Incubation temperature affects the development of calipash related traits and collagen deposition in embryos of soft-shelled turtle Pelodiscus sinensis

Abstract

Chinese soft-shelled turtle Pelodiscus sinensis possesses a distinctive soft and pliable apron around its dorsal carapace termed calipash, of which the formation and its relation to extracellular matrix remain largely unclear. Herein, we investigated calipash quality traits and collagen deposition of turtle embryos from eggs incubated at two different temperatures (26 °C and 32 °C) to evaluate the involvement of collagen in calipash development during embryogenesis. We found that the calipash related traits including embryo mass, embryo length and calipash mass showed an overall increasing tendency as embryos developed. The positive correlation between collagen content and the above morphologic traits in calipash was also found. Embryos incubated at 32 °C incubation temperature had significant bigger embryo size, heavier calipash and higher collagen content at most developmental stages as compared with those embryos incubated at 26 °C. Strong birefringence color was observed from the starting of developmental stage 23 and there were much more collagen fibers presented polarized orange or red colors from embryos incubating at 32 °C. The percentage of type I collagen areas in turtle calipash tissue was found to increase overall and with significantly higher value in embryos incubated at 32 °C. The observed promoted mRNA level of type I collagen gene of turtle eggs incubated at 32 °C in developmental stage 23 indicated that the biosynthesis of collagen in P. sinensis embryos might be induced. The present work indicated that 32 °C incubation temperature is conducive to more collagen deposition and related more preferable calipash traits during the embryonic development of P. sinensis. The data provided the possible manipulation of calipash trait development by incubation temperature changing. High incubation temperature is suggested when attempting to develop large calipash tissue in P. sinensis aquaculture.