It is increasingly recognized that the study of the mechanisms underlying the evolution and maintenance of biodiversity is indispensable. Adaptive radiation, one of the main mechanisms of biodiversity evolution, is usually triggered when ancestral animals colonize new environments. However, the evolutionary mechanisms of adaptation to new environments are still poorly understood. A research team led by Assistant Professor Jun Kitano at Graduate School of Life Sciences, Tohoku University, has discovered that evolutionary change in the thyroid hormone signaling pathway plays an important role in colonization of ancestral marine stickleback fishes
to new environments, freshwater streams.

 Hormones are key substances that regulate diverse physiological responses important for survival against environmental stress. Both excess and shortage of certain hormones can cause several human diseases. Although subclinical individual or racial variations in plasma hormone levels have been reported, we do not know well about the ecological significance or evolutionary mechanisms of such variations.

 In the present study, an evolutionary biologist Jun Kitano collaborated with fish endocrinologists to investigate the inter-population variation in the thyroid hormone signaling in fish. Thyroid hormone is known important for metabolic regulation. They found that stickleback fish that colonized small stream reduced the levels of plasma thyroid hormone and pituitary thyroid-stimulating hormone. They also found that the fish reduced the metabolic rate and swimming activity. Furthermore, they found that reduction of the thyroid-stimulating hormone is partially caused by a genetic change at a genomic locus. The results demonstrate that evolutionary change in the thyroid hormone signaling was a key for colonization of stickleback fish into a new environment, stream.

 "Reduction of metabolic rate and swimming activity might be adaptive for residency in small streams," said study leader Jun Kitano, because not so many foods are available in small streams as in marine environments, but the fish do not have swim a lot in a small place." Our study clearly demonstrates that hormonal changes can play key roles when animals colonize novel environments. Further collaborations between evolutionary geneticists and endocrinologists will be really exciting, " Jun Kitano said.

 This study was published online in Current Biology on November 18, 2010.
 

Marine stickleback (Photos by Seiichi Mori)

 

Stream stickleback (Photos by Seiichi Mori)

[Contact]
Assistant Professor Jun Kitano
Graduate School of Life Sciences, Tohoku University
TEL: +81-22-795-6689
E-mail: jkitano*m.tohoku.ac.jp (Replace * with @)
Website: http://www.lifesci.tohoku.ac.jp/teacher/environmental/a_kitano.html