Daring females,devoted males,and reversed sexual size dimorphism in the sand-dwelling spider <Emphasis Type="Italic">Allocosa brasiliensis</Emphasis> (Araneae,Lycosidae)

Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females. Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows. Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Thresholds in Songbird Occurrence in Relation to Landscape Structure

Abstract:  Theory predicts the occurrence of threshold levels of habitat in landscapes, below which ecological processes change abruptly. Simulation models indicate that below critical thresholds, fragmentation of habitat influences patch occupancy by decreasing colonization rates and increasing rates of local extinction. Uncovering such putative relationships is important for understanding the demography of species and in developing sound conservation strategies. Using segmented logistic regression, we tested for thresholds in occurrence of 15 bird species as a function of the amount of suitable habitat at multiple scales (150–2000-m radii). Suitable habitat was defined quantitatively based on previously derived, spatially explicit distribution models for each species. The occurrence of 10 out of 15 species was influenced by the amount of habitat at a landscape scale (≥500-m radius). Of these species all but one were best predicted by threshold models. Six out of nine species exhibited asymptotic thresholds; the effects of habitat loss intensified at low amounts of habitat in a landscape. Landscape thresholds ranged from 8.6% habitat to 28.7% (     = 18.5 ± 2.6%[95% CI]). For two species landscape thresholds coincided with sensitivity to fragmentation; both species were more likely to occur in large patches, but only when the amount of habitat in a landscape was low. This supports the fragmentation threshold hypothesis. Nevertheless, the occurrence of most species appeared to be unaffected by fragmentation, regardless of the amount of habitat present at landscape extents. The thresholds we identified may be useful to managers in establishing conservation targets. Our results indicate that findings of landscape-scale studies conducted in regions with relatively high proportions of habitat and low fragmentation may not be applicable in regions with low habitat proportions and high fragmentation.     

Sex ratios,mating behavior and sexual size dimorphism of the northern water snake,Nerodia sipedon

Competition among males to mate is generally associated with male-biased size dimorphism. In this study we examine mating behavior in the northern water snake (Nerodia sipedon), a species in which males are much smaller than females despite substantial competition among males to mate. Competition among males was a consequence of a male-biased operational sex ratio due to slightly higher female mortality from a birth sex ratio of 1 : 1, and, in 1 year, more synchronous and longer mating activity by males. Approximately one-third of both males and females appeared not to mate in a given year. Larger males were generally more likely to attempt mating, but size did not explain the variance in the number of aggregations in which individual males participated. Within aggregations, males that were successful at achieving intromission were larger than unsuccessful males in 1 of 2 years. Variation in condition (mass relative to length) and relative tail length were not generally useful predictors of either mating effort or success in males. Because large size was often advantageous to males, sexual size dimorphism appeared not to be a consequence of sexual selection favoring smaller males. Because sexual dimorphism was evident at birth, and both males and females matured sexually at about 4 years, sexual dimorphism was not simply a consequence of one sex growing at the maximum rate for longer. Female fecundity increased with size, and sex differences in size-fecundity relations may underly the pattern of sexual size dimorphism. However, because multiple mating by females is common, sperm competition is likely to be important in determining male reproductive success. Therefore, allocation of energy to sperm rather than growth may also prove to be an important influence on male growth rates and sexual size dimorphism.     

大气CO2浓度升高对农田土壤颗粒组成及其碳周转的影响

采集FACE(Free Air CO2 Enrichment)平台下运行3年的水稻(Oryza sativaL.)/小麦(Triticum aestivumL.)轮作土壤(0~15cm耕作层土壤),利用超声波分散-湿筛分法对烘干土样进行颗粒分级,分析土壤各粒级及其碳、氮的分布特征,研究大气CO2浓度升高对土壤碳周转的影响。结果表明:高浓度大气CO2条件下稻/麦轮作3年后,土壤颗粒组成较对照发生了改变,>53μm粒级的质量分数减小27%(p<0.05),约占土壤总质量20%;53~25μm粒级的质量分数增大35%(p<0.05),约占土壤总质量25%;<25μm无明显变化,约占土壤总质量55%,三种粒级之间质量分数呈显著差异(p<0.05)。FACE条件下,不同粒级土壤颗粒碳质量分数在两个氮水平下平均为:>53μm(30.60g·kg-1),<25μm(13.08g·kg-1),25~53μm(12.85g·kg-1),氮质量分数分别为2.42g·kg-1,1.33g·kg-1,1.12g·kg-1。>53μm粒级的土壤颗粒碳、氮质量分数均极显著高于其它两个粒级(p<0.001)。FACE条件下土壤总碳、氮质量分数高于对照,增幅分别为6.2%和6.7%。从各粒级土壤颗粒碳、氮质量分数变化分析,新增碳、氮主要进入>53μm粒级中,表明该粒级土壤颗粒对土壤碳氮循环(转化和保存)起着重要作用。该研究结果表明高浓度大气CO2条件下,稻/麦轮作农田土壤将成为大气CO2的汇,这将为预测我国未来农田土壤碳的变化趋势提供科学依据。     

The influence of parental age and weather on testosterone concentration and offspring survival in broods of tawny owl Strix aluco

Previous research has suggested that parental condition may affect offspring mortality patterns by affecting offspring testosterone levels. Accordingly, we hypothesized that there is a relationship between offspring testosterone concentration and survival during the early nestling period, and that both are influenced by parent age/experience and by prey availability. We tested our hypothesis on tawny owls Strix aluco in their first and third known breeding seasons, when they bred either in adverse or mild weather conditions, in Duna-Ipoly National Park, Hungary. Plasma testosterone concentrations of the nestlings were analyzed and related to parental condition, hatching order and nestling mortality. Inexperienced parents breeding in all weather conditions and experienced parents breeding in adverse conditions were both in poor condition compared to experienced parents breeding in mild conditions. Parents in poor condition produced broods with large between-sibling differences in testosterone concentrations and their later-hatched nestlings (which had low testosterone levels) died during the early nestling period, whereas parents in good condition produced broods with lower variation in offspring testosterone concentrations and all offspring survived the early nestling period. We discuss environmental influences on the amount of testosterone deposited in eggs, and also how maternal testosterone might induce those mechanisms producing testosterone in the nestlings.Communicated by M. Webster, T. Czeschlik     

A test of male mating and hunting success in the kestrel: the advantages of smallness?

We tested female choice for male wing and tarsus length and body mass in the kestrel (Falco tinnunculus), a species in which males average about 10% smaller than females. We also studied how male characters are related to their hunting success. In the laboratory, females preferred lighter males with shorter tarsi as mates, if the difference in those characters between competing males was larger than average. Lighter and shorter-winged males seemed to be better hunters than heavier and longer-winged males. Field observations in a year in which voles were scarce suggested that shorter-winged males were also better food providers in courtship feeding than longer-winged males,although in good vole years such a relationship was not found. We argue that females may prefer to pair with smaller males, because they have higher flight performance and better hunting success than heavier males. By doing so, females may gain direct breeding advantages. We conclude that both female choosiness and the hunting efficiency of males well contribute to reversed sexual size dimorphism (RSD, females larger than males) in the kestrel. Received: 18 July 1995/Accepted after revision: 17 August 1996     

Qualitative and quantitative assessment of the risk from the exposure to fetotoxic chemical compounds

A new mathematical dose-response model for the expected probability of toxic response and also for the expected measure of the overdispersion parameter for the reproductive and developmental risk assessment is proposed. The model for the expected probability of toxic response is an improvised Weibull dose-response model incorporating the litter-size effect while the model for the overdispersion parameter is a polynomial function of the dose level. A beta-binomial distribution for the number of offspring showing toxic responses in a litter satisfactorily accounts for the extra-binomial variation and the intralitter correlation of responses of these pups. Confidence limits for low-dose extrapolation are based on the asymptotic distribution of the likelihood ratio. The safe dose for human exposure is then calculated by simple linear extrapolation. The model for overdispersion allows us to obtain the estimates of the overdispersion parameter at these dosages. This was not possible in the earlier models. The proposed model is illustrated by an application to a study on the effect of exposure to diethylhexylphthalate in mice. The results are compared with those obtained by Chen and Kodell (1989) who have applied the simple Weibull dose-response model to the same data set.This paper was prepared with partial support from the United States Environmental Protection Agency under a Cooperative Agreement Number CR-815273. The contents have not been subject to Agency review and therefore do not necessarily reflect the views or policies of the Agency and no official endorsement should be inferred.     

三种空气微生物采样方法的比较

在室内自然条件下，对三种空气微生物采样方法进行比较。结果表明，ＡＮＤＥＲＳＥＮ采样器法，ＬＷＣ－１笄样器法和平皿沉降法测定的室内空气微生物粒子浓度分别为２６３４个／ｍ＾％３，２３９５个／ｍ＾３和１３８０个／ｍ＾３，ＬＷＣ－１型和ＡＮＤＥＲＳＥＮ二种采样器的采样结果之间没有明显差异，二种采样器的采样结果均明显高于平皿沉降法的采样结果。ＡＮＤＥＲＳＥＮ采样器的采样效率高，且可同时测定空气微生物粒子的浓