Genetic diversity and population structure of coconut crab around the Ryukyu Islands has been clarified

Summary of AIST Press Release June 22, 2020
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　Coconut crab (Birgus latro), an edible species of crustacean (Fig. 1), is widely distributed around the Ryukyu Islands, southern Japan. Coconut crab is terrestrial and disperses in the sea during the larval period. It has been endangered by overharvesting for a long time and is concerned to go locally extinct without effective stock management. To obtain the scientific information to establish the conservation strategy for the crab in the Ryukyu Islands, researchers from National Institute of Advanced Industrial Science and Technology, University of Miyazaki, and Okinawa Prefectural University of Arts collected DNA samples from 8 sites in the area (Fig. 2) and surveyed the sex ratio and body size of individuals in each site.

Fig. 1. Coconut crab, a large crustacean species.

Fig. 2. Sampling sites in this study.

　They found that the sex ratio is skewed toward females (Fig. 3) and large males are rare possibly due to overharvesting. Analyzing DNA of the samples, they also found that the population connectivity is widely maintained around the Ryukyu Islands (Fig. 4). Based on these data, they proposed that stock management measures currently taken in some areas should be applied to wider areas so as to make the reduced population due to overharvesting recovered in the future by recruitment of larvae from other places.

Fig. 3. Female ratio in each site. Error bars show 95% credible intervals.

Fig. 4. Patterns of genetic connectivity among the population in each site, shown by MIG-seq analysis.
Blue figures show relative migration values.

Publication details

Yorisue T, Iguchi A, Yasuda N, Yoshioka Y, Sato T, Fujita Y. Evaluating the effect of overharvesting on genetic diversity and genetic population structure of the coconut crab. Scientific Reports 10:10026, 2020