Can synchronous spawning be predicted from environmental parameters? A case study of the lugworm Arenicola marina

The annual epidemic spawning period of a Scottish population of Arenicola marina (L.) has been recorded over a period of 13 yr. This population spawns between mid-October and mid-November in a discrete spawning event over a period of 4 to 5 d. Endocrine manipulation experiments showed that spawning is induced in females only if sufficient titres of PMH (prostomial maturation hormone) are present in the prostomia. These levels are attained during the 2 to 3 wk prior to the natural spawning date. The East Sands, St. Andrews population always spawns during periods of spring tides regardless of tidal amplitude or whether they are full- or new-moon tides. Meteorological data, including sea-temperature data were collected for each year, and correlation of the environmental data with spawning time was attempted. Correlation of spawning times with weather patterns showed that mean daily air pressures were significantly higher during the spawning period than from September to November as a whole. Evidence also suggests that a reduction in sea temperature is required prior to spawning. A significant moderate negative correlation was found between May to July air temperatures and spawning date, suggesting that higher May to July temperatures may induce early spawning. Daily rainfall and wind speed were also lower during the spawning period, but not significantly so. These results indicate that air pressure (or changes therein) may act as a final spawning cue, and the advantages of this are discussed in relation to fertilization success. A model of the interplay between environmental parameters and the endocrine mechanisms controlling the induction of spawning is proposed. Higher than average summer temperatures may advance gametogenesis to bring the population into a state of maturity (full-size oocytes, well-developed sperm morulae), and may also advance spawning time. Once the population has completed gametogenesis, a drop in sea temperature is then required to trigger an increase in endocrine titres within the prostomium, without which spawning cannot be induced by prostomial injection. The population spawns on spring tides; however a lack of clement weather coinciding with the spring tide will result in population-wide spawning being aborted, as in 1996. Clement weather (high pressure, low rainfall and wind speed) in conjunction with spring tides permits spawning to proceed to completion. Received: 21 June 1999 / Accepted: 25 January 2000     

Contrasting life histories and secondary production of populations of Munnopsurus atlanticus (Isopoda: Asellota) from two bathyal areas of the NE Atlantic and the NW Mediterranean

The isopod Munnopsurus atlanticus occupies bathyal depths in both the Bay of Biscay (NE Atlantic; between 383 and 1022 m) and in the Catalan Sea (Northwestern Mediterranean; between 389 and 1859 m). The species was dominant in both assemblages, reaching bathymetric peaks of abundance on the upper part of the continental slope (400 m depth) in the Bay of Biscay and at ˜600 m in the Catalan Sea. Both the Atlantic and the Mediterranean populations are bivoltines. Demographic analysis of the Bay of Biscay population revealed the production of two generations per year with different potential longevity (5 mo for G₁ and 11 mo for G₂). The mean cohort-production interval (CPI) was estimated at 8 mo, and results of the demographic analysis were also used to estimate production for the Catalan Sea populations. Mean annual density (D) and biomass (B) were higher in the Bay of Biscay (D = 356.7 individuals 100 m⁻²; B = 0.803 mg dry wt m⁻² yr⁻¹) than in the Mediterranean (D = 16.3 individuals 100 m⁻²; B = 0.078 mg dry wt m⁻² yr⁻¹). Also, mean annual production was an order of magnitude higher in the Atlantic (between 4.063 and 4.812 mg dry wt 100 m⁻² yr⁻¹ depending on the method used) than in the Catalan Sea (between 0.346 and 0.519 mg dry wt 100 m⁻² yr⁻¹). M. atlanticus feeds on a wide variety of benthic and pelagic food sources. In both study areas, phytodetritus was not important in the diet of M. atlanticus. In contrast, gut-content data suggested an indirect coupling with phytoplankton production in both areas via foraminiferans. The life history and the recorded production are considered in respect to both the dynamics and levels of primary production and the total mass flux in the respective study areas. Differences in the secondary production of both populations seemed to be more consistently explained by differences in total mass flux than by differences in the primary production levels; this is also consistent with the variety of food sources exploited by M. atlanticus. Received: 22 February 1999 / Accepted: 3 February 2000     

Reproductive variability over a four-year period in the sea urchin Evechinus chloroticus (Echinoidea: Echinodermata) from differing habitats in New Zealand

 The endemic New Zealand echinoid, Evechinus chloroticus (Valenciennes), was sampled approximately monthly from September 1990 to October 1994 at three sites in Tory Channel, Marlborough Sounds, New Zealand. These channel sites (outer, mid and inner) were up to 20 km from the open ocean and differed in their shore type, exposure to wave action and macrophyte abundance. E. chloroticus showed an annual reproductive cycle at each site, with gametogenesis commencing in the late austral winter and spawning in summer. Maximum gonad indices (reproductive potential) varied spatially, with the outer site generally having higher maximum gonad indices than the inner site, and temporally, with maximum gonad indices occurring earlier in 3 of the 4 seasons at the outer site than the inner site. The mid and inner sites showed much greater variation in maximum gonad indices (range 15.83 to 26.99% and 11.87 to 20.90%, respectively) than the outer site (range 19.31 to 22.95%). Reproductive output (weight of gametes released per gram echinoid) also varied, with the different sites showing significantly different outputs in the different years. A regression of maximum reproductive potential against reproductive output was significant ( p < 0.001), and had a positive slope with an r ² of 0.79. While, the initiation of gametogenesis was relatively synchronous between sites and years, and is possibly cued by increasing daylength, it progressed at different rates among populations. Spawning did show spatial and temporal variability, occurring near the time of highest sea-surface temperatures (∼15 °C). The observed variations in reproductive cycle may be related to small-scale variability in diet and environmental conditions. Furthermore, asynchronous spawning, variable spawning duration, and variable reproductive output are likely to strongly influence annual recruitment variability in E. chloroticus, with different larval subpopulations contributing unequally in different years. The ecological consequences of this, both for the ability of E. chloroticus to propagate itself in space and time and for the management of the developing E. chloroticus fishery in New Zealand, are discussed. Received: 9 December 1998 / Accepted: 13 June 2000     

Meiofauna response to a dynamic river plume front

 The benthic response to a plume front was studied in two areas of the northern Adriatic (Mediterranean Sea) differently influenced by the Po River freshwater input. Sediment samples were collected in June 1996 and February 1997 from 12 stations. The adopted sampling strategy was able to identify the front line in real time by satellite images and to locate sampling stations along an inner–outer plume gradient in order to cover the benthic area beneath the river plume, where enhanced biological production was expected, and open-sea sediments not directly influenced by freshwater inputs. Meiofaunal parameters were compared to the physical conditions and to phytodetritus inputs, organic matter accumulation and bacterial secondary production. The sediments of the Adriatic Sea were characterised by high concentrations of phytopigments (0.6 to 13.9 μg g⁻¹ for chlorophyll a and 1.2 to 17.7 μg g⁻¹ for phaeopigments) and biopolymeric organic carbon (0.15 to 3.02 mg g⁻¹). The plume system extended for a large sector of the northern Adriatic. In the northern area, a large and highly dynamic plume area was coupled with a sediment organic matter concentration significantly higher than in open-sea sediments. In the southern sector, where the plume area and the front line did not change markedly during the year, plume–benthic coupling was evident only in the sediments beneath the front, and corresponded to phaeopigment accumulation. Bacterial parameters and secondary production were high and significantly higher in the frontal area than at open-sea stations. Meiofauna density (1342 to 8541 ind. 10 cm⁻²) did not change either by season or between areas and was significantly correlated with phaeopigments and bacterial secondary production. Meiofauna displayed different responses to plume inputs in the two sampling areas. In the northern sector, meiofauna density was coupled with organic matter distribution and displayed highest values beneath the plume. In the southern sector, the densities of copepods, turbellarians and kinorhynchs displayed highest values under the front in summer, and the same applied to total meiofauna density in winter. Juvenile decapods and copepod nauplii significantly increased their densities in sediments beneath the front. Data presented in the present study suggest that plume inputs and frontal systems, enhancing phytodetritus accumulation and benthic bacterial response, might influence density, composition and distribution of meiofaunal assemblages. As river plumes are highly variable systems affecting the trophic characteristics of the sediments underneath, their dynamics should be considered when analysing mesoscale spatial changes of meiofaunal assemblages. Received: 30 November 1999 / Accepted: 24 May 2000     

The influence of potential reproductive rate and variation in mate quality on male and female choosiness in the sand goby, Pomatoschistus minutus

Recent models of choosiness in mate choice have identified two particularly important factors: the potential reproductive rate (PRR) of the choosing sex relative to that of the chosen sex, and the variation in quality of potential mates. This experimental study tested how these factors affected choosiness in male and female sand gobies, Pomatoschistus minutus. We manipulated relative PRR by means of water temperature, and mate quality by means of body length. The choosing male or female was offered a choice between two mates with either a small or a large difference in body length representing a small or a large variation in mate quality. Choosiness was measured as (1) preference for the larger mate, and (2) as whether or not spawning occurred with the smaller mate, while the larger mate was visible but screened off. We found that females preferred large males, and that their level of choosiness was affected by variation in male quality, but not by their own relative PRR. Males, on the other hand, seemed unselective in all treatments and were in general more likely than females to spawn with their provided partner. This suggests that in the sand goby, variation in male mate quality has a greater influence than relative PRR on facultative changes in female choosiness. However, a general difference in PRR between males and females may be one important factor explaining the observed sex difference in choosiness. Received: 17 April 2000 / Revised: 24 June 2000 / Accepted: 17 July 2000     

Experimental evidence of a testosterone-induced shift from paternal to mating behaviour in a facultatively polygynous songbird

Previous studies have suggested that testosterone (T) profiles of male birds reflect a trade-off between mate attraction behaviours (requiring high T levels) and parental care activities (requiring low T levels). In this study, we experimentally elevated T levels of monogamous males in the facultatively polygynous European starling (Sturnus vulgaris), and compared mate attraction and paternal behaviour of T-treated males with those of controls (C-males). T-males significantly reduced their participation in incubation and fed nestlings significantly less often than C-males. Females paired to T-treated males did not compensate for their mate’s lower paternal effort. The observed reduction in a male’s investment in incubating the eggs was accompanied by an increased investment in typical female-attracting behaviours: T-males spent a significantly higher proportion of their time singing to attract additional females. They also occupied more additional nestboxes than C-males, although the differences just failed to be significant, and carried significantly more green nesting materials into an additional nestbox (a behaviour previously shown to serve a courtship function). T-males also behaved significantly more aggressively than C-males. During the nestling period, the frequency of mate-attracting behaviours by T-treated and control males no longer differed significantly. Despite the reduced paternal effort by T-males and the lack of compensation behaviour by females, hatching and breeding success did not differ significantly between T- and C-pairs. Received: 7 February 2000 / Revised: 10 August 2000 / Accepted: 3 September 2000     

Aggression and resource sharing among foundresses in the social wasp Polistes dominulus: testing transactional theories of conflict

Tug-of-war models of within-group conflict predict that the frequency of conflict will be positively related to the degree of reproductive sharing within the group; in contrast, a negative relationship supports transactional models, in which reproductive payments among group members limit the degree of within-group selfishness. We tested predictions of the tug-of-war and transactional models by examining cofoundress interactions during the founding (preworker) phase of colony development in 30 naturally nesting colonies of the paper wasp Polistes dominulus. We found that the mean rate of foundress aggression and the mean probability of food sharing were significantly negatively associated, which supports the prediction of the transactional, not the tug-of-war model. Further, cofoundress aggression significantly increased over the founding phase (independently of temperature), while the fraction of aggression initiated by the dominant (alpha) foundress significantly decreased over this period. We show that both of these results are predicted by the transactional model of within-group conflict. Interestingly, the alpha’s rate of aggression was significantly positively temperature dependent, while the beta’s was not. This indicates that the alpha’s aggression level may often be near her physiological maximum, while the beta’s aggression is limi- ted by other factors, contradicting the prediction of the tug-of-war model. Moreover, the alpha’s aggression was significantly positively temperature dependent only in the second half of the founding period, as predicted by the transactional model since this is when there is least reproductive sharing. Finally, our results indicate that the alpha’s level of aggression depends on the resources controlled by the beta. Received: 18 January 2000 / Revised: 19 June 2000 / Accepted: 24 June 2000     

Life history costs of olfactory status signalling in mice

Large body size confers a competitive advantage in animal contests but does not always determine the outcome. Here we explore the trade-off between short-term achievement of high social status and longer-term life history costs in animals which vary in competitive ability. Using laboratory mice, Mus musculus, as a model system, we show that small competitors can initially maintain dominance over larger males by increasing investment in olfactory status signalling (scent-marking), but only at the cost of reduced growth rate and body size. As a result they become more vulnerable to dominance reversals later in life. Our results also provide the first empirical information about life history costs of olfactory status signals. Received: 15 December 1999 / Revised: 6 June 2000 / Accepted: 24 June 2000     

Accounting for Uncertainty in Risk Assessment: Case Study of Hector's Dolphin Mortality due to Gillnet Entanglement

Abstract: Uncertainties about biological data and human effects often delay decisions on management of endangered species. Some decision makers argue that uncertainty about the risk posed to a species should lead to precautionary decisions, whereas others argue for delaying protective measures until there is strong evidence that a human activity is having a serious effect on the species. We have developed a method that incorporates uncertainty into the estimate of risk so that delays in action can be reduced or eliminated. We illustrate our method with an actual situation of a deadlock over how to manage Hector's dolphin ( Cephalorhychus hectori ). The management question is whether sufficient risk is posed to the dolphins by mortalities in gillnets to warrant regulating the fisheries. In our quantitative risk assessment, we use a population model that incorporates both demographic ( between-individual) and environmental ( between-year) stochasticity. We incorporate uncertainty in estimates of model parameters by repeatedly running the model for different combinations of survival and reproductive rates. Each value is selected at random from a probability distribution that represents the uncertainty in estimating that parameter. Before drawing conclusions, we perform sensitivity analyses to see whether model assumptions alter conclusions and to recommend priorities for future research. In this example, uncertainty did not alter the conclusion that there is a high risk of population decline if current levels of gillnet mortality continue. Sensitivity analyses revealed this to be a robust conclusion. Thus, our analysis removes uncertainty in the scientific data as an excuse for inaction.     

Bushmeat Markets on Bioko Island as a Measure of Hunting Pressure

Abstract: Counts of the number of animal carcasses arriving at Malabo market, Bioko Island, Equatorial Guinea, were made during two, 8-month study periods in 1991 and 1996. Comparisons of the availability and abundance of individual species between years showed that more species and more carcasses appeared in 1996 than in 1991. In biomass terms, the increase was significantly less, only 12.5%, when compared with almost 60% more carcasses entering the market in 1996. A larger number of carcasses of the smaller-bodied species (i.e., rodents and the blue duiker [ Cephalophus monticola ] ) were recorded in 1996 than in 1991. Although an additional four species of birds and one squirrel were recorded in 1996, these were less important in terms of their contribution to biomass or carcass numbers. Concurrently, there was a dramatic reduction in the larger-bodied species, Ogilby's duiker ( C. ogilbyi ) and seven diurnal primates. We examined these changes, especially the drop in the number of larger animals. We considered the possible following explanations: (1) the number of hunters dropped either because of enforced legislation or scarcity of larger prey; (2) a shift in the use of hunting techniques occurred (   from shotguns to snares); or (3) consumer demand for primate and duiker meat dropped, which increased demand for smaller game. Our results suggest that the situation in Bioko may be alarmingly close to a catastrophe in which primate populations of international conservation significance are being hunted to dangerously low numbers. Although there is still a need for surveys of actual densities of prey populations throughout the island, working with the human population on Bioko to find alternatives to bushmeat is an urgent priority.