Phenotypic Plasticity: Cause of the Successful Spread of the Genus
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Aquatic Botany 120 (2014) 283–289 Contents lists available at ScienceDirect Aquatic Botany jou rnal homepage: www.elsevier.com/locate/aquabot Phenotypic plasticity: Cause of the successful spread of the genus Potamogeton in the Kashmir Himalaya a,∗ a a b Aijaz Hassan Ganie , Zafar A. Reshi , B.A. Wafai , Sara Puijalon a Department of Botany, University of Kashmir, 190 006 Jammu & Kashmir, India b Université de Lyon, UMR 5023 “Ecologie des hydrosystèmes nature lsetanthropisés”, Université Lyon 1, CNRS, ENTPE, 69622 Villeurbanne Cedex, France a r a t i b s c t l e i n f o r a c t Article history: Morphological variations observed for a given species according to habitat conditions are generally asso- Received 29 January 2014 ciated with plant adaptation to local conditions enhancing the plants ability to occupy a wide range of Received in revised form environments, and hence ecological niche breadth. Morphological variations can result from genetic dif- 18 September 2014 ferentiation or from phenotypic plasticity in response to environmental conditions. The present study Accepted 19 September 2014 was undertaken to assess phenotypic variations in the most widespread, as well as one of the largest, Available online 28 September 2014 aquatic genera of the Kashmir Himalaya. The study was conducted in 10 species of Potamogeton across habitats with different water flow types and a common garden experiment was carried out to test for the Keywords: plastic origin for the morphological differences observed under natural conditions. Significant differences Morphological characters were observed in morphological characters such as the leaf dimensions, spike and peduncle length; and Phenotypic plasticity Potamogeton number of spikes, flowers, fruits and turions/tubers per ramet in both lentic and lotic waters. The results Ecological niche breadth of the transplantation experiments revealed that when plants of the same species collected from different habitats (standing and running waters) were grown under similar conditions, the differences in the mor- phological traits were no longer observed at the end of the transplantation period. These results suggest that the morphological differences observed between the plants sampled under different conditions are due to phenotypic plasticity and not to genetic differentiation. The capacity of these species to colonise a wide range of environmental conditions may rely on this high level of morphological variation. © 2014 Elsevier B.V. All rights reserved. 1. Introduction research on phenotypic plasticity has largely attempted to disen- tangle these three factors, focusing on the genotype–environment Two different adaptive mechanisms that improve the survival, interaction (DeWitt and Scheiner, 2004). reproduction and dispersal of plant species are phenotypic plas- Potamogeton, one of the largest genera of aquatic angiosperms, ticity and local adaptation. Phenotypic plasticity is the capacity is ecologically diverse and distributed in various freshwater of a given genotype to express different phenotypes in different (lakes, marshes, ponds, rivers, etc.) and brackish water habitats environments (Sultan, 2000; Riis et al., 2010). Phenotypic plastic- (Hutchinson, 1975; Kadono, 1982). Residing in aquatic habitats, ity leads to rapid changes of plant phenotypic characters induced by the species of the genus display, as in many aquatic plant species environmental conditions in the habitat, and adaptive phenotypic (Santamaria, 2002), a high degree of variability (Wiegleb, 1988; plasticity can support the spread of plants into a range of habi- Kaplan, 2002, 2008). There are both phenotypic variations in tats (Riis et al., 2010). In response to environmental stress, many response to environmental conditions (phenotypic plasticity) and plant species display adaptive plastic responses in developmen- genotypic variations as a result of isolation and predominant tal, morphological, physiological, anatomical or reproductive traits vegetative reproduction (Wiegleb, 1988). The origin of the morpho- that can support functional adjustments, possibly compensating logical variations (phenotypic plasticity or genetic differentiation) for the detrimental effect of stress (Sultan, 2000, 2003). The extent reported to occur in this genus has not been studied system- of ‘niche breadth’ may reflect physiological tolerance, local adap- atically; transplantation experiments conducted by Fryer (1890) tation and/or adaptive phenotypic plasticity (Dudley, 2004). The were repeated for several seasons and revealed that the difference between the states of species and varieties were only temporary. The species of the genus Potamogeton have been demonstrated ∗ to display morphological variations in response to various environ- Corresponding author. Tel.: +91 09622493652; fax: +91 01942421357. E-mail address: [email protected] (A.H. Ganie). mental factors. The effects of light conditions and water chemistry http://dx.doi.org/10.1016/j.aquabot.2014.09.007 0304-3770/© 2014 Elsevier B.V. All rights reserved. 284 A.H. Ganie et al. / Aquatic Botany 120 (2014) 283–289 on the leaf shape of P. perfoliatus were studied by Pearsall and of glaciated streams and rivers, as well as alpine, sub-alpine and Hanbay (1925), and this study revealed that in addition to other Valley Lakes that support arich diversity of aquatic vegetation. The factors, light intensity was operating to produce leaf variations details of the exact geographical location of the selected sites and in this species. Recently, several studies have described changes their characteristic features are summarised in Table 1. in response to environmental conditions. The influence of plant- The study sites can be grouped into two sets according to the ing depth on tuber size in P. pectinatus was studied by Ogg et al. overall current conditions: (1969) and Spencer (1987); the influence of planting depth on tuber weight in P. gramineus was studied by Spencer and Ksander (1990). A. Standing water: Anchar Lake (AL); Dal Lake (DL); Manasbal Lake At greater depths, individuals of P. gramineus exhibited a decrease (ML) and Nigeen Lake (NL). in the shoot elongation, rhizome length and the number of flow- B. Running water: Aarpath rivulet of Anantnag (ARRA); Achabal ers, ramets, leaves and floating leaves. Morphological responses stream, Anantnag (ACSA); Bal-kol, Baramulla (BLBK); Irrigation to sediment and above-sediment conditions were observed by channel of Sundoo, Anantnag (ICSA); Nagrad stream, Anantnag Kautsky (1987) and Idestam-Almquist and Kautsky (1995) for sev- (NGSA); Nambal stream, Anantnag (NBSA); Spring stream of eral morphological traits (e.g., biomass allocation to roots, rhizome Sundoo, Anantnag (SSA) and Spring stream of Thajiwara, Anant- length and branching). Water movement has long been consid- nag (STA). ered as one of the primary factors that determines the growth and distribution of submerged aquatic plants in streams and rivers The water flow of the running water study sites (Table 1) was (Chambers, 1991). As early as the 1920s, Butcher (1933) recog- measured by float and cross section methods following the meth- nised that changes in water flow altered the biomass and species ods of Kuusisto (1996). composition of submerged plant communities. The role of water movement in regulating the growth of riverine plants is not as well 2.2. Species sampled understood (Chambers, 1991), and very little is known about the plastic responses of aquatic plants with respect to flow conditions Ten Potamogeton species were sampled: P. lucens L., P. natans L., (Puijalon and Bornette, 2006; Puijalon et al., 2008). P. pusillus L., P. amblyphyllus C.A. Meyer (=Stuckenia amblyphylla C.A. In the present study, phenotypic variation was studied in Meyer), P. berchtoldii Fieb., P. crispus L., P. nodosus Poir., P. pectina- response to a major environmental factor in aquatic habitats: tus L. (=Spartina pectinata (L.) Börner), P. perfoliatus L. and P. wrightii water movement. Ten species of the genus Potamogeton were Morong. Not all species could be collected at all the sites; on aver- studied, forming two sets of species according to their ecologi- age, each species was sampled in three or four sites. Three species cal range: Potamogeton crispus, Potamogeton nodosus, P. pectinatus were sampled only in standing water (P. lucens, P. natans, and P. and P. wrightii are widespread (inhabiting both running and stand- pusillus), two only in running water (P. amblyphyllus and P. berch- ing waters, water bodies with different trophic levels and depths), toldii) and five in both habitats (P. crispus, P. nodosus, P. pectinatus, where as Potamogeton amblyphyllus, Potamogeton berchtoldii, Pota- P. perfoliatus, and P. wrightii). mogeton lucens, Potamogeton natans and Potamogeton pusillus are Only the well identified individuals of each Potamogeton species less widespread (with restricted distribution in terms of flow were sampled for use in this study. For each species, 25 fully conditions and trophic levels; Ganie et al., 2012). Both sets of developed individuals (the clonal unit consisted of complete unit species were examined in a common garden growth experiment of ramets connected by rhizomes) were sampled in each samp- 2 to assess whether differences in phenotypic characters across dif- ling site. These individuals were randomly collected from 10-m ferent habitats would disappear after transplantation in common quadrats (8 quadrats at each site, approximately 20 m apart). conditions, suggesting a plastic origin