A major challenge in biology is to understand how species evolve. Today, about 150 years after the publication of Darwin “On the Origin of Species” we really still do not understand the process of speciation. This is partly due to the fact that most classical studies of speciation are based on species that have diverged, and therefore, we speculate back in time to infer the causes of speciation. A effet, two of the best known examples of “sympatric speciation”, cichlids of Lake Victoria and horseshoe bats of Wallace, suggest that the sensory ecology (how an animal perceives and interacts with its environment) plays a major role in the speciation process, that the populations are geographically isolated or not. However, in these studies, researchers were unable to study the factors involved in the early stages of the process of speciation.
Bumblebee bats, smallest mammal in the world; photo taken in Burma 2006 by the field team.
«Our study is unique in the sense that it captures the speciation “in action” in populations that are currently diverge ecologically. These populations are those of the smallest mammal in the world, the bumblebee bat (Craseonycteris thonglongyai) found only in Thailand and Burma. These people represent a unique natural experiment that allows “capture” the evolutionary process has a time scale for identifying the nature of these processes that result in nature speciation” says Dr Emma Teeling who led the research team during this study.
By studying the process of early speciation at different evolutionary time scales, this study shows that in the case of this species, a limited gene flow, resulting from the geographical distance, is needed to promote ecological speciation sensory.
“To do, we examined the spatial structure, genetic structure and ecological traits between sensory and within only two known populations of the smallest mammal in the world, the bumblebee bat (Craseonycteris thonglongyai). We generated and collected a large set of molecular data, Ecological and acoustic show that geographic distance plays a key role in limiting gene flow rather than the divergence of echolocation. Our results support the idea that sensory ecology acts as a strengthening mechanism in the speciation process rather than being the main driver as was previously assumed in other well-documented empirical. Our results raise the question of whether sympatric speciation actually occurs, or if some level of geographic isolation and thus restricted gene flow is still required to initiate the process of speciation », said Dr. Sebastien Puechmaille, lead author of the study.
Another interesting finding of this study is the identification of a gene “echolocation” (RBP-J) showing signs of divergent selection corresponding to the divergence of echolocation in this Thai population. This is the first association of this gene identified with capacities of echolocation. This gene is involved in the formation of hair cells in the cochlea (receptor organ sounds in the inner ear). As bats use the highest frequencies (above 200 kHz) of all mammals, their auditory system, especially the hair cells in the organ of Corti, where the sound is received and amplified, needs special adaptations.
«We also show that interspecific competition with another species of bat, Myotis siligorensis, is probably the cause of localization sensory, as opposed to random drift or abiotic factors such as temperature and humidity», said Dr. Sebastien Puechmaille.
From the standpoint of conservation, this is the first study to investigate the population structure and evolutionary history of the world's smallest mammal, the bumblebee bat, Craseonycteris thonglongyai. “This species of bat is rare and endangered charismatic, limited to a region of 2000 km2 in the border area between Thailand and Burma and is considered one of the ten species evolutionarily distinct and globally endangered (Evolutionary Distinct and Globally Endangered, EDGE, species)“, said Dr. Emma Teeling.
Phylogenetic analyzes of markers transmitted through the maternal line, paternal, or inherited by both parents and ecological data demonstrate the presence of two species of bumblebee bat, one in Thailand and Burma, which are separated there are about 0,4 million years. Limited dispersal abilities of individuals combined with a very limited range (less 2000 km2) suggest that both species are threatened and require management plans and conservation distinct.
This paper is published 6 December 2011 so is available free in the journal Nature Communications (http://www.nature.com/ncomms/journal/v2/n12/pdf/ncomms1582.pdf). The reference of this paper is :
Puechmaille, S.J., Ar Gouilh, M., Piyapan, P., Yokubol, M., Khin Mie Mie, Bates, P.J.J., Satasook, C., Tin Nwe, Si Si Hla Bu, Mackie, I.J., Small E.J., and Teeling E.C. (2011). The evolution of sensory divergence in the context of limited gene flow in the bumblebee bat. Nature Communications 2, 573, DOI: 10.1038/ncomms1582. [The evolution of sensory discrepancy in the context of limited gene flow in the bumblebee bat].
This work represents an Irish project, IFC-financed, an Irish Foundation for Science and awarded to Dr.. Emma Teeling. This project was a collaboration between researchers in France, Thailand, and Birmanie, UK and Ireland to address a fundamental question in biology with implications for conservation.