Prenatal cannibalism in an insect

Host selection and infection strategies of parasitoids often correlate with high parental investment and low numbers of progeny. In this study, we investigate how additional internal mechanisms might shape brood size and fitness of the offspring. Emblemasoma auditrix is a parasitoid fly in which about 38 larvae hatch simultaneously in utero. After host location, a single larva is deposited into the host, where it rapidly develops and pupates after about 5 days. The search for hosts can take several weeks, and during that time, the larvae arrest their development and remain in the first larval instar. Nevertheless, the larvae increase in weight within the uterus, and this growth correlates to a decrease in the number of larvae, although no larvae are deposited. Thus, our data indicate a first case of prenatal cannibalism in an invertebrate with larvae feeding on each other within the uterus of the adult.     

Evolution of tolerance to PCBs and susceptibility to a bacterial pathogen (Vibrio harveyi) in Atlantic killifish (Fundulus heteroclitus) from New Bedford (MA, USA) harbor

A population of the non-migratory estuarine fish Fundulus heteroclitus (Atlantic killifish) resident to New Bedford (NB), Massachusetts, USA, an urban harbor highly contaminated with polychlorinated biphenyls (PCBs), demonstrates recently evolved tolerance to some aspects of PCB toxicity. PCB toxicology, ecological theory, and some precedence supported expectations of increased susceptibility to pathogens in NB killifish. However, laboratory bacterial challenges of the marine pathogen Vibrio harveyi to wild fish throughout the reproductive season and to their mature laboratory-raised progeny demonstrated comparable survival by NB and reference killifish, and improved survival by NB males. These results are inconsistent with hypothesized trade-offs of adaptation, and suggest that evolved tolerance in NB killifish may include mechanisms that minimize the immunosuppressive effects of PCBs. Compensatory strategies of populations persisting in highly contaminated environments provide a unique perspective for understanding the long-term ecological effects of toxic chemicals.     

Female seed beetles, <Emphasis Type="Italic">Callosobruchus maculatus,</Emphasis> remate for male-supplied water rather than ejaculate nutrition

Female seed beetles, Callosobruchus maculatus, mate multiply even though association with males and copulations carry costs, such as injury to the genital tract. Multiple mating (polyandry) may, however, offset these costs through the acquisition of food and water, two material benefits hypothesized to be obtained from the large ejaculates produced by males. The material benefits hypothesis can be tested by increasing female access to nutrients and water, with the prediction that female mating frequency will decrease as copulation is no longer required to derive these materials. Females were given water, 5% sugar–water or baker’s yeast, and were compared with females deprived of these. We presented females with virgin males daily for 8 days and recorded female mating frequency, survivorship, and fecundity. Females provided with water and sugar–water decreased mating frequency. Thus, water, rather than nutrients in the ejaculate, appears to be important to females of this species. In addition, both life span and fecundity were extended for females in the sugar–water and water treatments. Since water is scarce in the arid environment in which this species is found, we conclude that polyandry provides material benefits to females that may offset some of the costs of associating with males.     

Effects of gene flow from IMI resistant sunflower crop to wild Helianthus annuus populations

Wild sunflower, H. annuus ssp. annuus, is an invasive species widely distributed in several regions of the world, including central Argentina where it shares a large area with domesticated sunflower. The discovery of imidazolinone resistance in a wild sunflower population allowed the development of Clearfield^® technology in cultivated sunflower. This technology was rapidly adopted in Argentina but the trait could possibly be transferred to the naturalized wild populations through natural hybridization. The aim of this study was to evaluate the transfer of IMI resistance to wild sunflower populations and its effect on wild plants’ fitness. Plants of five wild populations and their progenies of crosses with an IMI-resistant hybrid were evaluated through a dormancy, herbicide resistance, and SSR markers study. Relative fitness was compared in the five populations, F1s and backcrosses with wild and crop parental plants. Hybridization with an IMI-resistant hybrid did not alter seed dormancy. F1 individuals were more resistant to imazapyr than their wild ancestors but less tolerant than the commercial variety. SSR markers confirmed the transfer of resistance and identified resistant plants within the wild populations. Fitness was reduced in the first generation after crossing but was recovered in the following generations. Thus, to ensure durability and efficiency of Clearfield^® technology, management practices like crop rotation and herbicide usage with different modes of action should be considered.     

Offspring sex ratio in relation to parental structural size and body condition in the long-lived wandering albatross (<Emphasis Type="Italic">Diomedea exulans</Emphasis>)

Sex ratio theory is one of the most controversial topics in evolutionary ecology. Many deviations from an equal production of males and females are reported in the literature, but few patterns appear to hold across species or populations. There is clearly a need to identify fitness effects of sex ratio variation. We studied this aspect in a population of a long-lived seabird, the wandering albatross (Diomedea exulans), using molecular sex-identification techniques. We report that parental traits affect both (1) fledgling traits in a sex-dependent way and (2) chick sex: Sons are overproduced when likely to be large at fledging and, to a lesser extent, daughters are overproduced when likely to be in good body condition at fledging. Because for the same population, a previous study reported that post-fledging survival was positively affected by size in males and by body condition in females, our results suggest that wandering albatrosses manipulate offspring sex to increase post-fledging survival.     

Sexual selection and female fitness in <Emphasis Type="Italic">Drosophila simulans</Emphasis>

There is a current debate over the net fitness consequences of sexual selection. Do preferred males increase female fitness or are these males manipulating females for their own benefit? The evidence is mixed. Some studies find that mating with attractive males increases female fitness components, while others show that preferred males decrease measures of female fitness. In this study, we examined some of the fitness consequences of pre-copulatory sexual selection in Drosophila simulans. Virgin females were either paired with one male and given an opportunity for one copulation or were exposed simultaneously to two males. This allowed us to compare female preference (copulation latency) and fitness (longevity, lifetime productivity and rate of offspring production) both with and without the influence of male–male competition. When females had access to a single male, neither female longevity, productivity, nor short-term rate of productivity were associated with female preference, and although females mated more quickly with larger males, male size was also not associated with any female fitness measure. Inclusion of male–male competition showed that female longevity was negatively affected by preference, while productivity and rate of productivity was unaffected. This latter experiment also indicated that females preferred larger males, but again, male size was not associated with female fitness. These results indicate that females may not benefit from mating with preferred males, but they may incur survival costs.     

Low nutrient levels as drinking water conditions can reduce the fitness cost of efflux pump-mediated ciprofloxacin resistance in Pseudomonas aeruginosa

The long-term persistence of antibiotic resistance in the environment, especially in drinking water, is a public health concern. Expression of an efflux pump, an important mechanism of resistance to antibiotics, usually confers a fitness cost in bacteria. In this study, we aimed to determine why antibiotic resistance conferred by overexpression of an efflux pump persisted in low-nutrient environments(TOC 10 mg/L) such as drinking and source water in which antibiotic selective pressure might be very low or even absent.Competition experiments between wild-type Pseudomonas aeruginosa and ciprofloxacinresistant mutants revealed that the fitness cost of ciprofloxacin resistance significantly decreased(p 0.05) under low-nutrient(0.5 mg/L total organic carbon(TOC)) relative to high-nutrient(500 mg/L TOC) conditions. Mechanisms underlying this fitness cost were analyzed. The mexD gene expression in resistant bacteria(cip_3 strain) was significantly lower(p 0.05) in low-nutrient conditions, with 10 mg/L TOC((8.01 ± 0.82)-fold), than in high-nutrient conditions, with 500 mg/L TOC((48.89 ± 4.16)-fold). Moreover, rpoS gene expression in resistant bacteria((1.36 ± 0.13)-fold) was significantly lower(p 0.05) than that in the wild-type strain((2.78 ± 0.29)-fold) under low-nutrient conditions(10 mg/L TOC),suggesting a growth advantage. Furthermore, the difference in metabolic activity between the two competing strains was significantly smaller(p 0.05) in low-nutrient conditions(5 and 0.5 mg/L TOC). These results suggest that nutrient levels are a key factor in determining the persistence of antibiotic resistance conferred by efflux pumps in the natural environment with trace amounts or no antibiotics.     

Fitness Landscapes and the Precautionary Principle: The Geometry of Environmental Risk

The Precautionary Principle is a legal mechanism for managing the environmental risk arising from incomplete scientific knowledge of a proposal's impacts. The Precautionary Principle is applied to actions that carry with them the potential for serious or irreversible environmental change. The model proposed in this paper draws on methods used in a range of disciplines for modeling (potentially highly nonlinear) interactions between multiple parts of a complex system. These methods have been drawn together under the common mathematical umbrella of Fitness Landscape Theory. It is argued that the model, called “Environmental Impact Fitness Landscapes,” allows statements about the sensitivity of the gross effect from a set of impacts to be made when the number of impacts in the set, and/or their degree of interaction, is varied. It is argued that this can be achieved through identification of “meta” or “emergent” properties of the set itself, without reference to the specific causal chains determining behavior in specific instances. While such properties are very general, they may at least allow for the parameterization of the effects of sets of impacts where interactions are highly uncertain and empirical data severely limited, i.e., situations that would typically invoke the Precautionary Principle.     

Multiple mating increases the sperm stores of Atta colombica leafcutter ant queens

Multiple mating is likely to be costly for ant queens and yet it is common. Whether multiple mating brings benefits to queens that outweigh the costs has, therefore, received considerable theoretical attention. Empirical tests of hypotheses have been scarce and no clear evidence has been reported. We tested the “multiple-mating-for-more-sperm” hypothesis on individual young queens in a natural population of the leafcutter ant Atta colombica, a monogynous ant characterised by very large colonies and high colony longevity. We found that the number of sperm stored by queens was positively correlated with the number of mates per queen estimated through mother-offspring analysis with microsatellite DNA markers. Queen sperm stores increased on average by 30 million sperm for each additional mate. Life-history information for Atta indicate that the number of stored sperm observed is likely to constrain the reproductive lifespan of queens in nature. Multiple mating, despite costs, may therefore enhance the fitness of Atta queens because it enables them to store more sperm. Received: 19 September 1997 / Accepted after revision: 7 December 1997