Past and current gene flow in the selfing, wind-dispersed species Mycelis muralis in western Europe

The distribution of genetic diversity in Mycelis muralis, or wall lettuce, was investigated at a European scale using 12 microsatellite markers to infer historical and contemporary forces from genetic patterns. Mycelis muralis has the potential for long-distance seed dispersal by wind, is mainly self-pollinated, and has patchily distributed populations, some of which may show metapopulation dynamics. A total of 359 individuals were sampled from 17 populations located in three regions, designated southern Europe (Spain and France), the Netherlands, and Sweden. At this within-region scale, contemporary evolutionary forces (selfing and metapopulation dynamics) are responsible for high differentiation between populations (0.34 < F(ST) < 0.60) but, contrary to expectation, levels of within-population diversity, estimated by Nei's unbiased expected heterozygosity (H(E)) (0.24 < H(E) < 0.68) or analyses of molecular variance (50% of the variation found within-populations), were not low. We suggest that the latter results, which are unusual in selfing species, arise from efficient seed dispersal that counteracts population turnover and thus maintains genetic diversity within populations. At the European scale, northern regions showed lower allelic richness (A = 2.38) than populations from southern Europe (A = 3.34). In light of postglacial colonization hypotheses, these results suggest that rare alleles may have been lost during recolonization northwards. Our results further suggest that mutation has contributed to genetic differentiation between southern and northern Europe, and that Sweden may have been colonized by dispersers originating from at least two different refugia.     

Cryptic niche conservatism among evolutionary lineages of an invasive lizard

Aim There is increasing evidence that the quality and breadth of ecological niches vary among individuals, populations, evolutionary lineages and therefore also across the range of a species. Sufficient knowledge about niche divergence among clades might thus be crucial for predicting the invasion potential of species. We tested for the first time whether evolutionary lineages of an invasive species vary in their climate niches and invasive potential. Furthermore, we tested whether lineage‐specific models show a better performance than combined models. Location Europe. Methods We used species distribution models (SDMs) based on climatic information at native and invasive ranges to test for intra‐specific niche divergence among mitochondrial DNA (mtDNA) clades of the invasive wall lizard Podarcis muralis. Using DNA barcoding, we assigned 77 invasive populations in Central Europe to eight geographically distinct evolutionary lineages. Niche similarity among lineages was assessed and the predictive power of a combination of clade‐specific SDMs was compared with a combined SDM using the pooled records of all lineages. Results We recorded eight different invasive mtDNA clades in Central Europe. The analysed clades had rather similar realized niches in their native and invasive ranges, whereas inter‐clade niche differentiation was comparatively strong. However, we found only a weak correlation between geographic origin (i.e. mtDNA clade) and invasive occurrences. Clades with narrow realized niches still became successful invaders far outside their native range, most probably due to broader fundamental niches. The combined model using data for all invasive lineages achieved a much better prediction of the invasive potential. Conclusions Our results indicate that the observed niche differentiation among evolutionary lineages is mainly driven by niche realization and not by differences in the fundamental niches. Such cryptic niche conservatism might hamper the success of clade‐specific niche modelling. Cryptic niche conservatism may in general explain the invasion success of species in areas with apparently unsuitable climate.     

Infra-red irradiance and set point temperatures in behaviourally thermoregulating lacertid lizards

1. 1. Set point temperatures at which Podarcis muralis and Lacerta vivipara ceased basking (T_move; upper set point) and commenced basking (T_bask; lower set point) increased incrementally with increasing i.r. irradiance; values for all set point temperatures were higher in the former species.

2. 2. Changing the i.r. irradiance during a bask resulted in a shift in the upper set point temperature to a level intermediate between the values expected at constant previous and new irradiances (experiment with L. vivipara only).

3. 3. The changes in set-point temperatures following changes in i.r. irradiance were not due to changes in light intensity.

4. 4. The ability to respond to immediate changes in i.r. irradiance is adaptive for lizards in areas in which rapid changes in amounts of sunshine are a feature of the climate.

     

Characterization of microsatellite loci in the wall lizard Podarcis muralis (Sauria: Lacertidae)

In natural populations the mating success of males depends on different factors. By enhancing the intensity of secondary sexual characters, testosterone can play a role in mate choice. However, paradoxically, testosterone can also decrease immunocompetence and thus potentially diminish attractiveness. To estimate the influence of testosterone on male mating success in the wall lizard, Podarcis muralis, we characterized nine polymorphic microsatellite loci. There were three to 12 alleles per locus in the five to 16 individuals screened. These microsatellites will also be useful in determining population structure in this species.     

Microgeographic variation of colour morph frequency and biometry of common wall lizards

The throat and belly of both sexes of the common wall lizard Podarcis muralis exhibit a polymorphic coloration with three morphs (white, yellow and red). We documented the occurrence of this polymorphism in 11 populations of northern Italy, and investigated the morphometric features of the three morphs in both sexes. The white morph was more frequent (56.6%), while yellow and red morphs accounted for 28.7 and 14.7% of the lizards, respectively. Moreover, the red morphotype was more frequent among males while the white one was more frequent among females. The occurrence of the three morphs varied microgeographically from populations with a higher proportion of white individuals to those where all morphs were more equally represented. The comparisons of morphometry between morphs did not reveal any significant difference among males, while snout–vent length and head height in females increased from the white-throated to the yellow-throated morph, and from the yellow-throated morph to the red-throated one. Possible functions of this polymorphic coloration are discussed.     

Male behaviour drives assortative reproduction during the initial stage of secondary contact

Phenotypic divergence in allopatry can facilitate speciation by reducing the likelihood that individuals of different lineages hybridize during secondary contact. However, few studies have established the causes of reproductive isolation in the crucial early stages of secondary contact. Here, we establish behavioural causes of assortative reproduction between two phenotypically divergent lineages of the European wall lizard (Podarcis muralis), which have recently come into secondary contact. Parentage was highly assortative in experimental contact zones. However, despite pronounced divergence in male phenotypes, including chemical and visual sexual signals, there was no evidence that females discriminated between males of the two lineages in staged interactions or under naturalistic free‐ranging conditions. Instead, assortative reproduction was driven by male mate preferences and, to a lesser extent, male–male competition. The effects were more pronounced when the habitat structure promoted high lizard densities. These results emphasize that assortative reproduction can occur in the absence of female choice and that male behaviour may play an important role in limiting hybridization during the initial stages of secondary contact.     

Role of antioxidant systems in wild plant adaptation to salt stress

Wild plants differing in the strategies of adaptation to salinity were grown for six weeks in the phytotron and then subjected to salt stress (100 mM NaCl, 24 h). The activities of principal antioxidant enzymes and the accumulation of sodium ions and proline were studied. Independently of the level of constitutive salt tolerance, plants of all species tested accumulated sodium ions under salinity conditions but differed in their capability of stress-dependent proline accumulation and superoxide dismutase (SOD) and guaiacol-dependent peroxidase activities. Proline-accumulating species were found among both halophytes (Artemisia lerchiana and Thellungiella halophila) and glycophytes (Plantago major and Mycelis muralis). The high activities of ionically-bound and covalently bound peroxidases were characteristic of Th. halophila plants. High constitutive and stress-induced SOD activities were, as a rule, characteristic of glycophytes with the low constitutive proline level: Geum urbanum and Thalictrum aquilegifolium. Thus, a negative correlation was found between proline content and SOD activity in wild species tested; it was especially bright in the halophyte Th. halophila and glycophyte G. urbanum. An extremely high constitutive and stress-induced levels of proline and peroxidase activity in Th. halophila maybe compensate SOD low activity in this plant, and this contributed substantially into its salt resistance. Thus, monitoring of stress-dependent activities of some antioxidant enzymes and proline accumulation in wild plant species allowed a supposition of reciprocal interrelations between SOD activity and proline accumulation. It was also established that the high SOD activity is not obligatory trait of species salt tolerance. Moreover, plants with the high activity of peroxidase and active proline accumulation could acclimate to salts stress (100 mM NaCl, 24 h) independently of SOD activity.