How geitonogamous selfing affects sex allocation in hermaphrodite plants

Does the mode of self-pollination affect the evolutionarily stable allocation to male vs. female function? We distinguish the following scenarios. (1) An ‘autogamous’ species, in which selfing occurs within the flower prior to opening. The pollen used in selfing is a constant fraction of all pollen grains produced. (2) A species with ‘abiotic pollination’, in which selfing occurs when pollen dispersed in one flower lands on the stigma of a nearby flower on the same plant (geitonogamy). The selfing rate increases with male allocation but a higher selfing rate does not mean a reduced export of pollen. (3) An ‘animal-pollinated’ species with geitonogamous selfing. Here the selfing rate also increases with male allocation, but pollen export to other plants in the population is a decelerating function of the number of simultaneously open flowers. In all three models selfing selects for increased female allocation. For model 3 this contradicts the general opinion that geitonogamous selfing does not affect evolutionarily stable allocations. In all models, the parent benefits more from a female-biased allocation than any other individual in the population. In addition, in models 2 and 3, greater male allocation results in more local mate competition. In model 3 and in model 2 with low levels of inbreeding depression, hermaphroditism is evolutionarily stable. In model 2 with high inbreeding depression, the population converges to a fitness minimum for the relative allocation to male function. In this case the fitness set is bowed inwards, corresponding with accelerating fitness gain curves. If the selfing rate increases with plant size, this is a sufficient condition for size-dependent sex allocation (more allocation towards seeds in large plants) to evolve. We discuss our results in relation to size-dependent sex allocation in plants and in relation to the evolution of dioecy.     

Sex determination: ways to evolve a hermaphrodite

Most species of the nematode genus Caenorhabditis reproduce through males and females; C. elegans and C. briggsae, however, produce self-fertile hermaphrodites instead of females. These transitions to hermaphroditism evolved convergently through distinct modifications of germline sex determination mechanisms.     

How spermatozoa come to be confined to surfaces

In most detailed studies, sea urchin sperm movement has been analyzed mainly from observations of spermatozoa swimming at the interface between two media: water/air or water/glass. When spermatozoa are placed on a microscope slide, they rapidly appear to swim near those interfaces. The aim of this article is to determine how they become confined to the vicinity of surfaces. High-speed observations of moving spermatozoa reveal blurred portions in the flagellum images that propagate from base to tip, suggesting that flagellar waves contain an out-of-plane component. The model we have developed depicts how this tri-dimensional component tends to keep spermatozoa close to interfaces and, as a consequence, increases the time of contact between the egg surface and spermatozoa.     

How to be an ant on figs

Mutualistic interactions are open to exploitation by one or other of the partners and a diversity of other organisms, and hence are best understood as being embedded in a complex network of biotic interactions. Figs participate in an obligate mutualism in that figs are dependent on agaonid fig wasps for pollination and the wasps are dependent on fig ovules for brood sites. Ants are common insect predators and abundant in tropical forests. Ants have been recorded on approximately 11% of fig species, including all six subgenera, and often affect the fig–fig pollinator interaction through their predation of either pollinating and parasitic wasps. On monoecious figs, ants are often associated with hemipterans, whereas in dioecious figs ants predominantly prey on fig wasps. A few fig species are true myrmecophytes, with domatia or food rewards for ants, and in at least one species this is linked to predation of parasitic fig wasps. Ants also play a role in dispersal of fig seeds and may be particularly important for hemi-epiphytic species, which require high quality establishment microsites in the canopy. The intersection between the fig–fig pollinator and ant–plant systems promises to provide fertile ground for understanding mutualistic interactions within the context of complex interaction networks.     

How poliomyelitis is to be eradicated completely

In 1988 the World Health Assembly resolved to eradicate poliomyelitis globally by the year 2000. The work continues. The problem arose how to quit the system of mass immunization with oral poliovirus vaccine (OPV) without trouble and to achieve the disappearance of polioviruses worldwide. After the cessation of the OPV use a certain number of vaccine viruses may remain that will circulate among the ever growing number of nonimmune population. Live enterovirus vaccines prepared from nonpathogenic serotypes of ECHO virus are proposed for application to stop the circulation of vaccine poliovirus. These vaccines will make it possible to eliminate the remaining vaccine viruses from circulation and to complete the process of worldwide poliomyelitis eradication.     

Resource-dependent sex-allocation in a simultaneous hermaphrodite

Most sex allocation theory is based on the relationship between the resource investment into male and female reproduction and the consequent fitness returns (often called fitness-gain curves). Here we investigate the effects of resource availability on the sex allocation of a simultaneously hermaphroditic animal, the free-living flatworm Macrostomum lignano. We kept the worms under different resource levels and determined the size of their testes and ovaries over a period of time. At higher resource levels, worms allocated relatively more into the female function, suggesting a saturating male fitness-gain curve for this species. A large part of the observed effect was due to a correlated increase in body size, showing size-dependent sex allocation in M. lignano. However, a significant part of the overall effect was independent of body size, and therefore likely due to the differences in resource availability. Moreover, in accordance with a saturating male fitness-gain curve, the worms developed the male gonads first. As the group size was kept constant, our results contrast with expectations from sex allocation models that deal with local mate competition alone, and with previous experiments that test these models.     

One hundred years ago: How to be happy though a doctor

ObjectivesTo assess the growth of quality of life measures and to examine the availability of measures across specialties.DesignSystematic searches of electronic databases to identify developmental and evaluative work relating to health outcome measures assessed by patients.Results3921 reports that described the development and evaluation of patient assessed measures met the inclusion criteria. Of those that were classifiable, 1819 (46%) were disease or population specific, 865 (22%) were generic, 690 (18%) were dimension specific, 409 (10%) were utility, and 62 (1%) were individualised measures. During 1990-9 the number of new reports of development and evaluation rose from 144 to 650 per year. Reports of disease specific measures rose exponentially. Over 30% of evaluations were in cancer, rheumatology and musculoskeletal disorders, and older people''s health. The generic measures—SF-36, sickness impact profile, and Nottingham health profile—accounted for 612 (16%) reports.ConclusionsIn some specialties there are numerous measures of quality of life and little standardisation. Primary research through the concurrent evaluation of measures and secondary research through structured reviews of measures are prerequisites for standardisation. Recommendations for the selection of patient assessed measures of health outcome are needed.

What is already known on this topic

Quality of life measures are increasingly used for measuring health outcomes in evaluative researchThere is little standardisation in the use of such measures within clinical trials

What this study adds

There has been exponential growth in reports relating to the development and evaluation of quality of life measuresThe number of reports varies considerably according to the health problem     

Salix martiana,a regularly hermaphrodite willow

Sex distribution in a neotropical willow,Salix martiana Leybold, has long escaped the attention of botanists. Its catkins are regularly composed of female, hermaphrodite and male flowers. The present paper discusses some aspects of its possible morphological and/or evolutionary significance.