Tropical Natural History

Phylogeography of Red Spiny Rats Maxomys surifer (Miller, 1900) (Mammalia: Rodentia: Muridae) based on Cytochrome b in peninsular Thailand

Awatsaya Pimsai, Yugo Ikeda, Shinya Okabe, Masaharu Motokawa — Fri, 20 Mar 2026 00:00:00 +0700

Spiny rats (Genus Maxomys) are an endemic rodent species in Southeast Asia belonging to the family Murinae. There are currently 18 species recognized in the genus Maxomys, with a general distribution extending from mainland Southeast Asia eastward over the Sunda Shelf to some nearby islands. The phylogeography of M. surifer (Miller, 1900) in Thailand, particularly in peninsular Thailand, is presented in this study. A phylogenetic tree and haplotype networks were reconstructed to comprehend the geographic variation in the study area. Analyses included 898 base pairs of mitochondrial cytochrome b sequence data for 92 individuals of M. surifer, comprising 59 newly obtained sequences and 33 sequences from GenBank. The phylogenetic tree with the maximum likelihood inference revealed five highly divergent lineages within M. surifer. Three lineages (Clades I - III) were found in peninsular Thailand: Clade I includes specimens from a small area in the southern part of the peninsula; Clade II consists of specimens from both the mainland of peninsular Thailand and nearby islands in the Andaman Sea, including those from the type locality; Clade III comprises specimens from the central to northern parts of peninsular Thailand, extending toward the Kra Isthmus. Clades IV and V involved specimens from the Indochinese subregion. The results extend a view proposed in previous studies that M. surifer comprises several highly differentiated and well-supported phylogenetic lineages, possibly belonging to several distinct species. This study, for the first time, clearly showed five distinct clades found in Thailand with geographic overlap between Clades I and II, Clades II and III, and Clades IV and V. As well, the island populations in the Andaman Sea were included in Clade II, and also showed genetic difference between the distant islands (Adang and Rawi islands) and the island closer to the peninsular Thailand (Tarutao island). We propose that Peninsular Thailand acted as a center of isolation and diversification for three clades (Clades I, II, and III), and that subsequent dispersal events shaped their current complex and mosaic distribution with overlapping ranges in the Peninsular Thailand.

Reproductive Phenology and Breeding Ecology of Panha’s Crocodile Newt, Tylototriton panhai, at Phu Soi Dao National Park, Thailand

Fri, 20 Mar 2026 00:00:00 +0700

The Panha’s crocodile newt, Tylototriton panhai, has a narrow distribution range in Northeastern Thailand and adjacent Laos PDR. This cryptic species is listed as vulnerable with a decreasing population trend. A local population of T. panhai at Phu Soi Dao National Park, Thailand with a limited distribution through the high mountainous protected area was examined for its reproductive phenology and environmental conditions inducing reproductive period. A total of 269 adult newts (257 males, 12 females) and 298 larvae were captured using a visual encounter survey method, conducted twice a day at daytime and nighttime, and four sets of three-fence arrays with pit fall traps installed at breeding sites and checked daily. The study area (breeding sites) was approximately one square kilometer at 1,633 meters above mean sea level, and was investigated from July 2020 to May 2022. Adult newts were found to be seasonal breeders, with a strongly male biased sex ratio of caught individuals, and visited breeding sites only in the wet season (May–October) with the exception of one male recorded in November 2021. Males stayed at breeding sites for several months (May–November), whereas females visited for a shorter period of time (May to July). Numbers of adults decreased in the breeding sites after breeding, whereas larvae were initially observed in June and had been found in seasonal aquatic habitats until early dry season. Both adults and larvae disappeared in March 2021. A quasi-Poisson regression model showed a significant correlation between the number of adult newts visiting breeding sites and air temperature, humidity, or water pH. Furthermore, drought-induced water scarcity influenced the duration that adults and larvae remained in aquatic habitats. Adult newts were weighed and measured for 16 morphometric characters. Females were larger in body size and exhibited larger traits than males, as shown by ANCOVA with snout–vent length as a covariate (p < 0.05). A total of 108 adults (99 males, 9 females) were tagged with a 7-mm PIT tag, from which 20 recaptured males (20.20%) were found from May, 2021–April, 2022. The longest duration of the same male in aquatic habitats was from May to November in 2021, but no females were recaptured in the aquatic habitats, suggesting either lower site fidelity, different habitat use, or lower survival of females during this period. The estimated population size using RMark with the POPAN model was 249 individuals with an increasing abundance trend (227–249), and the estimate detection probability for males (0.26 ± 0.04) was higher than for females (0.02 ± 0.01).

Testis-Ova in Male Rice Frog (Fejervarya limnocharis) - A Natural Process of Sex Differentiation or a Suitable Biomarker of Effect for Ecotoxicology?

Fri, 20 Mar 2026 00:00:00 +0700

A previous study found that adult male rice frogs (Fejervarya limnocharis) inhabiting agricultural areas with varying levels of herbicide use exhibited testis-ova (TO). However, it remained unclear whether the occurrence of TO is associated with underlying herbicide contamination in agricultural areas or represents a natural aspect of testicular development in this species. This study aimed to examine the gonadal histology and intersex condition of the male rice frog, F. limnocharis, living in an agricultural area in central Thailand with no history of herbicide utilization over the last 10 years. The results showed that the incidences of testicular ovarian follicles (TOFs) in adult, subadult, and juvenile frogs were 46/50 (92%), 7/7 (100%), and 6/6 (100%), respectively. Crucially, these TOFs were observed in rice frogs even when herbicide analysis showed paraquat tissue residue below detection limits. These findings suggest that the presence of oocytes within the testis in F. limnocharis may represent a natural, transition phase of testicular development in the undifferentiated and semi-differentiated types of the normal sex differentiation process in amphibians. This prompted an evaluation of whether the TOFs could serve as a biomarker for assessing the effect of and susceptibility to herbicide contamination in this frog species.