Survival of Slender-billed Gull chicks during the crèching period

Capsule Crèches formed early in the season lasted longer than those formed later, but a longer crèching period did not appear to confer higher chick survival.

Aims To investigate the ecological factors influencing the benefit to parents of crèching behaviour by measuring chick survival.

Methods Mark–recapture was used to model apparent daily survival of 505 chicks during the crèching period in three different crèches. We contrasted models with different tipping points to assess possible differences across crèches in chick survival during the first week and in the moment at which chick departures began.

Results We did not find a clear difference across crèches on daily chick survival during the first stages of the crèche. By modelling chick apparent survival as a linear function of time we showed that the latest formed crèche dispersed more rapidly.

Conclusions The two crèches formed early in the season lasted longer than the one formed later but chicks did not appear to have a higher survival over the first week of crèching. We suggest that a longer period at the crèche should result in a higher survival in the period soon after fledging because chicks leave the crèche 4–7 days older than other chicks. Furthermore, early crèches are synchronous with those of other species breeding in the same area, thus perhaps diluting predation. We discuss the limitations of our analysis and the possible implications for the community of waterbirds breeding at our study site.     

Cooperation, conflict, and crèching behavior in goldeneye ducks

Crèching behavior, or brood amalgamation, results in offspring being reared by adults other than their genetic parents. Although a variety of hypotheses have been proposed to explain this behavior, most assume either that brood amalgamation is accidental (i.e., nonselected) or that adoption of young is selected for because of social benefits to the young and/or adopting parents. We propose, instead, that brood amalgamation is a function of two separate processes: brood desertion and brood adoption. To examine brood desertion, we develop a graphic model to predict when parents should abandon their young and we test this model experimentally for the Barrow's goldeneye (Bucephala islandica). As predicted, females deserted their offspring when the size of the brood was experimentally reduced. Brood adoption occurred when deserted ducklings joined other broods. However, the success of ducklings in doing so was strongly dependent on the availability of potential host broods and on the age of the recipient broods. Foreign ducklings were readily accepted into young broods (<10 d old) but invariably were rejected from old broods. We could detect no benefits or costs of brood adoption to the host females, contrary to the expectations of a social benefit hypothesis. Our experiments indicate that Crèching behavior is driven by selection on adults to abandon their brood when the benefits of continued investment are outweighed by the reduction in future reproduction and selection on deserted ducklings to join other broods to obtain parental care. Rather than a form of cooperative brood care, Crèching in goldeneyes is perhaps best considered as a form of reproductive parasitism, entailing parent-offspring conflict over brood desertion and intergenerational conflict over adoption of abandoned young.     

A novel insight into the cost–benefit model for the evolution of botanical carnivory

Background The cost–benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (A_N) in the microsites inhabited by carnivorous plants.Scope This review summarizes results from the classical interpretation of the cost–benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost–benefit model.Conclusions Traps of carnivorous plants have lower A_N than leaves, and the leaves have higher A_N after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, R_D) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted.     

Toxocara in the mouse: a model for parasite-altered host behaviour?

The objective of this paper is to critically evaluate the significance of parasite-altered host behaviour in the Toxocara mouse model particularly in the light of the Manipulation Hypothesis. Murine behaviours were examined in both outbred and inbred strains of mice infected with different doses of Toxocara canis ova. Behaviours investigated included activity, exploration, response to novelty, anxiety, learning, memory and social behaviour. Subsequent modifications to the behaviour of infected mice were investigated with respect to dose administered and larval accumulation in the brain. There was substantial variation in the number of larvae recovered from brains of individual mice, which received similar doses of Toxocara ova. Furthermore, the numbers of larvae recovered at different doses differed significantly between an outbred and inbred strain of mouse. Alterations in infected host behaviour occurred and were related to the number of larvae recovered from the brain. For social behaviour in outbred mice, a high infection in the brain reduced levels of aggressive behaviour and increased levels of flight and defensive behaviours. In contrast, outbred mice with a low infection in the brain displayed a greater level of risk behaviour in respect of predator odour and the light/dark box compared to control or high infection mice. Post-infection, outbred mice were more immobile whereas inbred mice showed reduced immobility and increased digging and climbing. Impaired learning ability was observed in outbred mice with moderate and high levels of infection in the brain compared to control and low infection mice. Toxocara infection has an impact upon a diverse range of murine behaviours with little evidence for a specific and hence an adaptive alteration. Many of the effects on murine host behaviour by Toxocara are likely to be pathological side effects of infection rather than as a consequence of adaptive host-manipulation. Observed changes in murine behaviour may be relevant to human toxocariasis.     

Studying the evolution of social behaviour in one of Darwin’s Dreamponds: a case for the Lamprologine shell-dwelling cichlids

The link between the evolution of advanced sociality and cognition has been an important concept across fields and taxonomic boundaries. However, in many study systems, ecological and phylogenetic confounds impair evolutionary inferences drawn when comparing social organization. Here, we highlight the value of the shell-dwelling Lamprologine cichlids of Lake Tanganyika in studies of cognitive and social evolution. These species show differences in social organization, both within and across species, but otherwise exhibit remarkable similarities in their ecology and life history. We focus on the ecological and social attributes of 15 Lamprologine cichlids that live in permanent association with empty gastropod shells, often in syntopy and with largely overlapping ecological niches. We then discuss difficulties with terminology and categorization of social organization, outlining current and emerging methodologies to address these limitations. Our goal is twofold: (i) to gather available empirical evidence on the behaviour, life history, and ecology of shell-dwelling Lamprologine cichlids, highlighting their potential in comparative studies of cognition and evolution, and (ii) to stimulate debate and critical appraisal of current terminology and categorizations of social structure, ideally leading to more precise and empirically standardized definitions of sociality in cichlids.

     

A model for the regulation of δ-aminolaevulinate synthetase induction in rat liver

A reciprocal relationship exists between the cytochrome P-450 content and delta-aminolaevulinate synthetase activity in adult rats. In young rats the basal delta-aminolaevulinate synthetase activity is higher and the cytochrome P-450 content is lower compared with the adult rat liver. Administration of allylisopropylacetamide neither induces the enzyme nor causes degradation of cytochrome P-450 in the young rat liver, unlike adult rat liver. Allylisopropylacetamide fails to induce delta-aminolaevulinate synthetase in adrenalectomized-ovariectomized animals or intact animals pretreated with successive doses of the drug, in the absence of cortisol. The cortisol-mediated induction of the enzyme is sensitive to actinomycin D. Allylisopropylacetamide administration degrades microsomal haem but not nuclear haem. Haem does not counteract the decrease in cytochrome P-450 content caused by allylisopropylacetamide administration, but there is evidence for the formation of drug-resistant protein-bound haem in liver microsomal material under these conditions. Phenobarbital induces delta-aminolaevulinate synthetase under conditions when there is no breakdown of cytochrome P-450. On the basis of these results and those already published, a model is proposed for the regulation of delta-aminolaevulinate synthetase induction in rat liver.     

Challenging the trade-off model for the evolution of virulence: is virulence management feasible?

Progress in understanding the evolution of infectious diseases has inspired proposals to manage the evolution of pathogen (including parasite) virulence. A common view is that social interventions that lower pathogen transmission will indirectly select lower virulence because of a trade-off between transmission and virulence. Here, we argue that there is little theoretical justification and no empirical evidence for this plan. Although a trade-off model might apply to some pathogens, the mechanism appears too weak for rapid selection of substantial changes in virulence. Direct selection against virulence itself might be a more rewarding approach to managing the evolution of virulence.     

A primordial tRNA modification required for the evolution of life?

The evolution of reading frame maintenance must have been an early event, and presumably preceded the emergence of the three domains Archaea, Bacteria and Eukarya. Features evolved early in reading frame maintenance may still exist in present-day organisms. We show that one such feature may be the modified nucleoside 1-methylguanosine (m(1)G37), which prevents frameshifting and is present adjacent to and 3' of the anticodon (position 37) in the same subset of tRNAs from all organisms, including that with the smallest sequenced genome (Mycoplasma genitalium), and organelles. We have identified the genes encoding the enzyme tRNA(m(1)G37)methyltransferase from all three domains. We also show that they are orthologues, and suggest that they originated from a primordial gene. Lack of m(1)G37 severely impairs the growth of a bacterium and a eukaryote to a similar degree. Yeast tRNA(m(1)G37)methyltransferase also synthesizes 1-methylinosine and participates in the formation of the Y-base (yW). Our results suggest that m(1)G37 existed in tRNA before the divergence of the three domains, and that a tRNA(m(1)G37)methyltrans ferase is part of the minimal set of gene products required for life.     

Why care? Inferring the evolution of complex social behaviour

Phylogenetic comparative analyses of complex traits often reduce the traits of interests into a single (or a few) component variables. Here, we show that this may be an over‐simplification, because components of a complex trait may evolve independently from each other. Using eight components of parental care in 400 bird species from 89 avian families that represent the relative contribution of male vs. female to a particular type of care, we show that some components evolve in a highly correlated manner, whereas others exhibit low (or no) phylogenetic correlation. Correlations were stronger within types of parental activity (brooding, feeding, guarding) than within stages of the breeding cycle (incubation, prefledging care, post‐fledging care). A phylogenetically corrected cluster analysis identified two groups of parental care components that evolved in a correlated fashion: one group included incubation and brooding, whereas the other group comprised of the remaining components. The two groups of components provide working hypotheses for follow‐up studies to test the underlying genetic, developmental and ecological co‐evolutionary mechanism between male and female care. Furthermore, the components within each group are expected to respond consistently to different ambient and social environments.     

Parasitic gastro-enteritis in lambs — A model for estimating the timing of the larval emergence peak

The life history of the nematode parasites of domestic ruminants usually involves the development and survival of free-living stages on pasture. The pasture is, therefore, the site of deposition, development and transmission of nematode infection and meteorological factors affecting the pasture will affect the parasites. Recently Thomas and Starr (1978) discussed an empirical technique for forecasting the timing of the summer wave of gastro-intestinal parasitism in North-East England in the lamb crop using meteorological data and in particular estimates of the duration of surface wetness. This paper presents an attempt to model surface wetness and the temperature limitation to nematode development.Presented at the Eighth International Congress of Biometeorology, 8–14 September 1979, Shefayim, Israel.     

A model of mate searching and territorial behaviour for “flier” type dragonflies

First, the mating system of a “flier” odonate species that continues patrolling without perching,Cordulia aenea amurensis Selys, is briefly reviewed. Adult males of this species search for mates for a long distance along the shore of a pond if male density is very low, but localize their patrol within a short range and defend the ranges if the density is high (Ubukata 1975, 1979). Secondly, a model of mate searching by vision and territoriality for flier dragonflies is proposed. The main assumptions of the model are: (1) a male with a fixed length of visual range (D) patrols with a constant velocity (V) on a straight line; (2) he turns in the opposite direction at 2 fixed points (distance=L); (3) female arrival probability is uniform in both spatial and temporal dimensions; (4) the females stay at the arrival point for a fixed time (C); (5) if a male discovers a female he copulates with her without fail and leaves the line. From the model the following are predicted: if , the species (type 1) has an optimal length of patrol range even if the female arrival rate is uniform; ifD is smaller than the right hand side of the inequality (type 2), the mating probability becomes higher as the patrol range increases, if there is no other male. On the basis of the above model the concept of an “unusurpable territory” is defined to exist at a given time after the start of patrol and the probability of unusurpability (P) is calculated as a function ofD, V, L, M (male density-1) andT (duration of patrol).P drops abruptly if the length of patrol range (L) exceeds that of unusurpable territory at high male densities. Therefore, there appears to be an optimal length of patrol range when there are other males, agreeing with the data fromC. a. amurensis. Finally, the model is discussed in comparison with some other models. Ecological studies ofCordulia aenea amurensis Selys, VIII.     

A model for the rate of enzymatic hydrolysis of cellulose in heterogeneous solid–liquid systems

Hydrolysis of cellulose by cellulase enzymes has been studied in a stirred batch reactor at 50°C. A kinetic model has been devised by which the behaviour of such a reaction could be described. The model has been developed on the basis of shrinking particle theory and Langmuir isotherm concept. The applicability of the model has been tested by comparing the experimental results for diverse reaction systems, obtained in the present study or taken from the literature, and those predicted from the model. The degree of agreement was within ±2–11%.     

Current advances in the phylogenetic reconstruction of metazoan evolution. A new paradigm for the Cambrian explosion?

The study of metazoan evolution has fascinated biologists for centuries, and it will certainly keep doing so. Recent interest on the origin of metazoan body plans, early metazoan evolution, genetic mechanisms generating disparity and diversity, molecular clock information, paleontology, and biogeochemistry is contributing to a better understanding of the current phyletic diversity. Unfortunately, the pattern of the metazoan tree of life still shows some important gaps in knowledge. It is the aim of this article to review some of the most important issues related to the inference of the metazoan tree, and point towards possible ways of solving certain obscure aspects in the history of animal evolution. A new hypothesis of the metazoan diversification during the Cambrian explosion is proposed by synthesizing ideas from phylogenetics, molecular evolution, paleontology, and developmental biology.     

A role for genetic accommodation in evolution?

Whether evolutionary change can occur by genetic assimilation, or more generally by genetic accommodation, remains controversial. Here we examine some of the experimental evidence for both phenomena. Several experiments in Drosophila suggest that assimilation is possible, and a new paper shows that a color polyphenism in the tobacco hornworm, Manduca sexta, can evolve by genetic accommodation. We argue that genetic accommodation, including assimilation, is a plausible mechanism in evolution; however, more work is required to test how this mechanism acts and how often it is involved in evolutionary change.     

A model for the coevolution of resistance and virulence in coupled host—parasitoid interactions

A coevolutionary model is developed of the interaction between a host and an internal parasitoid, where the outcome of parasitism depends upon the extent to which individual hosts invest in resistance mechanisms and individual parasitoids in countermeasures (virulence). The host and parasitoid are assumed to have coupled population dynamics (of Nicholson–Bailey form) and to be composed of a series of asexual clones with different levels of resistance and virulence. Investment in resistance and virulence mechanisms is assumed to be costly. The model has two main outcomes. First, if resistance is relatively costly compared to virulence, the host may be selected not to invest in resistance mechanisms despite parasitoid investment in virulence, in effect trading off the risks of parasitism against the savings in costs. A number of cases which appear to correspond to this result have been reported. Second, for most other feasible parameter values, an arms race occurs between host and parasitoid, until effective resistance becomes so costly that the host abandons defence. This abandonment is followed by a reduction in parasitoid virulence and the cycle begins again. These cycles may explain reports of persistent additive genetic variation in resistance and virulence, and may also contribute towards population dynamic stability.     

Radioimmunoscintigraphic approach for the in vivo detection of tuberculomas—A preliminary study in a rabbit model

Radioimmunoscintigraphic approach could provide a viable non-invasive alternative for the diagnosis of deeply situated tuberculomas. We have evaluated this in a rabbit model constructed to give a characteristic localized tubercular lesion, with complimentary morphological, histological and antigenic profiles. ¹³¹I-anti Myobacterium bovis (BCG) antibody was shown to localize at the lesion, where as ¹³¹I-bovine serum albumin and ^99mTc-red blood cell scans were negative. The clearance of intradermally-injected tuberculous antigen could be traced into ascending lymph nodes using ¹³¹I-anti M. bovis (BCG) antibody.     

A model for the lateral diffusion of “stiff” chains in a lipid bilayer

We present random walk models for the diffusive motion of lipid probe molecules in a lipid bilayer and calculate the diffusion constants for probes spanning the entire bilayer and for probes extending through one lipid layer only. The stiffness of such molecules can explain the observed value of 2/3 for the ratio of these diffusion constants.     

A chemically explicit model for the mechanism of proton pumping in heme–copper oxidases

A mechanism for proton pumping is described that is based on chemiosmotic principles and the detailed molecular structures now available for cytochrome oxidases. The importance of conserved water positions and a step-wise gated process of proton translocation is emphasized, where discrete electron transfer events are coupled to proton uptake and expulsion. The trajectory of each pumped proton is the same for all four substrate electrons. An essential role for the His-Tyr cross-linked species is discussed, in gating of the D- and K-channels and as an acceptor/donor of electrons and protons at the binuclear center.