Potential Causative Mutation for Melanism in Rats Identified in the Agouti Signaling Protein Gene (Asip) of the Rattus rattus Species Complex on Okinawa Island, Japan

Abstract

The occurrence of black fur, or melanism, in many mammalian species is known to be linked to DNA sequence variation in the agouti signaling protein (Asip) gene, which is a major determinant of eumelanin and pheomelanin pigments in coat color. We investigated 38 agouti (i.e., banded wildtype) and four melanistic Rattus rattus species complex (RrC) lineage II specimens from Okinawa Island, Ryukyu Islands, Japan, for genetic variation in three exons and associated flanking regions in the Asip gene. On Okinawa, a predicted loss-of-function mutation caused by a cysteine to serine amino acid change at p.124C>S (c.370T>A) in the highly conserved functional domain of Asip was found in melanistic rats, but was absent in agouti specimens, suggesting that the p.124C>S mutation is responsible for the observed melanism. Phylogeographic analysis found that Asip sequences from Okinawan RrC lineage II, including both agouti and melanistic specimens, differed from: 1) both agouti and melanistic RrC lineage I from Otaru, Hokkaido, Japan, and 2) agouti RrC lineages I and II from South Australia. This suggests the possibility of in-situ mutation of the Asip gene, either within the RrC lineage II population on Okinawa or in an unsampled RrC lineage II population with biogeographic links to Okinawa, although incomplete lineage sorting could not be ruled out.

The Genetic Basis of Melanism in Abert’s Squirrel (Sciurus aberti)

“…However, the new mutation in S. aberti is very similar to a melanism-causing mutation that has been found in rats (Rattus rattus) [44]. This mutation occurs at the same base pair in the ASIP gene, but instead of a T→C (cysteine → arginine) mutation as found in S. aberti, it is a T→A (cysteine → serine) mutation [44]. Among other tree squirrels, the mutation found in S. aberti is similar to the mutation in the southeastern populations of S. niger.…”

“…This novel mutation is different than the 24 base pair deletion in MC1R previously documented in S. carolinensis and western S. niger and the single base pair mutation in ASIP causing melanism in southeastern S. niger. However, the new mutation in S. aberti is very similar to a melanism-causing mutation that has been found in rats (Rattus rattus) [44]. This mutation occurs at the same base pair in the ASIP gene, but instead of a T→C (cysteine → arginine) mutation as found in S. aberti, it is a T→A (cysteine → serine) mutation [44].…”

Large scale phenotypic characterisation of Hierophis viridiflavus (Squamata: Serpentes): climatic and environmental drivers suggest the role of evolutionary processes in a polymorphic species

“…Body colourations have been widely investigated from the genetic point of view: past research on American colubrids suggests that polymorphisms in colour and ornamentations can be inherited in a simple Mendelian way (Zweifel 1981) or, alternatively, that melanism can be inherited as a recessive character (King 2003). Nevertheless, colour polymorphisms including melanism can be the result of complex genetic processes such as gene flow via introgression among closely related lineages (Sasamori et al 2017;McRobie et al 2019). Therefore, melanism has been of great interest for zoologists to investigate the underlying mechanisms that drive species adaptation to specific environments (Muggleton et al 1975;Portik et al 2010).…”

Large scale phenotypic characterisation of Hierophis viridiflavus (Squamata: Serpentes) suggests genetic admixture between closely related lineages

“…Body colourations have been widely investigated from the genetic point of view: past research on American colubrids suggests that polymorphisms in colour and ornamentations can be inherited in a simple Mendelian way (Zweifel, 1981) or, alternatively, that melanism can be inherited as a recessive character (King, 2003). Nevertheless, colour polymorphisms including melanism can be the result of complex genetic processes such as gene ow via introgression among closely related lineages (Sasamori et al 2017;McRobie et al 2019). Therefore, melanism has been of great interest for zoologists to investigate the underlying mechanisms that drive species adaptation to speci c environments (Muggleton et al 1975, Portik et al 2010.…”