Shifting latitudinal clines in avian body size correlate with global warming in Australian passerines

Intraspecific latitudinal clines in the body size of terrestrial vertebrates, where members of the same species are larger at higher latitudes, are widely interpreted as evidence for natural selection and adaptation to local climate. These clines are predicted to shift in response to climate change. We used museum specimens to measure changes in the body size of eight passerine bird species from south-eastern Australia over approximately the last 100 years. Four species showed significant decreases in body size (1.8–3.6% of wing length) and a shift in latitudinal cline over that period, and a meta-analysis demonstrated a consistent trend across all eight species. Southern high-latitude populations now display the body sizes typical of more northern populations pre-1950, equivalent to a 7° shift in latitude. Using ptilochronology, we found no evidence that these morphological changes were a plastic response to changes in nutrition, a likely non-genetic mechanism for the pattern observed. Our results demonstrate a generalized response by eight avian species to some major environmental change over the last 100 years or so, probably global warming.     

Sensitivity of intraspecific latitudinal clines of body size for tetrapods to sampling, latitude and body size

Recent studies have shown that most tetrapod groups (mammals,birds, chelonians, amphibians) show general intraspecific tendenciesfor increasing body size with latitude, whereas squamates (lizardsand snakes) show an intraspecific tendency towards decreasingbody size with latitude. Here I evaluate whether these sizetrends are general by using independent contrasts analysis toinvestigate the dependence of intraspecific size-latitude relationships(r), and the magnitude alone of size-latitude relationships([r]), for tetrapod vertebrates, on sample size, range of latitudessampled, average latitude sampled, and body size. Range of latitudessampled, average latitude sampled, and body size did not influencebody size-latitude relationships (r) or the magnitude aloneof body size-latitude relationship ([r]). Sample size did notinfluence size-latitude relationships (r), but did influencethe magnitude alone of size-latitude relationships ([r]), possiblyindicating increased precision of estimating size-latitude relationshipswith increased sampling. In short, intraspecific size-latituderelationships are similar for species of different sizes, occurringat different latitudes, sampled over different latitudinal ranges,and differing in number of populations sampled (though magnitudealone is influenced by sample size). These results suggest thatintraspecific size-latitude trends are general, and biologicallysignificant (i.e., are not artifacts of sampling), thus deservingexplanation.     

The significance of latitudinal variation in body size in a holarctic ant, Leptothorax acervorum

The mean body size of workers of the holarctic ant Leptothorax acervorum increases with latitude. Workers from populations near the Polar Circle were 10% larger than workers from central Europe. This gradient does not appear to be associated with variation in colony size. According to controlled rearing experiments with brood from populations in Cape Kartesh, Karelia (67°N) and Erlangen, Germany (49.7°N), larger adult body size in boreal populations is not an epiphenomenon of slow cell growth and larger cell size at lower temperatures. Larger workers survived longer without food both at room temperature and <0°C, suggesting that selection for increased fasting endurance in boreal habitats might lead to this Bergmann's rule-like pattern in an ectothermic ant.     

Testing for latitudinal and other body-size gradients

Testing for a relationship between the body size of animals and a gradient such as latitude is complicated by the fact that typically there is a single average size for each species, and each species occurs at several sample stations over the gradient. This results in standard tests for statistical significance being invalid. This problem can be overcome by using a randomization test. A more difficult problem, however, is determining whether the relationship between size and latitude is the same for two subfamilies of species. In this paper a general method for relating body size to latitude and subfamily differences is proposed, with the significance of effects determined by randomization. A simulation study suggests that this procedure has good properties. This approach to data analysis has promise both for the particular situation considered and for other related problems in biogeography.     

Geographic body size gradients in tropical regions: water deficit and anuran body size in the Brazilian Cerrado

A recent interspecific study found Bergmann's size clines for Holarctic anurans and proposed an explanation based on heat balance to account for the pattern. However, this analysis was limited to cold temperate regions, and exploring the patterns in warmer tropical climates may reveal other factors that also influence anuran body size variation. We address this using a Cerrado anuran database. We examine the relationship between mean body size in a grid of 1° cells and environmental predictors and test the relative support for four hypotheses using an AIC-based model selection approach. Also, we considered three different amphibian phylogenies to partition the phylogenetic and specific components of the interspecific variation in body size using a method analogous to phylogenetic eigen vector regression (PVR). To consider the potential effects of spatial autocorrelation we use eigenvector-based spatial filters. We found the largest species inhabiting high water deficit areas in the northeast and the smallest in the wet southwest. Our results are consistent with the water availability hypothesis which, coupled with previous findings, suggests that the major determinant of interspecific body size variation in anurans switches from energy to water towards the equator. We propose that anuran body size gradients reflect effects of reduced surface to volume ratios in larger species to control both heat and water balance.     

Altitudinal body size clines: latitudinal effects associated with changing seasonality

Within ectotherms, increases in body size with latitude are thought to be the consequence of the effect of a decline in development temperature, which results in a larger final body size. In contrast, latitudinal declines in body size are usually ascribed to limited resources. It has been suggested that if generation time is similar to or constitutes a significant proportion of the growing season length, then season length is likely to have a considerable influence on body size because of constraints on resource availability, so resulting in a decline in body size with temperature (latitude). However, if generation time declines relative to season length, resources effectively become available for longer. Temperature influences on growth and differentiation are likely to be most significant, resulting in an increase in body size with latitude. Here, we test the hypothesis by comparing intraspecific altitudinal body size clines in a monophyletic group of weevils from two regions that differ substantially in seasonality. On the relatively aseasonal Marion Island, body size increases with altitude, whereas on the more seasonal Heard Island the opposite is found. In addition, overlapping generations on Marion Island indicate year-round resource availability, whereas more discrete generations on Heard Island indicate winter cessation of growth and development. Our data provide support for the hypothesis that the seasonality of resource availability has a major influence on body size clines. Furthermore, we argue that analysis of interspecific body size clines should be preceded by nested analyses of variance to determine the influence of clinal replacement of higher taxa on these patterns.     

The role of host seed size in mediating a latitudinal body size cline in an introduced bruchid beetle in Japan

A wide variety of animals show latitudinal cline in body size, which can be caused not only by abiotic factors such as temperature but also by biotic ones such as diet quality. In seed feeding insects, adult body size is affected by seed size. Therefore, seed size may be an important factor to explain the latitudinal cline in body size if the seed size also shows a latitudinal cline. In the present study, we detected a latitudinal cline in body size of an alien bruchid, Acanthoscelides pallidipennis, which was introduced into Japan from North America with its host plant Amorpha fruticosa. In 13 out of 24 populations that we collected in Japan, A. fruticosa seeds were infested with A. pallidipennis. Both body size of A. pallidipennis and host seed weight increased with latitude in the infested populations, but not in the non‐infested populations. There was a significant positive correlation between body size and seed weight in both field observation and laboratory experiment. In a common environmental condition, there was no significant difference in body size among three latitudinally different populations. Our results show that the latitudinal cline in adult body size of A. pallidipennis across a non‐native range could be explained by the latitudinal cline in seed weight of A. fruticosa, but not by genetic differentiation among populations.     

Development time and body size in Eupolyphaga sinensis along a latitudinal gradient from China

The responses of organisms to temperature variations may be via short term responses of the phenotype (phenotypic plasticity), or they could involve long-term evolutionary change and adaptation (via selection) to the genotype. These could involve changes to the mean size of the animal or to the thermal reaction norm. We examined the effects of various temperatures (of 22, 25, 28, and 31 °C) on development time, adult body size and preadult survivorship in three populations of the cockroach, Eupolyphaga sinensis (Walker), collected at different latitudes. We found substantial temperature-induced plasticity in development time, body size, and preadult survivorship, indicating that developmental temperatures have strong impacts on growth and life history traits of E. sinensis. Genetic differences for development time, body size, and preadult survivorship were detected among populations, and the three traits exhibited highly significant variations in the responses of different populations to various temperature conditions, indicating genetic differences among populations in terms of thermal reaction norms. We also found that two populations seem to support the beneficial acclimation hypothesis whereas the third mid-latitude population does not. The results are likely because of differences in season length and voltinism, indicating that not only temperature regime but also its interactions with generation time (and development time), voltinism, and season length are likely to have considerable effects on insect development time and body size. Overall, changes in development time, body size, and preadult survivorship in E. sinensis can all be regarded as adaptations to changing thermal regimes.     

Geographic gradients in body size: a clarification of Bergmann's rule

1997 marked the sesquicentenary of the publication by Carl Bergmann of the observation that, in general, large-bodied animal species tend to live further north than their small-bodied relatives. This has been dubbed Bergmann's rule in his honour. However, more than 150 years on, we appear to be little closer to a general understanding of the rule, or even to any consensus as to whether it exists. This is due in large part to confusion about the taxonomic level at which the rule is considered to operate, and to the conflation of pattern and mechanism. In this paper, we attempt to resolve this confusion by highlighting its sources, and by providing a definition of Bergmann's rule that is practical and useful, yet that retains the essential features of its original formulation. We conclude by briefly reviewing the mechanisms proposed to explain Bergmann's rule as we define it.     

Anti-predator behavior along elevational and latitudinal gradients in dark-eyed juncos

Flight-initiation distance (FID),the distance between an individual and experimenter when it begins to flee,can be used to quantify risk-assessment.Among other ...     

Population divergence in plant species reflects latitudinal biodiversity gradients

The trend for increasing biodiversity from the poles to the tropics is one of the best-known patterns in nature. This latitudinal biodiversity gradient has primarily been documented so far with extant species as the measure of biodiversity. Here, we evaluate the global pattern in biodiversity across latitudes based on the magnitude of genetic population divergence within plant species, using a robust spatial design to compare published allozyme datasets. Like the pattern of plant species richness across latitudes, we expected the divergence among populations of current plant species would have a similar pattern and direction. We found that lower latitudinal populations showed greater genetic differentiation within species after controlling for geographical distance. Our analyses are consistent with previous population-level studies in animals, suggesting a high possibility of tropical peaks in speciation rates associated with observed levels of species richness.     

Historical processes enhance patterns of diversity along latitudinal gradients

One of the more vexing issues in ecology is how historical processes affect contemporary patterns of biodiversity. Accordingly, few models have been presented. Two corollary models (centre of origin, time-for-speciation) can be used to make quantitative predictions characterizing the tropical niche conservatism hypothesis and describe diversification as diffusion and subsequent cladogenesis of species away from the place of origin of a higher taxon in the tropics. Predictions derived from such models are: (i) species richness declines toward the periphery of the range of a higher taxon; (ii) taxa are more derived toward the periphery than the centre; (iii) ages of taxa are lower toward the periphery than the centre; and (iv) ages and measures of derivedness are less variable toward the periphery of the range of a higher taxon. I tested these predictions to better understand the formation of one of the most ubiquitous patterns of biodiversity-the latitudinal gradient in species richness. Results indicate well-supported predictions for New World leaf-nosed bats and that diversification has had strong influences on latitudinal gradients of species richness. A better understanding of how evolutionary diversification of taxa contributes to formation of patterns of species richness along environmental gradients is necessary to fully understand spatial variation in biodiversity.     

The effect of fast created inbreeding on litter size and body weights in mice

This study was designed to reveal any differences in effects of fast created versus total inbreeding on reproduction and body weights in mice. A line selected for large litter size for 124 generations (H) and a control line (K) maintained without selection for the same number of generations were crossed (HK) and used as a basis for the experiment. Within the HK cross, full sib, cousin or random mating were practised for two generations in order to create new inbreeding (IB_F) at a fast rate. In the first generation of systematic mating, old inbreeding was regenerated in addition to creation of new inbreeding from the mating design giving total inbreeding (IB_T). The number of pups born alive (NBA) and body weights of the animals were then analysed by a model including both IB_T and IB_F. The IB_T of the dam was in the present study found to reduce the mean NBA with -0.48 (± 0.22) (p < 0.05) pups per 10% increase in the inbreeding coefficient, while the additional effect of IB_F was -0.42 (± 0.27). For the trait NBA per female mated, the effect of IB_T was estimated to be -0.45 (± 0.29) per 10% increase in the inbreeding coefficient and the effect of IB_F was -0.90 (± 0.37) (p < 0.05) pups. In the present study, only small or non-significant effects of IB_F of the dam could be found on sex-ratio and body weights at three and six weeks of age in a population already adjusted for IB_T.     

Geographical and latitudinal variation in growth patterns and adult body size of Swedish moose (Alces alces)

We examined the geographical pattern in growth and adult body size among 14 populations of Swedish moose (Alces alces) using data from 4,294 moose (1.5 years old) killed during the hunting season in 1989–1992. In both sexes, adult body mass was significantly positively correlated with latitude. Moose in northern populations had a 15–20% larger adult body mass than moose in the south. Juvenile body mass was correlated with neither latitude nor adult body mass. Thus, variation in time (years) and rate of body growth after the juvenile stage were responsible for most of the variation in adult body mass among populations. Moose in northern populations grew for approximately 2 more years of life than southern moose. In contrast to adult body mass, skeletal size (measured as jawbone length) was not correlated with latitude, suggesting that variation in adult body mass was primarily due to differences in fat reserves. Discrimination between population characteristics, such as moose density, climate, and the amount of browse available to moose, showed climatic harshness to be the most important variable explaining geographical variation in body mass among populations. The results support the notion that in mammals body size increases with latitude in accordance with Bergmann's rule. We conclude that (1) variation in patterns of growth after the juvenile stage is the main cause of the latitudinal trend in adult body size in moose, and (2) climatic conditions are a more important factor than population density and availability of food in explaining geographical variation in growth patterns and adult body mass between populations of Swedish moose.     

Life history traits associated with body size covary along a latitudinal gradient in a generalist grasshopper

Animal body size often varies systematically along latitudinal gradients, where individuals are either larger or smaller with varying season length. This study examines ecotypic responses by the generalist grasshopper Melanoplus femurrubrum (Orthoptera: Acrididae) in body size and covarying, physiologically based life history traits along a latitudinal gradient with respect to seasonality and energetics. The latitudinal compensation hypothesis predicts that smaller body size occurs in colder sites when populations must compensate for time constraints due to short seasons. Shorter season length requires faster developmental and growth rates to complete life cycles in one season. Using a common garden experimental design under laboratory conditions, we examined how grasshopper body size, consumption, developmental time, growth rate and metabolism varied among populations collected along an extended latitudinal gradient. When reared at the same temperature in the lab, individuals from northern populations were smaller, developed more rapidly, and showed higher growth rates, as expected for adaptations to shorter and generally cooler growing seasons. Temperature-dependent, whole organism metabolic rate scaled positively with body size and was lower at northern sites, but mass-specific standard metabolic rate did not differ among sites. Total food consumption varied positively with body size, but northern populations exhibited a higher mass-specific consumption rate. Overall, compensatory life history responses corresponded with key predictions of the latitudinal compensation hypothesis in response to season length.     

Month-of-birth effect on further body size in a pig model

Previous studies unanimously confirmed the existence of a dependence of human body size on the month of birth. The cause of the phenomenon has not been identified yet, although some possible causes were proposed e.g. seasonal changes of climatic and nutritional conditions. This study explored the issue in an animal model of 20,513 pigs. We found that body weights of 6-month-old pigs were the highest for subjects born in February, but for 2-month-old pigs the peak fell in May. Any statistical correlation between the month of birth and later body weight may be induced by (1) a long-term effect of the month of birth on further growth potential (LTE), or by (2) a short-term effect of seasonal factors differentiating the growth rate (STE), so we developed a mathematical method to separate the effects. The analysis proved that (1) the observed correlations resulted only from the STE, with May-June being the months of the highest growth tempo, and that (2) there was no significant LTE. The short-term effect was responsible for differences between patterns of weight for 2- and 6-month-old animals by the month of birth: since a pig monthly gain of weight increases with age, it is favorable for it to be born in February to attain the greatest weight at the age of 6 months, whereas 2-month-old piglets are heaviest when born a month or two before the May/June optimum for growth. The lack of a long-term effect of the month of birth on pigs’ weight supports the hypothesis of the cultural character of factor(s) responsible for the relationship between the month of birth and later body size in humans.     

Plant community patterns in Moroccan temporary ponds along latitudinal and anthropogenic disturbance gradients

Background: Temporary ponds, an abundant habitat in the Maghreb region and notably in Morocco, have a high conservation value. However, they are mainly known from the north of the country.

Aims: The aim of this work was to characterise the vegetation of Moroccan temporary ponds along a combined gradient of latitude and anthropogenic pressure.

Methods: Eighty-five ponds distributed along a north–south gradient of 750 km were sampled. For each pond, all vegetation was surveyed (flooded and dry parts) and the local abiotic characteristics were measured during two successive hydrological cycles. The prevailing anthropogenic pressures were also identified and were attributed an impact score.

Results: Eighty-one characteristic pond species (including 17 rare species) were recorded, with several new distribution data in the southern part of the latitudinal gradient. Plant communities were related to climatic and anthropogenic factors, but mostly to local factors, such as maximum water depth and soil pH. The northern ponds (wettest macroclimate) were rich in characteristic species and rare species, while the southern (driest macroclimate) ponds were more species poor.

Conclusions: In addition to the direct impact of increasing human activity, a further reduction of the floristic richness of temporary ponds is expected due to climatic changes. This is particularly the case for characteristic species which have a high conservation value.