Ecomorphological Adaption Of Habitat Use In Turtle And Its Empirical Study On Two Species Of Asian Box Turtle(Cuora)

Animal morphological structure can influence behavior and how a species adapts to the environment.Turtles with different morphology occupy a wide range of habitats from aquatic to highly terrestrial,making them an ideal group for ecomorphological studies.Current studies indicate that niche divergence,such as habitat shift,may be correlated with morphological differences of turtles.Although turtle ecomorphological studies are extensive,many issues,including subjective and simple classification of habitat,lack of sympatric and special species data,may prevent the identification of the ecological mechanisms responsible for divergent morphologies of turtles.Moreover,there are only a few ecomorphological studies involving native Chinese vertebrate species,and there are no studies on native Chinese turtle ecomorphologies.We performed a quantitative study on the relationship between turtle‘s morphology and habitat which from different type and subtype to reveal ecological causes that are responsible for morphological variations in turtles.We also examined the relationship among morphological characteristics,locomotor performance,and microhabitat use in sympatric species of turtles by using the keeled box turtle(Cuora mouhotii)and the Indochinese box turtle(C.galbinifrons).The main results are presented as follows:The correlation between habitat and body size or shape : we had body size(maximum carapace length)data for 331 species from the literature,accounting for 98.8% of the total number of 335 species,and divided each species into four habitat types(sea,freshwater,mailand and island)or five habitat subtypes for freshwater habitat(moving and large bodies of water,stagnant and large bodies of water,moving and samll bodies of water,stagnant and small bodies of water,and all bodies of water)and three habitat subtypes for mainland terrestrial habitat(wilderness,lowland and highland).The results indicated that turtle body size was correlated with their habitat types;the sea turtle has the biggest body size,the mainland freshwater turtle and tortoise have the smallest size,and the island tortoise was intermediate size.There was no significant difference on body size between the mainland freshwater turtle and tortoise.However,the body size was positively correlated with the total area of water bodies in habitat subtypes for the freshwater turtles.Although there was a trend to grow bigger from highland to lowland,and from lowland to wilderness for body size of mailand tortoise,there were no significant difference among these habitat subtypes.We also collected carapace length,width and height from 6664 adult individuals of 115 species(accounting for 34.33% of the total species),and calculated ratio between carapace height and width as indictor of body shape.The results showed that the body shape became more flat with increasing body size in freshwater turtles,whereas the opposite trend was noted for male mainland tortoise.Turtle body shape gradually became more domed from sea to freshwater habitat,from freshwater to mainland terrestrial habitat,and from mainland to island terrestrial habitat.However,there were no siginifacant difference between the body shape and habitat subtype for both freshwater turtles and mainland tortoise.Divergence in microhabitat use,performance,and morphology of two sympatric box turtle specie:we examined the relationship among microhabitat use,performance(climbing ability and self-righting abilitye),and ecomorphological characteristics(head,carapace,and limb dimensions)in two sister species of turtles(Cuora mouhotii and C.galbinifrons)with sympatric distributions at the Diaoluoshan Natural Reserve in Hainan Province,China from April 2015 to February 2016.We found that C.mouhotii preferred microhabitats with rock crevices and mostly observed the species on steep slopes.In addition,we also observed that C.mouhotii had a flat shell and large head to enhance its climbing and self-righting abilities.In contrast,C.galbinifrons had a domed shell that was more adapted to the species‘ microhabitat of deciduous leaves under bamboo clumps and gentle slopes.We conclude that morphological divergence allows the two sympatric Cuora spp.to partition the available resources and that such partitioning enhances the performance of the species by reducing interspecific competition.Rock crevice selection and morphological adaptation for C.mouhotii:in order to investigate the relationship between the morphology and crevice size selection by C.mouhotii,we measured the crevice size and structure trait in the field,and conducted a controlled experiment in the laboratory.We found that horizontal,deep and moderately wide crevices that are low enough to touch the carapace were preferred by C.mouhotii.Turtles mostly positioned their head toward the interior of the crevice and positioned their carapace with serrated posterior edges outward when they hide in crevices.In conclusion,turtle body size and shape adapt to their habitat.And morphological divergence allows the two sympatric Cuora spp.to partition the available microhabitats and that such partitioning enhances the performance of the species by reducing interspecific competition.Interpreting the causes and consequences of morphological variation remains an important corner-stone of evolutionary biology.Therefore,this study will help advance the evolutionary biology because it elucidates the ecological reasons for divergent morphology of turtles.As far as we know,this is the first study investigating the relationship between morphology and habitat use of turtles in China,this work will help advance the field of turtle ecomorphology within China.Furthermore,this work will also have theoretical and practical significance for the conservation,management of endangered species and establishment of captive breeding population,and for reintroduction project.