Diet of the endangered big-headed turtlePlatysternon megacephalum

Abstract

Populations of the big-headed turtle Platysternon megacephalum are declining at unprecedented rates across most of its distribution in Southeast Asia owing to unsustainable harvest for pet, food, and Chinese medicine markets. Research on Asian freshwater turtles becomes more challenging as populations decline and basic ecological information is needed to inform conservation efforts. We examined fecal samples collected from P. megacephalum in five streams in Hong Kong to quantify the diet, and we compared the germination success of ingested and uningested seeds. Fruits, primarily of Machilus spp., were most frequently consumed, followed by insects, plant matter, crabs and mollusks. The niche breadth of adults was wider than that of juveniles. Diet composition differed between sites, which may be attributable to the history of illegal trapping at some sites, which reduced the proportion of larger and older individuals. Digestion of Machilus spp. fruits by P. megacephalum enhanced germination success of seeds by about 30%. However, most digested seeds are likely defecated in water in this highly aquatic species, which limits the potential benefit to dispersal. The results of our study can be used by conservation-related captive breeding programs to ensure a more optimal diet is provided to captive P. megacephalum.

Non‐marine turtle plays important functional roles in Indonesian ecosystems

“…We documented an ontogenetic shift in diet, with subadult turtles consuming a higher proportion of invertebrates and vertebrates, and adults becoming more omnivorous. Similar ontogenetic changes in diet have been documented in other species of semi‐aquatic turtles (Clark & Gibbons, 1969; Sung et al., 2016) and, in the case of C. amboinensis , this shift is probably related in part to gape and bite force limitations in younger individuals. Many of the fruits we documented around wetland habitats were too large to have been swallowed whole by smaller turtles and a tough exocarp may limit access to the fleshy pulp inside.…”

“…We compared germination rates for ingested and control seeds of the same six plants (Figure 2 We documented an ontogenetic shift in diet, with subadult turtles consuming a higher proportion of invertebrates and vertebrates, and adults becoming more omnivorous. Similar ontogenetic changes in diet have been documented in other species of semi-aquatic turtles (Clark & Gibbons, 1969;Sung et al, 2016) and, in the case of C.…”

“…Some evidence suggests that nonmarine turtles are important vectors for seed dispersal and enhance seed germination. Turtles swallow fruits whole, without crushing the seeds, and seeds of some plants that have passed through the guts of turtles exhibit increased germination success (Cobo & Andreu, 1988; Sung, Hau, & Karraker, 2016). Long passage duration in turtles, relative to other vertebrates, results in a weakening of the seed coat, increasing the probability and rate of germination, and allows seeds to be transported longer distances where they may have a higher likelihood of survival because of reduced competition with the parent plant and removal from the allelopathic zone beneath the parent plant (Herrera, 2002).…”

The anatomy, paleobiology, and evolutionary relationships of the largest extinct side-necked turtle

“…Because of its huge gape size, S. geographicus could have swallowed even the largest South American fruits and thus qualify as a megafaunal frugivore and seed disperser [sensu (56)]. In general, larger turtles also include more fruits in their diet than do smaller ones; for example, in the extant Asian big-headed turtle, Platysternon megacephalum, there is a positive relationship between body size and amount of fruit in their diet (57). Overall, S. geographicus could thus have been a highly efficient seed disperser [sensu (58)].…”

Draft genome of the big-headed turtle Platysternon megacephalum

“…The species inhabits flowing cool rocky mountain streams with water temperatures usually between 12–28 °C 2 . It is an aquatic predator with strong climbing abilities, preying on lizard, frogs, fish, shrimps, crabs, snails, earthworms, insects, and even small birds and mammals, along with consuming some fruit and plant matter 3 . The big-headed turtle has some defining features, such as an extra-large head, long tail, and flat carapace.…”