The dispersal-gene flow paradox in zooplankton: the case of rotifers dwelling in temporary environments
- Autores: Sergi Campillo Fernández
- Directores de la Tesis: Manuel Serra (dir. tes.), M. Jose Carmona Navarro (codir. tes.)
- Lectura: En la Universitat de València ( España ) en 2009
- Idioma: español
- Tribunal Calificador de la Tesis: Diego Fontaneto (presid.), J Francesc Mezquita Juanes (secret.), Ana González Garrido (voc.), Thorid Zierold (voc.), Andy John Green (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
Small-sized organisms have been traditionally considered to possess high dispersal capacities, which would hamper both geographical speciation and within-species genetic populations. Nonetheless, the introduction of molecular techniques has enabled the accumulation of evidences of a high divergence in neutral molecular markers among populations of the same species in zooplanktonic organisms dwelling in continental waters, even at a local scale. These findings gave place to the so called Dispersal-Gene Flow Paradox, which is strongly manifested in the case of the cyclically parthenogenetic zooplankters, which combines sexual and asexual reproduction. This paradox is intended to be solved by the Monopolisation Hypothesis, which states that a long-lasting founder effect occurs in these populations, caused by (1) the numerical effect of the enormous local population that establishes soon after the foundation by firsts colonisers, and (2) the rapid local adaptation of these organisms. Within this theoretical framework, this thesis focussed on within-species variation in the monogonont rotifer Brachionus plicatilis, and secondarily on its co-generic species B. manjavacas, both belonging to the same cryptic species complex. After performing a morphometric analysis, the morphological similarity found implies that individuals of these two species can only be identified by genetic analysis. When compared to phylogenetic data, morphometry shows a morphological stasis in the evolution of these species. Mitochondrial phylogeography of both species was performed, confirming persistent founder effects previously reported. B. plicatilis and B. manjavacas share a similar phylogeographic pattern in the Iberian Peninsula, where at least one glacial refugium for each species is located. A high population structuring in monogonont rotifers was confirmed, both in mitochondrial (COI) and nuclear DNA markers (i.e. 11 microsatellite loci; four characterised in this thesis). For the first time in rotifers, a high variation in life-history traits, both within and among populations, was found, especially in the traits related to sexual reproduction. A comparison between the indexes of differentiation in neutral genetic markers (F-ST) and in quantitative traits (Q-ST) among six populations of B. plicatilis dwelling in ponds and lakes from Eastern Spain was performed. Evidence of divergent selection among some populations was found, especially for the production of diapausing eggs, a trait considered to be strongly correlated with fitness. The results suggest local adaptation with respect to habitat predictability. Moreover, the high unpredictability of the abiotic conditions in lakes and ponds from Eastern Spain is proposed to explain the high within-population variation found in monogonont rotifer life-history traits. No pattern of isolation-by-adaptation was found. In summary, the thesis supports a pattern with low gene flow and local adaptation in rotifers, but it opens the question on how important the last mechanism is in maintaining the population differentiation.
