Effects Of Food Diversity On The Relationship Between Brain And Intestine During The Ontogenetic Process Of Anuran Species

As a central system of study,memory,cognition and information processing,the organisms’ brains are with great importance and the adaptive evolution of brains is one of the core topics in evolutionary biology.It is well known that organs which consume a high amount of energy,such as the digestive tract,are important driving forces for the evolution of the brain as well as the brain is a kind of organ with high energy consumption.The Cognitive Buffer Hypothesis(CBH)states that relatively large brain can enhance the cognitive abilities to select high quality food and hence improve the digestion and absorption to gain more abilities.And It is noteworthy that better food can decrease the intestinal length via enhancing the rate of digestion.Exploring the evolutional trade-off between intestinal length and brains and addressing whether food diversity influence the evolutional trade-off can be helpful to better understand the driving mechanisms of brain evolution.In the present study,a total of 12 anuran species collected from Hengduan Mountains and Sichuan Basin were used to assess food diversity via food composition identify,and we dissected and measured the brain size and intestinal lengths.Subsequently,we aim to reveal the influences of food diversity on the intestinal length and the trade-off between brain size and the intestinal length for these species.We investigated the changes of the trade-off relationships between brain size and the intestinal length and influences of food diversity on the trade-off between brain size and the intestinal length during different individual development stages.The main results and conclusions are summarized as below:1.All individuals were dissected and intestinal lengths were measured,and the result of one-way analysis of variance revealed that there was a significant difference in the intestinal length among all species(F = 165.818,P < 0.001).We identified the food compositions in stomachs and the insects around the habitat of each individual,and then evaluated the food diversity.We found a significantly positive correlation between food diversity and the intestinal length(F = 69.159,P < 0.001)by the linear regression analysis,according with the digestion theory which implied the decreasing intestinal length with the increasing food quality.When it comes to a single species,the same relationship just was found in two species,Bufo minshanicus(F = 4.338,P = 0.043)and Odorrana grahami(F = 5.129,P = 0.029).2.There are five brain structures in the brains of amphibians,respectively Olfactory nerves,Olfactory bulbs,Telencephalon,Optic tectum and Cerebellum.The brains were integrally removed and the five structures as well as the whole brain were respectively measured.We found that there were significant differences among 12 species in the five brain structures and in the whole brain volume: Olfactory nerves(F = 125.718,P < 0.001),Olfactory bulbs(F = 68.008,P < 0.001),Telencephalon(F = 137.716,P < 0.001),Optic tectum(F = 144.320,P < 0.001),Cerebellum(F = 132.417,P < 0.001)and the whole brain(F = 117.757,P < 0.001).When controlling the influences of the phylogenetic relationships and body size,the results of the phylogenetically controlled generalized least-squared analysis(PGLS)documented that there were significantly negative correlation between the intestinal length and Olfactory nerves volume(t =-3.347,P = 0.009),Optic tectum volume(t =-3.096,P = 0.013),Cerebellum volume(t =-2.509,P = 0.033).3.In the study,we used the skeletochronological method to estimate the age of 499 individuals covering 12 species.Age ranged from zone to six years,and the difference in ages among all species was significant(F= 19.789,P <0.001).When three individuals being six years were ignored,the other individuals were used in subsequent analyses.We measured the mean values of the size of five brain structures volume and the whole brain volume,body size,and the intestinal length for each species.We implemented PGLS and ultimately found increasing Olfactory nerves volume and decreasing intestinal length along with increasing age,and we also found a negative correlation between Olfactory nerves volume and the intestinal length for species being three distinct age classes(respectively,two years,three years and four years).Meanwhile,the negative correlation was stronger with increasing age.The same trends were also be found when considering the relationship between Cerebellum volume and the intestinal length for species being four age classes(from one to four years).It’s should be noted that food diversity inevitably influenced the relationship between brain size and the intestinal length.When the impact of food diversity was controlled,the negative correlation between the whole brain volume and intestinal length among species being one year was not found anymore,and the same phenomenon also appeared when examining the correlation between Olfactory nerves volume and the intestinal length among species being four years,while the negative correlation between Telencephalon volume and the intestinal length occurred among species being five years.At age classes of three and four,the trade-off between Cerebellum volume and intestinal length was significantly affected by food diversity,and the negative correlation was significantly stronger(slope: from-0.425 to-0.601 and from-0.461 to-0.644 at age classes of three and four years respectively).Overall,the study exhibited the influences of food diversity on the intestinal length,and the trade-off relationship between brain size and the intestinal length in different individual development stages,showed different food composition in different individual development stages and highlighted the great importance of food diversity.The variation of food diversity in different developmental stages plays an important role in the artificial breeding of amphibians,especially in the rejuvenation of endangered species.Exploring the influences of food diversity on the relationship between brain size and the intestinal length in different developmental stages provides a new approach for amphibian conservation.