Hermaphrodite sex role preferences: the role of partner body size, mating history and female fitness in the sea slug Chelidonura sandrana

Costs and benefits associated with matings and the effects of mating frequency on fitness commonly differ between the sexes. As a result, outcrossing simultaneous hermaphrodites may prefer to copulate in the more rewarding sex role, generating conflicts over sperm donation and sperm receipt between mates. Because recent sex role preference models remain controversial, we contrast here some of their assumptions and predictions in the sea slug Chelidonura sandrana. For this hermaphrodite with sperm storage and internal fertilisation, risk-averse models assume that fitness pay-offs are constantly higher in the female than in the male function in any single mating. Moreover, excluding mutual partner assessment, these models predict male mating behaviour to be independent of receiver traits. The competing gender ratio hypothesis assumes that relative fitness pay-offs, and thus the preferred mating roles, vary and may reverse between matings and predicts that ejaculation strategies co-vary with receiver quality. We found that field mating rates of C. sandrana substantially exceeded what is required to maintain female fertility and fecundity, indicating large variation in direct female benefits between matings. We further demonstrate that male copulation duration adaptively increased with partner body size (i.e. fecundity) but decreased with recent partner promiscuity. These findings are compatible with the gender ratio hypothesis but contradict risk-averse models.     

Changing Farmers' Land Management Practices in the Hills of Nepal

This paper sheds light on changing farmers' land management practices in two mountain watersheds, with and without external assistance, in the western hills of Nepal. Information used in the analysis were obtained through a survey of 300 households, group discussion, key informant interviews, and field observation conducted during April–September 1999. Confronted with ever-decreasing landholding size due to a steadily growing population and scarcity of nonfarming employment opportunities, farmers in both watersheds have increasingly adopted assorted types of structural and biological measures to control soil erosion, landslides, gully expansion, and soil nutrient loss to maintain or even enhance land productivity. Adoption of gully control measures, construction of the retention walls, alley cropping, use of vegetative measures for landslide control, mulching, and use of green manure and chemical fertilizers are found significantly high in the project area due to the provision of technical and financial support, whereas composting is found significantly high in the nonproject area. Different from the traditionally held beliefs, population pressure on a finite land resource has brought positive change in land management. However, the experience from both watersheds indicates that there is limit to the extent that resource poor farmers can respond to land degradation without any external assistance. Required is the arrangement for appropriate polices and support services and facilities enabling farmers to adopt locationally suitable and economically attractive land management technologies.     

Effect of Isoflavones on Reproductive Performance,Testosterone Levels,Lipid Peroxidation,and Seminal Plasma Biochemistry of Male Rabbits

Abstract

The objective of this study was to determine the effect of either 2.5 mg/kg Body Weight or 5 mg/kg Body Weight (BW) doses of isoflavones on semen quality, testosterone levels, lipid peroxidation and semen biochemistry of male New Zealand White rabbits. Animals were given both 2.5 mg/kg BW and 5 mg/kg BW doses of isoflavones. The tested doses were given to rabbits orally every other day for 13 weeks. Treatment with isoflavones caused an increase (p < 0.05) in libido (by decreasing the reaction time), sperm concentration, sperm motility (%), total motile sperm per ejaculate (TMS), packed sperm volume (PSV), total functional sperm fraction (TFSF), total sperm output, initial fructose concentration and normal sperm, while dead sperm was reduced compared to control animals. On the other hand, ejaculate volume, initial hydrogen ion concentration (pH) and plasma testosterone levels did not change in treated animals with both doses of isoflavones as compared to control. Concentrations of thiobarbituric acid-reactive substances (TBARS), total lipids, and low density lipoprotein were significantly (p < 0.05) reduced in seminal plasma of rabbits treated with either 2.5 mg/kg BW or 5 mg/kg BW doses of isoflavones. While, the activities of glutathione S-transferase (GST), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), acid phosphatase (AcP), and alkaline phosphatase (AlP) were significantly (p < 0.05) increased in seminal plasma of treated animals. Also, total cholesterol, percentage cholesterol (out of total lipids), and high density lipoprotein were significantly (p < 0.05) increased, while triglyceride did not change in seminal plasma of treated animals. Supplementation at either level of isoflavones did not cause changes in live body weight (LBW), dry matter intake (DMI), and relative weights of testes and epididymis. The present results showed that either 2.5 mg/kg BW or 5 mg/kg BW doses of isoflavones caused an improvement of some semen characteristics and did not have negative effects on male fertility.     

Fitness benefits of multiple mating versus female mate choice in the cellar spider (Pholcus phalangioides)

Recent studies have demonstrated that mating with multiple males can be beneficial for females and her offspring even if males contribute nothing but sperm. This was mainly established for species in which sperm from several males mix in the reproductive tract of the female, thus allowing sperm competition and/or female sperm choice. However, in species with last male sperm precedence, female re-mating decides against the previous male by strongly limiting his reproductive success. We tested the effect of female re-mating behaviour using the cellar spider Pholcus phalangioides, which shows strong last males sperm precedence and moderate levels of polyandry under natural situations. We predicted that females prevented from remating even though they are receptive would show reduced reproductive success compared to females that accept two copulations and females that reject a second male, since the latter two treatments were allowed to behave according to their decisions. However, if the number of matings per se had an effect on oviposition or on offspring performance, double-mated females should perform better compared to both treatments of once-mated females. We measured female fecundity and fertility over a period of 140 days, comparable to the species' natural reproductive peak season. Two thousand one hundred and fifty-two offspring from 67 first egg sacs were reared under two feeding levels. We registered development time and survival, and measured offspring adult size and mass. We found a positive effect of double mating, as in this treatment, oviposition probability was higher compared to the other treatments. Interestingly, adult female offspring of the DM treatment that were raised under low food level had a higher condition index compared to those from FS and RM, but development time, size and mass at adulthood were not affected by mating treatment. Female choice only seemed to affect hatching latency of the offspring. Overall, the main predictor of female reproductive output and success was female body size.     

Aggressive reproductive competition among hopelessly queenless honeybee workers triggered by pheromone signaling

In the honeybee, Apis mellifera, the queen monopolizes reproduction, while the sterile workers cooperate harmoniously in nest maintenance. However, under queenless (QL) conditions, cooperation collapses and reproductive competition among workers ensues. This is mediated through aggression and worker oviposition, as well as shifts in pheromones, from worker to queen-like composition. Many studies suggest a dichotomy between conflict resolution through aggression or through pheromonal signaling. In this paper, we demonstrate that both phenomena comprise essential components of reproductive competition and that pheromone signaling actually triggers the onset of aggression. We kept workers as QL groups until first aggression was observed and subsequently determined the contestants' reproductive status and content of the mandibular (MG) and Dufour's glands (DG). In groups in which aggression occurred early, the attacked bee had consistently more queen-like pheromone in both the MG and DG, although both contestants had undeveloped ovaries. In groups with late aggression, the attacked bee had consistently larger oocytes and more queen-like pheromone in the DG, but not the MG. We suggest that at early stages of competition, the MG secretion is utilized to establish dominance and that the DG provides an honest fertility signal. We further argue that it is the higher amount of DG pheromone that triggers aggression.     

Hierarchical perception of fertility signals and nestmate recognition cues in two dolichoderine ants

In social insects, queens are likely to “honestly” inform their nestmates of their presence and fertility status through pheromonal communication. Cuticular hydrocarbons (CHCs) have been reported to be effective nestmate discriminators and strongly suspected to act as fertility signals, at least in some species. The use of the same chemical bouquet (i.e., the CHC profile) to convey two fundamentally different information seems puzzling. However, a recent threshold model proposes a hierarchy in the discriminating processes, i.e., fertility signals can only be perceived if nestmate recognition has been reached (Le Conte and Hefetz, Annu Rev Entomol 53:523–542, 2008). Here, we developed a simple behavioral bioassay based on chemical recruitment toward a queen placed outside the nest in two dolichoderine ants (Linepithema humile and Tapinoma erraticum), which allowed us to investigate the interplay between fertility signaling and colonial recognition. Using queen corpses of various origins (nestmates or aliens) and physiological states (fertile or infertile; mated or unmated), we demonstrated that nestmate recognition cues clearly override fertility signals under our experimental conditions. Indeed, while nestmate infertile queens were largely ignored by the workers, nestmate fertile queens (mated or not) induced worker recruitment, whereas alien fertile queens did not and were aggressed by the workers.     

长期定位施肥对土壤生理转化菌群的影响

针对哈尔滨黑土28 a长期定位施肥现状进行土壤生理转化菌群测试分析,采用稀释平板法和MPN法测定不同施肥处理土壤的微生物各生理群的数量.结果表明:施肥处理的土壤微生物多样性指数最高,微生物种类多,群落结构较复杂,同不施肥处理之间的土壤微生物群落结构组成存在显著差异.     

Dufour’s gland pheromone as a reliable fertility signal among honeybee (Apis mellifera) workers

When a colony becomes queenless and without the possibility of requeening, honeybee workers initiate reproduction and lay male eggs about a week later. Assays in which two bees were confined in a small arena revealed that they establish a reproductive dominance hierarchy, i.e., one worker demonstrates greater ovarian development than her paired bee. Reproductive dominance is independent of relatedness, and can be established between full sisters, cousins, or random nestmates. A social environment, however, is obligatory, as singly housed bees fail to develop ovaries on the same time scale. Allowing varying degrees of social interactions between the paired bees revealed that olfaction of volatile bee compounds, as well as tactile communication, seem to provide the necessary social environment. Ovarian development was accompanied by the production of queen-like Dufours gland secretion in these workers. Especially notable was the increase in the queen-like esters. This increase was tightly linked to ovarian development and not necessarily to the dominance status of the bees in the pair. Thus, the occurrence of queen-like esters can serve as a reliable fertility signal. Advertising ovarian status may recruit helper workers with less developed ovaries (and which are less likely to successfully reproduce before colony breakdown) to assist their nestmates and thereby gain inclusive fitness. Revealing the role of Dufours gland secretion as a fertility signal adds another dimension to our understanding of how queen pheromones operate. The mandibular-gland secretion is a good predictor of dominance hierarchy, being correlated with false-queen characteristics but not fertility, whereas Dufours gland secretion is a good predictor of fertility but not dominance hierarchy.Communicated by R.F.A. Moritz     

Fertility Intentions and Risk Management: Exploring the Fertility Decline in Eastern Europe During Transition

Between 1985 and 1995, fertility in Eastern Europe declined from 2.2 children per woman to merely 1.5 on region-average. Previous research has emphasized mainly the economic turmoil during transition or the influx of new ideas regarding fertility and family relations. This article suggests that applying a risk management perspective on fertility patterns may put additional light on the reasons behind the fertility decline in post-communist Europe. The complexity of modern social systems has made people increasingly dependent on the state for risk evaluation and risk management. The article formulates the hypothesis that transition itself disrupted the mental models that helped people to navigate among the risks associated to having and raising children. Left to their own devices, women in Eastern Europe became more inclined to postpone childbirth or discard this option altogether.     

Fertility status and management implications of wetland soils for sustainable crop production in Akwa Ibom State, Nigeria

Fertility status of soils of three wetland types in Akwa Ibom State, Nigeria, was investigated. The wetland types are Inland Valley (IV), Flood Plain (FP) and Mangrove (MG). The soils have silt-clay ratios above 0.15 and 0.25 indicating that they are of young parent materials with low degree of weathering and possible weatherable minerals for plant nutrition. The pH of the soils was near neutral (>6.4) when wet but extremely acid (>3.5) when dried indicating that the soils are potential acid sulphate soils. Organic matter content was high with mean values of 12.59, 6.03 and 3.20% for IV, FP and MG soils, respectively. Total N (nitrogen) was low except in IV soils where the value was above the 0.30% critical level. The C:N ratios were narrow with mean of 20.90, 12.17 and 12.12 for IV, FP and MG soils, respectively. The contents of basic cations [Calcium (Ca), Magnesium (Mg), Potasium (K) and Sodium (Na)] were low while acidic cations [Aluminium (Al) and Hydrogen (H)] were high. The Ca:Mg ratios were below the optimum range of 3:1 to 4:1 required for most crops. The Mg:K ratios were above 1.2, below which yields of crops like corn and soybean may be reduced. Effective cation exchange capacity (ECEC) was below the 20 cmol/kg. Percent base saturation was low (<38) indicating that the soils are potentially less fertile. Exchangeable Al and percent Al saturation were high, above 60% in IV and FP soils. Electrical conductivity was above the critical value of 2 dsm⁻¹ while exchangeable sodium percentage was less than 15. Available Phosphorus (P) and low, <10 ppm and free Fe₂O₃/clay ratios were <0.15. Positive correlation existed between silt and ECEC, implying that silt contributed to nutrient status of the soils. Generally, fertility status of the soil is low and would require maintenance of adequate organic matter, application of lime and organic and inorganic fertilizers, drainage and irrigation if the land is to be used for intensive/sustainable crop production. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.