Nejvíce citovaný článek - PubMed ID 31831851
Universality of indeterminate growth in lizards rejected: the micro-CT reveals contrasting timing of growth cartilage persistence in iguanas, agamas, and chameleons
Osteoderms, also called dermal armour, often play a role in predator defence. The presence of osteoderms is highly irregularly distributed across the squamate phylogeny and they have not been found in snakes. In this study, we searched for candidate snake species that would benefit from such armour to protect their body, focusing primarily on fossorial species with defensive tail displays. We examined the tail morphology of 27 snake species from different families using micro-computed tomography (µCT) and micro- radiography. We discovered dermal armour in four species of sand boas (Erycidae) that also feature enlarged and highly modified caudal vertebrae. This is the first description of dermal armour in snakes. Ancestral state reconstructions revealed that osteoderms likely evolved once or multiple times in Erycidae. We have not found osteoderms in any other examined snake species. Nevertheless, similar structures are known from unrelated squamate clades, such as gerrhosaurids and geckos. This supports the idea of underlying deep developmental homology. We propose the hypothesis that osteoderms protect sand boas like the "brigandine armour" of medieval warriors. We interpret it as another component of the sand boas' rich defence strategy.
Squamate reptiles have been considered to be indeterminate growers for a long time. However, recent studies demonstrate that bone prolongation is stopped in many lizards by the closure of bone growth plates. This shift in the paradigm of lizard growth has important consequences for questions concerning the proximate causes of sexual size dimorphism. The traditional model of highly plastic and indeterminate growth would correspond more to a long-term action of a sex-specific growth regulator. On the other hand, determinate growth would be more consistent with a regulator acting in a sex-specific manner on the activity of bone growth plates operating during the phase when a dimorphism in size develops. We followed the growth of males and females of the male-larger Madagascar ground gecko (Paroedura picta) and monitored the activity of bone growth plates, gonad size, levels of steroids, expression of their receptors (AR, ESR1), and expression of genes from the insulin-like growth factor network (IGF1, IGF2, IGF1R, and IGF2R) in livers. Specifically, we measured gene expression before the onset of dimorphic growth, at the time when males have more active bone growth plates and sexual size dimorphism was clearly visible, and after a period of pronounced growth in both sexes. We found a significant spike in the expression of IGF1 in males around the time when dimorphism develops. This overexpression in males comes long after an increase in circulating testosterone levels and sexual maturation in males, and it might be suppressed by ovarian hormones in females. The results suggest that sexual size dimorphism in male-larger lizards can be caused by a positive effect of high levels of IGF1 on bone growth. The peak in IGF1 resembles the situation during the pubertal growth spurt in humans, but in lizards, it seems to be sex-specific and disconnected from sexual maturation.
- Klíčová slova
- IGF1, body size, bone, growth, hormones, reptiles, sexual size dimorphism, testosterone,
- Publikační typ
- časopisecké články MeSH
(1) In contrast to mammals and birds, reptiles have been considered as indeterminate growers, whose growth reflects differential allocation of resources to growth versus other energetically demanding processes such as reproduction. (2) We monitored the growth and activity of bone growth plates, hormonal profiles, and reproductive activity in males and females of the male-larger gecko Paroedura picta. We show that growth plates fuse in this species in a sex-specific manner. The more abrupt epiphyseal closure and more pronounced growth deceleration in females coincide with the increased activity of their reproductive organs. (3) We conclude that at least some lizards are determinate growers whose sexual size dimorphism is potentially driven by ovarian hormones. The major difference in growth between endothermic and ectothermic amniotes appears to be in the magnitude of growth before and after the first reproduction, not in the mechanistic processes such as senescence of growth plate cells.
- Klíčová slova
- Evolutionary biology, Evolutionary developmental biology, Ichthyology, Zoology,
- Publikační typ
- časopisecké články MeSH
Body growth is typically thought to be indeterminate in ectothermic vertebrates. Indeed, until recently, this growth pattern was considered to be ubiquitous in ectotherms. Our recent observations of a complete growth plate cartilage (GPC) resorption, a reliable indicator of arrested skeletal growth, in many species of lizards clearly reject the ubiquity of indeterminate growth in reptiles and raise the question about the ancestral state of the growth pattern. Using X-ray micro-computed tomography (µCT), here we examined GPCs of long bones in three basally branching clades of squamate reptiles, namely in Gekkota, Scincoidea and Lacertoidea. A complete loss of GPC, indicating skeletal growth arrest, was the predominant finding. Using a dataset of 164 species representing all major clades of lizards and the tuataras, we traced the evolution of determinate growth on the phylogenetic tree of Lepidosauria. The reconstruction of character states suggests that determinate growth is ancestral for the squamate reptiles (Squamata) and remains common in the majority of lizard lineages, while extended (potentially indeterminate) adult growth evolved several times within squamates. Although traditionally associated with endotherms, determinate growth is coupled with ectothermy in this lineage. These findings combined with existing literature suggest that determinate growth predominates in both extant and extinct amniotes.
- Klíčová slova
- determinate growth, endothermy, growth plate cartilage, indeterminate growth, micro-CT, squamata,
- MeSH
- biologická evoluce MeSH
- fylogeneze MeSH
- hadi MeSH
- ještěři MeSH
- plazi růst a vývoj fyziologie MeSH
- rentgenová mikrotomografie MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
