Victor Noguerales. Estación Biológica de Doñana e Instituto de Investigación en Recursos Cinegéticos. Supervisors: Joaquín Ortego & Pedro J. Cordero. Julio 2017.
Summary:
Understanding the mechanisms that determine genetic and
phenotypic divergence among populations, lineages and species is a
paramount goal in evolutionary biology. Recent evolutionary radiations
constitute a well-suited study system to address the study of such
mechanisms because the genetic signatures left by divergence processes
have not been erased by time and can be used to infer the evolutionary
and demographic trajectories of lineages and species. This PhD thesis
employs a multi-disciplinary approach in order to address the study of
neutral and adaptive processes, and their links with landscape
composition, throughout the whole spatiotemporal spectrum at which
genetic and phenotypic divergence takes place. Specifically, the main
objective of this PhD thesis is to understand the relative contribution
of environment, climatic fluctuations and geography on the spatial
patterns of genetic and phenotypic variation at the species, lineage and
population levels, using as study model a recent evolution radiation of
grasshoppers: the Chorthippus group binotatus species complex (Acrididae:
Gomphocerinae). Our species delimitation analyses integrating genomic
and morphological information revealed that the taxonomic status of
species and subspecies is statistically equivalent and, hence, the
Chorthippus group binotatus complex is composed of eight different
biological entities that merit full species recognition. The study of
Chorthippus binotatus binotatus at a range-wide phylogeographic scale
shows that this taxon presents four main mitochondrial lineages that
probably diverged in allopatry as a consequence of its isolation by
geographic barriers (i.e. the Pyrenees[JO1] ) and in different climatic
refugia during the Pleistocene. The existence of a lineage exclusive
from western and central France indicates that the species long-term
persisted in areas located at the present northern limit of its
distribution range, although such populations were likely submitted to
severe demographic bottlenecks and currently present very low levels of
genetic diversity. At a lower spatial scale, landscape genetic analyses
revealed that isolation by resistance defined by topographic complexity
was the best-fitting scenario explaining population genetic
differentiation of both C. binotatus binotatus in southeastern Iberia
and C. saulcyi moralesi in the Pyrenees. Although environmental
conditions did not explain the spatial patterns of genetic
differentiation of C. saulcyi moralesi, we found that divergent
selection mediated by climatic gradients had an important role on
phenotypic differentiation processes in this taxon. In particular, our
results indicate that the degree of development of forewings is
associated to local environmental conditions. This fact suggests that
variation in genomic regions involved in the expression of such trait
may have resulted from an adaptive response to different climatic
regimes. The populations located at the limits of the species
distribution range presented proportionally longer forewings, a trait
linked with dispersal capability. Such peripheral populations exhibited
lower genetic diversity in comparison to those located at the core of
the species distribution range, which suggests that the former are
subjected to considerable demographic instability and this leads to
directional selection towards more dispersive phenotypes. Overall, the
results from this PhD thesis highlight the importance of combining
genetic, phenotypic and environmental data in order to better understand
the evolutionary mechanisms that are at play at different spatiotemporal
scales and drive divergence processes along the speciation continuum.