Size-related Differences Research Articles

COMPARISON BETWEEN Trachypithecus auratus AND Trachypithecus cristatus BRAIN SIZE IN INDONESIA

Taxonomic studies on Trachypithecus species in Indonesia define that this genus separated into two species that are Trachypithecus auratus and Trachypithecus cristatus with Trachypithecus auratus auratus as a subspecies. To determine relative brain size differences between species of the genus Trachypithecus in Indonesia and to examine clinal variation, a study related to brain size and morphological characters that affect the brain size is carried out. This study analyzes the brain volume between both species and examines its relationship with morphometric measurement and variables such as sex, age, and specimen location. Brain volumes were calculated from braincase volumes using 0.5 mm silica gel as mini beads. This study reveals that there are significant differences in relative brain size inter-species, sex, age and interaction among variable. Overall, T. auratus have a bigger brain size than T. cristatus, and the brain size of males are larger than females. The older individual tends to have similar brain size with younger ones. The different relative brain size on age level influenced by GSL size. Allometric body size affects the size of the brain directly. Also, there is a clinal trend in relative brain size. Trachypithecus auratus brain size is increasing from West Java to Lombok island. Further study is needed to understand the influence of external factor such as ecological and social factors on brain size in Trachypithecus.

Using regression tree analysis to determine size class intervals and sexual dimorphism in the Morelet's crocodile Crocodylus moreletii

Assignment of Morelet's crocodile Crocodylus moreletii individuals into size groups or classes based on ecological and morphological similarities has not yet been associated with species‐specific ontogeny related changes. Age or size of first reproductive behavior is not precisely known for C. moreletii, but differences in allometric patterns and relative cranial size between juveniles and adults might be used as an indicator of sexual maturity. In this study, a regression tree analysis was used to investigate the relationship between age and body size in 1266 crocodiles by using both simple and generalized linear models, with gender and origin (captivity or wild) as factors. Total length (TL), snout–vent length (SVL) and cranial length (CL) were used as predictor variables and the logarithm of body mass as the response variable. Four length intervals with well‐defined thresholds (514, 899 and 1497 mm of TL) were established using all three predictors (TL, SVL and CL). Relationship between SVL and TL was described, and a strong positive relationship (r2 = 0.98), unaffected by crocodile gender, was observed. The observed CL–TL and CL–SVL relationships were also positive but significantly different between males and females (p < 0.001) and length interval classes (p = 0.01). These results suggest that our estimated size thresholds seem to correspond to important ontogenetic changes in C. moreletii and that sexual maturity is closely related to size in this species, where sexual dimorphism in body length occurs, particularly in large individuals (size group IV).

Upeneus floros, a new goatfish from South Africa and Mozambique, with updated taxonomic accounts for U. guttatus and U. pori and a key to Western Indian Ocean Upeneus species (Mullidae).

The highly diverse goatfish genus Upeneus (Mullidae) requires enhanced attention regarding the possible occurrence of undescribed species in insufficiently explored regions. This study focuses on the South-Western Indian Ocean region (SWIO), and on the so-called japonicus-group, a taxonomic species group of Upeneus. Based on in-situ observations and collections in Sodwana Bay, KwaZulu-Natal, South Africa, the Floros goatfish, U. floros n. sp., is described. Detailed comparative studies of colour patterns and morphological characters of all other 13 japonicus-group species were undertaken as well as COI barcoding. The new species occurs in the coastal area between Angoche, N Mozambique and KwaZulu-Natal and partly overlaps in distribution with two similar species, U. guttatus, widely distributed in the Indo-W Pacific, and U. saiab, assumed to be endemic in a small area off Angoche. Two additional japonicus-group species occurring in the SWIO, U. seychellensis from the Seychelles Bank and U. pori from the Mediterranean Sea (as Lessepsian migrant), Northern Red Sea and Madagascar, were also compared. Because specimens as well as in-situ photographs of U. floros have been erroneously identified as either U. guttatus or U. pori during previous studies, updated taxonomic accounts and diagnoses are provided for these species taking size-related and population differences into account. For U. pori, of which a single preserved specimen from SW Madagascar was known so far, a new record from NE Madagascar is reported based on three specimens and a fresh-colour photo. Upeneus floros can be distinguished from U. guttatus and U. pori by a combination of three characters: head length, first dorsal-fin height and number of gill rakers. Upeneus guttatus can be distinguished from the other two species by disproportionally higher anterior dorsal-fin spines vs. a proportional decrease of dorsal-fin spines in height, barbels mostly yellow vs. white or creamy-white, and slightly fewer pectoral-fin rays. COI barcoding detected a clear distinction between U. guttatus and U. floros and U. pori, respectively, but no significant divergence between the two latter species. COI barcoding also failed to differentiate several other Upeneus species which are clearly distinguished morphologically. Possible interrelationships between species distribution patterns and physical oceanography are discussed. An identification key for the 22 WIO Upeneus species is provided.

Relative Cerebellum Size Is Not Sexually Dimorphic across Primates

Background/Aims: Substantive sex differences in behavior and cognition are found in humans and other primates. However, potential sex differences in primate neuroanatomy remain largely unexplored. Here, we investigate sex differences in the relative size of the cerebellum, a region that has played a major role in primate brain evolution and that has been associated with cognitive abilities that may be subject to sexual selection in primates. Methods: We compiled individual volumetric and sex data from published data sources and used MCMC generalized linear mixed models to test for sex effects in relative cerebellar volume while controlling for phylogenetic relationships between species. Given that the cerebellum is a functionally heterogeneous structure involved in multiple complex cognitive processes that may be under selection in males or females within certain species, and that sexual selection pressures vary so greatly across primate species, we predicted there would be no sex difference in the relative size of the cerebellum across primates. Results: Our results support our prediction, suggesting there is no consistent sex difference in relative cerebellum size. Conclusion: This work suggests that the potential for sex differences in relative cerebellum size has been subject to either developmental constraint or lack of consistent selection pressures, and highlights the need for more individual-level primate neuroanatomical data to facilitate intra- and inter-specific study of brain sexual dimorphism.

Males of a sexually cannibalistic spider chemically assess relative female quality

BackgroundMate choice is a taxonomically wide-spread phenomenon, mostly exerted by females although male mate choice occurs as well. While costs and benefits of choosiness have been well studied, the underlying mechanisms are largely unclear. Different models exist, namely best-of-n or threshold rules, based on sequential or simultaneous sampling, which differ in the required cognitive demands. We applied an experimental approach to shed light on the underlying mechanisms of male mate choice in the sexually cannibalistic spider Argiope bruennichi. Males are limited to two copulations and preferentially monopolise large females, while they may leave smaller females after a single copulation and resume mate search. Here, we utilised significant size-differences between females from Northern and Southern populations and presented males with three different-sized females that were matched for origin: all three females originated either from the same Northern European population as the males or from Southern populations where the smallest female was about the same size as the largest Northern female. This allowed testing the hypothesis that males base their mating tactic on a fixed local size threshold. We predicted Northern males to be choosy among Northern females, but to accept all Southern females since they would all be above that threshold.ResultsMales copulated with the first female they encountered, which was independent of her body size. Regardless of the females’ origins, males chose a monogynous tactic with the largest female in the trio, while they left the smallest female after one copulation. The same pattern applied to Southern females even though the smallest females in the trio were of a similar size as monopolised Northern females. Since males have poor eyesight and did not actively sample all females, they likely have gained information about relative size differences between females based on volatile chemical cues only.ConclusionsOur findings suggest that male A. bruennichi can assess relative differences in mate quality and adjust their mating tactic to the prevailing conditions (Northern vs. Southern). We reject the presence of a locally-adapted fixed threshold and argue that our results are best explained by an adjustable threshold that was raised under Southern conditions.

Reference values and sex differences in absolute and relative kidney size. A Swiss autopsy study

BackgroundMen have larger kidneys than women, but it is unclear whether gender remains an independent predictor of kidney size (expressed as weight or length) after correction for body size. We analysed autopsy data to assess whether relative renal length and weight (e.g. corrected for body weight, height or body surface area (BSA)) are also larger in men. Assuming that kidney size is associated with nephron number, opposite findings could partly explain why women are less prone to the development and progression of chronic kidney disease than men.MethodsAll forensic autopsies performed between 2009 and 2015 at the local university hospital of Geneva in individuals of European descent aged ≥18 years without a known history of diabetes and/or kidney disease were examined. Individuals with putrefied or severely injured bodies were excluded. Relative renal weight and length were respectively defined as renal weight divided by body weight or BSA and renal length divided by body height or BSA.ResultsA total of 635 autopsies (68.7% men) were included in the analysis. Left kidneys were on average 8 g heavier and 2 mm longer than right kidneys (both: p < 0.05). Absolute renal weight (165 ± 40 vs 122 ± 29 g) and length (12.0 ± 1.3 vs 11.4 ± 1.1 cm) were higher in men. Relative renal weight was also higher in men, but relative renal length was larger in women. In multivariable regression analysis, body height, body weight, the degree of blood congestion or depletion at autopsy and age were determinants of renal weight, whereas arterial hypertension and smoking were not. Percentile curves of renal weight and length according to sex and body height were constructed.ConclusionAbsolute and relative renal weights were both smaller in women. This is in line with recent studies stating that nephron numbers are also lower in women. Relative renal length was longer in women, suggesting that female kidneys have a more elongated shape. In comparison with older autopsy studies, renal weight appears to be stable over time.

Regionalism With and Without Metropolitanism: Governance Structures of Rural and Non-Rural Regional Intergovernmental Organizations

While prior scholarship has investigated many tools for regional governance across the rural-to-urban spectrum, the literature on regional organizations (councils of governments, planning district commissions, etc.) has been dominated by metropolitan regions. As a result, we know very little about the plethora of these regional organizations serving rural local governments. The omission of rural regions as a control variable from this conversation limits our ability to determine what traits are truly intergovernmental across this spectrum and what traits are specific to metropolitan and rural regions. Using a new, nationwide database of Regional Intergovernmental Organizations (RIGOs) and original governance documents, I present two unexpected empirical similarities between rural and non-rural RIGOs. First, I demonstrate that the quantity and relative dominance of the local governments within the territorial footprint of rural and non-rural RIGOs are nearly identical when population is held constant. Given the smaller populations within most rural RIGOs, this finding raises serious questions about how limited capacity is diffused and the need for multijurisdictional collaboration in rural areas. Second, I demonstrate that rural and non-rural RIGOs do not substantially differ in the way representational rights are apportioned to local governments on RIGO governing boards. Both rural and non-rural RIGOs similarly balance institutional membership with population proportionality in these collective choice arrangements. This evidence supports a broader intergovernmental hypothesis that an individual local government’s representational rights on a RIGO board are more likely to result from relative size differences among members than facets specific to a city–suburb dynamic.

Green purchasing frameworks considering firm size: a multicollinearity analysis using variance inflation factor

ABSTRACT Significant differences exist among companies in terms of their green purchasing practices. One of the explanatory factors for the former is company size. This article examines how to capture related differences in purchasing goals, corporate environment systems, purchasing and supply management tools, and motivation. The investigation of such complex issues usually requires the measurement and examination of a large number of variables. A rarely used analytical tool for doing this is the variance of inflation factor (VIF), which helps by filtering out multicollinearity. In this study, size-related differences were identified in terms of management systems, supplier management practices, and motivational background. However, there is uncertainty concerning the routine application of the method in relation to the determination of the appropriate threshold value.

Species specificity and sexual dimorphism in tooth shape among the three sympatric haplochromine species in Lake Kivu cichlids.

Tooth shape is used to differentiate between morphologically similar species of vertebrates, including fish. This study aimed to quantify tooth shape of three sympatric species: Haplochromis kamiranzovu, H. insidiae, and H. astatodon endemic to Lake Kivu, whose existing identification criteria are currently only qualitative. A quantitative tooth shape analysis was performed based on digitized tooth outline data with a subsequent elliptic Fourier analysis to test for differences among the three species. We looked at crown shape and size differences within H. kamiranzovu and H. insidiae at geographical, habitat, and gender levels. No comparison at habitat level was done for H. astatodon because it is found only in littoral zone. The analysis revealed significant tooth shape differences among the three species. Haplochromis astatodon had a significantly longer major cusp height and a longer and larger minor cusp than that of H. insidiae. It had also a longer major cusp height and a longer and larger minor cusp than that of H. kamiranzovu. Tooth shape differences of H. kamiranzovu and H. insidiae species were not significantly different between littoral and pelagic fish (p > .05) while differences were significant between southern and northern Lake Kivu populations (p < .05). Tooth sizes in H. kamiranzovu and H. insidiae were significantly different, both in height and width as well as in their ratios, and this was true at sex and geographic levels (p < .05), but not at habitat level (p > .05). Tooth shape was also significantly different with sharp teeth for males compared with females of southern populations versus northern ones. These shape‐ and size‐related differences between sexes suggest differences in the foraging strategies toward available food resources in the lake habitat. Further research should explain the genetic basis of the observed pattern.

Importance of suspended particulate organic matter in the diet of Nephrops norvegicus (Linnaeus, 1758)

The extent to which commercially important Nephrops norvegicus lobsters feed on particulates in the wild is unknown, even though this could be an important way for burrow-dwelling females to avoid starvation during the long breeding season. This was investigated using δ13C and δ15N isotopic signatures in tissues with long and short turnover rates to provide diet discrimination and compare this between males and females. Secondary objectives examined size-related differences and calculated the trophic position based on the new results. Almost half the diet (47%) was made up of suspended particulate organic matter (POMsusp) alone. Fish was another important item in the diet, with plankton and invertebrate sources coming much lower down in dietary importance. Significantly more suspension feeding was observed in small or medium sized individuals than large ones in both sexes. However, there were no sex-related patterns, despite females being restricted to burrows for part of the analysis period. Female diet was almost identical to males and POMsusp comprised a large component of the diet in both sexes. The trophic position was estimated at 2.94 ± 0.16 (mean ± SD), which was at the lower end of the range reported in previous studies (2.60 to 4.32).

Magnetic resonance imaging reveals specific anatomical changes in the brain of Agat- and Gamt-mice attributed to creatine depletion and guanidinoacetate alteration.

Arginine:glycine amidinotransferase- and guanidinoacetate methyltransferase deficiency are severe neurodevelopmental disorders. It is not known whether mouse models of disease express a neuroanatomical phenotype. High-resolution magnetic resonance imaging (MRI) with advanced image analysis was performed in perfused, fixed mouse brains encapsulated with the skull from male, 10-12 week old Agat -exc and B6J.Cg-Gamt tm1Isb mice (n = 48; n = 8 per genotype, strain). T2-weighted MRI scans were nonlinearly aligned to a 3D atlas of the mouse brain with 62 structures identified. Local differences in brain shape related to genotype were assessed by analysis of deformation fields. Creatine (Cr) and guanidinoacetate (GAA) were measured with high-performance liquid chromatography (HPLC) in brain homogenates (n = 24; n = 4 per genotype, strain) after whole-body perfusion. Cr was decreased in the brain of Agat- and Gamt mutant mice. GAA was decreased in Agat-/- and increased in Gamt-/- . Body weight and brain volume were lower in Agat-/- than in Gamt-/- . The analysis of entire brain structures revealed corpus callosum, internal capsule, fimbria and hypothalamus being different between the genotypes in both strains. Eighteen and fourteen significant peaks (local areas of difference in relative size) were found in Agat- and Gamt mutants, respectively. Comparing Agat-/- with Gamt-/- , we found changes in three brain regions, lateral septum, amygdala, and medulla. Intra-strain differences in four brain structures can be associated with Cr deficiency, while the inter-strain differences in three brain structures of the mutant mice may relate to GAA. Correlating these neuroanatomical findings with gene expression data implies the role of Cr metabolism in the developing brain and the importance of early intervention in patients with Cr deficiency syndromes.

Testing four hypotheses to explain partial migration: balancing reproductive benefits with limits to fasting endurance

Seasonal migration is ubiquitous in animals, and yet its underlying cause(s) remain poorly known. Species exhibiting short-distance altitudinal migration and intraspecific variation in migratory behavior (partial or differential migration) are ideal study systems for examining the selective pressures that affect individual migratory decisions. We used an individually marked population of yellow-eyed juncos, breeding along a 1000-m elevational gradient and migrating up and down that gradient, to examine the morphological, behavioral, and reproductive traits associated with migratory behavior. We tested the four most well-known hypotheses proposed to explain partial migration: the thermal tolerance, fasting endurance, dominance, and arrival time hypotheses. Our results indicate that: (1) limits to juncos’ fasting endurance constrain their ability to overwinter at high elevations, in support of the fasting endurance hypothesis, (2) differences in body size mediate fasting ability and are associated with variation in migratory behavior and overwinter apparent survival, (3) migratory behavior interacts with reproductive success, in partial support of the arrival time hypothesis, and (4) additional mechanisms that are not captured by the four well-known hypotheses might better explain individual variation in migratory behavior. Less migratory females achieved greater nesting success the following breeding season. Among males, nesting success influenced migratory tendency the following winter. Successful males may either migrate to a more benign winter climate without paying reproductive costs, or high levels of parental effort might physiologically constrain their ability to overwinter in harsh climates. Migration is a costly behavior, so migration must yield fitness benefits, at least for some individuals. Species in which migratory behavior varies among individuals in the same population provide an under-utilized opportunity to understand the costs and benefits that mediate individual migratory decisions. By marking and tracking a population of yellow-eyed juncos, we found that larger individuals were less likely to migrate, and this held true even within a sex class (males). Smaller individuals were not only more likely to migrate but also had lower apparent survival, and these differences were driven by size-related differences in fasting ability. Less migratory females accrued reproductive benefits, but males with the highest reproductive success were not less likely to migrate as predicted by the arrival time hypothesis. Our study demonstrates that migratory decisions balance the potential reproductive benefits and survival risks of overwintering on high-elevation breeding grounds.

A survey of biosecurity measures and serological status for bovine viral diarrhoea virus and bovine herpesvirus 1 on dairy cattle farms in north-west and north-east Spain

BackgroundBiosecurity is a key measure to reduce and prevent the introduction of diseases to farms and minimise spread of diseases within a herd. The aim of the study was to...

Sexual dimorphism in Belostoma angustum Lauck (Insecta: Heteroptera: Belostomatidae) may be related to paternal care

Abstract The structures involved in parental care are often dimorphic. Female Belostoma angustum water bugs lay eggs on the hemelytra of their mates, where the eggs are brooded until hatching. Males use their hind legs to carry, aerate and protect the eggs. After controlling for covariance between variables, we fitted a series of structural equation models (SEMs) and evaluated the existence of sexual dimorphism in the size of the body and hind legs, in the shape and centroid size of the hemelytrum, and among the static allometry slopes of the size-related differences. Landmarks were used to capture phenotypic variation, by eliminating all non-shape variations with a Procrustes superimposition. Neither the shape of the hemelytrum nor its centroid size was related significantly to the aforementioned linear body measurements. Instead, the differences in the size of the hind legs were mediated by body dimensions only in males. We also found that males were wider and had longer heads than females, according to the SEM intercept values. Our findings suggest that sexual dimorphism in B. angustum may be related to a balance between sexual role reversal and viability costs.

Environmental Innovation and Firm Profitability – An Analysis with Respect to Firm Size

This paper investigates the effect of environmental innovations on firm profitability with respect to differences between small and medium-sized (SME) and large (LE) enterprises. Using data from the Mannheim Innovation Panel (MIP) 2015, results show that, in general, SME benefit more from environmental innovations than LE. This effect is particularly strong for resource efficiency-improving innovations induced by regulation. These environmental innovations are significantly related to an increase in profits of SME, whilst related to a decrease in profits of LE. A robustness check with data from the MIP 2009, however, does not confirm this result as the effect for LE is insignificant and differences between the two groups cannot be found in this survey wave. A reason why negative effects for LE are observed in the MIP 2015 - but not in the MIP 2009 - might be that most LE had already exploited the potentials of environmental innovations when they were surveyed in the MIP 2015. This is supported by evidence suggesting that size-related differences in the MIP 2015 are driven by a negative relationship between LE’s profits and environmental innovations related to externalities that were reduced by innovations in periods before.

Effect of Phosphorus on the Phase Stability of a High Refractory Content Powder-Processed Ni‐Base Superalloy

The effect of P on the phase stability of a high refractory content powder-processed Ni-base superalloy was systematically studied with a variation of P addition. The microstructural evolution of nominally identical alloys with three levels of P additions (0.013, 0.026, and 0.041 wt pct) were investigated in the as-solutioned state and after thermal exposures at 800 °C for up to 1000 hours. Additions of P were found to segregate strongly at grain boundaries and depress the incipient melting temperature. The presence of P contributed to the formation of a C14 Laves as resolidification of incipiently melted liquid occurred. P additions also affected the solid-state phase stability of the alloys as aging at 800 °C led to the formation of C36 Laves phase precipitates. An increase in the fraction of C36 Laves phase correlated directly to the increases in the P content of the alloy. The extensive precipitation of C36 Laves phase eventually led to the formation of a basket-weave structure composed of an intertwined mixture of C14 Laves and sigma phase during the long-term thermal exposure at 800 °C. The stabilization of the Laves phase structure due to the minor additions of P was found to be consistent with density functional theory calculations and could be rationalized through structure maps that relate the valence electron concentration and relative size differences.

Species- and size-related differences in dopamine-like immunoreactive clusters in the brain of Nasonia vitripennis and N. giraulti

An extreme reduction in body size has been shown to negatively impact the memory retention level of the parasitic wasp Nasonia vitripennis. In addition, N. vitripennis and Nasonia giraulti, closely related parasitic wasps, differ markedly in the number of conditioning trials required to form long-term memory. These differences in memory dynamics may be associated with differences in the dopaminergic neurons in the Nasonia brains. Here, we used dopamine immunoreactivity to identify and count the number of cell bodies in dopaminergic clusters of normal- and small-sized N. vitripennis and normal-sized N. giraulti. We counted in total a maximum of approximately 160 dopaminergic neurons per brain. These neurons were present in 9 identifiable clusters (D1a, D1b, D2, D3, D4a, D4b, D5, D6 and D7). Our analysis revealed that N. giraulti had fewer cells in the D2 and D4a clusters but more in D4b, compared with normal-sized N. vitripennis. In addition, we found fewer cells in the D5 and D7 cluster of small-sized N. vitripennis compared to normal-sized N. vitripennis. A comparison of our findings with the literature on dopaminergic clusters in the fruit fly Drosophila melanogaster and the honey bee Apis mellifera indicates that clusters D2, D3 and D5 may play a role in memory formation in Nasonia wasps. The results from both the species comparison and the size comparison are therefore of high interest and importance for our understanding of the complex intricacies that underlie the memory dynamics of insects.

The Inhibitory Cascade Model is Not a Good Predictor of Molar Size Covariation

The inhibitory cascade (IC) model is a widely used evolutionary developmental explanation of among-species differences in relative molar tooth size. The IC model posits that, as molars develop from front to back, the relative strength of activating and inhibiting influences establishes a “ratcheting” mechanism leading to predictable relative molar sizes. Such a constraint on molar covariation would lead to strong variational biases on the evolutionary paths that the molar row can traverse through phenotypic space. These constraints manifest themselves in characteristic patterns of variation among species that loosely match observed macroevolutionary patterns. In this paper, we write out the predictions of the IC model for within-species covariation in molar size in a framework that unifies evolutionary developmental biological and quantitative genetic perspectives on the evolution of complex traits. We then evaluate these predictions about aspects of molar covariation in eight anthropoid primate species. We find that the IC model tends to over-predict aspects of within-species covariation by substantial margins. Only macaques exhibit covariation in and among individual teeth consistent with the IC model, but they do not show signs of the strong evolutionary constraint predicted by the model. Gorillas meet none of the predictions. While we cannot rule out an IC-like process as a contributor, causes of molar size covariation other than those described in the IC model must be major contributors to covariation in molar teeth within populations.

Large brains, short life: selection on brain size impacts intrinsic lifespan

The relationship between brain size and ageing is a paradox. The cognitive benefits of large brains should protect from extrinsic mortality and thus indirectly select for slower ageing. However, the substantial energetic cost of neural tissue may also impact the energetic budget of large-brained organisms, causing less investment in somatic maintenance and thereby faster ageing. While the positive association between brain size and survival in the wild is well established, no studies exist on the direct effects of brain size on ageing. Here we test how brain size influences intrinsic ageing in guppy (Poecilia reticulata) brain size selection lines with 12% difference in relative brain size. Measuring survival under benign conditions, we find that large-brained animals live 22% shorter than small-brained animals and the effect is similar in both males and females. Our results suggest a trade-off between investment into brain size and somatic maintenance. This implies that the link between brain size and ageing is contingent on the mechanism of mortality, and selection for positive correlations between brain size and ageing should occur mainly under cognition-driven survival benefits from increased brain size. We show that accelerated ageing can be a cost of evolving a larger brain.

Influence of body size, topography, food availability and tree-fall gaps on space use by yellow-footed tortoises (Chelonoidis denticulatus) in Central Amazonia.

Habitat selection and extension of the area used by a given species may vary during different phases of its life and are often determined by the distribution and availability of resources throughout the landscape, such as food, breeding sites, and shelters. In this study, we assessed the influence of body size on the areas used by 21 individuals of the yellow-footed tortoises (Chelonoidis denticulatus) from January to June 2017 in a dense rain forest area in Central Amazonia. We also investigated whether individuals selected different ranges of terrain slope, elevation, areas with high food availability, or areas with treefall gaps that could be used for shelter or thermoregulation. We monitored tortoise movements using thread-bobbins, and sampled terrain characteristics, availability of potential food resources and forest gaps along the routes used by the tortoises. We also measured the same variables in plots distributed systematically throughout the study area to evaluate resource availability. Tortoises used an average area of 1.56 ha (SD = 1.51, min = 0.03, max = 6.44). The size of the area used was positively associated with the individual body size, but did not vary between sexes. Small individuals selected higher and flatter areas where the availability of fallen flowers was higher, whereas the area used by larger individuals did not differ from the natural availability of topographic traits and food in the region. Although tortoises did not select areas according to availability of tree-fall gaps, most larger tortoises were found sheltered under fallen trees (85%). Conversely, small individuals were mainly found hidden under litter (66%). Body size determined the patterns of landscape use by tortoises; larger individuals were mainly generalists, but small individuals occupied high and flat areas. The yellow-footed tortoise is endangered by hunting, illegal collection for the pet trade, habitat destruction and effects of climate change. Size-related differences in habitat selection should be taken into account in species-distribution models for the identification of suitable areas for reintroduction and the development of management plans in protected areas.