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The dynamics of species range borders may be difficult to study due to the local rarity of populations and individuals. This hindrance applies less when range borders are parapatric contact zones. Analysis of species in parapatry has the further advantages of no (inferred) absence data and that shortcomings in data gathering such as uneven sampling apply to the counterpart species about equally. The large-bodied newts Triturus cristatus and T. marmaratus are spatially segregated within a wide area of range overlap in the west of France. They locally show abutting or slightly overlapping distributions with many isolated occurrences (here called ‘patches’) of either species within the continuous range section of the other. Historical and genetic data suggest that T. cristatus has been superseding T. marmoratus. Species replacement should be also discernible from local species distributions, with more, larger and more distantly positioned patches in the receding than the advancing species. Atlas data for France and from the French region Pays de la Loire largely confirm these predictions. The data also indicate that T. marmoratus patches may be void of T. cristatus, suggesting that they are persisting strongholds, whereas the more admixed T. cristatus patches are in flux. The species’ differential ecological signature is that of forested, hilly terrain for T. marmoratus and open, flat terrain for T. cristatus. Accordingly, the main dispersal route for T. cristatus towards the Atlantic coast has been through the valley of the Loire River, with a secondary, intraspecific contact zone at the Normandy coast. A literature survey revealed several other species pairs of European herpetofauna that may be amenable to patch analysis, as will be species pairs in other groups of organisms characterized by limited, habitat dependent dispersal. In such efforts the availability of species occurrence data from atlases and digital databases is an indispensable asset.

Amphibian populations are increasingly sampled with traps instead of the traditional dipnet, because of high yields at a comparatively low workload. Observations on sympatric newt species in the west of France uncovered a size effect in which the larger species Triturus cristatus and T. marmoratus were more frequently captured than the smaller species Lissotriton helveticus and L. vulgaris. The small juveniles of T. cristatus and the large Triturus interspecies hybrids fitted this series. The lightweight, collapsable, and easy to clean funnel traps here employed are useful for population studies because, due to a high capture efficiency, sampling biases can accurately be quantified and be accounted for.

Two morphologically and genetically distinct salamander species (the crested newt, Triturus cristatus and the marbled newt, T. marmoratus) engage over a large area in the west of France where they hybridize at ca. 4%. The species interaction is characterized by ecological differentiation and limited gene flow beyond the F1 hybrid generation. Incompletely isolated species like these allow to investigate the genetic mechanisms and evolutionary forces that maintain their identity in the face of ongoing gene flow, to which a large mosaic hybrid zone provides excellent opportunities. A reanalysis of published morphological data supports the partial breakdown of the species barrier whereas extensive genetic data show that introgression is low yet asymmetric, in line with the dynamics of species replacement inferred earlier. The current work, with seven diagnostic nuclear markers studied for a large sample, revises the estimates of introgression in both T. cristatus (to 0.24%) and T. marmoratus (to 0.11%). Difficulties remain in the recognition of potential triploid hybrids versus backcross hybrids. Haldane's rule is partially supported, but deeper analyses require the use of a molecular marker for sex that is not yet available. [ABSTRACT FROM AUTHOR]

The large-bodied newts Triturus cristatus and T. marmoratus possess ranges that overlap in western France where they frequently share breeding ponds. I test the hypothesis that the aquatic phenology differs between them, as associated with a more aquatic and terrestrial life style respectively. Total adult population sizes were determined in spring in 13 experiments by the capture-mark-recapture methodology, followed by equivalent experiments in summer. Population sizes dropped by an order of magnitude on average whereas species frequencies changed in favour of T. cristatus , suggesting that T. marmoratus leaves the breeding site earlier than T. cristatus. Interspecies hybrids behaved like T. marmoratus. Descriptions are provided of other features (in ecology, morphology, demography, and colouration pattern) that support the different, aquatic versus terrestrial life styles of T. cristatus and T. marmoratus. [ABSTRACT FROM AUTHOR]

Snakes are limbless predators, and many species use venom to help overpower relatively large, agile prey. Snake venoms are complex protein mixtures encoded by several multilocus gene families that function synergistically to cause incapacitation. To examine venom evolution, we sequenced and interrogated the genome of a venomous snake, the king cobra (Ophiophagus hannah), and compared it, together with our unique transcriptome, microRNA, and proteome datasets from this species, with data from other vertebrates. In contrast to the platypus, the only other venomous vertebrate with a sequenced genome, we find that snake toxin genes evolve through several distinct co-option mechanisms and exhibit surprisingly variable levels of gene duplication and directional selection that correlate with their functional importance in prey capture. The enigmatic accessory venom gland shows a very different pattern of toxin gene expression from the main venom gland and seems to have recruited toxin-like lectin genes repeatedly for new nontoxic functions. In addition, tissue-specific microRNA analyses suggested the co-option of core genetic regulatory components of the venom secretory system from a pancreatic origin. Although the king cobra is limbless, we recovered coding sequences for all Hox genes involved in amniote limb development, with the exception of Hoxd12. Our results provide a unique view of the origin and evolution of snake venom and reveal multiple genome-level adaptive responses to natural selection in this complex biological weapon system. More generally, they provide insight into mechanisms of protein evolution under strong selection.

Morphological and genetic variation of organisms is generally lower in northern than in southern regions of the Palearctic. This ubiquitous geographical pattern has been associated with extinction and recolonization processes in the north versus persistence in the Mediterranean area, as governed by climate change in the Pleistocene. One area of differentiation and complexity is the Iberian Peninsula where two distinct sister-species of marbled newts possess adjoining and geographically sharply delimited ranges over the north (Triturus marmoratus) and the south of the peninsula (T. pygmaeus). Within the latter species two forms are here documented, with different colouration patterns and non-overlapping ranges. The southern form is striped, much as in T. marmoratus, and occurs to the south of the Guadalquivir River. The northern form, here described as a new subspecies, has a reticulated dorsal colouration. It occurs only north of the Guadalquivir and is thus sandwiched in between two striped marbled newt taxa. Both T. pygmaeus subspecies engage inside the Doñana National Park in a ca. 2,500 m narrow contact zone. Although an inferred substantial selection against hybrids goes a long way to support species status, a reanalysis of published genetic data is required to solve this issue, along with the wider investigation of the same type of (microsatelite) data for the southern, nominotypical subspecies. [ABSTRACT FROM AUTHOR]

The major histocompatibility complex (MHC) genes are central to the adaptive immune response in vertebrates. Selection generally maintains high MHC variation because the spectrum of recognized pathogens depends on MHC polymorphism. Novel alleles favoured by selection originate by interallelic recombination or de novo mutations but may also be acquired by introgression from related species. However, the extent and prevalence of MHC introgression remain an open question. In this study, we tested for MHC introgression in six hybrid zones formed by six Triturus newt species. We sequenced and genotyped the polymorphic second exons of the MHC class I and II genes and compared their interspecific similarity at various distances from the centre of the hybrid zone. We found evidence for introgression of both MHC classes in the majority of examined hybrid zones, with support for a more substantial class I introgression. Furthermore, the overall MHC allele sharing outside of hybrid zones was elevated between pairs of Triturus species with abutting ranges, regardless of the phylogenetic distance between them. No effect of past hybrid zone movement on MHC allele sharing was found. Finally, using previously published genome‐wide data, we demonstrated that MHC introgression was more extensive than genome‐wide introgression, supporting its adaptive potential. Our study thus provides evidence for the prevalence of MHC introgression across multiple Triturus hybrid zones, indicating that MHC introgression between divergent hybridizing species may be widespread and adaptive. [ABSTRACT FROM AUTHOR]

Related species often engage in abutting or overlapping contact zones with various strengths of interspecific competition. Biotic interactions such as these preclude the registration of the full profile of environmental variables that would describe the otherwise larger species ranges. Here, I advocate to forego full range species distribution modelling and instead focus on the ecography of the contact zone, for example with 'two-species distribution models' (TSDMs), in which presence data are contrasted against the background of environmental data. The newts Triturus cristatus and Triturus marmoratus meet in the west of France. A countrywide TSDM suggests that the contact zone of the species is located at a climatic gradient, in line with their north-eastern vs. south-western ranges. The species are also ecologically segregated by elevation and forestation, which is in line with a documented movement of the contact zone caused by hedgerow removal in lowland areas. Hindcasts for the Holocene suggest that the species contact zone was positioned at either the same place as at present or more to the south, depending on the amount of forestation. A forecast under climate warming predicts a fast movement to the north, but this scenario is deemed unrealistic. One reason is that recent habitat loss compromises dispersal and range expansion. Other species pairs to which TSDMs have been applied are listed for comparison. [ABSTRACT FROM AUTHOR]