Reproductive Systems and Sibling Competition in Plants

Abstract Competition among relatives can modify the genetic structure of plant populations; in turn, competitive outcomes can depend on the genetic relatedness of the individuals competing. The offspring from individual parents exhibit a continuum of genetic relatedness, depending on parental reproductive systems. Competition among relatives may have evolutionary significance as a selection pressure; sibling competition, for example, has been invoked to explain the evolution of sexual systems, seed packaging within fruits, seed dispersal dimorphisms, and germination behavior.
Density-dependent fitness consequences of sibling competition have been documented in a population of the annual grass Sporobolus vaginiflorus . This species produces seeds matured in cleistogamous spikelets within leaf sheaths along tillers in autumn: when seeds along the tillers of a maternal parent (i.e. a sibship) germinate in situ the following spring in close proximity to one another, sibling competition results in a high-density zone centered around the original senescent parent. Both intra- and intersibship interactions can occur within a population. Although fitness is much reduced for siblings inside the zone of competition, potential seed rain and net primary productivity per unit area are significantly higher relative to outside the zone. This annual is functionally analogous to a perennial ramet producer with a phalanx growth strategy and the unit of selection may be the sibling group. It is not yet known whether sibling competition is a significant selection pressure in other species, but indirect evidence suggests it may be relatively widespread.     

Vocal Tract Morphology Determines Species-Specific Features in Vocal Signals of Lemurs (Eulemur)

The source-filter theory describes vocal production as a two-stage process involving the generation of a sound source, with its own spectral structure, which is then filtered by the resonant properties of the vocal tract. This theory has been successfully applied to the study of animal vocal signals since the 1990s. As an extension, models reproducing vocal tract resonance can be used to reproduce formant patterns and to understand the role of vocal tract filtering in nonhuman vocalizations. We studied three congeneric lemur species —Eulemur fulvus, E. macaco, E. rubriventer— using morphological measurements to build computational models of the vocal tract to estimate formants, and acoustic analysis to measure formants from natural calls. We focused on call types emitted through the nose, without apparent articulation. On the basis of anatomical measurements, we modeled the vocal tract of each species as a series of concatenated tubes, with a cross-sectional area that changed along the tract to approximate the morphology of the larynx, the nasopharyngeal cavity, the nasal chambers, and the nostrils. For each species, we calculated the resonance frequencies in 2500 randomly generated vocal tracts, in which we simulated intraspecific length and size variation. Formant location and spacing showed significant species-specific differences determined by the length of the vocal tract. We then measured formants of a set of nasal vocalizations (“grunts”) recorded from captive lemurs of the same species. We found species-specific differences in the natural calls. This is the first evidence that morphology of the vocal tract is relevant in generating filter-related acoustic cues that potentially provide receivers with information about the species of the emitter.     

Assessing the Patterns of Evolution in Anuran Vocal Sexual Signals

Many animal species have evolved signalling traits to mediate various intra-specific interactions. Signals are particularly important for inter-sexual selection, where females use male signalling traits to select mates. Female preferences are therefore a major selective force in the evolution of these male signals, and these preferences can facilitate rapid changes in these traits in an evolutionary timeframe. This introduction of high levels of variation in inter-sexual signals may overshadow any phylogenetic patterns present. Such shadowing effects, however, should be dependant on the characteristics of traits (e.g. morphological, physiological and behavioural). Using male advertisement calls from 72 species of anuran amphibians, we tested the levels of phylogenetic signal present for a variety of call features in relation to trait types, and for calls as whole units using phylogenetic principal components analysis. We found that most call features displayed some level of phylogenetic autocorrelation (or signal), with traits that are dependent on morphology having much stronger phylogenetic signals than those based on behaviour. In addition, when calls were analysed as whole units, closely related species were found to be similar to each other, indicating that phylogenetic patterns had not been cancelled out by selection via female preferences. We suggest that signal functions, such as indicating male quality (e.g. mediated by body size) to potential mates, may place constraints on the amount of variation that can be introduced by female preferences. More research, particularly studies on other taxa, will be required to elucidate whether the patterns found in anurans are general across the animal kingdom.     

The Acoustic Structure and Information Content of Female Koala Vocal Signals

Determining the information content of animal vocalisations can give valuable insights into the potential functions of vocal signals. The source-filter theory of vocal production allows researchers to examine the information content of mammal vocalisations by linking variation in acoustic features with variation in relevant physical characteristics of the caller. Here I used a source-filter theory approach to classify female koala vocalisations into different call-types, and determine which acoustic features have the potential to convey important information about the caller to other conspecifics. A two-step cluster analysis classified female calls into bellows, snarls and tonal rejection calls. Additional results revealed that female koala vocalisations differed in their potential to provide information about a given caller’s phenotype that may be of importance to receivers. Female snarls did not contain reliable acoustic cues to the caller’s identity and age. In contrast, female bellows and tonal rejection calls were individually distinctive, and the tonal rejection calls of older female koalas had consistently lower mean, minimum and maximum fundamental frequency. In addition, female bellows were significantly shorter in duration and had higher fundamental frequency, formant frequencies, and formant frequency spacing than male bellows. These results indicate that female koala vocalisations have the potential to signal the caller’s identity, age and sex. I go on to discuss the anatomical basis for these findings, and consider the possible functional relevance of signalling this type of information in the koala’s natural habitat.     

Competition of Multiple Species in Advective Environments

We study the effect of changes in flow speed on competition of an arbitrary number of species living in advective environments, such as streams and rivers. We begin with a spatial Lotka–Volterra model which is described by n reaction–diffusion–advection equations with Danckwerts boundary conditions. Using the dominant eigenvalue \(\lambda \le 0\) of the diffusion–advection operator subject to boundary conditions, we reduce the model to a system of ordinary differential equations. We impose a “transitive arrangement” of the competitors in terms of their interspecific coefficients and growth rates, which means that in the absence of advection, we have the following situation: for all \(1\le i<j\le n\), species i out-competes species j, while species j has higher intrinsic growth rate than species i. Changing advection speed in the original spatial model corresponds to changing the value of \(\lambda \) in the spatially implicit model. Considering the cases of the odd and even n separately, we obtain explicit intervals of the values of \(\lambda \) that allow all n species to be present in the habitat (coexistence interval). Stability of this equilibrium is shown for \(n\le 4\).     

Signals Regulating Multiple Responses to Wounding and Herbivores

Damage inflicted by herbivore feeding necessitates multiple defense strategies in plants. The wound site must be sealed and defense responses mounted against the herbivore itself and against invading opportunistic pathogens. These defenses are controlled both in time and space by highly complex regulatory networks that themselves are modulated by interactions with other signaling pathways. In this review, we describe the signaling events that occur in individual wounded leaves, in systemic unwounded regions of the plant, and between the plant, and other organisms, and attempt to place these events in the context of a coordinated system. Key signals that are discussed include ion fluxes, active oxygen species, protein phosphorylation cascades, the plant hormones jasmonic acid, ethylene, abscisic acid and salicylic acid, peptide signals, glycans, volatile chemicals, and physical signals such as hydraulic and electrical signals. Themes that emerge after consideration of the published data are that glycans and peptide elicitors are likely primary triggers of wound-induced defense responses and that they function through the action of jasmonic acid, a central mediator of defense gene expression, whose effect is modulated by ethylene. In the field, wound signaling pathways are significantly impacted on by other stress response pathways, including pathogen responses that often operate through potentially antagonistic signals such as salicylic acid. However, gross generalisations are not possible because some wound and pathogen responses operate through common jasmonate- and ethylene-dependent pathways. Understanding the ways in which local and systemic wound signaling pathways are coordinated individually and in the context of the plants wider environment is a key challenge in the application of this science to crop-protection strategies.     

Accurate Simulation and Detection of Coevolution Signals in Multiple Sequence Alignments

Background

While the conserved positions of a multiple sequence alignment (MSA) are clearly of interest, non-conserved positions can also be important because, for example, destabilizing effects at one position can be compensated by stabilizing effects at another position. Different methods have been developed to recognize the evolutionary relationship between amino acid sites, and to disentangle functional/structural dependencies from historical/phylogenetic ones.

Methodology/Principal Findings

We have used two complementary approaches to test the efficacy of these methods. In the first approach, we have used a new program, MSAvolve, for the in silico evolution of MSAs, which records a detailed history of all covarying positions, and builds a global coevolution matrix as the accumulated sum of individual matrices for the positions forced to co-vary, the recombinant coevolution, and the stochastic coevolution. We have simulated over 1600 MSAs for 8 protein families, which reflect sequences of different sizes and proteins with widely different functions. The calculated coevolution matrices were compared with the coevolution matrices obtained for the same evolved MSAs with different coevolution detection methods. In a second approach we have evaluated the capacity of the different methods to predict close contacts in the representative X-ray structures of an additional 150 protein families using only experimental MSAs.

Conclusions/Significance

Methods based on the identification of global correlations between pairs were found to be generally superior to methods based only on local correlations in their capacity to identify coevolving residues using either simulated or experimental MSAs. However, the significant variability in the performance of different methods with different proteins suggests that the simulation of MSAs that replicate the statistical properties of the experimental MSA can be a valuable tool to identify the coevolution detection method that is most effective in each case.     

Corticosterone Promotes Scramble Competition Over Sibling Negotiation in Barn Owl Nestlings (Tyto alba)

In species with parental care, siblings compete for access to food resources. Typically, they vocally signal their level of need to each other and to parents, and jostle for the position in the nest where parents deliver food. Although food shortage and social interactions are stressful, little is known about the effect of stress on the way siblings resolve the conflict over how food is shared among them. Because glucocorticoid hormones mediate physiological and behavioral responses to stressors, we tested whether corticosterone, the main glucocorticoid in birds, modulates physical and vocal signaling used by barn owl siblings (Tyto alba) to compete for food. Although corticosterone-implanted (cort-) nestlings and placebo-nestlings were similarly successful to monopolize food, they employed different behavioral strategies. Compared to placebo-nestlings, cort-individuals reduced the rate of vocally communicating with their siblings (but not with their parents) but were positioned closer to the nest-box entrance where parents predictably deliver food. Therefore, corticosterone induced nestlings to increase their effort in physical competition for the best nest position at the expense of investment in sib?Csib communication without modifying vocal begging signals directed to parents. This suggests that in the barn owl stress alters nestlings?? behavior and corticosterone could mediate the trade-off between scramble competition and vocal sib?Csib communication. We conclude that stressful environments may prevent the evolution of sib?Csib communication as a way to resolve family conflicts peacefully.     

Significance of Mother and Sibling Experience for Mating Preferences in the Mallard (Anas platyrhynchos)

Social attachment seems necessary for sexual imprinting. In mallards the likely period of social attachment is from hatching until the broods disperse. The potential imprinting objects are mother and siblings. Four combinations of mother-sibling groups of same and different colour were used (N = 131). The groups were kept together from hatching until the young were 12 weeks old. When sexually mature, the birds' choices of mate were recorded. Colouration is an important cue in mate selection. Both mother and siblings are of importance. The effect of experimental factors cannot be attributed to any particular sex.     

光敏色素互作因子PIFs是整合多种信号调控植物生长发育的核心元件

光敏色素互作因子（PIFs）蛋白家族隶属于bHLH转录因子家族,参与多种信号转导途径,调控植物的生长发育进程,如抑制种子萌发、促进幼苗的暗形态建成和调控开花时间等。作为一个胞内信号调控的重要组分,PIFs广泛参与到由多种植物内源激素如赤霉素、乙烯、生长素、油菜素内酯、脱落酸和外部环境因素如高温、光等所介导的信号网络中。本文AKPIFs的结构、参与途径及调控植物发育进程3个方面,简要介绍近年来国内外对PIFs在信号网络调控方面的最新研究进展。     

不同分泌信号对豹蛙酶在巴斯德毕赤酵母中分泌效率的影响

目的：研究不同分泌信号对豹蛙酶（ONC）在巴斯德毕赤酵母中分泌效率的影响。方法：根据已知天然ONC的氨基酸序列,结合酵母偏爱密码子,设计并合成了ONC基因序列,通过融合PCR获得了不同分泌信号与ONC的融合基因,将其克隆至表达载体pPIC9k中,然后将线性化的重组表达载体电击转化GS115毕赤酵母感受态细胞,通过SDS-PAGE检测目的蛋白表达量。结果：糖基化ONC表观相对分子质量为（14～16）×103,且其糖基化不均匀,非糖基化蛋白肽链的相对分子质量约为12×103;采用不含EAEA结构的α交配因子作为分泌信号时ONC没有表达,利用含EAEA结构的α交配因子和α交配因子的pre肽作为分泌信号时均能够显著提高其表达量。结论：采用含EAEA结构的α交配因子和α交配因子的pre肽作为分泌信号均能够显著提高ONC在巴斯德毕赤酵母中的表达量。     

Trade-Offs and Upper Limits to Signal Performance during Close-Range Vocal Competition in Gray Tree Frogs Hyla versicolor

Abstract Performance limitations on signal production constrain signal evolution. Variation in signaling performance may be related to signaler quality and therefore is likely to be a salient aspect of communication systems. When multiple signal components are involved in communication, there may be trade-offs between components, and performance can be measured as the degree to which signalers approach the upper limits of the trade-off function. We examined vocal performance in the gray tree frog Hyla versicolor, in which females prefer values of call duration and rate exceeding the usual range of variation within and among males. We recorded interactions between pairs of males calling on mobile platforms that allowed us to manipulate intermale distance and place males in highly competitive environments. We found that, although there was a clear upper boundary on the ability of males to maximize call duration and call rate simultaneously, call effort did not remain constant in this highly competitive situation. Our estimates of an upper limit to vocal performance were corroborated by analyses of calling behavior in the context of close-range mate attraction. We discuss potential constraints on signaling performance and the relevance of this measure of performance for both intrasexual and intersexual communication.     

Call Transmission Efficiency in Native and Invasive Anurans: Competing Hypotheses of Divergence in Acoustic Signals

Invasive species are a leading cause of the current biodiversity decline, and hence examining the major traits favouring invasion is a key and long-standing goal of invasion biology. Despite the prominent role of the advertisement calls in sexual selection and reproduction, very little attention has been paid to the features of acoustic communication of invasive species in nonindigenous habitats and their potential impacts on native species. Here we compare for the first time the transmission efficiency of the advertisement calls of native and invasive species, searching for competitive advantages for acoustic communication and reproduction of introduced taxa, and providing insights into competing hypotheses in evolutionary divergence of acoustic signals: acoustic adaptation vs. morphological constraints. Using sound propagation experiments, we measured the attenuation rates of pure tones (0.2–5 kHz) and playback calls (Lithobates catesbeianus and Pelophylax perezi) across four distances (1, 2, 4, and 8 m) and over two substrates (water and soil) in seven Iberian localities. All factors considered (signal type, distance, substrate, and locality) affected transmission efficiency of acoustic signals, which was maximized with lower frequency sounds, shorter distances, and over water surface. Despite being broadcast in nonindigenous habitats, the advertisement calls of invasive L. catesbeianus were propagated more efficiently than those of the native species, in both aquatic and terrestrial substrates, and in most of the study sites. This implies absence of optimal relationship between native environments and propagation of acoustic signals in anurans, in contrast to what predicted by the acoustic adaptation hypothesis, and it might render these vertebrates particularly vulnerable to intrusion of invasive species producing low frequency signals, such as L. catesbeianus. Our findings suggest that mechanisms optimizing sound transmission in native habitat can play a less significant role than other selective forces or biological constraints in evolutionary design of anuran acoustic signals.     

A Cervid Vocal Fold Model Suggests Greater Glottal Efficiency in Calling at High Frequencies

Male Rocky Mountain elk (Cervus elaphus nelsoni) produce loud and high fundamental frequency bugles during the mating season, in contrast to the male European Red Deer (Cervus elaphus scoticus) who produces loud and low fundamental frequency roaring calls. A critical step in understanding vocal communication is to relate sound complexity to anatomy and physiology in a causal manner. Experimentation at the sound source, often difficult in vivo in mammals, is simulated here by a finite element model of the larynx and a wave propagation model of the vocal tract, both based on the morphology and biomechanics of the elk. The model can produce a wide range of fundamental frequencies. Low fundamental frequencies require low vocal fold strain, but large lung pressure and large glottal flow if sound intensity level is to exceed 70 dB at 10 m distance. A high-frequency bugle requires both large muscular effort (to strain the vocal ligament) and high lung pressure (to overcome phonation threshold pressure), but at least 10 dB more intensity level can be achieved. Glottal efficiency, the ration of radiated sound power to aerodynamic power at the glottis, is higher in elk, suggesting an advantage of high-pitched signaling. This advantage is based on two aspects; first, the lower airflow required for aerodynamic power and, second, an acoustic radiation advantage at higher frequencies. Both signal types are used by the respective males during the mating season and probably serve as honest signals. The two signal types relate differently to physical qualities of the sender. The low-frequency sound (Red Deer call) relates to overall body size via a strong relationship between acoustic parameters and the size of vocal organs and body size. The high-frequency bugle may signal muscular strength and endurance, via a ‘vocalizing at the edge’ mechanism, for which efficiency is critical.     

Allozyme Variation Patterns and Multiple Hybridization Origins: Clonal Variation Among Four Sibling Parthenogenetic Caucasian Rock Lizards

Allozyme electrophoresis of four sibling parthenogenetic Caucasian rock lizards Darevskia unisexualis, D.uzzelli, D.sapphirina, and D.bendimahiensis found seven clones and five variable loci. The data supported the hypothesis that D.raddei and D.valentini are the parental species of all four parthenogens. Variation patterns in Darevskia were summarized. Species that originated from a single F₁ typically consisted of one widespread clone with a few rare clones. Species with multiple origins displayed variation only slightly higher than species with a single origin. This is contrary to other genera of parthenogenetic lizards, in which cases massive clonal variations were observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

RESEARCH PAPER: Multiple Sexual Ornamentation Signals Male Quality and Predicts Female Preference in Minnows

Sexual ornamentation often consists of multiple components. Different sexual signals may indicate different aspects of mate quality or reflect quality in different time scales. On the other hand, same signals can have a dual function and are used both in male–male competition and courtship. Many fish species are capable of rapidly altering their colouration (ephemeral colour changes), but this capability is usually ignored in sexual selection studies. Here, we used experimentally manipulated social environments to study the ephemeral colour changes in multicomponent sexual signals of male minnows (Phoxinus phoxinus) during male–male competition and female choice. We found that the dominant males courted the females more actively and had redder and/or darker skin colouration than the subordinate males. Furthermore, darkness difference between subordinate and dominant males increased in the presence of female, which suggests that the male–male competition may increase the honesty of signalling and thus facilitate female choice. In support of this hypothesis, females had a strong behavioural preference towards the more colourful males, which may indicate female choice. As colourful males often had a higher social status than paler individuals, it is possible that females base their preference on male status, not only the colouration per se. In any case, our results suggest that sexual ornamentation of male minnows may signal status, courting activity and superior quality of the males and that these signals may have a dual function in both male–male competition and female choice. Females preferred different ornamental traits (dark and red colour patterns) relatively equally, indicating that mate choice is based on multiple cues.     

Specialized Motor-Driven dusp1 Expression in the Song Systems of Multiple Lineages of Vocal Learning Birds

Mechanisms for the evolution of convergent behavioral traits are largely unknown. Vocal learning is one such trait that evolved multiple times and is necessary in humans for the acquisition of spoken language. Among birds, vocal learning is evolved in songbirds, parrots, and hummingbirds. Each time similar forebrain song nuclei specialized for vocal learning and production have evolved. This finding led to the hypothesis that the behavioral and neuroanatomical convergences for vocal learning could be associated with molecular convergence. We previously found that the neural activity-induced gene dual specificity phosphatase 1 (dusp1) was up-regulated in non-vocal circuits, specifically in sensory-input neurons of the thalamus and telencephalon; however, dusp1 was not up-regulated in higher order sensory neurons or motor circuits. Here we show that song motor nuclei are an exception to this pattern. The song nuclei of species from all known vocal learning avian lineages showed motor-driven up-regulation of dusp1 expression induced by singing. There was no detectable motor-driven dusp1 expression throughout the rest of the forebrain after non-vocal motor performance. This pattern contrasts with expression of the commonly studied activity-induced gene egr1, which shows motor-driven expression in song nuclei induced by singing, but also motor-driven expression in adjacent brain regions after non-vocal motor behaviors. In the vocal non-learning avian species, we found no detectable vocalizing-driven dusp1 expression in the forebrain. These findings suggest that independent evolutions of neural systems for vocal learning were accompanied by selection for specialized motor-driven expression of the dusp1 gene in those circuits. This specialized expression of dusp1 could potentially lead to differential regulation of dusp1-modulated molecular cascades in vocal learning circuits.     

Diversity of the Vocal Signals of Concave-Eared Torrent Frogs (Odorrana tormota): Evidence for Individual Signatures

Male concave-eared torrent frogs ( Odorrana tormota ) have an unusually large call repertoire and have been shown to communicate ultrasonically. We investigated the individual specificity of male advertisement calls in order to explore the acoustic bases of individual recognition, which was demonstrated in an accompanying study. Vocalizations of 15 marked males were recorded in the field. A quantitative analysis of the signals revealed eight basic call-types. Two of them (the single- and multi-note long-calls) were investigated in more detail. Long-calls were characterized by pronounced and varying frequency modulation patterns, and abundant occurrence of nonlinear phenomena (NLP), i.e., frequency jumps, subharmonics, biphonations and deterministic chaos. The occurrence of NLP was predictable from the contour of the fundamental frequency in the harmonic segment preceding the onset of the NLP, and this prediction showed individual-specific patterns. Fifteen acoustic variables of the long calls were measured, all of which were significantly different among individuals, except biphonic segment duration. Discriminant function analysis (DFA) showed that 54.6% of the calls could be correctly assigned to individual frogs. The correct classification was above chance level, suggesting that individual specificity of calls underlie the ability of males to behaviorally discriminate the vocal signals of their neighbors from those of strangers, a remarkable feat for a frog species with a diverse vocal repertoire. The DFA classification results were lower than those for other anurans, however. We hypothesize that there is a tradeoff between an increase in the fundamental frequency of vocalizations to avoid masking by low-frequency ambient background noise, and a decrease in individual-specific vocal tract information extractable from the signal.