Mosaic hybrid zones arise when ecologically differentiated taxa hybridize across a network of habitat patches. Frequent interbreeding across a small-scale patchwork can erode species differences that might have been preserved in a clinal hybrid zone. In particular, the rapid breakdown of neutral divergence sets an upper limit to the time for which differences at marker loci can persist. We present here a case study of a mosaic hybrid zone between the fire-bellied toads Bombina bombina and B. variegata (Anura: Discoglossidae) near Apahida in Romania. In our 20 x 20 km study area, we detected no evidence of a clinal transition but found a strong association between aquatic habitat and mean allele frequencies at four molecular markers. In particular, pure populations of B. bombina in ponds appear to cause massive introgression into the surrounding B. variegata gene pool found in temporary aquatic sites. Nevertheless, the genetic structure of these hybrid populations was remarkably similar to those of a previously studied transect near Pescenica (Croatia), which had both clinal and mosaic features: estimates of heterozygote deficit and linkage disequilibrium in each country are similar. In Apahida, the observed strong linkage disequilibria should stem from an imperfect habitat preference that guides most (but not all) adults into the habitats to which they are adapted. In the absence of a clinal structure, the inferred migration rate between habitats implies that associations between selected loci and neutral markers should break down rapidly. Although plausible selection strengths can maintain differentiation at those loci adapting the toads to either permanent or temporary breeding sites, the divergence at neutral markers must be transient. The hybrid zone may be approaching a state in which the gene pools are homogenized at all but the selected loci, not dissimilar from an early stage of sympatric divergence.
442.9 KB
276Northern records of the red-bellied toad (Bombina bombina) are discussed. The most north-western populations in Sweden and Denmark are fragmented and scarce, many of them are related to introductions or re-introductions. On the continent, the northern margin runs along the sea shore from north-eastern Germany through Poland and Russia. Then the margin comes to north of Lithuania, south of Latvia, then through Belarus and central Russia to the Urals. The most north-eastern records are known from Chelyabinskaya Province. Northernmost populations reach 54–57° N; the margin is overlapped with the southern part of the subtaiga forest zone. List and map of the northernmost localities of B. bombina are given. Correlates of this margin with vegetation and climate are briefly discussed. We provide also data on introductions, extinctions and habitats.
The pattern of ventral spots of 72 individuals of Bombina bombina from 8 localizations in Latvia were investigated. The typification of variations was carried out on the basis of the analysis of relative length and the form of the prevailing fragments of orange spots. 15 variations were distinguished, which were united into 5 clusters. The analysis of ventral spots of Bombina bombina showed the domination of definite variations in concrete localizations that indicates the high degree of the relationship of individuals. When combining the variations into clusters and localizations in the population, the domination of definite clusters was registered. For the first time the rare in Latvia variation was noted: one large monolithic orange spot practically without any black spots.
The direction and level of sexual size dimorphism (SSD) was examined in fire-bellied toads from the central Balkans. Samples were taken from 12 populations: three Bombina bombina, three B. variegata variegata and six B. variegata scabra populations. Intersexual variation of 20 morphometric characters was analysed. In addition, correspondence analysis of eight qualitative characters was performed. The results showed that, though body length had an inconsistent pattern of intersexual variation across taxa, other traits contributed to statistically significant level of SSD. The analysis on multivariate level revealed a highly significant effect of population in all three taxa, and significant effect of sex on character variation. Discriminant analysis confirmed a higher level of intersexual differences in B. variegata compared to B. bombina. Correspondence analysis showed that females and males were similar with respect to qualitative traits in all three taxa. At the univariate level, the most prominent features were: significant differences in tibia length in all three taxa, and highly significant differences in head width in B. bombina and in humerus length in B. v. scabra. These results are discussed with respect to specific reproductive behaviour and possible ecological differences between sexes.
Using five restriction enzymes, geographical variation of mitochondrial DNA (mtDNA) in Bombina bombina and B. variegata was studied in samples from 20 locations. Each restriction enzyme produced a species-specific fragment pattern. B. bombina haplotypes A and B were closely related to each other. In contrast, haplotypes A and B of B. variegata formed two distinct lineages. A very distinctive haplotype (C) was found in the Carpathian Mountains, whereas two other haplotypes, D and E (differing by a single AvaI site), were present in western Europe and the Balkans, respectively. Populations polymorphic for haplotypes D and E occurred in the central Balkans where the haplotypes could replace each other clinally. mtDNA sequence divergence between B. bombina and B. variegata was estimated as 6.0-8.1% and 4.7-5.2% between type C and types D/E of B. variegata. The latter divergence is contrary to allozyme and morphological data that place the western and Carpathian B. v. variegata together (Nei's D = 0.07) and separate them from the Balkan subspecies B. v. scabra (Nei's D = 0.18). Broad interspecific correlation among morphology, allozymes and mtDNA types in European fire-bellied toads argues that, despite continuous hybridization (interrupted perhaps during Pleistocene glacial maxima), little or no mtDNA introgression between the species has occurred outside the narrow hybrid zones that separate these parapatric species.
We analyzed the trophic spectrum of 331 samples of Bombina bombina, belonging to four populations. We found vegetal remains, mineral fragments and exuvia in the stomach contents. The 2708 animal preys were grouped in 30 categories, representing 22 taxon preys. Gasteropods, Araneids, Colembolans, Coleopterans, Isopods, Heteropternas and Hymenopterans were appear almost constantly in the stomach contents. Three of the investigated populations consumed mostly Colembolans, and one population ate Coleopterans. The most frequently consumed taxon preys are Isopods and Hymenopterans. The weight of aquatic and terrestrial taxon preys varies depending on the environmental conditions. Because of the drying of the puddles the aquatic taxon preys disappear, thus terrestrial taxon preys dominate the stomach contents.
We analyzed the trophical spectrum of three Bombina variegata populations, from forest ecosystems situate in Luncani, Valea Budului and Runc within Bacău County. The most abundant prey taxon in the food of Bombina variegata populations is represented by the species from Coleoptera order, followed by those of Diptera among insects, and by araneids among spider. The considerable number of small and gregarious species (Formicidae – Hymenoptera) emphasizes the opportunistic behavior of preying in this species, using the sit and wait foraging behavior. The terrestrial prey taxons prevail in comparison with aquatic organisms. Like the other amphibian species, Bombina variegata is a zoophagous – polyphagous species. Yellow-bellied toads eat all moving objects in their sight range that they can ingest.
