Drop of blood, a sea of information

GENE TRACKING

Drop of blood, a sea of information

Sahas Barve talks about the advances in technology that are helping in analysing the genetic material of small animals

At a Baya weaver bird colony at the beginning of the monsoon, bright yellow males feverishly build extravagant grass nests.

Females ‘window shop’ multiple nests before choosing a nest they like and mate with the owner. But what does the quality of the nest tell the female about the quality of the male as a mate? Are males that make the best nests successful at attracting the most females?

There is a simple biological metric for gauging an individual’s success at mating. It is called ‘lifetime fitness’ — the number of offspring an individual leaves behind.

We could assume that males with the most intricate nests would have high lifetime fitness. However, such males might be bad parents, leading to low chick survival and low lifetime fitness. When females choose males based on nest quality, are they using the right cues to choose between males? A drop of blood from some of the birds can reveal all. To really knit together Baya weaver male lifetime fitness and the complexity of their nests, we can do a simple study.

Uniquely band males so they can be identified from a distance and record the complexity of their individual nest. Take a small drop of blood from the male birds and their chicks, from which genetic information can be extracted. Carry out paternity analyses to see if males with the most ornate nests successfully fathered more offspring.

Most birds are known to flirt around many partners and score some matings on the side. Hence, determining paternity and therefore fitness is only possible using genetic techniques. In fact, now more than ever before, research has demonstrated beyond doubt that the ecology and behaviour of a species has a genetic basis. Because evolution is strongly governed by ecology, ecology and evolution cannot be studied in isolation. Modern DNA sequencing has now made it possible to test many ecological and behavioural hypotheses concerning evolution.

Non-invasive techniques

Today, most evolutionary studies involve sampling and analysing genetic material. Advancing technology has enabled many analyses to be done with very little genetic material.

This has helped studies that involve large, rare and endangered species through data collection using “non-invasive techniques”, which use faecal and hair samples as DNA sources. Acquiring genetic material for small animals (birds, lizards, frogs) is tricky because unlike large mammals, they don’t leave behind hair and scat as retrievable biological samples. Hence, non-invasive techniques can almost never be used for collecting genetic material. Most sample collection techniques involve capturing animals for brief periods, obtaining samples and then letting them go alive.

This process varies according to the species: a drop of blood for birds, toe or tail clips for small mammals, amphibians and lizards. Most of these methods, if properly executed, guarantee little stress for the animal and a wealth of information. There is no doubt these sample collection techniques could be stressful for animals. However, a number of independent studies have confirmed that the stress is momentary and that these practices do not significantly affect the lifespan or behaviour of the individual animal.

Correct classification

In order to collect genetic samples, researchers undergo extensive institutional training and follow strict guidelines to ensure the most comfort and optimal hygiene conditions for the animals. With the correct training and a bit of practice, both these can be easily achieved. So what can a drop of blood from a bird or part of a rodent’s tail tell us about that individual or its species? Until the mid-20th century, taxonomists used physical attributes to classify organisms. But this technique misclassified animals with ‘convergent traits’.

For example, cyanobacteria, a kind of bacteria that forms the green film over village ponds, was classified as an algae (blue-green algae) for hundreds of years until DNA analysis proved otherwise. Since DNA is found in every living organism, scientists now classify all life forms on earth based on the differences in their DNA sequence. DNA sequences diverge with time as two groups cease to breed with one another. This divergence can not only classify humans and horses to different families, but can also be used to study gene flow between populations of the same species, be it plants or bacteria or animals.

At the other end of the spectrum, we can measure genetic ‘distance’ or divergence between individuals and populations of the same species. This can help us quantify the gene flow or connectivity between populations like the tiger study mentioned earlier. It can also help us understand the effects of historical events on present distributions. A study looking at divergence between the populations of leopard cats in India showed that the northern and southern populations are completely disconnected due to warming of the climate in central India since the last Ice Age restricting the habitat of the leopard cat, inhibiting further gene flow between these populations.

There is not only a pressing need for exploratory research to discover new species in unexplored areas but also to better understand the ecology and evolution of species we have long known. Genetic analysis offers an invaluable tool for accomplishing these tasks. Using genetic analyses of abundant species we can study a wide range of topics like the biological basis for adaptation to cold climates, the connectivity between patches of important habitats and sexual selection in Baya weavers to name a few. In a rapidly developing country like India, such research can help us better appreciate our natural heritage.

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