The evolution of body armor in mammals: plantigrade constraints of large body size

Predictions associated with opposing selection generating minimum variance in basal metabolic rate (BMR) in mammals at a constrained body mass (CBM; 358 g) were tested. The CBM is presumed to be associated with energetic constraints linked to predation and variable resources at intermediate sizes on a logarithmic mass scale. Opposing selection is thought to occur in response to energetic constraints associated with predation and unpredictable resources. As body size approaches and exceeds the CBM, mammals face increasing risks of predation and daily energy requirements. Fast running speeds may require high BMRs, but unpredictable and low resources may select for low BMRs, which also reduce foraging time and distances and thus predation risks. If these two selection forces oppose each other persistently, minimum BMR variance may result. However, extreme BMR outliers at and close to the CBM should be indicative of unbalanced selection and predator avoidance alternatives (escapers vs. defenders), and may therefore provide indirect support for opposing selection. It was confirmed that body armor in defenders evolves at and above the CBM, and armored mammals had significantly lower BMRs than their nonarmored counterparts. However, analyses comparing the BMR of escapers--the fastest nonarmored runners (Lagomorpha)--with similar-sized counterparts were inconclusive and were confounded by limb morphology associated with speed optimization. These analyses suggest that the risks and costs of predation and the speed limitations of the plantigrade foot may constrain the evolution of large body sizes in plantigrade mammals.     

The relative merits of foregut and hindgut fermentation

Mammalian herbivores cannot break down cellulose except by fermentation, and may have Termentation chambers at either end of the gut: ruminants have their principal fermentation chamber in the stomach but horses ferment only in the hindgut. A mathematical model (Alexander, 1991) predicted that foregut fermenters should do better than hindgut fermenters on poor foods, and the reverse on richer. less fibrous foods. Further, the optimum gut for poor foods would have the hindgut fermentation chamber only a little smaller than the foregut chamber. However. it has been claimed that horses do better than ruminants on poor food, and the hindgut of ruminants is much smaller than the rumen.
In this paper, the basic model is modified in ways designed to make it more realistic and the effects are investigated. None of the modifications alters the conclusion that the optimum gut for poor food has a large foregut fermentation chamber. However, the optimum proportions of fore-to hindgut, for poor diets, become more like those of real ruminants when account is taken of the diminishing volume of the food passing through the gut, and of incomplete mixing in the rumen.     

Patterns of maximum body size evolution in Cenozoic land mammals: eco-evolutionary processes and abiotic forcing

There is accumulating evidence that macroevolutionary patterns of mammal evolution during the Cenozoic follow similar trajectories on different continents. This would suggest that such patterns are strongly determined by global abiotic factors, such as climate, or by basic eco-evolutionary processes such as filling of niches by specialization. The similarity of pattern would be expected to extend to the history of individual clades. Here, we investigate the temporal distribution of maximum size observed within individual orders globally and on separate continents. While the maximum size of individual orders of large land mammals show differences and comprise several families, the times at which orders reach their maximum size over time show strong congruence, peaking in the Middle Eocene, the Oligocene and the Plio-Pleistocene. The Eocene peak occurs when global temperature and land mammal diversity are high and is best explained as a result of niche expansion rather than abiotic forcing. Since the Eocene, there is a significant correlation between maximum size frequency and global temperature proxy. The Oligocene peak is not statistically significant and may in part be due to sampling issues. The peak in the Plio-Pleistocene occurs when global temperature and land mammal diversity are low, it is statistically the most robust one and it is best explained by global cooling. We conclude that the macroevolutionary patterns observed are a result of the interplay between eco-evolutionary processes and abiotic forcing.     

Is maximum sustainable yield independent of body size for mammals (and others)?

Summary Provided carrying capacity (K) for non-primate mammals scales with the –0.75 power of adult body weight (W), MSY (in weight) should be approximately one-sixth ofC, whereC is defined byK =CW ^–0.75.     

Circulation,metabolic rate,and body size in mammals

Summary This paper attempts to explain Kleiber's rule, which relates metabolic rate of mammals to their body mass, from the structure and function of the blood circulation system.Abbreviations a scaling factor - fractal dimension - hydrodynamic conductivity - l _n length of an arterial blood vessel at bifurcation level n - M body mass - N maximal number of bifurcation levels - p pressure - Q flow - r size of Bohr effect - r _n radius of an arterial blood vessel at bifurcation level n - V volume - VO ₂ rate of oxygen unloading - Z _n number of arterial blood vessels at bifurcation level n     

Assessing metabolic constraints on the maximum body size of actinopterygians: locomotion energetics of Leedsichthys problematicus (Actinopterygii,Pachycormiformes)

Maximum sizes attained by living actinopterygians are much smaller than those reached by chondrichthyans. Several factors, including the high metabolic requirements of bony fishes, have been proposed as possible body‐size constraints but no empirical approaches exist. Remarkably, fossil evidence has rarely been considered despite some extinct actinopterygians reaching sizes comparable to those of the largest living sharks. Here, we have assessed the locomotion energetics of Leedsichthys problematicus, an extinct gigantic suspension‐feeder and the largest actinopterygian ever known, shedding light on the metabolic limits of body size in actinopterygians and the possible underlying factors that drove the gigantism in pachycormiforms. Phylogenetic generalized least squares analyses and power performance curves established in living fishes were used to infer the metabolic budget and locomotion cost of L. problematicus in a wide range of scenarios. Our approach predicts that specimens weighing up to 44.9 tonnes would have been energetically viable and suggests that similar body sizes could also be possible among living taxa, discarding metabolic factors as likely body size constraints in actinopterygians. Other aspects, such as the high degree of endoskeletal ossification, oviparity, indirect development or the establishment of other large suspension‐feeders, could have hindered the evolution of gigantism among post‐Mesozoic ray‐finned fish groups. From this perspective, the evolution of anatomical innovations that allowed the transition towards a suspension‐feeding lifestyle in medium‐sized pachycormiforms and the emergence of ecological opportunity during the Mesozoic are proposed as the most likely factors for promoting the acquisition of gigantism in this successful lineage of actinopterygians.     

Little effect of climate change on body size of herbivorous beetles

Ongoing climate change affects various aspects of an animal's life, with important effects on distribution range and phenology. The relationship between global warming and body size changes in mammals and birds has been widely studied, with most findings indicating a decline in body size over time. Nevertheless, little data exist on similar size change patterns of invertebrates in general and insects in particular, and it is unclear whether insects should decrease in size or not with climate warming. We measured over 4000 beetle specimens, belonging to 29 beetle species in 8 families, collected in Israel during the last 100 years. The sampled species are all herbivorous. We examined whether beetle body size had changed over the years, while also investigating the relationships between body size and annual temperature, precipitation, net primary productivity (NPP) at the collection site and collection month. None of the environmental variables, including the collection year, was correlated with the size of most of the studied beetle species, while there were strong interactions of all variables with species. Our results, though mostly negative, suggest that the effect of climate change on insect body size is species‐specific and by no means a general macro‐ecological rule. They also suggest that the intrapopulation variance in body size of insects collected as adults in the field is large enough to conceal intersite environmental effects on body size, such as the effect of temperature and NPP.     

The controlling factors limiting maximum body size of insects

The purpose of this study is to consider the controlling factors limiting maximum body size of insects. For this analysis, we set up and quantitatively verify the following working hypothesis: insect body sizes can be explained only by the historical changes in the oxygen supply. The present study focuses on the body size of the Protodonata and Odonata. The amount of oxygen needed and that of oxygen entering the insect body was calculated using allometric equations. The theoretical maximum sizes at each geologic time were estimated from palaeo‐atmospheric oxygen partial pressure and compared with the maximum size of known fossilized insects. The historical change in fossilized insect sizes was much larger than that in theoretical sizes. Additionally, from the Jurassic, despite an increase in the partial pressure of oxygen, which would theoretically increase maximum size, the maximum size of fossilized insects became smaller. These findings are inconsistent with the expectations of the working hypothesis. Oxygen supply is likely to partially limit the maximum size of insects with additional factors.     

Correlates of species richness in mammals: body size, life history, and ecology

We present the most extensive examination to date of proposed correlates of species richness. We use rigorous phylogenetic comparative techniques, data for 1,692 mammal species in four clades, and multivariate statistics to test four hypotheses about species richness and compare the evidence for each. Overall, we find strong support for the life-history model of diversification. Species richness is significantly correlated with shorter gestation period in the carnivores and large litter size in marsupials. These traits and short interbirth intervals are also associated with species richness in a pooled analysis of all four clades. Additionally, we find some support for the abundance hypotheses in different clades of mammals: abundance correlates positively with species richness in primates but negatively in microchiropterans. Our analyses provide no evidence that mammalian species richness is associated with body size or degree of sexual dimorphism.     

Climatic influences on human body size and proportions: Ecological adaptations and secular trends

This study reevaluates the long-standing observation that human morphology varies with climate. Data on body mass, the body mass index [BMI; mass (kg)/stature (m)²], the surface area/body mass ratio, and relative sitting height (RSH; sitting height/stature) were obtained for 223 male samples and 195 female samples derived from studies published since D.F. Roberts' landmark paper “Body weight, race, and climate” in 1953 (Am. J. Phys. Anthropol. 11:533–558). Current analyses indicate that body mass varies inversely with mean annual temperature in males (r = −0.27, P < 0.001) and females (r = −0.28, P < 0.001), as does the BMI (males: r = −0.22, P = 0.001; females: r = −0.30, P < 0.001). The surface area/body mass ratio is positively correlated with temperature in both sexes (males: r = 0.29, P < 0.001; females: r = 0.34, P < 0.001), whereas the relationship between RSH and temperature is negative (males: r = −0.37, P < 0.001; females: r = −0.46, P < 0.001). These results are consistent with previous work showing that humans follow the ecological rules of Bergmann and Allen. However, the slope of the best-fit regressions between measures of body mass (i.e., mass, BMI, and surface area/mass) and temperature are more modest than those presented by Roberts. These differences appear to be attributable to secular trends in mass, particularly among tropical populations. Body mass and the BMI have increased over the last 40 years, whereas the surface area/body mass ratio has decreased. These findings indicate that, although climatic factors continue to be significant correlates of world-wide variation in human body size and morphology, differential changes in nutrition among tropical, developing world populations have moderated their influence. Am J Phys Anthropol 106:483–503, 1998. © 1998 Wiley-Liss, Inc.     

Cuckoos, cowbirds and hosts: adaptations, trade-offs and constraints

The interactions between brood parasitic birds and their host species provide one of the best model systems for coevolution. Despite being intensively studied, the parasite-host system provides ample opportunities to test new predictions from both coevolutionary theory as well as life-history theory in general. I identify four main areas that might be especially fruitful: cuckoo female gentes as alternative reproductive strategies, non-random and nonlinear risks of brood parasitism for host individuals, host parental quality and targeted brood parasitism, and differences and similarities between predation risk and parasitism risk. Rather than being a rare and intriguing system to study coevolutionary processes, I believe that avian brood parasites and their hosts are much more important as extreme cases in the evolution of life-history strategies. They provide unique examples of trade-offs and situations where constraints are either completely removed or particularly severe.     

Breathing with your belly: Abdominal exhalation,loco-ventilatory integration and size constraints on locomotion in small mammals

In mammals, diaphragmatic contractions control inhalation while contraction of some thoracic hypaxial muscles and the transversus abdominis muscle contribute to exhalation. Additional thoracic hypaxial muscles are recruited as accessory ventilatory muscles to improve inhalation and exhalation during locomotion. However, the contribution of abdominal hypaxial muscles to resting and locomotor ventilation is little understood in mammals and loco-ventilatory integration has not been studied in small basal mammals. We show for the first time that all of the abdominal hypaxial muscles actively contribute to both resting and locomotory ventilation in mammals but in a size-dependent manner. In large opossums (Didelphis), hypaxial muscles exhibit uniform mild tonus during resting ventilation (pressurizing the gut to aid in exhalation) and shift to phasic bursts of activity during each exhalation during locomotion. Smaller opossums (Monodelphis) actively exhale by firing the abdominal hypaxial muscles at ～10 Hz at both rest and at preferred locomotor speeds. Furthermore, the large opossums entrained ventilation to limb cycling as speed increased while the small opossums entrained limb cycling to the resting ventilation rate during locomotion. Differences in these species are related to size effects on the natural frequency of the ventilatory system and increasing resting ventilation rates at small size. Large mammals, with lower resting ventilation rates, can increase ventilatory rates during locomotion, while the high resting ventilation rates of small mammals limits their ability to increase ventilation rates during locomotion. We propose that increase in mammalian body size during the Cenozoic may have been an adaptation or exaptation to overcome size effects on ventilation frequency.     

Loading constraints,body size and mating preference in Gammarus species

Size relationships among pairing Gammarus were examined with reference to two hypotheses for sexual size dimorphism and assortative mating among aquatic Peracarida (Crustacea). The sizes of pairing and non-pairing animals were compared in different experimental conditions where the size of one or both sexes was controlled. The experimental results present a complex picture which suggests that both sexual selection and loading constraints are likely to play a role in determining mating decisions in these animals.Department of Adult & Continuing Education, University of Durham     

Ecological and phylogenetic constraints on body size in Indo-Pacific fishes

Synopsis Regional Indo-Pacific fish faunas were examined for broad patterns in species size composition. An analysis of the New Guinea fauna, based on data compiled by Munro (1967), revealed that (i) maximum body size for a species tended to be larger in the more advanced teleost families; (ii) intrafamilial size variation (expressed by the standard deviation of log-transformed maximum body size) was significantly lower in the suborder Percoidei than in families drawn from broader taxonomic groupings; and (iii) size variation was significantly positively correlated with mean maximum body size and, in the percoids only, with the number of species in a family. An analysis of Marshall Islands reef fish assemblages, based mainly on the data of Matt & Strasburg (1960), indicated, that (i) mean maximum body size varied significantly between habitats and feeding categories, and tended to increase with openness of habitat and with trophic level; (ii) size variation within feeding categories increased with the number of species, but not significantly so; and (iii) confamilial species generally exhibited close similarities in terms of preferred habitats, trophic levels and foraging modes. These findings indicate that interspecific body size variation is both phylogenetically and ecologically constrained. Size variation within ecological categories (especially habitats) was much greater than within families. Thus, confamilial species generally did not exhibit the range of body sizes theoretically open to members of their habitat feeding guilds. The results are also consistent with aspects of resource-partitioning theory, notably that resource-utilisation breadth should increase with the number of coexisting species.     

Heterothermy,body size,and locomotion as ecological predictors of migration in mammals

1. Migration is ubiquitous among animals and has evolved repeatedly and independently. Comparative studies of the evolutionary origins of migration in birds are widespread, but are lacking in mammals. Mammalian species have greater variation in functional traits that may be relevant for migration. Interspecific variation in migration behaviour is often attributed to mode of locomotion (i.e. running, swimming, and flying) and body size, but traits associated with the evolutionary precursor hypothesis, including geographic distribution, habitat, and diet, could also be important predictors of migration in mammals. Furthermore, mammals vary in thermoregulatory strategies and include many heterothermic species, providing an alternative strategy to avoid seasonal resource depletion.
2. We tested the evolutionary precursor hypothesis for the evolution of migration in mammals and tested predictions linking migration to locomotion, body size, geographic distribution, habitat, diet, and thermoregulation. We compiled a dataset of 722 species from 27 mammalian orders and conducted a series of analyses using phylogenetically informed models.
3. Swimming and flying mammals were more likely to migrate than running mammals, and larger species were more likely to migrate than smaller ones. However, heterothermy was common among small running mammals that were unlikely to migrate. High-latitude swimming and flying mammals were more likely to migrate than high-latitude running mammals (where heterothermy was common), and most migratory running mammals were herbivorous. Running mammals and frugivorous bats with high thermoregulatory scope (greater capacity for heterothermy) were less likely to migrate, while insectivorous bats with high thermoregulatory scope were more likely to migrate.
4. Our results indicate a broad range of factors that influence migration, depending on locomotion, body size, and thermoregulation. Our analysis of migration in mammals provided insight into some of the general rules of migration, and we highlight opportunities for future investigations of exceptions to these rules, ultimately leading to a comprehensive understanding of the evolution of migration.

     

Pharmacological studies of proctolin receptors on foregut and hindgut of blaberus craniifer

Proctolin (Arg-Tyr-Leu-Pro-Thr) and proctolin analogs modified at position 1, 2, or 5 caused dose dependent contractions of Blaberus fore- and hindgut. The varying contractile effects between both tissues revealed the possible presence of receptor subtypes as identified by [GABA¹]-proctolin. A single population of binding sites (K_d ≈ 100 n ) was deduced from Scatchard analysis. In addition, nanomolar concentrations of proctolin induced a dose-dependent hydrolysis of phosphoinositides (PIns) augmented by GTPγS (1 μ ) on foregut membranes but no accumulation of cAMP. Proctolin induced contractions are likely mediated via a phospholipase C linked to a heptahelical receptor bound to heterotrimeric G-proteins.