The Relationship between Shell Morphology and Crevice Size Affecting Retreat Selection of the Keeled Box Turtle(Cuora mouhotii)

Rock crevices are important retreat sites for many reptiles.Unlike lizards and snakes,crevicedwelling turtles have rigid shells which severely limit the size and shape of crevices they are able to use.Few studies have addressed the relationship between turtle's shell morphology,behavior,and crevice size.Here,we investigate the relationship between morphology and crevice size selection in the Keeled box turtle(Cuora mouhotii).We radio tracked turtles in the field to document crevice dimensions and turtle behavior associated with crevices,and we conducted a controlled experiment in the lab to understand how a turtle's morphology influences its decision to select crevices with different dimensions.Both laboratory and field experiments demonstrate that turtles select deep and moderately wide crevices that are low enough to barely accommodate the carapace.Crevices used by turtles tend to be about 2 times as wide,1.2 times as high,and 3 times longer than the turtle's shell.Moreover,turtles tended to prefer crevices with horizontal openings in the field and position themselves head first in the crevice.We conclude that morphology,especially carapace height,influences the Keeled box turtles' decision to select specific sizes of crevice.We argue that the tendency for turtles to select crevices that come into contact with their carapace contributes to successful defense against predators,as it would be more difficult for a predator to remove a turtle when the crevice is nearly touching the turtles shell.

Partial Masquerading and Background Matching in Two Asian Box Turtle Species(Cuora spp.)

Animals living in heterogeneous natural environments adopt different camouflage strategies against different backgrounds,and behavioral adaptation is crucial for their survival.However,studies of camouflage strategies have not always quantified the effect of multiple strategies used together.In the present study,we used a human visual model to quantify similarities in color and shape between the carapace patterns of two Cuora species and their preferred habitats.Our results showed that the color of the middle stripe on the carapace of Cuora galbinifrons(Indochinese box turtle)was significantly similar to the color of their preferred substrates.Meanwhile,the middle stripe on the carapace of C.mouhotii(keeled box turtle)contrasted more with their preferred substrates,and the side stripe matched most closely with the environment.Furthermore,the carapace side stripe of C.galbinifrons and the carapace middle stripe of C.mouhotii highly contrasted with their preferred substrates.We quantified the similarity in shape between the highcontrast stripes of both Cuora species and leaves from their habitats.The carapace middle stripe of C.mouhotii was most similar in shape to leaves from the broadleaves substrate,and the carapace side stripe of C.galbinifrons was the most similar in shape to leaves from the bamboo-leaves substrate.We determined that these species adopt partial masquerading when their entire carapace is exposed and partially match their background when they semi-cover themselves in leaf litter.To the best of our knowledge,this is the first study to demonstrate that partial masquerading and background matching improve the camouflage effect of Asian box turtles in their preferred habitats.This is a novel study focusing on the influence of the shape and color of individual carapace segments on reducing detectability and recognition.

Effect of Morphology and Age on the Closure Ability of Asian Box Turtles(Cuora)

The ability of box turtles to close their shell as an antipredation adaptation and the potential impact of the anterior and posterior lobes of the plastron on the closing force and closing time remain relatively unexplored.Here,keeled(Cuora mouhotii)and flowerback(C.galbinifrons)box turtles,whose shell cannot and can be completely closed,respectively,were studied.Anterior and posterior closing forces were measured using a force transducer,and the closing time was recorded.The anterior closing force in both turtle species was substantially greater than the posterior closing force,reaching approximately 4-fold in adults.Moreover,the anterior closing time in adults was significantly longer than the posterior closing time.This closing force difference can be attributed to the substantially smaller anterior plastron lobe than the posterior lobe in the two species.Additionally,the anterior and posterior closing forces in both species positively correlated with body weight and showed no relationship with the length of the bridge and hinge.Interspecies comparison showed that the anterior and posterior closing forces were significantly greater(approximately 2–4-fold)in flowerback box turtle than in keeled box turtles,regardless of age,and the closure time was significantly longer in adult flowerback box turtles than in adult keeled box turtles.Although the closing forces in both species showed negative allometry,the increase rate was significantly higher in flowerback box turtle than in keeled box turtle.The closing forces in both species were observed to be approximately 4-fold stronger in adults than in juveniles.No sexual dimorphism concerning the anterior and posterior closing forces was observed in either species.In summary,this is the first study to comparatively evaluate the anterior and posterior closing ability of box turtles,demonstrating that age,weight,plastron shape,and the degree of shell closure are important factors affecting closing ability.