Divergence between populations of a monogamous polychaete with male parental care: Premating isolation and chromosome variation

Low dispersal and sexual selection are characteristic of the coastal polychaeteNereis acuminata Ehlers 1868 [also known asNereis arenaceodentata Moore 1903 andNereis (Neanthes) caudata Delle Chiaje 1841]. We assessed levels of premating isolation between populations of this polychaete. Four North American populations were used, two from the Atlantic and two from the Pacific. Worms from all sites (1) were collected in 1987 and 1988 from the same habitat type, (2) were morphologically similar and keyed out asN. acuminata, and (3) reproduced monogamously and exhibited male parental care, an extremely rare reproductive mode in marine invertebrates. There was no evidence from 10-min or 36-h trials of premating isolation between the two Pacific populations. Incomplete premating isolation was found between the two Atlantic populations. High aggression and non-pairing occurred in some 10-min trials between males and females. However, in 36-h trials males and females from the two Atlantic populations always paired to mate. Complete premating isolation was found between Atlantic and Pacific populations. During 10-min trials, males and females from different oceans often attacked and then avoided each other, and they never paired to mate. Nor did they pair to mate in longer, 36-h trials. One Pacific and one Atlantic population were compared for tolerance to cold temperature. Pacific individuals were less able to tolerate cold water than Atlantic individuals. Two Atlantic populations studied had karyotypes with 11 pairs of small acrocentric chromosomes (2n=22), while the two Pacific populations had nine pairs of large metacentric or submetacentric chromosomes (2n=18). Such extreme dissimilarity in karyotype was not expected considering the similarity in morphology, habitat, and reproductive mode. Results suggest strongly that the Atlantic and Pacific populations have been allopatric for a long time, and are different species.     

Effects of an oil spill on leafpack-inhabiting macroinvertebrates in the Chariton River, Missouri

Artificial leaf packs were used to determine the effects of an oil spill on stream macroinvertebrate communities in the Chariton River, Missouri. Plastic mesh leaf retainers with approximately 10 g of leaves from five tree species were deployed at five sites (two upstream of the spill and three downstream) immediately after the spill and one year later. Four macroinvertebrate species dominating the community at upstream sites were virtually eliminated below the spill, including the stonefly Isoperla bilineata, the caddisfly Potamyia flava, the midge Thienemanniella xena, and blackfly larvae (Simulium sp.). Density of collector and shredder functional groups, and number of shredder taxa differed between upstream sites and the two furthest downstream sites during the 1990 sample period (Kruskal-Wallis w/Bonferroni paired comparisons, experiment wise error rate = 0.05). With one exception, no differences between sites were detected in the 1991-1992 sample period, indicating that the benthic community had at least partially recovered from the oil spill after one year. The odds of obtaining a sample with a small abundance of shredders (abundance < median) in 1990 was significantly greater downstream of the spill than upstream, and the odds of obtaining a sample with a small abundance of shredders at downstream sites was greater in 1990 than in 1991-1992. A similar pattern was observed in abundance and taxa richness of the collector functional group. No significant differences between the two sampling periods were detected at upstream sites. Observed effects appeared to be associated with oil sorption and substrate coating, creating conditions unsuitable for successful colonization.     

“Embedded” at hire? Predicting the voluntary and involuntary turnover of new employees

Embeddedness theory has been invoked to describe factors that constrain employee turnover, such as fit with the environment, interpersonal links, and potentially sacrificed benefits. In contrast with previous assumptions that embeddedness requires considerable time to develop on the job, we extend theory by demonstrating how biographical characteristics (i.e., biodata), assessed at or before the point of hire, are related to individual's propensity to be embedded, while also showing how such characteristics predict one's future turnover likelihood. Beyond voluntary turnover, we also build embeddedness‐based theoretical explanations for involuntary turnover (i.e., terminations). To test these ideas, we conducted two studies at and before employees' point of hire, respectively: Study 1 examined how assessed biodata items of new employees relate to established embeddedness measures, whereas Study 2 linked the same biodata items assessed during the application process to employees' future involuntary, avoidable voluntary, and unavoidable voluntary turnover. Study 1 results revealed various biodata items predicted embeddedness in two distinct samples. In Study 2, results showed that biodata predicted turnover forms in unique ways. Our study highlights the utility of point‐of‐hire embeddedness propensity as a means to explain organizational exit, thereby demonstrating how organizations can use embeddedness tenets for employee recruitment and selection purposes.     

Community‐based water supplies in Cikarang,Indonesia: are they sustainable?

Community‐based water supply (CBWS) is an example of how a community manages common pool resources (CPR). This results in an alternative approach to solve water supply problems in developing countries by enhancing community participation in managing water supply. This research evaluates the sustainability of five CBWS projects in Cikarang, Indonesia by using Ostrom's design principles, with additional sustainability factors found in the Sustainable Development Goal (SDG) on drinking water and groundwater sustainability. Quinn et al. (2007) criteria were used in the analysis, and the results show that the management of four CBWS institutions were absent and one CBWS institution was weak. With regards to the SDG's drinking water target, the CBWS institutions were unable to comply with safe water standards, and in terms of groundwater sustainability, efforts to monitor and sustain groundwater tables were absent. Results from this research suggest that more focus must be placed on water quality and groundwater sustainability for CBWS projects.     

Sitting Comfort of Ergonomic Office Chairs—Developed Versus Intuitive Evaluation

The sitting comfort of office chairs with different ergonomic layouts (inferior, superior) was examined. Fifty participants were randomly assigned to a 2 × 5 factorial experimental design with 2 different conditions of ergonomic chair layout (inferior or superior) and 5 different conditions of instruction to explore the chair. Four conditions were created to differentiate between various levels of perceptual awareness and processing of chair-related information (guided exploration and developed evaluation). In a 5th condition, participants remained uninstructed (free exploration and intuitive exploration). Under guided exploration, the participants’ perception of sitting comfort was in line with objective differences in the chair layout. Different conditions of guided exploration, however, did not influence the evaluations. Under free exploration, the participants’ perceptions did not match the ergonomic chair layout. In contrast to participants under guided exploration, they even rated the ergonomically inferior office chair more favourably than the ergonomically superior chair.     

Feeding, metabolism and growth in the Antarctic limpet, Nacella concinna (Strebel 1908)

Post-prandial increases in metabolism, the specific dynamic action of feeding (SDA), were evaluated in the Antarctic limpet Nacella concinna. O₂ consumption rose to a peak value 2.3 times higher than pre-feeding standard metabolic rates. This peak rise is low for marine ectotherms, but is typical of polar species. There were three peaks in the SDA, the first lasted only for the 1st day, was caused by handling, and was minor. The second was the major peak. It lasted from post-prandial days 4–9 inclusive, and accounted for around 70% of the SDA response. The third peak lasted from day 11 to day 15 and accounted for 30% of the total SDA. A 15-day SDA is much longer than values for temperate species, but is again typical for polar marine ectotherms. NH₃ excretion declined post-prandially from around 0.4 μmol animal⁻¹ h⁻¹ to values between 0.025 and 0.223 μmol animal⁻¹ h⁻¹ throughout the SDA. The total O₂ consumed in the SDA was 90.2 μmol O₂, which converts to 44.7 J of energy. This was 45–50% of the energy consumed in the meal (93.5 J). Pre-feeding O:N ratios, after 26 days without food, were around 1, indicating protein as the sole metabolic substrate prior to initiating the SDA. After feeding, O:N ratios rose to between 2.5 and 19, indicating significant use of lipid or carbohydrate from the food. Experiments were conducted in ambient seawater with enhanced levels of Sr (SrCl added at 800 mg kg⁻¹), and limpets were fed microalgal films also grown in enhanced Sr media. Sr incorporated in the shells during the experiment allowed the measurement of shell increments deposited during the SDA. Between five and eight microgrowth bands were present in the Sr-enhanced increments, which was similar to the number of days in the second SDA peak. The mean shell increment laid down was 17.6 μm. Estimating tissue deposition from measured growth increments and published ash-free dry mass (AFDM) to length relationships produced a value of 0.81 mg AFDM, which converted to 26.4 J of energy, or 25–30% of the energy ingested in the meal. Estimates of growth increments associated with a single SDA have not previously been possible. Overall energy used in the SDA and tissue deposition accounted for 75–80% of the energy ingested; the remainder was probably accounted for by unmeasured costs such as mucus production. Received: 6 June 2000 / Accepted: 20 September 2000