Evolution of cold adaptation in subtropical snakes : A study on ecological factors

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Research was conducted on Yanaha-jima, Okinawa-jima, Amami-ohshima, and Uke-jima Islands. On Yanaha-jima, radio-tracking study, nighttime census to examine seasonal activity patterns of Ovophis okinavensis and prey animals, mark-recapture study to examine movement patterns and diet of the snake, and measurements of operative temperature were conducted. On Amami-ohshima, in addition to the above studies, preferred body temperature of the snake was tested in the laboratory. On Okinawa-jima, where long-term field study had been conducted, only the examination of operative temperature and preferred body temperature were made. Because of the scarcity of O. okinavensis, only a brief preliminary survey was conducted on Uke-jima. Eight snakes each were radio-tracked from August 2006 and February 2007 on Yanaha-jima and Amami-ohshima, respectively, and their location, body temperature, and microhabitat use were recorded every month. Laboratory experiments on preferred body temperature were cond … More ucted using 12 snakes each in January and February 2008 on Okinawa-jima and Amami-ohshima, respectively. Phylogenetic relationships among six islands including Yanaha-jima, Okinawa-jima, and Amami-ohshima were investigated using 1114 by of the Mitochondrial cytochrome b gene. The results showed that 1) snakes on Okinawa-jima and Amami-ohshima are most active in winter with a body temperature of 10-20℃ and predominantly feed on frogs, 2) their preferred body temperature exhibits two peaks, ca. 25℃ and 15℃, and is lower at night than in the daytime, and 3) snakes on Yanaha-jima are most active in summer with a body temperature of 25-30℃ and exclusively feed on lizards. Obtained phylogenetic tree indicated a close affinity of the Okinawa-jima and Yanaha-jima populations, which are clearly separated from the Amami-ohshima population. Overall, these results suggest that O. okinavensis has relatively low preferred body temperature compared to other snakes hitherto reported and that seasonal activity patterns may largely depend on local availability of food resources rather than phylogenetic affinity. Less