Applying life-history strategies for freshwater macroinvertebrates to lentic waters

• 1 Effective environmental management requires a sound understanding of the causal mechanisms underlying the relationship of species with their environment. Mechanistic explanations linking species and environment are ultimately based on species traits. Many tools for ecological assessment and biomonitoring lack such explanations. Elsewhere, we have defined life‐history strategies, based on the interrelations between species traits and their functional implications.
• 2 This study tests the hypothesis that life‐history strategies represent different solutions to particular ecological problems, thus connecting species and their environment through species traits. Data on aquatic macroinvertebrates in a variety of waterbodies were analysed in terms of life‐history strategies. These waterbodies differed in environmental conditions and macroinvertebrate assemblages. Solutions to the ecological problems present in each type of water body were expected to be reflected in the abundance of (species exhibiting) different life‐history strategies.
• 3 Results show clear differences in strategy composition between the different water types, which could be related to the prevailing environmental conditions through mechanistic explanations. For example, species with a long period of juvenile development and a synchronized emergence of short‐lived adults were most dominant in large mesotrophic waterbodies with stable and predictable environmental conditions. In contrast, species that have a rapid development and spread successive reproduction attempts over a longer time period were most abundant in waterbodies with fluctuating and less predictable environmental conditions.
• 4 Differences in strategy composition provide insight into the prevailing environmental conditions related to temporal predictability, and habitat favourability, from the perspective of the species themselves. By reducing diverse species assemblages to a small number of strategies, representing easily interpretable relationships, this approach may be useful in environmental quality assessment programmes, including those required by the European Water Framework Directive. Based on mechanistic explanations, life‐history strategies may generate testable predictions and guide future research. Further research may focus on expanding life‐history strategies to include other species groups and ecosystems.

     

Answer to “Reevaluation of the conclusion that IRES-activity reported within the 5′ leader of the TIF4631 gene is due to promoter activity”

The accuracy of the data we reported in an RNA Letter to the Editor earlier this year on the promoter activity within the 5′ leader of the TIF4631 gene is questioned by V.P. Mauro and others in this issue. We reply here that we see no inaccuracy in our data.     

Effect of Cercospora zeae-maydis infested maize residue on progress and spread of grey leaf spot of maize in central Uganda

The spread of grey leaf spot caused by Cercospora zeae‐maydis from infested maize residue on the soil surface and progress over time were studied under tropical conditions at two locations in central Uganda, Kabanyolo and Namulonge, using a susceptible local cultivar, LP16. Infested maize residue collected the previous season was used as the inoculum source in varying amounts; 80% coverage, 40% coverage and 0% soil coverage were used to simulate no tillage, minimum tillage and maximum tillage with complete burial of residues. In all the seasons, disease spread was adequately described by a power law model, whereas disease progress over time was equally well represented by both Gompertz and logistic models. The time factor was highly significant (P < 0.05) for disease development, indicating both increases in disease intensity over time and change in gradients with time. The amount of infested residue on the soil surface in the maize planting was highly significant (P < 0.05) for slope (b) and intercept (a) of the linearised disease gradient. The gradient parameter (b) based on the average for the four directions from the residue source ranged from ?0.96 to ?0.08 in the second cropping season of 1999, from ?2.16 to ?0.01 and from ?0.87 to ?0.03 in the first and second seasons of 2000, respectively. The distance from the infested residue significantly affected foliar disease, but the direction from the residue inoculum source did not, nor was the distance by direction interaction significant. However, interactions between amount of residue and distance were significant. Percentage leaf area affected by grey leaf spot, the areas under disease progress curves and disease intercepts decreased with distance at both locations, but rate of disease increase (r) was generally constant with distance from residue source at Kabanyolo, but not at Namulonge. The relationship between disease severity and amount of residue cover appeared to be affected by the level of background inoculum. At Kabanyolo, where little background inoculum was present, differences were detected in disease severity parameters between the no‐residue plots and residue plots, whereas at Namulonge, where high background levels existed, there was no effect of residue on disease.     

Taphonomy as a guide to hnctional morphology of Holocrinus, the first post-Paleozoic crinoid

Baumiller, T. K. & Hagdorn, H. 1995 1130: Taphonomy as a guide to functional morphology of Holoainus , the first post-Paleozoic crinoid.
A taphonomic approach, in which patterns of fragmentation are used to infer the organization of soft tissue and function in crinoid stalks, was applied to pluricolumnals of the first post-Paleozoic crinoid, Holocrinus . The observed patterns are analogous to those for isocrinid crinoids, suggesting that Holoctinus and isocrinid stalks are functionally similar in having specialized sites for autotomy. Stalk autotomy in Holocrinus could not have been predicted based on morphological criteria alone: the stalk of Holocrinus lacks synostosial articulations, which among the isocrinids are the sites of autotomy. This implies that taphonomic data can supplement and sometimes supersede morphological data as a basis for functional reconstructions. Stalk autotomy in Holocrinus indicates that this trait was not derived independently by the isocrinids and comatulids, but rather that it was primitively shared by them. If pentacrinitids could not autotomize their stalks, as is likely, this would represent a loss of this ability through paedomorphosis. □ Holocrinus, articulates, arinoids, taphonomy, autotomy, heterochrony .     

The Minimum Intercellular-space CO2-Concentration (T) of Maize Leaves and its Influence on Stomatal Movements

Unlike other leaves investigated, maize leaves were found tobe able to exhaust atmospheric CO₂-content to zero concentration.This occurred at 20? C. with a light intensity of 100 f.c. andat 30? C. with a light intensity of 500 f.c. The influences of temperature, light intensity, and waterstrainon this property of maize leaves were investigated systematicallyand a permanent aftereffect of waterstrain on the leaves wasfound. Stomatal conductance measurements showed that maize stomataare sensitive to CO₂-concentrations between zero and 100 p.p.m.,a circumstance not yet reported for other leaves.     

A sublethal effect on native Anthocoris nemoralis through competitive interactions with invasive Harmonia axyridis

1. The invasive ladybird Harmonia axyridis Pallas (Coleoptera: Coccinellidae) is implicated in declines of native ladybirds with intraguild predation identified as an underlying mechanism, however, less studied are the effects on non‐coccinellid predators. Intraguild predation between Anthocoris nemoralis Fabricius (Heteroptera: Anthocoridae) and H. axyridis and the relative effects of inter‐ and intraspecific competition on predators on potted Tilia cordata Mill. was investigated, at two aphid densities. 2. Intraguild predation was unidirectional in favour of H. axyridis in Petri dishes although a low level of ladybird egg predation by A. nemoralis occurred. However, on trees intraguild predation was rare. 3. A positive effect of aphid density on H. axyridis weight gain, and increased survival when reared with A. nemoralis on potted trees indicated stronger effects of intraspecific competition on H. axyridis. Consistent suppression of aphids by ladybirds revealed their superior competition for aphids. 4. Anthocoris nemoralis weight gain was reduced when reared with H. axyridis on potted trees, indicating a potential for a sublethal effect through interspecific competition. Survivorship of A. nemoralis did not differ between con‐ and heterospecific treatments, but high aphid density enhanced A. nemoralis survival. Overall, high mortality among nymphs across treatments suggested effects related to both inter‐ and intraspecific competition for resources. 5. Results provide evidence of a sublethal effect by invasive H. axyridis through resource competition, suggesting that where these predators co‐occur, competitive interactions for shared prey are more likely to affect A. nemoralis populations than intraguild predation by H. axyridis.     

Effects of diet and host access on fecundity and lifespan in two fruit fly species with different life‐history patterns

The reproductive ability of female tephritids can be limited and prevented by denying access to host plants and restricting the dietary precursors of vitellogenesis. The mechanisms underlying the delayed egg production in each case are initiated by different physiological processes that are anticipated to have dissimilar effects on lifespan and reproductive ability later in life. The egg‐laying abilities of laboratory‐reared females of the Mediterranean fruit fly (Ceratitis capitata Wiedmann) and melon fly (Bactrocera cucurbitae Coquillett) from Hawaii are delayed or suppressed by limiting access to host fruits and dietary protein. In each case, this is expected to prevent the loss of lifespan associated with reproduction until protein or hosts are introduced. Two trends are observed in each species: first, access to protein at eclosion leads to a greater probability of survival and a higher reproductive ability than if it is delayed and, second, delayed host access reduces lifetime reproductive ability without improving life expectancy. When host access and protein availability are delayed, the rate of reproductive senescence is reduced in the medfly, whereas the rate of reproductive senescence is generally increased in the melon fly. Overall, delaying reproduction lowers the fitness of females by constraining their fecundity for the remainder of the lifespan without extending the lifespan. © 2013 The Royal Entomological Society     

Proportioning a Hydra

SYNOPSIS. Pieces of hydra tissue of various sizes and shapeswere cut from the body columns of adult hydra and allowed toregenerate. The proportions of the resulting animals were determinedfirst by counting cells in the head and body, and secondly bymeasuring the structures directly using an ocular micrometer. Head-body proportions were found to be constant over a tenfoldsize range. Very small regenerates had a larger head fractionand large budding regenerates had a smaller head fraction. Extrastructures developed in certain shape pieces, but total head-bodytissue remained proportional. More detailed measurement of thehead showed that the hypostome regulated only slightly withtotal size change, while the tentacle tissue varied considerablyto maintain the head-body ratio. This suggested that the patterningof the hypostome and the tentacles might involve separate processes,with the latter being responsible for proportion regulation.While the body mass appeared to be determined by the proportioningmechanism, its circumference was related to the circumferenceof the hypostome, suggesting a causal relationship between thetwo organizers and the column shaping. The basal disc remainedproportional to the body except in the smallest pieces. A Gierer-Meinhardtpattern formation scheme could account for the results found.     

Zur Feinstruktur der spermatogenetischen Stadien von Myxine glutinosa L. (Cyclostomata)

The fine structure of the spermatogonia, spermatocytes, spermatids, the Sertoli cell and the epithelial cells of the mesorchial sheath is described. In an early spermatid stage a transient close relationship between the Chromatoid body and the acrosome is demonstrated.