Variability of male gametophyte traits in morphological forms of Taraxacum officinale Wigg. s.l. under conditions of technogenic soil transformation

The paper studies endogenous, individual and group variability of the traits pollen grain fertility and size of fertile pollen grains among two morphological forms of Taraxacum officinale Wigg. s.l., growing in coenopopulations in the gradient of technogenic soil transformation. The study area is the Pritagil zone of the Middle Urals (Nizhny Tagil city, Sverdlovsk Region, N 58, E 60). It was found that the studied morphological forms of dandelion in most cases are characterized by average endogenous, individual and group variability of the trait pollen grain fertility and low endogenous and individual variability of the trait pollen grain size. The group variability for this trait is medium and low. The endogenous variability of pollen grain fertility and size among f. dahlstedtii on agrozems is slightly higher than on technozems. Among f. pectinatiforme the endogenous variability of pollen grain fertility is higher on agrozems only. An increase in the level of soil contamination on agrozems leads to a decrease in the endogenous variability of pollen grain fertility among both forms of dandelion. On technozems a similar reaction is expressed only among f. pectinatiforme . The analysis of the studied trait in the entire gradient of technogenic soil transformation indicates a significant influence of this factor only on the endogenous variability of pollen grain fertility among f. dahlstedtii . Despite the absence of statistically significant differences in the individual variability of the pollen grain fertility trait between dandelion forms, on average, the coefficients of its variation on agrozems are lower among f. dahlstedtii , and on technozems - among f. pectinatiforme . The same conclusion applies to the individual variability of the trait size of fertile pollen grains. In general, among f. dahlstedtii the coefficients of variation of the studied signs of the male gametophyte are lower in agrozems than in technozems, among f. pectinatiforme the picture is reversed. On average, the proportion of plants with low ( C ᵥ 11%) individual variability in pollen grain fertility among f. dahlstedtii out of all the studied coenopopulations is 43,3% versus 61,7% among f. pectinatiforme . The influence of technogenic transformation of the environment is manifested in an increase in the proportion of f. pectinatiforme plants with a low level of variability of the studied traits in the coenopopulations of the buffer and impact zones. Among f. dahlstedtii the reverse pattern is characteristic only for pollen fertility. The group variability of pollen grain fertility in both agrozems and technozems is higher among f. dahlstedtii . With an increase in pollution on agro-soils, this indicator increases among both forms of dandelion, and decreases in technozems. There is a tendency to increase the group variability of pollen grain fertility among plants of both forms of T . officinale on technozems. An increase in the level of soil contamination on agrozems leads to an increase in the group variability of the trait size of fertile pollen grains among f. dahlstedtii and a decrease among f. pectinateforme . On technozems the opposite effect is noted. In general, the group variability of the studied trait among plants of both morphological forms of dandelion on agrozems is higher than on technozems.

Stage-dependent Plasticity in Biomass Allocation and Allometry of Abutilon Theophrasti in Response to Population Density

How plants respond to density via modular plasticity is obscure, probably because relevant studies using covariance and allometry analyses rarely focus on multiple stages of plant growth, and also the two approaches are seldom used simultaneously in a same study. To address this issue, a field experiment was conducted by subjecting plants of Abutilon theophrasti to low, medium and high densities and measuring the mass of various plant modules, before covariance and allometry analyses at three stages of plant growth. Results showed inconsistent responses in allocation traits and allometric relationships at each growth stage. At 30 d, high density increased root:stem, root:leaf and stem:leaf ratios, but did not affect any allometric relationships. At 50 d, density altered most allocation traits, but not for allometric exponents. At 70 d, density altered allometric relationships, with no effects on allocation traits. The stage-dependent allometric relationships and inconsistent results of allometric and covariance analyses suggested one-stage allometric plasticity might be apparent plasticity. In response to the increase of density, plants first altered the strategy of biomass partitioning, then growth rate or developmental stage, indicating density effects intensified over time. For plasticity in a modular trait, size effects can be regarded as a component of (indirect) environmental effects, with the left variation after removal of size effects being the other component of plant (direct) active response. The insights into apparent plasticity of allometry and two components of plasticity should be of essential importance to investigating phenotypic plasticity and its implications in plants.

The dark ventral patch: A bimodal flexible trait related to male competition in red deer

Sexual signals play a central role in male-male competition in polygynous species. In red deer (Cervus elaphus), male’s ventral area become dark during the rutting season due to urine spraying behaviour and retains many chemical compounds potentially revealing individual features. Here we investigate the variation in size of this trait, exploring its relationship with age and male competitive features such as antlers or body size, as well as populational level of intrasexual competition for mates. We found that the size of the dark ventral patch followed a clearly bimodal distribution, i.e. males mostly expressed the full-size trait or just developed a very small one. For these two groups of males according to trait expression, the relationships of trait size with age and antler size differed. Populational level of intrasexual competition appeared to affect the relationship between antler size and the probability of a fully developed ventral patch. These results indicate that the trait encodes information on body size, antler size, age and populational level of mate competition, thus suggesting a role in signalling male’s competitive features and willingness to allocate reproductive effort within a particular season.

A comparison of two methods for estimating measurement repeatability in morphometric studies

SummaryMeasurement repeatability is often reported in morphometric studies as an index of the contribution of measurement error to trait measurements. However, the common method of remeasuring a mounted specimen fails to capture some components of measurement error, and could therefore yield inflated repeatability estimates. Remounting specimens between successive measurements is likely to provide more realistic estimates of repeatability, particularly for small structures that are difficult to measure.Using measurements of 22 somatic and genitalic traits of the neriid fly Telostylinus angusticollis, we compared repeatability estimates obtained via remeasuring (where a mounted specimen is measured twice) versus remounting (where a specimen is remounted between measurements). We also asked whether the difference in repeatability estimates obtained via the two methods depends on trait size.Repeatability estimates obtained via remounting were lower than estimates obtained via remeasuring for each of the 22 traits, and the difference between estimates obtained via the two methods was generally greater for small structures (genitalic traits) than for large structures (legs, wings).Remounting specimens between successive measurements can provide more accurate estimates of measurement repeatability than remeasuring from a single mount, especially for small structures that are difficult to measure.

Static Scaling and the Evolution of Extreme Canine Size in a Saber-Toothed Cat (Smilodon fatalis)

The canines of saber-toothed cats are a classic example of an extreme morphology, yet important questions pertaining to their evolution remain unanswered. Recent analyses suggest these structures functioned as tools of intrasexual combat where trait size acts as both a weapon of battle and signal of competitive ability. However, classic skeletal reconstructions suggest saber-tooth canines evolved as specialized hunting tools. Either scenario could have led to the evolution of extreme canine size and distinguishing between these hypotheses is therefore difficult. This is made more challenging by the fact that natural observation of saber-toothed cats is impossible, and biologists must rely on measures of static morphology to study the patterns of selection that favored extreme canine size. Here I analyze the static intraspecific scaling relationship between canine size and body size in the saber-toothed cat, Smilodon fatalis, to determine whether or not extreme canine size functioned as a sexually selected signal. I review the literature surrounding the evolution of sexually selected signals and the methods recently established by O’Brien et al. (2018), show how static scaling relationships can be useful, reliable tools for inferring patterns of selection, especially in fossil organisms, and provide evidence that extreme canine size in saber-toothed cats was not the product of selection for effective sexual signals, but instead evolved as either a pure intrasexually selected weapon or a hunting tool.

Why the long face? Static allometry in the sexually dimorphic phenotypes of Neotropical electric fishes

The evolution of sexually dimorphic traits is thought to have marked effects on underlying patterns of static allometry. These traits can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male–male interactions. We also estimate jaw-closing performance between the sexes of both species to track changes in kinematic transmission associated with the development of sexual weaponry. We find significantly different patterns of static allometry between the sexes of both species, with males exhibiting more positive allometric slopes relative to females. We also find a negative relationship between skull shape and mandibular kinematic transmission in C. samueli, suggesting a trade-off where males with longer faces exhibit lower mechanical advantages, suggesting weaker jaw leverage. In contrast, males and females of A. rostratus exhibit no difference between sexes in mechanical advantage associated with facial elongation.

From Armament to Ornament: Performance Trade-Offs in the Sexual Weaponry of Neotropical Electric Fishes

The evolution of sexual weaponry is thought to have marked effects on the underlying static allometry that builds them. These weapons can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male-male interactions. We quantify jaw mechanical advantage between the sexes of both species to track changes in velocity and force transmission associated with the development of sexual weaponry. We find evidence for trade-offs between skull shape and mechanical advantage in C. samueli, where males with longer faces exhibit lower mechanical advantages, suggesting weaker bite forces. In contrast, males, and females of A. rostratus exhibit no difference in mechanical advantage associated with facial elongation. We hypothesize that differences in the functionality of the sexual weaponry between the two species may drive divergences in the allometric scaling of mechanical advantage.

The sex-specific effects of diet quality versus quantity on morphology in Drosophila melanogaster

Variation in the quality and quantity of nutrition is a major contributor to phenotypic variation in animal populations. Although we know much of how dietary restriction impacts phenotype, and of the molecular-genetic and physiological mechanisms that underlie this response, we know much less of the effects of dietary imbalance. Specifically, although dietary imbalance and restriction both reduce overall body size, it is unclear whether both have the same effect on the size of individual traits. Here, we use the fruit fly Drosophila melanogaster to explore the effect of dietary food versus protein-to-carbohydrate ratio on body proportion and trait size. Our results indicate that body proportion and trait size respond differently to changes in diet quantity (food concentration) versus diet quality (protein-to-carbohydrate ratio), and that these effects are sex specific. While these differences suggest that Drosophila use at least partially distinct developmental mechanisms to respond to diet quality versus quantity, further analysis indicates that the responses can be largely explained by the independent and contrasting effects of protein and carbohydrate concentration on trait size. Our data highlight the importance of considering macronutrient composition when elucidating the effect of nutrition on trait size, at the levels of both morphology and developmental physiology.