- Article -
| In Silico Biology 7, 0024 (2007); ©2007, Bioinformation Systems e.V. |
Positive Darwinian selection on crustacean hyperglycemic hormone (CHH) of the green shore crab, Carcinus maenas
Abinash Padhi1*, Bindhu Verghese1, Subhendu K. Otta2, Binu Varghese3 and Karri Ramu4
1 Department of Biological Science, University of Tulsa, 600 S. College Ave., Tulsa, OK- 74104, USA
2 Baylor College of Medicine, Department of Pediatrics-Hematology/Oncology, 6621 Fannin Street, MC 3-3320, Houston, TX-77030, USA
3 Central Marine Fisheries Research Institute, Vizhinjam Research Center, Trivandrum, Kerala, India
4 Center for Marine Environmental Studies, Ehime University, Bunkyo Cho 2-5, Matsuyama 790 - 8577, Japan
* Corresponding author
Email: abinash-padhi@utulsa.edu
Edited by E. Wingender; received December 28, 2006; revised March 12, 2007; accepted April 03, 2007; published June 16, 2007
Abstract
The tissue-specific expression and differential function of the crustacean hyperglycemic hormone (CHH) in Carcinus maenas indicate an interesting evolutionary history. Previous studies have shown that CHH from the sinus gland X-organ (XO-type) has hyperglycemic activity, whereas the CHH from the pericardial organ (PO-type) neither shows hyperglycemic activity nor it inhibits Y-organ ecdysteroid synthesis. Here we examined the types of selective pressures operating on the variants of CHH in Carcinus maenas. Maximum likelihood-based codon substitution analyses revealed that the variants of this neuropeptide in C. maenas have been subjected to positive Darwinian selection indicating adaptive evolution and functional divergence among the CHH variants leading to two unique groups (PO and XO-type). Although the average ratio of nonsynonymous to synonymous substitution (ω) for the entire coding region is 0.5096, few codon sites showed significantly higher ω (10.95). Comparison of models that incorporate positive selection (ω > 1) with models not incorporating positive selection (ω < 1) at certain codon sites failed to reject (p = 0) evidence of positive Darwinian selection.
Keywords: molecular evolution, crustacean hyperglycemic hormone, positive Darwinian selection, synonymous and nonsynonymous substitution, Carcinus maenas