Egg composition, in contrast, was affected by selection, with larger eggs containing relatively more lipid and water, but less protein and energy compared to smaller eggs. Hence, females producing large eggs did not have to sacrifice fecundity due to adjustments in egg composition. Food limitation per se caused only minor changes in egg composition, and there was no general reduction in egg provisioning with female age. The latter was restricted to food-limited females, whereas egg quality remained remarkably similar throughout the females' life in control groups. We conclude that neglecting changes in biochemical egg composition, depending on genetic background, food availability, and female age, may introduce substantial error when estimating reproductive effort, and may ultimately lead to invalid conclusions.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 403–418.     

Benthic–pelagic coupling in the population dynamics of the harmful cyanobacterium Microcystis

1. In eutrophic lakes, large amounts of the cyanobacterium Microcystis may overwinter in the sediment and re‐inoculate the water column in spring. 2. We monitored changes in pelagic and benthic populations of Microcystis in Lake Volkerak, The Netherlands. In addition, sedimentation rates and the rate of recruitment from the sediment were measured using traps. These data were used to model the coupling between the benthic and pelagic populations and to calculate the contribution of overwintering benthic and pelagic populations to the magnitude of the pelagic summer bloom. 3. Changes in the benthic Microcystis population showed a time lag of 3–14 weeks compared with the pelagic population. This time lag increased with lake depth. The largest amount of benthic Microcystis was found in the deepest parts of the lake. These observations suggest horizontal transport of sedimented Microcystis from shallow to deep parts of the lake. 4. Recruitment from and sedimentation to the sediment occurred throughout the year, with highest recruitment and sedimentation rates during summer. Model simulations indicate that the absence of benthic recruitment would reduce the summer bloom by 50%. 5. In spring, the total pelagic population was three to six times smaller than the total benthic population. Yet, model simulations predict that the absence of this small overwintering pelagic population would reduce the summer bloom by more than 64%. 6. Reduction of the overwintering pelagic populations, for instance by flushing, may be a useful management strategy to suppress or at least delay summer blooms of Microcystis.     

Effects of rearing and induction temperature on the temporal dynamics of heat shock protein 70 expression in a butterfly

The temporal dynamics of heat shock protein 70 (HSP70) expression in response to longer‐term acclimation and rapid hardening in the butterfly Lycaena tityrus is investigated. After a 1‐h exposure to 1 °C or 37 °C, HSP70 is quickly up‐regulated within 1 h and down‐regulated within 2 h. The fast dynamic of HSP70 expression is in contrast to the patterns found in organisms inhabiting more stable thermal environments, and is interpreted as an adaptation to the large and rapid temperature variation experienced by flying ectotherms. HSP70 expression is higher in males than in females, as well as in animals reared at 27 °C than at 20 °C, although it is very similar across the high and low induction temperatures. Animals reared at the higher temperature, however, respond less strongly to high‐temperature stress.     

Distribution of chironomids (Diptera) in low arctic West Greenland lakes: trophic conditions, temperature and environmental reconstruction

1. Surface sediment samples of subfossil chironomid head capsules from 47 lakes in southern West Greenland were analysed using multivariate numerical methods in order to explore the relationship between chironomid assemblages and selected environmental variables. The study lakes are located along a climate gradient ranging from coastal maritime conditions near the Davis Strait to a continental climate near the margin of the Greenland ice sheet. 2. High‐resolution surface water temperatures were measured through the summer season using automatic data loggers in 21 of the study lakes. The mean July surface water temperature (1999) ranged from 7.3 to 16.5 °C in the data set. 3. In all lakes, a total of 24 chironomid taxa were recorded; Micropsectra, Psectrocladius, Chironomus and Procladius were the dominant genera. There was a strong correlation between the trophic variables [total nitrogen and total phosphorus (TN, TP)] and temperature, and in redundancy analysis (RDA) the three variables explained almost equal significant amounts of variation in the chironomid data (19.8–22.3%). However, temperature lost significant explanatory power when the effect of TN was partialled out in RDA. 4. The lakes were classified using two‐way indicator species analysis (TWINSPAN ) into eight groups defined by temperature, trophic variables, salinity (conductivity) and lake‐morphometric data. Fourteen chironomid taxa showed significant differences in percentage abundances among groups, with Heterotrissocladius, Micropsectra, Ablabesmyia and Chironomus as the most robust group‐indicator taxa. Forward selection of taxa in multiple discriminant analysis was used to fit chironomid assemblages into lake groups. Using only eight taxa, 95% of lakes were correctly classified at a second TWINSPAN division level (four groups) and 85% of lakes at a third division level (eight groups). 5. This study showed that there is considerable potential in using subfossil chironomid head capsules as paleoenvironmental indicators in both short‐ and long‐term (down‐core) studies of lake ontogeny and palaeoclimate conditions in West Greenland. However, because of the strong correlation between temperature and trophic variables, a quantitative reconstruction of lake‐ and habitat‐type is recommended, in combination with direct reconstruction of single variables such as temperature.     

Limited male dispersal in a social spider with extreme inbreeding

Cooperatively breeding animals commonly avoid incestuous mating through pre-mating dispersal. However, a few group-living organisms, including the social spiders, have low pre-mating dispersal, intra-colony mating, and inbreeding. This results in limited gene flow among colonies and sub-structured populations. The social spiders also exhibit female-biased sex ratios because survival benefits to large colonies favour high group productivity, which selects against 1 : 1 sex ratios. Although propagule dispersal of mated females may occasionally bring about limited gene flow, little is known about the role of male dispersal. We assessed the extent of male movement between colonies in natural populations both experimentally and by studying colony sex ratios over the mating season. We show that males frequently move to neighbouring colonies, whereas only 4% of incipient nests were visited by dispersing males. Neighbouring colonies are genetically similar and movement within colony clusters does not contribute to gene flow. Post-mating sex ratio bias was high early in the mating season due to protandry, and also in colonies at the end of the season, suggesting that males remain in the colony when mated females have dispersed. Thus, male dispersal is unlikely to facilitate gene flow between different matrilineages. This is consistent with models of non-Fisherian group-level selection for the maintenance of female biased sex ratios, which predict the elimination of male dispersal.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society 2009, 97 , 227–234.     

Contribution of cyclic parthenogenesis and colonization history to population structure in Daphnia

Cyclic parthenogenesis, the alternation of parthenogenetic and sexual reproduction, can lead to a wide scope of population structures, ranging from almost monoclonal to genetically highly diverse populations. In addition, sexual reproduction in aquatic cyclic parthenogens is associated with the production of dormant stages, which both enhance potential gene flow among populations as well as impact local evolutionary rates through the formation of dormant egg banks. Members of the cladoceran genus Daphnia are widely distributed key organisms in freshwater habitats, which mostly exhibit this reproduction mode. We assessed patterns of genetic variation within and among populations in the eurytopic and morphologically variable species Daphnia longispina , using data from both nuclear (13 microsatellite loci) and mitochondrial (partial sequencing of the 12S rRNA gene) markers from a set of populations sampled across Europe. Most populations were characterized by very high clonal diversity, reflecting an important impact of sexual reproduction and low levels of clonal selection. Among-population genetic differentiation was very high for both nuclear and mitochondrial markers, and no strong pattern of isolation by distance was observed. We also did not observe any substantial genetic differentiation among traditionally recognized morphotypes of D. longispina . Our findings of high levels of within-population genetic variation combined with high among-population genetic differentiation are in line with predictions of the monopolization hypothesis, which suggests that in species with rapid population growth and potential for local adaptation, strong priority effects due to monopolization of resources lead to reduced levels of gene flow.     

Evolution of sperm morphology in potamid freshwater crabs (Crustacea: Brachyura: Potamoidea)

We investigated sperm cells and spermatophores of four species of Old World freshwater crabs belonging to three different genera of the subfamily Potaminae (family Potamidae). Characters previously believed to be apomorphic for the potamid subfamily Potamiscinae were also found to occur in the Potaminae. To infer the morphological ancestral character state combination of the Potamidae, ancestral character state analysis of four different sperm traits was performed, based on a 16S rDNA phylogeny of the investigated species. Comparing molecular phylogeny and character state distribution, several cases of convergent evolution could be identified. The densely packed, coenospermic spermatophores and the occurrence of a ‘tongue‐and‐groove’ connection between operculum and acrosomal zones are probably apomorphies for the whole Potamidae. The spermatozoa of Socotrapotamon socotrense show several unique characters. We also analysed the evolution of acrosome size. The sperm cells of the Potamidae and their sister‐group Gecarcinucidae only slightly overlap in acrosome size. Within the investigated species, the ‘East Asia’ subclade (subfamily Potamiscinae) developed significantly larger acrosomes than the subfamily Potaminae. Our results suggest that the use of brachyuran acrosome morphology for phylogenetic inference at the family level is strongly affected by small sample size, and by convergent character evolution. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Short-Term Fixation of 14Carbon by the Submerged Aquatic Angiosperm Potamogeton pectinatus

In ¹⁴C fixation experiments, 3-phosphoglyceric acid was thefirst product of carbon assimilation in the light in Potamogetonpectinatus. The pattern of early ¹⁴C-labelled compounds wasthe same over a range of pH values of the medium from 3.5 to8.1. Rates of ¹⁴C incorporation declined with increasing pHof the medium indicating that free CO₂ is the major exogenoussource of carbon for photosynthesis in Potamogeton pectinatus.     

Ultrastructural studies of epidermis, sense receptors and sperm of Craspedella sp. and Didymorchis sp. (Platyhelminthes, Rhabdocoela)

Craspedella has a non-ciliated epidermis with nuclei located in the epidermis and with short microvilli. There is a thin basal lamina and thick underlying fibrous matrix. Rhabdites are secreted through ducts lined by microtubules. Multiciliate sense receptors consist of bundles of dendrites in a depression of the epidermis. Each dendrite has a cilium with a cross-striated rootlet; there are no electron-dense collars. Spermatozoa have peripheral microtubules which in cross-section are arranged in a ring-like or spiral fashion, numerous electron-dense granules, mitochondria and a nucleus; axonemes of the 9 +'1'type are free for most of their length. Centrioles occur in some nerve fibres. In Didymorchis parts of the epidermis are ciliated and epidermal perikarya are 'insunk', connected to the surface part of the epidermis by a single cytoplasmic process. Epidermal cilia have cross-striated vertical and horizontal rootlets. In the ciliary tips a short electron-dense rod along the central pair of tubules extends to the tip, where it widens to become a terminal plate; peripheral doublets gradually disappear by losing their microtubules. Receptors observed are uniciliate. Spermatozoa are as in Craspedella . Ultrastructural evidence indicates that Craspedella and Didymorchis arc closely related and belong to the Rhabdocoela.