The effect of genome and sex on recombination rates in Pennisetum species

The effects of homoeology and sex on recombination frequency were studied in crosses between cultivated pearl millet, Pennisetum glaucum, and two wild subspecies, P. violaceum and P. mollissimum. For the two wild x cultivated crosses, reciprocal three-way crosses were made between the F₁ hybrid and an inbred line (Tift 23DB₁). The three-way cross populations were mapped to produce a female map of each wide cross (where the F₁ was the female) and a male map (where the F₁ was the male). Total genetic map lengths of the two inter-subspecies crosses were broadly similar and around 85 % of a comparable intervarietal map. In the P. glaucumxP. mollissimum crosses, the map was further shortened by a large (40 cM) inversion in linkage group 1. Comparison of the recovered recombinants from male and female meiocytes showed an overall trend for the genetic maps to be longer in the male (10%) in both inter-subspecific crosses; however, analysis of individual linkage intervals showed no significant differences. Gametophytic selection was prevalent, and sometimes extreme, for example 121 in favour of wild alleles in the P. glaucumxP. mollissimum male recombinant population. One of the loci which determines panicle type in cultivated pearl millet and wild relatives, H, was mapped 9 cM from Xpsm812 on linkage group 7 in the P. violaceum cross.     

When should a female avoid adding eggs to the clutch of another female? A simultaneous oviposition and sex allocation game

Summary Avoidance of double oviposition (ADO) is the strategy not to oviposit on food patches where another female has oviposited before. If two females oviposit on the same patch, competitive and mating interactions within and between broods may lead to both a clutch size game and a sex allocation game between the two visitors. Though the two games interact, they are usually considered separately. Here, the ESS conditions for ADO are investigated in an analysis that combines the two games into one. The analysis strengthens the notion that it is really ADO that needs to be explained, because role-dependent net pay-off from an additional egg is most likely to favour double oviposition (DO). To a first female, the net payoff includes the effect on the eggs already present, whereas to a second female only the egg's gross pay-off matters. ADO is the evolutionary stable strategy (ESS) if there are enough patches still without eggs and either (1) the fitness of an additional egg is so low that the first female would not lay it even in the absence of detrimental effects on earlier offspring, so neither would a second female, or (2) differences in either the survival probability of the offspring or their reproductive success are sufficient to counterbalance the differential interest in the eggs already present. The first condition requires that eggs are relatively large, because then the decrease in pay-off between two successive eggs can be large. The second condition may be met when there is a time interval between ovipositions of subsequent females. The resulting developmental lag of the second clutch will (1) diminish its ability to compete for food and (2) lower its reproductive success when there is local mate competition and sons are too late to mate with daughters of the first female. If sons of first and second females compete on equal terms, however, ADO is unlikely. Male migration between patches reduces the influence of sex allocation strategies on clutch size decisions; the same holds for small clutch sizes. To illustrate the importance of considering sex allocation and clutch size decisions in an integrated way, oviposition strategies of plant-inhabiting predatory mites (Acari: Phytoseiidae) are discussed.     

Sperm competition and sex allocation in simultaneous hermaphrodites

Summary Sex allocation theory is developed for hermaphrodites having frequent copulations and long-term sperm storage. Provided the sperm displacement mechanisms are similar to those known in insects, the ESS allocation to sperm versus eggs satisfies a rather simple rule. There are no data to test this rule, as yet.     

Temperature affects male and female potential reproductive rates differently in the sex-role reversed pipefish, Syngnathus typhle

The differences in potential reproductive rate between the sexescan be used to predict the operational sex ratio and the patternsand intensity of mating competition and hence sexual selectionin a population. This article describes how one environmentalcomponent, temperature, affects potential reproductive ratesof the two sexes in the paternally brooding, sex-role reversedpipefish (Syngnathus typhle). Males brooded embryos much longer(on average 58 days) in cold water (about 10°C) than inwarmer water (35 days at about 15°C). As a consequence,the potential reproductive rate (number of eggs brooded perday) of males was significantly higher in warm water. In females,however, potential reproductive rate, i.e., number of eggs producedper day given an unlimited access to mates, was not significantlydifferent between temperatures. In both sexes, potential reproductiverate was positively related to body size. At both temperatures,females had the potential to reproduce faster than males. Asa result, the operational sex ratio will become female biasedand sex-roles reversed, as is the case in this species. Sincetemperature differently influenced the potential reproductiverates of males and females, with the sexual difference largerat lower temperatures, more intense female-female competitionis predicted at low temperatures.     

Vertical bars on male Xiphophorus multilineatus: a signal that deters rival males and attracts females

We examined the function of the vertical bar pattern on maleswordtails (Xiphophorus multilinneatus) as a signal in bothmale-male competition and female choice. This pattern had previouslybeen described as an aggressive signal because males intensifiedthe bars during male-male encounters in the laboratory. Ourfield observations supported this observation and also showedthat bars intensified when males courted females. The intensityof bars was correlated with access to females in the field.Within the size range of males that have bars, however, neitherbar number nor male size appeared to influence access to females.We used freeze-branding to remove the bars from males in thelaboratory so that we could control for characters correlatedwith bar intensity, and tested males and females separatelyso that we could separate the influence of these two componentsof sexual selection. We compared the responses of males andfemales to males that had their bars removed and control malesfreeze-branded between the bars. Test males responded more aggressivelyto males without bars as compared to control males. In addition,females showed a preference for control males over males thathad their bars removed. These results suggest that the barsmay function as a signal that deters rival males and attractsfemales.     

Dominance, competition, and energetic reserves in the European starling, Sturnus vulgaris

We investigated the relationships between social dominance,competition for food, and strategies of body mass and fat regulationin the European starling (Sturnus vulgaris). In birds housedin groups of three, subdominant birds stored more fat than dominants.A removal experiment established a causal link between socialdominance and fat reserves; in groups that had the dominantindividual removed, the remaining birds reduced body mass andfat, relative to control groups that had the subordinate removed.In a second experiment, we investigated the influences of degreeof competition for food and dominance on body mass and fat reserves.Birds under high competition increased fat reserves and tendedto have higher body mass than birds under low competition. Theincrease in fat reserves was higher in the subdominants thanin the dominants. These results are consistent with hypothesesconcerning dominance-dependent access to food; subdominant birds,or birds under increased competition, may store more fat asan insurance against periods when food cannot be obtained. However,relations between dominance, body mass, and fat reserves mayalso arise through other proximate factors relating to dominance-dependentcosts and benefits of fat storage, such as predation risk andenergetic expenditure.     

The Hawk—Dove game revisited: Effects of continuous variation in resource-holding potential on the frequency of escalation

Summary The classic Hawk—Dove game is extended to deal with continuous variation in resource-holding potential or RHP, when RHP is observable (via any sensory modality) but RHP difference is less than perfectly reliable as a predictor of the outcome of an escalated contest. The relationship between sensory and physical magnitudes of RHP is assumed to be governed by Fechner's psychophysical law, whose effect is that contestants interact as if they had perfect information about their relative RHP (as opposed to RHP difference). Thus, an animal is aggressive if its RHP exceeds a certain fraction, called its threshold, of its opponent's RHP and otherwise is non-aggressive; and the classic Hawk and Dove strategies correspond to zero and infinite thresholds, respectively. For RHPs drawn at random from an arbitrary Gamma distribution there is a unique evolutionarily stable strategy or ESS, which depends on a parameter measuring the reliability of RHP as a predictor of the outcome of a fight, on the ratio of the valueV of winning to the costC of losing (both measured in units of reproductive fitness) and on the mean µ and variance ² of the RHP distribution. In a population at this ESS, ifV/C < 1 then the threshold is 1 and there is no fighting. AsV/C increases beyond 1 to a second critical value , however, the threshold decreases steadily from 1 to 0 and remains 0 forV/C > ; is an increasing function of , but a decreasing function of ². That a lower variance of RHP can imply a lower escalation frequencyp is a novel insight of the analysis. The prediction is at first counterintuitive, because if the aggression threshold were fixed then larger variance would imply lowerp (dispersion effect of variance). When natural selection acts on the threshold, however, increasing the variance not only reduces the probability that an animal with larger RHP will be attacked by an animal with lower RHP at the existing threshold, but also reduces the expected costs of adopting that particular threshold, so that a mutant with a somewhat lower threshold can invade the population (selection effect of variance). Forp, the selection effect dominates toward the upper end of the interval 1 V/C .     

Complex ecological models with simple dynamics: From individuals to populations

The aim of this work is to study complex ecological models exhibiting simple dynamics. We consider large scale systems which can be decomposed into weakly coupled subsystems. Perturbation Theory is used in order to get a reduced set of differential equations governing slow time varying global variables. As examples, we study the influence of the individual behaviour of animals in competition and predator-prey models. The animals are assumed to do many activities all day long such as searching for food of different types. The degree of competition as well as the predation pressure are dependent upon these activities. Preys are more vulnerable when doing some activities during which they are very exposed to predators attacks rather than for others during which they are hidden. We study the effect of a change in the average individual behaviour of the animals on interspecific relationships. Computer simulations of the whole sets of equations are compared to simulations of the reduced sets of equations.     

Assessment of five cultivars of potato (Solatium tuberosum L.) in a competition diallel

In 1992 and 1993, potato cultivars Cara, Estima, Pentland Dell, Pentland Javelin and Torridon were assessed in all possible pairings in three consecutive drills, such that one member of the pair (the cultivar) was the centre-drill, and the other member (the neighbour) was in the two adjacent drills. Each year the trial was a randomised complete block design with four replicates. Inter-cultivar competition was present for height, total tuber yield, ware yield and dry matter content, but not for emergence and maturity. Cultivar heights and dry matter contents under inter-cultivar competition and in pure-stands were highly correlated, whereas for total and ware yields, the rankings of cultivars in pure-stands were different from those under competition. Pure-stand yields were predicted for the two years separately because of year × cultivar and year × neighbour interactions. When the average total yield of the outer-drills was used as a covariate to adjust centre-drill yields to pure-stands, predicted yields were closer to those observed than were yields under competition, but there was little improvement in the correlations. In contrast, not only were the predicted values even closer to the observed ones when based on individual neighbour effects, the correlations were much higher (r = 0.76–0.94). Unfortunately, in plant breeding trials with large numbers of entries, precise estimation of individual neighbour effects would require an unrealistically large number of replicates. Hence, for the final stages of yield assessment of new cultivars, it is still desirable to use multiple-drill plots and to discard the outside drills where inter-cultivar competition can occur.     

Metabolic interactions between anaerobic bacteria in methanogenic environments

In methanogenic environments organic matter is degraded by associations of fermenting, acetogenic and methanogenic bacteria. Hydrogen and formate consumption, and to some extent also acetate consumption, by methanogens affects the metabolism of the other bacteria. Product formation of fermenting bacteria is shifted to more oxidized products, while acetogenic bacteria are only able to metabolize compounds when methanogens consume hydrogen and formate efficiently. These types of metabolic interaction between anaerobic bacteria is due to the fact that the oxidation of NADH and FADH₂ coupled to proton or bicarbonate reduction is thermodynamically only feasible at low hydrogen and formate concentrations. Syntrophic relationships which depend on interspecies hydrogen or formate transfer were described for the degradation of e.g. fatty acids, amino acids and aromatic compounds.