Genetic and clonal diversity of the endemic ant-plant Humboldtia brunonis (Fabaceae) in the Western Ghats of India

Abstract

Humboldtia brunonis (Fabaceae, Caesalpinioideae) is a dominant self-incompatible ant-plant or myrmecophyte, growing as an understorey tree in high-density patches. It is endemic to the biodiversity hotspot of the southern Western Ghats of India and, besides ants, harbours many endemic invertebrate taxa, such as bees that pollinate it as well as arboreal earthworms, within swollen hollow stem internodes called domatia. Using inter simple sequence repeat (ISSR) markers, three geographically separated populations were found to be multiclonal, characterized by high levels of clonal diversity. Values for the Simpson diversity index ranged between 0.764 and 0.964, and for Fager's evenness index between 0.00 and 0.036 for neighbourhoods within populations. This myrmecophyte was found to combine sexual recruitment (66.7%) and clonal production (33.3%) as methods of reproduction. Moderate amounts of genetic diversity at the species level were observed, with 52.63% polymorphism, and moderate values of Shannon's diversity index (0.1895) as well as of Nei's gene diversity (0.1186). In each population, observed genotypic diversity was significantly lower than expected, indicating significant genetic structure. Neighbour-joining trees demonstrated that Agumbe, which is the most northern population examined and geographically twice as far away from the other two populations, grouped separately and with larger bootstrap support from a larger cluster consisting of the Sampaji and Solaikolli populations, which are closer to each other geographically. Some neighbourhoods within each population showed spatial genetic structure even at small spatial scales of less than 5 m. A combination of clonality and short-distance pollen movement by small pollinating bees (Braunsapis puangensis) coupled with primary ballistic seed dispersal, and possible secondary seed dispersal by rodents, may contribute to spatial genetic structure at such small scales. The clonality of H. brunonis may be a factor that contributes to its dominance in Western Ghat forests where it supports a rich diversity of invertebrate fauna.

Genetic diversity of a rare species Aristolochia contorta Bunge (Aristolochiaceae) in Primorsky Krai

“…The values of Simpson's diversity index (D) in all but one (BK) populations examined were considerably high (Table 5) relative to mean value for clonal plants (D = 0.62 [28]; D = 0.75 [39]). Similarly high geno typic diversity indices were reported for the popula tions of other vine species, Pueraria lobata [22], Mon itopetalum chinense, and clonal plant Humboldtia brunonis [40]. All localities examined in the present study were multiclonal.…”

“…At the species level, the value of G/N index consti tuted 0.377. Upon maximum genotypic diversity, the value of G/N was equal to one, i.e., in this case each plant represents an independent genet [27], and it can be treated as an indicator of sexual propagation, as it was reported for Humboldtia brunonis [40]. Corre spondingly, the level of sexual propagation for A. con torta constituted 37.7%, and the level of clonal repro duction, 62.3% (1-G/N).…”

Nutritional benefits from domatia inhabitants in an ant–plant interaction: interlopers do pay the rent

“…Humboldtia brunonis (Fabaceae) is a dominant understorey tree, 6–10 m tall, endemic to the low elevation, tropical, wet evergreen forests of the Western Ghats of India (Ramesh & Pascal ) and found in a narrow mountainous strip between 11°10′N and 13°45′N. The plant is clonal with a maximum distance of 8·75 m between any two neighbouring non‐clones (Dev, Shenoy & Borges ). It occurs in dense patches of about 0·25 km 2 (J. Chanam, pers.…”

Context dependency of rewards and services in an Indian ant–plant interaction: southern sites favour the mutualism between plants and ants

“…These sites span a rainfall seasonality gradient in the Ghats with longer dry seasons (8 mo) towards the north compared with the south (6 mo) since the southern Western Ghats receive rain from both the south-west monsoon (June-September) as well as the north-east or retreating monsoon (October-November) (Davidar et al 2005, Gadgil & Joshi 1983, Pascal 1988 and also suggested a natural geographical grouping between northern sites: Agumbe and Kudremukh, and southern sites: Uppangala, Sampaje and Solaikolli. Humboldtia brunonis occurs in clonal clumps (Dev et al 2010) and is so abundant that it features within two forest type associations: (1) Dipterocarpus indicus-Humboldtia brunonis-Poeciloneuron indicum type, and (2) Dipterocarpus indicus-Kingiodendron pinnatum-Humboldtia brunonis type (Pascal 1988, Rai 2000. Agumbe and Kudremukh occur within the first, and the other three sites within the second forest type.…”