The increase in risk of predation with begging activity in broods of Magpies Pica pica

Begging activity in broods of Magpies Pica pica was measured as the average total number of begging nestlings and the number of nestlings giving begging calls between 5 and 9 days since the first nestling hatched. There was considerable between-brood variation in begging activity relative to day-to-day variation within broods. Predation between 7 and 20 days of age was more frequent among those broods which had not previously suffered from brood reduction due to nestling starvation. Broods which were preyed upon showed significantly higher levels of begging activity than broods of a comparable size that were not preyed upon. In addition, the time elapsed from hatching to predation showed a negative correlation with the total number of begging nestlings. Within broods, those nestlings with the highest begging motivation (measured as the latency to respond when stimulated) seemed to be more readily taken by predators. These results confirm the existence of costs associated to begging in the form of an enhanced risk of being detected by predators.     

Fractionation by centrifugation of leaf proteins in press juices from Brassica and other species as a function of pH

Non-green leaf protein concentrates can be produced after separation of chlorophyll-associated proteins from chlorophyll-free proteins by sedimenting the chlorophyll-containing membranes suspended in press juice. To make the use of low speed centrifugation possible, the influence of pH on protein sedimentation rate was investigated, especially for Brassica Oleracea (17 cultivars). Press juices produced on a laboratory scale from greenhouse grown plant material were adjusted to the desired pH and centrifuges briefly at 5000 g or 15,000 g. The chlorophyll-associated protein from B. Oleraces sedimented rapidly at pH values both below and above 6.0(original pH of the press juice). When the pH of the press juice was adjusted to 7.5, all the chlorophyll-associated protein sedimented at 15,000 g, whereas about 45%of the original protein remained in the supernatant. An increase in sedimented chlorophyll-associated protein at higher pH was also observed for Brassica napus, Helianthus annuus and Vicia faba, but not for Beta vulgaris and Dactylis glomerata. Theoretically, the protein sedimentation pattern typical for B. oleracea might depend primarily on protein aggregation, but shrinking of thylakoids at pH values higher than 6 could contribute. The deviation from this pattern observed for B. vulgaris and D. glomerata might be caused by differences in composition of proteins or low molecular species. In practice, a pH above 7.0 seems to be useful for separation of chlorophyll-associated proteins from chlorophyll-free proteins by centrifugation of press juice from Brassica species without heat treatment.     

A stable,genetically determined colour dimorphism in the dung beetle Aphodius depressus: patterns and mechanisms

1. Melanism – the occurrence of dark morphs – in insects has been attributed to differences in, among other things, thermoregulation and immune defence. Dark individuals are hypothesised to perform better in colder areas, and to exhibit stronger melanin‐based immune defence. 2. In the present study, the geographical distribution of two colour morphs in Aphodius depressus (Kugelann), its climatic correlates, and temporal stability was described. Underlying mechanisms were then targeted through experiments: the inheritance of colour through controlled crosses, heating rates by thermal imaging, physiological tolerance by critical thermal limits, and immune efficiency by melanisation of implants. 3. In A. depressus, colour appears inherited by simple Mendelian principles, with red dominating over black. The frequency of two colour morphs forms a large‐scale cline. In the South West of Finland, all individuals are black, whereas, in the North East, most are red. This pattern has remained constant over 13 years (1996–2008). 4. The geographical pattern was not attributable to thermoregulation: black morphs were more abundant in warmer rather than colder parts of the country. In experiments, we found no differences in the heating rate of the two morphs, or in their upper temperature maxima. Neither did the morphs differ in their response to artificial objects inserted in their haemolymph. 5. Overall, colour variation in A. depressus occurs as a stable, genetically determined dimorphism, governed by Mendelian inheritance. Yet, no support for prevailing theory of factors sustaining melanism was found. The reasons for colour polymorphism in insects may thus be complex, and should be sought on a case‐by‐case basis.     

Additive effects of predator diversity on pest control caused by few interactions among predator species

1. Studies of the impact of predator diversity on biological pest control have shown idiosyncratic results. This is often assumed to be as a result of differences among systems in the importance of predator–predator interactions such as facilitation and intraguild predation. The frequency of such interactions may be altered by prey availability and structural complexity. A direct assessment of interactions among predators is needed for a better understanding of the mechanisms affecting prey abundance by complex predator communities. 2. In a field cage experiment, the effect of increased predator diversity (single species vs. three‐species assemblage) and the presence of weeds (providing structural complexity) on the biological control of cereal aphids were tested and the mechanisms involved were investigated using molecular gut content analysis. 3. The impact of the three‐predator species assemblages of aphid populations was found to be similar to those of the single‐predator species treatments, and the presence or absence of weeds did not alter the patterns observed. This suggests that both predator facilitation and intraguild predation were absent or weak in this system, or that these interactions had counteracting effects on prey suppression. Molecular gut content analysis of predators provided little evidence for the latter hypothesis: predator facilitation was not detected and intraguild predation occurred at a low frequency. 4. The present study suggests additive effects of predators and, therefore, that predator diversity per se neither strengthens nor weakens the biological control of aphids in this system.     

An invasive crayfish affects egg survival and the potential recovery of an endangered population of Arctic charr

1. Many fish stocks have declined, because of overharvesting, habitat destruction and introduced species. Despite efforts to rehabilitate some of these stocks, not all are responding or are recovering only slowly. 2. In freshwater systems, introduced crayfish are often problematic, and it has been suggested that their egg predation could reduce recruitment in depleted stocks of native fish. 3. Here, we report the results of a field experiment, using experimental cages, on the extent of predation on eggs of great Arctic charr (Salvelinus umbla) in Lake Vättern, Europe’s fifth largest lake. Here, the great Arctic charr has declined dramatically and is listed as critically endangered. 4. We were able to partition the total loss rate of eggs into background mortality, predation by introduced signal crayfish (Pacifastacus leniusculus) and predation by native fish. The mortality rate of charr eggs because of crayfish was estimated at more than five times that because of native fish. Of the total loss of eggs, 80% is believed to be caused by crayfish and 14% by fish, with 6% being natural background mortality. 5. In a worst case scenario, our data infer that only 25% of the original number of eggs would survive, compared with 75% in the absence of crayfish. This could impair recovery of the stock of the endangered great Arctic charr in Lake Vättern. 6. Contrary to earlier claims that crayfish predation on eggs of great Arctic charr is insignificant, our results indicate that crayfish predation may exceed fish predation and suggest that the abundance of signal crayfish on the spawning sites of great Arctic charr should be managed.     

Life history of Xenodexia ctenolepis: implications for life history evolution in the family Poeciliidae

Xenodexia ctenolepis (Hubbs, 1950) is a uniquely asymmetrical species in the fish family Poeciliidae that is endemic to a remote region of Guatemala. In the present study, we describe its life history based on the dissection of 65 adult females from three different collections. We show that it is a livebearer, has superfetation, or the ability to carry multiple litters of young in different stages of development, and has matrotrophy, or placentation, which results in the dry mass of young at birth being three- to four-fold greater than the egg at fertilization. The size distribution of males is non-normal in a fashion that suggests a genetic polymorphism for age and size at maturity. Most phylogenies place Tomeurus gracilis as the sister taxon to the remaining members of the family Poeciliidae. Because Tomeurus is the sole egg-layer in the family, egg-laying is thought to represent the life history of the common ancestor. Because Xenodexia possesses three supposed derived traits (livebearing, superfetation and matrotrophy), this phylogenetic hypothesis suggests that Xenodexia has a highly derived life history with respect to other members of the family. By contrast, the most recent DNA-based phylogeny suggests Xenodexia is the sister taxon to the remainder of the family. If this proves to be true, it suggests that some or all of these life history traits may have been characteristic of the common ancestor to the family, then lost and re-evolved multiple times within the family.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 77–85.     

Modelling hydration and photosystem II activation in relation to in situ rain and humidity patterns: a tool to compare performance of rare and generalist epiphytic lichens

A dynamic water and activity model was developed to assess how efficiently lichens can exploit in situ rain and humid air. The capacity to rehydrate and activate photosynthesis [i.e. photosystem II (PSII)] by these water sources was compared among four hydrophilic and one generalist epiphytic lichen. Hydration status, potential (instant activation) and realized (delayed activation) day‐light activity were simulated using a model based on species‐specific hydration, PSII activation characteristics and in situ water content for Platismatia norvegica in three microclimatic scenarios. The results showed that delayed PSII activation could have profound effects on lichens' ability to exploit environmental water sources. During rain, realized activity was reduced by 19, 34 and 56% compared to simulations assuming instant activation for three hydrophilic lichens in the driest microclimate. During humid air, the reduction was 81% for the most extreme species and scenario, because of slow hydration and low equilibrium water content. Many and brief hydration events may thus hamper species with slow activation and fast desiccation kinetics. No evidence of compensation by a ‘water‐holding’ morphology was observed among studied species. The developed model may provide a tool for identifying suitable habitats for long‐term persistence of lichens with physiological constraints.     

Species‐specific activation time‐lags can explain habitat restrictions in hydrophilic lichens

Photosystem II (PSII) activation after hydration with water or humid air was measured in four hydrophilic and a generalist lichen to test the hypothesis that slow activation might explain habitat restriction in the former group. For the hydrophilic species, activation was after 4 h nearly completed in Lobaria amplissima and Platismatia norvegica, while only c. 50% for Bryoria bicolor and Usnea longissima. The generalist Platismatia glauca was activated instantaneously. The effect of this on lichen field performance was investigated using a dynamic model separating the two water sources rain and humid air. Model simulations were made using the species‐specific characteristics and climate data from 12 stream microhabitats. For U. longissima, slow PSII activation could reduce realized photosynthesis by a factor of five. Bryoria bicolor was almost as severely affected, while P. norvegica displayed moderate reductions. Lobaria amplissima displayed longer realized activity periods even in unfavourable microclimates, possibly because of a higher water loss resistance. Both close proximity to streams and presence of turbulent water had a positive impact on realized activity among the slowly activated species, coinciding with observed distribution patterns of hydrophilic species. The results presented here may thus partly explain observed habitat restrictions of rare hydrophilic lichens.     

Vocal mimicry of hosts by Great Spotted Cuckoo Clamator glandarius: further evidence

Great Spotted Cuckoo nestlings were shown, after some days in the nest, to have begging calls that differed depending on whether they were being reared by Magpies or Carrion Crows. They also produced calls of a pitch and repetition rate that implied a high level of hunger.