Diversity and distribution of mayflies (Insecta: Ephemeroptera) in the “sky islands” of Palni Hills, Western Ghats, India

Chellappa Selvakumar

Department of Zoology, The Madura College (Autonomous), Madurai-625 011, Tamil Nadu, India.

https://orcid.org/0000-0002-4296-5682

Chandran Ashokkumar

Department of Zoology, The Madura College (Autonomous), Madurai-625 011, Tamil Nadu, India.

https://orcid.org/0009-0002-2400-7453  

Shunmugavelayutham Sundar

Division of Ecology and Environmental Sciences, S.S.Research Foundation, Kallidaikurichi -627416, Tamil Nadu, India.

https://orcid.org/0000-0001-6456-1147

Fabio De Oliveira Roque

Departamento de Biología, Universidade Federal de Mato Grosso do Sul, Cidade Universitaria, Pioneiros, Campo Grande, MS, 79070-900, Brazil [1]; Centre for Tropical Environmental and Sustainability Science and College of Science and Engineering, James Cook University, Douglas, Cairns, 4811, Queensland, Australia.

https://orcid.org/0000-0001-5635-0622

Mariappan Gunasekaran

Division of Plant Sciences, S.S.Research Foundation, Kallidaikurichi -627416, Tamil Nadu, India.

https://orcid.org/0000-0002-6664-0057

ABSTRACT. The Palni Hills, part of the Western Ghats Mountain range in southern India, constitute a biodiversity hotspot, and their high elevation creates unique ecological conditions. Despite global recognition of the region as a biodiversity hotspot, many taxonomic groups remain poorly studied, including mayflies. We conducted a survey of mayflies in the Palni Hills to document the current diversity profile and analyse their altitudinal distribution patterns, ranging from 346 to 1685 m asl. Our sampling from April to October 2023 covered eleven sites, resulting in the collection of 788 individuals, representing 24 species, 16 genera, and six families. Four species are reported for the first time from Palni Hills. Notably, the families Baetidae, Heptageniidae, and Leptophlebiidae were the most species-rich, although individual population densities remained low. We have provided the updated taxonomic hierarchy, current diversity profile, and abundance of mayflies of Palni Hills. We have also highlighted the knowledge gaps in the taxonomy and distribution of Ephemeroptera within this study area.

Keywords: aquatic insects, biodiversity hotspot, conservation, elevation, richness

Citation: Selvakumar, C., Ashokkumar, C., Sundar, S., De Oliveira Roque, F. & Gunasekaran, M. (2025) Diversity and distribution of mayflies (Insecta: Ephemeroptera) in the “sky islands” of Palni Hills, Western Ghats, India. Journal of Insect Biodiversity and Systematics, 11 (x), xx–xx.

Present-day patterns of montane diversity, be it aquatic or terrestrial, are broadly structured by geological, eco-climatic, hydrological and human-impacted historical events, which can shape species coexistence at different spatio-temporal scales (Gaston, 2000; Benton et al., 2009; Baker et al., 2014). The genetic consequences of these historical events are manifested in phylogeographic patterns, especially for lentic and lotic macroinvertebrates in “sky islands”, which are montane regions isolated from one another by intervening valleys with dramatically different environmental conditions in a similar way to how the sea separates oceanic islands (Mc Cormack et al., 2009). Species restricted to “sky islands”, aquatic taxa in particular, often show unique patterns of population genetic structure influenced by historical climate-induced distributional shifts (Pan et al., 2019). In other words, “sky islands” are critical ‘natural laboratories’ for understanding the ecological and evolutionary consequences of geographical isolation, range shifts and genetic diversity distribution under climate change scenarios (Taubmann et al., 2011).

Despite the ecological and evolutionary importance of “sky islands”, many taxonomic groups remain poorly studied, including mayflies. Gaps in taxonomic knowledge of mayflies, particularly the undescribed species (Linnean shortfalls), and the lack of comprehensive data on species’ geographical distribution (Wallacean shortfall) hinder our understanding of biodiversity, speciation, and conservation, especially in isolated ecosystems like “sky islands” (Hortal et al., 2015; Gueuning et al., 2017; Love et al., 2023). Mayflies (Ephemeroptera) are primitive and ancient extant insect groups. They are considered as efficient biological indicators and model organisms for integrated phylogenetic, biogeographic, and phylogeographic studies (Selvakumar et al., 2016a). 3,700 species, 465 genera, and 42 families are reported globally, except for Antarctica (Jacobus et al., 2019). Ephemeroptera fauna of India is represented by four suborders, 15 families, 63 genera, and 247 species, including 182 endemic species (Subramanian et al., 2024). The Western Ghats, being a biodiversity hotspot region, harbours 13 families, encompassing 42 genera and 82 species, and of these, seven genera and 60 species are endemic. Tamil Nadu, which is part of the Western Ghats, has more species diversity than other parts and has 44 species that belong to 29 genera and 10 families (Sivaramakrishnan et al., 2020).

In tropical biodiversity hotspots, such as the Western Ghats, aquatic ecosystems have been increasingly threatened, directly or indirectly, by human activities (Sundar et al., 2020). In addition to the challenges posed by land-use change, environmental pollution, and water diversion, aquatic systems experience the added stress of climate change and global warming (Sundar et al., 2021). Despite previous studies (Sivaramakrishnan & Job, 1981; Sivaramakrishnan et al., 1990; Selvakumar et al., 2014a; Barathy et al., 2020, 2021a), there is limited information on the diversity and distribution of mayflies in the “sky islands” of the Western Ghats in general and Palni Hills in particular (Sivaramakrishnan & Venkataraman, 1990; Barathy et al., 2021a, 2021b). Hence, the present study aims to contribute to the current diversity profile and abundance of mayfly communities across the “sky islands” of southern and northern Palni Hills and an altitudinal gradient in the Palni Hills of the Western Ghats. This documentation will serve as a foundation for further research and conservation efforts in the region.                         

MATERIAL AND METHODS

Study area. The Palni Hills in the Dindigul District of Tamil Nadu form an eastward extension of the Western Ghats of India. They span a maximum east-west length of 65 km and a north-south width of 40 km, situated between latitudes 10.12° N and 10.15° N, and longitudes 77.26° E and 77.33° E, covering an area of 2068². The peaks rise to over 2500 m asl, marking the region as one of the significant global biodiversity hotspots known for its high endemism. The Palni Hills are divided into two different mountains, namely southern and northern Palni Hills. Sampling was conducted at eleven sites: Kumbakkarai Falls I, Kumbakkarai Falls II, Moolaiyaru River, a stream near Munishwararkovil, Adukkam Falls, Perumalmalai Stream, Varaiyaru Falls, Umaiyaru River, Thaliyuthu Falls, Thalakuthu Main Falls, and Nallathangal Streams (Fig. 1). The first six study sites were selected from the southern Palni Hills, and the remaining five from the northern Palni Hills (Table 1). This study underscores the significance of selecting diverse habitats based on factors such as altitude, accessibility, and the presence of suitable habitats to get representative samples of the mayfly population in the region.

Specimen collection, preservation and identification. Nymphs or larvae were collected from April to October, 2023 using an aquatic D-frame net, hand picking with a brush or forceps, and kick net method (mesh size; 0.5 to 1.0 mm) at the study sites. The kick net was placed in the opposite direction to the water current to collect organic debris and insects. At each site, the substratum, bed rocks, boulders, and cobbles were vigorously disturbed. The collected specimens were preserved in 70–80% ethyl alcohol and brought to the laboratory. The specimens were examined under a Leica^® S-APO stereo-zoom microscope. Photos were processed, and plates were made using Adobe^® Photoshop version CS5. The mayfly larvae were classified up to the genus level using a handbook on morphological and molecular identification of southern Indian mayflies by Selvakumar et al. (2019) and further identified up to the species level through relevant published mayfly taxonomic articles. Linear regression was done using the Microsoft Office tool and analysed to evaluate the relationship between species abundance and elevation.

Figure 1. Geographic locations of the sampling sites in the Palni Hills, Western Ghats of India.

Table 1. Details of the collection sites in Palni Hills, Western Ghats of India.

RESULTS

A total of 788 individuals were collected from 11 sampling sites, classified into 24 species, 16 genera, and six families (Tables 2 & 3). The family Leptophlebiidae is represented by seven species belonging to 5 genera, each genus with a single species, except the genus Choroterpes Eaton, 1881, which includes three species. The family Baetidae is represented by eight species from 6 genera, with each genus containing a single species, except for the genus Baetis Leach, 1815 and Labiobaetis Novikova & Kluge, 1987, each of which is represented by two species. The family Heptageniidae includes two genera and four subgenera, each subgenus with a single species. The families Teloganodidae and Caenidae are represented by a single genus with two species. The family Ephemeridae consisted of 1 genus with a single species.

Taxonomic hierarchy

Class Insecta Linnaeus, 1758

Order Ephemeroptera Hyatt & Arms, 1891

Family Leptophlebiidae Banks, 1900

Genus Choroterpes Eaton, 1881       

Subgenus Euthraulus Barnard, 1932

Choroterpes (Euthraulus) alagarensis Dinakaran, Balachandran & Anbalagan, 2009 (Fig. 2A)

Choroterpes (Euthraulus) alagarensis Dinakaran, Balachandran & Anbalagan, 2009, 2064:22, Holotype ♂ imago, Nuburagangai stream, Tamil Nadu, India.

Material examined. 1 larva, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 3 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 6 larvae, Munishwarar Kovil, 10°16'30" N, 77°35'38" E, 1271 m, 27-iv-2023; 7 larvae, Thaliyuthu Water Falls, 10°26'33" N, 77°41'09" E, 346 m, 02-vii-2023; 3 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 10 larvae, Nallathangal Stream, 10°23'58" N, 77°36'49" E, 586 m, 02-vii-2023; 1 larva, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Karnataka, Kerala & Tamil Nadu (Dinakaran et al., 2009; Kluge et al., 2022a).

Table 2. List of mayflies collected from Southern Palni Hills.

Choroterpes (Euthraulus) atelobranchis Kluge, Srinivasan, Vasanth, Sivaruban, Barathy, & Isack, 2022 (Fig. 2B)

Choroterpes (Euthraulus) atelobranchis Kluge, Srinivasan, Vasanth, Sivaruban, Barathy, & Isack, 2022, 5181:13, Holotype L-S-I♂ Veerapandi River, Theni district, Tamil Nadu, India.

Material examined. 29 larvae, Thaliyuthu Water Falls, 10°26'33" N, 77°41'09" E, 346 m, 02-vii-2023; 3 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Kluge et al., 2022a).

Choroterpes (Euthraulus) nambiyarensis Selvakumar, Arunachalam & Sivaramakrishnan, 2013 (Fig. 2C)

Choroterpes (Euthraulus) nambiyarensis Selvakumar, Arunachalam & Sivaramakrishnan 2013, 47:71, Holotype, mature nymph – Nambiyar River, Tamil Nadu, India.

Material examined. 50 larvae, Kumbakkarai Falls I, 10°10’24" N, 77°32'13" E, 353 m, 14-x-2023; 11 larvae, Kumbakkarai Falls II, 10°12'11" N, 7°32'56" E, 448 m, 14-x-2023; 63 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 11 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Selvakumar et al., 2013; Kluge et al., 2022a), Karnataka, and Kerala (Kluge et al., 2022a).

Table 3. List of mayflies collected from Northern Palni Hills.

Genus Isca Gillies, 1951       

Isca sp. (Fig. 2D)

Material examined. 2 larvae, Kumbakkarai Falls I, 10°10'24" N, 77°32'13" E, 353 m, 14-x-2023; 1 larva, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 3 larvae, Adukkam Falls, 10°15'08" N, 77°31'22" E, 1685 m, 27-iv-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Sivaramakrishnan & Venkataraman, 1990).

Genus Megaglena Peters & Edmunds, 1970

Megaglena agasthiya Vasanth, Subramnian & Selvakumar, 2021 (Fig. 2E)

Megaglena agasthiya Vasanth, Subramnian & Selvakumar, 2021, 5076:64, Holotype ♂ larva, Pandipath stream, Peppara Wildlife Sanctuary, Trivandrum district, Kerala, India.

Material examined. 8 larvae, Perumalmalai Stream, 10°15'13" N, 77°31'26" E, 1670 m, 27-iv-2023; 10 larvae, Adukkam Falls, 10°15'08" N, 77°31'22" E, 1685 m, 27-iv-2023, Coll. C. Selvakumar & party.

Distribution. India: Kerala (Vasanth et al., 2021b), Tamil Nadu (New report).

Nathanella indica Demoulin, 1955 (Fig. 2F)

Nathanella indica Demoulin, 1955, 31:2, Holotype ♂ imago – Kodaikanal, Tamil Nadu, India.

Material examined. 1 larva, Perumalmalai Stream, 10°15'13" N, 77°31'26" E, 1670 m, 27-iv-2023; 42 larvae, Adukkam Falls, 10°15'08" N, 77°31'22" E, 1685 m, 27-iv-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Demoulin, 1955).

Figure 2. The mayfly larvae from the Sky Islands of Palni Hills, Western Ghats. A. Choroterpes (Euthraulus) alagarensis Dinakaran, Balachandran & Anbalagan, 2009; B. Choroterpes (Euthraulus) atelobranchis Kluge, Srinivasan, Vasanth, Sivaruban, Barathy, & Isack, 2022; C. Choroterpes (Euthraulus) nambiyarensis Selvakumar, Arunachalam & Sivaramakrishnan, 2013; D. Isca sp.; E. Megaglena agasthiya Vasanth et al., 2021, 1985; F. Nathanella indica Demoulin, 1955; G. Petersulla courtallensis Sivaramakrishnan, 1984;
H. Ecdyonurus (Afronurus) kumbakkariensis (Venkataraman & Sivaramakrishnan, 1989); I. Ecdyonurus (Rhithrogeniella) ornatus (Ulmer, 1939); J. Ecdyonurus (Thalerosphyrus) flowersi Venkataraman & Sivaramakrishnan, 1987; K. Epeorus (Epeorus) gilliesi Braasch, 1981; L. Ephemera (Aethephemera) nadinae McCafferty & Edmunds, 1973; M. Caenis americani Srinivasan, Sivaruban, Barathy, Malzacher & Isack, 2021; N. Caenis maduraiensis Balasubramanian & Muthukatturaja, 2021; O. Teloganodes (Dudgeodes) palnius Selvakumar, Sivaramakrishnan & Jacobus, 2014.

Genus Petersula Sivaramakrishnan, 1984               

Petersula courtallensis Sivaramakrishnan, 1984 (Fig. 2G)

Petersula courtallensis Sivaramakrishnan, 1984, 26:199, Holotype ♂ imago – Courtrallam main falls, Tamil Nadu, India.

Material examined. 1 larva, Munishwarar Kovil, 10°16'30" N, 77°35'38" E, 1271 m, 27-iv-2023; 1 larva, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 1 larva, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Sivaramakrishnan, 1984), Karnataka (Selvakumar et al., 2018a), and Kerala (Kluge et al., 2022b).

Family Heptageniidae Needham, 1901        

Genus Ecdyonurus Eaton, 1868

Subgenus Afronurus Lestage, 1924             

Ecdyonurus (Afronurus) kumbakkariensis (Venkataraman & Sivaramakrishnan, 1989) (Fig. 2H)

Cinygmina kumbakkaraiensis Venkataraman & Sivaramakrishnan, 1989, 1:117, Holotype ♂ imago, Kumbakkarai, Tamil Nadu, India.

Material examined. 28 larvae, Kumbakkarai Falls I, 10°10’24" N, 77°32'13" E, 353 m, 14-x-2023; 7 larvae, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 3 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 6 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023; Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Venkataraman & Sivaramakrishnan, 1989).

Subgenus Rhithrogeniella Ulmer, 1939

Ecdyonurus (Rhithrogeniella) ornatus (Ulmer, 1939) (Fig. 2I)

Rhithrogeniella ornata Ulmer, 1939, 16:576, Holotype ♂ imago, Sunda Islands.

Material examined. 13 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 5 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Karnataka and Tamil Nadu (Kluge et al., 2023b). Elsewhere: Indochina and the great Sunda Islands (Kluge et al., 2023b).

Subgenus Thalerosphyrus Eaton, 1881       

Ecdyonurus (Thalerosphyrus) flowersi Venkataraman & Sivaramakrishnan, 1987 (Fig. 2J)

Thalerosphyrus flowersi Venkataraman & Sivaramakrishnan, 1987, 56:1126, Holotype ♂ imago, Kumbakkarai, Tamil Nadu, India.

Material examined. 8 larvae, Kumbakkarai Falls I, 10°10’24" N, 77°32'13" E, 353 m, 14-x-2023; 7 larvae, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 11 larvae, Nalla Thangal Stream, 10°23'58" N, 77°36'49" E, 586 m, 02-vii-2023; 3 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Venkataraman & Sivaramakrishnan, 1987).

Genus Epeorus Eaton, 1881  

Subgenus Epeorus Eaton, 1881

Epeorus (Epeorus) gilliesi Braasch, 1981 (Fig. 2K)

Epeorus gilliesi Braasch, 1981, 19 (20), 117, Holotype larva, Khandala River, Maharashtra.

Material examined. 28 larvae, Kumbakkarai Falls I, 10°10’24" N, 77°32'13" E, 353 m, 14-x-2023; 5 larvae, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 1 larva, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 3 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Maharashtra (Braasch, 1981), Karnataka & Goa (Vasanth et al., 2021a), Tamil Nadu (Sivaruban et al., 2013).

Family Ephemeridae Latreille, 1810

Genus Ephemera Linnaeus, 1758

Subgenus Aethephemera McCafferty & Edmunds, 1973

Ephemera (Aethephemera) nadinae McCafferty & Edmunds, 1973 (Fig. 2L)

Ephemera (Aethephemera) nadinae McCafferty & Edmunds, 1973, 49:306, Holotype mature larva – Kodaikanal, Tamil Nadu, India.

Material examined. 8 larvae, Munishwarar Kovil, 10°16'30" N, 77°35'38" E, 1271 m, 27-iv-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (McCafferty & Edmunds, 1973).

Family Caenidae Newman, 1853

Genus Caenis Stephens, 1835

Caenis americani Srinivasan, Sivaruban, Barathy, Malzacher & Isack, 2021 (Fig. 2M)

Caenis americani Srinivasan, Sivaruban, Barathy, Malzacher & Isack, 2021, 4926:106, Holotype ♀ imago, Kodaikanal, Tamil Nadu, India.        

Material examined. 1 larva, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 8 larvae, Munishwarar Kovil, 10°16'30" N, 77°35'38" E, 1271 m, 27-iv-2023, Coll: C. Selvakumar & party.

Distribution. India: Tamil Nadu (Srinivasan et al., 2021).

Caenis maduraiensis Balasubramanian & Muthukatturaja, 2021 (Fig. 2N)

Caenis maduraiensis Balasubramanian & Muthukatturaja, 2021, 4980:367, Holotype ♂ imago, Vandiyur pond, Madurai district, Tamil Nadu state, India.

Material examined. 2 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 1 larva, Nalla Thangal Stream, 10°23'58" N, 77°36'49" E, 586 m, 02-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Muthukatturaja & Balasubramanian, 2021; Srinivasan et al., 2023).

Family Teloganodidae Allen, 1965

Genus Teloganodes Eaton, 1882

Subgenus Dudgeodes Sartori, 2008

Teloganodes (Dudgeodes) palnius Selvakumar, Sivaramakrishnan & Jacobus, 2014 (Fig. 2O)

Dudgeodes palnius Selvakumar, Sivaramakrishnan & Jacobus, 2014, 3846:95, Holotype ♂ larva, Palni hills, Tamil Nadu, India.

Material examined. 14 larvae, Kumbakkarai Falls I, 10°10'24" N, 77°32'13" E, 353 m, 14-x-2023; 9 larvae, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 10 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E         , 1217 m, 27-iv-2023; 15 larvae, Perumalmalai Stream, 10°15'13" N, 77°31'26" E, 1670 m, 27-iv-2023; 1 larva, Adukkam Falls, 10°15'08" N, 77°31'22" E, 1685 m, 27-iv-2023; 1 larva, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023; 16 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Selvakumar et al., 2014b) and Karnataka (Kluge et al., 2023a).

Subgenus Teloganodes Eaton 1882

Teloganodes (Teloganodes) kodai Sartori, 2008 (Fig. 3A)

Teloganodes kodai Sartori, 2008, 1957:15, Holotype larva, Kodaikanal, Tamil Nadu, India.

Material examined. 1 larva, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 2 larvae, Perumalmalai Stream, 10°15'13" N, 77°31'26" E, 1670 m, 27-iv-2023; 14 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Sartori et al., 2008; Selvakumar et al., 2018b).

Figure 3. The mayfly larvae from the Palni Hills of the Western Ghats. A. Teloganodes (Teloganodes) kodai Sartori, 2008; B. Acentrella (Liebebiella) vera (Müller-Liebenau, 1982); C. Baetis (Tenuibaetis) frequentus (Müller-Liebenau & Hubbard, 1985); D. Baetis venkataramani Sivaruban, Srinivasan, Barathy & Isack, 2023; E. Centroptella (Chopralla) ceylonensis (Müller-Liebenau, 1984); F. Labiobaetis jacobusi Kubendran & Balasubramanian, 2015; G. Labiobaetis pulchellus (Müller-Liebenau & Hubbard, 1985); H. Nigrobaetis klugei Sivaruban, Srinivasan, Barathy & Isack, 2022; I. Procloeon (Procloeon) kottagudiensis Muthukatturaja & Balasubramanian, 2022.

Family Baetidae Leech, 1815

Genus  Acentrella Bengtsson, 1912

Subgenus Liebebiella Waltz & McCafferty, 1987

Acentrella (Liebebiella) vera (Müller-Liebenau, 1982) (Fig. 3B)

Pseudocloeon verum Müller-Liebenau, 1982, 95:285, Holotype mature nymph, Gombak River, Malaysia.

Material examined. 55 larvae, Kumbakkarai Falls I, 10°10’24" N, 77°32'13" E, 353 m, 14-x-2023; 10 larvae, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 31 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 2 larvae, Nalla Thangal Stream, 10°23'58" N, 77°36'49" E, 586 m, 02-vii-2023; 6 larvae, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023; 11 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Karnataka and Tamil Nadu (Kluge et al., 2013). Elsewhere: Malaysia (Müller-Liebenau, 1982), Sri Lanka and Indonesia (Kluge et al., 2013), Java, Lombok and Thailand (Kluge & Novikova, 2011).

Genus  Baetis Leach, 1815

Subgenus Tenuibaetis Kang & Yang, 1994

Baetis (Tenuibaetis) frequentus (Müller-Liebenau & Hubbard, 1985) (Fig. 3C)

Baetis frequentus Müller-Liebenau & Hubbard, 1985, 68:537, Holotype nymph, Sri Lanka.

Material examined. 4 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 15 larvae, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023; 13 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar.

Distribution. India: Tamil Nadu (Kluge et al., 2023c). Elsewhere: Sri Lanka (Müller-Liebenau & Hubbard, 1985, Kluge et al., 2023c).

Baetis venkataramani Sivaruban, Srinivasan, Barathy & Isack, 2023 (Fig. 3D)

Baetis venkataramani Sivaruban, Srinivasan, Barathy & Isack, 2023, 24:150, Holotype ♀ mature nymph, Puliyuthu Falls, Theni, Tamil Nadu, India.

Material examined. 2 larvae, Kumbakkarai Falls I, 10°10’24" N, 77°32'13" E, 353 m, 14-x-2023; 1 larva, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 2 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 1 larva, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Sivaruban et al., 2023).

Genus Centroptella Braasch & Soldán, 1980

Subgenus Chopralla Waltz & McCafferty, 1987

Centroptella (Chopralla) ceylonensis Müller-Liebenau, 1983 (Fig. 3E)

Centroptella ceylonensis Müller-Liebenau 1983, 97:486, Holotype mature nymph, Sri Lanka.

Material examined. 2 larvae, Kumbakkarai Falls I, 10°10'24" N, 77°32'13" E, 353 m, 14-x-2023; 27 larvae, Kumbakkarai Falls II, 10°12'11" N, 77°32'56" E, 448 m, 14-x-2023; 1 larva, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023; 3 larvae, Nalla Thangal Stream, 10°23'58" N, 77°36'49" E, 586 m, 02-vii-2023; 6 larvae, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023, Coll. C. Selvakumar.

Distribution. India: Tamil Nadu (Selvakumar et al., 2017), Kerala and Karnataka (Kluge, 2021). Elsewhere: Sri Lanka (Müller-Liebenau, 1983).

Genus Labiobaetis Novikova & Kluge, 1987

Labiobaetis jacobusi Kubendran & Balasubramanian, 2015 (Fig. 3F)

Labiobaetis jacobusi Kubendran & Balasubramanian, 2015, 3957:195, Holotype ♂ larva, Vaigai River, Madurai, Tamil Nadu, India.

Material examined. 4 larvae, Kumbakkarai Falls I, 10°10'24" N, 77°32'13" E, 353 m, 14-x-2023; 17 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 4 larvae, Adukkam Falls, 10°15'08" N, 77°31'22" E, 1685 m, 27-iv-2023; 4 larvae, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023; 14 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Kubendran et al., 2015).

Labiobaetis pulchellus (Müller-Liebenau & Hubbard, 1985) (Fig. 3G)

Baetis pulchellus Müller-Liebenau & Hubbard, 1985, 68:544, Holotype ♂ nymph, Sri Lanka.

Material examined. 3 larvae, Thaliyuthu Water Falls, 10°26'33" N, 77°41'09" E, 346 m, 02-vii-2023; 3 larvae, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Karnataka, Kerala and Tamil Nadu (Kluge et al., 2023d). Elsewhere: Sri Lanka (Müller-Liebenau & Hubbard, 1985; Kluge et al., 2023d).

Genus Nigrobaetis Novikova & Kluge, 1987

Nigrobaetis klugei Sivaruban, Srinivasan, Barathy & Isack, 2022 (Fig. 3H)

Nigrobaetis klugei Sivaruban, Srinivasan, Barathy & Isack, 2022, 5091:183, Holotype ♀ mature nymph, Sastha falls, Rajapalayam district, Tamil Nadu, India.

Material examined. 3 larvae, Kumbakkarai Falls I, 10°10'24" N, 77°32'13" E, 353 m, 14-x-2023; 1 larva, Thalakuthu Main Falls, 10°26'16" N, 77°41'07" E, 450 m, 02-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Tamil Nadu (Sivaruban et al., 2022).

Genus Procloeon Bengtsson, 1915

Subgenus Procloeon Bengtsson, 1915

Procloeon (Procloeon) kottagudiensis Balasubramanian & Muthukatturaja, 2022 (Fig. 3I)

Procloeon (Procloeon) kottagudiensis Balasubramanian & Muthukatturaja, 2022, 5094:322, Holotype ♂ imago, Kottagudi stream, Tamil Nadu, India.

Material examined. 3 larvae, Moolaiyaru River, 10°16'13" N, 77°36'34" E, 1217 m, 27-iv-2023; 4 larvae, Thaliyuthu Water Falls, 10°26'33" N, 77°41'09" E, 346 m, 02-vii-2023; 3 larvae, Nalla Thangal Stream, 10°23'58" N, 77°36'49" E, 586 m, 02-vii-2023; 17 larvae, Varaiyaru Falls, 10°19'41" N, 77°42'54" E, 1172 m, 01-vii-2023; 15 larvae, Umaiyaru River, 10°20'56" N, 77°41'27" E, 1236 m, 01-vii-2023, Coll. C. Selvakumar & party.

Distribution. India: Kerala and Tamil Nadu (Muthukatturaja & Balasubramanian, 2022).

The following four mayfly species: Megaglena agasthiya, Choroterpes (Euthraulus) atelobranchis, Caenis maduraiensis and Nigrobaetis klugei are reported for the first time from the Palni Hills. The endemic species Megaglena agasthiya and Nathanella indica were found only in the high elevation sites (above 1670 m), whereas Isca sp. and Teloganodes (Dudgeodes) palnius were found in low elevation sites (353 m) as well as high elevation site (1685 m). The oriental species, Ecdyonurus (Rhithrogeniella) ornatus occurs in the moderate high elevation ranges between 1217 m and 1236 m. Ephemera (Aethephemera) nadinae is found at only one high elevation site (1271 m), which is characterised by slower water current and sandy bottom. In contrast, other mayflies exhibit overlapping distributions across different altitudes (Table 2). Out of 24 species distributed throughout Palni Hills, 12 occur in the low to moderate elevation study sites. Megaglena agasthiya, Isca sp., and Nathanella indica are distributed only in the southern Palni Hills, whereas Baetis (Tenuibaetis) frequentus is only distributed in the northern Palni Hills. Caenis americani occurs only in the southern Palni Hills, whereas Caenis maduraiensis is only found in the northern Palni Hills. The number of individuals and richness of species is decreasing with the increasing elevation, while the abundance of species and elevation are negatively correlated (r=0.26) (Fig. 4).

Figure 4. Simple linear regression analysis of elevation and number of individuals.

DISCUSSION

The present study reports 24 species of mayflies from the Palni Hills of the Western Ghats. The families Baetidae, Heptageniidae, and Leptophlebiidae are the most species-rich families, however their abundance was found to be low in freshwater ecosystems of the Western Gath hotspot as previously found in Palni Hills by Sivaramakrishnan and Venkataraman (1990) and in Courtallam Hills by Sivaramakrshnan and Job (1981). Most genera of Leptophlebiidae are widely distributed in different habitats, but the genera Megaglena Peters & Edmunds, 1970, and Nathanella were only found in the pristine stream habitat. Sivaramakrishnan & Venkataraman (1990) have reported the following three leptophlebiid genera, namely Edmundsula Sivaramakrishnan, 1985, Notophlebia Peters & Edmunds, 1970 and Klugephlebia Selvakumar, Subramanian & Sivaramakrishnan, 2016 in the Palni Hills. However, we were unable to find these three genera during this investigation, including the same sites from where they were reported before. Edmundsula and Notophlebia occur in other parts of the Western Ghats (Selvakumar et al., 2018a), while Klugephlebia was described and reported only from the Pillar Rock of Kodaikkanal, Palni Hills by Selvakumar et al. (2016b) and also reported as a new genus by Sivaramakrishnan and Venkataraman (1990). In our rigorous attempt to collect samples from the type locality of Klugephlebia at Pillar Rock in Kodaikanal, we were unable to find any mayfly larvae. This absence raises a concerning possibility: the species may be facing local extinction or may have already vanished due to habitat degradation and anthropogenic impacts. This situation necessitates further intensive field collections across the Palni Hills to confirm its actual distribution and occurrence. Furthermore, this finding highlights the urgent need for conservation measures to protect these ecologically significant aquatic insects and their habitats. Previously, Choroterpes (Euthraulus) sp. was the only species reported from the Palni Hills by Sivaramakrishnan and Venkataraman (1990). However, the current study identifies three species belonging to the subgenus Euthraulus, reflecting advancements in taxonomic knowledge of mayflies and detailed observations of their morphological features. Many baetid species were previously misidentified due to a lack of taxonomic expertise, the absence of molecular techniques, and the inherent complexity of the group (Sivaramakrishnan & Venkataraman, 1990; Barathy et al., 2021a).

Significant discoveries of new mayfly species, including new genera, have been made in the Western Ghats over the past two decades (Selvakumar et al., 2014b, 2016b; Kluge et al., 2022a, 2022b). Additionally, species delimitation has been further refined through DNA barcoding techniques, as demonstrated by Selvakumar et al. (2016a). Table 4 provides a comparison of mayfly diversity in the Palni Hills between 1990 and 2023. Further intensive field studies are required to comprehensively understand the distribution and evolutionary dynamics of mayflies in the streams and rivers of the Palni Hills.

Table 4. Comparison of mayfly diversity in Palni Hills between the years 1990 and 2023.

Our study revealed a weak relationship between mayfly species richness and abundance and the elevational gradient. Generally, species richness showed a decline at higher elevations (Sivaramakrishnan & Venkataraman, 1990; Selvakumar et al., 2014a). The distribution of mayflies in the Palni Hills of southern India appears to be primarily influenced by factors such as pristine waters, perennial flow, substratum characteristics, the availability of allochthonous organic matter, temperature, and riparian forest cover. Given that many mayfly species are highly sensitive to anthropogenic impacts, as well as to temperature, riparian land use, and water velocity gradients that often covary with elevation, it is likely that these factors partially explain our findings (Selvakumar et al., 2014a, 2014c). However, streams in this region experience pronounced seasonal fluctuations in environmental factors (e.g., water level, turbidity, and velocity) and are subject to significant hydrological disturbances during monsoons. Therefore, future studies should investigate the role of these drivers in shaping mayfly species richness and abundance.

AUTHOR′S CONTRIBUTION

The authors confirm their contribution to the paper as follows: C. Selvakumar, C. Ashokkumar, S. Sundar and M. Gunasekaran: Field studies and specimen samplings; C. Selvakumar and C. Ashokkumar: Identification of the specimens; C. Selvakumar, S. Sundar and F.O. Roque: drafting, editing and proofreading the manuscript. All authors read and approved the final version of the manuscript.

FUNDING

This research received a grant from DST-SERB, Government of India.

AVAILABILITY OF DATA AND MATERIAL

The specimens listed in this study are deposited in the Centre for Research in Aquatic Entomology, Department of Zoology, The Madura College (Autonomous), Madurai, and are available from the first author upon request.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

This study only included arthropod material, and all required ethical guidelines for the treatment and use of animals were strictly adhered to in accordance with international, national, and institutional regulations. No human participants were involved in any studies conducted by the authors for this article.

CONSENT FOR PUBLICATION

Not applicable.

CONFLICT OF INTERESTS

The authors declare that there is no conflict of interest regarding the publication of this paper.

ACKNOWLEDGMENTS

C. Selvakumar is grateful to the Science and Engineering Research Board, Government of India, New Delhi, for financial support under the Empowerment and Equity Opportunities for Excellence in Science (F. N. EEQ/2022/000317). He also thanks Dr. K.G. Sivaramakrishnan, former head of the Department of Zoology at The Madura College (Autonomous), Madurai, for his motivation and encouragement. The authors are thankful to
D. Venkatesh, Conservator of Forests, Working Plan Circle, Coimbatore, District Forest Officer, and other Officials of Dindigul Forest Division for their permission and support. Authors also thank "the Institutional Program of Internationalization sponsored by the CAPES-PRINT (Process: 88881.311897/2018-01). The authors are grateful to the subject editor and three anonymous reviewers for their valuable comments on improving this manuscript.