Evolutionary history of Mexican domesticated and wild Meleagris gallopavo

Abstract

Background: The distribution of the wild turkey (Meleagris gallopavo) extends from Mexico to southeastern Canada and to the eastern and southern regions of the USA. Six subspecies have been described based on morphological characteristics and/or geographical variations in wild and domesticated populations. In this paper, based on DNA sequence data from the mitochondrial D-loop, we investigated the genetic diversity and structure, genealogical relationships, divergence time and demographic history of M. gallopavo populations including domesticated individuals.

Results: Analyses of 612 wild and domesticated turkey mitochondrial D-loop sequences, including 187 that were collected for this study and 425 from databases, revealed 64 haplotypes with few mutations, some of which are shared between domesticated and wild turkeys. We found a high level of haplotype and nucleotide diversity, which suggests that the total population of this species is large and stable with an old evolutionary history. The results of genetic differentiation, haplotype network, and genealogical relationships analyses revealed three main genetic groups within the species: mexicana as a population relict (C1), merriami (C2), and mexicana/intermedia/silvestris/osceola (C3). Haplotypes detected in domesticated turkeys belong to group C3. Estimates of divergence times agree with range expansion and diversification events of the relict population of M. gallopavo in northwestern Mexico during the Pliocene-Pleistocene and Pleistocene-Holocene boundaries. Demographic reconstruction showed that an expansion of the population occurred 110,000 to 130,000 years ago (Kya), followed by a stable period 100 Kya and finally a decline ~ 10 Kya (Pleistocene-Holocene boundary). In Mexico, the Trans-Mexican Volcanic Belt may be responsible for the range expansion of the C3 group. Two haplotypes with different divergence times, MGMDgoB/MICH1 and MICH2, are dominant in domesticated and commercial turkeys.

Conclusions: During the Pleistocene, a large and stable population of M. gallopavo covered a wide geographic distribution from the north to the center of America (USA and Mexico). The mexicana, merriami, and mexicana/intermedia/silvestris/osceola genetic groups originated after divergence and range expansion from northwestern Mexico during the Pliocene-Pleistocene and Pleistocene-Holocene boundaries. Old and new maternal lines of the mexicana/intermedia/silvestris/osceola genetic group were distributed within the Trans-Mexican Volcanic Belt where individuals were captured for domestication. Two haplotypes are the main founder maternal lines of domesticated turkeys.

Fig. 1

Geographical origin of the turkey samples used for this study. Localities of sampling of turkeys for this study (green dots), and locations of the NCBI GenBank database sequences (blue dots); the shaded polygons correspond to the following geographical regions of Mexico: SMOc = Sierra Madre Occidental (yellow), SMOr = Sierra Madre Oriental (green), TMVB = Trans-Mexican Volcanic Belt (blue), and the MP = Mexican Plateau (not shaded)

Fig. 2

Median-joining haplotype network. The relationships between haplotypes identified in domesticated and wild M. gallopavo, including 612 individuals and 64 haplotypes are shown. The size of the circles is proportional to the haplotype frequency. Black circles represent hypothetical intermediates or unsampled haplotypes. Dotted gray lines indicate loops that were broken according to Crandall and Templeton [70]

Fig. 3

Genealogy of M. gallopavo obtained with Bayesian inference (BI) and maximum likelihood (ML) analyses. Estimates were based on 441 characters of M. gallopavo mitochondrial control region DNA sequences. The out-group is the sister species M. ocellata. Names of distinct clades/groups are indicated. Values over the branches represent posterior probabilities and bootstrap values (PP/BP). (*) Values below PP = 0.5 or PB = 50. The keys of the taxa are in Table 2

Fig. 4

Mismatch distribution and Bayesian skyline plots. Mismatch distribution for the domesticated group (a). Histograms correspond to the observed frequencies; the line represents expected frequencies under the sudden expansion model. Bayesian skyline plots shows the population history of M. gallopavo (b), with the black line indicating median population size estimates expressed in N_e. through time; colored areas represent 95% HPD intervals

Fig. 5

Map of the geographical distribution of M. gallopavo. The shaded areas represent the distribution of the species according to Porter and Kirwan [2]. Pie charts represent the geographical distribution of haplotypes found in each sampling locality