Ecophysiology Tracks Phylogeny and Meets Ecological Models in an Iberian Gecko.

Because fitness of ectotherms, including reptiles, is highly dependent on temperature and water availability, the study of ecophysiological traits, such as preferred temperature (T p) and water loss rates (WLRs), may provide mechanistic evidence on the restricting factors to the species ranges. The Moorish gecko, Tarentola mauritanica, is a species complex with a circum-Mediterranean distribution. In the Iberian Peninsula, two sister parapatric forms of the complex, known as the Iberian and the European clades, are found. Ecological models previously performed using presence records and bioclimatic variables suggest niche divergence between both lineages correlated with precipitation rather than with temperature. In this study, we test this correlative hypothesis using ecophysiological evidence. In the laboratory, we analyzed the T p and WLRs for 84 adult males from seven distinct populations ascribed to one of the two lineages present in Iberia. Specifically, we evaluated the existence of trait conservatism versus adaptation among populations, lineages, or both. In addition, we tested for a trade-off between water and thermal traits and assessed whether climate regime of sampling localities had any influence on the ecophysiological patterns found. We found that T p is quite conserved at both the population and lineage levels and independent from body size. In contrast, water loss experiments revealed some variation among populations, but the regression analysis failed to detect correlation between T p and WLR at any level. Overall, the European lineage displayed a trend for higher water loss and was more diverse among populations when compared with the Iberian lineage. The lack of correspondence between ecophysiological traits and local climatic conditions favors phylogenetic signal versus adaptation. This suggests divergent evolutionary responses to the environment, mainly acting on water ecology, in both lineages, which may account for the differences in their range expansion.

Evolutionary patterns of the mitochondrial genome in the Moorish gecko, Tarentola mauritanica.

A previous study on the evolutionary patterns of Tarentola mauritanica demonstrated that low levels of mitochondrial diversity observed in the European populations relative to nuclear markers were consistent with a selective sweep hypothesis. In order to unravel the mitochondrial evolutionary history in this European population and two other lineages of T. mauritanica (Iberian and North African clades), variation within 22 nearly complete mitogenomes was analyzed. Surprisingly, each clade seems to have a distinct evolutionary history; with both the European and Iberian clades presenting a decrease of polymorphism, which in the former is consistent with departure from neutrality of the mtDNA (positive or background selection), but in the latter seems to be the result of a bottleneck after a population expansion. The pattern exhibited by the North African clade seems to be a consequence of adaptation to certain mtDNA variants by positive selection.

When selection deceives phylogeographic interpretation: the case of the Mediterranean house gecko, Hemidactylus turcicus (Linnaeus, 1758).

A previous study on Hemidactylus turcicus based on mtDNA makers indicated that this gecko has a Middle-East origin, and that the current phylogeographic pattern is the result of a very rapid spread from the east to the west of the species' range. The same study identified two distinct mitochondrial lineages with low differentiation and genetic diversity. Since H. turcicus is known to be closely associated to humanized environments, its present distribution range and phylogeography is frequently interpreted to be the result of recurrent human-mediated introductions. These conclusions used to be the same as those used to interpret the results obtained for the European populations of another gecko, Tarentola mauritanica. However, a recent study has revealed that the phylogeographic pattern of T. mauritanica is not solely the result of a recent colonization, but also of a mitochondrial selective sweep. Could the same be occurring in H. turcicus? To answer this question, two mitochondrial (12S rRNA and cytochrome b) and two nuclear genes (ACM4 and Rag2) were used in this study. From the mtDNA data we confirmed the existence of two distinct phylogeographic lineages; one occurring exclusively in the northern Mediterranean (Clade A), and another one more widespread that is the only lineage present in North Africa (Clade B). In light of these results, we could hypothesize that H. turcicus had its origin in Turkey, and from there Clade A moved to Europe and Clade B to North Africa spreading latter into Europe. However, Clade A presents significantly higher nucleotide diversity for the nuclear DNA compared to the mtDNA, and neutrality tests gave significant results for the mitochondrial data. These results suggest that the lack of mtDNA genetic diversity and structure in the European population of H. turcicus could also be due to a selective sweep, and not only because of a recent colonization. Together with the situation reported in T. mauritanica, the identification of a hitch-hiking process occurring in H. turcicus, represents two unprecedented cases of a selective sweep taking place in the same geographic area shaping the phylogeographic patterns of two unrelated genera of geckos.

Conflicting patterns of nucleotide diversity between mtDNA and nDNA in the Moorish gecko, Tarentola mauritanica.

The gecko Tarentola mauritanica is a Mediterranean species that is widely distributed across southern Europe and North Africa. Initial phylogeographic studies based on mtDNA concluded that the European populations originated from recent colonizations from North Africa, possibly involving man-mediated introductions. A distinct lineage, found to be a sister taxon to the widespread European lineage, was subsequently reported from parts of the Iberian Peninsula. Like many gecko species, T. mauritanica contains several deep intraspecific genetic lineages within North Africa. However, in contrast to this diversity, a single mtDNA haplotype is widespread across a large part of its European range. In this work, we analysed a total of 834 base pairs from two mtDNA genes (12SrRNA and 16SrRNA) for 154 specimens, and a total of 1876bp from three nuclear genes (ACM4, MC1R and Rag2) for 51 specimens to test the phylogenetic and phylogeographic patterns proposed for T. mauritanica based on mtDNA sequences. The mtDNA results reveal a Moroccan lineage basal to the common "European" haplotype, thus suggesting that the latter probably originated in Morocco. The remaining lineages obtained are the same as those observed in previous studies. In contrast, the nDNA data do not support the majority of the mtDNA phylogenetic relationships, possibly due to incomplete lineage sorting of these markers. Moreover, the mtDNA data suggest that the Iberian clade seems to have undergone a population expansion. Surprisingly, the European clade presents a higher nucleotide diversity for the nuclear genes when compared to the combined mtDNA dataset. These analyses suggest that the low mtDNA variability that characterises the European populations of T. mauritanica is the result of a selective sweep process and not solely due to a recent colonization event.

Signalling pathways in pollen germination and tube growth.

Signalling is an integral component in the establishment and maintenance of cellular identity. In plants, tip-growing cells represent an ideal system to investigate signal transduction mechanisms, and among these, pollen tubes (PTs) are one of the favourite models. Many signalling pathways have been identified during germination and tip growth, namely, Ca(2+), calmodulin, phosphoinositides, protein kinases, cyclic AMP, and GTPases. These constitute a large and complex web of signalling networks that intersect at various levels such as the control of vesicle targeting and fusion and the physical state of the actin cytoskeleton. Here we discuss some of the most recent advances made in PT signal transduction cascades and their implications for our future research. For reasons of space, emphasis was given to signalling mechanisms that control PT reorientation, so naturally many other relevant works have not been cited.