Do reproductive characteristics of the species explain differences in the investment in weapon size present in males?

Sexually selected traits, such as male weapons, are highly variable in shape and size across species. However, little is known about the mechanisms that may govern this variation. Because males with greater investment in weapon size tend to win more fights, but also pay higher costs related to weapon development and maintenance, larger weapons should be expected only in species in which victory in male–male fights generate reproductive benefits that outweigh investment costs. Here, we hypothesized that the reproductive characteristics that increase the chances of winners to access females or to fertilize eggs will favor the evolution of larger weapons. To evaluate this hypothesis, we conducted a meta-analysis using arthropods as model organisms. To measure investment in weapon size, we gathered both Pearson correlation coefficient and the standardized (but non centralized) slope values for the relationship between weapon size and body size. We found that none of the reproductive characteristics we investigated was related to male weapon size. Thus, it seems that greater certainty of accessing a female or fertilizing female eggs with a victory does not modulate the investment in male weapon size. Perhaps the cost–benefit ratio between weapon size investment and reproductive success is not the main factor driving the variation in weapon size.     

Do Rotifers show “avoidance of the shore”?

Summary The term avoidance of shore was used in literature to describe the observation that pelagic crustacea are in general absent near the shore. Experiments in the field show, that Rotifers—which form, together with crustaceans, the main mass of zooplankton—can also be divided not only by morphological criteria but also as a result of their horizontal distribution into inhabitants of either the littoral or the pelagic zone of a lake.These differences of horizontal distribution can be explained by a typical behavioral difference between the littoral rotifer Euchlanis dilatata and the pelagic Asplanchna priodonta: when exposed in the shore zone, Asplanchna wanders in the direction of the pelagic zone, while Euchlanis on the contrary does not prefer any particular direction under the same conditions. Experiments at different lakes with other pelagic rotifers confirm that the avoidance of shore shown by Asplanchna is a general phenomenon.The influence of the analyzed behavior on the horizontal distribution patterns of rotifers and the factors which cause and determine the direction of the migration are discussed.This publication is a part of my inaugural-thesis (1974)     

Genome size and DNA base composition of geophytes: the mirror of phenology and ecology?

Background and Aims

Genome size is known to affect various plant traits such as stomatal size, seed mass, and flower or shoot phenology. However, these associations are not well understood for species with very large genomes, which are laregly represented by geophytic plants. No detailed associations are known between DNA base composition and genome size or species ecology.

Methods

Genome sizes and GC contents were measured in 219 geophytes together with tentative morpho-anatomical and ecological traits.

Key Results

Increased genome size was associated with earliness of flowering and tendency to grow in humid conditions, and there was a positive correlation between an increase in stomatal size in species with extremely large genomes. Seed mass of geophytes was closely related to their ecology, but not to genomic parameters. Genomic DNA GC content showed a unimodal relationship with genome size but no relationship with species ecology.

Conclusions

Evolution of genome size in geophytes is closely related to their ecology and phenology and is also associated with remarkable changes in DNA base composition. Although geophytism together with producing larger cells appears to be an advantageous strategy for fast development of an organism in seasonal habitats, the drought sensitivity of large stomata may restrict the occurrence of geophytes with very large genomes to regions not subject to water stress.     

Do group size and laying order influence maternal deposition of testosterone in smooth-billed ani eggs?

The avian egg contains maternal hormones that affect behavior, growth, morphology, and offspring survival. Evidence to date suggests that patterns of yolk androgen deposition could provide females with a means to manipulate sibling competition and, thereby, increase their fitness. We examined yolk testosterone (T) concentrations in eggs of the smooth-billed ani (Crotophaga ani) to understand patterns of androgen deposition in eggs of this plural-breeding joint-nesting cooperatively breeding species. We tested the hatching asynchrony adjustment hypothesis, which states that increases in yolk androgen levels over the laying sequence function to mitigate the disadvantage of being a later-hatched chick in species without adaptive brood reduction. We also investigated the effect of group size on yolk T deposition to test the hypothesis that females in multi-female groups could give a competitive edge to their own chicks by depositing higher T levels in their eggs. Predictions of the hatching asynchrony adjustment hypothesis were supported in both single- and multi-female groups as yolk testosterone levels increased from early- to late-laid eggs. This suggests that ani females can influence nestling competition and chick survival by within-clutch differential T allocation. Unexpectedly, we did not observe an effect of group size on yolk T deposition. Yolk testosterone concentrations may not be a mere reflection of a female's hormonal status as female plasma circulating levels of T did not vary in the same direction as yolk T levels. Results of this study therefore support the idea that females may adaptively manipulate chick behavior through hormonal deposition in eggs.     

Cellular calcium and redox regulation: the mediator of vertebrate environmental sex determination?

Many reptiles and some fish determine offspring sex by environmental cues such as incubation temperature. The mechanism by which environmental signals are captured and transduced into specific sexual phenotypes has remained unexplained for over 50 years. Indeed, environmental sex determination (ESD) has been viewed as an intractable problem because sex determination is influenced by a myriad of genes that may be subject to environmental influence. Recent demonstrations of ancient, conserved epigenetic processes in the regulatory response to environmental cues suggest that the mechanisms of ESD have a previously unsuspected level of commonality, but the proximal sensor of temperature that ultimately gives rise to one sexual phenotype or the other remains unidentified. Here, we propose that in ESD species, environmental cues are sensed by the cell through highly conserved ancestral elements of calcium and redox (CaRe) status, then transduced to activate ubiquitous signal transduction pathways, or influence epigenetic processes, ultimately to drive the differential expression of sex genes. The early evolutionary origins of CaRe regulation, and its essential role in eukaryotic cell function, gives CaRe a propensity to be independently recruited for diverse roles as a ‘cellular sensor’ of environmental conditions. Our synthesis provides the first cohesive mechanistic model connecting environmental signals and sex determination pathways in vertebrates, providing direction and a framework for developing targeted experimentation.     

Human evolution and the brain representation of semantic knowledge: is there a role for sex differences?

A sexual asymmetry has been recently found on semantic memory tasks: after brain damage, a disproportionate deficit for information about biological categories has been reported more frequently for male patients. A review of cases shows that the fine-grained pattern is more complicated in that there is a strong interaction with sex: Disproportionate plant-knowledge deficits are restricted to males, whereas disproportionate animal-knowledge deficits are rare and show no sex bias. These clinical data are consistent with semantic-knowledge data from normal subjects indicating a task-invariant female advantage with plant categories. In this study, we seek an explanation for this sex-by-semantic category interaction and discuss the possible roles of a greater female experience with plant items, both ontogenetically and over evolutionary time.     

Why do the mounds of Mus spicilegus vary so much in size and composition?

Mound-building mice (Mus spicilegus) construct large and often enormous mounds, which may have several functions, including food storage, thermoregulation, and protection from predators. We examined variation in mound size and composition to help determine their adaptive significance. Like previous studies, we found much variation in mound size within and between geographic populations, and the main differences were between habitats: we found up to a 700-fold variation in mound size between corn fields and harvested grain fields. Mice mainly utilized three plants (Amaranthus spp., Chenopdium spp. and Setaria spp.) as building materials, and the availability of these may affect mound size. We found a positive correlation between the availability of plant material in the surrounding of the mound and mound size. Surprisingly, mound size was independent of the number of inhabitants within the mounds, which indicates that larger mounds are not constructed to shelter more individuals. Future studies need to examine how variation in mound size and composition affects overwinter survival, and also which individuals contribute to mound construction.     

Proximate causes of Rensch's rule: does sexual size dimorphism in arthropods result from sex differences in development time?

A prominent interspecific pattern of sexual size dimorphism (SSD) is Rensch's rule, according to which male body size is more variable or evolutionarily divergent than female body size. Assuming equal growth rates of males and females, SSD would be entirely mediated, and Rensch's rule proximately caused, by sexual differences in development times, or sexual bimaturism (SBM), with the larger sex developing for a proportionately longer time. Only a subset of the seven arthropod groups investigated in this study exhibits Rensch's rule. Furthermore, we found only a weak positive relationship between SSD and SBM overall, suggesting that growth rate differences between the sexes are more important than development time differences in proximately mediating SSD in a wide but by no means comprehensive range of arthropod taxa. Except when protandry is of selective advantage (as in many butterflies, Hymenoptera, and spiders), male development time was equal to (in water striders and beetles) or even longer than (in drosophilid and sepsid flies) that of females. Because all taxa show female-biased SSD, this implies faster growth of females in general, a pattern markedly different from that of primates and birds (analyzed here for comparison). We discuss three potential explanations for this pattern based on life-history trade-offs and sexual selection.     

Inflammatory obstruction of the olfactory clefts and olfactory loss in humans: a new syndrome?

The first step in the olfactory perception is the activation by odorants of sensory neurones in the olfactory epithelium. In humans, this sensory epithelium is located at 2 narrow passages, the olfactory clefts, at the upper part of the nasal cavities. Little is known about the physiology of these clefts. We examined, in 34 patients, the impact of obstructed clefts upon detection and postlearning identification of 5 odorants. The location and extension of the obstructions were assessed using endoscopy, CT scans, and MRI. The inflammatory obstruction was usually bilateral, extending anteroposteriorly, and confined to the clefts, with no sign of obstruction or any inflammatory disease in the rest of the nasal cavities and sinuses. When tested with 5 odorants, these patients showed greatly impaired olfaction compared with a group of 73 normosmic subjects. The majority of these 34 patients had sensory deficits equivalent to that found in another group of 41 congenital anosmic patients, where inspection with MRI indicated the lack of olfactory bulbs. This study demonstrates that the olfactory clefts, in human, function as an entity that is different from other regions of the nasal cavity and is the target for local inflammatory events that are apparently not responding to corticoid and antibiotic treatments.     

Predicting the environmental niche of the genus Phymaturus: Are palluma and patagonicus groups ecologically differentiated?

The genus Phymaturus (Reptilia: Liolaemidae) is distributed in the mountains and rocky plateaux of Argentina and Chile and comprises two groups of species, palluma and patagonicus. The two lineages have diverged early in the evolution of the genus and up to today, there is very little geographical overlap between them. We worked with records of localities from the literature, herpetological collections and field data to evaluate habitat suitability of the genus Phymaturus. We used 11 environmental variables to develop environmental niche models (ENMs) for each group within the genus using the Maxent software, and to determine those variables that best explain the distribution of each group. We also estimated measures of niche similarity using ENMTools to determine whether niche differentiation is real or apparent. The geographical overlap between the groups was very low considering the large geographical range of the genus. Some variables, such as mean annual temperature, soil type and bare soil cover, have a high contribution to the models for both groups. The current niche overlap between Phymaturus groups indicates that the environmental niches of the palluma and patagonicus groups are not equivalent. Based on background analysis, we cannot reject the hypothesis that similarity (or divergence) between groups of Phymaturus is no more than expected based on the availability of habitat. The results of this study are a first approximation to the knowledge of the environmental variables associated with the palluma and patagonicus groups, and reveal that the ecological differences found between these groups are more likely due to habitat availability in their respective regions than to differences in habitat preferences.     

Gender differences in parameters of lipid metabolism and of level of antioxidants in groups of juveniles—the Even and the Europeans

There was performed a comparative evaluation of the mean values of lipid metabolism parameters in youths and girls of the indigenous population (the Even), of the coming population of the north of Irkutsk province, and of the province center (the Europeoids). Gender differences in HDLP have been revealed in adolescents of the coming population, in the glutathione status and the content of liposoluble vitamins in the Even and coming adolescents and in retinol concentration in the province center adolescents. Adaptive changes in the ROS system were found in the Even girls (the higher α-tocopherol and GSH concentrations and the GSH/GSSG ratio as well as a decrease of GSSG relative to the Even youths and the coming population girls, an increase of α-tocopherol relatively to the coming population Europeoids) and youth of the coming population (the higher GSH content and the GSH/GSSG parameter relatively to the Even youths).     

Does the timing of attainment of maturity influence sexual size dimorphism and adult sex ratio in turtles?

The attainment of sexual maturity has been shown to affect measures of sexual size dimorphism (SSD) and adult sex ratios in several groups of vertebrates. Using data for turtles, we tested the model that sex ratios are expected to be male‐biased when females are larger than males and female‐biased when males are larger than females because of the relationship of each with the attainment of maturity. Our model is based on the premise that the earlier‐maturing sex remains smaller, on average throughout life, and predominates numerically unless the sexes are strongly affected by differential mortality, differential emigration, and immigration, or biased primary sex ratios. Based on data for 24 species in seven families, SSD and sex ratios were significantly negatively correlated for most analyses, even after the effect of phylogenetic bias was removed. The analyses provide support for the model that SSD and adult sex ratios are correlated in turtles as a result of simultaneous correlation of each with sexual differences in attainment of maturity (bimaturism). Environmental sex determination provides a possible mechanism for the phenomenon in turtles and some other organisms. © 2014 The Authors. Biological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112 , 142–149.     

Predation risk, gender and the group size effect: does elk vigilance depend upon the behaviour of conspecifics?

Many animals benefit from the presence of conspecifics by reducing their rate of scanning for predators while increasing their time spent foraging. This group size effect could arise from a decreased perception of individual risk (dilution hypothesis) and/or an increased ability to detect predators (detection hypothesis). We compared individual and group vigilance of Rocky Mountain elk, Cervus elaphus, in three regions of Yellowstone National Park, Wyoming, U.S.A. that varied in their encounter frequency with coyote, Canis latrans, grizzly bear, Ursus arctos, and grey wolf,Canis lupus , predators. Adult females without calves increased scanning and decreased foraging with high encounter risk and small herd size. Adult females with calves increased scanning and decreased foraging with high encounter risk, but showed no decrease in scanning with large herd size. Yearlings increased scanning and decreased feeding with small herd size, but not with high encounter risk. Adult males were least vigilant, fed most and were not influenced by encounter risk or herd size. These age-sex class differences led to significant differences in group vigilance depending on the composition of the herd. Herds with a majority of mothers were significantly more vigilant than herds with a majority of adult males. However, these differences in group vigilance had no influence on the individual scanning of females without calves. Thus, the decrease in individual scanning with herd size may depend more on changes in individual risk than on cooperative detection of predators. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Long-term trends in the population size of king penguins at Crozet archipelago: environmental variability and density dependence?

We examined the growth rate of the breeding population of king penguins of Crozet archipelago over 41 years. Most colonies showed positive growth rates from the 1960s. However, there was evidence for a decrease in the larger colonies since the early 1990s, and for lower growth rates in the smaller colonies during the 1990s. The overall population size was estimated using log linear models, and the average annual growth rate was +6.3% for the 41-year period. Four change points were detected in the annual growth rate: +21.1% during 1978–1985, +4.3% during 1985–1995, –19.2% during 1995–1999, and +10.9% during 1999–2003. Time-series analyses of the population-size estimates and the relationship between growth rate and population size both indicated density-dependence in population growth rate. Variations in population sizes are also discussed in relation to environmental fluctuations. Our results suggest that important changes occurred over the past 10 years.