Status, distribution, and morphometric analysis of the genus Trichopodus in Sumatra, Indonesia

Abstract

Trichopodus, the genus of dwarf gourami fish, is the oldest genus in the Osphronemidae family, with six valid species, three of which are found in Sumatra. In this study, the status, distribution, and morphometrics of Trichopodus leerii, T. pectoralis, and T. trichopterus from Sumatra were observed and analyzed. Although these species can be distinguished based on phenotypic characteristics, it is still possible to misidentify them in small or preserved samples. In this study, analyses were carried out on specimens in the collection of the Museum Zoologicum Bogoriense, combined with literature on the species status. The results showed that T. trichopterus and T. pectoralis were in the least concern category. T. trichopterus had the widest distribution, followed by T. pectoralis. T. leerii had the smallest distribution and is in a near-threatened conservation status. Further analysis revealed that 23 of the 25 measured morphological characteristics were informative, with the first three axes of a principal component analysis on morphometric data explaining 51.28% of the total variance in the sample. The three species were distinguished using a combination of pectoral fin length, eye diameter, pelvic fin length, and anterior snout width. Cluster analysis showed that there is consistency in the morphometrics of the species from various sample locations, where the same species are in the same clade. This research contributes to our understanding of the status and distribution of the species in genus Trichopodus and employs morphometric analysis to provide a practical key to classifying them in Sumatra.

Keywords:

• Status
• distribution
• morphometric
• Trichopodus
• Sumatra

Introduction

The dwarf gourami fish belongs to the genus Trichopodus, which was formerly included in the genus Trichogaster (Paepke, 2009; Töpfer & Schlindler 2009; Supiwong et al. 2010). It is a tropical freshwater labyrinth fish (Regan 1909). Trichopodus is the oldest genus in the family Osphronemidae, which spread across Southeast Asia (Berra 1981). Trichopodus is closely related to Trichogaster; both of these species have long, thread-like pelvic fins known as “feelers”, which function to feel the environment (Nelson 1994). Trichopodus has a shorter dorsal fin as a juvenile, but it grows longer as an adult (Paepke 2009; Töpfer & Schlindler 2009). The gourami fish also show sexual dimorphism in body size (Dorado et al. 2010; Boonanuntanasarn et al. 2020). In nature, gourami fish can live in lowland wetlands (Gustiano et al. 2015), swamps and canals (Kottelat et al. 1993; Haryono & Agus 2000; Haryono 2012), and lakes (Haryono 2010). These fish are also found in paddy fields, ditches, and rivers with dense vegetation, as well as in shallow waters with slow or stagnant currents or seasonally flooded habitats (Smith 1945; Mohsin 1983; Roberts 1989; Rainboth 1996).

Currently, this group of gouramis has been successfully bred in non-Asian countries due to the increased trade as ornamental fish (Ng & Tan 1997). Aside from being an ornamental fish, this gourami also has economic value as a food fish (Nguyen et al. 2019; Gustiano et al. 2021; Kurniawan et al. 2021). There are six valid species in the Trichopodus genus, namely T. leerii, T. microlepis, T. pectoralis, T. trichopterus, T. cantoris, and T. poptae (Low et al. 2014). In Indonesia, there are four species of gourami fish, identified as T. leerii, T. pectoralis, T. poptae, and T. trichopterus (Low et al. 2014; Tan et al. 2019; Ahmadi 2021). Trichopodus poptae is the lates described which is only reported from Kalimantan. The snakeskin gourami, T. pectoralis, is a commercial species that has economic value as a food fish (Yoonpundh & Little 1997; Nguyen 2014; Nguyen et al. 2019; Gustiano et al. 2022). Meanwhile, the other three species have economic value as ornamental fish.

Although sometimes considered “classical”, the biometric characterization is still a powerful method to determine different taxa. In many cases, biometrics can be used to distinguish between different taxa in the field. Over the last decade, many gourami families and fish in general have been subjected to biometric analyses to provide accurate taxonomic and key identifications (Sneath & Sokal 1973; Sokal & Rohlf 1980; Roberts 1992; Eviota et al. 2016; Jumawan et al. 2016; Ahmadi 2021; Gustiano et al. 2021; Perdana et al. 2021; Nur et al. 2022b). There is currently no information on the status, distribution, and morphometric differences among Trichopodus species found in Sumatra, Indonesia. As a result, the purpose of this research is to gain a better understanding of the species’ status, distribution, morphometric variation, and distinct character, which can be used as practical keys.

Materials and methods

The specimens used for this study form part of the Museum Zoologicum Bogoriense (MZB) collection. All specimens are categorized by type, location, and quantity. Meanwhile, gravid females and deformed fish were not used for morphometric analysis, but the location of the fish was recorded. A total of 84 fish samples were selected for morphometric analysis.

Status and distribution

The conservation status of each species was validated and confirmed through the online data in the IUCN Red List database www.iucnredlist.org. While the local distribution (LD) was calculated based on Muchlisin et al. (2015): LD = $\frac{N.st}{Ni.st}$ x 100, where: Ni.st = The number of locations where fish were found; N.st = The total number of locations. LD analysis was carried out based on specimen data available at the Zoologicum Bogoriense Museum.

Morphometric analysis

Morphometric measurements were performed on 19 samples of T. leerii, 15 samples of T. pectoralis, and 50 samples of T. trichopterus. A total of 25 morphometric characteristics were measured on the 84 specimens of Trichopodus spp. (Figure 1). The specimens were measured using a digital caliper (Insize 1108–200 made in China). The data were then transformed using the following formula: M_trans = M/SL x 100, where M is the original measurement result, M_trans is the transformation result, and SL is the standard length. Four characteristics (PFL, ED, PeFL, and SNW) were transformed using HL for further analysis.

Figure 1. Morphometric characteristics measured in fish samples Trichopodus spp.: 1. Snout length (SnL); 1a. Anterior snout width (SNW); 2. Head length (HL); 3. Prepectoral length (PrePL); 4. Eye diameter (ED); 5. postorbital length (POL); 6. head depth (HD); 7. Predorsal length (PrDL); 8. dorsal spine length (DSpL); 9. Dorsal fin base length (DFBL); 10. Postdorsal length (PoDL); 11. Pectoral fin length (PFL); 12. Body depth (BD); 13. Caudal peduncle depth (CPD); 14. Prepelvic length (PrPL); 15. Pelvic fin length (PeFL); 16. Anal spine length (ASL); 17. Anal fin length (AFL); 18. Standard length (SL); 19. Head width (HW); 20. Lower jaw length (LWJ); 21. Mouth width (MW); 22. Interorbital length (IOL); 23. Distance snout to isthmus (DstL); 24. Body width (BW).

Data analysis

The morphometric data were analyzed using univariate analysis (one-way ANOVA) and multivariate analysis (Principal Component Analysis, PCA) using the SPSS version 26.0 and PAST version 4.03. Before running PCA on the covariance matrix, data measurements were log transformed to reduce the effect of non-normality. To determine morphological similarities among individuals, a hierarchical cluster analysis based on morphometric data was performed using the unweighted pair-group method with arithmetic average algorithm (UPGMA).

Results

Species composition, distribution, and conservation status

A total of 338 samples of Trichopodus spp. consisting of T. leerii (n = 19), T. pectoralis (n = 16), and T. trichopterus (n = 294) were dispersed across Sumatra (Table I and Figure 2). The results showed that T. trichopterus was widely distributed at 49 sites covering 7 provinces (LD 76.56%), followed by T. pectoralis (LD 12.50%), and T. leerii, which had the lowest distribution and was only found in seven locations (LD 10.94%) (Table II). Based on the IUCN Red List database, among three species of gourami found in Sumatra, one is categorized as a Near Threatened species (T. leerii), while the two other species (T. pectoralis and T. trichopterus) in the Least Concern category (Table II).

Table I. Types and locations of specimen collection Trichopodus spp. at the Museum Zoologicum Bogoriense from Sumatra, Indonesia.

Species	Location	n	No. Catalog (MZB)
Trichopodus leerii	Batang Umbilin, West Sumatra	1	4672
	Teluk Bangka lake, South Sumatra	2	10,247
	Lubuk Lampam, South Sumatra	1	4252
	Lempuing river, South Sumatra	3	102,218
	Sekapas Rokan river, Riau	1	10,137
	Kandang river, Jambi	2	22,237
	Lalan river, Jambi	8	22,195
Trichopodus pectoralis	Lempuing river, South Sumatra	5	10,214
	Siring Purwasari, South Lampung	2	2181
	Sekapas, Riau	1	10,138
	Menggala, Lampung	2	14,278
	Peingsewu, Lampung	1	1393
	Sragi swamp, Lampung	2	1811
	Way Batang Hari, Lampung	2	14,177
	Teluk Rendah, Jambi	1	5151
Trichopodus trichopterus	South Aceh, Aceh	15	5618
	Air Belida, South Sumatra	1	14,912
	Alus Jerembaning, South Aceh	17	5616
	Danau Teluk Bangka, South Sumatra	3	10,248
	Kali Geren, Central Lampung	1	1824
	Kanal Bandhurip, South Lampung	2	1640
	Kepulauan Riau	1	12,163
	Kluet Selatan, South Aceh	11	19,864
	Kolong Hijau, Riau	2	12,169
	Kota Batu, South Sumatra	1	5003
	Kp Bukit Semen, Riau	1	12,163
	Kp. Rundeng, Meulaboh, Aceh	3	4661
	Labung Sekampung, Central Lampung	2	2138
	Lubuk Lampam, South Sumatra	1	4253
	Meulaboh, Aceh	1	4661
	Peingsewu, Lampung	6	1896
	Pinang Sebatang, Bangkalis, Riau	6	2606
	Pring Kumpul, South Lampung	2	1896
	Pulau Panggul, South Lampung	3	2234
	Kijing swamp, South Lampung	2	2198
	Klonpang swamp, Batang Hari, Jambi	5	22,211
	Maris swamp, Asaha, Central Lampung	6	1775
	Tanjung Putus swamp, Central Lampung	55	1781
	Rulung Helik, South Lampung	2	1880
	Kp Pasir Teripa, Aceh	1	14,211
	Mambang, Central Lampung	3	2354
	Teripa river, Aceh	4	14,205
	Srurejari, Jepara, Central Lampung	9	1677
	Alas river, South Aceh	2	5659
	Bohorok river, Bukit Lawang, North Sumatra	2	10.306
	Bungur Copong river, Asaha, Central Lampung	27	1803
	Kahyapu river, Nort Bengkulu	3	22,834
	Kandang river, Jambi	5	22,188
	Kemali river, East Lampung	4	10,265
	Kramat river, Central Lampung	20	1714
	Lempuing river, South Sumatra	3	10,213
	Way Jepara river, South Lampung	2	1677
	T.N. Way Kambas, Lampung	5	13,673
	Teluk Rendah, Jambi	3	5165
	Way Betung, Lampung	1	14,007
	Way Capan, Central Lampung	5	1864
	Way Jantan, South Lampung	3	1980
	Way Kambas, Lampung	5	13,673
	Way Kandis Bawang, Central Lampung	3	1838
	Way Pandamaran, Lampung	1	1395
	Way Penet, Lampung	1	1394
	Way Pisang, South Lampung	4	1629
	Way Sekampung, Central Lampung	1	1856
	Way Seputih, Lampung	23	14,140

Table II. Status and distribution of Trichopodus spp. in Sumatra Waters, Indonesia.

Species	Province								IUCN Category
	South Sumatra	Riau	Jambi	Lampung	Aceh	Nort Sumatra	Bengkulu	West Sumatra
T. leerii	+	+	+	-	-	-	-	+	NT
T. pectoralis	+	+	+	+	-	-	-	-	LC
T. trichopterus	+	+	+	+	+	+	+	-	LC

+: exist; -: not exist; NT: Near Threatened; LC: Least Concern.

Figure 2. Map of Sumatra Island showing the distribution of Trichopodus spp. in Sumatra waters.

Morphometric Trichopodus spp.

Trichopodus leerii had a standard length that ranged between 46.30 and 72.10 mm (average 59.24 ± 7.83 mm), T. pectoralis ranged from 82.24 to 151.80 mm (average 110.73 ± 19.12 mm), T. trichopterus, from 30.42 to 82.77 mm (average 53.52 ± 11.94 mm). The ANOVA test showed significant variations for individual characteristics among the investigated Trichopodus species (p < 0.01) (Table III). However, T. pectoralis and T. trichopterus display high morphological similarity across 11 morphometric characteristics, namely SnL, HL, PrePL, PoDL, BD, CPD, PrPL, PeFI, AFL, IOL, and BW. Overall, there are only four different characteristics, namely SNW, POL, ASL, and HW among the three species (Table IV).

Table III. Result of univariate ANOVA applied to a total 24 morphometric characteristics of Trichopodus spp. specimens collected from Sumatra waters.

Character	Wilks’ Lambda	F value	P value
SnL	0.869	6.089	0.003
SNW	0.551	32.999	0.000*
HL	0.851	7.067	0.001
PrePL	0.936	2.779	0.068
ED	0.614	25.421	0.000*
POL	0.514	38.218	0.000*
HD	0.840	7.729	0.001
PrDl	0.920	3.546	0.033
DSpL	0.885	5.248	0.007
DFBL	0.780	11.410	0.000*
PoDL	0.907	4.168	0.019
PFL	0.693	17.901	0.000*
BD	0.776	11.695	0.000*
CPD	0.831	8.227	0.001
PrPL	0.849	7.176	0.001
PeFI	0.509	39.099	0.000*
ASL	0.586	28.593	0.000*
AFL	0.916	3.735	0.028
HW	0.357	72.959	0.000*
LJL	0.925	3.279	0.043
MW	0.876	5.748	0.005
IOL	0.604	26.500	0.000*
DStI	0.846	7.393	0.001
BW	0.414	57.246	0.000*

*Significant level p < 0.001

Table IV. The mean value ± SD of the morphometric character of Trichopodus spp. from Sumatra waters.

Character	Trichopodus leerii (n = 19)	Trichopodus pectoralis (n = 15)	Trichopodus trichopterus (n = 50)
% HL
SnL	26.13 ± 3.08^a	24.15 ± 2.13^a	24.90 ± 3.39^a
SNW	30.82 ± 2.79^a	34.38 ± 1.52^b	37.14 ± 2.86^c
ED	32.31 ± 2.55^b	27.64 ± 2.86^a	32.70 ± 2.79^b
HD	77.36 ± 6.60^a	80.97 ± 5.56^a	80.97 ± 5.56^b
% SL
SnL	7.44 ± 0.98^b	6.42 ± 0.46^a	6.69 ± 0.98^a
SNW	8.76 ± 0.71^a	9.16 ± 0.45^b	10.04 ± 0.61^c
HL	28.47 ± 1.31^b	26.66 ± 1.29^a	27.12 ± 1.74^a
PrePL	31.59 ± 1.18^b	30.29 ± 1.46^a	31.17 ± 1.75^ab
ED	9.19 ± 0.65^a	7.37 ± 0.80^b	8.87 ± 0.94^a
POL	12.41 ± 0.66^a	14.47 ± 0.94^c	13.62 ± 0.67^b
HD	21.98 ± 1.54^b	20.45 ± 1.04^a	21.91 ± 1.38^b
PrDl	55.34 ± 4.28^ab	55.22 ± 1.32^a	57.04 ± 2.44^b
DSpL	4.07 ± 0.80^ab	3.85 ± 0.54^a	4.54 ± 0.85^b
DFBL	20.76 ± 2.57^a	25.07 ± 1.43^b	21.75 ± 3.28^a
PoDL	23.68 ± 2.47^b	22.10 ± 1.16^a	22.58 ± 1.25^a
PFL	28.57 ± 1.83^a	31.74 ± 1.07^b	28.79 ± 1.81^a
BD	43.46 ± 3.88^b	40.53 ± 2.19^a	39.89 ± 2.37^a
CPD	13.81 ± 1.06^a	15.39 ± 0.78^b	14.77 ± 1.27^b
PrPL	29.10 ± 2.38^b	26.89 ± 2.91^a	26.71 ± 2.01^a
PeFI	119.55 ± 8.95^b	95.89 ± 9.36^a	99.25 ± 8.14^a
ASL	8.29 ± 0.85^c	5.75 ± 0.61^a	6.83 ± 1.09^b
AFL	62.32 ± 4.98^a	64.91 ± 2.03^b	63.20 ± 2.42^ab
HW	13.00 ± 1.19^a	14.98 ± 0.78^b	15.74 ± 0.70^c
LJL	5.82 ± 0.49^ab	5.69 ± 0.55^a	6.10 ± 0.62^c
MW	6.58 ± 0.89^a	6.86 ± 0.60^ab	7.50 ± 1.24^c
IOL	10.25 ± 0.72^a	11.53 ± 0.65^b	11.51 ± 0.71^b
DStI	20.06 ± 1.35^b	18.88 ± 0.90^a	20.25 ± 1.30^b
BW	5.32 ± 0.35^a	6.13 ± 0.30^b	6.37 ± 0.44^b

Values followed by different superscripts show significant differences (p < 0.01).

Principal Component Analysis (PCA) generated three functions (see Table V). PC1 had an eigenvalue of 5.77, explaining 24.02% of the total variance. The major characteristics that contributed to this function are POL (Postorbital Length), CPD (caudal peduncle depth), PeFI (pelvic fin length), HW (head width), IOL (interorbital distance), and BW (body width). These factors are those related to head, body form and fins. PCA 2 had an eigenvalue value of 4.31, which explains 17.98% of the total variance, and the contributing characteristics are SNW (anterior snout width), PrePL (Prepectoral length), HD (head depth), LJL (lower jaw length), and DStI (distance snout to isthmus). PCA 3 had an eigenvalue value of 2.22, which explains 9.26% of the total variance, with the contribution of BD (body depth) characteristics (Table V). T. leerii was distinguished from two other species by plotting ED%HL and PFL characteristics against PeFL characteristics, whereas T. pectoralis was distinguished from two other species by plotting SNW%HL characteristics against PeFL (Figure 3(a,b)). On the basis of morphometric data, a dendrogram of the species was derived by the unweighted pair group (UPGMA) cluster analysis. The UPGMA cluster analysis based on the Euclidean distances between group centroids showed that the three species produced two major clusters. T. leerii (cluster I) and T. pectoralis and T. Trichopterus (cluster II) (Figure 4).

Table V. Eigenvalue, percentage of variance, and percentage of cumulative variance for three character factors on Trichopodus spp. from Sumatra waters.

	PCA 1	PCA 2	PCA 3
Eigenvalues	5.77	4.31	2.22
% of Variance	24.02	17.98	9.26
Cumulative %	24.02	42.00	51.26
SnL	−0.522	0.296	−0.055
SNW	0.517	0.624	0.004
HL	−0.530	0.537	0.169
PrePL	−0.489	0.682	0.051
ED	−0.566	0.554	0.036
POL	0.659	0.218	−0.016
HD	−0.171	0.656	0.329
PrDl	0.014	0.268	−0.575
DFL	−0.053	0.443	−0.420
DFBL	0.479	−0.273	0.457
PoDL	−0.222	0.061	0.335
PFL	0.266	0.028	0.435
BD	−0.154	−0.252	0.710
CPD	0.621	0.135	0.352
PrPL	−0.566	0.270	0.085
PeFI	−0.707	−0.028	0.414
ASL	−0.600	0.154	0.108
AFL	0.314	−0.134	−0.055
HW	0.734	0.468	0.025
LJL	0.117	0.617	0.208
MW	0.457	0.511	0.318
IOL	0.763	0.455	0.161
DStI	−0.315	0.724	−0.142
BW	0.661	0.403	−0.222

Significant loadings > 0.60.

Figure 3. (a). Scatter plot ED% HL vs PFL; (b). SNW% HL vs PeFL (

 = Trichopodus leerii,

 = Trichopodus pectoralis;

 = Trichopodus trichopterus). PFL = pectoral fin length; ED = eye diameter; PeFL = pelvic fin length; SNW = anterior snout width.

Figure 4. Dendrogram of Trichopodus spp. from Sumatra waters base on morphometric data.

Discussions

A total of three species of Trichopodus were recorded during the study, namely T. trichopterus, T. pectoralis, and T. leerii (Figure 5). Based on the total number of specimens, T. trichopterus was most predominant (76.56%) and had a wider local distribution, followed by T. pectoralis (12.50%) and T. leerii (10.94%). The results showed that the number of fish samples varies depending on the habitat types. Areas of river where water flows have fewer fish samples compared to stagnant waters. The findings indicated that the quantity of fish samples changes according to the kind of habitat. Compared to stagnant waters, areas of rivers where water is flowing have less fish samples. This shows that T. trichopterus is highly adaptable in various types of waters, which is reflected in a larger distribution and population number compared to the other two species (Haryono 2012; Huwoyon & Gustiano 2013; Gustiano et al. 2022). Nur et al. (2022a) reported the exact same phenomenon on Betta spp. from Aceh waters. Trichopodus leerii, on the other hand, has a limited distribution and has been labelled as “near threatened”, therefore that it is essential to maintain this species in nature even if there are more samples of T. leerii than T. pectoralis.

Figure 5. Representative specimens of each species (a) T. leerii; (b) T. pectoralis; (c) T. trichopterus.

Based on the MZB collection, T. trichopterus lives in various habitats. For example, in Aceh, this fish was found in paddy field and river, while in South Lampung and Riau, it was found in swamps and river. Thus, this study also shows that T. trichopterus is more adaptable than the other two species. This distinctive adaptability is probably related to the presence of a breathing apparatus (labyrinth), which enables oxygen (O₂) absorption directly from the atmosphere (Mendez‐Sanchez & Burggren 2019; Degani et al. 2021). T. leerii has been discovered in four provinces, namely West Sumatra at Teluk Bangka Lake, Lubuk Lampan, and Lempuing River in South Sumatra; at most of the rivers in Jambi and Riau Province. Trichopodus pectoralis has been discovered in four provinces, namely South Sumatra, Lampung, Riau and Jambi. In three provinces the species were found in the rivers except in Lampung where the species found in swamp.

Gustiano et al. (2021) found that closely related species have a significant amount of phenotypic similarities in terms of biometrics. Based on this study, it may be assumed that T. pectoralis and T. trichopterus, which share numerous morphometric characteristics, are likely to have a closer kinship. Three of the species under investigation share the same diploid number and fundamental number, which is 46 when all the chromosomes are telocentric. The chromosome numbers for T. leerii, T. pectoralis, and T. trichopterus’ (large-medium-small karyotypes) are 16–28-2, 20–26-0, and 10–30-6, respectively (Supiwong et al. 2021). Additionally, all species have a single pair of the marker chromosomes that display the NOR positions, but there are variations in their locations and pairs, such as pairs nos. 1, 7, 2, and 1, respectively. Most species, except for T. trichopterus, have NOR sites near the centromere in an interstitial region. Telomeric NORs are expressed in T. trichopterus. Constitutive heterochromatin blocks occurred at the centromeric/pericentromeric regions of all the chromosomes in T. leerii, whereas in T. pectoralis and T. trichopterus, they formed at interstitial sites in addition to the centromeres of many chromosomal pairs.

The same species were in the same cluster in this study despite coming from different places and habitat types, demonstrating the consistency of the results (Figure 4). Based on morphometric findings, genetic research carried out by other experts revealed conclusions that reinforced one another. One could claim that genetic analysis findings and morphometric data are consistent. Genetic diversity results in morphological changes, mostly in body shape, as a result of interactions between genetic and environmental factors, according to Hebert et al. (2003) and Crispo (2008). Barlow (1961) asserts that this is true particularly in the early phases of growth. Numerous non-genetic factors, such as those connected to water conditions like temperature, turbidity, water currents, geography or habitat, and dietary habits, can contribute to the presence of this variance. The water’s depth can also play a significant role in significantly influenced by the differences in sex, predators, populations, physiology, and food sources (Langerhans et al. 2004).

Conclusion

Regarding distribution, T. trichopterus is the widest, where it was found in 49 locations covering 7 provinces (LD 76.56%), followed by T. pectoralis (LD 12.50%), and T. leerii with the smallest one, found in only seven locations (LD 10.94%). Status of T. leerii is the near-threatened category, while the other two species belong to the least concern category. Plotting anterior snout width (SNW) characteristics against pelvic fin length (PeFL) was successful in differentiating T. leerii from 2 other species, while eye diameter (ED) and pectoral fin length (PFL) characteristics were successful in separating T. pectoralis from two other species. The three species, which come from different locations, are frequently seen together in one cluster. The research showed that the findings from morphometrics and genetics are consistent.

Authors’ contribution

There is equal contribution from each author. FMN wrote the initial draft after gathering and analyzing the facts. RG planned the study, examined and interpreted data, edited the writing, and completed the manuscript. H developed the project and contributed samples, and completed the manuscript. AWP edited the writing, and completed the manuscript.

Acknowledgements

The authors thanks to Dr. Bayu Adjie, Director of Research Center for Biosystematics and Evolution, National Research and Innovation Agency (BRIN) for his support and financing of the project. Mr. Sopian Sauri for his assistance in preparing materials. Thanks to Martin Wilkes for proofreading the article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by post doctoral fellowship in the Museum Zoologicum Bogoriense (MZB), Research Center for Bioystematics and Evolution, National Research and Innovation Agency, Indonesia, Contract Number 151/II/HK/2022.