Looks aren't everything
Over the last two decades, new species are being uncovered at a rapid rate in India. What, beyond looks, do scientists consider to describe a new species? Sandhya Sekar finds out.
doi:10.1038/nindia.2012.32 Published online 29 February 2012
When trying to differentiate between two species, external physical characteristics are not the only indicators. Scientists have to dig deeper to rake up other clues that can define a species better.
For instance, animal sounds — calls or songs which males deploy to serenade females, such as, the musical call of a cuckoo, frogs croaking or crickets calling — are unique to individual species. Again, species that have similar lifestyles end up looking alike but that doesn't fool scientists. For instance, birds, bats and butterflies have wings because they all fly. This does not mean they are closely related.
It's not just about the looks.
Piecing the puzzle
The most widely used clues are buried in snippets of the genetic code (DNA), found in all living organisms. If two species evolved from one ancestor but went their separate ways during evolution, scientists can read the separation story in their DNA. Humans and chimpanzees had a common ancestor 5 to 7 million years ago, after which the two species 'diverged'.
The ecology of a species informs scientists about other characters that can help differentiate between species. Male butterflies and moths have special scent organs that leave a trail of 'pheromones', only for females of their own species. These species-specific scents, and songs in birds, frogs and some insects, attract mates. These features make excellent diagnostic characters for describing species.
The species diagnostic toolkit
Ranjana Jaiswara and Rohini Balakrishnan from the Centre for Ecological Sciences, Indian Institute of Science, Bangalore, along with collaborators, have been examining a group of crickets of the genus Itaropsis. When they started, this genus had one species reported from India and Sri Lanka — Itaropsis tenella. From Bombay till south Tamil Nadu, they looked the same, but the males sang very differently. This made the researchers suspicious: there could well be more than one species, mistakenly placed under the same bracket because they looked very alike.
A female cricket uses male song to choose her mate — the male who hits the right note nails her. This means, rather than external appearance ('morphology'), male songs are probably better indicators of species differences.
The group recorded sample male songs across four habitats. Similar looking males sang very differently, in at least three different tunes. So they reached for the next piece of the jigsaw puzzle: DNA evidence.
The singing males were examined morphologically and genetically. The researchers analysed the songs on parameters such as duration and frequency. They looked at 40 different morphological characters such as wing pattern and male genital structure.
Three in one
A 'phylogenetic analysis' was used to analyze the DNA and morphological data. This analysis uses available data and algorithms to reconstruct evolutionary relationships. The DNA snippets used in this study evolved at a rapid rate, and could catch the signature of recent divergence.
The analysis revealed a 'phylogeny' that depicts how individuals were related over evolutionary time. Using advanced computation techniques, scientists can get an idea about what happened millions of years ago.
Similar songs were grouped together.
Then came the acid test: did the evidence from DNA, morphology and songs give similar results?
Turns out, three groups emerged in all of them. The scientists could not arrive at a single distinguishing diagnostic character in either the song pattern, or the morphological features. This implies, the three groups did not differentiate because of different songs; they were different because of geographic distance.
As a result of this study, the Sri Lankan Itaropsis will remain Itaropsis tenella, while the Indian species will be Itaropsis parviceps, with three subspecies based on geographic regions.
Over the last two decades, there has been a revolutionary number of new species described in India, with over 40 new species of amphibians alone. A new family of caecilians — worm like, soil dwelling amphibians — has recently been described from North East India.
Think of this: lions, tigers, leopards, and domestic cats all belong to the cat family. A new 'cat family' from India would imply discovery of a new carnivore, cat like in appearance, but so different in other aspects that it has to be put in a different family.
The discovery of new species at such a rate shows that there is a lot of biodiversity yet to be studied in India. Fine scale inventories, detailed study of morphological characters, and molecular studies where possible, will help in revealing these hidden riches. There is a sense of urgency in this exploration now, given the huge population pressure on most of these species.
- Jaiswara, R. et al. Testing concordance in species boundaries using acoustic, morphological, and molecular data in the field cricket genus Itaropsis (Orthoptera: Grylloidea, Gryllidae: Gryllinae). Zoo. J. Linn. Soc-Lond. 164, 285-303 (2012) | Article |