Interspecific variation in plumage colour among birds: species recognition or light environment?

Abstract The traditional explanation for interspecific plumage colour variation in birds is that colour differences between species are adaptations to minimize the risk of hybridization. Under this explanation, colour differences between closely related species of birds represent reproductive character displacement. An alternative explanation is that interspecific variation in plumage colour is an adaptive response to variation in light environments across habitats. Under this explanation, differences in colour between closely related species are a product of selection on signal efficiency. We use a comparative approach to examine these two hypotheses, testing the effects of sympatry and habitat use, respectively, on divergence in male plumage colour. Contrary to the prediction of the Species Isolation Hypothesis, we find no evidence that sympatric pairs of species are consistently more divergent in coloration than are allopatric pairs of species. However, in agreement with the Light Environment Hypothesis, we find significant associations between plumage coloration and habitat use. All of these results remain qualitatively unchanged irrespective of the statistical methodology used to compare reflectance spectra, the body regions used in the analyses, or the exclusion of areas of plumage not used in sexual displays. Our results suggest that, in general, interspecific variation in plumage colour among birds is more strongly influenced by the signalling environment than by the risk of hybridization.     

Fungal entomopathogens as endophytes: can they promote plant growth?

Two experimental replicates were conducted to test whether strains of Beauveria brongniartii (BIPESCO2 and 2843) and Metarhizium brunneum (BIPESCO5) can endophytically colonise Vicia faba plants and improve their growth by comparing them with an endophytic strain of B. bassiana (NATURALIS^®). The plants were inoculated through foliar spray and the effect of inoculation on plant height, leaf pair number, fresh root and shoot weights was measured at 7 and 14 days post inoculation (dpi). Endophytic colonisation of different plant parts with the tested fungal strains were confirmed 7 and 14?dpi through re-isolation of inoculated fungi onto selective media and subsequent Simple Sequence Repeat (SSR) marker-based genetic identification. All tested strains were able to endophytically colonise leaves, stems, and even roots of inoculated plants 7 and 14?dpi, but per cent colonisation varied significantly among strains and plant parts within each sampling date. Foliar inoculation of plants with the tested strains increased plant height, leaf pair number, fresh shoot and root weights; however the increase was not always consistent across sampling dates in both experimental replicates. This study provides the first evidence for the endophytic colonisation of plants with two strains of B. brongniartii, an important biocontrol agent of Melolontha melolontha and other scarab beetles in several European countries, and thus extends previous reports on the ability of entomopathogenic fungi to act as endophytes. It also presents possible explanations for the lack of consistency in the plant growth promotion obtained by the foliar inoculation of entomopathogenic fungi.     

Chick begging as a signal: are nestlings honest?

Begging by dependent avian offspring is known to correlate withhunger level, and parents use this as a signal of brood demandto adjust their chick feeding behavior. While there is informationon how each chick adjusts its begging to its own condition,little is known of how chicks adjust to the state of their nestmates. In two experiments we manipulated the competitive environmentof individual European starling (Sturnus vulgaris) chicks byaltering the state of nest mates while holding the state oftarget chicks constant In the first experiment we placed thetarget chick's nest mates in neighboring nests with brood sizesof two, five, or eight chicks. Following the manipulation wereturned them to their own nests and recorded begging behavioron videotape. In the second experiment we separated a targetchick from its siblings and manipulated feeding level in thelaboratory. The siblings were fed at one of three levels; meanwhile,all the target chicks were fed at the intermediate level. Afterthe manipulation we placed the target chicks with their siblingsand recorded their begging in response to an artificial stimulus.In neither experiment was the begging effort of the unmanipulatedtarget chicks affected by the changes in begging behavior oftheir siblings. This result supports the view that begging isa reliable signal of individual chick state and does not involveresponses to the effort of nest mates.     

Dispersal ability of island endemic plants: What can we learn using multiple dispersal traits?

Island endemic species are expected to have lower dispersal ability than their non-endemic congeners. Several studies have demonstrated differences in diaspore morphology between endemic species and their non-endemic congeners. It is, however, relatively difficult to translate the differences in morphology of the diaspores into differences in dispersal ability. To avoid this problem, we measured directly dispersal values (anemo-, hydro-, exozoo- and endozoo-chory) of 27 pairs of closely related endemic and non-endemic species from Canary Islands. We did not explicitly support the hypothesis about the loss of dispersal ability of island species. The comparison of pairs of endemic and non-endemic species showed the reduction in dispersal potential only for endozoochory. In many cases, endemic species had, in fact, the same or better dispersal ability than their non-endemic congeners. Higher dispersal ability of endemic species could have been evolved as a consequence of species subsequent dispersal to neighboring islands. As a support for this we found that the endemic species dispersing better than their non-endemic congeners also occupy more islands within the archipelago. We conclude that reduction of dispersal ability of species on islands may not be as general as previously expected and we need to take into account multiple species traits to understand the possible evolution of species dispersal potential.     

Dipeptidyl peptidase IV inhibitors: how do they work as new antidiabetic agents?

A number of new approaches to diabetes therapy are currently undergoing clinical trials, including those involving stimulation of the pancreatic beta-cell with the gut-derived insulinotropic hormones (incretins), GIP and GLP-1. The current review focuses on an approach based on the inhibition of dipeptidyl peptidase IV (DP IV), the major enzyme responsible for degrading the incretins in vivo. The rationale for this approach was that blockade of incretin degradation would increase their physiological actions, including the stimulation of insulin secretion and inhibition of gastric emptying. It is now clear that both GIP and GLP-1 also have powerful effects on beta-cell differentation, mitogenesis and survival. By potentiating these pleiotropic actions of the incretins, DP IV inhibition can therefore preserve beta-cell mass and improve secretory function in diabetics.     

A meta-analysis of the traits affecting dispersal ability in butterflies: can wingspan be used as a proxy?

1. Dispersal ability of a species is a key ecological characteristic, affecting a range of processes from adaptation, community dynamics and genetic structure, to distribution and range size. It is determined by both intrinsic species traits and extrinsic landscape-related properties. 2. Using butterflies as a model system, the following questions were addressed: (i) given similar extrinsic factors, which intrinsic species trait(s) explain dispersal ability? (ii) can one of these traits be used as a proxy for dispersal ability? (iii) the effect of interactions between the traits, and phylogenetic relatedness, on dispersal ability. 3. Four data sets, using different measures of dispersal, were compiled from published literature. The first data set uses mean dispersal distances from capture-mark-recapture studies, and the other three use mobility indices. Data for six traits that can potentially affect dispersal ability were collected: wingspan, larval host plant specificity, adult habitat specificity, mate location strategy, voltinism and flight period duration. Each data set was subjected to both unifactorial, and multifactorial, phylogenetically controlled analyses. 4. Among the factors considered, wingspan was the most important determinant of dispersal ability, although the predictive powers of regression models were low. Voltinism and flight period duration also affect dispersal ability, especially in case of temperate species. Interactions between the factors did not affect dispersal ability, and phylogenetic relatedness was significant in one data set. 5. While using wingspan as the only proxy for dispersal ability maybe problematic, it is usually the only easily accessible species-specific trait for a large number of species. It can thus be a satisfactory proxy when carefully interpreted, especially for analyses involving many species from all across the world.     

Bycatch quotas in the Gulf of Mexico shrimp trawl fishery: can they work?

Bycatch of unwanted, prohibited, or protected species is a problem in most commercial fisheries. Trawl fisheries are particularly prone to bycatch problems because trawls are not species-selective. In this paper, I review the history of finfish bycatch research in the Gulf of Mexico shrimp trawl fishery and explore the use of quotas to reduce finfish bycatch by examining four fisheries that currently use bycatch quotas: (1) the arrow squid trawl fishery of New Zealand, which uses fleet bycatch quotas for sea lion bycatch, (2) the Alaskan groundfish trawl fisheries, which use fleet quotas under a vessel incentive program for prohibited species, (3) the groundfish trawl fishery of British Columbia, Canada which uses individual vessel bycatch quotas for prohibited species, and (4) the multi-species trawl fisheries of New Zealand, which use catch balancing, or individual transferable quotas, for most commercially landed species. Based on the bycatch quota experiences in these fisheries, elements of successful bycatch quota programs include: (1) individual accountability, in the form of individual or cooperative bycatch quotas, rather than fleet quotas, (2) 100% observer coverage, (3) relatively small, manageable fleets, (4) limited landing ports that can be easily monitored, particularly if observer coverage is incomplete, (5) reliable enforcement, (6) penalties that are true disincentives, and (7) some flexibility in the system for fishermen to have alternatives to manage their bycatch. The Gulf of Mexico shrimp trawl fishery, with an estimated 20,000 licensed boats, is currently too large for individual bycatch quotas to be practical, although individual or cooperative bycatch quotas would be excellent strategies for reducing the bycatch of a smaller fleet. Mobile closed areas might be beneficial for reducing the bycatch of particular species, but these short-term closures would require real-time monitoring of bycatch rates and vessel monitoring systems on all vessels. However, under any management regime, incentives and/or rigorously enforced disincentives are the key to successful bycatch reduction.     

Canopy ergodicity: can a single leaf represent an entire plant canopy?

While leaves typically emerge near shoot apices around the outer surface of a plant canopy, their relative position “moves” deeper into the canopy as additional leaves emerge. The photosynthetic capacity (A _max) of a given leaf can be expected to decline over time as its relative position (P _r) in the canopy becomes progressively deeper; this can be observed as a spatial gradient with the A _max of leaves declining distally from the shoot apex. As a consequence, we propose that the photosynthetic capacity averaged over a single leaf’s lifespan is equivalent to the average photosynthetic capacity of the entire plant canopy at a given time; in other words, there is an ergodic time to space averaging in the organization and development of plant canopies. We tested this “canopy ergodic hypothesis” in two woody (Alnus sieboldiana and Mallotus japonica) and two herbaceous (Polygonum sachalinensis and Helianthus tuberosus) species by following the photosynthetic capacity in 100 individual leaves from the time of their emergence until their death. We compared the average photosynthetic capacity of individual leaves through time (time-average) to the average photosynthetic capacity of all the leaves along a shoot at the time of emergence of the focal leaf (space-average). We found that A _max and P _r were positively correlated and that the time-averages of three plant species (Alnus, Mallotus, and Helianthus) were not significantly different from the corresponding space-averages, although the averages differed among individual plants. Polygonum, however, did show significant differences between time and space averages. Ergodicity appears to apply to the leaf–canopy relationship, at least approximately—the average photosynthetic capacity of a single leaf through time (time-average) can represent the average photosynthetic capacity of the entire canopy.     

How can the Yelkouan shearwater survive feral cat predation? A meta-population structure as a solution?

The Yelkouan shearwater, Puffinus yelkouan, is an endangered Mediterranean endemic species of burrowing petrel threatened by feral cats. The life-history parameters of a small population of Yelkouan shearwaters on the Mediterranean island, Port-Cros, were studied in conjunction with the diet of feral cats, to examine the birds’ vulnerability to introduced cats. Yelkouan shearwaters were the birds most frequently found in cat scats, with 431 ± 72 birds killed per year, and predation highest during the pre-laying period. A demographic model was created using data for P. yelkouan and for closely related shearwater species. Without cat predation, only two of four survival rate scenarios led to a mean growth rate (λ) ≥ 1. The model was constrained to have a stable population growth rate and used to predict predation scenarios compatible with the observed population stability, because the population under study has remained stable at around 180 pairs for at least 20 years despite feral cat predation. The results of assuming that the population is closed were inconsistent with the estimated mortalities due to feral cats, while it was possible to reconcile the observed numbers of breeding pairs with the observed mortalities due to cats by assuming that Port-Cros Island is a sink sustained by immigration. This illustrates that small colonies may need to be sustained by larger ones to avoid being driven to extinction. Unfortunately, the absence of a large geographic-scale ringing program makes the precise identification of the origin of the immigrants impossible in this case.     

Acoustic signalling in a wolf spider: can signal characteristics predict male quality?

While there has been considerable interest in female choice for male sexual signals, there have been few studies of the underlying information that different aspects of the signal calls convey. Such studies, however, are essential to understand the significance of signals as honest handicaps, arbitrary Fisherian traits and/or in species recognition. We studied the somewhat exceptional system of audible drumming in the wolf spider Hygrolycosa rubrofasciata. We estimated the repeatabilities of signal components, the levels of between-male variance, the symmetry of the signal, the correlations between different aspects of drumming and their correlations with body weight. While in other taxa the frequency of audible signals may convey honest information of male size, in this species signal frequency was not related to male size and had a low repeatability. The pulse rate within each drum was highly repeatable but had a relatively small between-male coefficient of variation. In previous studies on this species, these traits were not important for male mating success. Among the traits directionally preferred by females, signal volume had considerable repeatability. Signal length was repeatable with high variability between males. In one population, signal length and volume were positively correlated with the rate at which males produced the drumming signals, a trait essential for male mating success. Thus, while signal length may reliably indicate male quality, other signal characteristics such as peak frequency and symmetry were not repeatable or were static and not related to any other male traits. Copyright 2000 The Association for the Study of Animal Behaviour.     

Beta-arrestins as regulators of signal termination and transduction: how do they determine what to scaffold?

Over the last decade β-arrestins have emerged as pleiotropic scaffold proteins, capable of mediating numerous diverse responses to multiple agonists. Most well characterized are the G-protein-coupled receptor (GPCR) stimulated β-arrestin signals, which are sometimes synergistic with, and sometimes independent of, heterotrimeric G-protein signals. β-arrestin signaling involves the recruitment of downstream signaling moieties to β-arrestins; in many cases specific sites of interaction between β-arrestins and the downstream target have been identified. As more information unfolds about the nature of β-arrestin scaffolding interactions, it is evident that these proteins are capable of adopting multiple conformations which in turn reveal a specific set of interacting domains. Recruitment of β-arrestin to a specific GPCR can promote formation of a specific subset of available β-arrestin scaffolds, allowing for a higher level of specificity to given agonists. This review discusses recent advances in β-arrestin signaling, discussing the molecular details of a subset of known β-arrestin scaffolds and the significance of specific binding interactions on the ultimate cellular response.     

Dissecting the correlation structure of a bivariate phenotype: Common genes or shared environment?

High correlations between two quantitative traits may be either due to common genetic factors or common environmental factors or a combination of both. In this study, we develop statistical methods to extract the genetic contribution to the total correlation between the components of a bivariate phenotype. Using data on bivariate phenotypes and marker genotypes for sib-pairs, we propose a test for linkage between a common QTL and a marker locus based on the conditional cross-sib trait correlations (trait 1 of sib 1—trait 2 of sib 2 and conversely) given the identity-by-descent (i.b.d.) sharing at the marker locus. We use Monte-Carlo simulations to evaluate the performance of the proposed test under different trait parameters and quantitative trait distributions. An application of the method is illustrated using data on two alcohol-related phenotypes from a project on the collaborative study on the genetics of alcoholism.     

Red leaf color as a warning signal against insect herbivory: Honest or mimetic?

The co-evolution theory for red leaf colors considers redness as a handicap signal against herbivory. We have examined whether the assumed signal is honest and, accordingly, costly, by seeking a correlation between anthocyanin and total phenolic levels in 11 plants exhibiting variation in the expression of the red character either between individuals or between modules on the same individual. Selection of total phenolics as a variable was based on their assumed anti-herbivore function and on their common biosynthetic origin with anthocyanins. Plants with young or senescing red leaves were tested. Confirming evidence was found in senescing leaves, where in three out of the four studied species a significant and strongly positive correlation between signal strength (redness) and actual defensive potential (total phenolics) was found, rendering the signal both honest and costly. In young, developing leaves a significant, yet weakly positive correlation was found only in three out the seven examined species. Accordingly, the handicap signal hypothesis may be questioned in the case of young leaves. Hence, young leaf redness fits more to the alternative hypotheses that red leaf color is less easily perceived by folivorous insect photoreceptors or that red leaf color undermines insect camouflage. These hypotheses do not demand an increased chemical defensive potential.     

Impact of urea on water structure: a clue to its properties as a denaturant?

A new investigation of the structure of urea-water solutions at a mole ratio of 1 urea to 4 water molecules is described. Neutron diffraction is used in conjunction with isotope labelling on the water and urea hydrogen atoms and on the nitrogen atom of urea. The diffraction data are analysed using the empirical potential structure refinement procedure to yield a set of site-site radial distribution functions and spatial density functions that are consistent with the diffraction data. The results are discussed in relation to recent and past X-ray and neutron diffraction experiments and theoretical studies of this system. It is found that urea incorporates readily into water, forming pronounced hydrogen bonds with water at both the amine and carbonyl headgroups. In addition the urea also hydrogen bonds to itself, forming chains or clusters consisting of up to approximately 60 urea molecules in a cluster. There, is however, little or no evidence of urea segregating itself from water, in marked contrast to a recent study of the methanol-water system. This behaviour is discussed in the context of the great propensity of urea to effect protein denaturation.     

Methyl jasmonate is blowing in the wind,but can it act as a plant–plant airborne signal?

Interplant communication in nature is beginning to look like a reality with the field demonstration that tobacco plants downwind of damaged sagebrush suffer less herbivory, a response that appears to be mediated by an airborne signal. Sagebrush constitutively releases methyl jasmonate (MeJA), a compound that is highly active in inducing a number of physiological responses in plants. Damage increases the absolute quantity of the MeJA released as well as the proportion of MeJA in the isomeric cis form. Several studies have shown that volatile MeJA, when released in sufficient quantities, can simulate responses elicited by direct MeJA applications. Additionally, the thermodynamically unstable cis isomer, which is responsible for the characteristic jasmine odor, is thought to be the biologically active form of MeJA. To examine the hypothesis that the cis-MeJA release is responsible for the apparent inter-plant communication, we developed methods to: (1) entrain sagebrush constituents in water which preserved the isomeric shift in the MeJA released after damage; (2) chemically manipulate the MeJA trans : cis ratio; and (3) isolate nearly pure cis-MeJA by HPLC. These treatments were applied as aqueous sprays to a natural population of tobacco plants, however, an outbreak of specialist herbivores consumed all treated plants and chemical analysis on previously harvested treated leaf material was inconclusive. The hypothesis is currently being carefully investigated with laboratory experiments.     

Host dispersal as the driver of parasite genetic structure: a paradigm lost?

Understanding traits influencing the distribution of genetic diversity has major ecological and evolutionary implications for host–parasite interactions. The genetic structure of parasites is expected to conform to that of their hosts, because host dispersal is generally assumed to drive parasite dispersal. Here, we used a meta‐analysis to test this paradigm and determine whether traits related to host dispersal correctly predict the spatial co‐distribution of host and parasite genetic variation. We compiled data from empirical work on local adaptation and host–parasite population genetic structure from a wide range of taxonomic groups. We found that genetic differentiation was significantly lower in parasites than in hosts, suggesting that dispersal may often be higher for parasites. A significant correlation in the pairwise genetic differentiation of hosts and parasites was evident, but surprisingly weak. These results were largely explained by parasite reproductive mode, the proportion of free‐living stages in the parasite life cycle and the geographical extent of the study; variables related to host dispersal were poor predictors of genetic patterns. Our results do not dispel the paradigm that parasite population genetic structure depends on host dispersal. Rather, we highlight that alternative factors are also important in driving the co‐distribution of host and parasite genetic variation.     

Host genetics as a cause of overdispersion of parasites among hosts: how general a phenomenon?

In the white-footed mouse, Peromyscus leucopus, the tapeworm Hymenolepis citelli occurs at low (2-3%) prevalence in the field. We found that mature infections (i.e., with egg production) developed in up to 100% of hosts. In the laboratory, a majority of hosts lost their infection by 28 days postintubation. In wild mice infected in the laboratory and returned to the field, infections were more prolonged, with half of the mice still infected at 100 days postintubation. A majority of previously infected hosts resisted challenge infection. Our introduction of laboratory-infected mice into a natural population of hosts appeared to cause infections among previously uninfected mice, leading to an increase in the prevalence of tapeworm infection among mice not intubated. Although genetically based expulsion of tapeworms before maturity is important in causing low prevalence in a similar host-parasite system, such resistance cannot explain low prevalence in the present system. It appears that both heterogeneous distribution and rarity of intermediate hosts as well as short parasite lifespan contribute to low prevalence and overdispersion. Host-parasite dynamics of 2 very similar systems appear to differ markedly.     

Enteric bacteria and osmotic stress: intracellular potassium glutamate as a secondary signal of osmotic stress?

Enteric bacteria have evolved an impressive array of mechanisms that allow the cell to grow at widely different external osmotic pressures. These serve two linked functions; firstly, they allow the cell to maintain a relatively constant turgor pressure which is essential for cell growth; and secondly they permit changes in cytoplasmic composition such that the accumulation of intracellular osmolytes required to restore turgor pressure does not impair enzyme function. The primary event in turgor regulation is the controlled accumulation of potassium and its counterion glutamate. At high external osmolarities the cytoplasmic levels of potassium glutamate can impair enzyme function. Rapid growth is therefore dependent upon secondary responses, principally the accumulation of compatible solutes, betaine (N-trimethylglycine), proline and trehalose. The accumulation of these solutes is achieved by the controlled activity of transport systems and enzymes in response to changes in external osmotic pressure. It has been proposed that the accumulation of potassium glutamate during turgor regulation acts as a signal for the activation of these systems [1,2]. This brief review will examine the evidence that control over the balance of cytoplasmic osmolytes is achieved by sensing of the intracellular potassium (and glutamate) concentration.