| Although the Four eye-spotted turtle (Sacalia quadriocellata) experiences thesame pressures of over-hunting and habitat destruction as other turtle species, itspopulation density maintains a higher level than which of many other local turtlespecies in China, suggesting that the Four eye-spotted turtle possesses a high fitnessof adaptation. Till now there were some researches tried to reveal such adaptability ofthe Four eye-spotted turtle, including habitat selection, feeding behavior andreproduction, but the morphological adaptation of this species has not beenreported.Body color and shape were both the key morphological traits that areimportant for studying morphological adaptation of turtles. Research on colorsimilarity between body color and substrate was reported in fish, frogs, lizards, birdsand mammals, but there was not reported in turtles. Body color studies of turtles havemainly focused on body color change, structure and regulation of pigment cell, and soon. Meanwhile, the moth larvae and branch similarity research was only one researchabout the shape similarity between body shape and habitat substrates, there was notreported in vertebrates. In order to reveal the morphological reasons that areresponsible for the high population density of the Four eye-spotted turtle, weconducted comparative study on the similarity of body color and shape to the habitatsubstrate among different density distribution segments in Four eye-spotted turtle.Although the Big-headed turtles (Platysternon megacephalum), and Asian yellowpond turtles (Mauremys mutica) coexist with the Four eye-spotted turtle in the sameriver, they both have a significantly lower population density than Four eye-spottedturtle. And we also compared body color and body shape similarities to theircorresponding habitat substrates among these three turtle species. This study wasconducted in Qiongzhong, Hainan province from December2012to October2013.The main results presented as follows：Similarity between body color and habitat substrate: quadrats were selectedby random sampling, and put turtles in each quadrat, then photographed them used digital photography. We quantified and calculated the color difference by usedphotoshop software and CIE L*a*b*color space. The results showed that colorsimilarity between shell color of the Four eye-spotted turtle and habitat substrates wassignificantly different among different segments of Hezonggou river. The similarity inmidstream(ΔE=12.24±0.17) was significantly higher than in upstream (ΔE=26.60±0.87)(Z=-14.378，P <0.0001) and downstream(ΔE=38.57±1.14)(Z=-17.641，P <0.0001); the lightness similarity was also significantly higher inmidstream (ΔL*=9.75±0.17) than in upstream(ΔL*=22.07±0.90)(Z=-11.952，P<0.0001) and downstream (ΔL*=37.08±1.18)(Z=-17.542，P <0.0001).In line withthese, the chroma similarity in midstream(Δa*b*=7.02±0.14) was also significantlyhigher than in upstream(Δa*b*=13.45±0.32)(Z=-15.255， P <0.0001) anddownstream(Δa*b*=8.96±0.17)(Z=-8.371，P <0.0001). These results indicated thatdegree of camouflage in midstream, for Four eye-spotted turtle, is significantly higherthan the upstream and downstream. Furthermore, the population density of Foureye-spotted was positively correlated with its color and chroma similarity(ΔE: r=-0.455，P<0.0001；Δa*b*: r=-0.586，P<0.0001).The similarities of color, lightness and chroma between shell color and habitatsubstrate was found to be signifcantly different among the Four eye-spotted turtle,Big-headed turtle and Asian yellow pond turtle. The similarities of color, lightness andchroma in Four eye-spotted turtle were significantly higher than Asian yellow pondturtle (Z=-17.98，P<0.0001； Z=-17.98，P<0.0001; and Z=-15.293，P<0.0001respectively).These results indicated that degree of camouflage in Foureye-spotted turtle was higher than Asian yellow pond turtle. The color and lightnesssimilarities in Four eye-spotted turtle were significantly higher than Big-headed turtle(Z=-3.439, P=0.001and Z=-3.867，P<0.0001respectively), but Its chromasimilarity was significantly lower than Big-headed turtle (Z=-3.371，P=0.001). Thisindicated that Four eye-spotted turtle more matching with habitat substate in color andlightness than Big-headed turtle, but less in chroma.Similarity between body shape and habitat substrate：ImageJ software wasused to measure shape descriptors of turtles and substates in the photos, and the similarities of each shape descriptor between turtles and substates were calculated.Then we calculated shape similarities between turtles and substates by used variationcoefficient method to determine the weight of each shape descriptor similarity. Theresults showed that similarity between body shape of the Four eye-spotted turtle andhabitat substrates was significantly different among different segments of Hezonggou(Z=-11.56, P <0.0001).It was significantly higher in midstream than in upstream(0.784±0.004and0.661±0.009, respectively).This indicated that the body shape ofFour eye-spotted turtle more matching with substates in midstream than in upstream.Furthermore, the shape similarity of Four eye-spotted turtle was significantly higherthan Big-headed turtle (0.705±0.008)(Z=-8.061, P <0.0001). It indicated that thebody shape of Four eye-spotted turtle more matching with substates than ofBig-headed turtle.Score by human as predator: the degree of camouflage was evaluated throughscore by human as predator. Mann-Whitney U test showed that the degree ofcamouflage of Four eye-spotted turtle was significantly different in different segmentsof Hezonggou, it was significantly higher in midstream (2) than in upstream (1) anddownstream (1)(Z=-5.394, P <0.0001and Z=-12.416, P <0.0001, respectively).This indicated that the camouflage effect of Four eye-spotted turtle in the midstreamwas better than other segments. Furthermore, The degree of camouflage was alsosignificantly different among the Four eye-spotted turtle, Big-headed turtle and Asianyellow pond turtle. The Four eye-spotted turtle’s degree of camouflage (2) wassignificantly higher than Asian yellow pond turtle (1)(Z=-11.823, P <0.0001), itindicated that Four eye-spotted turtle’s camouflage is more effective than Asianyellow pond turtle. However, the Four eye-spotted turtle’s degree of camouflage didnot differ when compared with Big-headed turtle (2)(Z=-1.439, P=0.15).In conclusion, body color and shape of Four eye-spotted turtle adapted to itsnatural environment, and its adaptation was stronger than other freshwater turtles ofsympatric distribution. This study illustrated that morphological adaptation canexplain the high population density of the Four eye-spotted turtle. This study alsoprovide theoretical basis and practice guidance for Four eye-spotted turtle’s conservation, management and captive breeding. As far as I know, this study isamong the first to quantify color matching of turtle and study shape matching ofvertebrate in the wild. It has reference value to study morphological adaptation ofChelonian. |
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