Striking habitat reduction, decreased genetic diversity, and imperilled conservation of natural populations of Terrapene coahuila
Por:
Cortes-Rodriguez, Xochiquetzal, Borja-Martinez, Gabriela, Vazquez-Dominguez, Ella
Publicada:
1 may 2021
Categoría:
Aquatic science
Resumen:
1. Long-term evolutionary history and demographic processes shape
current patterns of genetic variation in natural populations. Genetic
diversity is of prime importance for the long-term survival of species,
especially those threatened or endangered, which can be lost in a few
generations and can take hundreds to recover. Notably, turtles are among
the most endangered vertebrate taxa in the world. The Coahuilan box
turtle Terrapene coahuila is the only aquatic species within the genus,
microendemic to the desert-spring ecosystem of the Cuatrocienegas Basin
(CCB). The CCB has experienced significant habitat changes during recent
decades, fragmenting otherwise interconnected wetlands systems. We aimed
to perform a detailed evaluation of the evolutionary and genetic
patterns of T. coahuila, both historical and contemporary, linked to the
biogeography of the CCB and processes governing the species
distribution.
2. We assessed the contributions of historical and contemporary
population demographic processes to genetic diversity and structure, by
using two mitochondrial DNA genes (cytochrome b and d-loop), one nuclear
gene (GAPD), and 12 nuclear microsatellite loci. We comprehensively
analysed these data to address historical patterns of demography,
migration, genetic diversity, and times of divergence across the valley
for T. coahuila. We also evaluated recent patterns of genetic variation
and structure, inbreeding, bottleneck signals, and effective population
size.
3. Our results dated the time to the most recent common ancestor for T.
coahuila in the CCB at c. 10.1 million years ago, with highest
diversification during the Holocene. Structure consistently comprised
two genetic clusters, Cuatrocienegas East and Cuatrocienegas West on
either side of the main historical barrier, the Sierra San Marcos.
Demographic results supported a divergence between western and eastern
populations from 47,500 to 110,950 years ago, and colonisation of the
southernmost Cuatrocienegas West distribution (Churince) 28,500-66,500
years ago, which experienced a recent bottleneck. All populations showed
low values of haplotype and nuclear genetic diversity, migration,
effective population size, and relatedness; significant inbreeding and
bottleneck signals were also identified within genetic clusters.
4. In accordance with the biogeographic history of the basin, our
results show that T. coahuila's diversification across the
Cuatrocienegas valley continued throughout the Pleistocene, peaking
during the Holocene, when the valley started to gradually dry. As
predicted, T. coahuila exhibited an overall, long-term, and probably
continuing decrement in genetic variation, increased genetic
differentiation, and low population sizes, as a consequence of
contemporary habitat loss and fragmentation across the CCB.
5. Changes in species demography and population connectivity have the
potential to permanently alter the genetic patterns of freshwater
species. Hence, given its restricted distribution, high habitat
specificity and habitat loss, Terrapene coahuila is at utmost risk of
extinction. Captive breeding programmes of the Coahuilan box turtle
should consider our results, to prevent further loss of genetic
diversity and truly expect reintroduction success. Also, it is crucial
to restore connectivity among wetlands, for the conservation of species
and the Cuatrocienegas valley altogether.
Filiaciones:
Cortes-Rodriguez, Xochiquetzal:
Univ Nacl Autonoma Mexico, Inst Ecol, Dept Ecol Biodiversidad, Mexico City 04510, DF, Mexico
Univ Nacl Autonoma Mexico, Posgrad Ciencias Biol, Mexico City, DF, Mexico
Borja-Martinez, Gabriela:
Univ Nacl Autonoma Mexico, Inst Ecol, Dept Ecol Biodiversidad, Mexico City 04510, DF, Mexico
Vazquez-Dominguez, Ella:
Univ Nacl Autonoma Mexico, Inst Ecol, Dept Ecol Biodiversidad, Mexico City 04510, DF, Mexico
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