Exploring the difficulties of studying futures in ecology: what do ecological scientists think?

In a mainly experimental science based traditionally on hypothesis testing such as ecology, studying futures may be difficult. However, in the last few decades, predicting the consequences of global changes on the dynamics and function of ecological systems has become a major challenge in ecological research. To study how ecological scientists deal with potential difficulties in studying futures, we adopted a reflexive viewpoint on how scientists address the study of ecological futures. To do so we questioned a panel of ecological scientists on their practical involvement and point of view. Quantitative and qualitative analyses of their responses showed that predictions or predictive models were the dominant theme. Many quantitative models, based on statistical correlations, empirical rules or processes have been developed and their methodological limitations explored by the researchers we interviewed. In a small proportion of studies, qualitative scenarios have been elaborated to explore the range of possible futures. Interviewees emphasized the problem of dealing with ecological complexity and multiple future possibilities. Specificities of futures compared to past or present events were not fully identified. In fact, researchers studying futures mainly adopted a reductionist approach, trying to simplify complex ecological systems. But methods and tools promoted by such an approach to science may not always be appropriate to deal with future ecological complexity. Indeed, an emphasis on prediction prevents ecologists from acknowledging the multiplicity and undetermined nature of futures.     

Can the meiotic sex ratio explain the sex ratio bias in adult populations in the dioicous moss Drepanocladus lycopodioides?

Sex ratio variation is commonly observed in natural populations of many organisms with separate sexes and genetic sex determination, including bryophytes. Most bryophyte populations exhibit female-skewed expressed adult sex ratios, generally inferred from counts of sexually mature plants. For the rarely sexually reproducing perennial dioicous moss Drepanocladus lycopodioides, we showed that a female bias also exists in the genetic adult sex ratio, using a specifically designed molecular sex-associated marker. Here, we investigated whether the meiotic spore sex ratio contributes to the observed bias in genetic adult sex ratio in natural populations. Earlier attempts to study meiotic sex ratios have involved commonly cultivated ruderals that rapidly express sex in the laboratory. We established single-spore cultures from field-collected sporophytes from these populations and used the marker to assess the sex of individual sporelings. Spore germinability was (near) complete, and mortality among sporelings was virtually absent. The true meiotic sex ratio did not differ from equality, but strongly differed both from the observed genetic sex ratios in the natural adult populations, and from the European scale genetic sex ratio. We conclude that the biased population sex ratios in this species arise at life cycle stages after spore germination. Sexual dimorphism may selectively favour female proliferation during some phase of gametophyte development. Based on methodological progress, we successfully used a perennial study species with rare sexual reproduction, which significantly broadens the life history spectrum investigated in bryophyte sex ratio studies.     

The secondary sex ratio in Israel: 1980–1995

Abstract

This study deals with models and hypotheses that attempt to explain the underlying mechanisms determining the sex ratios at birth in human populations. Since the factors responsible are still questionable and research results are contradictory, we examine data available in Israel on the sex ratios at birth among two different sociodemographic groups, Jews and Moslems. Results suggest a difference between Jewish and Moslem patterns of secondary sex ratios with respect to parental age, education, and birth number. The difference may be described as a more regular and, by existing models, a more predictable pattern of secondary sex ratio among Moslems than among Jews. The possibility that Jewish religious laws play a role in this difference is discussed.     

Is Canada's sex ratio in decline?

In this issue (see pages 37 to 41) Dr. Bruce B. Allan and associates report a small but statistically significant decrease--of about 0.2%--in the proportion of male live births in Canada over the period 1970-90. In this editorial, factors that have been reported in the literature to influence sex ratio are examined within a Canadian context. The authors suggest that although the reasons for the apparent decline in the sex ratio in Canada are unclear, the increasing use of ovulation induction may be a contributing factor. Data from the Nova Scotia Atlee Perinatal Database are discussed with a view to explaining the trend observed in Atlantic Canada, but no obvious explanation emerges. The authors argue that when the period of observation is extended no overall change in the sex ratio is apparent. This would suggest a tendency toward stabilization rather than decline.     

The effect of temperature on sex ratio in the isopod Porcellionides pruinosus: Environmental sex determination or a by-product of cytoplasmic sex determination?

The sex ratios of the progenies of woodlice Porcellionides pruinosus (Crustacea, Isopoda) raised at different temperatures were studied. Females from three French populations sampled in the wild produced highly female-biased broods at 20°C and male-biased broods above 30°C. The effect of high temperature was not due to selective mortality of females. Sex determination was thus sensitive to temperature in P. pruinosus. We also found an interpopulation variability of sex ratio thermosensitivity and a weak inheritance of male-biased sex ratios at high temperatures. Samples taken from a wild population throughout the year showed that while the thermal conditions required for changes in the sex ratio occurred, there was no significant variation in the sex ratio. On the other hand, almost all the females and many males in the four populations studied harboured intracytoplasmic bacteria. These maternally inherited symbionts belong to the genus Wolbachia and are known to possess a feminizing effect. While in other arthropods Wolbachia are destroyed at high temperatures, the symbionts of P. pruinosus were detected by a PCR procedure whatever the rearing temperatures. In light of these results, we propose that the thermosensitivity of sex determination in P. pruinosus could reflect the removal of the cytoplasmic effect on sex determination rather than environmental sex determination sensu stricto. The reduction in the amount of bacteria (but not their entire elimination), or the inhibition of bacterial metabolism, may be responsible for sex ratio variations relating to temperature. The incomplete inheritance of male-biased sex ratios at high temperatures might reflect a selection of thermo-tolerant bacterial strains.     

Against the odds? Nestling sex ratio variation in green-rumped parrotlets

We investigated nestling sex ratio variation in the green-rumpedparrotlet (Forpus passerinus), a small neotropical parrot breedingin central Venezuela. There are strong theoretical reasons topredict a female-biased sex ratio in this system according tothe local resource hypothesis; juvenile males are philopatricand there are high levels of competition between male siblingsfor access to breeding females. Data were collected from twobreeding sites over a 14-year period incorporating 564 broodswith a total of 2728 nestlings. The mean percentage of malenestlings across years was 51%. Despite extreme hatching asynchronyin this system and increased survival of earlier hatched offspring,there was no bias in sex allocation associated with egg sequence.Patterns in sex allocation were not associated with clutch size,age, or size of the breeding female or breeding site. The potentialfor selective resorption of eggs was considered; however, nosignificant relationship was found between extended laying intervalsand the sex of subsequent eggs. Together, these results suggestthat female parrotlets are unable to regulate the sex ratioof their clutch at laying or that facultative manipulation ofnestling sex ratio may not confer a fitness benefit to breedersin these populations.     

Cardiovascular risk and attitudes to lifestyle: what do patients think?

OBJECTIVE--To examine the relation between subjects'' level of cardiovascular risk and their beliefs about the harmfulness of their smoking habit, current diet, and level of exercise, together with their stated desire to modify such behaviour. DESIGN--Self administered postal health and life-style questionnaire followed by a structured health check conducted by a nurse. SETTING--Five general practices in Luton and Dunstable, Bedfordshire. SUBJECTS--5803 people aged 35-64 years enrolled in the OXCHECK trial who attended for a health check before 1 March 1992. MAIN OUTCOME MEASURES--Perceived risk to health of lifestyle behaviours, desire to modify behaviour, and a reported serious attempt to modify behaviour in the preceding year. RESULTS--A high proportion of smokers and those who were physically inactive perceived their behaviour to be harmful (1020; (76%; 95% confidence interval 74% to 79%) and 350 (74%; 70% to 78%) respectively) and wished to modify it (1212 (79%; 77% to 81%) and 375 (74%; 71% to 78%) respectively). In contrast, only 289 (45%; 41% to 48%) of obese people and 188 (14%; 12% to 16%) of people with a high dietary fat intake perceived their current diet to be harmful. The more cardiovascular risk factors present, the more likely subjects were to perceive a health risk attached to their diet and lack of exercise (p < 0.01 in both cases) and to want to improve their diet. CONCLUSION--Awareness of the health risk from smoking and motivation to stop is high. Further efforts are required, however, to educate the public about the risks associated with a high dietary fat intake. Although the health risks of inactivity were widely recognised, motivation to take more exercise needs to be increased.     

POPP the question: what do LEA proteins do?

Late embryogenesis abundant (LEA) proteins are produced in maturing seeds and anhydrobiotic plants, animals and microorganisms, in which their expression correlates with desiccation tolerance. However, their function has remained obscure for 20 years. We argue that novel computational tools devised for non-globular proteins might now overcome this problem. Predictions arising from bioinformatics fit well with recent data on Group 3 proteins, which potentially form cytoskeletal filaments, and suggest experimentally testable functions for these and other LEA protein groups.     

TRAM flap versus nonautologous breast reconstruction: what do patients really think?

Although there have been many reports of aesthetic outcomes after breast reconstruction, there have been comparatively few studies examining patient satisfaction and related subjective issues. The variables affecting satisfaction are only beginning to be understood, and patient satisfaction issues were explored in a more homogeneous patient population. A questionnaire surveying overall and aesthetic satisfaction, postoperative recuperation time, and symptoms was used to elicit candid patient responses. Fifty-seven patients replied (86 percent response rate), of whom 38 had undergone transverse rectus abdominis musculocutaneous (TRAM) flap (pedicled, n = 29; free, n = 9) reconstruction and 19 had undergone nonautologous reconstruction. Although the median patient satisfaction score was higher for the TRAM flap group, this was not statistically significant (p = 0.92). Recuperation was significantly longer for the TRAM flap group, with only 47 percent of patients being able to resume full activities within 2 months after the surgical procedure, compared with 95 percent of the implant group (p = 0.002). Of the TRAM flap-treated patients, 50 percent described some postoperative abdominal weakness, but only 5 percent of all TRAM flap-treated patients said that abdominal weakness was actually a functional problem. Our results suggest that patients may derive equal satisfaction with the two methods of reconstruction. The postoperative recuperation time after TRAM flap reconstruction is significantly longer than that after nonautologous procedures, although the postoperative abdominal weakness after TRAM flap reconstruction is not as significant a clinical problem as previously thought. The patient-derived information on satisfaction should assist both surgeons and patients in matching reconstructive options with patients' expectations and lifestyle.     

Host specificity in ectomycorrhizal communities: what do the exceptions tell us?

Classic ectomycorrhizal symbioses are mutualisms that involvethe exchange of fixed carbon for mineral nutrients between plantroots and fungi. They are unique in the way they contain featuresof both intimate and diffuse symbioses. The degree of host specificityvaries, particularly among the fungi. Here we examine two exceptionalcases of specificity to see what they tell us about the advantagesof specificity, how it is initiated, and the potential rolethat it plays in complex ecosystems. The first case involvesnon-photosynthetic epiparasitic plants, which contrary to virtuallyall other plants, exhibit high levels of specificity towardtheir fungal hosts. The second case involves suilloid fungi;this is the largest monophyletic group of ectomycorrhizal fungithat is essentially restricted to associations with a singleplant family. In both cases, new symbioses are initiated bydormant propagules that are stimulated to germinate by chemicalcues from the host. This reduces the cost of wasting propaguleson non-hosts. The advantages of specificity remain unclear inboth cases, but we argue that increased benefit to the specialistmay result from specialized physiological adaptations. We reexaminethe idea that specialist fungi may help their hosts competein complex ecosystems by reducing facultative epiparasitismby other plants, and suggest an alternative hypothesis for theobserved pattern.     

Facultative primary sex ratio variation: a lack of evidence in birds?

The facultative control of primary sex ratio by breeding birds has become a major focus in evolutionary biology in recent years. A combination of well-developed theoretical literature and rapid publication of empirical results has created considerable confusion, with controversial claims for both extreme control of primary sex ratio versus no control around inherent random variability. We present a robust and quantitative summary of published empirical literature to assess clearly the body of evidence for female birds to control sex assignment in their offspring. Our meta-analytical approach reveals that published studies do not exhibit any variability beyond that which could be expected owing to sampling error. Therefore, we conclude that facultative control of offspring sex is not a characteristic biological phenomenon in breeding birds.     

Clutch size: a major sex ratio determinant in fig pollinating wasps?

Under local mate competition, sex ratio theory predicts that increasing numbers of ovipositing females (foundresses) on a site should lead to higher proportions of males in their broods. Fig pollinators have confirmed this prediction. It is also predicted that with decreasing clutch size, solitary foundresses should produce increasing proportions of sons. We show this to be true. Further, when several females compete, brood size decreases. As a result, the proportion of males increases, and this could provide a mechanistic explanation of sex ratio response to numbers of colonizing females. Therefore, sex ratio data on fig wasps need to be reassessed to determine whether females 'count' other foundresses, as is generally accepted, or whether they simply 'count' the number of eggs that they lay.     

Does famine influence sex ratio at birth? Evidence from the 1959–1961 Great Leap Forward Famine in China

The current study examined the long-term trend in sex ratio at birth between 1929 and 1982 using retrospective birth histories of 310 101 Chinese women collected in a large, nationally representative sample survey in 1982. The study identified an abrupt decline in sex ratio at birth between April 1960, over a year after the Great Leap Forward Famine began, and October 1963, approximately 2 years after the famine ended, followed by a compensatory rise between October 1963 and July 1965. These findings support the adaptive sex ratio adjustment hypothesis that mothers in good condition are more likely to give birth to sons, whereas mothers in poor condition are more likely to give birth to daughters. In addition, these findings help explain the lack of consistent evidence reported by earlier studies based on the 1944-1945 Dutch Hunger Winter or the 1942 Leningrad Siege.