Late Quaternary Environmental and Human Impacts on the Mitochondrial DNA Diversity of Four Commensal Rodents in Myanmar

Region-Specific Genetic Diversity of Black Rats (Rattus rattus Complex) in Southeast and East Asia Shaped by Rapid Population Expansion Events

Among the six mitochondrial DNA lineages of the black rat (Rattus rattus Complex; RrC), lineages II and IV are widespread in Southeast and East Asia. This study explored their demographic history using 17 new sequences from the Miyako Islands in the Ryukyu archipelago, together with 178 publicly available cytochrome b sequences. We defined six and two haplotype groups showing rapid population expansion signals in Lineages II and IV, respectively. The six haplotype groups of Lineage II were represented by haplotypes from 1) Myanmar/Bangladesh/Northeast India, 2) Laos, 3) Thailand, 4) Indonesia/Philippines, 5) Vietnam/southern China, and 6) the Ryukyu archipelago. These expansion times were estimated using time-dependent evolutionary rates to be 115,300 years ago (ya), 128,500 ya, 9600 ya, 10,600 ya, 7200 ya, and 1400 ya, respectively, although all had large confidence intervals. The two groups of Lineage IV were recovered from the mainland and islands of Southeast Asia with predicted expansion times of 197,000 ya and 5800 ya, respectively. These results suggest that climatic fluctuations during the last 200,000 years of the Quaternary, affected the population dynamics in subtropical areas at different times. Furthermore, the results of the younger rapid expansion events of RrC suggest the possibility of agricultural advancement and dispersal of Neolithic farmers to different areas within the mainland and islands of Southeast Asia during the Holocene. A subset of rats from the Miyako Islands were found to have the same lineage IV haplotypes as those in Southeast Asia, suggesting a recent introduction of these new lineages.

Scanning electron microscopy of Quilonia renniei from Asian elephants revealing variation in coronal leaflet number

Although parasitic nematodes in the genera Murshidia and Quilonia (family Strongylidae) are recognized as major gastrointestinal parasites in Asian elephants, they have been poorly studied. Recently, light micrographs of these parasites in Myanmar have been presented, almost 100 years after the original drawings. However, the number of coronal leaflets, a key taxonomic feature of Quilonia species, has not been precisely determined based on light microscopy. The current study aimed to determine the exact number of coronal leaflets in Quilonia renniei specimens from Asian elephants in Myanmar. On the basis of scanning electron micrographs, leaflet number in females (19–20, average 19.7, n = 9) was significantly higher (P < 0.005) than that in males (16–19, average 18.1, n = 8). This compares with 18 coronal leaflets indicated in the original species description. Specimens bearing 19 coronal leaflets were most numerous, followed by those with 20 leaflets. Median-joining network analysis of mitochondrial cytochrome c oxidase subunit I gene sequences with 16 haplotypes from 19 individuals revealed no clear association between parasite populations and the number of coronal leaflets. These results highlight the importance of determining the number of coronal leaflets in the taxonomy of Q. renniei and other related Quilonia species infecting Asian elephants.