An experimental study of pleometrotic colony founding in the fire ant, Solenopsis invicta : what is the basis for association?

Many benefits and risks of cooperative colony founding (pleometrosis) have been identified, but rarely have the proximate factors that lead to association been considered. This study examined the choices queens make during the first few hours after mating, and some of the correlates of those choices. Queens had a strong affinity for preformed holes in the soil and readily used these as their initial founding chambers. This affinity was so strong that in a field experiment, the dispersion pattern of preformed holes controlled the final dispersion of colony-founding queens. Attraction to partially formed holes is thus an important cause of pleometrosis. The excavation of complete founding chambers incurred no measurable cost on the subsequent reproductive output of queens, suggesting that the primary benefit of using preformed holes is to remove the queen quickly from exposure to predation and desiccation. In the field, pairs of queens offered five equivalent preformed holes in soil were more likely to share the same hole if the holes were shallow and close together. In these experiments, queens modified preformed soil holes so that the test holes were no longer equivalent, causing the choice of queen and hole to become confounded. Laboratory experiments in plaster arenas with unmodifiable holes confirmed the field experiments: queens were more likely to share a hole when the holes were shallow than when they were deep. Because queens entering adequately deep holes seldom reemerged, this suggested that the likelihood of sharing increased with increasing contact between queens, that is, when queens were readily and frequently detected. Such contacts will also predict the future competitive environments to be experienced by incipient colonies, and may temper the tendency of queens to associate. However, experiments in which queens were exposed to high and low densities before pairing in the choice arenas failed to show an effect on the choice to join the resident queen. Queens that joined a resident queen differed in their robustness from queens that did not join. Queens choosing their own partners did no better reproductively than those assigned partners at random. Overall, this study suggests that (1) newly mated queens are under strong selection to leave the soil surface and do so by using any available holes, whether dug by another queen or of some other origin; (2) they are attracted to other queens, and are more likely to cofound as contact with the potential cofoundress becomes more frequent and (3) they choose whether or not to cofound partly on the basis of their own reproductive characteristics. Received: 20 November 1997 / Accepted after revision: 14 March 1998     

Effects of solar UV radiation on germination of conchospores and morphogenesis of sporelings in <Emphasis Type="Italic">Porphyra haitanensis</Emphasis> (Rhodophyta)

The effects of ultraviolet radiation (UVR 280–400 nm) on the germination of Porphyra haitanensis conchospores and on the growth and morphogenesis of the subsequent sporelings were investigated by culturing the released conchospores under natural sunlight from 29 September to 6 October 2005. Germination increased with time and was faster when UV-B was excluded using cut-off filters. There were significant negative effects of UV-B radiation on growth and cell division of sporelings, with decreases up to 18% for thallus length, between 6 and 18% for thallus width, up to 29% for thallus area, and between 6 and 14% for cell size as compared to PAR-controls. UV-A had a significant positive effect on morphogenesis, enhancing the formation of sporelings with cells dividing transversely; on the other hand, UV-B delayed the formation of such sporelings. We also tested the effects of solar UVR on the growth of P. haitanensis juveniles and found no significant effects. Our results indicate that UV-A has an important role in the germination and morphogenesis of the species, but on the other hand, sporelings of P. haitanensis are more sensitive to UV-B radiation than juveniles.     

The Importance of Systematic Biology in Defining Units of Conservation

Abstract: Conservation biology is linked inextricably with systematic biology. The principles of systematic biology, however, have not been integrated completely into the practice and principles of conservation biology. Systematists have recognized for some time that a number of evolutionary processes lead to the diversification of lineages. Yet some present units of conservation, such as the evolutionarily significant unit ( Waples 1991), primarily emphasize only one of these processes, adaptation. Allopatric speciation produces biodiversity without requiring any adaptive shift (and consequent adaptive differences between daughter species), so definitions of conservation units that emphasize adaptation may underestimate biodiversity. We estimated the frequency of different modes of speciation for three groups of vertebrates. The frequency of allopatric speciation varies among these groups, but is an important type of speciation in two of the three groups studied. Our results, and the results of other published studies of the frequency of modes of speciation, demonstrate that any unit of conservation defined solely in terms of adaptation is likely to underestimate biological diversity.     

Incorporating covariates into fisheries stock assessment models with application to Pacific herring.

We present a framework for evaluating the cause of fishery declines by integrating covariates into a fisheries stock assessment model. This allows the evaluation of fisheries' effects vs. natural and other human impacts. The analyses presented are based on integrating ecological science and statistics and form the basis for environmental decision-making advice. Hypothesis tests are described to rank hypotheses and determine the size of a multiple covariate model. We extend recent developments in integrated analysis and use novel methods to produce effect size estimates that are relevant to policy makers and include estimates of uncertainty. Results can be directly applied to evaluate trade-offs among alternative management decisions. The methods and results are also broadly applicable outside fisheries stock assessment. We show that multiple factors influence populations and that analysis of factors in isolation can be misleading. We illustrate the framework by applying it to Pacific herring of Prince William Sound, Alaska (USA). The Pacific herring stock that spawns in Prince William Sound is a stock that has collapsed, but there are several competing or alternative hypotheses to account for the initial collapse and subsequent lack of recovery. Factors failing the initial screening tests for statistical significance included indicators of the 1989 Exxon Valdez oil spill, coho salmon predation, sea lion predation, Pacific Decadal Oscillation, Northern Oscillation Index, and effects of containment in the herring egg-on-kelp pound fishery. The overall results indicate that the most statistically significant factors related to the lack of recovery of the herring stock involve competition or predation by juvenile hatchery pink salmon on herring juveniles. Secondary factors identified in the analysis were poor nutrition in the winter, ocean (Gulf of Alaska) temperature in the winter, the viral hemorrhagic septicemia virus, and the pathogen Ichthyophonus hoferi. The implication of this result to fisheries management in Prince William Sound is that it may well be difficult to simultaneously increase the production of pink salmon and maintain a viable Pacific herring fishery. The impact can be extended to other commercially important fisheries, and a whole ecosystem approach may be needed to evaluate the costs and benefits of salmon hatcheries.     

Linking atmospheric circulation to daily precipitation patterns over the territory of Bulgaria

An eight states non-homogeneous hidden Markov model is developed for linking daily precipitation amounts data at a network of 32 stations broadly covering the territory of Bulgaria to large-scale atmospheric patterns. At each site a 40-year record 1960?C2000 of daily October?CMarch precipitation amounts is modeled. The atmospheric data consists of daily sea-level pressure, geopotential height at 500 and 850?hPa, air temperature at 850?hPa and relative humidity at 700 and 850?hPa on a 2.5?×?2.5 grid based on NCEP-NCAR reanalysis data set covering the Europe-Atlantic sector 30W?C60E, 20N?C70N for the same period. The first 30?years data are used for model fitting purposes while the remaining 10?years are used for model evaluation. Detailed model validation is carried out on various aspects. The proposed model reproduces well the rainfall statistics for the observed and reserved data whereas the identified states are found to be physically interpretable in terms of regional climatology.     

From metamorphosis to maturity in complex life cycles: equal performance of different juvenile life history pathways

Performance in one stage of a complex life cycle may affect performance in the subsequent stage. Animals that start a new stage at a smaller size than conspecifics may either always remain smaller or they may be able to "catch up" through plasticity, usually elevated growth rates. We study how size at and date of metamorphosis affected subsequent performance in the terrestrial juvenile stage and lifetime fitness of spadefoot toads (Pelobates fuscus). We analyzed capture-recapture data of > 3000 individuals sampled during nine years with mark-recapture models to estimate first-year juvenile survival probabilities and age-specific first-time breeding probabilities of toads, followed by model selection to assess whether these probabilities were correlated with size at and date of metamorphosis. Males attained maturity after two years, whereas females reached maturity 2-4 years after metamorphosis. Age at maturity was weakly correlated with metamorphic traits. In both sexes, first-year juvenile survival depended positively on date of metamorphosis and, in males, also negatively on size at metamorphosis. In males, toads that metamorphosed early at a small size had the highest probability to reach maturity. However, because very few toadlets metamorphosed early, the vast majority of male metamorphs had a very similar probability to reach maturity. A matrix projection model constructed for females showed that different juvenile life history pathways resulted in similar lifetime fitness. We found that the effects of date of and size at metamorphosis on different juvenile traits cancelled each other out such that toads that were small or large at metamorphosis had equal performance. Because the costs and benefits of juvenile life history pathways may also depend on population fluctuations, ample phenotypic variation in life history traits may be maintained.     

Nutzen und Grenzen von Modellökosystemen zur Erfassung der Wirkung von Schadstoffen auf benthische Lebensgemeinschaften

The aim of this short article is to deliver insight into the prospects and constraints of model ecosystems in the assessment of effects of contaminants on benthic communities, especially the meiofauna. Numerous substances accumulate in sediments and thus a complex contamination exists which is able to impair benthic organisms. Besides direct effects, indirect effects are of importance and should be considered. Changes in competition and predator-prey-relationships lead to a variety of effects in the benthic food web that cannot be explained by direct toxicity of contaminants. In this article two microcosm studies, one with the heavy metal cadmium and one with the veterinary pharmaceutical Ivermectin, are presented which both showed direct as well as indirect effects. A significant change in abundance and composition of the meiofauna community has been observed. The prediction of field-effects of a certain substance as well as the interpretation of field data are the aims of model ecosystems. Both studies proofed that the investigation of meiofauna in microcosms is a promising tool to achieve these aims. Furthermore, microcosms with meiofauna might be able to assist the effect-directed analysis (EDA) in a risk assessment by identifying the effect-causing contaminants of complex environmental samples.     

Multimodal signaling in the Small Torrent Frog (Micrixalus saxicola) in a complex acoustic environment

Many animals use multimodal (both visual and acoustic) components in courtship signals. The acoustic communication of anuran amphibians can be masked by the presence of environmental background noise, and multimodal displays may enhance receiver detection in complex acoustic environments. In the present study, we measured sound pressure levels of concurrently calling males of the Small Torrent Frog (Micrixalus saxicola) and used acoustic playbacks and an inflatable balloon mimicking a vocal sac to investigate male responses to controlled unimodal (acoustic) and multimodal (acoustic and visual) dynamic stimuli in the frogs’ natural habitat. Our results suggest that abiotic noise of the stream does not constrain signal detection, but males are faced with acoustic interference and masking from conspecific chorus noise. Multimodal stimuli elicited greater response from males and triggered significantly more visual signal responses than unimodal stimuli. We suggest that the vocal sac acts as a visual cue and improves detection and discrimination of acoustic signals by making them more salient to receivers amidst complex biotic background noise.