Body Sizes of Poikilotherm Vertebrates at Different Latitudes

2023 Vulnerabilidad de cartilaginosos CAPÍTULO

Chapter

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Apr 2025

Alicia Cruz-Martínez

From biggest to smallest mud dragons: size-latitude trends in a group of meiobenthic animals worldwide

Article

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Jan 2021

Size-latitude trends in the meiobenthic phylum Kinorhyncha, commonly known as mud dragons, have been explored in oceans worldwide. Generalized least squares regression was used to assess relationships between size and latitude, as well as between size, latitude, and two selected environmental variables that exhibit latitudinal gradation: the sea surface temperature and the net primary productivity. Different structures of spatial autocorrelation and potential confounding factors, such as the species richness and the number of kinorhynch records that could affect latitudinal gradients, were also addressed. In addition, generalized mixed models were used to determine the influence of the phylogeny on body size. Size-latitude relationships of Kinorhyncha were commonly found globally, as well as for particular geographic regions (hemispheres and/or coastlines), with important differences between taxonomic groups. These size-latitude trends were heterogeneous and implied the influence of the latitude itself, environmental variables, and phylogeny. These facts indicate that a single underlying process is not likely to explain the observed relationships but a complex interaction of several macroecological patterns both present and past. Perhaps, the inclusion of future new reports, conducted in undersampled areas, may shed some light on the matter and reveal more generalized size-latitude patterns. Nevertheless, it is also likely that broadly generalizable size-latitude relationships may not exist in meiofaunal communities.

Morphological Variations in the Green Turtle (Chelonia mydas): A Field Study on an Eastern Mediterranean Nesting Population

Article

Full-text available

Jul 2019
ZOOL STUD

Bektaş Sönmez

Morphological studies in marine turtles might be used to obtain information about changes in developmental habitats. Information regarding mortality and growth rates can be obtained by collecting data on the size of nesting females on the nesting beach. Morphometric and meristic traits of female green turtles (Chelonia mydas) were recorded on Samandağ Beach, Turkey, during the 2006-2016 nesting seasons. The study aimed to determine the mean and minimum curved carapace length (CCL) of the nesting green turtle and the differences in body size and scute pattern over the years. The relationship between the body size of nesting green turtles and latitude was also analysed. CCL and curved carapace width (CCW) were recorded for 365 individuals and meristic measures were recorded for 292 individuals. The mean CCL and CCW were recorded as 86.9 (± 6.14) and 77.9 (± 5.95) cm, respectively. The minimum CCL of nesting green turtles was also recorded as 72 cm. The CCL and CCW showed differences over the years and they tended to become smaller from 2006 to 2016. However, this trend was not significant according to the Mann-Kendall trend test. The CCL value was negatively correlated with the latitude and rejected Bergmann's rule. There was no relationship between year and carapace scute deviation. The Samandağ green turtle population had the smallest nesting green turtle based on CCL. In addition to environmental factors, recruitment of females, and growth and mortality rates, and the nesting shift between nesting beaches may be some of the reasons behind a smaller value over the years.

The effects of climate on bat morphology across space and time

Article

Full-text available

Apr 2025
ECOGRAPHY

According to Bergmann's and Allen's rules, climate change may drive morphological shifts in species, affecting body size and appendage length. These rules predict that species in colder climates tend to be larger and have shorter appendages to improve thermoregulation. Bats are thought to be sensitive to climate and are therefore expected to respond to climatic changes across space and time. We conducted a phylogenetic meta‐analysis on > 27 000 forearm length (FAL) and body mass (BM) measurements from 20 sedentary European bat species to examine body size patterns. We assessed the relationships between body size and environmental variables (winter and summer temperatures, and summer precipitation) across geographic locations, and also analysed temporal trends in body size. We found sex‐specific morphological shifts in the body size of European bats in response to temperature and precipitation patterns across space, but no clear temporal changes due to high interspecific variability. Across Europe, male FAL decreased with increasing summer and winter temperatures, and BM increased with greater precipitation. In contrast, both FAL and BM of female bats increased with summer precipitation and decreased with winter temperatures. Our data can confirm Bergmann's rule for both males and females, while females' BM variations are also related to summer precipitation, suggesting a potential link to resource availability. Allen's rule is confirmed only in males in relation to summer temperature, while in females FAL and BM decrease proportionally with increasing temperature, maintaining a constant allometric relationship incompatible with Allen's rule. This study provides new insights into sex and species‐dependent morphological changes in bat body size in response to temperature and precipitation patterns. It highlights how body size variation reflects adaptations to temperature and precipitation patterns, thus providing insights into potential species‐level morphological responses to climate change across Europe.

Fish body size influenced by multiple drivers

Article

Full-text available

Oct 2023
ECOGRAPHY

There is evidence that organisms have become smaller during the past periods of global warming. Global change has substantial effects on biodiversity, with body size reduction being the third most common response to global warming. Body size allometry in ectotherms needs to be explored further; the objectives of this study were to better understand the mechanisms regulating body size in fish by testing: 1) Bergmann's rule with temperature and elevation, 2) additional environmental drivers, 3) the role of isolation, 4) ecoevolutionary hypotheses comparing native and exotic species and 5) the role of migration propensity in comparing migratory and resident species. We analyzed an extensive dataset of Chilean fish composed of 75 198 records which included 25 species from 12 different families between latitudes −28.80 to −51.42 using linear mixed models to discern the best environmental variables contributing to body size changes, as well as incorporating factors related to dispersal capabilities, biogeographic isolation and levels of exotic/native interactions. Bergmann's rule is supported by changes in elevation, and our study shows that freshwater fish body size also increases with increasing environmental heterogeneity and productivity. In general, inland native fish tend to be smaller than coastal ones, supporting the island rule with evidence of gigantism or dwarfism in selected species. Ecological variables affecting fish body size do not differ between native and exotic fish unless other factors are considered, such as dispersal capacity (migrating vs resident fish) or mechanisms related to their isolation. Although temperature is not a direct driver of body size in Chilean fish, heterogeneity, productivity, geography, migratory ability and species origin may affect body size. A better understanding of the mechanisms driving body size in ectotherms will aid in determining management priorities in the face of global climate disruption.

Altitudinal gradients and body size variation among Chinese lizards in different terrains

Article

Full-text available

Mar 2023
J ZOOL

Spatial patterns of body size are associated with environmental factors like temperature, seasonality, precipitation, resources, and altitude, among the most relevant. Latitudinal size patterns have been extensively studied. Studies on altitudinal gradients of body size, however, are relatively few. Besides, it is still unclear whether there is variation in the relationship between environmental factors and body size of species, or correlations within different altitudes. China provides a good opportunity to assess the altitudinal gradients of body size, because the entire terrain of China changes from high altitude in the west to low altitude in the east, with three natural terrain stages (low: less than 660 m.a.s.l.; medium: 660–2600 m.a.s.l.; and high: more than 2600 m.a.s.l.). Similarly, lizards are distributed across a wide altitudinal range (from −154.31 m to ~6000 m above sea level). We examined 211 lizard species in China and assessed the altitudinal gradients of Chinese lizard body sizes at assemblage and interspecific levels. Piecewise structural equation models (pSEM) were used to investigate the direct and indirect relationships between body size and environmental factors within different terrains (low, medium, and high altitudes). Overall, we found that body size in Chinese lizards decreases with increasing altitude. However, there were variations in the altitudinal gradients and drivers within the three terrain stages. Altitude has both direct (medium and low stages) and indirect (high stages) effects in shaping lizard size. We established that body size increased with increasing altitudes in the low and medium terrain stages. Seasonality had different effects on body size in medium (positively) and low (negatively) stages. However, among the three terrain stages, temperature was consistently negatively correlated with lizard size. Overall, we identified complex patterns and drivers of altitudinal gradients of body size within the three terrain stages, probably due to the different environmental conditions across altitudes.

For neither heat nor water conservation: Body size variation in Atlantic Forest frogs does not follow a general mechanism

Article

Full-text available

Jan 2022

Aim Animal body size is recurrently associated with climate. Bergmann's rule proposes that larger endotherms inhabit higher latitudes because higher latitudes are generally colder, and larger body sizes promote heat conservation. However, body size variation of ectotherms has been associated with other climatic variables as anurans in drier environments reach larger sizes for water conservation. We tested whether body size variation of anuran amphibians can be explained by the heat conservation or water conservation hypotheses. Location Brazilian Atlantic Forest. Taxon Anuran amphibians. Methods We selected anurans from different phylogenetic groups. The size was defined by snout-vent length (SVL) and stoutness. We implemented spatial regressions including morphological dimensions and variables describing temperature and water availability. Results Only Haddadus binotatus had SVL size negatively associated with temperature, in accordance with the heat conservation hypothesis (HCH). Itapotihyla langsdorffii had SVL positively associated with temperature, contrary to the HCH. Cycloramphus eleutherodactylus had SVL negatively associated with potential evapotranspiration, in accordance with the water conservation hypothesis (WCH). Thoropa miliaris+T. taophora and Ischnocnema guentheri showed no associations between SVL and climate. Stoutness was poorly associated with climate, with a negative relationship found only in Rhinella crucifer+R. ornata in accordance with the WCH. Main conclusions The heat conservation and water conservation hypotheses do not offer general explanations for the body size variation in anurans from the Brazilian Atlantic Forest. Natural history, functional and ecological traits are more likely to affect anuran body size and they should be considered in posterior analyses.

Water and Heat conservation hypotheses do not explain the geographical body size variation in Atlantic Coastal frogs

Poster

Full-text available

May 2021

200 million years of anuran body size evolution in relation to geography, ecology, and life history

Article

Jul 2020

Surprisingly little is known about body‐size evolution within the most diverse amphibian order, anurans (frogs and toads), despite known effects of body size on the physiological, ecological, and life‐history traits of animals more generally. Here we examined anuran body‐size evolution among 2434 species with over 200 million years of shared evolutionary history. We found clade‐specific evolutionary shifts to new body‐size optima along with numerous independent transitions to gigantic and miniature body sizes, despite the upper limits of anuran body size remaining quite consistent throughout the fossil record. We found a weak, positive correlation between a species’ body size and maximum latitude and elevation, including a dearth of small species at higher elevations and broader latitudinal and elevational ranges in larger anurans. Although we found modest differences in mean anuran body size among microhabitats, there was extensive overlap in the range of body sizes across microhabitats. Finally, we found that larger anurans are more likely to consume vertebrate prey than smaller anurans are, and that species with a free‐swimming larval phase during development are larger on average than those in which development into a froglet occurs within the egg. Overall, anuran body size does not conform to geographic and ecological patterns observed in other tetrapods but is perhaps more notable for variation in body size within geographic regions, ecologies, and life‐histories. Here we document this variation and propose target clades for detailed studies aimed at disentangling how and why variation in body size was generated and is maintained in anurans.

Seasonality drives body size variation in a widely distributed Neotropical treefrog

Article

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May 2020
J ZOOL

It is well known that body size variation can be related to genetic and environmental factors and that this variation may occur among species, and among and within populations. Scinax fuscomarginatus is a widely distributed Neotropical anuran that occurs in open areas of several South American ecoregions, exposed to different climatic conditions and showing high levels of body size variation. We tested if this variation in body size is related to phylogeny or to any climatic condition to which populations are subjected. We measured the snout‐vent length (SVL) of 285 individuals of S. fuscomarginatus from 37 populations, covering virtually all the known geographic distribution of the species. We constructed a phylogenetic tree under Bayesian inference based on mtDNA sequences to test for the existence of phylogenetic signal in body size variation and performed a multiple linear regression to examine the relationship between body size and environmental variables. Although S. fuscomarginatus shows a deep genetic structure, body size variation was randomly distributed across the phylogeny, indicating no phylogenetic signal. On the other hand, we found evidence that support some influence of climatic conditions in body size variation, being the precipitation seasonality and the temperature seasonality the most important variables. Our results are in accordance with the water conservation hypothesis, which predicts an increase in body size towards drier regions assuming that lower surface‐to‐volume ratio of larger bodies minimizes water loss by evaporation.

Latitudinal gradients in body size in marine tardigrades

Article

Full-text available

Mar 2020
ZOOL J LINN SOC-LOND

Homeotherms and many poikilotherms display a positive relationship between body size and latitude, but this has rarely been investigated in microscopic animals. We analysed all published records of marine Tardigrada to address whether microscopic marine invertebrates have similar ecogeographical patterns to macroscopic animals. The data were analysed using spatially explicit generalized least squares models and linear models. We looked for latitudinal patterns in body size and species richness, testing for sampling bias and phylogenetic constraints. No latitudinal pattern was detected for species richness, and sampling bias was the strongest correlate of species richness. A hump-shaped increase in median body size with latitude was found, and the effect remained significant for the Northern Hemisphere but not for the Southern. The most significant effect supporting the latitudinal gradient was on minimum body size, with smaller species disappearing at higher latitudes. Our results suggest that biogeographical signals were observed for body size, albeit difficult to detect in poorly studied groups because of swamping from biased sampling effort and from low sample size. We did not find a significant correlation with the latitudinal pattern of body size and ecologically relevant net primary productivity. ADDITIONAL KEYWORDS: Bergmann's rule-size-latitude relationship-ecogeographical rules-everything is everywhere-net primary productivity-species richness-Tardigrada-water bears.

Could 19th-Century Authors Have Noticed Bergmann’s “Rule” in Humans?

Article

Full-text available

Oct 2024

Robert Asher

The correlation of increasing size with latitude, known as “Bergmann’s rule”, was first articulated in the 1840s, but its potential applicability to humans was not recognized for another century. In this paper, I have tested if human craniometric data collected by 19th-century naturalists supported this “rule”. At least in the northern hemisphere, they did. Bergmann recognized a relationship between size and latitude in the 1840s, but others studying humans did not, possibly because they were preoccupied with applying anatomical data to debates about human intelligence. Links between cranial anatomy and racist dogma have long been debunked and profound similarities across human populations show that ethnic prejudice has no basis in evolutionary biology. Nonetheless, human populations are not homogeneous or less subject to evolutionary processes than other organisms. Some of these processes are evident in the datasets collected by 19th-century naturalists, whatever their socio-political views may have been.

Global Ecology and Biogeography Unifying Coral Reef States Through Space and Time Reveals a Changing Ecosystem

Article

Full-text available

Oct 2024
GLOBAL ECOL BIOGEOGR

Aim Ecological state shifts that alter the structure and function of entire ecosystems are a concerning consequence of human impact. Yet, when, where and why discrete ecological states emerge remains difficult to predict and monitor, especially in high‐diversity systems. We sought to quantify state shifts and their drivers through space and time in the most ecologically complex marine ecosystem: tropical coral reefs. Location Worldwide. Time Period 1987–2019. Major Taxa Studied Coral reef communities. Methods Using a global dataset of 3375 coral reef surveys, along with 13 time series datasets ranging between 1987 and 2019, we applied a novel double‐dichotomy approach to classify coral reefs into four simplified and discrete states based on the relative contributions of corals versus algae to benthic cover and small‐bodied versus large‐bodied fishes to fish standing stock. We then examined state shifts considering a range of spatial predictors and tested whether states have shifted directionally over time, and the nature of the most common transitions. Results We show that geographic, environmental and anthropogenic context fundamentally shapes coral reef states at the local scale, which explains disparities among case studies, and stakes out critical baseline expectations for regional management efforts. We also reveal clear multi‐decadal state shifts on coral reefs: over time, systems dominated by reef‐building corals and small‐bodied, planktivorous fishes tend to have been replaced with reefs characterised by algae and larger‐bodied fishes. Main Conclusions Our results suggest a previously unrecognised transition from systems that harness external subsidies through small‐bodied consumers associated with structurally complex live corals, to herbivore‐dominated systems with stronger bottom‐up dynamics. Overall, the partitioning of complex reef ecosystems into a small suite of discrete ecological states suggests that spatial context‐dependency, shifting baselines and changes in reef functioning are crucial considerations for coral reef management in the 21st century.

Geographic variation of lean body mass and a model of its effect on the capacity of the raccoon to fatten and fast

Article

Jan 1993

In the eastern United States, apparent lean body mass (ALBM) of raccoons (Procyon lotor) increased from south to north, and appeared to follow Bergmann's rule: subtropical Key Vaca, females = 2.0 kg, males = 2.4 kg; mild temperate southeastern United States, females = 3.2 kg, males = 3.5 kg; harsh to severe temperate Michigan and Minnesota, females = 4.5 kg, males = 5.0 kg. We postulated that selection has favored large lean mass in the cold parts of the raccoon's range because it provides greater fasting endurance. In mammals, as lean body mass (LBM) increases, the potential to store energy as fat (Fs = LBM1.0) increases out of proportion to the cost of basal metabolism (Hb = mass0.75). Thus, big fat raccoons should be able to fast for a longer period of time than small fat ones. We modeled these relationships for raccoons. We found that each increase in ALBM substantially increased the length of time they could fast. Since the increased fasting times were necessary for their winter survival, the model supported our hypothesis. We also concluded that the northern edge of their range is determined by the limits of their genetic potential to increase ALBM. The amount of fat deposited in the fall also varied geographically: subtropical raccoons achieved 14 to 17% apparent body fat (ABF), those from Florida to Virginia 19 to 42% ABF, and those around the Great Lakes 31 to 50% ABF. Geographic variation in ABF suggests that seasonal lipogenesis is coupled, via neuroendocrine mechanisms, to environmental cues that stimulate the appropriate degree of fat deposition in each local area. The data also suggest that there may be geographic differences in the capacity to fatten.

Size records and demographics of an Eastern Painted Turtle (Chrysemys picta picta) urban population near the northern limit of the species’ range in eastern Canada

Article

Jan 2024
Can Field Nat

Understanding variation in demographics and life history across species ranges and differing landcover types is valuable for conservation planning. We examined the population demographics of a small urban population of Eastern Painted Turtle (Chrysemys picta picta) in New Brunswick, Canada, near the northern limit of the species’ range. We captured turtles using hoop traps and by hand during four sampling periods. We estimated that our population included 17 females, nine males, and 29 juveniles in late summer 2015 using Jolly-Seber population size estimates. We captured several very large females at our study site; 5/17 females (29%) were larger than previous size records for the subspecies. Growth rates for juveniles were greater than most populations of Eastern Painted Turtles reported elsewhere. Growth rates at our site were significantly greater for smaller (younger) turtles and for females compared to males. Overwinter survivorship estimates were 100% from late summer 2014 to spring 2015. Active season (2015) survivorship was 100% for females, 89% for males, and 93% for juveniles. We speculate that the large body sizes found at our study site were achieved through high survivorship and larger growth rates compared to other areas reported previously. Our data supports previous findings that body size of Painted Turtles increases with latitude, and additionally, growth may have been enhanced by increased nutrient levels common in human-modified landscapes.

Temperature and precipitation gradients inform geographic patterns of body size variation in Gila Monsters (Heloderma suspectum)

Thesis

Full-text available

Dec 2022

Connor Hughes

Body size can influence nearly every aspect of an organism’s biology and ecology, and drivers of intraspecific variation in ectotherm body size are often poorly understood. We combine mechanistic modeling and empirical data to examine three previously described hypotheses regarding potential drivers of intraspecific variation in body size across the range of an iconic desert ectotherm, the Gila monster (Heloderma suspectum). We tested the hypotheses that body size is influenced by (i) potential foraging time and thermal constraints to activity; (ii) the abundance of resources (prey, water); and (iii) seasonality or consistency of resources. We found that body size across populations was primarily influenced by year-to-year precipitation variation and thermal environment, where individuals tend to be larger in cooler areas with less consistent precipitation patterns across years. These results support our third hypothesis, that body size is influenced by resource seasonality, but fail to support hypothesis one or two. Large body size may provide greater capacity for accumulating energy reserves, a potentially adaptive trait in environments where access to resources may be inconsistent. The strong effect of the thermal environment on body size also points to a potential alternate and more general effect of temperature not accounted for by our tested hypotheses.

Can neutral genetic differentiation explain geographical variation in body size of the natterjack toad, Epidalea calamita?

Article

Full-text available

Dec 2023

Federico Marangoni

Population genetic studies are crucial for evolutionary biologists because the population is the basic substrate on which evolution is forged. However little empirical evidence has been able to demonstrate the role that isolation and gene flow play in maintaining differentiation in populations at short geographic scales. Epidalea calamita exhibits a steep variation in body size and reproductive traits in southwestern Spain, associated with changes in the geological substrate. This implies a decrease of 70.9% of body mass and 28.5% in snout-vent length, on a micro-geographic scale of only 60 km. Previous results from both metamorphic and juvenile common garden experiments showed that genetic differentiation may be a causal determinant of geographic variation in adult. This study tested whether neutral genetic differentiation can explain the geographical variation in the body size observed in E. calamita. It was addressed analyzing the level of genetic structuring and gene flow among populations along the cline, comparing the genetic diversity between and within populations, as well as between ecological environments. The study showed that the geographic variation in body size observed in E. calamita has evolved in absence of geographic isolation, with moderate gene flow connecting the populations. Thus, neutral genetic differentiation cannot explain the geographical variation observed. Future studies are needed on the interaction between the genetic component with the environmental factors and will be necessary to analyze the contribution of the maternal effects in the origin and evolution of the geographical variation in the body size observed in E. calamita from southern Spain.

Factors limiting the spread of middle- and low-altitude fishes to the Qinghai-Tibet plateau

Article

Full-text available

May 2023

The distribution pattern of species is determined by the environment and their adaptability to the environment. Qinghai-Tibet Plateau has become a natural laboratory for studying adaptive evolution due to its extreme environmental characteristics such as low temperature, low oxygen, high salinity and high ultraviolet radiation (UVR). Fish are sensitive to the environmental stress, so they are ideal materials for studying high-altitude adaptation of animals. Previous studies have mainly focused on the adaptability of plateau species, but the reasons why plain species cannot spread to the plateau have been ignored. In this study, stress experiments and histological experiments were used to compare the tolerance of six Barbini fishes (family: Cyprinidae) distributed at different altitudes and regions to low temperature, low oxygen, salinity and UVR. Results showed that the tolerance of fishes to high-altitude environmental stress factors was closely related to the environmental stress of their main habitats. The high-altitude fish Gymnocypris eckloni had strong tolerance to all stress factors, while the other five fishes from middle and low altitudes could not adapt to single or multiple stress factors, with significant interspecific differences. Among these factors, middle- and low-altitude fishes showed common low tolerance to UVR, suggesting that high UVR, the factor lacking at low altitude areas, plays an important role. Moreover, during the uplift of the Qinghai-Tibet Plateau, Schizothorax fish disappeared from the middle of the plateau. We speculate that this was caused by its intolerance to the increasingly extreme plateau environment, especially salinity.

What drives the evolution of body size in ectotherms? A global analysis across the amphibian tree of life

Article

Full-text available

Apr 2023
GLOBAL ECOL BIOGEOGR

Aim The emergence of large‐scale patterns of animal body size is the central expectation of a wide range of (macro)ecological and evolutionary hypotheses. The drivers shaping these patterns include climate (e.g. Bergmann's rule), resource availability (e.g. ‘resource rule’), biogeographic settings and niche partitioning (e.g. adaptive radiation). However, these hypotheses often make opposing predictions about the trajectories of body size evolution. Therefore, whether underlying drivers of body size evolution can be identified remains an open question. Here, we employ the most comprehensive global dataset of body size in amphibians, to address multiple hypotheses that predict patterns of body size evolution based on climatic factors, ecology and biogeographic settings to identify underlying drivers and their generality across lineages. Location Global. Time Period Present. Major Taxa Studied Amphibians. Methods Using a global dataset spanning 7270 (>87% of) species of Anura, Caudata and Gymnophiona, we employed phylogenetic Bayesian modelling to test the roles of climate, resource availability, insularity, elevation, habitat use and diel activity on body size. Results Only climate and elevation drive body size patterns, and these processes are order‐specific. Seasonality in precipitation and in temperature predict body size clines in anurans, whereas caecilian body size increases with aridity. However, neither of these drivers explained variation in salamander body size. In both anurans and caecilians, size increases with elevational range and with midpoint elevation in caecilians only. No effects of mean temperature, resource abundance, insularity, time of activity or habitat use were found. Main Conclusions Precipitation and temperature seasonality are the dominant climatic drivers of body size variation in amphibians overall. Bergmann's rule is consistently rejected, and so are other alternative hypotheses. We suggest that the rationale sustaining existing macroecological rules of body size is unrealistic in amphibians and discuss our findings in the context of the emerging hypothesis that climate change can drive body size shifts.

Morphometric differentiation and sexual dimorphism in Limnomedusa macroglossa (Duméril & Bibron, 1841) (Anura: Alsodidae) from Uruguay

Article

Full-text available

May 2021

Intersexual morphological differences within a species occur in many traits, including body size and shape. Many processes that cause geographic variability in morphology have been proposed: population structure, phenotypic plasticity (environmental effects on development), and natural and/or sexual selection. Several hypotheses can explain patterns of sexual dimorphism in anurans, including natural or intra/inter-sexual selection, and differences in life history strategies between sexes. Limnomedusa macroglossa is considered a habitat specialist restricted to rocky outcrops in Brazil, Argentina, Paraguay, and Uruguay. We evaluated the extent of sexual (size and shape) dimorphism in L. macroglossa from Uruguay based on morphometrics and secondary sexual characteristics, while taking into account geographic variation. Sexual dimorphism in body size of adults was found, but multivariate analyses did not demonstrate the existence of significant differences in shape. There were also significant differences in body size and hind leg measurements among six hydrographic basins as a result from the phenotypic plasticity correlated with local temperature, representing a clinal variation along the latitudinal gradient of Uruguay. The sexual dimorphism found in body size is probably the consequence of higher growth rates and/or late sexual maturity in females, which favors larger body size for accommodating larger ovaries, and thus, higher reproductive output.

Resource availability modulates the effect of body size on reproductive development

Article

Full-text available

Jan 2023

Within-species variation in animal body size predicts major differences in life history, for example, in reproductive development, fecundity, and even longevity. Purely from an energetic perspective, large size could entail larger energy reserves, fuelling different life functions, such as reproduction and survival (the "energy reserve" hypothesis). Conversely, larger body size could demand more energy for maintenance, and larger individuals might do worse in reproduction and survival under resource shortage (the "energy demand" hypothesis). Disentangling these alternative hypotheses is difficult because large size often correlates with better resource availability during growth, which could mask direct effects of body size on fitness traits. Here, we used experimental body size manipulation in the freshwater cnidarian Hydra oligactis, coupled with manipulation of resource (food) availability to separate direct effects of body size from resource availability on fitness traits (sexual development time, fecundity, and survival). We found significant interaction between body size and food availability in sexual development time in both males and females, such that large individuals responded less strongly to variation in resource availability. These results are consistent with an energy reserve effect of large size in Hydra. Surprisingly, the response was different in males and females: small and starved females delayed their reproduction, while small and starved males developed reproductive organs faster. In case of fecundity and survival, both size and food availability had significant effects, but we detected no interaction between them. Our observations suggest that in Hydra, small individuals are sensitive to fluctuations in resource availability, but these small individuals are able to adjust their reproductive development to maintain fitness.

Genetic Landscape and Morphometrics of Historic and Contemporary Populations of Wood Turtle (Glyptemys insculpta) in New York State

Thesis

Full-text available

Jul 2016

Alexander Robillard

On a global scale amphibians and reptiles are in decline due to pressures including climate change, unsustainable harvest, habitat loss and habitat degradation (Gibbons et al. 2000). Of all reptile and amphibian species, turtles are the most threatened by commercial trade (Williams 1999). Members of the order Testudines are particularly vulnerable to increased decline when faced with increasing anthropogenic disturbances such as road mortality and illegal harvesting (Lieberman 1994, Garber and Burger 1995, Wood and Herlands 1997, Mockenhaupt 1999, Sharma 1999, Williams 1999, Levell 2000, Gibbons et al. 2000, Gibbs and Shriver 2002, Steen and Gibbs 2004, Gibbs and Steen 2005, Steen et al. 2006, USFWS 2015). Nearly 50% of all turtle species are currently listed as threatened or endangered by the IUCN (2015). Turtles are generally poor long-distance dispersers, which may enable habitat fragmentation along with illegal harvesting to put populations at risk of extinction due to demographic and genetic diversity loss (Gibbons et al. 2000). In North America alone there are several case studies which indicate the aforementioned anthropogenic disturbances have a direct negative impact on freshwater turtle species by skewing sex ratios and increasing the mortality of immigrating individuals (USFWS 2015, Buhlman and Gibbons 1997, Wood and Herlands 1997, Williams 1999, Levell 2000, Gibbons et al 2000, Gibbs and Shriver 2002, Steen and Gibbs 2004, Gibbs and Steen 2005, Steen et al. 2006). One such study by Garber and Burger (1995) examined the relationship between human recreation and the demographics of two wood turtle (Glyptemys insculpta) populations over 20 years in the context of a persistent and robust habitat. During periods allowing recreation such as hiking, fishing and camping they found that local wood turtle populations would decline dramatically whereas during stints where recreation was completely prohibited they appeared to recover. Their study insinuates that even the casual collection of these turtles as pets has dramatic negative long-term impacts on population viability (Garber and Burger 1995). The wood turtle is a freshwater species which resides in the family Emydidae (Van Dijk and Harding 2013). Originally grouped in the genus Clemmys along with the endangered spotted turtle (Clemmys gutatta) (Van Dijk 2013a) and critically endangered bog turtle (Glyptemys muhlenburgii) (Van Dijk 2013b), the wood turtle has only recently been reclassified to reside in the genus Glyptemys with just the bog turtle (Bickhan et al. 1996; Holman and Fritz 2001). The wood turtle ranges from northern Virginia through the northeast, and west through parts of Canada and the Midwest (Ernst et al. 1994) (Figure 1.1). In the southern most portion of their range, wood turtles are found to inhabit narrow streams and creeks, while their northern counterparts are found more commonly in large riparian deposit beaches (Jones et al. 2015). An inhabitant of open canopy alluvial Cobble Shore deposits (as classified by the NYS Natural Heritage Program, Edinger et al. 2002) along creeks and rivers, the wood turtle occupies a wide range of freshwater and terrestrial habitats (Jones et al. 2015). Considered omnivorous, the wood turtle is opportunistically carnivorous and will consume a wide variety of organisms from snails and slugs to road kill (Ernst et al. 1994). The wood turtle, like many other species of freshwater turtle, is considered threatened throughout much of its home-range (Fig 1.1) and is listed as endangered by the IUCN (Van Dijk and Harding 2013). Recent efforts to assess the current status of the wood turtle has taken the form of a range-wide collaboration between the USFWS and thirteen state agencies funded by the Northeast Regional Conservation Need state funding program (Akre 2011, Jones et al. 2015). Glyptemys insculpta is currently under review for listing as threatened by the U.S Fish and Wildlife Service under the Endangered Species Act while in the State of New York it is considered a Species of Special Concern (Breisch and Behler 2002, NYSDEC 2007, USFWS 2015). Species are recognized as Special Concern in New York because they are listed, or are considered for listing, as threatened or endangered by the federal government or several adjacent states (NYSDEC 2007, 2013). In order for the State of New York to list or delist a species as threatened or endangered they must gather sufficient evidence to answer criteria stated in Title 6, Chapter 1, Part 182, Sections 3-6 of the New York Codes, Rules and Regulations (NYSDEC 2013, Thompson Reuters 2016). This thesis’ focus is 3 to address some of these vital criteria such as identifying cyclical declines and total number of reproducing individuals of wood turtle in New York.

Rangewide Population Structure of the Clearnose Skate

Article

Mar 2022

Skates (family Rajidae) are benthic elasmobranchs that are highly vulnerable to incidental fishery bycatch, are discarded at sea, and are poorly accounted for in catch records. Many aspects of skate life history, such as population structure, are not well understood. Without this knowledge, indiscriminate removal may have deleterious effects on scientific, conservation, and management efforts. The Clearnose Skate Rostroraja eglanteria is seasonally migratory and widely distributed in the coastal waters of the eastern United States and in the northeastern Gulf of Mexico. This study used molecular techniques to assess the population structure of Clearnose Skate for use as a biological reference point for further research and management. Specimens were collected from 2014 to 2019 by fisheries‐independent surveys. High‐throughput genotyping‐by‐sequencing was used to identify single nucleotide polymorphisms, resulting in two data sets: one consisting of 8,914 loci (outlier and neutral) and the other comprised of 30 outlier loci. Results from all analyses and using both data sets indicated a high level of genetic differentiation between specimens from the Gulf of Mexico and specimens from the U.S East Coast. Using the outlier data set, a low but significant level of genetic differentiation was also found among specimens from the U.S. East Coast, with a subtle break near the North Carolina and South Carolina border. Genetic differences along the U.S. East Coast were spatially autocorrelated, indicating a latitudinal genetic gradient. The level of observed genetic differentiation between the Gulf of Mexico and the U.S. East Coast is likely due to physical barriers such as Florida and the Gulf Stream current, while the subtle structure along the U.S. East Coast is likely attributable to isolation caused by dispersal limitations and local temperature preferences. The results from this investigation of Clearnose Skate population structure can be used to better monitor and manage this vulnerable elasmobranch.

Funkcijsko-morfološke i etološke karakteristike barske kornjače, Emys orbicularis (Emydidae, Testudines)

Thesis

Full-text available

Aug 2019

Vukašin Bjelica

U ovom radu ispitivane su razlike u veličini i obliku oklopa, antipredatorskom ponašanju i agilnosti kod tri populacije barske kornjače (Emys orbicularis) u Srbiji. Na terenu su mereni morfološki parametri koji određuju veličinu i oblik oklopa, pri pretpostavci da ove karakteristike utiču na lokomociju i ponašanje kornjača. U svim populacijama primećen je seksualni dimorfizam u obliku oklopa, dok za dve od tri populacije je primećen seksualni dimorfizam u veličini oklopa. Generalno ženke imaju veći i obliji oklop od mužjaka. Rezultati ukazuju da na ispitivanim populacijama interseksualna selekcija deluje na mužjake povećavajući im mobilnost, dok su ženke pod selekcijom za fekunditet. Nedostatak seksualnog dimorfizma u jednoj populaciji barskih kornjača je potencijalno posledica slabijih selekcionih pritiska na mužjake. Pored merenja morfoloških parametara na terenu su izvođeni testovi antipredatorskog ponašanja i testovi agilnosti. U svim populacijama primećena je razlika između mužjaka i ženki u antipredatorskom ponašanju, gde mužjaci imaju brže reakcije od ženki. Ovo je verovatno uslovljeno karakteristikama njihovog oklopa, kao i različitim selekcionim pritiscima koji deluju na njih. Testovi antipredatorskog ponašanja ukazuju i na to da je za kornjače bezbednija pozicija kada se nađu na plastronu u odnosu na karapaks. Kada je kornjača na karapsku, faza prevrtanja iziskuje prekidanje praćenja predatora i iniciranje prevrtanja, što nosi veći rizik po jedinku. Nema razlike između parametara agilnost mužjaka i ženki. Kod ženki takođe odsustvuje korelacija između morfoloških karakteristika i njihovih preformansi. Moguće je da oblik i veličina oklopa ženki kod ove vrste nije dostigla granične vrednosti gde bi imala uticaj na njihove preformanse. Potencijalno je uočena različita strategije oslobađanja od vegetacije između mužjaka i ženki. Takođe, u našem uzorku, veće razlike u ponašanju i agilnosti su se javljale između polova, nego između populacija

The role of thermoregulation in the obstetrical dilemma

Thesis

Full-text available

May 2020

Jennifer Eyre

The modern human female pelvis is adapted for bipedal locomotion but must also birth highly-encephalized babies. Potentially a trade-off between locomotion and parturition created an “obstetrical dilemma”. The obstetrical dilemma asks why obstructed labor caused by cephalopelvic disproportion is relatively common in modern humans despite its reproductive cost. Although the obstetrical dilemma is traditionally framed as a trade-off between efficient locomotion and successful parturition, researchers have searched for other selective pressures antagonistic to an increase in the size of the birth canal. This dissertation explores the thermoregulation hypothesis, which argues selection for heat dissipation constrained the size of the birth canal. A central question that needs to be answered in order to determine why the obstetrical dilemma exists is when did it first evolve in the hominin lineage. Through the examination of pubic bones from two female australopiths, as well as other hominin fossils, modern humans, and non-human primates, it was determined that the “ventral sulcus” present in the australopiths is not indicative of difficult birth and does not support early hominins experiencing cephalopelvic disproportion. Instead, the ventral sulcus is hypothesized to be the result of intra-abdominal pressure on pelvic ligaments that had to support abdominal and pelvic viscera and potentially the weight of gestating fetuses. Bergmann’s rule states that mammalian ratios of surface area to mass are thermoregulatory adaptations. It has been argued that bi-iliac breadth determines this ratio in humans, with a decrease in bi-iliac breadth leading to a relative increase in surface area, and thus greater heat dissipation. Selection on body temperature regulation in hominins evolving in hot climates could have been in opposition to selection for a widening of the pelvis, potentially constraining the size of the birth canal. To test the relationship between core temperature and bi-iliac breadth, thirty human subjects ran for one hour at a set pace in a variety of climatic conditions. Bi-iliac breadth is a significant predictor of maximum core temperature, but not the increase in core temperature. This is explicable because bi-iliac breadth also plays a significant role in resting core temperature, meaning that individuals with smaller bi-iliac breadths start at a lower resting core temperature and reach a lower maximum temperature during running. This indicates that bi-iliac breadth is an important factor in humans’ ability to thermoregulate. However, a smaller bi-iliac breadth does not necessarily mean a smaller birth canal. The correlation between bi-iliac breadth and the areas and linear dimensions of the birth canal in the inlet, midplane, and outlet, was tested in an ecogeographically-varied modern human female skeletal sample. All mediolateral diameters and areas of the three birth canal planes are significantly correlated with BIB (with the exception of the outlet mediolateral diameter). This provides support for the thermoregulation hypothesis. The obstetrical dilemma is a complicated problem that most likely does not have a simple solution. Continued research is necessary to determine the relative contributions of different selective pressures on the hominin birth canal, and to determine when the obstetrical dilemma first evolved. However, the evidence from this dissertation suggests that because bi-iliac breadth is significantly correlated with birth canal size, and because thermoregulation is significantly correlated with bi-iliac breadth, selection related to thermoregulation may have played a role in constraining birth canal size in hominin evolution.

No evidence for reduced growth in resident fish species in the era of de-eutrophication in a coastal area in NW Europe

Article

Full-text available

May 2021
MAR ENVIRON RES

Coastal areas in north-western Europe have been influenced by elevated nutrient levels starting in the 1960s. Due to efficient measures, both nitrate and phosphate levels decreased since the mid-1980s. The co-occurring declines in nutrient loadings and fish productivity are often presumed to be causally linked. We investigated whether four resident fish species (twaite shad, bull-rout, thick-lipped grey mullet and eelpout), that spend the majority of their life in the vicinity of the coast, differed in growth between the historic eutrophication period compared to the recent lower nutrient-level period. Based on Von Bertalanffy growth models of length at age, and the analysis of annual otolith increments, we investigated the difference in sex-specific growth patterns and related these to temperature, eutrophication level (Chlorophyll a), growth window and fish density. In all four species, annual otolith growth rates during the early life stages differed between the two periods, mostly resulting in larger lengths at age in the recent period. All species showed significant correlations between increment size and temperature, explaining the observed period differences. The lack of an effect of total fish biomass provided no evidence for density dependent growth. A correlation with chlorophyll was found in bull-rout, but the relationship was negative, thus not supporting the idea of growth enhanced by high nutrient levels. In conclusion, we found no evidence for reduced growth related to de-eutrophication. Our results indicate that temperature rise due to climate change had a greater impact on growth than reduced food availability due to de-eutrophication. We discuss potential consequences of growth changes for length-based indicators used in management.

GEOGRAPHIC VARIATION IN THE LIFE HISTORY AND MORPHOLOGY OF THE PACIFIC GEODUCK, PANOPEA GENEROSA

Thesis

Full-text available

Dec 2015

The Pacific geoduck, Panopea generosa, is an ideal candidate to investigate patterns of life history variation and morphological plasticity in shell shape, as it occurs over a large geographic range, inhabits different marine environments, and experiences intense fishing pressure in some locations (i.e., Mexico and Washington). Six populations were sampled from Washington to Mexico to evaluate evidence for geographic variation in demography, life history, and morphology. Results provided evidence for a latitudinal cline with larger clams occurring in locations characterized by colder water temperature. Age structure and longevity analyses indicated that life expectancy was significantly lowered at intertidal sites compared to subtidal sites, potentially in response to fishing. Von Bertalanffy growth model (VBGM) analyses revealed significant spatial variation in asymptotic lengths across sampling locations. Correlations of climate (temperature and chlorophyll a) and growth parameters indicated that clams reached larger sizes at locations that were cooler and more productive. Morphological analyses revealed significant spatial differences that did not follow a latitudinal pattern, but may be better explained by site-specific habitat differences. Results will aid managers in developing regulations, tuned to the demographic variability present along the eastern Pacific coast.

Intraspecific trait variability and community assembly in hawkmoths (Lepidoptera: Sphingidae) across an elevational gradient in the eastern Himalayas, India

Article

Full-text available

Feb 2021

• We investigated some aspects of hawkmoth community assembly at 13 elevations along a 200‐ to 2770‐m transect in the eastern Himalayas, a little studied biodiversity hot spot of global importance. We measured the morphological traits of body mass, wing loading, and wing aspect ratio of 3,301 free‐ranging individuals of 76 species without having to collect or even constrain them. We used these trait measurements and T‐statistic metrics to assess the strength of intracommunity (“internal") and extra‐community (“external”) filters which determine the composition of communities vis‐a‐vis the regional pool of species. • The trait distribution of constituent species turned out to be nonrandom subsets of the community‐trait distribution, providing strong evidence for internal filtering in all elevational communities. The external filter metric was more ambiguous. However, the elevational dependence of many metrics including that of the internal filter provided evidence for external (i.e., environmental) filtering. On average, a species occupied as much as 50%–75% of the total community‐trait space, yet the T‐statistic metric for internal filter was sufficiently sensitive to detect a strong nonrandom structure in the trait distribution. • We suggest that the change in T‐statistic metrics along the environmental gradient may provide more clues to the process of community assembly than previously envisaged. A large, smoothly varying and well‐sampled environmental span would make it easier to discern them. Developing T‐statistics for combined analysis of multiple traits will perhaps provide a more accurate picture of internal/filtering and niche complementarity. Moths are a hyperdiverse taxon and a very important component of many ecosystems. Our technique for accurately measuring body and wing dimensions of free‐ranging moths can generate trait database for a large number of individuals in a time‐ and resource‐efficient manner for a variety of community assembly studies using this important taxon.

Water constraints drive allometric patterns in the body shape of tree frogs

Article

Full-text available

Jan 2021

The origin of morphological diversity is a critical question in evolutionary biology. Interactions between the environment and developmental processes have determining roles in morphological diversity, creating patterns through space and over time. Also, the shape of organisms tends to vary with increasing size as a result of those developmental processes, known as allometry. Several studies have demonstrated that the body sizes of anurans are associated with hydric conditions in their environments and that localities with high water stress tend to select for larger individuals. However, how environmental conditions alter those patterns of covariance between size and shape is still elusive. We used 3D geometric morphometric analyses, associated with phylogenetic comparative methods, to determine if the morphological variations and allometric patterns found in Arboranae (Anura) is linked to water conservation mechanisms. We found effects of the hydric stress on the shape of Arboranae species, favouring globular shapes. Also, the allometric patterns varied in intensity according to the water stress gradient, being particularly relevant for smaller frogs, and more intense in environments with higher water deficits. Our study provides empirical evidence that more spherical body shapes, especially among smaller species, reflect an important adaptation of anurans to water conservation in water-constrained environments.

Survival, natural selection and foraging efficiency in Soay sheep on St. Kilda

Thesis

Jan 1999

Jocelyn Margery Milner

The feral Soay sheep of St. Kilda exhibit dramatic population fluctuations and recurrent crashes, the survivors of which are favoured by natural selection. In this thesis, I establish which factors influence over-winter survival. I investigate phenotypic selection of body size traits, and demonstrate their heritability, so establishing the occurrence of natural selection. Finally I explore the relationships between body size and survival in terms of foraging behaviour and diet selection. Over-winter survival of lambs was influenced by both density and density-independent climatic fluctuations. Adults were less sensitive to both factors, especially females which showed no evidence of density-dependence. Generalised linear mixed modelling demonstrated that once between-year random variation was taken into consideration, body weight was the most significant determinant of survival in all age, sex classes. Evidence was found of repeated directional selection of the three traits, body weight, hindleg length and incisor arcade breadth. Whilst selection differentials showed strong positive selection for all these traits in high mortality years, selection gradients demonstrated that body weight experienced direct selection whereas selection of other traits was indirect due to their correlation with body weight. No evidence of opposing selection was found. All the morphometric traits were significantly heritable. An evolutionary response would therefore be expected, but heritabilities were low, and because of environmental noise, no significant increase in body size was detectable over the 12 year period of data. Observed grazing behaviour in relation to vegetation structure was not influenced by individual variation in body size during winter, although female body weight affected diet selectivity in summer. Seasonal patterns were very marked, with summer grazing behaviour influencing survival the following winter. Seasonal differences in faecal nitrogen content and a decline in faecal nitrogen with increasing body size were also apparent. These observations were interpreted using diet quality and body size arguments.

Temperature and the size of freshwater phytoplankton

Article

Full-text available

Jan 2021
HYDROBIOLOGIA

We review the literature on the relationship between water temperature and size of freshwater phytoplankton, to examine the hypothesis that freshwater phytoplankton, like marine phytoplankton and many other groups of organisms, conform to Bergmann’s Rule and become smaller with warming. We provide both experimental and field evidence in support of the above hypothesis, much of this evidence was hidden in studies focused on other issues, but presenting temperature and phytoplankton size data. Freshwater phytoplankton size shrinks with increasing temperature at both the species level (by cells or colonies becoming smaller) and at the community level (shift to smaller species). Exceptions to the Rule do occur but in most cases those exceptions can be explained by indirect effects of temperature on phytoplankton size, via processes such as grazing or nutrient availability. With global warming, freshwater phytoplankton are likely to be of smaller size. This article is dedicated to Colin S. Reynolds, who has had a leading role in our personal education and understanding of phytoplankton ecology.

Impact of Different Developmental Instars on Locusta migratoria Jumping Performance

Article

Full-text available

Mar 2020

Ontogenetic locomotion research focuses on the evolution of locomotion behavior in different developmental stages of a species. Unlike vertebrates, ontogenetic locomotion in invertebrates is poorly investigated. Locusts represent an outstanding biological model to study this issue. They are hemimetabolous insects and have similar aspects and behaviors in different instars. This research is aimed at studying the jumping performance of Locusta migratoria over different developmental instars. Jumps of third instar, fourth instar, and adult L. migratoria were recorded through a high-speed camera. Data were analyzed to develop a simplified biomechanical model of the insect: the elastic joint of locust hind legs was simplified as a torsional spring located at the femur-tibiae joint as a semilunar process and based on an energetic approach involving both locomotion and geometrical data. A simplified mathematical model evaluated the performances of each tested jump. Results showed that longer hind leg length, higher elastic parameter, and longer takeoff time synergistically contribute to a greater velocity and energy storing/releasing in adult locusts, if compared to young instars; at the same time, they compensate possible decreases of the acceleration due to the mass increase. This finding also gives insights for advanced bioinspired jumping robot design.

Butterfly-plant interactions and body size patterns along an elevational gradient in the Manang region of central Nepal

Article

Mar 2020

Butterflies are widely studied due to their key ecosystem functions. For this reason, they are used in ecosystem assessment, formulating conservation plans and in raising the environmental awareness. Quantification of different factors affecting diversity of butterflies is important for their effective conservation. In this study, we investigated abiotic and biotic factors affecting species richness and community composition of butterflies along an elevational gradient in Manang region, central Nepal. We also tested if butterfly species follow the Bergmann’s rule. A total of 57 butterfly species belonging to 39 genera and 8 families were recorded in the study area. Out of a total of 127 plant species in identified in the study region, only 67 plant species were visited by butterflies as nectar sources. Species richness of butterflies increased with increasing elevation. Species richness was significantly higher in places with shrubs compared to other places and also in autumn than in summer. Species richness of butterflies also depended on composition of plant species occurring at the localities. Butterfly species composition varied among sampling localities. It was also determined by habitat type, elevation, sampling time, plant species and interactions of elevation × time. The relationship between butterfly size and elevation was in the opposite direction than expected according to the Bergmann’s rule. In conclusion, protection of butterfly diversity can only be achieved by protecting different habitats across the diverse physiography of the region and different plant species, in particular herbs and shrubs. Our results do not support the Bergmann’s rule for butterflies along an elevational gradient in our region.

Ambient temperature correlates with geographic variation in body size of least horseshoe bats

Article

Full-text available

Feb 2020

Geographic variation in body size is common within many animal species. The causes of this pattern, however, remain largely unexplored in most vertebrate groups. Bats are widely distributed globally owing to their ability of powered flight. Most bat species encounter a variety of climatic conditions across their distribution range, making them an ideal taxon for the study of ecogeographic patterns in body size. Here, we used adult least horseshoe bats, Rhinolophus pusillus, to test whether geographic variation in body size was determined by heat conservation, heat dissipation, climatic seasonality, or primary productivity. We measured body mass and head-body length for 246 adult bats from 12 allopatric colonies in China. We quantified the ecological conditions inhabited by each colony, including mean maximum temperature of the warmest month, mean minimum temperature of the coldest month, temperature seasonality, precipitation seasonality, and annual net primary productivity. Body mass and head-body length, two of the most reliable indicators of body size, exhibited marked differences between colonies. After controlling for spatial autocorrelation, the mean minimum temperature of the coldest month explained most of the variation in body size among colonies, regardless of sex. The mean maximum temperature, climatic seasonality, and annual net primary productivity had limited power in predicting body size of males or females in comparison with mean minimum temperature. These results support the heat conservation hypothesis and suggest adaptive responses of body size to cold climates in cave-dwelling bats.

Ecological variability is associated with functional trait diversity in the western fence lizard (Sceloporus occidentalis)

Article

Full-text available

Nov 2019
BIOL J LINN SOC

A major goal of evolutionary ecology is to understand the ways in which ecological variability has structured morphological diversity. The aim of this study was to examine intraspecific phenotypic variation in the western fence lizard (Sceloporus occidentalis) for functional traits previously shown to be linked to variation across latitude and climate at a genus-wide level. We found that body size in S. occidentalis was negatively related to minimum temperatures during the coldest month, potentially implicating overwintering survival as a mechanism leading to this relationship. We also demonstrated that scale size in S. occidentalis was negatively associated with aridity, which is consistent with several other studies in squamate reptiles and the known functional role of scale size in moderating evaporative water loss. However, contrary to predictions of the thermal melanism hypothesis, we found no association between lizard colour and temperature during the active season. Overall, our results are largely at odds with interspecific patterns examining the relationship between these traits and environmental conditions. It is unclear to what degree intraspecific trait variation generally agrees with inferences made at the interspecific level. In any case, more studies at the intraspecific level are needed to resolve this question.

Global patterns of body size evolution are driven by precipitation in legless amphibians

Article

Full-text available

Jun 2019
ECOGRAPHY

Body size shapes ecological interactions across and within species, ultimately influencing the evolution of large‐scale biodiversity patterns. Therefore, macroecological studies of body size provide a link between spatial variation in selection regimes and the evolution of animal assemblages through space. Multiple hypotheses have been formulated to explain the evolution of spatial gradients of animal body size, predominantly driven by thermal (Bergmann's rule), humidity (‘water conservation hypothesis’), and resource constraints (‘resource rule’, ‘seasonality rule’) on physiological homeostasis. However, while integrative tests of all four hypotheses combined are needed, the focus of such empirical efforts needs to move beyond the traditional endotherm‐ectotherm dichotomy, to instead interrogate the role that variation in lifestyles within major lineages (e.g., Classes) play in creating neglected scenarios of selection via analyses of largely overlooked environment‐body size interactions. Here, we test all four rules above using a global database spanning 99% of modern species of an entire Order of legless, predominantly underground‐dwelling amphibians (Gymnophiona, or caecilians). We found a consistent effect of increasing precipitation (and resource abundance) on body size reductions (supporting the water conservation hypothesis), while Bergmann's, the seasonality and resource rules are rejected. We argue that subterranean lifestyles minimize the effects of aboveground selection agents, making humidity a dominant selection pressure – aridity promotes larger body sizes that reduce risk of evaporative dehydration, while smaller sizes occur in wetter environments where dehydration constraints are relaxed. We discuss the links between these principles with the physiological constraints that may have influenced the tropically‐restricted global radiation of caecilians.

Testing Bergmann's rule in marine invertebrates: Using global brachiopod data during the Permian glacial-interglacial transition

Article

Feb 2025
GLOBAL PLANET CHANGE

Does death drive the scaling of life?

Article

Nov 2024
BIOL REV

Douglas S. Glazier

The magnitude of many kinds of biological structures and processes scale with organismal size, often in regular ways that can be described by power functions. Traditionally, many of these “biological scaling” relationships have been explained based on internal geometric, physical, and energetic constraints according to universal natural laws, such as the “surface law” and “3/4‐power law”. However, during the last three decades it has become increasingly apparent that biological scaling relationships vary greatly in response to various external (environmental) factors. In this review, I propose and provide several lines of evidence supporting a new ecological perspective that I call the “mortality theory of ecology” (MorTE). According to this viewpoint, mortality imposes time limits on the growth, development, and reproduction of organisms. Accordingly, small, vulnerable organisms subject to high mortality due to predation and other environmental hazards have evolved faster, shorter lives than larger, more protected organisms. A MorTE also includes various corollary, size‐related internal and external causative factors (e.g. intraspecific resource competition, geometric surface area to volume effects on resource supply/transport and the protection of internal tissues from environmental hazards, internal homeostatic regulatory systems, incidence of pathogens and parasites, etc.) that impact the scaling of life. A mortality‐centred approach successfully predicts the ranges of body‐mass scaling slopes observed for many kinds of biological and ecological traits. Furthermore, I argue that mortality rate should be considered the ultimate (evolutionary) driver of the scaling of life, that is expressed in the context of other proximate (functional) drivers such as information‐based biological regulation and spatial (geometric) and energetic (metabolic) constraints.

Form, Function, and Locomotory Habits in Fish

Chapter

Jan 2024

C.C. Lindsey

Are Bergmann's and Jordan's rules valid for a neotropical pitviper?

Article

Full-text available

Jun 2024
J ZOOL

Morphological variation along the spatial distribution of species has been extensively investigated in ecological studies, and several ecogeographical rules explore the relationships between morphological traits and the environment. Many morphological traits are correlated, providing an opportunity to evaluate the validity of multiple ecogeographical rules simultaneously. Bergmann's rule predicts that endothermic animals in colder locations are larger than those in warmer locations. Jordan's rule predicts that fish from colder locations have more vertebrae than those from warmer locations. We tested the validity of Bergmann's and Jordan's rules for the neotropical lancehead snake Bothrops jararaca. We evaluated three morphological characters of 342 specimens: number of ventral scales (proxy for vertebrae number), snout–vent length (a linear measure of body size) and stoutness (volumetric body size). We implemented spatial regressions to evaluate the variation of morphological dimensions using climatic predictors: the minimum temperature and evapotranspiration. SVL was poorly related to minimum temperature and evapotranspiration. However, stouter individuals were found in colder places with greater evapotranspiration, following Bergmann's rule and the water conservation hypothesis. Individuals in warmer locations also had a greater number of ventral scales, reversing Jordan's rule. We showed that different selective pressures act on different morphological dimensions. Although stoutness follows Bergmann's rule, its variation would arise from an energy storage demand rather than heat conservation. Also, stoutness variation along evapotranspiration gradients could represent a mechanism to avoid hydric stress in environments with considerable climatic variations. The variation in vertebrae number along temperature gradients could be related to ecological factors and foraging. We highlight that physioecological mechanisms to deal with climatic variation and ecological aspects could be identified in snakes through intraspecific analyses, contrasting with interspecific studies that can hardly detect general trends. Due to different environmental effects on body size, we shed new light on the importance of exploring multiple morphological dimensions in macroecological studies.

Ecogeographic rules in a common Neotropical treefrog: No clinal variation along a mountain range

Article

Full-text available

May 2024
ACTA ZOOL-STOCKHOLM

Body and limb size are associated with many aspects of the biology of animals. Geographic variation in morphological traits has often been investigated through ecogeographical rules. Bergmann's rule posits an inverse relationship between body size and temperature in homeotherms, while Allen's rule posits that endothermic animals inhabiting colder climates have relatively shorter protruding parts (e.g., limbs) in comparison to populations from warmer climates. However, the applicability and validity of these rules in poikilotherms are currently contentious. In this study, we aimed to test predictions of Bergmann's and Allen's rules in populations of the Neotropical frog Boana platanera. We analysed 142 adult male museum specimens from 17 localities along a mountain range in western Venezuela. We obtained six external morphological measurements and assessed the correlation of body size and limb size with temperature data for each locality. Our results were contrary to the expectations but consistent with previous studies. All this together indicates that exceptions to the Bergmann's and Allen's rules are frequent and idiosyncratic in anurans. We discuss alternative hypotheses that could explain geographic variation of body and limb size in future studies.

The intestinal digesta microbiota of tropical marine fish is largely uncultured and distinct from surrounding water microbiota

Article

Full-text available

Feb 2024

Studying the gut microbes of marine fishes is an important part of conservation as many fish species are increasingly threatened by extinction. The gut microbiota of only a small fraction of the more than 32,000 known fish species has been investigated. In this study we analysed the intestinal digesta microbiota composition of more than 50 different wild fish species from tropical waters. Our results show that the fish harbour intestinal digesta microbiota that are distinct from that of the surrounding water and that location, domestication status, and host intrinsic factors are strongly associated with the microbiota composition. Furthermore, we show that the vast majority (~97%) of the fish-associated microorganisms do not have any cultured representative. Considering the impact of the microbiota on host health and physiology, these findings underpin the call to also preserve the microbiota of host species, especially those that may be exposed to habitat destruction.

Scaling species interactions: implications for community ecology and biological scaling theory

Article

Full-text available

Nov 2023

Douglas S. Glazier

Background: Various biological properties of organisms relate to body size, often in regular quantifiable ways. Traditionally, these biological scaling relationships have been explained in terms of internal physical constraints, but recently external ecological factors have gained increasing attention. A major goal of my review is to expand a currently developing ecological perspective of biological scaling (allometry) to include species (biotic) interactions, with a major emphasis on predation, herbivory, and parasitism. Results: I review evidence for two major kinds of interspecific body-size scaling patterns: (1) negative relationships of predator species richness and body-size range with prey body size and (2) positive relationships of parasite/herbivore species richness and body-size range with host body size. I argue that these patterns can provide new insights into the structure/function of ecological communities (including latitudinal and trophic-level gradients in biotic interactions) and various biological scaling patterns at the organism, population, community, and ecosystem levels. I further argue that exploration of the body-size scaling of other kinds of biotic interactions (e.g., competition, mutualism, commensalism, and amensalism) would also be worthwhile. Conclusion: The major findings of this review provide further foundation for a “mortality theory of ecology” and a comprehensive theory of allometry that embraces both internal physical and external ecological factors, both currently under development. Body-size scaling of biotic interactions has not only important implications for the development of synthetic theory bridging community ecology and biological scaling, but also practical applications for understanding the effects of human exploitation and climate change on living systems.

Body size and trophic level increase with latitude, and decrease in the deep-sea and Antarctica, for marine fish species

Article

Full-text available

Sep 2023

The functional traits of species depend both on species’ evolutionary characteristics and their local environmental conditions and opportunities. The temperature-size rule (TSR), gill-oxygen limitation theory (GOLT), and temperature constraint hypothesis (TCH) have been proposed to explain the gradients of body size and trophic level of marine species. However, how functional traits vary both with latitude and depth have not been quantified at a global scale for any marine taxon. We compared the latitudinal gradients of trophic level and maximum body size of 5,619 marine fish from modelled species ranges, based on (1) three body size ranges, <30, 30–100, and >100 cm, and (2) four trophic levels, <2.20, 2.20–2.80, 2.81–3.70, >3.70. These were parsed into 5° latitudinal intervals in four depth zones: whole water column, 0–200, 201–1,000, and 1,001–6,000 m. We described the relationship between latitudinal gradients of functional traits and salinity, sea surface and near seabed temperatures, and dissolved oxygen. We found mean body sizes and mean trophic levels of marine fish were smaller and lower in the warmer latitudes, and larger and higher respectively in the high latitudes except for the Southern Ocean (Antarctica). Fish species with trophic levels ≤2.80 were dominant in warmer and absent in colder environments. We attribute these differences in body size and trophic level between polar regions to the greater environmental heterogeneity of the Arctic compared to Antarctica. We suggest that fish species’ mean maximum body size declined with depth because of decreased dissolved oxygen. These results support the TSR, GOLT and TCH hypotheses respectively. Thus, at the global scale, temperature and oxygen are primary factors affecting marine fishes’ biogeography and biological traits.

The gut microbiota of tropical marine fish is largely uncultured and distinct from surrounding water microbiota

Preprint

Full-text available

Mar 2023

Marine fishes along with their unique gut microbiotas are at threat of extinction. Studying the gut microbes of marine fishes is an important part of conservation. The gut microbiota of only a small fraction of the more than 32,000 known fish species has been investigated. In this study we analysed the gut microbiota composition of more than 50 different wild fish species from tropical waters. Our results show that the fish harbour gut microbiota that are distinct from that of the surrounding water and that location, domestication status, and host intrinsic factors strongly affect the microbiota composition. Furthermore, we show that the vast majority (~ 97%) of the fish-associated microorganisms do not have any cultured representative. Considering the impact of the microbiota on host health and physiology, these findings underpin the call to preserve the microbiota of host species, especially those that may be exposed to habitat destruction.

Geographical Variation in Body Size and the Bergmann’s Rule in Andrew’s Toad (Bufo andrewsi)

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Dec 2022

Simple Summary Understanding variations in the morphology and age of animals along a geographical gradient may aid in our comprehension of the evolution of these animals. In this view, we studied variation in the age and body size of Andrew’s toad (Bufo andrewsi) across 31 populations along a geographical gradient. The results revealed that along with a decrease in the annual mean temperature, the age structure increased, whereas body size did not indicate an increasing trend, showing no support for Bergmann’s rule. Precipitation seasonality negatively correlated with longevity and mean age, whereas precipitation of the driest month positively correlated with body size. Moreover, we also found that UV-B seasonality positively correlated with age structure traits and body size. The present study provided critical cues that explain the considerable variability observed in the ecogeographic patterns among Andrew’s toads. Abstract Environmental variation likely modifies the life-history traits of vertebrates. As ectothermic vertebrates, it is possible that the body size of amphibians is impacted by environmental conditions. Here, we firstly quantified age and body size variation in the Andrew’s toad (Bufo andrewsi) across the Hengduan Mountains. Then, we examined the environmental correlates of this variation based on the literature and our unpublished data on the age and body size of the Andrew’s toad from 31 populations distributed in southwestern China. Although our analysis revealed significant variations in age and body size across B. andrewsi populations, neither latitude nor altitude correlated with this variability in age and body size. We found that age at sexual maturity, mean age, and longevity increased with decreasing annual mean temperature, whereas age at sexual maturity increased with decreasing temperature seasonality, implying that temperature was a crucial habitat characteristic that modulated age structure traits. Moreover, we revealed positive associations between age structure and UV-B seasonality, and negative relationships between both mean age and longevity and precipitation seasonality. We also found that body size increased with increasing precipitation in the driest month and UV-B seasonality. However, body size did not covary with temperature, signifying no support for Bergmann’s rule. These findings help us to understand amphibians’ abilities to adapt to environmental variation, which is particularly important in order to provide a theorical basis for their conservation.

The Sizes, Growth and Reproduction of Arrow Worms (Chaetognatha) in Light of the Gill-Oxygen Limitation Theory (GOLT)

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Dec 2021

The Chaetognatha are a marine invertebrate phylum including 132 extant, carnivorous species in nine families and two orders, but with unclear protostomian affinities in the animal kingdom. We document the gradual recognition of the distinctiveness of chaetognaths by early taxonomists, with some emphasis on the often-overlooked studies by Chinese marine biologists. The carnivorous arrow worms are understudied relative to their importance in the marine zooplankton, where they rank second in abundance after the herbivorous copepods. Although arrow worms lack gills or other dedicated respiratory organs, we show that the Gill-Oxygen Limitation Theory (GOLT) can be used to explain how temperature and respiration affect their growth and related life-history traits. Notably, we present a reappraisal of evidence for size–temperature relationships between and within chaetognath species, and for the relationship between their temperature-mediated oxygen demand and their growth patterns. Von Bertalanffy weight growth curves of Ferosagitta hispida (family: Sagittidae) based on earlier aquarium experiments by various authors are presented, which suggest (a) a good fit and (b) that the life span of chaetognaths is much lower than suggested by the authors of several published growth curves drawn onto length–frequency samples from the wild. In addition, we show that chaetognaths attain first maturity at a fraction of the maximum length they can attain that is similar to the corresponding fraction in fishes. Overall, we suggest that the manner in which the oxygen they require enters the body of small marine invertebrates, although often neglected, is a crucial aspect of their biology. In addition, based on our result that arrow worms conform to the GOLT, we suggest that this theory may provide the theoretical framework for the study of growth in the other water-breathing ectotherms lacking gills.

Spatial patterns in the size of Chinese lizards are driven by multiple factors

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Jun 2021

For almost two centuries, ecologists have examined geographical patterns in the evolution of body size and the associated determinants. During that time, one of the most common patterns to have emerged is the increase in body size with increasing latitude (referred to as Bergmann's rule). Typically, this pattern is explained in terms of an evolutionary response that serves to minimize heat loss in colder climates, mostly in endotherms. In contrast, however, this rule rarely explains geographical patterns in the evolution of body size among ectotherms (e.g., reptiles). China. In this study, we assembled a dataset comprising the maximum sizes of 211 lizard species in China and examined the geographical patterns in body size evolution and its determinants. Specifically, we assessed the relationship between body size and climate among all lizard species and within four major groups at both assemblage and interspecific levels. Although we found that the body size of Chinese lizards was larger in warmer regions, we established that at the assemblage level, size was correlated with multiple climatic factors, and that body size–climate correlations differed within the four major groups. Phylogenetic analysis at the species level revealed that no single climatic factor was associated with body size, with the exception of agamids, for which size was found to be positively correlated with temperature. Geographical patterns in Chinese lizard body size are driven by multiple factors, and overall patterns are probably influenced by those of the major groups. We suggest that our analyses at two different levels may have contributed to the inconsistent results obtained in this study. Further studies investigating the effects of altitude and ecological factors are needed to gain a more comprehensive understanding of the evolution of ectotherm body size.

Impacts des changements globaux sur la distribution des poissons migrateurs amphihalins : Une approche par modélisation à l'échelle continentale

Thesis

Jan 2008

Gilles Lassalle

Les poissons migrateurs amphihalins évoluent dans un environnement qui est perturbé, à l'échelle globale, par le changement climatique et à l'échelle régionale, par les pressions anthropiques telles que les barrages et la pollution des cours d'eau. Cette étude, menée à l'échelle continentale, avait pour objectif d'évaluer, de comprendre et de prédire les impacts de changements globaux sur la distribution de ce groupe. Afin de répondre à cette problématique, des modèles empiriques de distribution ont été construits pour chacune des 28 espèces étudiées. Leurs distributions ont été décrites au début et à la fin du XXème siècle, en termes de présence-absence et de classes d'abondance. Les variables explicatives potentielles étaient de type physique, climatique, biotique et anthropique. Dans un premier temps, il a été mis en évidence que la répartition vers 1900 des poissons migrateurs amphihalins était fortement contrainte par leur histoire biogéographique et par les conditions thermiques et hydrauliques de l'habitat continental. La projection de ces distributions, à la fin du XXIème siècle, dans le contexte du changement climatique, a montré la forte sensibilité de ce groupe aux modifications du climat. Bien que spécifiques à chaque espèce, les réponses ont pu être classées en trois catégories : expansion de l'aire de répartition, contraction de l'aire de répartition et peu ou pas de changement. Dans un deuxième temps, pour la première fois à l'échelle continentale, l'importance des grands barrages et de la densité de populations humaines pour expliquer la distribution actuelle de ces espèces a été démontrée. Les relations sont apparues complexes et dépendantes des caractéristiques écologiques des espèces, notamment de la position de leurs habitats de croissance et de reproduction le long du réseau hydrographique et de leur place au sein du réseau trophique.

Do New World pitvipers “scale‐down” at high elevations? Macroecological patterns of scale characters and body size

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Jul 2019

Bergmann's rule describes the macroecological pattern of increasing body size in response to higher latitudes and elevations. This pattern is extensively documented in endothermic vertebrates, within and among species; however, studies involving ectotherms are less common and suggest no consistent pattern for amphibians and reptiles. Moreover, adaptive traits, such as epidermal features like scales, have not been widely examined in conjunction with Bergmann's rule, even though these traits affect physiological processes, such as thermoregulation, which are hypothesized as underlying mechanisms for the pattern. Here, we investigate how scale characters correlate with elevation among 122 New World pitviper species, representing 15 genera. We found a contra‐Bergmann's pattern, where body size is smaller at higher elevations. This pattern was mainly driven by the presence of small‐bodied clades at high elevations and large‐bodied clades at low elevations, emphasizing the importance of taxonomic scope in studying macroecological patterns. Within a subset of speciose clades, we found that only Crotalus demonstrated a significant negative relationship between body size and elevation, perhaps because of its wide elevational range. In addition, we found a positive correlation between scale counts and body size but no independent effect of elevation on scale numbers. Our study increases our knowledge of Bergmann's rule in reptiles by specifically examining characters of squamation and suggests a need to reexamine macroecological patterns for this group. New World Pitvipers show a contra‐Bergmann's pattern between elevation and body size.