Genotype-specific interactions and the trade-off between host and parasite fitness

Background  

Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete Hyaloperonospora arabidopsis (= parasitica), a natural pathogen of the Brassicaceae Arabidopsis thaliana.     

The duration of strong mate-guarding by males of the libellulid dragonflyPaltothemis lineatipes: Proximate causation

Males of the territorial libellulid dragonfly Paltothemis lineatipeschange the intensity with which they guard their mates during an oviposition bout. Immediately after copulation is completed, males exhibit strong guarding, remaining very close to their partners as they begin ovipositing. In less than a minute, however, they begin to drift away to resume territorial patrolling or even to perch while their partners continue to oviposit. The duration of strong guarding is not related to how long the male has been on territory. Nor is it an activity of fixed duration set by the release of the female following copulation or by the initiation of oviposition by a panner. Instead, males can extend the period of strong guarding if oviposition is interrupted experimentally early in a bout. Under these conditions, males follow their mates closely until they have found a new location at which they oviposit steadily. Thus, males apparently must see their panner oviposit for some time before reducing the intensity of mate-guarding.     

A model for studying the initiation of normal calcification in vivo

1. Rat costal cartilage was found to begin to calcify normally when the rats weigh 35-45g. 2. The cartilage is suggested as a model for the study in vivo of mechanisms concerned with normal calcification. 3. The model was tested by studying the incorporation of fluoride into the mineral deposited in the tissue. 4. The percentage of inorganic material in cartilage rose from approx. 3% of the dry weight in the uncalcified tissue to 62% in the tissue from rats weighing 300g. 5. Mineral deposited had a calcium/phosphorus molar ratio of 1.65. 6. After the oral administration of sodium fluoride to rats, fluoride was incorporated into cartilage mineral. 7. The concentration of fluoride in cartilage ash increased rapidly with calcification and the mineral became more highly fluoridated than the corresponding rib bone. 8. Fluoridated mineral showed a marked decrease in citrate concentration.     

SEX POLYMORPHISM IN SILENE ACAULIS (CARYOPHYLLACEAE) AND THE POSSIBLE ROLE OF SEXUAL SELECTION IN MAINTAINING FEMALES

Pollen accumulation rates and their relationship to stigma morphology and pollinator visitation behavior were compared between female and hermaphrodite sex morphs of the alpine plant Silene acaulis var. subacaulescens (Caryophyllaceae). Although stigmas of female and perfect flowers collected comparable pollen loads, stigmas of female flowers became receptive earlier in anthesis and therefore recruited a larger number of pollen tubes. Together with early receptivity young female flowers had a larger stigmatic area with longer papillae than did perfect flowers. Pollinator behavior also differed between morphs, with bumble bees spending more time probing female than perfect flowers. Differences in stigma receptivity schedules of female and perfect flowers have consequences for different opportunities for sexual selection in the two sex morphs. Female flowers, by providing a more effective gametophytic screen, have the potential to produce higher quality offspring. This is proposed as a further compensatory advantage maintaining females, with a single fitness function, in populations containing hermaphrodites which have both male and female fitness functions.     

Effect of the cholesterol content of small unilamellar liposomes on their stability in vivo and in vitro

Small unilamellar neutral, negatively and positively charged liposomes composed of egg phosphatidylcholine, various amounts of cholesterol and, when appropriate, phosphatidic acid or stearylamine and containing 6-carboxyfluorescein were injected into mice, incubated with mouse whole blood, plasma or serum or stored at 4°C. Liposomal stability, i.e. the extent to which 6-carboxyfluorescein is retained by liposomes, was dependent on their cholesterol content. (1) Cholesterol-rich (egg phosphatidylcholine/cholesterol, 7:7 molar ratio) liposomes, regardless of surface charge, remained stable in the blood of intravenously injected animals for up to at least 400min. In addition, stability of cholesterol-rich liposomes was largely maintained in vitro in the presence of whole blood, plasma or serum for at least 90min. (2) Cholesterol-poor (egg phosphatidylcholine/cholesterol, 7:2 molar ratio) or cholesterol-free (egg phosphatidylcholine) liposomes lost very rapidly (at most within 2min) much of their stability after intravenous injection or upon contact with whole blood, plasma or serum. Whole blood and to some extent plasma were less detrimental to stability than was serum. (3) After intraperitoneal injection, neutral cholesterol-rich liposomes survived in the peritoneal cavity to enter the blood circulation in their intact form. Liposomes injected intramuscularly also entered the circulation, although with somewhat diminished stability. (4) Stability of neutral and negatively charged cholesterol-rich liposomes stored at 4°C was maintained for several days, and by 53 days it had declined only moderately. Stored liposomes retained their unilamellar structure and their ability to remain stable in the blood after intravenous injection. (5) Control of liposomal stability by adjusting their cholesterol content may help in the design of liposomes for effective use in biological systems in vivo and in vitro.     

Male behaviour in two bumblebees, Bombus nevudensis auricomus and B. griseicollis (Hymenoptera: Apidae)

The mating system of the bumblebees Bombus nevadensis and B. griseicollis involves apparent territorial defence of perch sites near or within visually conspicuous trees. Non–contact chases between perch owners and intruders are rare in B. nevadensis and more common in B. griseicollis. The perches of B. nevadensis are in open areas whereas those of B. griseicoilis are within trees or in sites shaded by trees. The same locations may be occupied on 2 different years. Individual males may return to favoured perches over periods ranging from 2 to 24 days. Males of both species scent–mark spots near their perches early in the morning and then scan visually for passing females for as much as 7–8 h daily. The landmark–based mating system of these bumblebees is similar to that of some other insects and closely resembles the pure dominance (lek) mating system of certain vertebrates. Some hypotheses for the evolution of diversity in male mating tactics among bumblebee species are presented.     

Congruent population genetic structures and divergence histories in anther‐smut fungi and their host plants Silene italica and the Silene nutans species complex

Study of the congruence of population genetic structure between hosts and pathogens gives important insights into their shared phylogeographical and coevolutionary histories. We studied the population genetic structure of castrating anther‐smut fungi (genus Microbotryum) and of their host plants, the Silene nutans species complex, and the morphologically and genetically closely related Silene italica, which can be found in sympatry. Phylogeographical population genetic structure related to persistence in separate glacial refugia has been recently revealed in the S. nutans plant species complex across Western Europe, identifying several distinct lineages. We genotyped 171 associated plant–pathogen pairs of anther‐smut fungi and their host plant individuals using microsatellite markers and plant chloroplastic single nucleotide polymorphisms. We found clear differentiation between fungal populations parasitizing S. nutans and S. italica plants. The population genetic structure of fungal strains parasitizing the S. nutans plant species complex mirrored the host plant genetic structure, suggesting that the pathogen was isolated in glacial refugia together with its host and/or that it has specialized on the plant genetic lineages. Using random forest approximate Bayesian computation (ABC‐RF), we found that the divergence history of the fungal lineages on S. nutans was congruent with that previously inferred for the host plant and probably occurred with ancient but no recent gene flow. Genome sequences confirmed the genetic structure and the absence of recent gene flow between fungal genetic lineages. Our analyses of individual host–pathogen pairs contribute to a better understanding of co‐evolutionary histories between hosts and pathogens in natural ecosystems, in which such studies remain scarce.