Rediscovery of Nycticebus coucang insularis Robinson, 1917 (Primates: Lorisidae) at Tioman Island and its Mitochondrial Genetic Assessment

Abstract

Slow lorises (Nycticebus) consist of eight species native to Southeast Asia while three species are recognised in Malaysia-N. coucang, N. menagensis and N. kayan. This study reports on the rediscovery of the subspecies N. coucang insularis Robinson, 1917 in Tioman Island and the genetic assessment of its mitochondrial DNA variation. Morphological measurements conform the specimen as the putative N. coucang but with distinct colour and markings. Two mitochondrial DNA segments (cytochrome b and control region) were produced from the subspecies representing their first registered sequences in GenBank. Genetically, the subspecies showed 99% of nucleotide similarity to N. coucang species type for both the DNA segments and constitute its own unique haplotype. Phylogenetic trees constructed using three methods (neighbour joining, maximum likelihood and Bayesian inference) showed two major groups within Nycticebus; the basal group was formed by N. pygmaeus while the second group consisted of the remaining Nycticebus species. The phylogenetic position of the subspecies, however, remains unresolved due to the observed mixing between N. coucang and N. bengalensis. Several reasons could lead to this condition including the lack of well documented voucher specimens and the short DNA fragments used. In addition, the possibility of hybridisation event between N. coucang and N. bengalensis could not be excluded as a possible explanation since both species occur sympatrically at the Isthmus of Kra region until the Thailand-Malaysia border. The rediscovery of this subspecies displays the unique faunal diversity that justifies the importance of Tioman Island as a protected area.

Molecular data confirm the presence of Nycticebus bengalensis on Langkawi Island, Malaysia

“…The phylogenetic clade formation shown in this study is consistent with previous studies conducted on the molecular phylogeny of Nycticebus. While this study did not employ the real genetic samples of N. pygmaeus as others have done (Chen et al 2006;Somura et al 2012), we managed to produce the same tree topology in which N. pygmaeus diverged earlier as compared to N. bengalensis and N. coucang (Rovie-Ryan et al 2018). We also find support for following suggestions by Rovie-Ryan et al (2018) to utilize samples from known and credible localities only, thus increasing the confidence level of our analysis confirming the presence of N. bengalensis in Langkawi Island.…”

“…While this study did not employ the real genetic samples of N. pygmaeus as others have done (Chen et al 2006;Somura et al 2012), we managed to produce the same tree topology in which N. pygmaeus diverged earlier as compared to N. bengalensis and N. coucang (Rovie-Ryan et al 2018). We also find support for following suggestions by Rovie-Ryan et al (2018) to utilize samples from known and credible localities only, thus increasing the confidence level of our analysis confirming the presence of N. bengalensis in Langkawi Island. We are also aware of the notion put forth by Groves (2001) that there is a possibility of a hybridization event occurring between N. coucang and N. bengalensis near the Isthmus of Kra; however, our phylogenetic analysis shows a clear distinction between the species.…”

“…Thus, we hypothesize that the populations of N. bengalensis on Langkawi Island are natural populations not recorded by previous studies. This is not surprising as this understudied group of primates has received less attention as compared to other species (Blair et al 2011), further supported by the rediscovery of N. c. insularis in Tioman Island, Malaysia by Rovie-Ryan et al (2018). This attention-deprived situation can largely be attributed to two factors as highlighted by Nekaris et al (2008): Nycticebus species are abundant in some areas but genuinely rare in others, or it takes time for surveyors to learn how to survey nocturnal lorises accurately, or alternatively, it takes time for the lorises to adapt to the presence of surveyors.…”

“…Although this region is conserved (Md-Zain et al 2018a), it has proven to be effective locus to identify different species of slow loris. Rovie-Ryan et al (2018) reported an unresolved topology of a phylogenetic tree of Nycticebus based on the Cytochrome b region, although the data are not shown. For future study, we suggest the use of other loci which have been proven to resolve species-level phylogeny in primates such as the D-loop (Abdul-Latiff et al 2014b), ND4 (Takacs et al 2005) and also a reattempt of Cyt b using different, species-specific primers as compared to Rovie-Ryan et al (2018), as the vast data of Cyt b on GenBank is useful for comparative analysis purposes, especially in biogeography (Abdul-Latiff et al 2017;Abdul-Latiff et al 2019).…”

“…Previously, only N. coucang has been described as distributed in the Malay Peninsula, with several subspecies (Brandon-Jones et al 2004). Recently, Rovie-Ryan et al (2018) rediscovered N. c. insularis in Tioman Island using two mitochondrial loci, the Cyt b and D-loop region. The presence of N. bengalensis has been hypothesized in the Northern part of the Malay Peninsula; however, no scientific evidence is available to confirm the presence.…”