Brooding behaviour and cost of brooding in small body size brachyuran crabs

Dynamical complexity driven by water temperature in a size-dependent phytoplankton–zooplankton model with environmental variability

Competing hypotheses: (1) Large body size confers more efficient energy use (relative efficiency hypothesis). (2) Large body size requires more energy to be sustained, a disadvantage when food is limited (absolute energy demand hypothesis). Organism: Yellow dung flies, Scathophaga stercoraria (Diptera: Scathophagidae), artificially selected for large and small body size in the laboratory for 24 generations to augment the available phenotypic body sizes. Methods: Larvae were reared under limited and unlimited food (dung) conditions, and the energy content of pupae was measured at the beginning and the end of the pupal stage in different, size-matched individuals. Conclusions: Over the pupal period, lipids and glycogen decreased whereas sugar content increased. Net energy loss per unit body mass was higher at unlimited food. Contrary to expectation, males (the larger sex) lost less energy than females. Large selection line pupae showed the highest absolute and mass-specific energy loss during metamorphosis, indicating a correlated physiological response to body size selection because phenotypic body sizes do not differ between the lines at limited dung. We conclude that energetic costs due to greater absolute energy demand of larger individuals during the pupal phase outweigh the benefits due to greater metabolic efficiency.

Body size and fitness in plants: Revisiting the selection consequences of competition

Most life history traits are positively influenced by body size, while disadvantages of large size are poorly documented. To investigate presumed intrinsic costs of large body size in yellow dung flies (Scathophaga stercoraria; Diptera: Scathophagidae), we allowed larvae from replicate lines artificially selected for small and large body size for 21 generations to compete directly with each other at 20°C (benign) and 25°C (stressful) and low and high food (dung) availability. Greater mortality of large line flies was evident at low food independent of temperature, suggesting a cost of fast growth and/or long development for genetically large flies during larval scramble competition under food limitation. Our results are congruent with a previous study assessing mortality when competing within body size lines, so no additional mechanisms affecting scramble or contest behavior of larvae need be invoked to explain the results obtained beyond the costs of longer development and faster growth. Thus, artificial selection producing larger yellow dung flies than occur in nature revealed some, albeit weak mortality costs of large body size that otherwise might have remained cryptic. We conclude, however, that these costs are insufficient to explain the evolutionary limits of large body size in this species given persistently strong fecundity and sexual selection favoring large size in both sexes.

Animal species differ in the variability of their clutch sizes, as well as in mean clutch sizes. This phenomenon is particularly obvious in lizards, where virtually invariant clutch sizes have evolved independently in at least 23 lineages in seven families. Reduced variance in clutch size may arise either as an adaptation (because females with less variable clutch sizes have higher fitness) or as an indirect by-product of selection on other life-history characteristics. Comparative data on Australian scincid lizards indicate that variance in clutch sizes is lowest among species with low mean clutch sizes, small body sizes and a low variance in body sizes of adult females. Phylogenetic analysis shows that evolutionary decreases in the variance of clutch size have accompanied decreases in mean clutch sizes and decreases in the variance of adult female body sizes. Tropical lizards may also exhibit lower variance in clutch size. Most of these characteristics are correlated in occurrence, and may be allometrically tied to small body size. Hence, low variance in clutch size may be a consequence of allometric effects on a correlated suite of life-history characteristics. Exceptions to the general patterns noted above-especially, lizard species with invariant clutch sizes but large body sizes-may be due to loss of genetic variance for clutch sizes in lineages that have passed through a "bottleneck" of small body sizes and hence, low variance in clutch sizes.

Two new species of Atractus are described from Venezuela uplands and highlands on two northern Andean cordilleras. Atractus acheronius, known only from Sierra de Perijá, can be distinguished from congeners by having 17 dorsal scale rows, presence of preocular scales, seven upper and lower labials, seven maxillary teeth, 166 ventrals in the single female, 23 subcaudals, dorsum brown with small dark brown dots, large body size, huge body diameter, and small tail size. Atractus multidentatus, known only from north versant of the Cordillera de Mérida, can be distinguished from congeners by having 17 dorsal scale rows, eight upper and lower labials, 18 maxillary teeth, 153 ventrals in the single female, nine subcaudals, dorsum reddish brown with five longitudinal dark brown stripes, small body size, small body diameter, and small tail size. Additionally, a discussion concerning the species description of Atractus based on unique specimens is provided.

Summary 1 Large body size is typically strongly favoured by sexual selection in males and by fecundity selection in females, while disadvantages of large size are poorly documented. Two contrasting physiological hypotheses have been suggested to affect selection on body size. According to the relative efficiency hypothesis, large body size confers more efficient energy use; according to the absolute energy demand hypothesis, large body size requires more energy to be sustained, a disadvantage particularly when food is limited. 2 We investigated the effect of food availability on glycogen and lipid allocation to reproduction in Yellow Dung Flies (Scathophaga stercoraria; Diptera: Scathophagidae) of varying body sizes. Male and female flies stemmed from selection lines artificially selected for large and small body size for 11 generations. Flies were reared at unlimited and limited larval food (dung), and the emerging adults were further held at low and high adult food (prey). 3 Adult food conditions strongly influenced reproductive maturation and energy reserves in both sexes, while larval food conditions played a minor role primarily in males. Unlimited adult food led to earlier maturation and larger clutches and egg volumes, and female investment of glycogen and lipids into the clutch was proportionally greater, supporting the relative efficiency hypothesis. 4 In contrast, at limited adult food females selected for small size matured earlier and had relatively larger clutches than large line females (when correcting for body size), in correspondence with greater glycogen investment in reproduction. Small line males at limited prey also tended to reproduce sooner. These correlated genetic responses to artificial selection support the absolute energy demand hypothesis. How important these admittedly small effects are in nature remains to be investigated.

Body size at birth has implications for the quality of individuals throughout their life. Although large body size is generally considered an advantage, the relationship between body size at birth and long-term fitness is often complicated. Under spatial or temporal variation in environmental conditions, such as the seasonally changing densities of Fennoscandian vole populations, selection should favor variation in offspring phenotypes, as different qualities may be beneficial in different conditions. We performed an experiment in which a novel hormonal manipulation method was used to increase phenotypic variance in body size at birth in the bank vole (Myodes glareolus). The effects of body size on the future fitness of young males and females were then studied at varying population densities in outdoor enclosures. Our results show that small body size at birth and high breeding density increase the survival costs of reproduction. However, there was no interaction between the effects of body size and density on survival, which suggests that the fitness effects of body size were strong enough to persist under environmental variation. Moreover, litter size and the probability of breeding were more sensitive to variation in breeding density than offspring size. Therefore, it is unlikely that individual fitness could be optimized by adjusting offspring body size to the prevailing population density through adaptive maternal effects. Our results highlight the significance of the costs of reproduction in the evolution of life-history traits, and give strong experimental support for the long-term fitness effects of body size at birth.

A method is described to estimate the counting efficiency appropriate to the body size of each individual subject in 137 Cs whole-body counting, using voxel phantoms. Individual voxel phantoms approximate to the body sizes of subjects were prepared by expanding and contracting the standard voxel phantom that corresponds to a Japanese standard adult male. The individual phantom was made to have the same body height and weight as those of each individual subject. For a whole-body counter at NIRS (Japan), the counting efficiencies for ten subjects were calculated, using the voxel phantoms and a Monte Carlo simulation code. The differences in the counting efficiency between each individual phantom and a conventional phantom ranged from -5 to +12%. The counting efficiency is larger in small body sizes than in large body sizes. The results indicate that body burdens tended to be overestimated in subjects of small body sizes.

Theory predicts that bottom-heavy biomass pyramids or 'stacks' should predominate in real-world communities if trophic-level increases with body size (mean predator-to-prey mass ratio (PPMR) more than 1). However, recent research suggests that inverted biomass pyramids (IBPs) characterize relatively pristine reef fish communities. Here, we estimated the slope of a kelp forest fish community biomass spectrum from underwater visual surveys. The observed biomass spectrum slope is strongly positive, reflecting an IBP. This is incongruous with theory because this steep positive slope would only be expected if trophic position decreased with increasing body size (consumer-to-resource mass ratio, less than 1). We then used δ(15)N signatures of fish muscle tissue to quantify the relationship between trophic position and body size and instead detected strong evidence for the opposite, with PPMR ≈ 1650 (50% credible interval 280-12 000). The natural history of kelp forest reef fishes suggests that this paradox could arise from energetic subsidies in the form of movement of mobile consumers across habitats, and from seasonally pulsed production inputs at small body sizes. There were four to five times more biomass at large body sizes (1-2 kg) than would be expected in a closed steady-state community providing a measure of the magnitude of subsidies.

A cohort of tadpoles of the chorus frog, Pseudacris triseriata, on Isle Royale, Michigan, was marked to determine the effect of body size and date at metamorphosis on survivorship to maturity. The cohort was classified at metamorphosis into four categories based on size and date of metamorphosis: large—early, small—early, large—late, and small—late. The number of frogs in each category that returned to breed on the study area was monitored for the following 2 yr. Long larval period and small body size at metamorphosis influenced recruitment to the breeding population by delaying maturity. Frogs that metamorphosed at large size maintained their size advantage at maturity. Large body size and early date at metamorphosis increased survivorship to maturity by enhancing the chance that reproductive size was attained within 1 yr of metamorphosis. Frogs that were recaptured in the 2nd yr after metamorphosis, when all frogs had attained mature size, were from all four categories in the same proportions marked at metamorphosis, indicating that unless breeding during the 1st yr, led to higher mortality of large individuals, survival rate after metamorphosis was not related to size or date at metamorphosis.

Cell Size: A Matter of Life or Death?

Elevated instream fine sediment is one of the most important water quality stressors affecting both the structure and function of aquatic ecosystems. This study evaluates whether a predictable pattern of trait distribution of Ephemeroptera, Plecoptera, and Trichoptera (EPT) can be observed along a gradient of sediment stress in eight selected sites in the Tsitsa River and its tributaries. The sites were classified into four site groups according to their fine sediment loads. One‐way analysis of variance was used to test differences in the relative abundance of traits across the site groups. A predictable pattern was observed in 13 of the 27 trait attributes tested, with most traits displaying low abundances in highly disturbed site groups. The relationship between EPT traits and fine sediment stress was analysed using the multivariate RLQ analysis, and the result showed that traits such as swimming, shredding, operculate gill, small body size, and sclerotized body were the dominant traits in the sediment influenced site groups. In the less disturbed site groups, filter feeding, crawling, filamentous gill, soft and exposed body, and large body size were the dominant trait attributes. These observed relationships between EPT traits and sediment stress provide support for the potential usefulness of EPT traits as indicators of fine sediment stress in riverine ecosystems.

From a trophic perspective, a seasonal increase in air temperature and photoperiod propagates as bottom-up pulse of primary production by plants, secondary production by herbivores, and tertiary production by carnivores. However, food web seasonality reflects not only abiotic variation in temperature and photoperiod, but also the composition of the biotic community and their functional responses to this variation. Some plants and animals-here referred to as seasonal specialists-decouple from food webs in winter through migration or various forms of metabolic arrest (e.g., senescence, diapause, and hibernation), whereas some plants and resident animals-here referred to as seasonal generalists-remain present and trophically coupled in winter. The co-occurrence of species with divergent responses to winter introduces seasonal variation in interaction strengths, resulting in summer-to-winter differences in trophic organization. Autumn cooling and shortening day length arrests primary productivity and cues seasonal herbivores to decouple, leaving generalist carnivores to concentrate their predation on the few generalist herbivores that remain resident, active, and vulnerable to predation in winter, which themselves feed on the few generalist plant structures available in winter. Thus, what was a bottom-up pulse, spread among many species in summer, including highly productive seasonal specialists, reverses into strong top-down regulation in winter that is top-heavy, and concentrated among a small number of generalist herbivores and their winter foods. Intermediate-sized, generalist herbivores that remain active and vulnerable to predation in winter are likely to be keystone species in seasonal food webs because they provide the essential ecosystem service of turning summer primary productivity into winter food for carnivores. Empirical examination of terrestrial mammals and their seasonal trophic status in the boreal forest and across an arctic-to-tropics seasonality gradient indicates seasonal specialization is more common among herbivores, small body sizes, and in regions with intermediate seasonality, than among carnivores, large body size, and regions where summers are very short or very long. Better understanding of food webs in seasonal environments, including their vulnerability and resilience to climate change, requires a multi-season perspective.

r-Strategist/K-Strategists