Some structural and functional properties of nerves and muscles in the oviduct of the pink bollworm moth,Pectinophora gossypiella (Saund.)

The oviduct of the pink bollworm is innervated by an intrinsic neural network arising from 4 nerves from the terminal ganglion. The nerve tracts in this network often contained elliptical swellings, each with a central nucleus.

A distinct surface topography was evident in the muscular sheath of the common and lateral oviduct. A very thin muscular envelope consisting of an inner band of circular fibers and an outer layer of longitudinal fibers was also found in the ovarioles. Although conventional A and I bands were recognized, the z-disk was composed of an irregular and loose meshwork, suggesting that the visceral muscles of the reproductive tract possess super-contracting properties. Even when the oviduct and the ovarioles were isolated from the central nervous system, an endogenous rhythmic activity was evident.

Two types of spontaneous excitatory postsynaptic potentials were detected in the oviduct. The type most frequently observed had a complex of multiple spikes with a duration of 18–32 msec. The other type had a saw-tooth shape and a duration of 80–160 msec. Spontaneous action potentials with a plateau-type configuration and a duration of 280–320 msec were also observed. After the removal of the terminal ganglion, endogenous electrical activity distinct from the events just described was found in the midand upper common oviduct. Such discharges seem to originate from the intrinsic neural network and had durations similar to those found for neurosecretory cells.     

Assessment of soil calcium status in red spruce forests in the northeastern United States

Long-term changes in concentrations of available Ca in soils of redspruce forests have been documented, but remaining questions aboutthe magnitude and regional extent of these changes have precluded anassessment of the current and future status of soil Ca. To addressthis problem, soil samples were collected in 1992—93from 12 sites in New York, Vermont, New Hampshire, and Maine toprovide additional data necessary to synthesize all availableresearch results on soil Ca in red spruce forests. Sites werechosen to encompass the range of environmental conditionsexperienced by red spruce. Concentrations of exchangeableCa ranged from 2.13 to 21.6 cmol_ckg^–1 in the Oa horizon, and from 0.11 to 0.68cmol_c kg^–1 in the upper 10 cm of theB horizon. These measurements expanded the range of exchangeable Ca reported in the literature for both horizons in northeastern redspruce forests. Exchangeable Ca was the largest Ca fraction in theforest floor at most sites (92% ofacid-extractableCa), but mineral Ca was the largest fraction at the three sites that also had the highest mineral-matter concentrations. Theprimary factor causing variability in Ca concentrations among siteswas the mineralogy of parent material, but exchangeable concentrationsin the B horizon of all sites were probably reduced by acidicdeposition. Because the majority of Ca in the forest floor isin a readily leachable form, and Ca inputs to the forest floor from the mineral soil and atmospheric deposition have beendecreasing in recent decades, the previously documented decreasesin Ca concentrations in the forest floor over previous decades mayextend into the future.     

Chemosensory Adaptation to Lysozyme and GTP Involves Independently Regulated Receptors in Tetrahymena thermophila

ABSTRACT. Chemosensory adaptation is seen in Tetrahymena thermophila following prolonged exposure (ten minutes) to micromolar concentrations of the chemorepellents lysozyme or guanosine triphosphate (GTP). Since these cells initially show repeated backward swimming episodes (avoidance reactions) in these repellents, behavioral adaptation is seen as a decrease in this repellent-induced behavior. The time course of this behavioral adaptation is paralleled by decreases in the extents of surface binding of either [³²P]GTP or [³H]lysozyme in vivo. Scatchard plot analyses of repellent binding in adapted cells suggests the behavioral adaptation is due to a dramatic decrease in the number of surface binding sites, as represented by decreased Bmax values. The estimated K_D values for nonadapted cells are 6.6 μM and 8.4 μM for lysozyme and GTP binding, respectively. Behavioral adaptation and decreased surface receptor binding are specific for each repellent. The GTP adapted cells (20 μM for ten minutes) still respond behaviorally to 50 μM lysozyme and bind [³H]lysozyme normally. Lysozyme adapted cells (50 μM for ten minutes) still bind [³²P]GTP and respond behaviorally to GTP. All the behavioral and binding changes seen are also reversible (deadaptation). Neomycin was shown to be a competitive inhibitor of [³H]lysozyme binding and lysozyme-induced avoidance reactions, but it had no effect on either [³²P]GTP binding or GTP-induced or avoidance reactions. These results are consistent with the hypothesis that there are two separate repellent receptors, one for GTP and the other for lysozyme, that are independently downregulated during adaptation to cause specific receptor desensitization and consequent behavioral adaptation.     

Convergence and parallelism among cicadas of Argentina and the southwestern United States (Hemiptera: Cicadoidea)

Cicadas of the genera Derotettix in Argentina and Okanagodes in the south-western United States resemble each other in colour, live on salt-tolerant plants ( Atriplex spp. etc.), nearly match the colour of their respective host plants and produce songs above the range of avian hearing. The Argentine cicadas are smaller, but have nearly identical thermal limits for activity measured by the minimum temperature for flight (20–24 °C) and a body temperature at heat torpor (48–49 °C). The species shift activity from basking sites to shade at temperatures above 37 °C, although O .  gracilis rises to a significantly higher temperature (40.7 °C) than its congener (38.2 °C) or Derotettix (37.2 °C). The thermal tolerances are the highest reported for cicada species. A third group using halophytes in Argentina ( Babras sonorivox ) has similar temperature tolerances and is cryptically coloured. The genera are convergent with respect to morphology, coloration, body size, behaviour, habitat choice and host plant selection. The similarities of thermal tolerances and their influence on behaviour can be viewed as parallelism because the underlying mechanisms are the same in all species studied.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 281–288.     

Growth and provisioning strategies of Northern Fulmars Fulmarus glacialis

Growth and foraging strategies in procellariiforms show a great deal of variation, but the fulmarine petrels are notable in that chicks are fed frequently and develop unusually rapidly. This study examined age-related and daily variation in provisioning of the Northern Fulmar Fulmarus glacialis throughout the chick-rearing period at Fair Isle in 1997. In common with many other petrels, meal mass showed an initial rise with age, probably because of a gradual increase in chick gut capacity, but then levelled off. By comparison, feeding frequency showed little age-specific variation until chicks reached the oldest age-class, when the number of meals declined to less than a third of the previous level as chicks underwent mass recession prior to fledging. Compared with the limited day-to-day variation in mean provisioning rates for the whole sample, food delivery to particular chicks was much more variable, suggesting that differences in feeding rates were determined by stochastic factors influencing the feeding success of individual parents. The caloric density of feeds and their size in relation to adult mass were lower in Northern Fulmars than in most other Procellariiformes. This implies that adults are not heavily dependent on stomach oil formation to raise the energy content of the payload, but rely on a high feeding frequency to maintain adequate rates of energy transfer to chicks.     

Egg maturation strategy and survival trade-offs in holometabolous insects: a comparative approach

One of the key predictions of general life-history theory is that reproduction incurs a survival cost. Although there is a convincing body of evidence to support this prediction at the intraspecific level in insects, evidence at the interspecific level is relatively scarce, as is the case for other animals. By employing two methods of phylogenetically controlled analysis, we demonstrate the existence of a negative correlation between life-span and early life investment in reproduction, across a wide diversity of Lepidoptera. The measure of initial reproductive effort used was the 'ovigeny index', defined as the proportion of the lifetime potential egg complement that is mature (ready to lay) upon female emergence. We present a graphical model for holometabolous insects, illustrating the trade-offs that are hypothesized to occur among capital resources (soma vs non-soma and initial eggs vs storage) in relation to variation in ovigeny index. These trade-offs, for which there is some empirical support, are postulated to underlie the life-span/ovigeny index relationship observed in the Lepidoptera and also in other insect orders.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 293–302.     

Colony characteristics influence the risk of nest predation of a polydomous ant by a monotreme

Although predation of individual social insect workers has little effect on colony fitness, nest predation may be a significant selective agent because it can result in substantial loss of reproductive success. Surprisingly, the consequences of predation on social insect nests are poorly understood. In the present study, we investigate the factors that correlate with the probability of predation by echidnas, Tachyglossus aculeatus , on nests and colonies of the facultatively polydomous meat ant, Iridomyrmex purpureus. In particular, we investigate whether colony fragmentation provides a mechanism for reducing the costs of echidna predation. Over 2 years, 138 of the 140 colonies on our study site were depredated. Nest predation was most common in woodlands but with no obvious seasonal patterns. The probability of nest predation was positively correlated with the size of the nest, and negatively correlated with the density of surrounding nests. Although polydomous colonies are at a similar risk of predation by echidnas, the proportion of depredated nests is negatively correlated with the number of nests; thus, the probability that one or more nests avoid predation is increased with increasing nest numbers. Surprisingly, we found no influence of the level of echidna predation on colony growth, measured by either changes in the number of nests or the number of nest entrance holes.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 92 , 1–8.