The ecology and biogeography of Sri Lanka: a context for freshwater fishes.
Abstract
Despite advances in biodiversity exploration, the origins of Sri Lanka's fauna and flora have never yet been treated in a synthetic work. This book draws together the threads that make up that fascinating 100-million year story. Encompassing the island's entire biota while emphasising the ecology, biogeography and phylogeography of freshwater fishes, it provides a comprehensive context for understanding how the island's plants and animals came to be as they are. The 258-page text contains more than 200 figures, photographs and maps. It provides a clear account of how, when and from where the ancestors of the plants and animals that now inhabit Sri Lanka came. For the first time, the island's unique biodiversity can be understood and appreciated in its historical and evolutionary context in this invaluable sourcebook, designed for scientists, students and biodiversity enthusiasts alike.
... Our study fills that gap by describing H. brachyotus in detail, with H. srilankaensis as an allied species. Substantial similarity exists between Peninsular Indian and Sri Lankan faunal elements (Pearson & Ghorpade 1989;Ripley & Beehler 1990;Pethiyagoda & Sudasinghe 2021). The Sri Lankan fauna has been known to include a subset of the Indian fauna (Bossuyt et al. 2004;Biswas & Pawar 2006;Lajmi et al. 2019) and shows a high degree of morphological overlap with a mix of Indian and Southeast Asian origins (Bossuyt et al. 2004;Bauer et al. 2010;Pyron et al. 2013;Grismer et al. 2016;Pethiyagoda & Sudasinghe 2021), suggesting recent colonization events and multiple autochthonous diversifications. ...
... Substantial similarity exists between Peninsular Indian and Sri Lankan faunal elements (Pearson & Ghorpade 1989;Ripley & Beehler 1990;Pethiyagoda & Sudasinghe 2021). The Sri Lankan fauna has been known to include a subset of the Indian fauna (Bossuyt et al. 2004;Biswas & Pawar 2006;Lajmi et al. 2019) and shows a high degree of morphological overlap with a mix of Indian and Southeast Asian origins (Bossuyt et al. 2004;Bauer et al. 2010;Pyron et al. 2013;Grismer et al. 2016;Pethiyagoda & Sudasinghe 2021), suggesting recent colonization events and multiple autochthonous diversifications. ...
... However, craniodental measurements show significant increases in adapting to island life without increases in body size. It is noteworthy, however, that Sri Lanka has not been an island for most of its Cenozoic history but was connected to India by a broad isthmus except during brief sea-level high-stands (Pethiyagoda & Sudasinghe 2021). ...
Hipposideros galeritus was described in 1846, with subsequent studies suggesting four subspecies across South and Southeast Asia. Our study indicates that the Indian and Sri Lankan populations previously considered subspecies of H. galeritus are, in fact, distinct species in need of taxonomic revisions. Based on the morphometric analysis, structure of the baculum, molecular phylogenetics, and echolocation call analysis, the Indian, Sri Lankan, and Southeast Asian populations of Hipposideros galeritus are distinct. We provide a detailed description of H. brachyotus Dobson, 1874 and describe a new species—H. srilankaensis sp. nov.—from Sri Lanka. Key morphological differences were found in the noseleaf, ear shape, and cranial features between the Indian (H. brachyotus), Sri Lankan (H. srilankaensis sp. nov.), and Southeast Asian populations (H. galeritus s.l.). Substantial genetic distances were found between H. galeritus populations, suggesting cryptic diversity that is yet to be resolved.
... To date, Sri Lanka hosts a total of 127 species of freshwater fish, with 61 endemic and 30 introduced to the island (Goonatilake et al. 2020). Pethiyagoda and Sudasinghe (2021) noted that the wet zone contains 70 species of freshwater fish, followed by the intermediate zone (46) and dry zone (36), emphasizing the role of geographical and environmental diversity in shaping freshwater diversity in Sri Lanka. However, Sudasinghe et al. (2020) show that the nomenclature of Sri Lankan freshwater fish has been extensively revised during the past two decades, and many freshwater fish genera have been revised in order to evolutionary relationships. ...
... This unique freshwater ecosystem supports a few other endangered native fish species each having specific ecological requirements and habitat sensitivities. As an example, P. reval is represented in Deduru oya to Kelaniya Basin in slow and stagnant water flows (Pethiyagoda and Sudasinghe 2021). ...
... In contrast, P. reval ranges from the Kelani River to the Deduru River basin, with a translocated population in the Mahaweli River Basin. Furthermore, the other Pethia sp. is Pethia bandula, a point endemic species recorded in a narrow range of the "Galapitamda" area, "Minimaru Kolaniya," a stream connected to the Kelani River basin (Pethiyagoda and Sudasinghe 2021). ...
The Pusseli Oya, a tributary in the Kelani River Basin was investigated preliminary to assess the freshwater fish diversity with a particular focus on the endangered endemic species Pethia reval. This study highlights the urgent need for conservation actions to protect these unique ecosystems. Five distinct sites were selected for the study, and sampling was conducted from August to October 2024 us ing snorkeling, hand nets, and trawl nets complemented by measurements of physio-chemical parameters, including temperature, pH, and flow rate with anthropogenic activities. A total of 29 freshwater fish species were recorded, representing eight orders and 12 families, with Cyprinidae being the most dominant family. Among these, 10 species were endemic, highlighting the area's ecological importance. P. reval was recorded at most of the selected sampling sites but was absent in one sampling site, which displayed a lower pH and increased anthropogenic activities than other sites. These conditions and the presence of aquatic plants likely impacted the species' distribution, emphasizing its sensitivity to habitat disturbances. Findings reveal that sites with stable water quality and m inimal anthropogenic influence are essential for sustaining diverse fish populations and conserving P. reval and other endemics. This research underscores the need for immediate area-based conservation actions to mitigate human impacts and maintain ecological balance within the Kelani River basin. Those area-based conservation activities will contribute to broader conservation throughout the country with a special focus on range-restricted and nationally important freshwater fish fauna on the island. Future studies should focus on longitudinal assessments to strengthen conservation strategies for Sri Lanka's endemic and native freshwater fish.
... In Sri Lanka, a tropical continental island in the Indian Ocean with a land area of 65,610 km 2 , there are five species of Devario, four of which are considered endemic (Pethiyagoda & Sudasinghe, 2021). ...
... Notably, three of these endemics (D. memorialis, D. monticola, and D. pathirana) are narrowly distributed, often restricted to a single locality or river basin (Pethiyagoda & Sudasinghe, 2021). The fourth endemic, D. micronema, by comparison, is the most widely distributed of the endemic species of Devario in Sri Lanka. ...
... Devario malabaricus is considered as a habitat generalist because it utilises a wider range of environments and ecoclimatic zones (lotic and lentic; shaded and unshaded; clear and turbid; disturbed and undisturbed; from lowland floodplains to hill streams and torrents, at elevations ranging from sea level to about 1300 m above sea level). By contrast, D. micronema is considered as a habitat specialist as it utilises only a narrow range of environments (lotic, shaded, clear, undisturbed, rainforest streams in the perhumid southwestern wet zone from sea level to about 500 m above sea level) (Pethiyagoda & Sudasinghe, 2021;Schluter, 2000). ...
Sexual dimorphism, the phenotypic differences between males and females within a species, is widespread in the animal kingdom. This study investigates the extent of sexual dimorphism and species divergence in external morphology in two closely related freshwater fish species, Devario malabaricus and D. micronema , in Sri Lanka. Devario malabaricus , a habitat generalist, inhabits a wide range of aquatic environments, while D. micronema , a habitat specialist, resides in shaded rainforest streams. The study reveals size differences between the two species: D. malabaricus is consistently larger than D. micronema . However, there are no size differences between the sexes within each species. Several additional morphological traits, such as head length, interorbital width, predorsal length and postdorsal length display divergence between the species as well as between the sexes within each species; these patterns are also consistent across populations. The sexually dimorphic traits are similar between the two species despite their distinct ecological habitats. However, Devario malabaricus exhibit stronger sexual dimorphism compared to D. micronema , supporting the prediction of a positive relationship between the extent of sexual dimorphism and ecological generalism. The study highlights the importance of considering sexual dimorphism in morphometric comparisons in taxonomic studies of Devario and suggests that divergent selection between the sexes contributes to morphological variation in this group.
... Gymnothorax polyuranodon is one of the most elusive freshwater fishes in Sri Lanka. Several freshwater fishes that were considered to be very rare or even extinct, such as Labeo lankae (Cyprinidae) and Macrognathus pentophthalmos (Mastacembelidae), have been rediscovered and redescribed in the recent past (Pethiyagoda & Sudasinghe 2021;Sudasinghe et al. 2018). Three of the most rarely encountered fishes in Sri Lankan freshwaters are known to have a marine lifehistory phases (Pethiyagoda & Sudasinghe 2021): Kuhlia marginata (Cuvier) (kuhliidae), Stiphodon martenstyni Watson (gobiidae) and G. polyuranodon (Muraenidae). ...
... Several freshwater fishes that were considered to be very rare or even extinct, such as Labeo lankae (Cyprinidae) and Macrognathus pentophthalmos (Mastacembelidae), have been rediscovered and redescribed in the recent past (Pethiyagoda & Sudasinghe 2021;Sudasinghe et al. 2018). Three of the most rarely encountered fishes in Sri Lankan freshwaters are known to have a marine lifehistory phases (Pethiyagoda & Sudasinghe 2021): Kuhlia marginata (Cuvier) (kuhliidae), Stiphodon martenstyni Watson (gobiidae) and G. polyuranodon (Muraenidae). In all three cases, Sri Lanka seems to be the westernmost extremity of their ranges. ...
... Our record is in some 7 km along the river from Dodangoda, from where Deraniyagala (1952) reported his second specimen (Fig. 1A). While G. polyuranodon has not been reported from any other country bordering the Bay of Bengal, all records of this species appear to be associated with rainforest habitats (Pethiyagoda & Sudasinghe, 2021). If there is in fact an association with climate, perhaps as reflected in water quality, the distribution of G. polyuranodon could add another layer of complexity to the largely unknown life history of this species (Pethiyagoda & Sudasinghe, 2021). ...
Morays of the genus Gymnothorax are the most speciose of the Muraenidae. The genus consists of some 140 described
species distributed in the Atlantic, Pacific, and Indian Oceans (Fricke et al. 2023). While almost all the members of
Gymnothorax are obligatorily marine, adults of a single species, Gymnothorax polyuranodon (Bleeker), occupy freshwaters
(Ebner et al. 2011, 2016) and low salinity environments (Ebner et al. 2020).
... These claims by Vitanage are consistent with that of Emmel et al. (2012) who suggest that Sri Lanka is one of the most stable shield regions in the post-Gondwanan geological history. However, it should be noted that the orogeny of the physiography and geomorphology of Sri Lanka, especially of its highlands is still being understood (Cooray, 1984;Pethiyagoda and Sudasinghe, 2021). ...
... Northeasterlies blown above the Bay of Bengal before entering the island also bring a fair amount of water vapor that will again be intercepted by the highlands and distributed over a vast track of land, making the dry zone receive an annual precipitation less than 1800 mm per year, which is seasonal. In general agreement, the monsoons partition the country into four major climatic zones, such as the SWWZ, vast dry zone in the north and east, a transitional intermediate zone in between the above two, and a semi-arid zone along rain shadows (see Figure 23.2; also see the map of annual rainfall isohyets in Pethiyagoda and Sudasinghe, 2021). The narrow belt of an intermediate zone is found with an average annual precipitation of 1800-2500 mm y -1 , which crosses the western coast between Chilaw and Negombo and the southern coast between Tangalla and Matara. ...
... Although the climatic zones of Sri Lanka are defined primarily based on the annual rainfall, a note on the temperature and relative humidity would support understanding the heterogeneity of habitats even within the same climate zone. The relative humidity in the morning is kept high throughout the island, usually above 70% in supporting a high taxonomic diversity, whereas it can be as high as 90% in the perhumid lowland wet zone (Punyawardena, 2009;Pethiyagoda and Sudasinghe, 2021). According to Punyawardena (2009), the average annual maximum and minimum temperatures vary between 29°C-38°C and 20°C-26°C throughout the dry zone, while the highest temperature is in the northern coastal belt. ...
... Puntius kelumi [1] Puntius dorsalis [3] Puntius mahecola Plesiopuntius bimaculatus [2] [3] ...
... Puntius terio [4] Bhava vittata [1] Puntius sophore [2] Plesiopuntius bimaculatus [1] Puntius thermalis [6] Plesiopuntius bimaculatus [3] [5] Puntius kelumi [2] Puntius kelumi [3] [7] [8] Puntius dorsalis [2] Puntius kamalika Figure 1. Bayesian time-calibrated tree, based on the cytb substitution rate, for the concatenated mitochondrial + nuclear (3964 bp, 22 taxa) dataset of Puntius s.l. ...
... Puntius terio [4] Bhava vittata [1] Puntius sophore [2] Plesiopuntius bimaculatus [1] Puntius thermalis [6] Plesiopuntius bimaculatus [3] [5] Puntius kelumi [2] Puntius kelumi [3] [7] [8] Puntius dorsalis [2] Puntius kamalika Figure 1. Bayesian time-calibrated tree, based on the cytb substitution rate, for the concatenated mitochondrial + nuclear (3964 bp, 22 taxa) dataset of Puntius s.l. ...
Sri Lanka's biota is derived largely from Southeast Asian lineages which immigrated via India following its early-Eocene contact with Laurasia. The island is now separated from southeastern India by the 30 km wide Palk Strait which, during sea-level low-stands, was bridged by the 140 km-wide Palk Isthmus. Consequently, biotic ingress and egress were mediated largely by the climate of the isthmus. Because of their dependence on perennial aquatic habitats, freshwater fish are useful models for biogeographic studies. Here we investigate the timing and dynamics of the colonization of-and diversification on-Sri Lanka by a group of four closely-related genera of cyprinid fishes (Puntius sensu lato). We construct a molecular phylogeny based on two mitochondrial and two nuclear gene markers, conduct divergence timing analyses and ancestral-range estimations to infer historical biogeography, and use haplotype networks to discern phylogeographic patterns. The origin of Puntius s.l. is dated to ~ 20 Ma. The source of diversification of Puntius s.l. is Sri Lanka-Peninsular India. Species confined to perhumid rainforests show strong phylogeographic structure, while habitat generalists show little or no such structure. Ancestral range estimations for Plesiopuntius bimaculatus and Puntius dorsalis support an 'Out of Sri Lanka' scenario. Sri Lankan Puntius s.l. derive from multiple migrations across the Palk Isthmus between the early Miocene and the late Pleistocene. Species dependent on an aseasonal climate survived aridification in rainforest refugia in the island's perhumid southwest and went on to recolonize the island and even southern India when pluvial conditions resumed. Our results support an historical extinction of Sri Lanka's montane aquatic fauna, followed by a recent partial recolonization of the highlands, showing also that headwater stream capture facilitated dispersal across basin boundaries.
... confined to the southwestern wet zone, while the former is distributed in both the wet zone and the 102 northern dry zone lowlands 1,11 . The remaining four species are shared between Sri Lanka and southern 103 ...
... Menik basins, reflecting the phylogeographic patterns observed also for Garra ceylonensis Bleeker. This 379 suggests that the headwaters of the island's south-eastern rivers, such as the Walawe, Menik, and Gal 380 once served as drought refugia 1,26 . This is evidenced also by their harboring greater genetic diversity even 381 now. ...
Sri Lanka’s biota is derived largely from Southeast Asian lineages which immigrated via India following its early-Eocene contact with Laurasia. The island is now separated from southeastern India by the 30 km wide Palk Strait which, during sea-level low-stands, was bridged by the 140 km-wide Palk Isthmus. Consequently, biotic ingress and egress were mediated largely by the climate of the isthmus. Because of their dependence on perennial aquatic habitats, freshwater fish are useful models for biogeographic studies. Here we investigate the timing and dynamics of the colonization of—and diversification on—Sri Lanka by a group of four closely-related genera of cyprinid fishes ( Puntius sensu lato). We construct a molecular phylogeny based on two mitochondrial and two nuclear gene markers, conduct divergence timing analyses and ancestral-range estimations to infer historical biogeography, and use haplotype networks to infer phylogeographic patterns. The origin of Puntius s.l. is dated to ~20 Ma. The source of diversification of Puntius s.l. is Sri Lanka-Peninsular India. Species confined to perhumid rainforests show strong phylogeographic structure, while habitat generalists show little or no such structure. Ancestral range estimations for Plesiopuntius bimaculatus and Puntius dorsalis support an ‘Out of Sri Lanka’ scenario. Sri Lankan Puntius s.l. derive from multiple migrations across the Palk Isthmus between the early Miocene and the late Pleistocene. Species dependent on an aseasonal climate survived aridification in rainforest refugia in the island’s perhumid southwest and went on to recolonize the island and even southern India when pluvial conditions resumed. Our results support an historical extinction of Sri Lanka’s montane aquatic fauna, followed by a recent partial recolonization of the highlands, showing also that headwater stream capture facilitated dispersal across basin boundaries.
... The island nation of Sri Lanka, has a diverse array of habitats (Gunatilleke et al., 2008) that support a rich biodiversity (Pethiyagoda & Sudasinghe, 2021). Of the 91 species of extant terrestrial mammals in the country, 31 belong to the order Chiroptera. ...
Sri Lanka supports a high biodiversity and nearly one third of its mammalian fauna comprise of bats. Sri Lanka’s bats are understudied with few data available about their roosting habits, particularly in agricultural ecosystems. Here we report the findings of a preliminary survey, conducted to explore how bats use available anthropogenic structures in rubber plantations. We inspected abandoned buildings within six rubber plantations in Deraniyagala for the presence of bats. Eleven of the 14 abandoned buildings inspected were occupied by bats, viz, lesser false vampire bat (Megaderma spasma) and rufous horseshoe bat (Rhinolophus rouxii). Our results indicate that bats use anthropogenic structures for day roosting and as maternity roosts, as the presence of young-of-the-year (YOY) were observed in one of the roosts. We recommend implementing economically viable conservation measures such as creating artificial tree hollows and erecting artificial roosts like bat boxes in rubber plantations to provide permanent habitats for bats, as abandoned buildings may be demolished or repurposed in the near future.
This study focuses on Macrognathus pentophthalmos, one of the two freshwater spiny eel species in Sri Lanka, which was once abundant in lowland floodplains. However, since the 1980s, this species has experienced a significant population decline, the causes of which remain unknown. It is presently assessed as Critically Endangered in the National Red List. Here, we report on a juvenile and an adult M. pentophthalmos discovered in the dry zone lowlands of the island. Using the mitochondrial cytochrome oxidase subunit 1 marker, we reveal subtle genetic differences between M. pentophthalmos and its Indian congener, M. aral. Additionally, we delve into the historical records of M. pentophthalmos in Sri Lanka, tracing its decline, and suggest strategic hotspots for further investigation into its current status. This study aims to contribute insights into the enigmatic decline of this species while shedding light on its genetic relationships and proposing targeted areas for conservation efforts.
During the past decade, the ca 120 species of small, colourful tropical Asian freshwater fishes previously referred to the cyprinid genus Puntius have been shown to consist of multiple morphologically distinct evolutionary lineages that resolve as monophyletic groups in molecular studies. Many of these clades have been allocated to new genera such as Dawkinsia, Desmopuntius, Haludaria, Oliotius,
Pethia, Puntigrus, Sahyadria, Striuntius and Waikhomia. Others have been assigned to existing but previously poorly delineated genera such as Barbodes and
Systomus, while some 40 species remain in Puntius. The divergent morphology
of several species retained in Puntius suggests, however, that the systematics of
this group requires further attention. Here, based on a phylogeny incorporating
newly generated data from the mitochondrial cytochrome b (cytb), mitochondrial
cytochrome c oxidase subunit 1 (cox1), nuclear recombination activating protein
1 (rag1), and interphotoreceptor retinoid-binding protein (irbp) gene markers,
we investigate the interrelationships of the species of Puntius in Sri Lanka in the
wider context of their Indian and Southeast Asian congeners. We identify three
well-supported monophyletic groups that warrant recognition as new genera:
Rohanella (type species Puntius titteya), Plesiopuntius (type species Gnathopogon
bimaculatus) and Bhava (type species Puntius vittatus). The first of these is endemic to rainforest streams in Sri Lanka's perhumid southwestern wet zone,
whereas the latter two are widely distributed in both Sri Lanka and southern
India, including the Western Ghats. Our study highlights the presence of distinct
evolutionary lineages among several widespread species.
Background
Sri Lanka is a continental island separated from India by the Palk Strait, a shallow-shelf sea, which was emergent during periods of lowered sea level. Its biodiversity is concentrated in its perhumid south-western ‘wet zone’. The island’s freshwater fishes are dominated by the Cyprinidae, characterized by small diversifications of species derived from dispersals from India. These include five diminutive, endemic species of Pethia ( P. bandula , P. cumingii , P. melanomaculata , P. nigrofasciata , P. reval ), whose evolutionary history remains poorly understood. Here, based on comprehensive geographic sampling, we explore the phylogeny, phylogeography and morphological diversity of the genus in Sri Lanka.
Results
The phylogenetic analyses, based on mitochondrial and nuclear loci, recover Sri Lankan Pethia as polyphyletic. The reciprocal monophyly of P. bandula and P. nigrofasciata , and P. cumingii and P. reval , is not supported. Pethia nigrofasciata , P. cumingii , and P. reval show strong phylogeographic structure in the wet zone, compared with P. melanomaculata , which ranges across the dry and intermediate zones. Translocated populations of P. nigrofasciata and P. reval in the Central Hills likely originate from multiple sources. Morphological analyses reveal populations of P. nigrofasciata proximal to P. bandula , a narrow-range endemic, to have a mix of characters between the two species. Similarly, populations of P. cumingii in the Kalu basin possess orange fins, a state between the red-finned P. reval from Kelani to Deduru and yellow-finned P. cumingii from Bentara to Gin basins.
Conclusions
Polyphyly in Sri Lankan Pethia suggests two or three colonizations from mainland India. Strong phylogeographic structure in P. nigrofasciata , P. cumingii and P. reval , compared with P. melanomaculata , supports a model wherein the topographically complex wet zone harbors greater genetic diversity than the topographically uniform dry-zone. Mixed morphological characters between P. bandula and P. nigrofasciata , and P. cumingii and P. reval , and their unresolved phylogenies, may suggest recent speciation scenarios with incomplete lineage sorting, or hybridization.
Asian pit vipers belonging to the genus Craspedocephalus are a complex group of vipers, distributed in South and Southeast Asia. Their taxonomy is unresolved in many lineages across their distributional range. Here, we reassess the taxonomy and systematics of pit vipers of the genus Craspedocephalus in Peninsular India based on extensive field sampling, in particular in the Western Ghats. We build and expand on the previous findings of genetic relatedness between the peninsular Indian lineages with the Sundaic clade ( C. puniceus complex) with greater evidence, based on additional taxa sequenced herein. We reconstruct the phylogeny of the group using three mitochondrial genes and delineated lineages using coalescent species delimitation methods. We then used multiple criteria including genetic divergence and separation in morphological and geographic space to designate taxonomic units. Our work revealed the presence of a South Asian radiation of the clade Craspedocephalus , with a few Sundaic members. Our study reveals the systematic relationships of four Peninsular Indian species of Craspedocephalus , including Peltopelor macrolepis and C. strigatus , sequenced here for the first time, that are classified or confirmed as members of Craspedocephalus . Hence, we place the genus Peltopelor in the synonymy of Craspedocephalus . Using our multi-criteria approach, we delimit four new cryptic evolutionary lineages within the Western Ghats escarpment of Peninsular India. These cryptic lineages belong to the C. malabaricus , C. gramineus and C. macrolepis complexes and are geographically and/or ecologically (in terms of habitat association) distinct from their sister lineages across their distributional range, while others are separated in morphological space. Our new phylogenetic tree and delimitation analysis thus reveals the presence of multiple clades with several cryptic lineages separated by geographical barriers or habitat association.
We examined the phylogenetic relationships of South Asian bulbuls with focus on endemic species to understand the historical biogeography of the region. Molecular phylogenetic analysis, divergence date estimation and ancestral area reconstruction were performed to understand the role of paleoclimate on extant bulbul diversity and their distribution. We tested for vicariance, dispersal and in situ speciation events that defined the bulbul assemblage in the region. Using morphometric data and phylogeny, we resolved taxonomic uncertainties. There was a single event of in situ speciation of a dry-zone species, and isolation of species to the wet zone, causing endemism. Diversification rates remained relatively constant during late Miocene and Pliocene. Sundaland-Philippines served as the seat of diversification of bulbul lineages, and Indochina was part of the dispersal route. Bulbul diversity in the region has been shaped due to dispersal events at different time periods ranging from late Miocene to early Pleistocene. Post-Miocene aridification was an important driver of diversification in the region, by creating barriers for wet-zone species, and opening up new habitats for dry-zone species.
The Indian subcontinent has an origin geologically different from Eurasia, but many terrestrial animal and plant species on it have congeneric or sister species in other parts of Asia, especially in the Southeast. This faunal and floral similarity between India and Southeast Asia is explained by either of the two biogeographic scenarios, ‘into-India’ or ‘out-of-India’. Phylogenies based on complete mitochondrial genomes and five nuclear genes were undertaken for ricefishes (Adrianichthyidae) to examine which of these two biogeographic scenarios fits better. We found that Oryzias setnai , the only adrianichthyid distributed in and endemic to the Western Ghats, a mountain range running parallel to the western coast of the Indian subcontinent, is sister to all other adrianichthyids from eastern India and Southeast–East Asia. Divergence time estimates and ancestral area reconstructions reveal that this western Indian species diverged in the late Mesozoic during the northward drift of the Indian subcontinent. These findings indicate that adrianichthyids dispersed eastward ‘out-of-India’ after the collision of the Indian subcontinent with Eurasia, and subsequently diversified in Southeast–East Asia. A review of geographic distributions of ‘out-of-India’ taxa reveals that they may have largely fuelled or modified the biodiversity of Eurasia.
Aim
Sea‐level changes have long been put forward to explain the colonization of Southeast Asian islands by freshwater aquatic organisms. We examined the relative impact of Sundaland geology since the Oligocene and of Pleistocene Eustatic Fluctuations on the mitochondrial lineage diversification of a species‐rich subfamily of freshwater fishes widely distributed in Southeast Asia. We specifically tested if the expansion of exposed lands and increased island connectivity during Pleistocene low sea levels (the paleoriver hypothesis) induced bursts of diversification.
Location
Sundaland.
Taxon
Rasborinae (Actinopterygii, Cypriniformes, Danionidae).
Methods
We aggregated 1,017 cytochrome oxidase I sequences and 79 mitogenomes to delineate Molecular Operational Taxonomic Units (MOTUs) and further reconstruct a time‐calibrated phylogeny of Rasborinae. Ancestral area estimations were conducted using both island and paleoriver partitioning to examine the impact of island connectivity during Pleistocene sea‐level changes on dispersal. Temporal trends of diversification are explored through statistical selection of best‐fit models.
Results
The origin of Sundaland mitochondrial lineages is dated at c. 33 Ma and four major clades are identified, which diversified between c. 31 and 22 Ma. The Island of Borneo and North Sunda paleoriver are identified as the source of Sundaland Rasborinae. Geographical patterns of lineage divergence indicate that most divergence events occurred within islands and diversification under constant birth rate models are the most likely for all clades.
Conclusions
The geographical and historical context of diversification of mitochondrial lineages in Rasborinae provides little support for the paleoriver hypothesis. The onset of isolation of Borneo from mainland Asia triggered the initial diversification of the group (c. 31–22 Ma). The late colonization of Java and Sumatra occurred through several independent dispersal events, poorly explained by Pleistocene sea‐level changes and frequently followed by in situ diversification.
The presence of eademic genera of restricted distribution occurring in Peninsular India and Sri Lanka is analysed in terms of its phytogeography. The genera are mainly of the palaeoendemic type. There are about 56 endemic genera in Peninsular India (Nayar, 1980) while in Sri Lanka there are only 20 genera. The presence of common genera (27 genera) with restricted distribution in Peninsular India and Sri Lanka is interesting from the phytogeographical angle.
There is comparatively high degree of endemism in Peninsular India and thus the flora is distinct. Blasco (1971) has estimated about 1,268 endemic dicotyledons in South India. The Peninsular India has an endemic concentration of 32% while rest of India has about 27% endemics. Out of the 304 families of flowering plants recorded from India, there is not a single endemic family. In this paper the phytogeography of endemic genera and characteristic endemic species of Peninsular India are analysed in relation to its distribution and affinities. The distribution is also analysed in relation to plate tectonics.The endemic angiosperms of Peninsular India consist of about 56 genera and they are distributed over 25 families. The families with the largest numbr of endemic genera are Gramineae (10 genera) and Acanthaceae (9 genera). There are about 2100 endemic species in Peninsular India of which 890 are woody species, 254 semi-woody and the rest 859 are herbaceous species. The endemic flora of Peninsular India is considered to be old one and the nature of endemics is analysed in terms of phytogeography, taxonomy and palaeobotany. The dynamics of characteristic endemic genera and their speciation is given. According to the analysis, majority of the endemics are palaeoendemics belonging to humid tropic belt. Wherever interphase of climatic shifts occur with different ecotones some endemic genera show epibiotic speciation.
The cyprinid genus Dawkinsia comprises 13 species distributed in lowland streams and rivers in southern peninsular India and Sri Lanka. Eleven species are endemic to India, largely restricted to streams draining the Western Ghats, while one is confined to the Knuckles Hills of Sri Lanka. One species, D. filamentosa, has a wide range, straddling the island and mainland. Here, based on 135 samples representative of all 13 species, collected from 45 locations in India and 17 in Sri Lanka, we present phylogenetic and phylogeographic analyses of Dawkinsia. We use two mitochondrial markers—cytochrome b and cytochrome c oxidase subunit 1. Dawkinsia is recovered as paraphyletic with respect to Sahyadria, with strong node support. The ‘filamentosa group’ which includes both Sri Lankan and Indian taxa (D. filamentosa, D. crassa, D. rohani, D. exclamatio, D. srilankensis, D. tambraparniei, D. arulius, D. rubrotincta and D. uttara) is recovered as the sister group of Sahyadria, a genus confined to the Western Ghats. The ‘assimilis group’, which consists entirely of Indian endemics (D. assimilis, D. austellus, D. apsara and D. lepida), is recovered as the sister group of the ‘filamentosa group’ + Sahyadria. Ancestral-range estimates indicate two colonization events from India to Sri Lanka, across the Palk Isthmus. The first of these, in the Pliocene, involved the common ancestor of D. tambraparniei and D. srilankensis, while the second was of D. filamentosa in the late Pleistocene. Dawkinsia filamentosa shows little phylogeographic structure within or between Sri Lanka and India. Ancestral-range analyses suggest that neither the Palghat nor Shencottah Gaps acted as barriers to the north–south dispersal of Dawkinsia along the Western Ghats. Instead, these valleys appear to have offered lowland passages for west–east colonization by some ancestral species across the Western Ghats ridge. Despite the Palk Isthmus having been subaerial for much of the Plio-Pleistocene and serving as the only terrestrial biotic corridor connecting Sri Lanka to the Asian mainland, it appears to have served also as a climatic filter to dispersal following the aridification of south-eastern India during the Late Miocene/early Pliocene.
In recent years, several studies have revealed significant unknown and cryptic diversity of agamids in peninsular India, particularly in the Western Ghats. Here, we examine the morphology, anatomy and genetics of the sole Indian representative of the otherwise Sri Lankan agamid genus Otocryptis from the Western Ghats. Our analyses reveal significant distinctions in O. beddomii Boulenger, 1885 with respect to the Sri Lankan members, the type species, O. wiegmanni Wagler, 1830, and O. nigristigma Bahir & de Silva, 2005, warranting a new generic placement. To accommodate the divergent and allopatric O. beddomii from the Western Ghats, we erect a new genus Agasthyagama gen. nov. We re-characterise Agasthyagama beddomii (Boulenger, 1885) comb. nov. based on a syntype (ZSI 15733) and recently collected material. In effect, we restrict the genus Otocryptis, represented by two species, O. wiegmanni and O. nigristigma, to Sri Lanka. We also provide a re-appraisal of the genus Otocryptis sensu stricto, based on data from its type species O. wiegmanni. Our finding adds another endemic agamid genus to the Western Ghats, following Salea Gray, 1845, and the recently described Monilesaurus Pal, Vijayakumar, Shanker, Jayarajan & Deepak, 2018, and Microauris Pal, Vijayakumar, Shanker, Jayarajan & Deepak, 2018. In turn, this complements Sri Lankan agamid endemism with Otocryptis, in addition to the accepted endemic radiations of Lyriocephalus Merrem, 1820, Ceratophora Gray, 1835 and Cophotis Peters, 1861. From a systematic perspective, our erection of Agasthyagama gen. nov. likely completes the description of known genus-level diversity in the clade containing Otocryptis Wagler 1830, Sitana Cuvier, 1829 and the recently described Sarada Deepak, Karanth & Giri, 2016.
Sri Lanka consists of only ten percent of sedimentary rocks, and high-grade metamorphic rocks underlie the rest. Most of these sedimentary terrains are post-Gondwanic and such formations help to understand the geological history of the island. We report the first record of an age diagnostic (Late Jurassic-Early Cretaceous) palynological assemblage of the sedimentary rocks in the Andigama basin (borehole AND BH01) Sri Lanka. The study was undertaken to assess the palaeoenvironmental settings in this basin based on palynological and palynofacies investigations. A palynofloral study suggests luxuriant gymnospermous forests proliferation in the Andigama Basin during this time. The palynological assemblage is characterized by the predominance of coniferous pollen grains of Araucariacites spp., Callialasporites spp. Along with some stratigraphically significant taxa viz., Cicatricosisporites spp., Aequitriradites verrucosus, Triporoletes sp., Impardecispora indica, Concavissimisporites verrucatus, Distaltriangulisporites perplexus, Verrucosisporites verrucosus, and Contignisporites fornicates of Tithonian-Berriasian time. Palynofacies records suggest three distinct Palynofacies Assemblages (PF 1-3). PF 1 indicates the forest swamp; PF 2 represents the mixed assemblage of forest swamp and reed marshes, while PF 3 suggests reed marshes/lakeshore deposits under oxic-anoxic environments. These palynofacies assemblage along with variable lithological counterparts varying from carbonaceous shale laminae interlayered with calcareous sandstone to brown shale and carbonaceous shale strata reflects diverse hydrodynamic conditions. Palynofloral and palynofacies records of the present study denote the warm and humid climatic conditions, which directly corroborates with global oxygen isotopic studies of the Late Jurassic-Early Cretaceous sediments.