What is the similarity between a bat and a dolphin? Most people’s immediate answer would be “not a lot.” However, a group of researchers have recently sought to investigate the genetic profiles of these two unrelated species, based upon a single similarity in their behavior. The group want to know whether their ability to use echolocation signifies they have rudimentary genetic ties, molded by their environment.

Convergent Evolution

A species’ evolution is typically thought to be based upon divergence of genes. Different genes code for different proteins and regulate various cellular processes and mechanisms; hence, evolution can result in a potential changeup on a cellular level, which can then have an impact upon what is known as an organism’s phenotype, the physical and behavioral traits an animal demonstrates based upon genetic expression.

However, according to recent studies, certain traits may appear around about the same period of time, across several species. This occurs due to selection pressures, where an environmental condition, to which several species are exposed, causes a number of species to develop the same traits and behaviors that confer them some new advantage and increases their chances of survival in the wild. This is referred to as adaptive phenotypic convergence.

An example of such convergent evolution has already been witnessed in a huge number of species, including birds, bats and a number of insects. These different species all developed wings, independently of one another and “converged” around this highly beneficial trait. Anatomically, however, the wings of these species differ considerably, with huge structural differences evident upon inspection.

Meanwhile, dolphins, sharks and, the now extinct, ichthyosaurs all demonstrated the same convergent evolution, with mirroring body shapes that facilitated streamlined movement through water. But, could bats and dolphins really have experienced the same genetic evolution to develop echolocation?

The Study

The study’s authors sought to investigate the genetic sequences of two species of animal that were thought to have evolved independently – bats and bottlenose dolphins. Both bats and bottlenose dolphins use a similar echolocation technique to navigate their surroundings. This led the research team to determine whether their might be genetic similarities between the two species, explaining their phenotypic trait for echolocation.

Researchers looked at the genomic sequences of 22 mammals, consisting of different species of bats (including the greater false vampire bat, Parnell’s mustached bat, the large flying fox and the straw-colored fruit bat) and the bottlenose dolphin. The genome-wide survey used specialized computer programs to analyze the probability that particular convergent adaptations were purely introduced by coincidence.

Echolocation

Echolocation relies upon the animal emitting bursts of ultrasonic waves and detecting the deflected waves, which bounce off environmental objects. Determining the distance between the animal and a particular object is achieved by measuring the delay between initial transmission of the sound wave and then receiving it. The greater the distance between the animal and the object, the longer the delay.

Ultimately, this is a very simplistic description of the process, which is far more complex when put into practice. The animal in question is also capable of computing the intensity of the waves reaching each ear, and the time delay for a given sound wave to reach each ear, which helps to generate a more comprehensive sense of any object’s location and also provides information regarding its size.

Echolocation helps animals find objects, hunt prey and move seamlessly through their environment. In addition, many animals, including dolphins, are thought to use echolocation as a form of communication between different members of their community.

Findings

Bottlenose dolphins and bats seemed to show considerable genetic convergence, including within genes that had been implicated in hearing and vision.

Dr. Joe Parker of the Queen Mary School of Biological and Chemical Sciences, who was the paper’s lead author, explained the startling results obtained from their research. He maintains the group were only expecting to identify around a dozen identical changes to some of the genes, but, in actual fact, they stumbled across 200 genes with these identical convergent alterations.

These 200 genes all demonstrated a “convergence signature” profile, showing that natural selection plays a major part in the convergent evolution of the species. These patterns only existed between echolocating bats and the bottlenose dolphin; non-echolocating bats did not reveal the same genetic changes.

Dr. Stephen Rossiter, the research group’s leader, claims their work to be “… the tip of the iceberg,” as the genetic sequencing and analysis of additional species could yield even further patterns of convergent evolution between different mammalian species. In addition, further research could also be conducted into other traits, including neurological, digestive and social behavior, to name but a few. So, now we know that bats and dolphins share some rather remarkable evolutionary similarities, and not just simply involving echolocation.

By: James Fenner

Nature Journal Link

Queen Mary Press Release

CBS Article Link

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