Morphological indicators
BM, BL, TL, EL, EW, FL1 and HL1 of E. miletus in low latitude and high temperature regions were greater than those in high latitude and low temperature regions (Fig 1 and Fig 2). BM, BL, TL, EL, EW, FL1 and HL1 in E. miletus from the five regions were significantly different (BM: F=11.504, P=<0.001; BL: F=7.458, P<0.001; TL: F=15.550, P<0.001; EL: F=43.174, P<0.001; EW: F=10.112, P<0.001; FL1: F=10.097, P<0.001; HL1: F=9.940, P<0.001).
Growth factor contents
The contents of IGF1, bFGF, GRIF, PDGF, TCEA1, ADAM7, BCAT1 and EGF, HMG1 in the five regions were significantly different (IGF: F=8.237,P=0.007; bFGF: F=22.034, P<0.001; EGF: F=6.951, P=0.012; GRIF: F=10.495, P=0.003; PDGF: F=9.840, P=0.003; TCEA1: F=13.495,P=0.001; ADAM7: F=7.722, P=0.009; BCAT1: F=11.821, P=0.001; HMG1: F=7.372, P=0.010). The contents of IGF, bFGF, EGF, PDGF and TCEA1 in DL, JC and LJ were higher than those in XGLL and DQ. The contents of GRIF, ADAM7, BCAT1 and HMG1 also had differences and decrease with the increase of regional latitude (Fig 3).
Redundancy analysis
The samples of XGLL and DQ were gathered together, which showed that the species in the two regions have high similarity and the samples of DL, JC and LJ also overlap to some extent. The results of the Permutation test showed that IGF1, bFGF, EGF, GRIF, PDGF, TCEA1, ADAM7, BCAT1, HMG1 were significantly correlated with BM, BL, TL, EL, EW, FL1 and HL1 of the
E. miletus (P=0.019). It can be seen from the figure that there is a correlation between the growth factors and the morphological indicators of
E. miletus and there was also a positive correlation between the growth factors and BCAT1 and HMG1 were very significantly positive correlation (Fig 4).
Multiple linear regression analysis
BM, BL, FL1 and HL1 of
E. miletus were positively correlated with IGF1, bFGF, EGF, GRIF, PDGF, TCEA1, ADAM7, BCAT1, HMG1 and increase with the content of growth factors. Tail length has no significant correlation with EGF, TCEA1, ADAM7 and HMG1, but has positive correlation with IGF1, bFGF GRIF, PDGF and BCAT1; Ear length was not significantly correlated with ADAM17 and HMG1, but positively correlated with IGF1, bFGF, EGF, GRIF, PDGF, TCEA1 and BCAT1. Ear width was not significantly correlated with IGF1, EGF, PDGF and TCEA1, but positively correlated with bEGF, GRIF, ADAM7, BCAT1 and HMG1 (Fig 5-8).
Body size of animals is affected by many factors, thus affecting the adaptability of animals. In the current study, it was found that the morphological indicators of
E. miletus in five regions had differentiated, which showed significant differences. BM, BL, TL, EL, EW, FL1 and HL1 of E. miletus in DL, JC and LJ were greater than those in XGLL and DQ, which does not conform to Bergmann's law, which is consistent with our previous study
(Ren et al., 2020).
Growth factors and their receptors play a role in regulating cell proliferation or differentiation, thus affecting the growth of its tissues and organs
(Li et al., 2023). IGF1 can promote the activation, proliferation and differ-entiation of osteoblasts, enhance the function of osteoblasts
(Zhao et al., 2012), promote bone formation, in-crease bone mass and bone density
(Cabrera et al., 2017). Some research results showed that the up-regulation of IGF1 expression can promote bone growth, thereby improving the activity of growth plates and promote lon-gitudinal and radial bone growth
(Yan et al., 2016). In our study, significant differences of IGF1 content were found in
E. miletus from five regions. The content of IGF1 in DL, JC and LJ was higher than that of in XGLL and DQ. Previous study found that BM and BL of
E. miletus in the five regions of Hengduan Mountain were different and there was differentiation in the morphological indicators of the whole body skeleton
(Liao et al., 2023). It showed that IGF1 can promote the growth of the bone and cause the difference of body size
(Tabnak et al., 2023), which can regulate the growth and differentiation of cells and the formation of tissues and organs
(Shah et al., 2022; Ramakrishnan et al., 2023). In addition to participating in the regulation of bone development, bFGF is also a heavy growth factor that activates Wnt signaling pathway. Research has found that bFGF activates Wnt signaling pathway by increasing the expression of CATENIN-BETA, TCF1, TCF3 and LEF, Cell proliferation activity in Wnt/ß-Catenin signal pathway is enhanced after being activated
(Fu et al., 2022). In this study, bFGF content in DL, JC and LJ was higher than that in XGLL and DQ and may also be higher than that in XGLL and DQ in terms of the expression of Wnt pathway and cell proliferation activity. EGF can promote cell proliferation and accelerate the growth of epidermal cells by binding with its homologous receptors
(Zambarda et al., 2022). In our study, EGF has a positive correlation with the BM, BL, FL1 and HL1 of
E. miletus from five regions, indicating that EGF may cause differences in the content of epidermal tissue in
E. miletus. BCAT1 can catalyze the catabolism of branched chain amino acids (BCAAs)
(Francois et al., 2022), which is the key enzyme of amino acid metabolism and can promote the growth of muscle cells. PDGF is essential for the maturation of smooth muscle cells, fibroblasts, glial cells and other cells. It can promote the proliferation of myoblasts, induce angiogenesis and help skeletal muscle regeneration
(Liu et al., 2022). There were significant differences in PDGF and BCAT1 in the five regions, BM, BL, FL1 and HL1 increased with the increase of PDGF and BCAT1 content, which may have an impact on the muscle mass in
E. miletus. Body size is controlled by the number or the size of cells, which together control the size of organs
(Ren et al., 2014). TCEA1 can combine with RNA polymerase II to restore the activity of the sites blocked by transcription and continue transcription, improve the efficiency of transcription and promote cell differentiation. ADAM17 is an important member of the metalloproteinase family. It can activate or release the growth factors, growth factor receptors or extracellular functional areas of cytokines that bind to the cell mem-brane by cutting them, thus regulating a variety of biological behaviors of cells, such as proliferation, transfer,
etc. (
Li and Yang, 2021). HMG1 is a highly conserved progenitor protein, which plays a role in the interaction between protein and DNA
(Liu et al., 2009). In the current study, the contents of TCEA1 and ADAM17 in DL, JC and LJ were higher than those in XGLL and DQ. It is possible that the activities of cell differentiation and proliferation in these three regions are stronger than those in the latter two regions, while the contents of HMG in DL, JC and DQ were higher and the contents of LJ and XGLL were relatively small, corresponding to the large body mass of DL and JC and HMG1 promotes cell proliferation and affects body size. Although DQ has more HMG1, it may be caused by individual differences of wild animals. GRIF is an inhibitory hormone, which can inhibit the secretion of insulin and reduce the response of pancreatin and cholecystokinin
(Heo et al., 2022). Cholecystokinin (CCK) acts on the feeding central nerve to inhibit the production of appetite and promote satiety (
Pérez-Arana et al., 2023), the GRIF contents in DL, JC and LJ were higher than that in XGLL and DQ. It may be that the feeling of fullness of
E. miletus in these three regions were weaker than that in the latter two regions, which increases the food intake and affects the body size change.
According to the results of RDA analysis, bFGF had the greatest impact on the morphological indicators of
E. miletus. bFGF can not only promote the growth and development of bones, but also activate the Wnt signal pathway that regulates the body size of animals, which may be two important aspects of the impact on the size of
E. miletus. In the current study, 9 growth factors were positively correlated with BM, BL, FL1 and HL1 and there was also a correlation between the 9 growth factors, indicating that the 9 growth factors may not act alone, but together to affect the body size of the
E. miletus, further support for anti Bergman’s law.