Beata Ujvari

Major histocompatibility complex and mate choice in sand lizards

In mice and man, females prefer males with a major histocompatibility complex (MHC) genotype different to their own. We tested whether this phenomenon also occurs in the Swedish sand lizard (Lacerta agilis). Females in a laboratory experiment preferred to associate with odour samples obtained from more distantly related males at the MHC class 1 loci. Data on free-ranging lizards suggest that associations between males and females are nonrandom with respect to MHC genotype. However, male spatial distribution and mobility during the mating season suggest that the non-random pairing process in the wild may also be driven by corresponding genetic benefits to males pairing with less related females.

Sexual dimorphism in lizard body shape: the roles of sexual selection and fecundity selection

Abstract Sexual dimorphism is widespread in lizards, with the most consistently dimorphic traits being head size (males have larger heads) and trunk length (the distance between the front and hind legs is greater in females). These dimorphisms have generally been interpreted as follows: (1) large heads in males evolve through male‐male rivalry (sexual selection); and (2) larger interlimb lengths in females provide space for more eggs (fecundity selection). In an Australian lizard (the snow skink, Niveoscincus microlepidotus), we found no evidence for ongoing selection on head size. Trunk length, however, was under positive fecundity selection in females and under negative sexual selection in males. Thus, fecundity selection and sexual selection work in concert to drive the evolution of sexual dimorphism in trunk length in snow skinks.

High Prevalence of Hepatozoon Spp. (Apicomplexa, Hepatozoidae) Infection in Water Pythons (Liasis fuscus) From Tropical Australia

Molecular methods were used to identify blood parasites frequently observed in blood smears of water pythons (Liasis fuscus) captured in our study area in the Northern Territory of Australia. A nested polymerase chain reaction (PCR) using primers amplifying the 18s ribosomal RNA (rRNA) nuclear gene resulted in a short PCR product (180 bp) matching this region in the genus Hepatozoon. However, because of the short sequence obtained, 2 new primers were designed based on 18s rRNA sequences of 3 Hepatozoon taxa available in GenBank. Using these primers, approximately 600 bp of the parasites 18s rRNA gene was amplified successfully and sequenced from 2 water python samples. The new primers were used to investigate the prevalence of blood parasites in 100 pythons. In 25 of these samples we did not observe any blood parasites when examining stained slides. All the samples revealed a 600-bp PCR product, demonstrating that pythons in which we did not visually observe any parasites were infected by Hepatozoon spp. We also analyzed the nucleotide sequences of blood parasites in 4 other reptile taxa commonly encountered in our study area. The sequences obtained from water pythons and from 1 of these taxa were identical, suggesting that the parasite is capable of infecting hosts at different taxonomic levels.

MHC class I variation associates with parasite resistance and longevity in tropical pythons

Using restriction fragment length polymorphism (RFLP) we identified 26 unique major histocompatibility complex (MHC) genotypes in 104 water pythons. We observed a significant independent association between reduced blood parasite load (Hepatozoon sp.) and python body length/age, presence of a specific RFLP fragment (C‐fragment) and the overall number of fragments. The parasite has a negative impact on several python life‐history traits such as growth, nutritional status and longevity. Thus, the C‐fragment could be considered a ‘good gene’ (a fitness‐enhancing genetic element). However, while the number of fragments affected parasite load, the association between level of parasitaemia and fragment number was not linear, and, hence, minimum parasite infection level was achieved at an intermediate number of fragments. Intermediate MHC fragment numbers were also observed among the largest/oldest pythons, suggesting that both a specific fragment and intermediate levels of MHC polymorphism enhanced python longevity. Thus, our results suggest python MHC is subject to both frequency‐dependent and balancing selection.

Major Histocompatibility Complex (MHC) Markers in Conservation Biology

Human impacts through habitat destruction, introduction of invasive species and climate change are increasing the number of species threatened with extinction. Decreases in population size simultaneously lead to reductions in genetic diversity, ultimately reducing the ability of populations to adapt to a changing environment. In this way, loss of genetic polymorphism is linked with extinction risk. Recent advances in sequencing technologies mean that obtaining measures of genetic diversity at functionally important genes is within reach for conservation programs. A key region of the genome that should be targeted for population genetic studies is the Major Histocompatibility Complex (MHC). MHC genes, found in all jawed vertebrates, are the most polymorphic genes in vertebrate genomes. They play key roles in immune function via immune-recognition and -surveillance and host-parasite interaction. Therefore, measuring levels of polymorphism at these genes can provide indirect measures of the immunological fitness of populations. The MHC has also been linked with mate-choice and pregnancy outcomes and has application for improving mating success in captive breeding programs. The recent discovery that genetic diversity at MHC genes may protect against the spread of contagious cancers provides an added impetus for managing and protecting MHC diversity in wild populations. Here we review the field and focus on the successful applications of MHC-typing for conservation management. We emphasize the importance of using MHC markers when planning and executing wildlife rescue and conservation programs but stress that this should not be done to the detriment of genome-wide diversity.

Mitochondrial DNA recombination in a free-ranging Australian lizard

Mitochondrial DNA (mtDNA) is the traditional workhorse for reconstructing evolutionary events. The frequent use of mtDNA in such analyses derives from the apparent simplicity of its inheritance: maternal and lacking bi-parental recombination. However, in hybrid zones, the reproductive barriers are often not completely developed, resulting in the breakdown of male mitochondrial elimination mechanisms, leading to leakage of paternal mitochondria and transient heteroplasmy, resulting in an increased possibility of recombination. Despite the widespread occurrence of heteroplasmy and the presence of the molecular machinery necessary for recombination, we know of no documented example of recombination of mtDNA in any terrestrial wild vertebrate population. By sequencing the entire mitochondrial genome (16 761 bp), we present evidence for mitochondrial recombination in the hybrid zone of two mitochondrial haplotypes in the Australian frillneck lizard (Chlamydosaurus kingii).

Low genetic diversity threatens imminent extinction for the Hungarian meadow viper (Vipera ursinii rakosiensis)

Meadow vipers (Vipera ursinii) are small venomous snakes whose range in Hungary has been greatly fragmented by anthropogenic habitat disturbance (especially, agriculture). We obtained DNA from a total of eight Hungarian snakes. Genetic variability at the major histocompatibility (Mhc) class I loci was much lower for these snakes than for specimens from two large Ukrainian populations. Within two Hungarian populations for which we had multiple individuals, band-sharing indices were 100 and 84.6% (versus 63.3 and 57% for the Ukraine populations). The Ukrainian snakes also displayed more RFLP fragments than the Hungarian vipers (mean 13.7 versus 9.0, respectively). In combination with reports of birth deformities, chromosomal abnormalities and low juvenile survival, these data strongly suggest that the Hungarian vipers are experiencing inbreeding depression. Genetic diversity is still present in the Hungarian vipers but among rather than within populations. Given the very low numbers of animals, the only feasible strategy to increase the genetic diversity and to save the Hungarian vipers from extinction is to implement a captive breeding program based on genetically screened animals.

Widespread convergence in toxin resistance by predictable molecular evolution

Significance Convergence has strong bearing on the fundamental debate about whether evolution is stochastic and unpredictable or subject to constraints. Here we show that, in certain circumstances, evolution can be highly predictable. We demonstrate that several lineages of insects, amphibians, reptiles, and mammals have utilized the same molecular solution, via the process of convergence, to evolve resistance to toxic cardiac glycosides produced defensively by plants and bufonid toads. The repeatability of this process across the animal kingdom demonstrates that evolution can be constrained to proceed along highly predictable pathways at molecular and functional levels. Our study has important implications for conservation biology by providing a predictive framework for assessing the vulnerability of native fauna to the introduction of invasive toxic toads. The question about whether evolution is unpredictable and stochastic or intermittently constrained along predictable pathways is the subject of a fundamental debate in biology, in which understanding convergent evolution plays a central role. At the molecular level, documented examples of convergence are rare and limited to occurring within specific taxonomic groups. Here we provide evidence of constrained convergent molecular evolution across the metazoan tree of life. We show that resistance to toxic cardiac glycosides produced by plants and bufonid toads is mediated by similar molecular changes to the sodium-potassium-pump (Na+/K+-ATPase) in insects, amphibians, reptiles, and mammals. In toad-feeding reptiles, resistance is conferred by two point mutations that have evolved convergently on four occasions, whereas evidence of a molecular reversal back to the susceptible state in varanid lizards migrating to toad-free areas suggests that toxin resistance is maladaptive in the absence of selection. Importantly, resistance in all taxa is mediated by replacements of 2 of the 12 amino acids comprising the Na+/K+-ATPase H1–H2 extracellular domain that constitutes a core part of the cardiac glycoside binding site. We provide mechanistic insight into the basis of resistance by showing that these alterations perturb the interaction between the cardiac glycoside bufalin and the Na+/K+-ATPase. Thus, similar selection pressures have resulted in convergent evolution of the same molecular solution across the breadth of the animal kingdom, demonstrating how a scarcity of possible solutions to a selective challenge can lead to highly predictable evolutionary responses.

MHC, health, color, and reproductive success in sand lizards

Abstract“Good genes” are genetic elements that contribute to lifetime reproductive success, regardless of an individual’s additional genotype. Their existence is debated, and most work has targeted their viability benefits to the offspring of choosy females. In the present study, we analyze a case of potential good genes effects in adult male sand lizards (Lacerta agilis). We show that males with a particular RFLP (Restriction Fragment Length Polymorphism) MHC genotype (O-males), as opposed to those that lack this genetic element (NO-males), have less ectoparasites under increasing physiological stress (indexed by baseline corticosterone level), and are not constrained by parasites at production of status coloration. Furthermore, O-males are more successful at mate acquisition and guard their partners longer. Ultimately, they have a higher genetic reproductive success as assigned by microsatellites.

Short telomeres in hatchling snakes: erythrocyte telomere dynamics and longevity in tropical pythons

Background Telomere length (TL) has been found to be associated with life span in birds and humans. However, other studies have demonstrated that TL does not affect survival among old humans. Furthermore, replicative senescence has been shown to be induced by changes in the protected status of the telomeres rather than the loss of TL. In the present study we explore whether age- and sex-specific telomere dynamics affect life span in a long-lived snake, the water python (Liasis fuscus). Methodology/Principal Findings Erythrocyte TL was measured using the Telo TAGGG TL Assay Kit (Roche). In contrast to other vertebrates, TL of hatchling pythons was significantly shorter than that of older snakes. However, during their first year of life hatchling TL increased substantially. While TL of older snakes decreased with age, we did not observe any correlation between TL and age in cross-sectional sampling. In older snakes, female TL was longer than that of males. When using recapture as a proxy for survival, our results do not support that longer telomeres resulted in an increased water python survival/longevity. Conclusions/Significance In fish high telomerase activity has been observed in somatic cells exhibiting high proliferation rates. Hatchling pythons show similar high somatic cell proliferation rates. Thus, the increase in TL of this group may have been caused by increased telomerase activity. In older humans female TL is longer than that of males. This has been suggested to be caused by high estrogen levels that stimulate increased telomerase activity. Thus, high estrogen levels may also have caused the longer telomeres in female pythons. The lack of correlation between TL and age among old snakes and the fact that longer telomeres did not appear to affect python survival do not support that erythrocyte telomere dynamics has a major impact on water python longevity.