Allometry between leg and body length of insects: lack of support for the size–grain hypothesis

• 1 The size–grain hypothesis ( Kaspari & Weiser, 1999 ) states that (1) as organisms decrease in size, they perceive their environment as being more rugose; (2) long legs allow organisms to step over obstacles but hinder them from entering small gaps; and (3) as the size of an organism decreases, the benefits of long legs begin to be outweighed by the costs of construction. Natural selection should therefore favour proportionally longer legs in larger organisms, thereby leading to a positive allometry between leg and body length (scaling exponent b > 1).
• 2 Here we compare the scaling exponent of leg‐to‐body length relationships among insects that walk, walk and fly, and predominantly fly. We measured the lengths of the hind tibia, hind femur, and body length of each species.
• 3 The taxa varied considerably in the scaling exponent b. In seven out of ten groups (Formicidae, Isoptera, Carabidae, Pentatomidae, Apidae, Lepidoptera, Odonata adult), b was significantly greater than one. However, there was no gradual decrease in b from walking to walking/flying to flying insects.
• 4 The results of the present study provide no support for the size–grain hypothesis. We propose that leg length is not only affected by the rugosity of the environment, but also by (1) functional adaptations, (2) phylogeny, (3) lifestyle, (4) the type of insect development (hemimetabolism or holometabolism), and (5) constraints of gas exchange.

     

Brood size and the cost of provisioning nestlings: interpreting Lack's hypothesis

A recent model of parental provisioning (the tradeoff model) suggests that the maximum delivery rate of food to nestlings represents a tradeoff between parental residual reproductive value and nestling survival. In contrast, Lack's hypothesis suggests that maximum provisioning rate determines brood size and therefore delivery rates are limited by shortages of food or foraging time, not by tradeoffs of parental investment. Several authors have examined the shape of the per-nestling feeding curves to test the tradeoff model against Lack's hypothesis. We show that Lack's hypothesis can produce per-nestling feeding curves consistent with the tradeoff model. Therefore, the shape of the per-nestling feeding curve cannot be used to distinguish between the models.     

The size-grain hypothesis: a phylogenetic and field test

Abstract.  1. The size-grain hypothesis predicts that environmental rugosity results in positive allometric scaling of leg length on body length because of changes in locomotion costs.
2. The scaling of leg length and body length in ants was re-examined using phylogenetic independent contrast methods, and the allometric relationship found by Kaspari and Weiser ( Functional Ecology , 13 , 530–538, 1999) was supported.
3. The size-grain hypothesis was tested further by comparing the body sizes of ants from areas of contrasting habitat complexity in two different savanna habitats. No support for the size-grain hypothesis was found. Small body size classes were no more speciose in the rugose than in the more planar environment, and small ants were more abundant in the planar environment.     

Testing the facilitation-competition paradigm under the stress-gradient hypothesis: decoupling multiple stress factors

While the facilitation-competition paradigm under the stress-gradient hypothesis has received recent attention, its rigorous testing is yet to be explored. Most of the studies have considered a switch in the net interactions from competition to facilitation with increasing environmental stress as primary evidence supporting the hypothesis, though few studies examined changes in interaction along a full range of a stress gradient. Here, we have conceptualized possible variations in the patterns of change in interaction strength along such gradient. Based on this, we empirically evaluated the temporal shift in the interaction between two marine sessile animals, goose barnacles (Capitulum mitella) and mussels (Septifer virgatus), under multiple stress factors. The net effect of goose barnacles on mussel survivorship was positively related to the total stress gradient encompassing two stress factors, physical disturbance and thermal stress, while no negative value occurred even under mild conditions. When the two stress factors were treated separately, however, the net effect demonstrated apparently different patterns: monotonic increase with physical disturbance versus a quasi-asymptotic pattern (no change over a wide range) with thermal stress. These variable situations have not previously been recognized in this discipline, and the present study emphasizes the importance of an integrative and mechanistic approach to testing and deciphering the facilitation-competition paradigm.     

Lack of rapid monoterpene turnover in rooted plants: implications for theories of plant chemical defense

Summary Evidence for the rapid metabolic turnover of leaf monoterpenes is a significant component of theories regarding the evolution and metabolic cost of plant chemical defenses. We re-examined whether monoterpenes are continuously synthesized and lost in intact peppermint plants, and demonstrate that the rapid monoterpene turnover previously observed using detached stems does not occur in intact plants. The apparent artifactual nature of rapid monoterpene turnover in peppermint suggests that a re-evaluation of the rates of metabolic turnover of plant defenses is needed before accurate hypotheses regarding the cost of plant chemical defense can be proposed.     

Habitat selection and home range in the Blanford's fox,Vulpes cana: compatibility with the resource dispersion hypothesis

Summary This paper presents analyses of habitat-use and home range size in the Blanford's fox. We predicted, from the resource dispersion hypothesis (RDH), that home ranges would encompass similar areas of combined fruitful habitats, but widely different areas of useless habitats, and thus that home ranges would be larger where such fruitful patches are fragmented and widely dispersed. Home range estimates of 0.5–2.0 km² were calculated for 16 adult Blanford's foxes, using three different methods. There were no significant differences in home range size between sexes or study sites. One habitat, dry creekbed, was the most frequently visited in all home ranges. Dry creekbed provided abundant prey for the foxes and only sparse cover for their predators. Both the available area of creekbed in each range, and the area of creekbed patches that was used by the foxes, were independent of home range size. However, the variance in home range size was explained by the mean distance between the main denning area and the most frequently used patches of creekbed. These results are in accord with some predictions of the resource dispersion hypothesis.     

Testing the enemy release hypothesis: a review and meta-analysis

One of the most cited hypotheses explaining the inordinate success of a small proportion of introduced plants that become pests is the ‘natural enemies hypothesis’. This states that invasive introduced plants spread rapidly because they are liberated from their co-evolved natural enemies. This hypothesis had not been properly tested until recently. Previous reviews on this topic have been narrative and vote counting in nature. In this review, we carried out quantitative synthesis and meta-analysis using existing literature on plants and their herbivores to test the different components of the enemy release hypothesis. We found supporting evidence in that (1) insect herbivore fauna richness is significantly greater in the native than introduced ranges, and the reduction is skewed disproportionally towards specialists and insects feeding on reproductive parts; and (2) herbivore damage levels are greater on native plants than on introduced invasive congeners. However, herbivore damage levels are only marginally greater for plants in native than in introduced ranges, probably due to the small numbers of this type of study. Studies quantifying herbivore impacts on plant population dynamics are too scarce to make conclusions for either comparison of plants in native vs introduced ranges or of co-occurring native and introduced congeners. For future research, we advocate that more than two-way comparisons between plants in native and introduced ranges, or native and introduced congeners are needed. In addition, the use of herbivore exclusions to quantify the impacts of herbivory on complete sets of population vital rates of native vs introduced species are highly desirable. Furthermore, three-way comparisons among congeners of native plants, introduced invasive, and introduced non-invasive plants can also shed light on the importance of enemy release. Finally, simultaneously testing the enemy release hypothesis and other competing hypotheses will provide significant insights into the mechanisms governing the undesirable success of invasive species.     

Applying the resource dispersion hypothesis to a fission–fusion society: A case study of the African lion (Panthera leo)

The relationship between the spatiotemporal distribution of resources and patterns of sociality is widely discussed. While the resource dispersion hypothesis (RDH) was formulated to explain why animals sometimes live in groups from which they derive no obvious benefits, it has also been successfully applied to species that benefit from group living. Some empirical tests have supported the RDH, but others have not, so conclusions remain equivocal and further research is required to determine the extent to which RDH predictions hold in natural systems. Here, we test four predictions of the RDH in an African lion population in the context of their fission–fusion society. We analyzed data on group composition of GPS‐collared lions and patterns of prey availability. Our results supported the first and second predictions of the RDH: Home range size (a) was independent of group size and (b) increased with distance between encounters with prey herds. Nonetheless, the third and fourth RDH predictions were not supported: (c) The measure of resource heterogeneity and (d) resource patch richness measured through prey herd size and body size had no significant effect on lion group size. However, regarding the fourth prediction, we added an adaptation to account for dynamics of fission–fusion society and found that the frequency of pride fission increased as group size increased. Our data set restricted us from going on to explore the effect of fission–fusion dynamics on the relationship between group size and patch richness. However, this should be investigated in future studies as including fission–fusion dynamics provides a more nuanced, realistic appreciation of lion society. Our study emphasizes the importance of understanding the complexity of a species' behavioral ecology within the framework of resource dispersion. Whatever larger theoretical framework may emerge to explain lion society, incorporating fission–fusion dynamics should allow the RDH to be refined and improved.     

Testing the shared-pathway hypothesis in the carotenoid-based coloration of red crossbills

The mechanisms involved in the production of red carotenoid-based ornaments of vertebrates are still poorly understood. These colorations often depend on enzymatic transformations (ketolation) of dietary yellow carotenoids, which could occur in the inner mitochondrial membrane (IMM). Thus, carotenoid ketolation and cell respiration could share biochemical pathways, favoring the evolution of ketocarotenoid-based ornaments as reliable indices of individual quality under sexual selection. Captive male red crossbills (Loxia curvirostra Linnaeus) were exposed to redox-active compounds designed to penetrate and act in the IMM: an ubiquinone (mitoQ) or a superoxide dismutase mimetic (mitoTEMPO). MitoQ can act as an antioxidant but also distort the IMM structure, increasing mitochondrial free radical production. MitoQ decreased yellow carotenoids and tocopherol levels in blood, perhaps by being consumed as antioxidants. Contrarily, mitoTEMPO-treated birds rose circulating levels of the second most abundant ketocarotenoid in crossbills (i.e., canthaxanthin). It also increased feather total red ketocarotenoid concentration and redness, but only among those birds exhibiting a redder plumage at the start of the study, that is, supposedly high-quality individuals. The fact that mitoTEMPO effects depended on original plumage color suggests that the red-ketocarotenoid-based ornaments indicate individual quality as mitochondrial function efficiency. The findings would thus support the shared pathway hypothesis.     

A preliminary test of the transitional growth spurt hypothesis using the protogynous coral trout Plectropomus maculatus

Estimates of back-calculated size at age provided no evidence of a growth spurt following sexual transition in the protogynous serranid Plectropomus maculatus. The results suggested that mature females that had a large size at age early in life changed sex to male.     

Testing the optimal defence hypothesis for two indirect defences: extrafloral nectar and volatile organic compounds

Many plants respond to herbivory with an increased production of extrafloral nectar (EFN) and/or volatile organic compounds (VOCs) to attract predatory arthropods as an indirect defensive strategy. In this study, we tested whether these two indirect defences fit the optimal defence hypothesis (ODH), which predicts the within-plant allocation of anti-herbivore defences according to trade-offs between growth and defence. Using jasmonic acid-induced plants of Phaseolus lunatus and Ricinus communis, we tested whether the within-plant distribution pattern of these two indirect defences reflects the fitness value of the respective plant parts. Furthermore, we quantified photosynthetic rates and followed the within-plant transport of assimilates with (13)C labelling experiments. EFN secretion and VOC emission were highest in younger leaves. Moreover, the photosynthetic rate increased with leaf age, and pulse-labelling experiments suggested transport of carbon to younger leaves. Our results demonstrate that the ODH can explain the within-plant allocation pattern of both indirect defences studied.     

The 2R hypothesis and the human genome sequence

One theory formalised in 1970 proposes that the complexity of vertebrate genomes originated by means of genome duplication at the base of the vertebrate lineage. Since then, the theory has remained both popular and controversial. Here we review the theory, and present preliminary results from our analysis of duplications in the draft human genome sequence. We find evidence for extensive duplication of parts of the genome. We also question the validity of the 'parsimony test' that has been used in other analyses.     

Testing the threat-sensitive predator avoidance hypothesis: physiological responses and predator pressure in wild rabbits

Predation is a strong selective force with both direct and indirect effects on an animal’s fitness. In order to increase the chances of survival, animals have developed different antipredator strategies. However, these strategies have associated costs, so animals should assess their actual risk of predation and shape their antipredator effort accordingly. Under a stressful situation, such as the presence of predators, animals display a physiological stress response that might be proportional to the risk perceived. We tested this hypothesis in wild European rabbits (Oryctolagus cuniculus), subjected to different predator pressures, in Doñana National Park (Spain). We measured the concentrations of fecal corticosterone metabolites (FCM) in 20 rabbit populations. By means of track censuses we obtained indexes of mammalian predator presence for each rabbit population. Other factors that could modify the physiological stress response, such as breeding status, food availability and rabbit density, were also considered. Model selection based on information theory showed that predator pressure was the main factor triggering the glucocorticoid release and that the physiological stress response was positively correlated with the indexes of the presence of mammalian carnivore predators. Other factors, such as food availability and density of rabbits, were considerably less important. We conclude that rabbits are able to assess their actual risk of predation and show a threat-sensitive physiological response.     

Interactive effects of habitat productivity and herbivore pressure on the evolution of anti-herbivore defense in invasive plant populations

The evolution of increased competitive ability (EICA) hypothesis predicts that plants released from natural enemies should evolve to become more invasive through a shift in resource allocation from defense to growth. Resource availability in the environment is widely regarded as a major determinant of defense investment and invasiveness, and thus should be incorporated into the conceptual framework of EICA. Analysis of a simple model from the optimal defense literature demonstrates that, in contrast to the EICA hypothesis, enemy release is neither sufficient nor necessary for evolution of reduced resistance among introduced plants when habitat productivity co-varies. In particular, if the invasive range is more nutrient-poor than the native range, there could be selection for more plant defenses even with enemy release.     

Sex differences in spatial ability: a test of the range size hypothesis in the order Carnivora

Sex differences in spatial cognition have been reported for many species ranging from voles to humans. The range size hypothesis predicts that sex differences in spatial ability will only occur in species in which the mating system selects for differential range size. Consistent with this prediction, we observed sex differences in spatial ability in giant pandas, a promiscuous species in which males inhabit larger ranges than females, but did not observe sex differences in Asian small-clawed otters, a related monogamous species in which males and females share home ranges. These results provide the first evidence of sex differences in spatial ability in the order Carnivora, and are consistent with the range size hypothesis.     

Processing power limits social group size: computational evidence for the cognitive costs of sociality

Sociality is primarily a coordination problem. However, the social (or communication) complexity hypothesis suggests that the kinds of information that can be acquired and processed may limit the size and/or complexity of social groups that a species can maintain. We use an agent-based model to test the hypothesis that the complexity of information processed influences the computational demands involved. We show that successive increases in the kinds of information processed allow organisms to break through the glass ceilings that otherwise limit the size of social groups: larger groups can only be achieved at the cost of more sophisticated kinds of information processing that are disadvantageous when optimal group size is small. These results simultaneously support both the social brain and the social complexity hypotheses.     

Testing the resource concentration hypothesis with tarnished plant bug on strawberry: density of hosts and patch size influence the interaction between abundance of nymphs and incidence of damage

Abstract. 1. Attributes of patches with strawberry plants were manipulated experimentally to assess the impact of patch size and host density on the abundance of tarnished plant bug (Hemiptera: Miridae) and incidence of fruit damage.
2. The density of nymphs per inflorescence increased with patch size and host density for some but not all generations of plant bug, providing partial support for the resource concentration hypothesis, while emphasising the importance of replicating experiments across several generations of herbivore.
3. Increasing density of nymphs with increasing patch size and host density did not translate into a high incidence of damage, which may be due to the relatively low feeding impact of nymphs in patches with numerous fruits and to the relatively high perimeter-to-area ratio in small patches resulting in a relatively high proportion of damaged fruits.
4. The decreasing proportion of damaged fruits with increasing density of fruits per patch suggests that nymphs exhibit a saturating functional response to density of strawberry fruits. Functional responses of herbivores may be a critical yet overlooked component that influences interactions between insects and their host plant. In particular, concentrated plant resources may result in increased numbers of herbivores yet sill have a negligible influence on plant damage and/or fitness.     

Evolutionary hypothesis of telomere length in primary breast cancer and brain tumour patients: a tracer for genomic-tumour heterogeneity and instability

It was previously reported that tumour samples had shorter telomeres than the surrounding normal tissue. Hereby, the initial sign of correlation between malignant tissue and telomere behaviour could be noticed. Bridging knowledge between germ and somatic cells could facilitate understanding cellular evolution. The aim of our investigation was to provide evidence for the evolutionary hypothesis of TL (telomere length) in primary BC (breast cancer) and BTs (brain tumours), which might be applied as a prognostic and/or predictive marker. DNA extraction from the frozen tissues was performed using high pure PCR template preparation kit. Standard protocol of Telo TTAGGG Telomere Length Assay kit, a non‐radioactive chemiluminescent assay, was used. The protein expression in extracted cells was analysed by immunofluorescence. We also detected telomerase activity. The G/T (genomic/tumour ratio) for TL in two groups of patients affected with primary BC and primary BT revealed significant differences in both BC patients (P=0.025) and in BTs (P=0.001). The pattern of telomere signals by Q‐FISH (quantitative fluorescent in situ hybridization) show that in all samples, except one, SI (signal intensity) has been significantly decreased in tissue related to blood, either in BC patients or in patients with BTs (0.041≥P≥0.001). However, the data achieved by Q‐FISH support the results of Southern blot. These data reflect a significant diversity either in BC or in BT patients, providing evidence for the evolutionary hypothesis of TL in cancer development and progression.     

Testing the growth-differentiation balance hypothesis: dynamic responses of willows to nutrient availability

Here, the growth-differentiation balance hypothesis (GDBH) was tested by quantifying temporal variation in the relative growth rate (RGR), net assimilation rate (NAR), and phenylpropanoid concentrations of two willow species (Salix sericea and Salix eriocephala) across five fertility levels. Initially, RGR increased and total phenylpropanoids declined (although every individual phenolic did not) as fertility increased, but NAR was unaffected. Subsequently, NAR and phenylpropanoids declined in the low fertility treatment, generating a quadratic response of secondary metabolism across the nutrient gradient. As above- and below-ground growth rates equilibrated, NAR and phenylpropanoids increased in the low fertility treatment, re-establishing a negative linear effect of fertility on secondary metabolism. A transient quadratic response of secondary metabolism is predicted when GDBH is integrated with models of optimal phenotypic plasticity, occurring when low NAR imposes carbon constraints on secondary metabolism in low nutrient environments. Once plants acclimate to nutrient limitation, the equilibrium allocation state is predicted to be a negative correlation between growth and secondary metabolism. Although both willow species generally responded according to GDBH, the complexity observed suggests that prediction of the effects of nutrient availability on secondary metabolism (and other plastic responses) in specific cases requires a priori knowledge of the physiological status of the plant and soil nutrient availability.