The balance between predictions and evidence and the search for universal macroecological patterns: taking Bergmann’s rule back to its endothermic origin

Geographical variation in environmental temperatures is expected to impose clinal phenotypic selection that results in the expression of large-scale gradients of body mass variation within animal clades. Body size is predicted to increase with increasing latitude and elevation, and hence, with decreasing temperature, a pattern broadly known as Bergmann’s rule. However, empirical observations are highly conflicting. Whilst most studies support this prediction in endotherms (birds and mammals), analyses conducted on ectotherms often fail to report this pattern. Does it reduce the validity of this macroecological rule? Since the original formulation of Bergmann’s rule only involved endothermic organisms, I argue that the controversy is not a consequence of its predictive power, but a result of the later inclusion of ectotherms as part of the prediction. Here, I propose that the common conception of Bergmann’s rule maintained for half a century is changed back to its original definition restricted to endotherms. This temperature–size relationship might therefore consolidate as a well-established macroecological rule if its original formulation is respected. Finally, I develop these claims on my initial suggestion that Bergmann’s rule should be recognized as the evolutionary outcome of a general process with no phylogenetic scale distinction of species or populations, being equally applicable amongst and within species.     

Interspecific pairwise relationships among body size, clutch size and latitude: deconstructing a macroecological triangle in birds

Aim Ecogeographical ‘rules’, large‐scale patterns in ecological variables across geographical space, can provide important insights into the mechanisms of evolution and ecological assembly. However, interactions between rules could obscure both the observation of large‐scale patterns and their interpretation. Here, we examine a system of three variables interrelated by ecogeographical rules – the latitudinal increase in body size within closely related homeotherms (Bergmann’s rule), the negative allometry of clutch size (Calder’s rule) and the latitudinal increase in clutch size (Lack’s rule) – in a global dataset of birds. Location Global. Methods We used linear regressions and meta‐analysis techniques to quantify the three rules across clades and through the taxonomic hierarchy. Path analysis was used to quantify interactions between rules at multiple taxonomic levels, as a function of both phylogenetic inheritance of traits and indirect feedbacks between the three rules. Independent contrasts analyses were performed on four clades with available phylogenies, and the taxonomic partitioning of variation in each trait was quantified. Results Standardizing across all clades, Lack’s and Bergmann’s rules were supported at all taxonomic levels, with Calder’s rule being supported at the order level. Lack’s rule was consistently stronger and more often detected than the other two rules. Path analysis showed that the indirect effects often outweighed the direct effects of Calder’s rule at the genus level and Bergmann’s rule at the order level. Strong interactions between Calder’s and Bergmann’s rules led to a trade‐off between the rules depending on taxonomic resolution. Main conclusions We found strong interactions between Bergmann’s, Lack’s and Calder’s rules in birds, and these interactions varied in strength and direction over the taxonomic hierarchy and among avian clades. Ecogeographical rules may be masked by feedbacks from other, correlated variables, even when the underlying selective mechanism is operating. The apparently conflicting pairwise relationships among clutch size, body size and latitude illustrate the difficulty of interpreting individual pairwise correlations without recognition of interdependence with other variables.     

Latitude, elevation and body mass variation in Andean passerine birds

• 1 Relationships between body mass and latitude, and body mass and elevation are examined in the assemblage of Andean passerine birds.
• 2 Across species, body mass is positively correlated with the mid‐point of the species elevational distribution, but there is no significant relationship between body mass and latitudinal range mid‐point.
• 3 When the assemblage is separated into Andean endemic and non‐endemic species, the former group shows a significant positive relationship between body mass and elevation, and the latter a significant positive relationship between body mass and latitude (‘Bergmann’s rule’). Andean endemic species exhibit Bergmann’s rule once elevation is controlled for using multiple regression.
• 4 These relationships are not a consequence of the phylogenetic non‐independence of species. All the effects shown are very weak, with latitude and elevation explaining only a few per cent of the variation in body mass. Relationships are strongest when phylogenetically controlled analyses are performed just within genera.
• 5 The implications of these results for the mechanistic understanding of Bergmann’s rule are discussed.

     

Bergmann's Rule – what's in a name?

Despite the great interest it generates, the definition of Bergmann's Rule is vague and often contested. Debate focuses on whether the rule should be described in terms of pattern or process, what taxa it should apply to and what taxonomic level it should be associated with. Here I review the historical development of studies of Bergmann's Rule. I suggest that Bergmann thought that his rule should be strongest at the intra‐specific level, rather than between closely related species as is usually thought. I argue that the rule is a pattern that can be studied regardless of mechanism in any taxon and at any taxonomic level.     

An interspecific test of Bergmann's rule reveals inconsistent body size patterns across several lineages of water beetles (Coleoptera: Dytiscidae)

1. Bergmann's rule sensu lato, the ecogeographic pattern relating animals' body size with environmental temperature (or latitude), has been shown to be inconsistent among insect taxa. Body size clines remain largely unexplored in aquatic insects, which may show contrasting patterns to those found in terrestrial groups because of the physiological or mechanical constraints of the aquatic environment. 2. Bergmann's rule was tested using data on body size, phylogeny and distribution for 93 species belonging to four lineages of dytiscid water beetles. The relationship between size and latitude was explored at two taxonomic resolutions – within each independent lineage, and for the whole dataset – employing phylogenetic generalised least‐squares to control for phylogenetic inertia. The potential influence of habitat preference (lotic versus lentic) on body size clines was also considered. 3. Within‐lineage analyses showed negative relationships (i.e. converse Bergmann's rule), but only in two lineages (specifically in those that included both lotic and lentic species). By contrast, no relationship was found between body size and latitude for the whole dataset. 4. These results suggest that there may be no universal interspecific trends in latitudinal variation of body size in aquatic insects, even among closely related groups, and show the need to account for phylogenetic inertia. Furthermore, habitat preferences should be considered when exploring latitudinal clines in body size in aquatic taxa at the interspecific level.     

Climate history,human impacts and global body size of Carnivora (Mammalia: Eutheria) at multiple evolutionary scales

Aim One of the longest recognized patterns in macroecology, Bergmann’s rule, describes the tendency for homeothermic animals to have larger body sizes in cooler climates than their phylogenetic relatives in warmer climates. Here we provide an integrative process‐based explanation for Bergmann’s rule at the global scale for the mammal order Carnivora. Location Global. Methods Our database comprises the body sizes of 209 species of extant terrestrial Carnivora, which were analysed using phylogenetic autocorrelation and phylogenetic eigenvector regression. The interspecific variation in body size was partitioned into phylogenetic (P) and specific (S) components, and mean P‐ and S‐components across species were correlated with environmental variables and human occupation both globally and for regions glaciated or not during the last Ice Age. Results Three‐quarters of the variation in body size can be explained by phylogenetic relationships among species, and the geographical pattern of mean values of the P‐component is the opposite of the pattern predicted by Bergmann’s rule. Partial regression revealed that at least 43% of global variation in the mean phylogenetic component is explained by current environmental factors. In contrast, the mean S‐component of body size shows large positive deviations from ancestors across the Holarctic, and negative deviations in southern South America, the Sahara Desert, and tropical Asia. There is a moderately strong relationship between the human footprint and body size in glaciated regions, explaining 19% of the variance of the mean P‐component. The relationship with the human footprint and the P‐component is much weaker in the rest of the world, and there is no relationship between human footprint and S‐component in any region. Main conclusions Bergmannian clines are stronger at higher latitudes in the Northern Hemisphere because of the continuous alternation of glacial–interglacial cycles throughout the late Pliocene and Pleistocene, which generated increased species turnover, differential colonization and more intense adaptive processes soon after glaciated areas became exposed. Our analyses provide a unified explanation for an adaptive Bergmann’s rule within species and for an interspecific trend towards larger body sizes in assemblages resulting from historical changes in climate and contemporary human impacts.     

Species size affects hatching response to different temperature regimes in a rotifer cryptic species complex

The strategy of decreasing size with increasing temperature known as Bergmann’s rule operates at geographic scale and in spite of extensive studies still presents a puzzle to researches. The aim of this work was to verify whether patterns of diapausing egg hatching of closely related species are consistent with the expectations from Bergmann’s rule. In a laboratory study of the cryptic species complex of the rotifer Brachionus plicatilis, the response to temperature (17.5, 22.5, and 25.0 °C) of diapausing eggs collected in a pond where the three tested species coexist was assessed by (1) the number of hatchlings emerging or (2) the time needed to hatch. Our results show that the response to temperature from the sediment egg bank is species-dependent. In line with Bergmann’s rule, an association was observed between the hatching response to temperature and organism size. The biggest species increased its proportion in the hatchlings as temperature decreased, and vice versa. The intermediate size species showed an intermediate pattern. Nevertheless, temperature showed a general positive effect on hatching success. Time needed to hatch suggests a signature of Bergmann’s rule, but other factors seem to be affecting this parameter. This is the first study to demonstrate differences in the thermal dependence of diapausing egg hatching among closely related species with different body sizes, and it supports that Bergmann’s rule can be applied to diapause, an important phase in many invertebrate lifecycles.     

Testing Bergmann’s rule and the Rosenzweig hypothesis with craniometric studies of the South American sea lion

We tested the validity of Bergmann’s rule and Rosenzweig’s hypothesis through an analysis of the geographical variation of the skull size of Otaria flavescens along the entire distribution range of the species (except Brazil). We quantified the sizes of 606 adult South American sea lion skulls measured in seven localities of Peru, Chile, Uruguay, Argentina, and the Falkland/Malvinas Islands. Geographical and environmental variables included latitude, longitude, and monthly minimum, maximum, and mean air and ocean temperatures. We also included information on fish landings as a proxy for productivity. Males showed a positive relationship between condylobasal length (CBL) and latitude, and between CBL and the six temperature variables. By contrast, females showed a negative relationship between CBL and the same variables. Finally, female skull size showed a significant and positive correlation with fish landings, while males did not show any relationship with this variable. The body size of males conformed to Bergmann’s rule, with larger individuals found in southern localities of South America. Females followed the converse of Bergmann’s rule at the intraspecific level, but showed a positive relationship with the proxy for productivity, thus supporting Rosenzweig’s hypothesis. Differences in the factors that drive body size in females and males may be explained by their different life-history strategies. Our analyses demonstrate that latitude and temperature are not the only factors that explain spatial variation in body size: others such as food availability are also important for explaining the ecogeographical patterns found in O. flavescens.     

A test of ecological and sexual selection hypotheses for geographical variation in coloration and morphology of golden-crowned kinglets (Regulus satrapa)

Aim To date, studies on geographical variation have extensively investigated Bergmann’s rule, yet Gloger’s rule remains infrequently tested, and climatic predictors of variation in carotenoid coloration have not yet been studied. In addition, hypotheses based on sexual selection, which predict that sexual dimorphism should vary with population density and climatic conditions, have received little attention. Our goals were to characterize geographical variation in the coloration and morphology of golden‐crowned kinglets, Regulus satrapa (Passeriformes, Regulidae), and to investigate possible ecological and sexual selection correlates of this variation. Location The entire species range of golden‐crowned kinglets, comprising North and Central America. Methods We collected data from 511 museum specimens, dating from 1847 to 2006, encompassing all five subspecies of golden‐crowned kinglets. We used reflectance spectrometry to quantify crown and mantle coloration, and measured wing‐chord and tarsus length to approximate body size. We obtained geographical and climatic data from online databases, and population density estimates from the literature. Results There were significant subspecific and gender differences in crown coloration and morphology: male kinglets were generally larger and more colourful. Our data revealed mixed support for Bergmann’s rule: tarsus length decreased with increasing latitude, while patterns of variation in wing‐chord and tarsus length showed conflicting results with temperature. Mantle coloration exhibited an opposite trend to that predicted by Gloger’s rule: upper parts became lighter with increasing relative humidity. Crown coloration was negatively correlated with actual evapotranspiration, suggesting that levels of primary productivity are not directly linked to carotenoid abundance. Sexual dimorphism and dichromatism generally increased with greater population density, lower latitudes and elevations, and warmer temperatures, supporting a previously observed pattern of variation in sexual dimorphism. Main conclusions Geographical variation in golden‐crowned kinglets yielded mixed support for Bergmann’s rule and contradicted Gloger’s rule, suggesting that other mechanisms may be operating. Allen’s rule is likely to be a stronger factor influencing tarsus length. Differences in the degree of sexual dimorphism and dichromatism in varying climatic conditions suggest that the intensity of sexual selection differs between habitats. Further studies on geographical variation in sexual dimorphism in various taxa may reveal a previously unrecognized ecogeographical rule.     

Latitudinal Influence on the Sexual Dimorphism of the Marine Fish <Emphasis Type="Italic">Bathygobius soporator</Emphasis> (Gobiidae: Teleostei)

Environmental gradients in a marine setting may have significant effects on morphological variations and evolutionary patterns, including sexual dimorphism variations within and between fish populations. We analyzed sexual shape and size dimorphism in accordance with Rensch and Bergmann’s rules in five coastal populations of the gobiid Bathygobius soporator along 4000 km of the Brazilian coastline. The populations differ significantly in sexual body shape dimorphism, with a tendency toward reduced intrapopulation dimorphism, increasing with latitude. Body size variation was significant between populations and population vs. sex, and inverse to Bergmann’s rule. Moreover, size dimorphism among populations of B. soporator does not follow Rensch’s rule. These data represent a rare example of inter and intrapopulation spatial variation in sexual dimorphism associated with latitude in marine fish. This suggests a complex and particularized scenario of biotic and abiotic interactions acting on local populations of B. soporator in extensive coastal areas of the Western Atlantic, with profound implications for species evolution.     

Segment number,body length,and latitude in geophilomorph centipedes: a ‘converse‐Bergmann’ pattern

There is a negative relationship between trunk segment number and latitude among geophilomorph centipedes in general. A similar relationship is known to exist within the most intensively‐studied geophilomorph species, Strigamia maritima, and also within several other species from this group. Previously, it was considered that this relationship did not involve body length; instead, individuals of S. maritima with more segments were considered to be more finely subdivided (not longer) than those with fewer segments. This incorrect interpretation arose from the difficulty of reliably separating post‐embryonic stages and thus of making a simple and direct comparison. In the present study, we build on recent work that facilitates such comparisons; and we show conclusively that individuals with more segments are longer. Our finding means that it is now possible to connect the work on S. maritima in particular, and on geophilomorph centipedes in general, with the debate about Bergmann's ‘rule’: the proposal that body size increases with increasing latitude. There is a clear ‘converse‐Bergmann’ pattern, as has been found in several other taxa. We propose an adaptive hypothesis that may explain why geophilomorphs show this pattern. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ?? , ??–??.     

WHEN RENSCH MEETS BERGMANN: DOES SEXUAL SIZE DIMORPHISM CHANGE SYSTEMATICALLY WITH LATITUDE?

Bergmann's and Rensch's rules describe common large-scale patterns of body size variation, but their underlying causes remain elusive. Bergmann's rule states that organisms are larger at higher latitudes (or in colder climates). Rensch's rule states that male body size varies (or evolutionarily diverges) more than female body size among species, resulting in slopes greater than one when male size is regressed on female size. We use published studies of sex-specific latitudinal body size clines in vertebrates and invertebrates to investigate patterns equivalent to Rensch's rule among populations within species and to evaluate their possible relation to Bergmann's rule. Consistent with previous studies, we found a continuum of Bergmann (larger at higher latitudes: 58 species) and converse Bergmann body size clines (larger at lower latitudes: 40 species). Ignoring latitude, male size was more variable than female size in only 55 of 98 species, suggesting that intraspecific variation in sexual size dimorphism does not generally conform to Rensch's rule. In contrast, in a significant majority of species (66 of 98) male latitudinal body size clines were steeper than those of females. This pattern is consistent with a latitudinal version of Rensch's rule, and suggests that some factor that varies systematically with latitude is responsible for producing Rensch's rule among populations within species. Identifying the underlying mechanisms will require studies quantifying latitudinal variation in sex-specific natural and sexual selection on body size.     

Of mice and mammoths: evaluations of causal explanations for body size evolution in insular mammals

Aim We investigated the hypothesis that the insular body size of mammals results from selective forces whose influence varies with characteristics of the focal islands and the focal species, and with interactions among species (ecological displacement and release). Location Islands world‐wide. Methods We assembled data on the geographic characteristics (area, isolation, maximum elevation, latitude) and climate (annual averages and seasonality of temperature and precipitation) of islands, and on the ecological and morphological characteristics of focal species (number of mammalian competitors and predators, diet, body size of mainland reference populations) that were most relevant to our hypothesis (385 insular populations from 98 species of extant, non‐volant mammals across 248 islands). We used regression tree analyses to examine the hypothesized contextual importance of these factors in explaining variation in the insular body size of mammals. Results The results of regression tree analyses were consistent with predictions based on hypotheses of ecological release (more pronounced changes in body size on islands lacking mammalian competitors or predators), immigrant selection (more pronounced gigantism in small species inhabiting more isolated islands), thermoregulation and endurance during periods of climatic or environmental stress (more pronounced gigantism of small mammals on islands of higher latitudes or on those with colder and more seasonal climates), and resource subsidies (larger body size for mammals that utilize aquatic prey). The results, however, were not consistent with a prediction based on resource limitation and island area; that is, the insular body size of large mammals was not positively correlated with island area. Main conclusions These results support the hypothesis that the body size evolution of insular mammals is influenced by a combination of selective forces whose relative importance and nature of influence are contextual. While there may exist a theoretical optimal body size for mammals in general, the optimum for a particular insular population varies in a predictable manner with characteristics of the islands and the species, and with interactions among species. This study did, however, produce some unanticipated results that merit further study – patterns associated with Bergmann’s rule are amplified on islands, and the body size of small mammals appears to peak at intermediate and not maximum values of latitude and island isolation.     

Comparing latitudinal and upstream–downstream gradients: life history traits of invasive mosquitofish

Aim Variation of life history traits along spatial gradients is poorly understood in invasive species and particularly in freshwater fish. We aimed to examine life history variation in a highly invasive fish (Gambusia holbrooki) along latitudinal and upstream–downstream river gradients and to assess the effects of age on this variation. We hypothesized similar responses in populations inhabiting environments more favourable to this species (lower latitudes and lower reaches of rivers). Location European rivers from southern Spain to southern France. Methods We sampled mosquitofish from the lowest reaches of ten river basins along 6° of latitude in the Mediterranean region and seven sites along the upstream–downstream gradient in three of the rivers. We examined abundance, population structure, size‐at‐age and other life history traits along these gradients. Results As hypothesized, lower reaches and lower latitudes both resulted in higher reproductive effort and lower body condition of mosquitofish. However, these patterns explained low per cent variation, were nonlinear and strongly depended on fish age. Independently of fish size, age groups differed in reproductive effort, in the gonadal weight–size relationship and its variation along spatial gradients. Mean size‐at‐age (or overall body size) did not vary with latitude (so the intra‐specific version of Bergmann’s rule or its converse does not apply) and in contrast increased upstream in rivers. Main conclusions Our findings suggest that for life history traits of freshwater organisms, river longitudinal variation plays a role as important as climate, with often differential effects. Our results also illustrate the poor knowledge of spatial variation of many life history traits, which precludes the understanding and prediction of biological invasions in a rapidly changing world.     

Body size explains interspecific variation in size–latitude relationships in geographically widespread beetle species

1. In most birds and mammals, larger individuals of the same species tend to be found at higher latitudes, but in insects, body size–latitude relationships are highly variable. 2. Recent studies have shown that larger‐bodied insect species are more likely to decrease in size when reared at increased temperature, compared with smaller‐sized species. These findings have led to the prediction that a positive relationship between body size and latitude should be more prevalent in larger‐bodied insect species. 3. This study measured the body size of > 4000 beetle specimens (12 species) collected throughout North America. Some beetle species increased in size with latitude, while others decreased. Importantly, mean species body size explained c. 30% of the interspecific variation in the size–latitude response. 4. As predicted, larger‐bodied beetle species were more likely to show a positive relationship between body size and latitude (Bergmann's rule), and smaller‐bodied species were more likely to show a negative body size–latitude relationship (inverse Bergmann's rule). 5. These body size–latitude patterns suggest that size‐specific responses to temperature may underlie global latitudinal distributions of body size in Coleoptera, as well as other insects.     

Body size evolution in insular vertebrates: generality of the island rule

Aim My goals here are to (1) assess the generality of the island rule – the graded trend from gigantism in small species to dwarfism in larger species – for mammals and other terrestrial vertebrates on islands and island‐like ecosystems; (2) explore some related patterns of body size variation in insular vertebrates, in particular variation in body size as a function of island area and isolation; (3) offer causal explanations for these patterns; and (4) identify promising areas for future studies on body size evolution in insular vertebrates. Location Oceanic and near‐shore archipelagos, and island‐like ecosystems world‐wide. Methods Body size measurements of insular vertebrates (non‐volant mammals, bats, birds, snakes and turtles) were obtained from the literature, and then regression analyses were conducted to test whether body size of insular populations varies as a function of body size of the species on the mainland (the island rule) and with characteristics of the islands (i.e. island isolation and area). Results The island rule appears to be a general phenomenon both with mammalian orders (and to some degree within families and particular subfamilies) as well as across the species groups studied, including non‐volant mammals, bats, passerine birds, snakes and turtles. In addition, body size of numerous species in these classes of vertebrates varies significantly with island isolation and island area. Main conclusions The patterns observed here – the island rule and the tendency for body size among populations of particular species to vary with characteristics of the islands – are actually distinct and scale‐dependent phenomena. Patterns within archipelagos reflect the influence of island isolation and area on selective pressures (immigration filters, resource limitation, and intra‐ and interspecific interactions) within particular species. These patterns contribute to variation about the general trend referred to as the island rule, not the signal for that more general, large‐scale pattern. The island rule itself is an emergent pattern resulting from a combination of selective forces whose importance and influence on insular populations vary in a predictable manner along a gradient from relatively small to large species. As a result, body size of insular species tends to converge on a size that is optimal, or fundamental, for a particular bau plan and ecological strategy.     

SHORT COMMUNICATION: Little evidence for Cope’s rule from Bayesian phylogenetic analysis of extant mammals

According to Cope’s rule, lineages tend to evolve towards larger body size, possibly because of selective advantages of being large. The status of Cope’s ‘rule’ remains controversial as it is supported in some but not all large‐scale fossil studies. Here, we test for Cope’s rule by Bayesian analyses of average body masses of 3253 extant mammal species on a dated phylogenetic tree. The data favour a model that does not assume Cope’s rule. When Cope’s rule is assumed, the best estimate of its strength is an average ancestor‐descendant increase in body size of only 0.4%, which sharply contrasts with the 9% bias estimated from fossil mammals. Thus, we find no evidence for Cope’s rule from extant mammals, in agreement with earlier analyses of existing species, which also did not find support for Cope’s rule.     

Shallow water ray-finned marine fishes follow Bergmann’s rule

Understanding the interspecific variation in body size across macroclimatic gradients has been of paramount importance to naturalists and biogeographers. Bergmann’s rule, which describes a trend of increasing body size polewards, is arguably the best-known ecogeographical rule in terrestrial environments but remains largely unexplored in the marine realm. In this study we tested Bergmann's rule in marine ray-finned fishes (Pisces, Actinopterygii), analyzing the relationship between body size and latitude in 5662 species. To examine possible underlying mechanisms, we adopted a cross-species approach to evaluate the association of body size with four predictors: Sea Surface Temperature, Net Primary Productivity, Salinity, and Human impact. We analyzed the relationships between body size and environmental and anthropogenic variables building mixed linear models, which considered the taxonomic structure in the data. We conducted complementary analyses dividing the data into five latitudinal bands. Actinopterygii showed a clear Bergmannian pattern, with the largest species observed in temperate regions, being the first global analysis on ray-finned fishes showing a pattern consistent with Bergmann’s rule. Sea Surface Temperature and Net Primary Productivity were the best predictors, in accordance with the time to sexual maturity and resource availability hypotheses. Our analyses based on latitudinal bands showed a differential response of body size to the environment, with temperature, salinity and human impact more strongly associated with size variation at cold environments. These results agree with previous studies on Bergmann’s rule for terrestrial ectothermic, freshwater and marine fishes. Our findings suggest that temperature rise in the ocean and growing human impact may have effects on the distribution of body size, thus altering ecosystem functioning. Fundamental differences often assumed to exist between marine and terrestrial systems are not so evidently reflected in the emergence of large-scale body size gradients.     

Mitochondrial DNA as a tool for reconstructing past life‐history traits in mammals

Reconstructing the ancestral characteristics of species is a major goal in evolutionary and comparative biology. Unfortunately, fossils are not always available and sufficiently informative, and phylogenetic methods based on models of character evolution can be unsatisfactory. Genomic data offer a new opportunity to estimate ancestral character states, through (i) the correlation between DNA evolutionary processes and species life‐history traits and (ii) available reliable methods for ancestral sequence inference. Here, we assess the relevance of mitochondrial DNA – the most popular molecular marker in animals – as a predictor of ancestral life‐history traits in mammals, using the order of Cetartiodactyla as a benchmark. Using the complete set of 13 mitochondrial protein‐coding genes, we show that the lineage‐specific nonsynonymous over synonymous substitution rate ratio (dN/dS) is closely correlated with the species body mass, longevity and age of sexual maturity in Cetartiodactyla and can be used as a marker of ancestral traits provided that the noise introduced by short branches is appropriately dealt with. Based on ancestral dN/dS estimates, we predict that the first cetartiodactyls were relatively small animals (around 20 kg). This finding is in accordance with Cope's rule and the fossil record but could not be recovered via continuous character evolution methods.     

Body size–climate relationships of European spiders

Aim Geographic body size patterns of mammals and birds can be partly understood under the framework of Bergmann’s rule. Climatic influences on body size of invertebrates, however, appear highly variable and lack a comparable, generally applicable theoretical framework. We derived predictions for body size–climate relationships for spiders from the literature and tested them using three datasets of variable spatial extent and grain. Location Europe. Methods To distinguish climate from space, we compared clines in body size within three datasets with different degrees of co‐variation between latitude and climate. These datasets were: (1) regional spider faunas from 40 European countries and large islands; (2) local spider assemblages from standardized samples in 32 habitats across Europe; and (3) local spider assemblages from Central European habitats. In the latter dataset climatic conditions were determined more by habitat type than by geographic position, and therefore this dataset provided a non‐spatial gradient of various microclimates. Spider body size was studied in relation to latitude, temperature and water availability. Results In all three datasets the mean body size of spider assemblages increased from cool/moist to warm/dry environments. This increase could be accounted for by turnover from small‐bodied to large‐bodied spider families. Body size–climate relationships within families were inconsistent. Main conclusions Starvation resistance and accelerated maturation can be ruled out as explanations for the body size clines recorded, because they predict the inverse of the observed relationship between spider body size and temperature. The relationship between body size and climate was partly independent of geographic position. Thus, the restriction of large‐bodied spiders to their glacial refugia owing to dispersal limitations can be excluded. Our results are consistent with mechanisms invoking metabolic rate, desiccation resistance and community interactions to predict a decrease in body size from warm and dry to cool and moist conditions.