Caste regulation in the pharaoh's ant Monomorium pharaonis: the influence of queens on the production of new sexual forms

ABSTRACT. In colonies of Monomorium pharaonis (L.), the presence of fertile queens normally prevents the production of new queens and males (sexuals). The inhibitory effect of the presence of fertile queens is not shared by virgin queens or by freshly killed dead queens, but can be substituted by the artificial introduction of eggs. Moreover, fertile queens made sterile by exposure to a Juvenile Hormone analogue lose their ability to prevent the rearing of new sexuals. Thus, the inhibitory action of queens is mediated via the eggs that they lay, such that the rearing of new sexuals is limited to the times when either the number or fecundity of extant queens is reduced. Workers appear able to detect changes in the number of eggs present in the colony. When eggs are plentiful (i.e. when queens are laying at maximum rates), only worker brood is reared, but if egg numbers decline, workers will respond by rearing a new batch of males and queens. This method of caste regulation is highly efficient, and the inhibitory action of eggs on the production of sexuals is comparable to the action of 'queen substances' reported in some other social insects.     

Tracing Genetic Lineages of Captive Desert Tortoises in Arizona

Abstract: We genotyped 180 captive desert tortoises (Gopherus agassizii) from Kingman (n = 45), Phoenix (n = 113), and Tucson (n = 22), Arizona, USA, to determine if the genetic lineage of captives is associated with that of wild tortoises in the local area (Sonoran Desert). We tested all samples for 16 short tandem repeats and sequenced 1,109 base pairs of mitochondrial DNA (mtDNA). To determine genetic origin, we performed assignment tests against a reference database of 997 desert tortoise samples collected throughout the Mojave and Sonoran Deserts. We found that >40% of our Arizona captive samples were genetically of Mojave Desert or hybrid origin, with the percentage of individuals exhibiting the Mojave genotype increasing as the sample locations approached the California, USA, border. In Phoenix, 11.5% were Sonoran–Mojave crosses, and 8.8% were hybrids between desert tortoise and Texas tortoise (G. berlandieri). Our findings present many potential implications for wild tortoises in the Sonoran Desert of Arizona. Escaped or released captive tortoises with Mojave or hybrid genotypes have the potential to affect the genetic composition of Sonoran wild populations. Genotyping captive desert tortoises could be used to inform the adoption process, and thereby provide additional protection to native desert-tortoise populations in Arizona.     

Aglaophyton major, a non-vascular land-plant from the Devonian Rhynie Chert

EDWARDS, D. S., 1986. Aglaophyton major , a non-vascular land-plant from the Devonian Rhynie Chert. The genus Aglaophyton is described to accommodate the plant formerly known as Rhynia major , re-examined using new material and techniques. The plant, which is a sporophyte, is suggested to have been shorter than originally supposed and to have formed extensive stands of decumbent axes. These features, with information on the angle of dichotomous branching and the frequency of sporangia, are incorporated into a new reconstruction of the plant. The conducting strand within the axes consists of three zones, a central region of thin-walled cells, a middle region of thick-walled cells and an outer region of thin-walled cells. There is no indication of differential wall thickenings in the cells of any of these zones and the strand is interpreted in terms of a bryophytic conducting strand, the inner two regions being comparable to hydroids and the outer region comparable to the leptoids found in polytrichaceous moss gametophytes and sporophyles. The plant thus exhibits characters intermediate between tracheophytes and some mosses and cannot be considered a member of either group; at the present time it is not assigned to a higher category. A rediagnosis of Rhynia gwynne-vaughanii , based on published results and new data, is also included.     

A new zosterophyll from the Lower Devonian of Wales

A new monotypic genus is described from impression and compression fossils preserved in the Senni Beds of the Lower Old Red Sandstone of S Wales. The new species has scattered reniform lateral sporangia suggesting zosterophyll affinity, but supporting anatomical evidence is lacking. The axes of the plant are characterized by occasional large surface protuberances, sometimes extended into lateral projections of variable length and morphology. Taphonomic factors account for some of the observed features of the fossils, and their unusual orientation in the sediment suggests that Tarella may have grown on exposed point bars.     

Studies on the Organisation of the Chicken Genome and its Expression during Myogenesis in vitro

DNA from the chicken genome was analysed both by isopycnic centrifugation in cesium salt density gradients and by reassociation analysis using hydroxyapatite (HAP) chromatography. Centrifugation in neutral CsCl revealed a single non-Gaussian band skewed toward the heavy side, but no discrete satellite components. In heavy metal (Ag⁺ or Hg⁺⁺)-Cs₂SO₄ gradients, 4–8 satellite bands were revealed, comprising 5–9% of the total DNA. Purification of the satellites and recentrifugation in neutral CsCl demonstrated that 80–90% of this DNA would band in the shoulder, with the remainder in the main band. These satellites can account at most for 30% of the heavy shoulder DNA, thus most of the heavy shoulder DNA must be of lower repetition frequencies.
Reassociation analyses of chicken DNA demonstrated that the complexity of the non-repetitive DNA is 9.49 × 10⁸ nucleotide pairs, equivalent to about 90% of the haploid genome. Repetitive DNA comprises only 8–10% of the genome and has the following composition, relative to total DNA: 3.7% intermediate repetitive, 1.9% highly repetitive, and 3.9%"zero-time binding" DNA. This unusually low repetitive DNA content may be related to the small genome size of chickens, relative to other vertebrates, and to the presence of many microchromosomes in the chicken karyotype.
Total cell RNA extracted from prefusion myoblasts, post-fusion myotubes, and myoblasts grown in BrdU was incubated in large excess with ³H-TdR labelled non-repetitive DNA and the resulting hybrids assayed by HAP chromatography. The amount of non-repetitive DNA represented in the RNA was found to increase from 7–8% in the myoblast stage to 10–11% in myotubes. An even smaller proportion, about 5%, is represented in the RNA of myoblasts prevented from differentiating by growth in BrdU.     

Re‐contemplate an entangled bank: The Power of Movement in Plants revisited

We review the ways in which two of Charles Darwin's lesser known works, The Movement and Habit of Twining Plants and The Power of Movement in Plants, stimulated 20th and 21st century research findings and philosophies. The legacy of Darwin's work permeates research on plant movement. For example, Darwin's demonstration that coleoptiles and roots fail to bend in response to light or gravity if their tips are removed helped researchers work toward the discovery of auxin and other plant hormones. Darwin's methodical observations on vine twining directions and circumnutation foreshadowed the recent discovery that 92% of vines twine in right‐handed helices, regardless of their location on the planet. Finally, Darwin's observation of the similarity between plant responses to stimuli and the responses of lower animals foreshadowed the current debate over whether plants have ‘behaviour’. Thus, even Darwin's lesser‐known works continue to influence research in the present day. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 111–118.