Size of brain, heart, liver, alimentary tract, and kidneys along altitudinal gradients in Asiatic toad
Data files
Dec 06, 2024 version files 32.98 KB
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README.md
1.79 KB
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totalmassdata.csv
31.19 KB
Abstract
Brain size variation is frequently linked to energetic trade-offs with other metabolically demanding tissues or organs, a concept central to the expensive brain hypothesis (EBH). In this study, we investigate Asiatic toads (Bufo gargarizans) along altitudinal gradients, focusing on the trade-offs in size between the brain and four key visceral organs: the heart, liver, alimentary tract, and kidney. We estimated brain volume by measurement. We measured the dry weight of four organs: the heart, liver, alimentary tract, and kidneys. Additionally, we measured the snout-vent length and body weight of individuals. Our results indicate that both body size and scaled mass index—an indicator of total energy intake—decrease at higher altitudes, suggesting increased energetic constraints in high altitudinal environments. As altitude rises, we observe a reduction in relative brain size, while the relative sizes of visceral organs tend to increase. Through structural equation modeling, we identify a significant negative correlation between brain size and a latent variable termed "budget," which reflects energy allocation to the four visceral organs in high-altitude toads. Notably, the heart shows the most pronounced and consistent response to variations in energy distribution. In contrast, no such relationships are observed in toads at mid- and low-altitudes, where higher energy intake may enable individuals to bypass these trade-offs. When considering EBH in poikilothermic species, it is essential to emphasize total energy intake alongside energy allocation strategies. Future research on EBH should focus on intra-specific comparisons and explore the fitness implications that extend beyond mere energy constraints.
README: Size of brain, heart, liver, alimentary tract, and kidneys along altitudinal gradients in Asiatic toad
We have submitted our raw data (totalmassdata.csv), R script (totalmassdata.R).
Data File: totalmassdata.csv
ID: Identification of each specimen used in this project
transect: Sampling altitudinal gradient along the river valley, which consists of 4 to 6 sampling populations
site: Sampling population, which consists of individuals captured near the same breeding pond
sex: Determining the sex of individuals through nuptial pads, in which m represents male and f represents female
ALT: Sampling altitude of individuals (km)
ELE: Altitudinal group, which is determined by unpublished principle analysis results with bioclimate data of sampling location. L represents the low altitudinal group, M is the middle altitudinal group, and H is the high altitudinal group
bodymass: Individual’s body weight that was measured by an electronic balance accurate to 0.1 g
heart: Dry weight of heart (g)
liver: Dry weight of liver (g)
digest: Dry weight of alimentary tract (g)
kidney: Dry weight of paired kidneys (g)
SVL: Snout-vent-length which was measured by photo (mm)
BRA: Whole brain volume which was calculated from measured length, width, and height (mm3)
SMI: Scaled body-mass index, which was calculated according to an equation with body mass and SVL
In the file, the null padding indicates that the observation for this sample is unavailable due to anatomical damage or other reasons.
Code/Software: totalmassdata.R
R is required to run totalmassdata.R Script; the script was created using version 4.2.2.
Annotations are provided throughout the script through 1) library loading, 2) dataset loading and cleaning, 3) analyses, and 4) figure creation.
Methods
A total of 434 individuals from 15 sites of 3 transects were sampled from west of the Sichuan Basin in 2018 and 2019. All toads were sampled in the breeding season and were breeding adults. All transects were controlled within a straight-line distance of 85 km, which reduces confounding ecological background variables.
Snout vent length (SVL) was used for body size and was measured from photos that were taken from a dorsal view with a ruler as a reference. We measured SVL three times using ImageJ version 1.53g, and used the average value. The scaled mass index (SMI) was used to assess body condition and was calculated by an equation which was described in the related article.
Brains were dissected out; the cranial nerves, pineal organs, meninx, and pituitary glands (but not the pituitary infundibulum) were removed. Photographs of brains were taken from dorsal, side, and ventral views with a ruler as a reference. The coronal plane and sagittal plane were placed parallel to the camera sensor. The length, width, and height of the brain were measured to the nearest 0.001 mm from the photographs. All measurements were conducted three times by the same investigator (ZY) and the average value was used. The volume of each brain region was calculated using the ellipsoid model as V= (L×H×W) π/ (6×1.43).
To obtain the dry mass of the heart, liver, alimentary tract, and kidneys, we use the dissection method. The liver included the overall liver and excluded the gall bladder. The alimentary tract includes the stomach and small and large intestine. The contents in the alimentary tract were softly eliminated before drying. Kidneys included the pair, and the heart included the overall heart. These organs were then washed by tap water overnight, and dried in a baking oven (55 ℃) until their weights stabilized. All dried organs were weighted to the nearest 0.0001 g by an electronic balance (STP2004). Organs that were damaged during the dissection process were excluded.