Affiliations: Department of Biological Science, University of Tulsa,
600 S. College Ave., Tulsa, OK-74104, USA | Baylor College of Medicine, Department of
Pediatrics-Hematology/Oncology, 6621 Fannin Street, MC 3-3320, Houston,
TX-77030, USA | Central Marine Fisheries Research Institute, Vizhinjam
Research Center, Trivandrum, Kerala, India | Center for Marine Environmental Studies, Ehime
University, Bunkyo Cho 2-5, Matsuyama 790-8577, Japan
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.
