Trade-offs between brain and digestive tissues across elevations inTyphlomys daloushanensis : evidence for sexual dimorphism
Abstract
To cope with highly stochastic and/or heterogeneous environmental conditions, animals must balance energy resource allocation across physiological processes. The digestive tract and brain exhibit structural variations under strong developmental and selective pressures that vary across environmental gradients both between and within species. Here, we measured body mass, body length, digestive tract segments lengths (stomach, cecum, small intestine, large intestine), brain weight, and relative brain size (scale mass index, SMI residuals) for 67 Chinese pygmy dormice (Typhlomys daloushanensis, 29 females and 38 males), an ancient, small, arboreal rodent species with echolocation abilities, captured at 37 sites between 414 and 1757 m. From Standardized Major Axis (SMA) regressions, we found no significant relationship between body size (SMI) and elevation. Notably, neither digestive tract segment lengths and their residuals nor brain weight (absolute and residual) correlated significantly with elevation in either sex, and slopes did not differ between males and females, providing no support for the Digestive Tract Theory (DTT) or the Cognitive Buffer Hypothesis (CBH). However, brain–digestive tract relationships exhibited sex-specific differences, partially supporting the Expensive Tissue Hypothesis (ETH), suggesting that energy allocation to high-cost organs is sex-dependent. Males maintained relatively heavier brain weight under comparable digestive tract lengths, likely to meet cognitive demands associated with mate competition, territorial defense, and exploratory behavior, whereas females tended to prioritize digestive tract investment to meet the energetic demands of gestation and lactation. Thus, classical predictions of body size–environment relationships may be overridden by sex-specific physiological trade-offs in specialized species, providing new insights into how small mammals may adapt to rapid environmental change.
Dataset DOI: 10.5061/dryad.cc2fqz6kp
Description of the data and file structure
The "data.xlsx" comprises measurements of physiological and morphological characteristics of Typhlomys daloushanensis. The dataset includes 67 samples, with 29 females and 38 males. The primary objective of this dataset is to investigate the impact of environmental gradients on the physiological traits of animals, particularly the structural variations in the brain and digestive organs.
The accompanying R script performs comprehensive data analysis on this dataset. It includes data cleaning, transformation (logarithmic transformation and residual calculation), and statistical modeling using Standardized Major Axis (SMA) regression to explore relationships between body traits and elevation. The script also generates visualizations to illustrate these relationships and their differences between sexes. The analysis aims to provide insights into how environmental gradients influence the physiological traits of Typhlomys daloushanensis.
Files and variables
File: data.xlsx
Description: This dataset comprises measurements of the physiological and morphological characteristics of Typhlomys daloushanensis. The dataset includes 67 samples, with 29 females and 38 males. Data were collected from 37 sites across different elevations, ranging from 414 to 1757 meters.The primary objective of this dataset is to investigate the impact of environmental gradients on the physiological traits of animals, particularly the structural variations in the brain and digestive organs.
Variables
- mouse_number: The unique identification number for each mouse, used to distinguish different samples.
- Weight: The weight of the mouse, measured in grams (g). This is an important indicator of the mouse's body size.
- SVL: Measured in centimeters (cm). SVL is a commonly used indicator of the mouse's body length and is often employed in ecological and morphological studies.
- Total_Intestine_Length: The length of the total intestine, measured in centimeters (cm)
- Stomach_Length: The length of the stomach, measured in centimeters (cm).
- Small_intestine_Length: The length of the small intestine, measured in centimeters (cm). As an important part of the digestive system, the length of the small intestine can reflect the mouse's digestive and absorption capabilities.
- Caecum_Length: The length of the cecum, measured in centimeters (cm).
- Large_intestine_Length: The length of the large intestine, measured in centimeters (cm).
- elevation: The elevation of the sampling site, measured in meters (m). Elevation is an important variable for studying the impact of environmental gradients on the physiological characteristics of animals.
- sex: The sex of the mouse, categorized as "Male" or "Female." Sex is an important variable for studying the impact of gender differences on physiological characteristics.
- brain_fresh: The fresh weight of the brain, measured in grams (g). This direct indicator of the mouse's brain size helps to study the relationship between the brain and other body organs.
- SMI: The Scale Mass Index (SMI) is a standardized indicator used to adjust the relationship between brain weight and body weight, thereby more accurately reflecting the relative size of the brain.
File: code.R
Description: This R script performs comprehensive data analysis on physiological and morphological measurements of Typhlomys daloushanensis, including data cleaning, transformation, and statistical modeling using SMA (Standardized Major Axis) regression to explore relationships between body traits and elevation. The script also generates visualizations to illustrate these relationships and their differences between sexes.