Definition and Meaning
An ecotype refers to a genetically similar variety, population, or race within a species that is specifically adapted to certain local environmental conditions.
The term was introduced by Gote Turesson. Ecotypes, also called ecological or physiological races, may display phenotypic differences, such as variations in morphology or physiology, depending on the habitat they inhabit.
Despite these differences, individuals from different ecotypes of the same species can interbreed successfully without losing fertility or vigor, and they remain classified within a single taxonomic species.
In plants, environmental adaptations can manifest as morphological changes, such as alterations in the size and number of branches, leaves, flowers, or seeds. These genetic adaptations are permanent and heritable, meaning they persist across generations and remain unchanged even when grown in neutral environments.
For example, the grass Euphorbia hirta exhibits two ecotypes: one permanently adapted to dry conditions and another suited to moist conditions.
Gote Turesson’s Findings
Gote Turesson in 1922 coined the term ecotype following a series of observations and experiments involving Plantago maritima. He collected live specimens from various regions of Sweden and cultivated them in the same garden to study their differences. Turesson identified the study of ecotypes as a new research field, which he named genecology.
The key findings from his research are as follows:
- Species with a broad ecological range (the ability to adapt to environmental changes) exhibit morphological and physiological variations that differ from one location to another within their habitat.
- These variations are strongly linked to differences in habitat conditions.
- The variations are not purely phenotypic but also result from natural selection acting on specific genotypes within the species’ genetic variability. Mutations and natural recombination within a species create a smaller gene pool that becomes increasingly adapted to the local environment.
Later in 1965 Ramakrishnan identified two ecotypes of Euphorbia thymifolia: a red ecotype and a green ecotype. The red ecotype thrives in both calcium-rich (calcicolous) and calcium-deficient soils, while the green ecotype is restricted to calcium-deficient soils (calcifugous). The red ecotype carries a pair of dominant alleles, whereas the green ecotype has a pair of recessive alleles.
Ecotypes have also been documented in several other plants, including Portulaca oleracea, Ageratum conyzoides, Cenchrus ciliaris, Euphorbia hirta, and Cassia tora.
Characteristics of Ecotypes
- Ecotypes of a single species can interbreed and produce fertile offspring, as they belong to the same taxonomic species.
- They are genetically unique, and their traits are inheritable.
- Their variations are stable and permanent, remaining unchanged even when grown in neutral environments.
- Ecotypes exhibit a broad ecological range and can be differentiated based on distinct morphological and physiological traits.
- The differences observed in ecotypes are not the result of temporary environmental responses but are due to natural selection favoring populations adapted to specific local conditions.
Formation of New Ecotypes
New ecotypes can arise through the following processes:
- Hybridization: Ecotypes can emerge through natural crosses between two species. For example, when Spartina stricta crosses naturally with S. alterniflora, the hybrid S. townsendii is formed. This hybrid species often outcompetes its parent species due to better adaptability to its environment, leading to the elimination of the parent species from the habitat.
- Mutation: Natural mutations and genetic recombination can lead to the accumulation of a small gene pool within a population, enhancing its adaptation to specific environmental conditions. Additionally, cultivation or protected growth conditions can eliminate competitive pressures, fostering the development of new ecotypes.
- Chromosomal Changes: Structural modifications in chromosomes, such as translocations, inversions, or the addition or loss of chromosomal segments, can result in genotypic and phenotypic changes that give rise to new ecotypes. Polyploidy, in particular, contributes to the development of new ecotypes because polyploids often exhibit different ecological tolerances compared to their parent species.
Types of Ecotypes
There are five types of ecotype viz, Climatic ecotypes, Edaphic ecotypes, Climato-Edaphic ecotypes, Altitudinal & Latitudinal ecotypes and Physiological ecotypes.
- Climatic Ecotypes:
These ecotypes develop in response to variations in climatic factors such as light, temperature, and water availability. Also referred to as climatic clines, they were identified by Turesson (1930) in Leontodon autumnalis. - Edaphic Ecotypes:
These ecotypes arise due to differences in soil characteristics, such as moisture levels, nutrient availability, and pH. Gregor (1939) described edaphic ecotypes of Plantago maritima adapted to waterlogged conditions. Examples also include Lindenbergia polyantha and L. urticaefolia. In Euphorbia thymifolia, the red and green ecotypes are linked to soil calcium levels. - Climato-Edaphic Ecotypes:
These ecotypes develop under the combined influence of climatic and soil factors. An example is Cenchrus ciliaris. - Altitudinal and Latitudinal Ecotypes:
These ecotypes are shaped by differences in altitude or latitude. Altitudinal ecotypes are seen in Pinus and other gymnosperms, as well as in Achillea (discovered by Clausen). Latitudinal ecotypes occur in plants like Cassia tora (Senna) and Anagallis arvensis. - Physiological Ecotypes:
These ecotypes emerge due to physiological adaptations, such as responses to photoperiod, water absorption, or nutrient uptake. Photoperiodic ecotypes are observed in plants like Bouteloua curtipendula (long-day and short-day types), Prosopis, Argemone, and Rumex.
Significance of Ecotypes
- Ecotypes enable a species to expand its ecological range and spread to new areas.
- They make it possible to cultivate economically valuable plants across diverse habitats.
- The development of new ecotypes allows a species to adapt to a wide variety of climatic and ecological conditions.
- The pronounced differences among populations in different habitats can drive the evolution or formation of new species.
