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                                                  Gene-ecological adaptations 
                                                                    (NOTES) 
                    
                   Species differ in their environmental requirements. They also differ in respect 
                   of their tolerance to environmental fluctuations. 
                    
                   The  species  occur  in  several  morphological  forms  in  different  habitat 
                   conditions. Gote Turesson (1922), a Swedish scientist, conducted a series of 
                   experiments on variations within species. He collected a group of 20 or more 
                   individuals of the same species (Plantago maritina) from different areas and 
                   planted  them  under  identical  environmental  conditions  in  his  experimental 
                   garden at Akark. 
                    
                   Gote Turesson noted that: 
                    
                        Several  intergrading  forms  existed  within  the  species,  which  differed 
                            from one another in morphological or physiological features. 
                    
                        Some of the differences might be temporary (unstable) and could be 
                            induced only by the environmental factors, while some others might be 
                            permanent (i.e. genetically fixed). 
                    
                   These observations led him to formulate the concept of “gene ecology”, which 
                   brought about many revolutionary changes in plant taxonomy. 
                    
                   The population, sampling and subsequent procedures that Turesson followed 
                   led  him  to  conclude  that  species  differ  from  one  another  morphologically, 
                   physiologically and in habitat-requirements. On the basis of such studies, he 
                   proposed the following classes of morphological forms within a species: 
                    
                                                                                      
                        1.  Ecads                                                4.  Ecospecies and 
                        2.  Ecotypes                                             5.  Coenospecies 
                        3.  Ecoclines                                        
                     
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            1. Ecads  
             
            Ecads are also called, ecophenes, epharmones or habitat forms. Ecads may 
            differ  to  such  an  extent  that  they  can  be  treated  as  different  species.  It  is 
            because they carry so diverse environmentally induced variations. Ecads belong 
            to the same genetic stock and the morphological variations (e.g. in shape, size, 
            number, reproductive capacity, etc.) between the ecads are induced by the 
            environmental influences. These variations are not fixed (genetically governed) 
            but are temporary, somatic and reversible. For example, there are two ecads of 
            a  species,  namely  Ecad  1  and  Ecad  2.    If  Ecad  1  is  transplanted  into  the 
            environment  of  Ecad  2,  the  differences  between  the  two  ecads  would 
            disappear.  
             
            The  morphological  variations  of  ecads  are  not  permanent  because  their 
            genetic composition is same. Since they are identical in their genetic makeup, 
            they are interfertile forms.  
             
            Example 1: Euphorbia hirta plants, growing in the grasslands, are prostrate and 
            profusely branched (Ecad 1), while the plants of the same species growing on 
            the footpaths are compact, small and cushioned-leaved (Ecad 2). When these 
            forms  (two  ecads)  are  grown  under  identical  habitat-conditions,  their 
            differences disappear.  
             
            Example  2:  In  Bothriochloa  pertusa  and  Dichanthium  caricosum,  several 
            distinct morphological forms of ecads were noted under different habitats by 
            Pandeya (1962). 
             
            In both the above mentioned species there are two ecads: 
             
                Basket-shaped habit is shown by the plants growing in protected areas 
                  (no grazing) 
                   
                Saucer-shaped  habit  is  shown  by  the  plants  growing  in  over-grazed 
                  areas. 
             
            Grazing caused morphological variations such as reduction in the size of erect 
            stem,  number of spikes  per  raceme,  number  of  spikelets  per  spike  and  in 
            length and breadth of lower glumes of spikelets. Grazing also resulted in some 
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            physiological variations such as development of anthocyanin pigment in the 
            leaves and early initiation of flowers. 
             
            2. Ecotypes 
             
            These are also called ecological races or physiological races. The term ecotype 
            was proposed by Turesson (1922) to the groups of populations or ecological 
            races  or  sub-species  of  a  species  in  relation  to  different  environmental  or 
            habitat-conditions.  These  are  interfertile  forms  (or  biotypes  of  a  species), 
            which  possess  different  genetic  compositions  (or  genotypes).  The  ecotypes 
            arise due to mutations, hybridization and isolation. 
             
            Though different ecotypes of a species are morphologically and genetically 
            distinct,  yet  because of their  interfertility,  they  are  put  into  one  taxonomic 
            species.  Ecotypes  are  morphologically,  physiologically  and  developmentally 
            adapted to live under varying environmental conditions. Ecotype is the product 
            of genetic response of a population to a habitat. In ecotypes, adaptations are 
            irreversible,  i.e.  they  retain  their  features  even  when  planted  in  a  neutral 
            habitat. 
             
            The differences in the ecotypes are so marked that some of them have been 
            treated as separate species by earlier taxonomists.  
             
            Example 1: Mishra and Shiva Rao (1948) found Lindenbergia polyantha and 
            Lindenbergia urticaefolia  to  be  the  ecotypes  of  the  same  species.  The  two 
            ecotypes differ from each other in respect of their tolerance to high doses of 
            lime (carbonates, oxides and hydroxides of calcium). Lindenbergia polyantha 
            can tolerate high doses of lime.  
             
            Example 2: In another study, Ramakrishnan (1959, 1960) showed that red and 
            green populations (red ecotype and green ecotype) of Euphorbia thymifolia are 
            two ecotypes. 
             
            The red ecotype is a calcicol (i.e. it grows in calcium-rich soil as well as in 
            calcium-deficient soils) and the green ecotype is a calcifuge (i.e. it cannot grow 
            in  calcium-rich  soil).  The  red  ecotype  possesses  a  pair  of  dominant  alleles, 
            whereas the green type possesses a pair of recessive alleles.  
             
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               Some more examples:  ecotypes  have  been  reported  in  several  species  of 
               plants, such as Euphorbia hirta, Cassia tora, Ageratum conyzoides, Cenchrus 
               ciliaris, etc. 
                
               Characteristics features of ecotypes: 
                
                1.   Ecotypes  of  a  species,  though  genotypically  distinct,  are  always 
                     interfertile. 
                 
                2.   They retain their original features when cultivated in a natural habitat 
                 
                3.   Variations of ecotypes are genetically fixed 
                 
                4.   Ecotypes occur in distinct habitats 
                 
                5.   Ecotypes are discrete entities with clear differences, which separate one 
                     ecotype from another 
                 
                6.   Differences between ecotypes are not due to plastic response to change 
                     in environment but are actually due to natural selection of locally adapted 
                     populations. 
                
               Formation of new ecotypes: Ecotypes are produced by the following methods: 
                
               1. Hybridization 
                
               The  ecotype  is  produced  by  the  natural  cross  between  two  species.  For 
               example, when Spartia stricta is naturally crossed with Spartia altemiflora, the 
               new hybrid Spartia townsendii results, which eliminates both the parents from 
               their natural habitats because of its greater adaptability. 
                
               2. Mutation 
                
               Due to natural mutation (sudden change in genes) and recombination (during 
               meiosis), small gene pools accumulate in a segregating population, which make 
               it better-adapted to the particular habitat or environment. Some new ecotypes 
               also  arise  by  cultivation  (or  protected  growth)  as  it  eliminates  competitive 
               selection.