L’ibridazione e le sue conseguenze ecologico-evolutive negli animali: studio longitudinale di un’area di simpatria artificiale tra due specie del complesso Aedes mariae
Author(s)
Mastrantonio, Valentina
Date Issued
June 26, 2015
Type
Doctoral Thesis
Abstract
During the last 150 years, hybridization has been one of the most highly debated process in ecology
and evolution. While in the first years, main interest was addressed to understand how much
hybridization was widespread in nature, particularly between animal species, to date, as it is largely
known that several species can hybridize, great attention is focused to understand how this process
can affect inter- and intra-specific diversity and what ecological factors can affect its final outcome.
Contrary to a posteriori studies, that allow to investigate the genetic pattern of hybridization only in a
single time point and then to infer the underlying processes, longitudinal studies allow to follow
hybridization and introgression along a multigenerational context, studying in itinere the action of
different ecological factors.
In this PhD thesis, it is reported a longitudinal study across more than 200 generations of an
artificial sympatric area, orginated by a translocation experiment between two mosquito species of
the Aedes mariae complex, Ae. mariae and Ae. zammitii. The specific aims were: i) to genetically
characterize all members of the Aedes mariae complex at nuclear and mitochondrial genes; ii) to
investigate, across time, the hybridization pattern between Ae. mariae and Ae. zammitii in the
artificial sympatric area; iii) to investigate the dynamic of introgression between Ae. mariae and Ae.
zammitii at mitochondrial DNA during the colonization of the new habitat by the introduced species
Ae. mariae.
The results obtained showed that today hybridazation persists between the two species in the
sympatric area, even if favourable conditions occur to complete the speciation process. The
characteristics of the study system allow to rule out some factors commonly invoked to explain the
scenario observed (e.g. allopatric gene flow, too recent contact, lack of polymorphism to mating
traits), and instead to underline the importance of the strenght of natural selection and the
mechanisms affecting it (e.g. trait involved in the pre-mating reproductive isolation). Likewise, the
results showed the occurrence of mitochondrial introgression between Ae. mariae and Ae. zammitii.
In particular, the observed genetic pattern was asymmetric between the two species, with the
introduced species, Ae. mariae, more introgressed than the local species, Ae. zammitii. This pattern,
in conjunction with the characteristics of the study-system, supports the view, only recently proposed
by theoretical models, that demographic processes that occur during species range expansion may
play a major role in shaping introgression pattern at neutral genes.
In conclusion, the case-study of Ae. mariae and Ae. zammitii supports, on one hand, the
importance of the ecological context in determining the evolutionary outcome of hybridization; on
the other hand, the “creative role” of this process in generating and maintaining inter- and intraspecific
diversity.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche