No abstract

The introduction of exotic species in aquatic habitats is one of the causes for the amphibian declines observed worldwide. In the 1970s, the red swamp crayfish Procambarus clarkii was introduced in the southwest Iberian Peninsula, where no native crayfish occur. In this study we assess the effect of P. clarkii presence in the breeding site distribution of each of the 13 southwest Iberian amphibians, while simultaneously accounting for the effects of potentially confounding habitat variables, as well as for the effects of the other large aquatic predators in the study area – predatory fish. Amphibian species richness was lower in places where P. clarkii was present than in places without P. clarkii, regardless of fish presence. After accounting for habitat variables and fish, crayfish presence was a negative predictor of the breeding probability for all urodeles (Pleurodeles waltl, Salamandra salamandra, Triturus boscai and T. marmoratus) and for two anurans (Pelobates cultripes and Bufo bufo). The majority of the species affected usually breed in temporary ponds without fish, but that may be colonized by the crayfish. The ongoing expansion of P. clarkii may eventually lead to a growing isolation of amphibian populations and ultimately to local extinctions and a permanent alteration of the amphibian communities in southwest Iberian Peninsula.

Phylogeographic analyses based on the sole use of the mitochondrial DNA (mtDNA) molecule reveal only a small part of the evolutionary history of a species or a set of related species. In this study, we have combined the application of slow- and fast-evolving nuclear markers (proteins and microsatellites, respectively) together with the analysis of two-gene genealogies to further understand the history of the Iberian endemic Schreiber's green lizard, Lacerta schreiberi, a species for which a well established phylogeographical scenario is available. In sharp contrast with the observation of four divergent and almost allopatric mtDNA clades, our nuclear data revealed how two groups of populations diverged, persisted and began to admix along the mountains of the Iberian Central System. In addition, the combination of mtDNA and nuclear data showed how the core area of the species distribution responded to ice ages, first by relatively old processes of population expansion to the south followed by episodes of contraction that are at the origin of present-day isolates, and more recently by a postglacial expansion to the Iberian Northwest where new habitats were made available after climatic amelioration. Taken together with recently published results for a variety of other organisms, our results suggest that complex processes of fragmentation, expansion and admixture can only be properly addressed through the use of several and complementary types of molecular markers. Finally, we also suggest that southern European refugia are both hotspots and melting pots of genetic diversity.

We compare the results, benefits and disadvantages of two techniques for modelling wildlife species distribution: Logistic Regression and Overlap Analysis. While Logistic Regression uses mathematic equations to correlate variables with presence/absence of the species. Overlap Analysis simply combine variables with the presence points, eliminating the non‐explanatory variables and recombining the others. Both techniques were performed in a Geographic Information System and we attempted to minimise the spatial autocorrelation of data. The species used was the Schreiber's green lizard Lacerta schreiberi and the study area was Portugal, using 10 X 10 km UTM squares. Both techniques identified the same group of variables as the most important for explaining the distribution of the species. Both techniques gave high average correct classification rates for the squares with presence of the species (79% for Logistic Regression and 92% for Overlap Analysis). Correct absence classification was higher with Logistic Regression (73%) than with Overlap Analysis (32%), Overlap Analysis tends to maximise the potential area of occurrence of the species, which induces a reduced correct classification of absences, since many absences will fall in the potential area. This is because a single presence in a given class of a variable makes all the area of that class to be considered as potential. The technique does not consider that the species may occasionally occupy an unfavourable region. Although, in Logistic Regression, modelling procedures are more complex and time‐consuming, the results are more statistically robust. Moreover. Logistic Regression has the capability of associating probability of occurrence to the potential area. Overlap Analysis is very simple in building procedures and swift in obtaining reliable potential areas. It is a valid technique especially in exploratory analysis of species distributions or in the initial stages of research when data may be scarce.

The study of nuclear genealogies in natural populations of nonmodel organisms is expected to provide novel insights into the evolutionary history of populations, especially when developed in the framework of well-established mtDNA phylogeographical scenarios. In the Iberian Peninsula, the endemic Schreiber's green lizard Lacerta schreiberi exhibits two highly divergent and allopatric mtDNA lineages that started to split during the late Pliocene. In this work, we performed a fine-scale analysis of the putative mtDNA contact zone together with a global analysis of the patterns of variation observed at the nuclear beta-fibrinogen intron 7 (beta-fibint7). Using a combination of DNA sequencing with single-strand conformational polymorphism (SSCP) analysis, we show that the observed genealogy at the beta-fibint7 locus reveals extensive admixture between two formerly isolated lizard populations while the two mtDNA lineages remain essentially allopatric. In addition, a private beta-fibint7 haplotype detected in the single population where both mtDNA lineages were found in sympatry is probably the result of intragenic recombination between the two more common and divergent beta-fibint7 haplotypes. Our results suggest that the progressive incorporation of nuclear genealogies in investigating the ancient demography and admixture dynamics of divergent genomes will be necessary to obtain a more comprehensive picture of the evolutionary history of organisms.