Utilizing laboratory and field studies to determine physiological responses of cattle to multiple environmental stressors

Heat stress studies are often conducted using controlled laboratory exposures or field exposures. Each approach has limitations and provides a partial understanding of complex interactions between simultaneous environmental stressors. The question is how similar the responses are in each situation. Several physiological measures of thermal status were used to compare heat stress responses of cattle in controlled chamber stress tests and fluctuating field conditions. Angus steers (N=23; 318±8 kg BW) were first placed on either endophyte-infected or -uninfected tall fescue pastures for the field exposure, followed by a controlled heat challenge, which exacerbates the condition known as fescue toxicosis. During the controlled heat challenge, steers were assigned to diets of either 0 or 40 μg ergovaline/kg/d to maintain the treatment states. Respiration rate (RR) was measured via flank counting and telemetric temperature transmitters in the rumen of each animal monitored core temperature (T_rum). Linear regression fit models for RR, T_rum, and air temperature (T_a) were utilized to compare relationships between field and chamber exposure. Correlation coefficients for RR were similar during both chamber (R=0.69) and field exposures (R=0.72). Respiration rate showed greater responsiveness to change in T_a under field conditions having twice the slope (4.40 versus 1.75 bpm/°C) and a lower Y-intercept (−42.14 versus +30.97 bpm) compared to the chamber run. Ruminal temperature was consistent between exposures showing a similar slope (0.04 versus 0.03 °C T_rum/°C T_a) and Y-intercept (38.40 versus 39.30 °C) for its relationship with T_a. Despite respiration rate being the more sensitive indicator of heat stress, ruminal temperature proved to be the most consistent between environments.     

Increased energy promotes size-based niche availability in marine mollusks

Variation in chemical energy, that is food availability, is posited to cause variation in body size. However, examinations of the relationship are rare and primarily limited to amniotes and zooplankton. Moreover, the relationship between body size and chemical energy may be impacted by phylogenetic history, clade-specific ecology, and heterogeneity of chemical energy in space and time. Considerable work remains to both document patterns in body size over gradients in food availability and understanding the processes potentially generating them. Here, we examine the functional relationship between body size and chemical energy availability over a broad assortment of marine mollusks varying in habitat and mobility. We demonstrate that chemical energy availability is likely driving body size patterns across habitats. We find that lower food availability decreases size-based niche availability by setting hard constraints on maximum size and potentially on minimum size depending on clade-specific ecology. Conversely, higher food availability promotes greater niche availability and potentially promotes evolutionary innovation with regard to size. We posit based on these findings and previous work that increases in chemical energy are important to the diversification of Metazoans through size-mediated niche processes.     

Arthropod abundance in tall fescue,Lolium arundinaceum,pastures containing novel ‘safe’ endophytes

Poor livestock performance on tall fescue is linked to infection by a fungal endophyte that enhances grass resistance to stress, including herbivory, while producing ergot alkaloids toxic to vertebrate grazers. Novel ‘safe’ endophyte/grass associations produce no ergot alkaloids yet retain stand persistence, but they could be more susceptible to insect outbreaks. We tested the hypothesis that grass‐feeding insects are more abundant in novel endophyte pastures compared with those containing common endophyte. Above‐ and below‐ground herbivores were sampled across two growing seasons in pastures containing common strain endophyte (KY31), novel endophytes (MaxQ or AR584) or endophyte free. We also sampled natural enemies as an indicator of possible tritrophic effects. With a few exceptions, numbers of predatory, chewing (grasshoppers, crickets, caterpillars) or sucking insects (leafhoppers, planthoppers) were similar in common and novel endophyte pastures. Contrary to our hypothesis, Aphrodes spp. leafhoppers were more abundant in KY31 than other pasture types in 2008; their nymphs also were more abundant in KY31 than in MaxQ in 2009. Adults (but not total numbers or nymphs) of another leafhopper, Psammotettix striatus, were less abundant in KY31 than other pasture types in 2009. Popillia japonica and Cyclocephala spp. grubs did not differ in density, weight or instar among the endophyte‐containing associations. In feeding assays, armyworm (Mythimna unipuncta) survival was higher on MaxQ and NE9301, and weight gain was higher on NE9301, suggesting armyworm outbreaks could be more severe on such grasses, but that result may not be attributable solely to alkaloids because common strain and endophyte‐free grasses did not differ in either parameter. Caterpillar abundance did not differ among pasture types in the field. Our results suggest that re‐seeding common strain endophytic pastures with livestock‐safe novel endophyte/grass associations to alleviate fescue toxicosis is unlikely to promote markedly higher populations of plant‐feeding insects.     

Morphological evolution through integration: a quantitative study of cranial integration in Homo, Pan, Gorilla and Pongo

Morphological integration refers to coordinated variation among traits that are closely related in development and/or function. Patterns of integration can offer important insight into the structural relationship between phenotypic units, providing a framework to address questions about phenotypic evolvability and constraints. Integrative features of the primate cranium have recently become a popular subject of study. However, an important question that still remains under-investigated is: what is the pattern of cranial shape integration among closely related hominoids? To address this question, we conducted a Procrustes-based geometric morphometrics study to quantify and analyze shape covariation patterns between different cranial regions in Homo, Pan, Gorilla and Pongo. A total of fifty-six 3D landmarks were collected on 407 adult individuals. We then sub-divided the landmarks corresponding to cranial units as outlined in the ‘functional matrix hypothesis.’ Sub-dividing the cranium in this manner allowed us to explore patterns of covariation between the face, basicranium and cranial vault, using the two-block partial least squares approach. Our results suggest that integrated shape changes in the hominoid cranium are complex, but that the overall pattern of integration is similar among human and non-human apes. Thus, despite having very distinct morphologies the way in which the face, basicranium and cranial vault covary is shared among these taxa. These results imply that the pattern of cranial integration among hominoids is conserved.     

Factors promoting maternal trophic egg provisioning in non-eusocial animals

The adaptive function of trophic egg-laying is generally regarded as extended parental investment to the offspring. However, the evolutionary factors promoting trophic egg-laying are still unclear, because the amount of maternal investment per offspring should be ideally equal between smaller offspring with trophic eggs and larger offspring without any additional investment. Several authors have suggested that trophic egg-laying should evolve only when egg size is constrained, but this hypothesis has not been evaluated. We investigated the evolutionary mechanisms of trophic egg-laying by two different approaches. First, we evaluated morphological constraints on egg size in two sibling ladybird species, Harmonia axyridis, which is known to produce trophic eggs, and H. yedoensis. Second, we theoretically predicted the optimal proportion of trophic eggs to total eggs and egg size in relation to environmental heterogeneity, predictability of environmental quality, and investment efficiency of trophic egg consumption. The intra- and interspecific morphological comparisons suggest that morphological constraints on the evolutionary determination of egg size are weak at best in the two ladybird species. Moreover, we theoretically showed that small egg size and trophic egg-laying are favoured in heterogeneous environments when mothers cannot adjust egg size plastically. We also showed that even a small reduction in investment efficiency makes a trophic egg strategy unlikely, despite relatively high environmental predictability. We conclude that trophic egg provisioning may be a flexible maternal adaptation to a highly heterogeneous environment rather than a response to a morphological constraint on egg size.     

Morphological traits determine the winner of “symmetric” fights in hermit crabs

This study aimed at investigating in the hermit crab Pagurus longicarpus whether some morphological traits and their slight variations might determine the winner of a contest in symmetric pairs, i.e. pairs composed of individuals matched by their overall size. In the pre-experimental phase, 400 crabs were individually kept in isolation for a week to eliminate the effects of their previous social experiences and were allowed to enter adequate shells to equalize their motivation to fight. Then, we formed 200 pairs matched for shell and body size and observed their agonistic behaviour for 15 min. Alphas (and betas) were deemed as those individuals that won more than half of the recorded fights. Finally, crabs were sacrificed and sexed, and 6 and 8 measures were taken of their shells and bodies, respectively. Raw data were converted to compositional data and subjected to an isometric log-ratio transformation prior to statistical analysis. Alphas were found to occupy heavier and wider shells than betas, both characteristics that, together with the correlated high level of encrustation, make the apparent dimension of the crab larger and thus favour that individual during agonistic encounters. As expected, hermit crabs were sexually dimorphic in their chelae, but sexes differed also in the length of the dactylus of their third walking leg and in their body weight. Alphas were heavier than betas and had longer propodi and wider dactyli on the third walking legs than betas. The latter character might be advantageous during shell fights when the walking legs of the attacker are used to hold the defender's shell in the spasmodic shaking and their wider dactyli might assure a firmer seizing of it. Indeed, a correct execution of this pattern allows for the eviction of the defender. Our results suggest that more attention towards variations in morphological traits other than body size might improve our understanding of the factors that affect individual Resource Holding Power and fight dynamics.     

Predator-induced changes in morphology of a prey fish: the effects of food level and temporal frequency of predation risk

In a series of experiments, we investigated the effects of food availability and risk frequency on the dynamics of predator-induced changes in growth and morphology of prey fish using goldfish (Carassius auratus) as our test species. In experiment 1, we fed goldfish high or low food rations and exposed them to either alarm cues from conspecifics, cues from swordtails or a water control. After 60 days, goldfish in the alarm cue treatment significantly increased their body depth and body weight but had smaller body length than goldfish exposed to swordtails cues or water, likely reducing their vulnerability to gape-limited predators. Importantly, food level had an impact on the amplitude of the morphological changes. In experiment 2, goldfish were exposed to two different frequencies of predation cues or a water control for 50 days. The cues were either continued or discontinued from day 51 to 100, and all cues were resumed from day 101 to 150. We found that goldfish exposed to predation cues increased their depth and weight at a faster rate than did the goldfish exposed to water, and of particular significance was the fact that frequency of risk had an effect on the amplitude of the change. When the cues were interrupted, the increase in growth rate parameters was reduced to the level of the goldfish exposed to water. However, when the cues were resumed, the rate increased to match the growth rate of the goldfish that were continuously exposed to the cues. Finally, we staged encounters between goldfish of differing morphologies and yellow perch (Perca flavescens) and found that deep-bodied goldfish had better survival than the shallow-bodied ones. These experiments illustrate the dynamic nature of inducible morphological defences.     

柳属的分支系统学分析

基于61个广义的形态学性状,以杨属为外类群对柳属进行了分支系统学分析.经简约性分析,得到了21个同等简约的分支树,其严格一致树支持柳属为一个自然的分类群,但不支持将钻天柳属和心叶柳属从柳属中划分出去独立成属,也不支持对柳属进行属级水平上的细分,后两个结果得到孢粉学和分子系统学研究的支持.柳亚属为一个单系分支,皱纹柳亚属和黄花柳亚属也形成了一个单系分支.根据本研究的结果,建议将柳属划分为钻天柳亚属、柳亚属及黄花柳亚属3个亚属.由于较低的靴带支持率,其系统发育关系难于探讨.鉴于分支分析的一致性指数、保持性指数、各分支内部的支持率均不高,柳属的属下分类系统的划分有待进一步的研究.