Growth and survivorship in juvenile woodlice: is birth mass important?

Growth and survivorship of individually reared offspring of the woodlice (Isopoda Oniscidae) Porcellionides pruinosus (Brandt) and Aphiloscia vilis (Budde-Lund) were measured under laboratory conditions These measures of offspring fitness were compared to birth mass, which is a realistic measure of parental investment in offspring for these species, to test a key assumption of life history theory that an increase in resource allocation to offspring will increase offspring fitness In both species birth mass had no significant effect on survivorship to 60 days and in P pruinosus birth mass did not correlate with mass at 15, 30 or 45 days after birth In A vilis larger young at birth had a slight growth advantage to 15 days but not thereafter There appears to be little effect of birth mass on offspring fitness despite a considerable range in birth mass within broods In these species high variance in juvenile growth may spread subsequent reproductive effort and avoid risks of total reproductive failure     

Growth,plant quality and leaf damage patterns in a dioecious tree species: is gender important?

Frequently, female plants allocate more resources to reproductive structures and defense-related secondary compounds in comparison with male plants that invest more resources to growth, reflecting trade-offs between reproduction, growth and defense. Therefore, differences in herbivory can be expected between genders. In this study, over two years, we analyzed the differences in plant chemical defense, nutritional quality, plant size and herbivory between genders in the dioecious tree, Spondias purpurea in a Mexican tropical dry forest. We estimated the total leaf area and the area consumed by folivory using a digital image of each leaf. The nutritional quality was estimated as water content, and the concentration of chlorophyll and total nonstructural carbohydrates. The secondary metabolites analyzed were total content of soluble phenolics, flavonoids, protein precipitation capacity of tannins, gallotannins, soluble proanthocyanidins, hydrolyzable tannins and ellagitannins. Our results differ from most of studies that analyze the differential herbivory patterns in dioecious plants. We found that female trees had higher levels of herbivory than male trees of S. purpurea. In the same way, female trees showed higher size and nutritional quality than males, while chemical defense was higher in male trees. The higher percentage of folivory in female trees of S. purpurea is associated with greater nutritional quality and lower chemical defenses. Our results show that male-biased herbivory might not be universal in dioecious species. Therefore, studies of fitness components affected by herbivory are necessary to understand the evolution of dioecy and the importance of herbivores as selective agents on breeding system features.     

Paedomorphosis in two small species of toothed whales (Odontoceti): how and why?

To evaluate and assess the ontogenetic background for paedomorphosis in phocoenids, samples of 144 harbour porpoises, 81 white‐beaked dolphins, and 130 Commerson's dolphins were compared in terms of the development of epiphyseal fusion, cranial suture fusion, and ontogeny of cranial shape. Harbour porpoises and Commerson's dolphins terminated growth and development of all investigated traits sooner than white‐beaked dolphins, leading to lesser degrees of fusion of skeletal elements and less postnatal allometric development. The latter occurred even though shape in the two paedomorphic species developed at twice the rate relative to the size of white‐beaked dolphins. These observations imply that progenetic evolution has occurred convergently in phocoenid and Cephalorhynchus ancestors. The truncated ontogenies allow sexual maturity to be attained earlier and provide a greater reproductive potential. Both species inhabit similar temperate productive habitats and, hence, ecological factors are proposed to have supplied the selection pressures leading to progenesis. Constant prey availability must be a prerequisite for the observed phenomena because frequent food‐intake is necessitated by the limited capacity for energy storage and high heat‐loss entailed by the resulting small body sizes. Progenesis has rarely been proposed in mammal species. This may reflect rarity or that mammalian expressions of progenesis are less obvious. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 278–295.     

Success of ectoparasites: how important is timing of host contact?

Hosts often differ in their degree of parasitism and their expression of resistance. Yet very little is known about how the availability (and allocation) of resources to parasites at pre-infective stages influences their success in initiating parasitism, or in inducing and succumbing to resistance from hosts. We studied a damselfly-mite association to address how experimental variation in the age of first contact with hosts (timing) influenced subsequent parasite fitness. We demonstrate that timing influenced the ability of larval mites to make the transition to parasitism, but was not associated with measures of physiological resistance by hosts. Timing presumably relates to the availability of resources remaining for individuals to exploit their hosts. More research is needed on the importance of such factors, from variation in host resistance and parasite success and, ultimately, to the numbers and distributions of parasites on hosts.     

Predicting the fate of a living fossil: how will global warming affect sex determination and hatching phenology in tuatara?

How will climate change affect species'' reproduction and subsequent survival? In many egg-laying reptiles, the sex of offspring is determined by the temperature experienced during a critical period of embryonic development (temperature-dependent sex determination, TSD). Increasing air temperatures are likely to skew offspring sex ratios in the absence of evolutionary or plastic adaptation, hence we urgently require means for predicting the future distributions of species with TSD. Here we develop a mechanistic model that demonstrates how climate, soil and topography interact with physiology and nesting behaviour to determine sex ratios of tuatara, cold-climate reptiles from New Zealand with an unusual developmental biology. Under extreme regional climate change, all-male clutches would hatch at 100% of current nest sites of the rarest species, Sphenodon guntheri, by the mid-2080s. We show that tuatara could behaviourally compensate for the male-biasing effects of warmer air temperatures by nesting later in the season or selecting shaded nest sites. Later nesting is, however, an unlikely response to global warming, as many oviparous species are nesting earlier as the climate warms. Our approach allows the assessment of the thermal suitability of current reserves and future translocation sites for tuatara, and can be readily modified to predict climatic impacts on any species with TSD.     

The CFTR and ENaC debate: how important is ENaC in CF lung disease?

Cystic fibrosis (CF) is caused by the loss of the cystic fibrosis transmembrane conductance regulator (CFTR) function and results in a respiratory phenotype that is characterized by dehydrated mucus and bacterial infections that affect CF patients throughout their lives. Much of the morbidity and mortality in CF results from a failure to clear bacteria from the lungs. What causes the defect in the bacterial clearance in the CF lung has been the subject of an ongoing debate. Here we discuss the arguments for and against the role of the epithelial sodium channel, ENaC, in the development of CF lung disease.     

Ultrastructure of hydathode trichomes of hemiparasitic Rhinanthus alectorolophus and Odontites vernus: how important is their role in physiology and evolution of parasitism in Orobanchaceae?

The Rhinanthoid clade of the family Orobanchaceae comprises plants displaying a hemiparasitic or holoparasitic strategy of resource acquisition. Some of its species (mainly Rhinanthus spp.) are often used as models for studies of hemiparasite physiology. Although there is a well‐developed concept covering their physiological processes, most recent studies have neglected the existence of hydathode trichomes present on leaves of these hemiparasitic plants. As a first step for the proposed integration of these structures in the theory of physiological processes of the hemiparasites, we described the outer micromorphology and ultrastructure of the hydathode trichomes on leaves of hemiparasitic Rhinanthus alectorolophus and Odontites vernus with scanning and transmission electron microscopy (SEM and TEM, respectively). The TEM inspections of both types of trichome revealed typical ultrastructural features: labyrinthine cell wall, high content of cytoplasm in cells with numerous mitochondria and presence of plasmodesmata. All these features indicate high metabolic activity complying with their function as glandular trichomes actively secreting water. The active secretion of water by the hydathode trichomes (evidence for which is summarised here) also presents a possible mechanism explaining results of previous gas exchange measurements detecting high dark respiration and transpiration rates and a tight inter‐correlation between them in hemiparasitic Orobanchaceae. In addition, this process is hypothesised to have allowed multiple evolutionary transitions from facultative to obligate hemiparasitism and unique xylem‐feeding holoparasitism of Lathraea with a long‐lived underground stage featuring a rhizome covered by scales of leaf origin.     

Integrated drought responses of black poplar: how important is phenotypic plasticity?

Climate change is expected to increase drought frequency and intensity which will threaten plant growth and survival. In such fluctuating environments, perennial plants respond with hydraulic and biomass adjustments, resulting in either tolerant or avoidant strategies. Plants' response to stress relies on their phenotypic plasticity. The goal of this study was to explore physiology of young Populus nigra in the context of a time‐limited and progressive water deficit in regard to their growth and stress response strategies. Fourteen French 1‐year‐old black poplar genotypes, geographically contrasted, were subjected to withholding water during 8 days until severe water stress. Water fluxes (i.e. leaf water potentials and stomatal conductance) were analyzed together with growth (i.e. radial and longitudinal branch growth, leaf senescence and leaf production). Phenotypic plasticity was calculated for each trait and response strategies to drought were deciphered for each genotype. Black poplar genotypes permanently were dealing with a continuum of adjusted water fluxes and growth between two extreme strategies, tolerance and avoidance. Branch growth, leaf number and leaf hydraulic potential traits had contrasted plasticities, allowing genotype characterization. The most tolerant genotype to water deficit, which maintained growth, had the lowest global phenotypic plasticity. Conversely, the most sensitive and avoidant genotype ceased growth until the season's end, had the highest plasticity level. All the remaining black poplar genotypes were close to avoidance with average levels of traits plasticity. These results underpinned the role of plasticity in black poplar response to drought and calls for its wider use into research on plants' responses to stress.     

Facultative primary sex ratio variation: a lack of evidence in birds?

The facultative control of primary sex ratio by breeding birds has become a major focus in evolutionary biology in recent years. A combination of well-developed theoretical literature and rapid publication of empirical results has created considerable confusion, with controversial claims for both extreme control of primary sex ratio versus no control around inherent random variability. We present a robust and quantitative summary of published empirical literature to assess clearly the body of evidence for female birds to control sex assignment in their offspring. Our meta-analytical approach reveals that published studies do not exhibit any variability beyond that which could be expected owing to sampling error. Therefore, we conclude that facultative control of offspring sex is not a characteristic biological phenomenon in breeding birds.     

A morphological and molecular perspective of Trichoderma viride: is it one or two species?

Trichoderma (Ascomycetes, Hypocreales) strains that have warted conidia are traditionally identified as T. viride, the type species of Trichoderma. However, two morphologically distinct types of conidial warts (I and II) have been found. Because each type corresponds to a unique mitochondrial DNA pattern, it has been questioned whether T. viride comprises more than one species. Combined molecular data (sequences of the internal transcribed spacer 1 [ITS-1] and ITS-2 regions and of part of the 28S rRNA gene along with results of restriction fragment length polymorphism analysis of the endochitinase gene and PCR fingerprinting), morphology, physiology, and colony characteristics distinguish type I and type II as different species. Type I corresponds to "true" T. viride, the anamorph of Hypocrea rufa. Type II represents a new species, T. asperellum, which is, in terms of molecular characteristics, close to the neotype of T. hamatum.     

Estimating sex ratio biases in X-linked disorders: is there an excess of males in families with X-linked ichthyosis?

We derive the conditional probabilities for estimating the sex ratio in families ascertained through affected males for the study of X-linked recessive diseases. These conditional probabilities correct for the fact that the probability that a family will be ascertained increases with the number of males in the family. Data from four published studies for X-linked ichthyosis vulgaris are analyzed, three having an excess of males and one having a highly statistically significant excess of males. It is not known if this difference in the two samples represents a biological difference between the two populations or an unrecognized ascertainment bias.     

Hsp70 duplication in the Drosophila melanogaster species group: how and when did two become five?

To determine how the modern copy number (5) of hsp70 genes in Drosophila melanogaster evolved, we localized the duplication events that created the genes in the phylogeny of the melanogaster group, examined D. melanogaster genomic sequence to investigate the mechanisms of duplication, and analyzed the hsp70 gene sequences of Drosophila orena and Drosophila mauritiana. The initial two-to-four hsp70 duplication occurred 10--15 MYA, according to fixed in situ hybridization to polytene chromosomes, before the origin and divergence of the melanogaster and five other species subgroups of the melanogaster group. Analysis of more than 30 kb of flanking sequence surrounding the hsp70 gene clusters suggested that this duplication was likely a retrotransposition. For the melanogaster subgroup, Southern hybridization and an hsp70 restriction map confirmed the conserved number (4) and arrangement of hsp70 genes in the seven species other than D. melanogaster. Drosophila melanogaster is unique; tandem duplication and gene conversion at the derived cluster yielded a fifth hsp70 gene. The four D. orena hsp70 genes are highly similar and concertedly evolving. In contrast, the D. mauritiana hsp70 genes are divergent, and many alleles are nonfunctional. The proliferation, concerted evolution, and maintenance of functionality in the D. melanogaster hsp70 genes is consistent with the action of natural selection in this species.     

Spatial–temporal patterns of flowering asynchrony and pollinator fidelity in hybridizing species of Narcissus

Speciation requires the evolution of reproductive barriers to achieve isolation between species. In this paper, we examine the role of two major pre-zygotic barriers in reducing the chance of F₁ hybrid formation between two pairs of Narcissus species. Field experiments were performed over 5?years in eight natural populations to determine whether flowering phenology and pollinator fidelity could act as reproductive isolation barriers in Narcissus. Our results show that reproductive isolation due to flowering phenology is highly variable and asymmetric. In some populations, pollinator fidelity was so strong that the quantification of reproductive isolation was complete and a strong negative correlation was found between the strength of this barrier and the abundance of hybrids. Nevertheless, the degree of pollinator fidelity was quite variable among populations indicating that reproductive isolation varies geographically but very consistent across years indicating that plant-pollinator interactions are well established. In fact, the finding that hybrid formation between these species occurs only in sites where pollinator fidelity is incomplete suggests that hybrid formation also varies geographically and that divergent evolutionary outcomes may occur in different sympatric populations of Narcissus.     

Sympatry and allopatry in two desert ant sister species: how do Cataglyphis bicolor and C. savignyi coexist?

Two extremely morphologically similar sister species of desert ants, Cataglyphis bicolor and C. savignyi, exhibit broadly overlapping distributional ranges within Tunisia. In order to analyse the microhabitats of C. bicolor and C. savignyi within the sympatric and allopatric areas of both ant species, the plant species located at 113 different nest sites of the two ant species were determined. In the sympatric area, the two species exhibit a clear-cut nest site segregation. This is not the case in the allopatric areas. Hence the two species differentiate their microhabitat only when they are sympatric. The plant species associated mainly with the nest sites of C. bicolor indicate that this species prefers a type of vegetation that needs irrigation. This is in contrast to the nest sites of C. savignyi, which are usually found around plants that characterize typical dry steppe areas. As the ants' foraging paths recorded in the sympatric area reveal, C. bicolor performs significantly shorter foraging runs with respect to both length and time, and covers a much smaller foraging range than C. savignyi does. This result reflects the fact that the microhabitat occupied by the colonies of C. bicolor is richer in food abundance. When direct interspecific interactions were investigated by placing a bait midway between two heterospecific nests, C. bicolor foragers dominated over those of C. savignyi. The same dominance of C. bicolor over C. savignyi occurred in laboratory experiments. These results suggest that the dominant species drives the subordinate one out of the high quality microhabitats, and that the subordinate species is forced to survive in the less lucrative habitats. In conclusion, coexistence seems to be maintained by the asymmetric competitive relationship between the two species and the fact that the subordinate species has the ability to endure in the less favourable microhabitat.     

Sex ratio variation and mixed pairs in roe deer: evidence for control of sex allocation?

Sex allocation has provided rich ground for the development of evolutionary theory. The dominant models in vertebrates have provided predictions of sex ratio based on asymmetry in variance in breeding success between sexes in the breeding system, and the relative effect of local competition. In ungulates, empirical work has provided some support for these models, but has also generated apparently contradictory observations. Recent models have provided some predictions for both individual and population sex ratio, showing that the availability of high-quality habitat patches and dispersal rates can critically affect both population- and individual-level expectations. We explore patterns in offspring sex ratio among a large sample of roe deer, a species with some interesting aspects of the breeding system. We found that in singleton pregnancies (the minority) there was an excess of male embryos, which was more marked in does in good condition at most sites. While the sex ratio among twins was close to parity, and unaffected either by average condition among populations or by individual condition within populations, we observed a clear excess of mixed pregnancies (sub-binomial variance, SBV). The excess was greater where the average condition was high. Within sites, population changes in average condition were associated with changes in SBV: in populations declining in condition, SBV also declined. There was no tendency for mixed twins to be more likely in individuals in better condition within a population. We conclude that condition-dependent allocation of sex does occur in roe deer. We suggest that in these "income breeders", mixed pairs might offer the greatest opportunity to optimize maternal investment during lactation, when conditions will be unpredictable, and that this is increasingly the case when average condition is poor.