Competition between near and far dispersers in spatially structured habitats

Competitive interactions and invasibility between short- and long-distance dispersal was investigated in a population on a heterogeneous landscape with spatial correlations in habitat types, and where the driving interaction between individuals is competition for space. Stochastic spatially explicit simulations were used, along with differential equation models based on pair approximations. Conditions under which either dispersal strategy can successfully invade the other were determined, as a function of the amount and clustering of suitable habitat and the relative costs involved in the two dispersal strategies. Long-distance dispersal, which reduces intraspecific competition, is sometimes advantageous even where aggregation of suitable habitat would otherwise favor short-distance dispersal, although certain habitat distributions can lead to either strategy being dominant. Coexistence is also possible on some landscapes, where the spatial structure of the populations partitions suitable sites according to the number of suitable neighboring sites. Mutual competitive exclusion, where whichever strategy is established first cannot be invaded, is also possible. All of these results are observed even when there is no intrinsic difference in the two strategies' costs, such as mortality or competitive abilities.     

Testing the status-dependent ESS model: population variation in fighter expression in the mite Sancassania berlesei

The conditional evolutionarily stable strategy (ESS) with status-dependent tactics is the most commonly invoked ESS for alternative reproductive tactics within the sexes. Support for this model has recently been criticized as apparent rather than real. We address key predictions of the status-dependent ESS in three populations of the male dimorphic mite Sancassania berlesei. In S. berlesei'fighter' males are characterized by a thickened pair of legs used for killing rivals; 'scramblers' are benign. Most males in each population could be manipulated to become fighters by decreasing density, fulfilling the prediction that males make a 'decision'. There was evidence of genetic covariance between sire status and offspring morph, but also a strong effect of sire morph on offspring morph ratio. This was consistent with considerable genetic variation for the status-dependent switch point as a breeding experiment found no support for single-locus inheritance. We also found evidence that switch points evolve independently of distributions of status. This study supports the current status-dependent ESS model.     

Family background and female sexual behavior

Since the seminal works of Draper and Harpending (1982) and Belsky et al. (1991) there has been considerable interest in the link between the family environment experienced as a child and consequent mating and reproductive strategy of females. In this paper, predictions from the hypothesis were tested using postal survey data from a cross-section of 415 women in Merseyside, UK. No relationships were found between father-absence, unrelated male-presence, parental divorce or parental death with age at first coitus, number of sexual partners, mean length of sexual relationships or mean length of relationships prior to coitus occurring. This work was supported by an Economic and Social Research Council Studentship. This paper was completed as part of the author’s doctoral research that focused on differences in age at first reproduction between social classes in the UK, conducted at the University of Liverpool. The author now works for the Scottish Executive, Edinburgh.     

Male morphological variation and the determinants of body size in two Otiteselline fig wasps

The chalcid wasps (Hymenoptera) that develop in fig tree inflorescences(Ficus: Moraceae) have often been used to study alternativereproductive behaviors. However, recent work suggests that suchbehaviors are more complex than previously thought. We investigatedthis in Otitesella longicauda and O. rotunda. In addition toknown dimorphisms in the two species (each have "religiosa"males that use their mandibles to fight for mates in the fig,and "digitata" males that disperse from the fig to mate), wefound that religiosa males below species-specific body sizeswitch points have relatively larger mandibles and are lesssclerotized than those above. Thus, they are actually trimorphic.We suggest that the religiosa morph variation is linked to fighter/nonfighteralternative mating behaviors, with small (nonfighting) maleshaving relatively larger mandibles because they also use themto pull females out of their galls before mating. Also, we investigatedthe determinants of wasp body size, and whether females (foundresses)adjust their offspring allocation strategies according to expectedoffspring size. We found that wasp size is larger in ovariesnear the center of the fig, and more females and fewer religiosamales are laid in such ovaries than in those further away. Thisprobably indicates that foundresses lay females when they areexpected to be large because their fitness is more body size–dependentthan that of religiosa males. We then discuss the implicationsof our findings for the study of alternative reproductive behaviorsand foundress offspring allocation strategies.     

Planktonic encounter rates in homogeneous isotropic turbulence: the case of predators with limited fields of sensory perception

It is a well-established fact that encounter rates between different species of planktonic microorganism, either swimming, or passively advected by the flow, are enhanced in the presence of turbulence. However, due to the complexity of the various calculations involved, current encounter rate theories are based on a number of simplifying approximations, which do not reflect reality. In particular, a typical planktonic predator is usually assumed to have perfect 'all round vision', i.e. it can perceive a prey particle at any relative orientation, provided it lies within some given contact radius R. Unfortunately, there is a wide body of experimental evidence that this is not the case. In this study the encounter problem for a predator with a limited field of sensory perception, swimming in a turbulent flow, is examined from first principles and a number of new modelling ideas proposed. A wide range of kinematic simulations are also undertaken to test these predictions. Particular attention is paid to the swimming strategy such a predator might undertake to enhance its encounter rate. It turns out that the predicted optimum swimming strategies differ radically from the results of previous work. Empirical evidence is also presented which appears to support these new findings.     

Effect of methanol feeding strategies on production and yield of recombinant mouse endostatin from Pichia pastoris

Pichia pastoris, a methylotrophic yeast, is an efficient producer of recombinant proteins in which the heterologous gene is under the control of the methanol-induced AOX1 promoter. Hence, the accepted production procedure has two phases: In the first phase, the yeast utilizes glycerol and biomass is accumulated; in the second phase, the yeast utilizes methanol which is used both as an inducer for the expression of the recombinant protein and as a carbon source. Since the yeast is sensitive to methanol concentration, the methanol is supplied gradually to the growing culture. Three methanol addition strategies were evaluated for the purpose of optimizing recombinant endostatin production. Two strategies were based on the yeast metabolism; one responding to the methanol consumption using a methanol sensor, and the other responding to the oxygen consumption. In these two strategies, the methanol supply is unlimited. The third strategy was based on a predetermined exponential feeding rate, controling the growth rate at 0.02 h(-1), in this strategy the methanol supply is limited. Throughout the induction phase glycerol, in addition to methanol, was continuously added at a rate of 1 g L h(-1). Total endostatin production was similar in all three strategies, (400 mg was obtained from 3 L initial volume), but the amount of methanol added and the biomass produced were lower in the predetermined rate method. This caused the specific production of endostatin per biomass and per methanol to be 2 times higher in the predetermined rate than in the other two methods, making the growth control strategy not only more efficient but also more convenient for downstream processing.     

Non-warning odors trigger innate color aversions--as long as they are novel

Warning signals made by unpalatable insects to potential predatorscommonly target more than one sense: such signals are "multimodal." Pyrazines are odors produced by warningly colored insects whenattacked, and have been shown to interact with food coloration,biasing avian predators against novel and typically aposematicfood. However, at present it is not known whether this is anadaptation by prey to exploit a general feature of avian psychology,or an evolutionary response by birds to enhance their avoidanceof unpalatable prey. Here we investigate the effect of otherodors on the innate responses of naive domestic chicks (Gallusgallus domesticus) to food that is of novel color, or of acolor that is associated with warning coloration, yellow. Inthe first experiment, we demonstrate that natural and artificialodors that have no association with aposematism in the wildcan produce biases against both novel colored foods and yellowcolored foods. In a second experiment, we also show that odor novelty is vital for eliciting such effects. These results supportthe idea that warning odors have evolved in response to preexistingpsychological biases against novel odors in predators, ratherthan predators evolving specific responses against odors associatedwith unpalatable prey.     

Male bimaturism and reproductive success in Sumatran orang-utans

Although orang-utans live solitary lives most of the time, theyhave a complex social structure and are characterized by extremesexual dimorphism. However, whereas some adult male orang-utansdevelop full secondary sexual characteristics, such as cheekflanges, others may stay in an "arrested" unflanged conditionfor up to 20 years after reaching sexual maturity. The resultis a marked bimaturism among adult males. Flanged males allowfemales to overlap with their home range and often toleratethe presence of unflanged males. However, wherever possibleflanged males actively prevent unflanged males from copulatingwith females. Two competing hypotheses, previously untested,have been advanced to explain male reproductive behavior andbimaturism in orang-utans: (1) the "range-guardian" hypothesis,which asserts that the flanged males are postreproductive anddefend a range in which they tolerate sexually active, unflangedmale relatives; and (2) the "female choice" hypothesis, whichasserts that flanged males tolerate unflanged males in their range because they rely on female preference to favor flangedmales. We investigated these hypotheses and a third hypothesisthat the two male morphs represent co-existing alternativemale reproductive strategies ("sitting, calling, and waiting"for flanged males versus "going, searching, and finding" forunflanged males). Fecal samples were collected from a well-studiedpopulation in Indonesia, and eight human microsatellites wereanalyzed for 30 individuals that have been behaviorally monitoredfor up to 27 years. By carrying out paternity analysis on 11offspring born over 15 years, we found that unflanged malesfathered about half (6) of the offspring. Relatedness betweensuccessful unflanged males and resident dominant males wassignificantly lower than 0.5, and for some unflanged/flangedmale pairs, relatedness values were negative, indicating thatunflanged males are not offspring of the flanged males.     

Interspecific Differences of Leaf Gas Exchange and Water Relations of Three Evergreen Mediterranean Shrub Species

Leaf gas exchange and plant water relations of three co-occurring evergreen Mediterranean shrubs species, Quercus ilex L. and Phillyrea latifolia L. (typical evergreen sclerophyllous shrubs) and Cistus incanus L. (a drought semi-deciduous shrub), were investigated in order to evaluate possible differences in their adaptive strategies, in particular with respect to drought stress. C. incanus showed the highest annual rate of net photosynthetic rate (P _N) and stomatal conductance (g _s) decreasing by 67 and 69 %, respectively, in summer. P. latifolia and Q. ilex showed lower annual maximum P _N and g _s, although P _N was less lowered in summer (40 and 37 %, respectively). P. latifolia reached the lowest midday leaf water potential (₁) during the drought period (–3.54±0.36 MPa), 11 % lower than in C. incanus and 19 % lower than in Q. ilex. Leaf relative water content (RWC) showed the same trend as ₁. C. incanus showed the lowest RWC values during the drought period (60 %) while they were never below 76 % in P. latifolia and Q. ilex; moreover C. incanus showed the lowest recovery of ₁ at sunset. Hence the studied species are well adapted to the prevailing environment in Mediterranean climate areas, but they show different adaptive strategies that may be useful for their co-occurrence in the same habitat. However, Q. ilex and P. latifolia by their water use strategy seem to be less sensitive to drought stress than C. incanus.     

Parasitic worms: strategies of host finding, recognition and invasion

Many parasitic worms enter their hosts by active invasion. Their transmission success is often based on a mass production of invasive stages. However, most stages show a highly specific host-finding behaviour. Information on host-finding mechanisms is available mainly for trematode miracidia and cercariae and for nematode hookworms. The larvae find and recognise their hosts, in some cases even with species specificity, via complex sequences of behavioural patterns with which they successively respond to various environmental and host cues. There is often a surprisingly high diversity of host-recognition strategies. Each parasite species finds and enters its host using a different series of cues. For example, different species of schistosomes enter the human skin using different recognition sequences. The various recognition strategies may reflect adaptations to distinct ecological conditions of transmission. Another question is how, after invasion, parasitic worms find their complex paths through their host's tissues to their often very specific microhabitats. Recent data show that the migrating parasite stages can follow local chemical gradients of skin and blood compounds, but their long-distance navigation within the host body still remains puzzling.

The high complexity, specificity and diversity of host-recognition strategies suggest that host finding and host recognition are important determinants in the evolution of parasite life cycles.