RESEARCH ARTICLE
Major Histocompatibility Complex Allele Persistence in Eurasia and America in the Genus During Million Years

Genus Carduelis (Fringillidae family) includes goldfinches, siskins, redpolls, greenfinches and crossbills. Many of the species classified within this genus and other related genera have been grouped by using molecular systematics and the mitochondrial cytochrome b (mt cyt b) gene. According to this, the Eurasian siskin (C. spinus) is the only one extant direct ancestor of several North American finches; North American / South American radiations may have been originated by Eurasian siskin (or extinct relative). In the present work, we aim to perform a study of transpecies and transcontinental analyses of MHC (Major Histocompatibility Complex) Class I alleles in several genus Carduelis / Spinus species in order to draw evolutionary conclusions in several wild bird species belonging to the genus Carduelis / Spinus.

Blood was taken from worldwide wild bird species. Passerine phylogeny was done after analysing mtDNA with Maximun Likelihood and Bayesian dendrograms. Major histocompatibility complex alleles were obtained by standard DNA cloning and sequencing.

We found two matches between MHC-I DNA alleles from different South American siskins at DNA level. Also, it was observed that the Eurasian siskin shares a protein with pine siskin and another with three South American siskins. Eight South American siskins species also share the same MHC protein. In addition, studied songbirds MHC class I intron 2 is longer than that of Gallus gallus.

We have drawn the following conclusions: 1) We present the first direct evidence that “Minimal Essential MHC” does not exist for birds; one of its main definition characters, i.e.: small intron size does not hold for songbirds. 2) We also report that MHC genes transpecies evolution exist in birds by showing also for the first time that worldwide bird species keep the same MHC protein and DNA alleles. 3) New evidences on MHC alleles conservation from Eurasian Carduelis spinus (most ancient) to South American siskins (most recent) during million years support that Eurasian siskin is the parental species for American Genus Carduelis (Spinus) species. It is uncertain whether Eurasian siskin (or extant relative) had initially an Holoartic distribution, including America.