Radio tagging reveals the roles of corpulence,experience and social information in ant decision making

Ant colonies are factories within fortresses (Oster and Wilson 1978). They run on resources foraged from an outside world fraught with danger. On what basis do individual ants decide to leave the safety of the nest? We investigated the relative roles of social information (returning nestmates), individual experience and physiology (lipid stores/corpulence) in predicting which ants leave the nest and when. We monitored Temnothorax albipennis workers individually using passive radio-frequency identification technology, a novel procedure as applied to ants. This method allowed the matching of individual corpulence measurements to activity patterns of large numbers of individuals over several days. Social information and physiology are both good predictors of when an ant leaves the nest. Positive feedback from social information causes bouts of activity at the colony level. When certain social information is removed from the system by preventing ants returning, physiology best predicts which ants leave the nest and when. Individual experience is strongly related to physiology. A small number of lean individuals are responsible for most external trips. An individual’s nutrient status could be a useful cue in division of labour, especially when public information from other ants is unavailable.     

Differential sperm expenditure by male sailfin mollies, Poecilia latipinna, in a unisexual–bisexual species complex and the influence of spermiation during mating

Selection should favor strategies that reduce costs associated with spermatogenesis. This is especially true when males are sympatric with closely related species, and must avoid heterospecific matings, as in the unisexual–bisexual species complex of mollies. Male sailfin mollies, Poecilia latipinna, are sexually parasitized by Amazon mollies (P. formosa), and produce more sperm in the presence of female sailfin mollies than in the presence of Amazon mollies. We tested the hypothesis that male sailfin mollies differentially expend sperm when mating with either conspecific or heterospecific females. We measured sperm expenditure by determining the amount of sperm males have remaining after mating. Male sailfin mollies had more sperm available after mating with female sailfin mollies than after mating with Amazon mollies. While this result could indicate higher sperm expenditure to Amazon mollies, males mating with female sailfin mollies had more sperm available after mating than their baseline sperm reserves. Spermiation, the last stage of spermatogenesis, could be triggered by physical contact with females, and could increase sperm availability during mating. We examined the relationship between sperm availability and the amount of time that males mated with females. We found that sperm availability increased as mating trial time increased with female sailfin mollies, but not with Amazon mollies. Spermiation in the presence of conspecific female stimuli could reduce physiological costs associated with spermatogenesis while increasing the amount and quality of sperm available for sperm competition. We suggest that future studies examining sperm priming and expenditure should consider the potential for spermiation.     

Implications from Mitochondrial DNA for Management to Conserve the Eastern Barred Bandicoot (Perameles gunnii)

On mainland Australia, the eastern barred bandicoot, Perameles gunnii , is confined to a relic wild population numbering less than 100 individuals in the city of Hamilton. Animals derived from this population are being bred in captivity in order to promote their recovery. The species also exists in Tasmania, where tittle is known of its conservation and taxonomic status. Mitochondrial DNA variability was compared within and between populations of P. gunnii using restriction fragment length polymorphisms. Genetic variability was found to be high among P. gunnii in Hamilton compared to those in Tasmania (higher diversity index, nucleotide sequence divergence, and greater number of haplotypes), despite the known decline and subdivision of the Hamilton population. Restriction fragment length polymorphisms distinguished animals from the east and the west of Hamilton and from the north and south of Tasmania. Nucleotide sequence divergence was substantial (2.2–2.5%) between Hamilton and Tasmania. Implications are that captive breeding and reintroduction should be designed to genetically represent the structure within Hamilton in order to minimize inbreeding and that the introduction of Tasmanian P. gunnii would not benefit the Hamilton population. It is concluded that mitochondrial DNA markers clearly can provide useful information about the history and current status of endangered marsupial populations, to the benefit of conservation management.     

A new dose model for assessment of health risk due to contaminants in air

The problem of making quantitative assessments of the risks associated with human exposure to toxic contaminants in the environment is a pressing one. This study demonstrates the capability of a new computational technique involving the use of fuzzy logic and neural networks to produce realistic risk assessments. The systematic analysis of human exposure involves the use of measurements and models, the results of which are sometimes used in regulatory decisions or in the drafting of legislation. Because of limited scientific understanding, however, interpretation of models often involves substantial uncertainty. Extensive measurement programs can be very expensive. The high complexity and inherent heterogeneity of exposure analysis is still a major challenge. The approach to this challenge tested here is to use a new model incorporating sophisticated artificial intelligence algorithms. Exposure assessment often requires that a number of factors be evaluated, including exposure concentrations, intake rates, exposure times, and frequencies. These factors are incorporated into a system that can "learn" the relevant relationships based on a known data set. The results can then be applied to new data sets and thus be applied widely without the need for extensive measurements. In this analysis, an example is developed for human health risk through inhalation exposure to benzene from vehicular emissions in the cities of Auckland and Christchurch, New Zealand. Risk factors considered were inhaled contaminant concentration, age, body weight, and activity patterns of humans. Three major variables affecting the inhaled contaminant concentration were emissions (mainly from motor vehicles), meteorology (wind speed, temperature, and atmospheric stability), and site factors (hilly, flat, etc.). The results are preliminary and used principally to demonstrate the technique, but they are very encouraging.     

Regulation of honey bee division of labor by colony age demography

The age at which worker honey bees begin foraging varies under different colony conditions. Previous studies have shown that juvenile hormone (JH) mediates this behavioral plasticity, and that worker-worker interactions influence both JH titers and age at first foraging. These results also indicated that the age at first foraging is delayed in the presence of foragers, suggesting that colony age demography directly influences temporal division of labor. We tested this hypothesis by determining whether behavioral or physiological development can be accelerated, delayed, or reversed by altering colony age structure. In three out of three trials, earlier onset of foraging was induced in colonies depleted of foragers compared to colonies depleted of an equal number of bees across all age classes. In two out of three trials, delayed onset of foraging was induced in colonies in which foragers were confined compared to colonies with free-flying foragers. Finally, in three out of three trials, both endocrine and exocrine changes associated with reversion from foraging to brood care were induced in colonies composed of all old bees and devoid of brood; JH titers decreased and hypopharyngeal glands regenerated. These results demonstrate that plasticity in age-related division of labor in honey bee colonies is at least partially controlled by social factors. The implications of these results are discussed for the recently developed ‘‘activator-inhibitor” model for honey bee behavioral development. Received: 8 November 1995/Accepted after revision: 10 May 1996     

Abnormal gonadal morphology in intersex,<Emphasis Type="Italic"> Echinogammarus marinus</Emphasis> (Amphipoda): a possible cause of reduced fecundity?

Recent reports have demonstrated a cost associated with intersexuality in Amphipoda, including reduced fecundity and fertility. In this study, the gross morphology of the gonads in normal and intersex Echinogammarus marinus (Amphipoda) were compared to determine whether resource allocation to gonadal tissue accounted for this reduced fitness. Evidence for the presence of the male sex-determining hormone, androgenic gland hormone (AGH), was compared between sexual phenotypes using MALDI mass spectrometry. Two distinct intersex phenotypes (male intersex and female intersex) were found, with variation in gonadal structure corresponding with external phenotype. Examination of male intersexes revealed normal testicular development (testes, seminal vesicles and vas deferens), but also revealed the formation of an oviduct. Ovaries of intersex females showed normal ovarian development, but were reduced in length by approximately 20% due to the presence of vas deferens. The number of vas deferens in intersex females was equal to the number (one or two) of genital papillae. We hypothesise that the reduced ovarian length observed in intersex females is a likely cause of the reduced brood size previously reported in intersex females of this species. Variation in the sexual phenotype corresponded both to development of the androgenic gland and to expression of a peptide fragment corresponding to the A chain of androgenic gland hormone (AGH). Androgenic glands and a putative AGH peptide were present in males. However, in both normal and intersex females, the androgenic glands were only present in a rudiment form and the peptide was not detected. Intersex males were found to possess abnormal glands that appeared hypertrophied. However, AGH peptides were not detected, supporting the suggestion that the intersex phenotype is manifested via perturbations of AGH.An erratum to this article can be found at Communicated by J.P. Thorpe, Port Erin     

Effects of worker genotypic diversity on honey bee colony development and behavior (Apis mellifera L.)

There have been numerous reports of genetic influences on division of labor in honey bee colonies, but the effects of worker genotypic diversity on colony behavior are unclear. We analyzed the effects of worker genotypic diversity on the phenotypes of honey bee colonies during a critical phase of colony development, the nest initiation phase. Five groups of colonies were studied (n = 5–11 per group); four groups had relatively low genotypic diversity compared to the fifth group. Colonies were derived from queens that were instrumentally inseminated with the semen of four different drones according to one of the following mating schemes: group A, 4 A-source drones; group B, 4 B-source drones; group C, 4 C-source drones; group D, 4 D-source drones; and group E, 1 drone of each of the A-D drone sources. There were significant differences between colonies in groups A-D for 8 out of 19 colony traits. Because the queens in all of these colonies were super sisters, the observed differences between groups were primarily a consequence of differences in worker genotypes. There were very few differences (2 out of 19 traits) between colonies with high worker genotypic diversity (group E) and those with low diversity (groups A-D combined). This is because colonies with greater diversity tended to have phenotypes that were average relative to colonies with low genotypic diversity. We hypothesize that the averaging effect of genotypic variability on colony phenotypes may have selective advantages, making colonies less likely to fail because of inappropriate colony responses to changing environmental conditions.     

Effects of intracolony variability in behavioral development on plasticity of division of labor in honey bee colonies

There is a genetic component to plasticity in age polyethism in honey bee colonies, such that workers of some genotypes become precocious foragers more readily than do workers of other genotypes, in colonies lacking older bees. Using colonies composed of workers from two identifiable genotype groups, we determined that intracolony differences in the likelihood of becoming a precocious forager are a consequence of differences in rates of behavioral development that are also evident under conditions leading to normal development. An alternative hypothesis, that differences in the likelihood of becoming a precocious forager are due to differences in general sensitivity to altered colony conditions, was not supported. In three out of three trials, workers from the genotype group that was more likely to exhibit precocious foraging in single cohort colonies also foraged at relatively younger ages in colonies in which workers exhibited normal behavioral development. In contrast, in three out of three trials, workers from the genotype group that was more likely to exhibit precocious foraging in single-cohort colonies did not show disproportionately more overaged nursing in colonies in which workers exhibited delayed development. These results indicate that genotypic differences in plasticity in age-related division of labor are based on genotypic differences in rates of behavioral development.     

Prenatal diagnosis of osteogenesis imperfecta type III

Ultrasonographic and radiographic evaluation of a fetus at risk for osteogenesis imperfecta (O.I) type III was performed. Real-time ultrasound measurements at 15 weeks gestation were interpreted as normal, but at 20 and 22 weeks of gestation revealed marked shortening of the long bones and deformity of the femurs. The findings were confirmed by fetal radiography at 22 weeks gestation. Radiographic and histologic changes characteristic of O.I. were observed in the aborted fetus. Thus the antenatal manifestations of O.I. type III maybe severe enough to make prenatal diagnosis possible in the second trimester for families at risk for recurrence of this disorder.