Earthworms (Annelida: Clitellata: Megadrili) of Solan, a constituent of Himalayan Biodiversity Hotspot, India

The present work is an update on the earthworm fauna of Solan District, Himachal Pradesh State, a constituent of Himalayan biodiversity hotspot. It is based on the field collection and published literature data. Hereby, it is provided an updated list of 32 species belonging to 18 genera and seven families, namely Moniligastridae, Lumbricidae, Ocnerodrilidae, Acanthodrilidae, Benhamiidae, Octochaetidae and Megascolecidae. These mainly include exotic and native peregrine species, including exotic peregrine Amynthas hupeiensis (Michaelsen, 1895), which was recently recorded for the first time from India. A systematic account of earthworm species with their distribution and a dichotomous key is provided for their identification.

Migration of earthworms mostly takes place through active and passive dispersal (Edwards and Bohlen 1996), but in active dispersal the deserts, mountains and oceans create effective physical barrier. The active dispersal in earthworm is very slow, estimated at about 5-10 meter / year (Addison 2009), whereas passive dispersion is common through anthropogenic activities and through transportation of cocoons in soil attached to feet of birds and animals Blakemore 2002;Brown et al. 2006;Julka 2014). Passive dispersal contributes majorly toward the spread of earthworm species far away from their home range (Brown et al. 2006). Species which are successfully established outside their native ranges are called peregrine (Michaelsen 1903). These peregrine species are generally found in disturbed habitats, near to human settlements (Brown et al. 2006). More than 100 such species which are considered peregrine (Blakemore 2002) are present globally. In India, their number is estimated to be 53, representing about 12.1% of the country's earthworm diversity (Julka 2014;Ahmed and Julka 2017;Kharkongor 2018;Narayanan et al. 2019a). On the basis of endemicity and dispersal, Indian earthworms are categorized into: i) endemic or native species, which are restricted to India; ii) exotic peregrine species, which originated in other biogeographical regions; iii) native peregrine species, which evolved in India and now gained widespread distribution in the country and also in other biogeographical regions (Julka and Paliwal 2005b;Narayanan et al. 2016a).
The present paper aims to update the existing knowledge on earthworm communities of Solan District, a constituent of the Himalayan biodiversity hotspot, which is facing problems of fast deteriorating ecology and impacts of climate change. The studies are also hampered in the absence of simple ready to use regional keys for the identification of earthworms. Therefore, a simple dichotomous key primarily based on the easily recognizable character for the identification of earthworm species for the use of non-specialists is also provided. three endemic or near endemic to the study site. The detailed distribution of the earthworm species of district Solan has been plotted in Figures 2 and 3. A running key is provided for their identification. In the present study for earthworm species distribution mainly the works of Julka (1988); Paliwal and Julka (2005); Joshi et al. (2010); Narayanan et al. (2016aNarayanan et al. ( , 2016bNarayanan et al. ( , 2019b; Kumari et al. (2017); Ahmed and Julka (2017); Goswami (2018); Ahmed and Gupta (2019) for India, and ; Julka (1988); Csuzdi and Pavliček (2009);Blakemore (2007bBlakemore ( , 2013Blakemore ( , 2014Blakemore ( , 2016; Valchovski (2014); Mısırlıoğlu et al. (2019) for the distribution outside the country are followed. Further, the habitat of the species reported in the present study is based on the present collection and published literature.

Systematic account
The taxa marked with asterisk (*) are recorded from literature.

Discussion
The present paper reveals the presence of 32 species / subspecies of earthworms from Solan, which represent about 60% of the fauna (53 species) of western Himalaya (Paliwal and Julka 2005;Kumari et al. 2017;Ahmed and Julka 2017), and about 7.5% (426 species / subspecies) of country (Narayanan et al. 2019a). The earthworm species reported in the present study belong to seven families viz. Moniligastridae, Lumbricidae, Ocnerodrilidae, Acanthodrilidae, Benhamiidae, Octochaetidae and Megascolecidae. Among the recorded families, Megascolecidae is the most diverse, represented by 13 species, followed by Lumbricidae 7 species, Octochaetidae 6 species, Benhamiidae 2 species, and Ocnerodrilidae and Acanthodrilidae with one species each.
Although the earthworm fauna of the country is represented with high level of endemism, about 71% of genera and 89% species are endemic ), but in the present study area exotic peregrine species predominate the native species. Among the recorded species, 19 are exotic peregrine, 10 native peregrine and three endemic or near endemic to the study area. The exotic peregrine species are Drawida japonica, Aporrectodea caliginosa caliginosa, A. caliginosa trapezoides, A. rosea rosea, Eisenia fetida, Eiseniella tetraedra tetraedra, Octolasion tyrtaeum (Palearctic origin); Bimastos parvus, Ocnerodrilus occidentalis (Nearctic origin); Microscolex  Julka 1988;Paliwal and Julka 2007;Narayanan et al. 2016a). These exotic peregrine species are possibly transported to these hills through the soil around roots of exotic plants and other agencies (Julka and Paliwal 2005a). At present, these exotic species are highly distributed near human habitations. Till date, there is no such report which shows the impact of exotic earthworm species on forest ecosystem of the region, but several studies in North America have documented the effect of invasive earthworm species on forest ecosystem e.g. decrease in the thickness of forest floor, increase the soil compaction, nutrient leaching and also negatively effects the native plants and animal species (Scheu and Parkinson 1994;Bohlen et al. 2004;Hale et al. 2008;Maerz et al. 2009;Loss and Blair 2011).
Ten species from other biogeographical regions of the country are also found in the study area, among them, Drawida nepalensisis, endemic to the Nepal, Eutyphoeus incommodus and E. waltoni are endemic to the adjacent Indo-Gangetic plains, the species of genera Lennogaster, Octochaetona and Ramiella reported in the present manuscript are endemic to the central highlands of the peninsula, Perionyx excavatus (eastern Himalaya), Perionyx sansibaricus (Indian Peninsula) and Lampito mauritii is endemic to the Western Ghat (Gates 1947;Paliwal and Julka 2007).
The endemic or near endemic earthworm species of region comprise of three species Argilophilus sadhupulensis, Perionyx simlaensis and P. bainii. Several studies were undertaken on the earthworm diversity of Himachal Pradesh, except (P. simlaensis) no one report the presence of these endemic species near or in the region of their type localities. However, a recent study of Joshi et al.(2010) documented Argilophilus sadhupulensis from Uttarakhand, and Perionyx bainii from Odisha (Goswami 2018). More studies are required to understand the present status of these endemic species. The area of the present study is dominated by exotic peregrine species, and it may also became interested to study the impact of invasive earthworm species on the endemic element. As, Vitousek (1990) and Bholen et al. (2004) reported that by altering the habitat and available resources the biological invasion compete or replace the native species.
Further range expansion of Lampito mauritii, Eutyphoeus waltoni and Metaphire posthuma are observed during the present study, as Lampito mauritii is recorded first time from Western Himalaya, whereas Metaphire posthuma and Eutyphoeus waltoni are recorded first time from the study sites. Warming of the western Himalayan region may be the reason for range expansion of these species. The temperature of western Himalaya is rising (Kothawale et al. 2010), and Addison (2008) reported that even a small increase in winter temperature leads to increase in earthworms habitat.

Conclusion
To date, 32 (past and present record) species of earthworm have been reported from district Solan. Among the recorded families, Megascolecidae is the most diverse family with 13 species, and the largest genera having maximum species are Amynthas and Perionyx each with four species in the study site. Further range expansion of Lampito mauritii, Eutyphoeus waltoni and Metaphire posthuma are observed during the present study, as Lampito mauritii is recorded first time from Western Himalaya, whereas Metaphire posthuma and Eutyphoeus waltoni are recorded first time from the study sites. Earthworm act as an indicator of biotic pressure and vegetation change, the predominance of exotic peregrine species (59.3%) over native indicates a high degree of disturbance in the area.
Solan for providing facilities during the course of present studies. We wish to thank Dr. Ionuț Ștefan Iorgu (editor), Dr. S. Prasanth Narayanan and anonymous reviewer for their valuable suggestions and inputs. We also wish to thanks Mr. Paromit Chatterjee, SRF Zoological Survey of India for their contribution in preparation of maps.