Chemical behavior and risk assessment of four pesticidesin soil and water

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Time constraints and multiple choice criteria in the sampling behaviour and mate choice of the fiddler crab,Uca annulipes

Active female sampling occurs in the fiddler crab Uca annulipes. Females sample the burrows of several males before remaining to mate in the burrow of the chosen partner. Females time larval release to coincide with the following nocturnal spring tide and must therefore leave sufficient time for embryonic development after mating. Here we show how this temporal constraint on search time affects female choosiness. We found that, at the start of the sampling period (when time constraints are minimal), females selectively sample the larger males in the population. Towards the end of the sampling period (when the temporal constraints increase the costs of sampling), females are less selective. Furthermore, we suggest that the number of males sampled (and other indices of ‘‘sampling effort’’) may not be reliable indicators of female choosiness and may not reflect the strength of female mating preferences under certain conditions. Burrow quality also emerged as an important criterion in final mate choice. Burrow structure potentially influences reproductive success, and mate acceptance based on burrow structure appears to involve a relatively invariant threshold criterion. Since there is no relationship between male size and burrow quality, females are using at least two independent criteria when choosing potential mates. We envisage mate choice as a two-stage process. First, females select which males to sample based on male size. They then decide whether or not to mate with a male based on burrow features. This sampling process explains how two unrelated variables can both predict male mating success. Received: 23 March 1995/Accepted after revision: 14 January 1996     

Prey odor discrimination by ingestively naive coachwhip snakes(Masticophis flagellum)

Summary Ingestively naive hatchling coachwhip snakes(Masticophis flagellum) detected integumentary chemicals from several potential prey species and discriminated them from chemical stimuli from other animals and from distilled water, strongly suggesting a genetic basis for these abilities. The strongest responses were to lizard and snake stimuli, which form a major part of the diet. Variable responses to chemical cues from other taxa are discussed. Responses by coachwhip snakes to prey chemicals appear to be highly specific, as suggested by the stronger reaction to vomodors of sympatric than of allopatric lizard species. The highly developed use of chemical cues by the diurnal, visually oriented coachwhip snake emphasizes the general importance of chemical senses to predation by nonvenomous snakes, regardless of the involvement of vision.     

Sex allocation in the solitary bee Osmia cornuta: do females behave in agreement with Fisher's theory?

Fisher's theory of sex allocation predicts that, in a panmictic population, parental investment will be equally distributed between male and female progeny. Most studies on parental investment in nesting solitary bees and wasps use offspring or provision weight as estimators of parental investment and do not corroborate Fisher's theory. The measurement of parental investment may be confounded by several factors. First, the use of offspring or provision size does not account for seasonal variation in foraging costs associated with aging of nesting females. Second, provision or offspring size do not reflect parental investment associated with nest construction. In this two-year study we measured parental investment in a solitary bee. We calculated sex allocation using both provision weight and foraging time as parental investment estimators. Investment in pollen-nectar provisions decreased, while investment in mud structures (nest construction) increased, as the nesting period progressed. Overall investment in provisions per nest was ∼25 times higher than investment in mud. Pollen-nectar foraging trips became longer as the season progressed, but mud trip duration did not vary. Due to weather differences between years, more offspring per female were produced in the first year, but progeny sex ratio and mean offspring size of both sexes were similar between years. Mortality did not differ between sexes. As predicted by Fisher's theory, production cost ratios did not differ from 1 in either year, irrespective of the currency used to estimate parental investment (provision weight or foraging time). Our results strongly support Fisher's theory.     

Self-organized digging activity in ant colonies

Many ant species adjust the volume of their underground nest to the colony size. We studied whether the regulation of the volume of excavated sand could result from an interplay between recruitment processes and ant density. Experiments were performed with different group sizes of workers in the ant Messor sancta. When presented with a thin homogeneous sand disk, these groups excavated networks of galleries in less than 3 days. The excavation dynamics were logistic shaped, which suggests the existence of a double feedback system: a positive one resulting in an initial exponential growth phase, and a negative one leading the dynamics to a saturation phase. The total volume of excavated sand was almost proportional to the number of workers. We then developed a model in which we incorporated the quantitative behavioral rules of the workers digging activity. A positive feedback was introduced in the form of a recruitment process mediated by pheromones. The model predicts that the excavation dynamics should be logistic shaped and the excavation should almost stop despite the absence of any explicit negative feedback. Moreover, the model was able to reproduce the positive linear relationship between nest volume and colony size.Communicated by K. Ross     

Direct-push geochemical profiling for assessment of inorganic chemical heterogeneity in aquifers

Discrete-depth sampling of inorganic groundwater chemistry is essential for a variety of site characterization activities. Although the mobility and rapid sampling capabilities of direct-push techniques have led to their widespread use for evaluating the distribution of organic contaminants, complementary methods for the characterization of spatial variations in geochemical conditions have not been developed. In this study, a direct-push-based approach for high-resolution inorganic chemical profiling was developed at a site where sharp chemical contrasts and iron-reducing conditions had previously been observed. Existing multilevel samplers (MLSs) that span a fining-upward alluvial sequence were used for comparison with the direct-push profiling. Chemical profiles obtained with a conventional direct-push exposed-screen sampler differed from those obtained with an adjacent MLS because of sampler reactivity and mixing with water from previous sampling levels. The sampler was modified by replacing steel sampling components with stainless-steel and heat-treated parts, and adding an adapter that prevents mixing. Profiles obtained with the modified approach were in excellent agreement with those obtained from an adjacent MLS for all constituents and parameters monitored (Cl, NO(3), Fe, Mn, DO, ORP, specific conductance and pH). Interpretations of site redox conditions based on field-measured parameters were supported by laboratory analysis of dissolved Fe. The discrete-depth capability of this approach allows inorganic chemical variations to be described at a level of detail that has rarely been possible. When combined with the mobility afforded by direct-push rigs and on-site methods of chemical analysis, the new approach is well suited for a variety of interactive site-characterization endeavors.     

Health-dependent vulnerability to predation affects escape responses of unguarded chinstrap penguin chicks

Predators may select more often to attack the more vulnerable prey or those with an inferior health status. Thus, prey should be able to assess their own vulnerability to predation and modify their antipredatory behavior accordingly. When approached by predator skuas, unguarded penguin chicks flee short distances, and usually aggregate in dense packs, but there is a clear interindividual variability in their responses under similar conditions. We hypothesized that this variability in escape responses might be related to the perceived vulnerability to predation of each individual chick. We simulated predator attacks to chinstrap penguin chicks and analyzed the sources of variation in their escape response, such as the presence of adults or the density of other chicks, and the sex, age, body condition, and health status of responding chicks. Chicks allowed shorter approach distances when they had a better health condition (i.e., a greater T-cell-mediated immunity, CMI), when they were younger, and when the density of adults around was higher. Sex and density of other chicks were not important. Similarly, chicks fled from the experimenter to longer distances when they had a lower CMI and when the density of adults was lower. Therefore, escape characteristics of chicks depended on the presence of adults that can deter predators and on the health-dependent vulnerability of chicks.     

The reproductive behavior and energetics of male gray seals (Halichoerus grypus) breeding on a land-fast ice substrate

The reproductive behavior of male gray seals (Halichoerus grypus) breeding on land-fast ice at Amet Island, Nova Scotia, was studied. Data on energy expenditure (rate of mass loss over time) were collected. The average time budget of males at Amet Island was comparable to that of land-breeding males. The behavior of males showed seasonal changes, with a decrease in the proportion of time spent in the water and an increase in agonistic behavior during the peak mating period. The estimated amount of body mass lost over the season ranged between 25.6 and 77.1 kg, and the estimated percent of initial body mass lost ranged between 7.7 and 26.5% (n=10). The maximum number of observed copulations for an individual male was nine. Only 15 out of 42 males observed during 1992 and 1993 were seen copulating. The number of observed copulations per male was strongly correlated with success in remaining close to, or attending, females (r=0.91, P<0.001, n=42). The mean duration of attendance was 4.5 ± 5.54 days (n=42). Large size was not an important factor in determining attendance success, but reproductive effort (the estimated proportion of body mass lost over the season) and success in agonistic interactions with other males were both correlated with male success.     

中国穿山甲的食性与觅食行为初步观察

通过野外观察及粪便和胃内容物分析,对中国穿山甲的食性进行了调查和研究.结果表明,中国穿山甲的觅食行为可分为6个类别,即行走、搜寻、行走/搜寻、挖掘、取食、暂停;取食地点主要发生在杂草、乔木、灌木的基部,落叶层下,倒木/枯枝、死树桩附近及白蚁巢内;以蚁类为食,且表现出明显的选择和偏爱,被拒食的蚂蚁和白蚁种数分别占83.87%(26/31)和53.85%(7/13),最喜爱的蚁类是台湾乳白蚁(Coptotermesformosanus)、黄翅大白蚁(Macrotermesbarneyi)、双齿多刺蚁(Polyrhachisdives);食谱由11种蚁类构成,占大雾岭保护区蚁类组成25%,其中蚂蚁5属5种,白蚁4属6种,夏季食谱主要由蚂蚁构成,冬季食谱主要由白蚁构成,台湾乳白蚁、黄翅大白蚁很可能是穿山甲食谱中的关键食物.表6参25     

铜绿微囊藻、四尾栅藻和小环藻竞争实验培养基的选择

改变培养基的氮源形态和碳源浓度,研究铜绿微囊藻、小环藻和四尾栅藻的单藻增长行为,筛选适宜的培养基作为混藻竞争实验的共培养基。研究表明,铜绿微囊藻和四尾栅藻在氨氮培养基中的最大生物量K和最大比增长速率r均不及以硝态氮为氮源的培养基;添加高浓度HCO3-(NaHCO3 1.410 mmol/L)能够提高铜绿微囊藻和四尾栅藻藻细胞对氨氮的吸收能力;较低碳源浓度(NaCO3 0.0943 mmol/L)的培养基中,四尾栅藻的初始比增长速率及生物量远高于铜绿微囊藻,但其最大比增长速率r低于铜绿微囊藻,在实验的第10天左右铜绿微囊藻的生物量超过四尾栅藻;小环藻不能在较高浓度碳源(NaHCO3 1.504 mmol/L)下存活;铜绿微囊藻、四尾栅藻与小环藻均可在以氨氮(HA)或硝态氮(HN)为氮源的培养基中单独培养并达到实验所需生物量,因此,HN和HA可以作为实验室内这三种藻共培养适宜的培养基,为今后研究藻类种间资源竞争机制提供实验依据。