Exploring The Molecular Basis Of The Evolution Of Body Size Differences In Carnivora

Body size is one of the basic life history characteristics.The difference in body size is the result of ecological adaptation.Large-sized species can obtain more food resources,mate probability,and face a lower risk of predation;while Small-sized species have the flexibility to access food resources that larger species cannot,reproduce more efficiently,and cope with environmental emergencies.Carnivora is at the top of the food chain,and the range of body size in Carnivora is unparalleled by any other mammalian group.The largest male southern elephant seal(Mirounga leonina)and the smallest least weasel(Mustela nivalis)have the huge difference in body mass of more than 130,000 times and in head body length of more than 50 times.However,the molecular basis for the huge diversity of body size among carnivores is currently unclear.In this study,we selected 20 representative species covering eight families in Carnivora.Through literature and database searches,we obtained two body size indexes of carnivores,namely head body Length and body mass.By searching the public database,we obtained the genome data of 20 carnivores and an outgroup species--cow(Bos taurus),and used Orthofinder software to identify 6667 one-to-one orthologous genes based on the dataset of 21 species.Subsequently,we calculated the molecular evolutionary rate of each one-to-one orthologous gene in each branch by using PAML software.Through PGLS regression analysis,we respectively correlated the both body size indexes(i.e.head body length and body mass)of carnivores with the evolutionary rate of one-to-one orthologous genes.The results showed that 1132 genes were significantly related to head body length,668 genes were significantly related to body mass,337 genes were significantly related to both head length and body weight after correction,and we defined these 337 genes as body size associated genes(BSAGs).The results of further GO and KEGG functional enrichment showed that these BSAGs were mainly enriched in pathways such as metabolism,growth and development,DNA repair,and apoptosis,suggesting that these pathways may play a key role in the differential evolution of body size in Carnivora.Among these,we identified fourteen positively-related BSAGs associated with “obesity,” and three genes have rapid evolved in extremely large carnivores.This suggests these BSAGs related to the obesity might have driven the body size expansion in carnivores.We also identified six negativelycorrelated BSAGs(ADGRG6,BRCA2,FANCC,LONP1,MARS and SIL1),and it has been previously confirmed that mutations in these six genes all lead to short stature and arrested development.They all have a relatively high evolutionary rate in small carnivores,indicating that the evolution of these genes may have contributed to the decreased body size of carnivores.Furthermore,for extremely small carnivores,we also identified fixed amino acid site changes in six genes: CDC7(S513L),ENG(V367I),LIG4(S784P),MMP2(S579T),TSPAN8(S178T)and POLE(E701D),and these sites are located in functional domain of these genes.Previous studies have found that variations in these genes can cause “short stature” or other reduced-body-sized related phenotypes,suggesting these sites may be responsible for the restriction of development and growth in small carnivores.Interestingly,100 BSAGs are related to cancer control(immunity,DNA damage monitoring and repair,etc.),including twentyone tumor suppressor genes.And fifteen cancer-related BSAGs have undergone rapid evolution in extremely large carnivores.These results above indicate that the largesized Carnivora species may have evolved effective tumor suppressor mechanisms,which can be regarded as molecular evidence supporting the “Peto's Paradox.” This study screened out key candidate genes related to the variant body size in Carnivora at the whole genome level for the first time,initially revealing the molecular mechanism of diversified body size evolution in carnivores,and a number of key target genes related to body size were obtained,which also laid a foundation for the study of body size evolution in mammals.