Distribución, ecología, genética y conservación de la musaraña de campo, Crocidura suaveolens, en el Golfo de Cádiz

Abstract

The lesser white-toothed shrew, Crocidura suaveolens, is continuously distributed, common and abundant throughout most Eurasia. However, in Western Europe its distribution is fragmented and it is a rare and poorly known species. In the Iberian Peninsula, the lack of knowledge about its history, its genetic diversity or its ecology hampers a proper assessment of its conservation priority and status. The populations of the Gulf of Cádiz, in particular, being located in the southwestern limit of the global distribution of the species and given the prominent role of the Iberian Peninsula as glacial refugia, could harbour a unique genetic diversity which may be key for the species persistence in the current scenario of global change. This doctoral thesis aims to describe the evolutionary and demographic history of C. suaveolens in the Iberian Peninsula and to assess its distribution, genetic status and ecology in the Gulf of Cádiz, with the final intention of contributing to the assessment of its conservation status and, where appropriate, to the design of a management plan for the species in this region. For this purpose, I used barn owl, Tyto alba, pellets and Trip Trap live traps to sample individuals, and applied different molecular genetic techniques for the genetic characterization of these samples. All the C. suaveolens populations in the Iberian Peninsula cluster within the previously described clade IV of the C. suaveolens group. Within this clade, three evolutionary mitochondrial lineages have been identified, two of which are exclusively Iberian. Two sublineages within one of these Iberian lineages are exclusive of the populations in the gulf of Cádiz. The evolutionary history of C. suaveolens in the Iberian Peninsula can be explained by the existence of multiple refugia within the Iberian Peninsula and the competition with the greater white-toothed shrew, Crocidura russula, that started with its arrival from Africa ca. 126 Kya. In the Gulf of Cádiz C. suaveolens is present only in six tidal marshes located in four isolated marsh areas: the marshes of the rivers Guadiana (Spanish shore), Piedras, Odiel, Tinto, Estero Domingo Rubio and Guadalquivir. The species has a marked genetic structure as a result of a high level of population isolation, with six differentiated genetic groups corresponding to the six marshes occupied by the species. Guadalquivir and Estero Domingo Rubio are the most genetically differentiated populations, while the populations of Guadiana, Piedras, Odiel and Tinto are genetically more similar to each other. Gene flow between populations is restricted because the species does not disperse through non-marsh habitats. Wider river channels also limit gene flow, but they do not appear to be absolute barriers to dispersal. Moderate levels of local and high levels of regional genetic diversity have been observed, making the Gulf of Cádiz a region with a great evolutionary potential to face future threats. C. suaveolens is a tidal marsh habitat specialist in the Gulf of Cádiz, being the only known case of habitat specialization described for the species. Its habitat specialization in the region seems to be an evolutionary effect of past competition with C. russula, which is allowing the coexistence of the two species through the spatial and temporal segregation of their ecological niches. C. suaveolens is currently outcompeting C. russula in tidal marshes, reversing the dominance pattern observed elsewhere. The evolutionary history of the C. suaveolens populations of the Gulf of Cádiz, its distribution, genetic composition and ecology, can be explained by the competition with C. russula, the specialization of C. suaveolens in tidal marsh and the geomorphological evolution of tidal marshes of this region.