Research Article |
Corresponding author: Ricardo Serna-Lagunes ( rserna@uv.mx ) Academic editor: Ana Maria Leal-Zanchet
© 2020 Ruth Guadalupe Castillo-Rodríguez, Ricardo Serna-Lagunes, Anabel Cruz-Romero, Rosalía Núñez-Pastrana, Luz Irene Rojas-Avelizapa, Carlos Llarena-Hernández Régulo, José Antonio Dávila.
This is an open access article distributed under the terms of the CC0 Public Domain Dedication.
Citation:
Castillo-Rodríguez RG, Serna-Lagunes R, Cruz-Romero A, Núñez-Pastrana R, Rojas-Avelizapa LI, Régulo CL-H, Dávila JA (2020) Characterization of the genetic diversity of a population of Odocoileus virginianus veraecrucis in captivity using microsatellite markers. Neotropical Biology and Conservation 15(1): 29-41. https://doi.org/10.3897/neotropical.15.e47262
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The genetic diversity and effective population size (Ne) of a population of Odocoileus virginianus veraecrucis in captivity were characterized in the Wildlife Management Unit “El Pochote”, located in Ixtaczoquitlán, Veracruz, Mexico. Blood tissue was collected from 20 individuals of the reproductive nucleus, its genomic DNA was extracted, and genetic diversity was characterized by six microsatellites amplified by PCR and visualized in polyacrylamide gels. With four polymorphic microsatellites, 66.7% of the population’s genetic variation was explained, which was characterized by an allelic diversity that fluctuated between 9 and 28 alleles (18 average alleles), suggesting a mean allelic diversity (Shannon index = 2.6 ± 0.25), but only 12 ± 2.9 effective alleles would be fixed in the next generation. The heterozygosity observed (Ho= 0.81) exceeded that expected (He= 0.79) and these were significantly different (P> 0.05), as a result of a low genetic structure in the population (fixation index F = -0.112 ± 0.03), due to the genetic heterogeneity that each sample contributed, since the specimens came from different geographical regions. The Ne was 625 individuals and a 1:25 male:female ratio, with which 100% of the genetic diversity observed can be maintained for 100 years. The information obtained in the study can help in the design of a reproductive management program to maintain the present genetic diversity, without risk of losses due to genetic drift and inbreeding.
allelic diversity, conservation, effective population size, Veracruz white-tail deer
Populations in nature, isolated or fragmented, are subject to the constant process of adaptation to different extreme environmental conditions and to the effects of anthropogenic nature, which can reduce genetic diversity. In addition to recombination, changes in genetic diversity derive from mutations in deoxyribonucleic acid (DNA) and their variation (polymorphism) determines the phylogenetic and evolutionary relationship of species (
In Mexico, an alternative for the conservation and utilization of wild populations is carried out in a productive diversification system called the Wildlife Conservation Management Unit (Unidad de Manejo para la Conservación de la Vida Silvestre; UMA in Spanish), where an alternative is the management of populations in captive conditions (
Of the cervids with distribution in Mexico, White-Tailed deer (Odocoileus virginianus Zimmermann, 1780) is the species of deer with the highest capacity to adapt to the environment (
The assessment of the genetic status of populations of O. virginianus has been useful for implementing risk prevention measures of a genetic nature; for example: multiple paternity (
In Mexico, O. virginianus management plans in UMAs, are mainly based on habitat management, but in captivity or ex situ UMA, do not contemplate programs of conservation of genetic diversity to reduce the risks caused by a Ne small or a few founders. In this sense, the objective of this study was to describe the characteristics of the genetic diversity of a population of O. v. veraecrucis, kept in a hatcheries (UMA) located in the municipality of Ixtaczoquitlán, Veracruz, Mexico. Captivity is highlighted as a means of conserving genetic diversity in an ex situ system.
Between March-September 2017, 20 individuals from the reproductive nucleus of the population of O. v. veraecrucis managed in the UMA “El Pochote”, were sedated (Xilacina of 0.5-1.25 ml per 25 kg of live weight) to extract by puncture in the jugular vein between 2 and 3 ml of blood with Vaccutainer® equipment with 4 g of EDTA as anticoagulant. Blood samples were stored in refrigeration at 15 °C (
The microsatellites were amplified from the DNA of the specimens by PCR to a final volume of 25 µl with the following content: 2.5 µl of DNA (<250 ng), 1.25 µl of the primer Forward and 1.25 µl of the primer Reverse, both at a final concentration of 10 µM, 12.5 µl of Promega® Brand Master Mix 2X PCR (25 mM Tris-HCl pH 9, 25 mM NaCl, 2.5 mM MgCl2, 100 µM dNTPs (dATP, dGTP, dCTP, dTTP), 0.5 U of Taq DNA polymerase, 0.05 mg / ml BSA) and 7.5 µl of nuclease-free water. The PCR amplification program included the following stages: initial denaturation at 95 °C for 2 min, denaturation at 95 °C at 1 min, alignment at 54 °C for 30 s, extension at 72 °C for 1 min; final extension at 72 °C for 5 min, and at 4 °C until samples are withdrawn. These conditions were adapted based on those reported by
The microsatellite PCR products were visualized on 7% polyacrylamide gel electrophoresis in 0.5X TBE buffer. 15 µl of the PCR product of each sample was loaded for each microsatellite. The electrophoresis was maintained at a constant voltage of 70 V for 24 h. The gels were stained with ethidium bromide and at the beginning of each gel, a molecular size marker of 500 bp was placed, with label fragments every 50 bp, which served as a reference to determine the size in bp of the observed alleles.
The size (in base pairs) of the amplified alleles was determined from each sample, based on the size of the molecular marker. In the Excel® program, a data matrix was built based on the design proposed by
The Hardy-Weinberg equilibrium test (HW) was applied to the microsatellite data matrix to determine the loci that were found or not in equilibrium; the test statistic was based on an X2 test. According to
Estimating the effective population size (Ne) in captive populations is important to preserve the genetic diversity characterized by microsatellite markers (
The analysis of the mixture model showed three possible sources of genetic origin (cluster 1 = 0.335 and He = 0.9042; cluster 2 = 0.332 and He = 0.9048; cluster 3 = 0.333 and He = 0.9046; estimated probability of Ln of the data = - 753.2; mean value Ln likelihood = -593.8 ± 318.9; average alpha = 3.9565; Fig.
Hardy-Weinberg equilibrium test for the loci in the populations of O. virginianus veraecrucis in the UMA EL Pochote.
Locus | Degrees of freedom | Chi-square | Probability | Significance |
BM203 | 91 | 95.000 | 0.366 | Ns |
BM848 | 36 | 34.833 | 0.524 | Ns |
MSTN01 | 378 | 380.000 | 0.461 | Ns |
TGLA126 | 210 | 198.333 | 0.708 | Ns |
BM4208 | 15 | 26.007 | 0.038 | * |
D | 91 | 117.718 | 0.031 | * |
The allelic frequencies obtained from the four microsatellite loci are presented in Figure
Table
Sample size (N), number of different alleles (Na), effective number of alleles (Ne), information index Shannon (I), observed Heterozygosity (Ho) and expected Heterozygosity (He), Unbiased Expected Heterozygosity (uHe) and fixation index (F) for four microsatellite loci of O. v. veraecrucis.
Locus | N | Na | Ne | I | Ho | He | uHe | F |
BM203 | 19 | 14 | 7.848 | 2.325 | 1.000 | 0.873 | 0.896 | -0.146 |
BM848 | 11 | 9 | 6.541 | 2.035 | 1.000 | 0.847 | 0.887 | -0.180 |
MSTN01 | 20 | 28 | 18.605 | 3.164 | 1.000 | 0.946 | 0.971 | -0.057 |
TGLA126 | 20 | 21 | 16.000 | 2.907 | 0.999 | 0.938 | 0.962 | -0.067 |
Media | 17.5 | 18 | 12.248 | 2.608 | 0.999 | 0.901 | 0.929 | -0.112 |
SE | 2.17 | 4.14 | 2.98 | 0.26 | 0.0004 | 0.02 | 0.02 | 0.03 |
The effective population size (Ne) was developed as follows: Ht/Ho = 0.99 (to maintain 100% of the existing genetic diversity), t (average life span) = 8 years, then, t = 100 / 8 = 12.5. Therefore, 0.98 = e - 12.5 / 2Ne = e - 6.25/Ne. Then, the natural logarithm (ln) of the equation was obtained and we established that Ln 0.99 = -6.25/Ne; Ne = -6.25 / ln0.99 (-0.01); Ne = 625 individuals; that is, 625 reproductive animals are required to maintain 100% of genetic diversity, a number of animals greater than the current reproductive nucleus and that the UMA can sustain.
In this study, microsatellites genotyped in the O. v. veraecrucis DNA showed an estimated 67% polymorphic loci and 33% monomorphic loci; the two monomorphic microsatellites may result from the low number of alleles (Na = 4.143) and, consequently, this may be affected by the founder effect. The presence of monomorphic loci reported in this work is also reported in other studies of wild populations of O. virginianus (
The mixing model shows three possible potential sources of the population of O. v. veraecrucis analyzed in this study. As a fundamental effect, this may be the result of the heterogeneity of the geographical origin of the specimens with which the reproductive nucleus of the UMA El Pochote was founded, which enables us to know the degree of mixing and genetic independence between the analyzed deer that can help technicians in the planning of crossbreeding programs that guarantee the conservation of existing genetic diversity. On the other hand, the geographical origin of the deer studied corresponds to the geographical distribution area of O. v. veraecrucis, which also gives it some spatial genetic heterogeneity (
In terms of heterozygosity, the results indicate a relatively high level of genetic diversity in the captive population of O. v. veraecrucis at the UMA El Pochote. When analyzing heterozygosity values, it can be inferred that wild parents of the examined specimens have experienced bottlenecks and population expansion. Although these demographic processes were not tested in this study, it is possible that anthropic use (use for self-consumption, illegal trade, habitat fragmentation) and hunting use (controlled and clandestine hunting) that is exercised on the wild populations of the different subspecies of O. virginianus with geographic distribution in Mexico (
In this study, it was found that Ho was significantly different from He. The deviation between these indicators is due to genetic differences between the individuals in the population and may be due to the variation in allele frequencies between the samples or to the independent mixture of genes (
The allelic diversity found in the population of O. virginianus studied, was present in a smaller range of alleles per locus than that found for many species of mammals.
The genetic diversity characteristics of O. v. veraecrucis at UMA El Pochote show similar parameters compared to studies conducted in wild populations and other captive management systems. This is possibly due to the fact that the individuals that make up the population under study have their geographical origin in different areas of the known geographical distribution for this subspecies in the state of Veracruz, Mexico, which may explain the genetic heterogeneity and the low genetic structure, since there is an independent mixture of alleles. This population showed a medium allelic diversity and conservation is required to guarantee population viability; but it is necessary to establish a Ne of 625 copies to retain 100% of the existing genetic diversity. However, it is important to consider the genetic characterization for the selection of specimens destined for mating with which the existing genetic variability is maintained, without the risk of drift losses and inbreeding.
To the project “Caracterización de recursos zoogenéticos de las Altas Montañas, Veracruz: implicaciones de la filogeografía y modelación ecológica (PRODEP: 511-6/18-9245/PTC-896) for the financial and technical support of the study. To the Unidad de Manejo y Conservación de Recursos Genéticos y al Programa de Fortalecimiento de la Calidad Educativa of the Facultad de Ciencias Biológicas y Agropecuarias, Universidad Veracruzana, for the materials provided; and to the Instituto de Investigaciones en Recursos Cinegéticos (IREC), Spain, for the team and training to the first author. To the UMA El Pochote for facilitating blood samples. We thank the two anonymous reviewers who, with their suggestions, nurtured the quality of the content of the work.