Switch from Asexual to Sexual Reproduction in the Planarian Dugesia ryukyuensis

Many metazoans convert the reproductive modes presumably depending upon the environmental conditions and/or the phase of life cycle, but the mechanisms underlying the switching from asexual to sexual reproduction, and vice versa, remain unknown. We established an experimental system, using an integrative biology approach, to analyze the mechanism in the planarian, Dugesia ryukyuensis (Kobayashi et al., 1999). Worms of exclusively asexual clone (OH strain) of the species gradually develop ovaries, testes and other sexual organs, then copulate and eventually lay cocoons filled with fertilized eggs, if they are fed with sexually mature worms of Bdellocephala brunnea (an exclusively oviparous species). This suggests the existence of a sexualizing substance(s) in sexually mature worms. Random inbreeding of experimentally sexualized worms (acquired sexuals) produces an F1 population of spontaneous sexuals (innate sexuals) and asexuals in a ratio of approximately 2:1. All regenerants from various portions of innate sexuals become sexuals. In the case of acquired sexuals, head fragments without sexual organs regenerated into asexuals though regenerants from other portions became sexuals. Thus, we conclude that neoblasts, the totipotent stem cells in the planarians, of acquired sexuals remain "asexual" and the worms require external supply of a sexualizing substance for the differentiation of sexual organs and gametes. On the other hand, some, if not all, neoblasts in innate sexuals are somehow "sexual" and do not require external supply of a sexualizing substance for the eventual differentiation of themselves and/or other neoblasts into sexual organs and gametes. It is also shown that sexuality in acquired sexuals is maintained by the putative sexualizing substance(s) of their own. The sexualization is closely coupled with cessation of fission, and the worms seem to have an unknown way of controlling the karyotype. Our integrative approach integrates multiple fields of study, including classic breeding, regeneration, and genetics experiments, as well as karyotyping, and biochemical and molecular biological analyses; none of which would have revealed much about the intricate mechanisms that regulate sex and fission in these animals.     

Positive Relationship between Signalling Time and Flight Capability in the Texas Field Cricket, Gryllus texensis

A trade‐off between dispersal ability and reproduction is generally thought to explain the persistence of wing dimorphism in insects, although this trade‐off has received minimal attention in male insects. Research on male sand cricket, Gryllus firmus, supports the trade‐off hypothesis insofar as flight capable cricket’s spend significantly less time signalling for potential mates than their flightless counterparts. By contrast, here I show that this expected trade‐off between signalling time and wing dimorphism does not exist in a male congener, the Texas field cricket (Gryllus texensis). In G. texensis, flight capable males signal twice as often as flightless males. Thus, unless male G. texensis express trade‐offs between dispersal ability and other, presently unmeasured components of reproduction, the trade‐off hypothesis may not explain the persistence of wing dimorphism in all male insects.     

Size-Related Advantages for Reproduction in a Slightly Dimorphic Raptor: Opposite Trends between the Sexes

Despite many comparative analyses and more than 20 proposed hypotheses, there is still little consensus over the factors promoting the evolution of reversed sexual dimorphism (RSD) in raptorial species. Furthermore, intrapopulation studies, which may elucidate how RSD is maintained once evolved, have been surprisingly scarce and only focused on a handful of species with medium to high dimorphism. We examined the reproductive advantages associated with body size and condition, measured in the pre‐laying period, in a diurnal raptor with low sexual dimorphism, the black kite (Milvus migrans). The study population was essentially monomorphic in size. For females, there was an evidence of reproductive benefits associated with larger size and/or with better body condition. Larger females had also access to higher quality partners and territories, consistent with the ‘intrasexual selection’ hypothesis, by which members of the larger sex enjoy size‐related advantages in intrasexual competition over a scarce resource, the smaller sex. Opposite trends emerged for males: smaller, leaner males had higher breeding output, consistent with the ‘small efficient male’ hypothesis. Overall, the fact that we observed in an essentially monomorphic population the same selection pressures previously found in species with marked dimorphism suggests that such reproductive advantages may be counterbalanced in our study model by opposite selection pressures during other stages of the life cycle. This casts some doubts on the evolutionary significance of studies focusing exclusively on reproduction and calls for the need of more comprehensive analyses incorporating trait‐mediated differentials in survival and recruitment.     

Intermediary Metabolism and Life History Trade-offs: Lipid Metabolism in Lines of the Wing-polymorphic Cricket, Gryllus firmus, Selected for Flight Capability vs. Early Age Reproduction

The extent to which modifications in intermediary metabolismcontribute to life history variation and trade-offs is an importantbut poorly understood aspect of life history evolution. Artificialselection was used to produce replicate genetic stocks of thewing-polymorphic cricket, Gryllus firmus, that were nearly pure-breedingfor either the flight-capable (LW[f]) morph, which delays ovariangrowth, or the flightless (SW) morph, which exhibits enhancedearly-age fecundity. LW(f) lines accumulated substantially moretriglyceride, the main flight fuel in Gryllus, compared withSW-selected lines, and enhanced accumulation of triglyceridewas strongly associated with reduced ovarian growth. Increasedtriglyceride accumulation in LW(f) lines resulted from elevatedde novo biosynthesis of fatty acid and two morph-specific trade-offs:(1) greater proportional utilization of fatty acid for glyceridebiosynthesis vs. oxidation, and (2) a greater diversion of fattyacids into triglyceride vs. phospholipid biosynthesis. Eventhough SW lines produced less total lipid and triglyceride,they produced more phospholipid (important in egg development)than did LW(f) lines. Differences between LW(f) and SW morphsin lipid biosynthesis resulted from substantial alterationsin the activities of all studied lipogenic enzymes, a resultthat is consistent with expectations of Metabolic Control Theory.Finally, application of a juvenile hormone analogue to LW(f)females produced a striking SW phenocopy with respect to allaspects of lipid metabolism studied. Global alterations of lipidmetabolism, most likely produced by alterations in endocrineregulation, underlie morph specializations for flight vs. early-agefecundity in G. firmus. Modification of the endocrine controlof intermediary metabolism is likely to be an important mechanismby which intermediary metabolism evolves and contributes tolife history evolution.     

Periodic Tail Motion Linked to Wing Motion Affects the Longitudinal Stability of Ornithopter Flight

During slow level flight of a pigeon,a caudal muscle involved in tail movement,the levator caudae pars vertebralis,is activated at a particular phase with the pectoralis wing muscle.Inspired by mechanisms for the control of stability in flying animals,especially the role of the tail in avian flight,we investigated how periodic tail motion linked to motion of the wings affects the longitudinal stability of omithopter flight.This was achieved by using an integrative ornithopter flight simulator that included aeroelastic behaviour of the flexible wings and tail.Trim flight trajectories of the simulated ornithopter model were calculated by time integration of the nonlinear equations of a flexible multi-body dynamics coupled with a semi-empirical flapping-wing and tail aerodynamic models.The unique trim flight characteristics of ornithopter,Limit-Cycle Oscillation,were found under the sets of wingbeat frequency and tail elevation angle,and the appropriate phase angle of tail motion was determined by parameter studies minimizing the amplitude of the oscillations.The numerical simulation results show that tail actuation synchronized with wing motion suppresses the oscillation of body pitch angle over a wide range of wingbeat frequencies.     

Critical Periods of Sensitivity of Sexually Dimorphic Spinal Nuclei to Prenatal Testosterone Exposure in Female Rats

Male rats normally have more neurons than do females in two nuclei of the lumbar spinal cord, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). Female rats exposed to testosterone propionate (TP) on the 2 days of gestation (Days 18 and 19) when males normally experience a surge in plasma testosterone showed a maximal increase in both SNB and DLN neuronal number. TP exposure just prior to, or following, Days 18 and 19 led to smaller increments. Administration of a small (5 μg) dose of TP after birth, while having no effect by itself, synergized with prenatal TP to enhance the number of SNB neurons. DLN neurons were less responsive to postnatal TP. The somal and nuclear size of SNB, but not DLN, neurons was increased by perinatal TP. Paradoxically, the number of DLN neurons with large somas (1358 μm²or larger) was reduced by perinatal TP, a finding congruent with a previous report that females and feminized males have more of these large DLN neurons than control males. Our data suggest an exquisite sensitivity of the developing spinal nuclei to the timing of hormonal surges normally found in fetal males. Exposure to androgens during a brief prenatal period is needed to assure responsiveness to the low amounts of androgen circulating during neonatal ontogeny, when the process of sexual differentiation is completed.     

Matching Gas Exchange in the Bat from Flight to Torpor

SYNOPSIS. Many microchiropteran bats can reduce their metabolicrate three orders of magnitude during heterothermic torpor.This extraordinary range provides a unique insight into theadaptability of mammalian ventilatory control and function.To enable powered flight, bats have developed the highest capacitygas exchange system among mammals. However, starving duringwinter may account for the greatest mortality among bats thathibernate, thus imposing a strong selective pressure to decreasemetabolic cost during torpor. This high capacity gas exchangesystem must therefore operate efficiently at very reduced rates,despite conflicting mechanical constraints imposed by an enormousfunctional overhead. The bat surmounts this dilemma by adjustingits control strategy to breathe intermittently during torpor.This allows instantaneous breathing rates and tidal volumesnear predicted optimal levels. In addition, a passive oxygeninflux coupled with a high acidotic tolerance facilitates longerintervals between the breathing bouts. The acidotic tolerancesupports the endurance of these apneas because the passive effluxof carbon dioxide does not match the rate of oxygen influx.The acidotic tolerance further helps by allowing carbon dioxideto enrich the alveolar gas during apnea to levels above thatof a nonacidotic, continuous pattern of breathing. Thus, thebat's carbon dioxide load can be cleared in fewer breaths whenbreathing resumes. By efficiently controlling a high capacitygas exchange system to meet the minuscule demands during torpor,the bat demonstrates how physiological control strategies canadapt to overcome limitations imposed by conflicting selectionpressures.     

Identification of a Major Dimorphic Region in the Functionally Critical N-Terminal ID1 Domain of VAR2CSA

The VAR2CSA protein of Plasmodium falciparum is transported to and expressed on the infected erythrocyte surface where it plays a key role in placental malaria (PM). It is the current leading candidate for a vaccine to prevent PM. However, the antigenic polymorphism integral to VAR2CSA poses a challenge for vaccine development. Based on detailed analysis of polymorphisms in the sequence of its ligand-binding N-terminal region, currently the main focus for vaccine development, we assessed var2csa from parasite isolates infecting pregnant women. The results reveal for the first time the presence of a major dimorphic region in the functionally critical N-terminal ID1 domain. Parasite isolates expressing VAR2CSA with particular motifs present within this domain are associated with gravidity- and parasite density-related effects. These observations are of particular interest in guiding efforts with respect to optimization of the VAR2CSA-based vaccines currently under development.     

The Influence of Weapon Asymmetry on Male-Male Competition Success in a Sexually Dimorphic Insect,the African King Cricket Libanasidus vittatus (Orthoptera: Anostostomatidae)

Journal of Insect Behavior -     

Switch from conventional to distributed kinetics in the bacteriorhodopsin photocycle

Below 195 K, the bacteriorhodopsin photocycle could not be adequately described with exponential kinetics [Dioumaev, A. K., and Lanyi, J. K. (2007) Proc. Natl. Acad. Sci. U.S.A. 104, 9621-9626] but required distributed kinetics, previously found in hemoglobin and myoglobin at temperatures below the vitrification point of the surrounding solvent. The aim of this study is to determine which factors cause the switch from this low-temperature regime to the conventional kinetics observed at ambient temperature. The photocycle was monitored by time-resolved FTIR between 180 and 280 K, using the D96N mutant. Depending on the temperature, decay and temporal redistribution of two or three intermediates (L, M, and N) were observed. Above approximately 245 K, an abrupt change in the kinetic behavior of the photocycle takes place. It does not affect the intermediates present but greatly accelerates their decay. Below approximately 240 K, a kinetic pattern with partial decay that cannot be explained by conventional kinetics, but suggesting distributed kinetics, was dominant, while above approximately 250 K, there were no significant deviations from exponential behavior. The approximately 245 K critical point is >/=10 K below the freezing point of interbilayer water, and we were unable to correlate it with any FTIR-detectable transition of the lipids. Therefore, we attribute the change from distributed to conventional kinetics to a thermodynamic phase transition in the protein. Most probably, it is related to the freezing and thawing of internal fluctuations of the protein, known as the dynamic phase transition, although in bacteriorhodopsin the latter is usually believed to take place at least 15 K below the observed critical temperature of approximately 245 K.     

A Catastrophe Model for the Switch from Vegetative to Reproductive Growth in the Shoot Apex

A mathematical model is constructed to describe the morphopneticswitch that occurs when a vegetative plant apex becomes reproductive.The cusp equation from catastrophe theory is modified, and isused to relate primordial size at initiation to apex size. Theresulting equation may be viewed as an equation of state definingthe allowed organizational modes of the shoot apex. The modelsimulates the growth of the apex from the vetative stage toearly reproductive growth, and makes reasonable predictionsabout apex size and growth rate, primordial sizes, and the lengthsof the plastochron. flowering, mathematical model, catastrophe theory, shoot apex     

A Critical Comparison of Two Long-term Zooplankton Time Series from the Central-west North Sea

Long-term changes in relative and absolute zooplankton abundanceand species composition were compared between the Dove MarineLaboratory and Continuous Plankton Recorder (CPR) time seriesin the central-western North Sea. The two time series employdifferent sampling mechanisms, with the Dove series beng obtainedby net sampling at a fixed station off the Northumberland coast,while the CPR series utilizes a network of fixed towed routes. It was found that there was a significant correlation (r =0.64, P < 0.001) between the relative year-to-year fluctuations of the two series and a significant agreement in the pattern of year-to-year variations in species composition of the dominant taxa (P = 0.01) over the majority of the time period. However, examination of absolute zooplankton abundances found large differences between the two time series. Differences in mesh size and in the sample processing methodologies were not wholly responsible for these. Model-derived catching efficiencies for the two sampling devices suggested that differences in absolute abundances may have been mainly due in some taxa to a greater degree of active avoidance of the CPR sampling device by zooplankton, although it is likely that passive avoidance as a result of hydrodynamic factors has a role.>     

Thermoregulation, Flight, and the Evolution of Wing Pattern in Pierid Butterflies: The Topography of Adaptive Landscapes

SYNOPSIS. This paper describes a case study of adaptation, constraint,and evolutionary innovation in pierid butterflies. I developa framework for discussing these issues that focuses on thequestions: What is the form of the adaptive landscape relatingfitness to phenotypic characters? How do such landscapes differfor evolutionarily related groups? I examine the evolution ofwing pigment patterns and thermoregulatory behavior for butterfliesin two subfamilies in the family Pieridae, with three principalresults. First, I show that thermoregulation can be an importantcomponent of fitness in pierids, and that wing color and thermoregulatorybehavior are important phenotypic characters determining thermoregulatoryperformance and the adaptive landscape. Second, I show how limitson possible variation in wing color and behavior constrain evolutionwithin one subfamily of pierids, and how these constraints areset by the physical and biochemical mechanisms of adaptation.Third, I show how evolutionary innovation may have resultedfrom the addition of a new, behavioral dimension to the landscape,and how this addition has altered the functional interrelationsamong various elements of the wing color pattern. I suggestthat comparative analyses of the form and determinants of theadaptive landscape may be useful in identifying evolutionaryinnovations, and complement theoretical analyses of evolutionarydynamics on such fitness surfaces.     

Depth-Independent Reproduction in the Reef Coral Porites astreoides from Shallow to Mesophotic Zones

Mesophotic coral ecosystems between 30–150 m may be important refugia habitat for coral reefs and associated benthic communities from climate change and coastal development. However, reduced light at mesophotic depths may present an energetic challenge to the successful reproduction of light-dependent coral organisms, and limit this refugia potential. Here, the relationship of depth and fecundity was investigated in a brooding depth-generalist scleractinian coral, Porites astreoides from 5–37 m in the U.S. Virgin Islands (USVI) using paraffin tissue histology. Despite a trend of increasing planulae production with depth, no significant differences were found in mean peak planulae density between shallow, mid-depth and mesophotic sites. Differential planulae production over depth is thus controlled by P. astreoides coral cover, which peaks at 10 m and ~35 m in the USVI. These results suggest that mesophotic ecosystems are reproductive refuge for P. astreoides in the USVI, and may behave as refugia for P. astreoides metapopulations providing that vertical larval exchanges are viable.     

A Simple Flight Mill for the Study of Tethered Flight in Insects

Flight in insects can be long-range migratory flights, intermediate-range dispersal flights, or short-range host-seeking flights. Previous studies have shown that flight mills are valuable tools for the experimental study of insect flight behavior, allowing researchers to examine how factors such as age, host plants, or population source can influence an insects'' propensity to disperse. Flight mills allow researchers to measure components of flight such as speed and distance flown. Lack of detailed information about how to build such a device can make their construction appear to be prohibitively complex. We present a simple and relatively inexpensive flight mill for the study of tethered flight in insects. Experimental insects can be tethered with non-toxic adhesives and revolve around an axis by means of a very low friction magnetic bearing. The mill is designed for the study of flight in controlled conditions as it can be used inside an incubator or environmental chamber. The strongest points are the very simple electronic circuitry, the design that allows sixteen insects to fly simultaneously allowing the collection and analysis of a large number of samples in a short time and the potential to use the device in a very limited workspace. This design is extremely flexible, and we have adjusted the mill to accommodate different species of insects of various sizes.