Browse results
Abstract
This is a preliminary and exploratory study of cranial variation in European populations of grayling. We investigated the correspondence between size/shape variation of the dorsal (dc), ventral (vc) and occipital (oc) cranium and phylogenetic relationships (inferred from mitochondrial control region – mtDNA cr and microsatellite dna data) of six grayling populations: three from Balkan phylogenetic clade and two from Caspian phylogenetic clade of the European grayling Thymallus thymallus and one population of the Adriatic grayling Thymallus aeliani, which until recently was considered the Adriatic phylogenetic clade of T. thymallus. Significant size and shape differences were found between populations in all three cranial views. However, significant size-related shape variation (allometry) was found for dc and vc, but not for oc. The size variation of each cranial view does not contain phylogenetic signal, but size variation of oc is consistent with genetic variation inferred from microsatellite dna. Regarding shape variation, a significant phylogenetic signal was detected only for oc, and only the shape variation of oc is consistent with the genetic variation inferred from the mtDNA cr. Moreover, the Adriatic grayling T. aeliani (Soča population) was clearly separated from the three T. thymallus populations of the Balkan phylogenetic clade and the two T. thymallus populations of the Caspian phylogenetic clade only at the level of oc. Thus, our results suggest that different cranial regions differ in allometry, reflect phylo(genetic) relationships differently, and exhibit differences in ecophenotypic plasticity, with oc seeming best suited to represent the phylogenetic relationships of the grayling populations studied.
Abstract
Satellite dna s (satDNA) have long been recognized as a major driving force in karyotypic repatterning, owing to their ability to recombine between non-homologous chromosomes. A quite extensively studied model is the Repetitive PvuII Ctenomys Sequence (rpcs), the main component of constitutive heterochromatin in rodents of the genus Ctenomys (Rodentia, Ctenomyidae). At the genus level, fluctuations in rpcs copy number have been previously associated with karyotypic instability. However, when a microevolutionary approach was assayed in the most karyotypically variable lineage of the genus, the vast population-level copy number variation precluded any possibility of analyzing it in a phylogenetic framework. The existence of sex-related differences as a source of variability was not considered until later, when chromosomal banding suggested that the Y chromosome may be a significant reservoir of rpcs. This study aimed to investigate the bias associated with the presence of the Y chromosome in rpcs copy number variation in the Corrientes group of Ctenomys. The results revealed that the Y chromosome harbors almost twice the amount of rpcs compared to the rest of the chromosome complement, explaining the high levels of intrapopulation variation. The evolution of rpcs copy number in males and females showed independent patterns, attributable to the presence/absence of the Y chromosome. The correlation between rpcs dynamics and diploid number fluctuations was also investigated, concluding that some karyotypic repatterning events could be explained by satDNA amplification/deletion, but not all of them. This study highlights the importance of considering differences resulting from the differential accumulation of satDNA in the heterogametic chromosome.
Abstract
The juvenile mandible is important in the investigation of ontogenetic and evolutionary changes among early hominins. We revisit the mandibular symphysis in juvenile specimens of Australopithecus africanus and Paranthropus robustus with two main contributions. First, we employ, for the first time, methods of computational anatomy to model complex symphyseal shape differences. Second, we present new fossil evidence from Kromdraai to improve our knowledge of symphyseal morphology. We describe differences between shapes by landmark-free diffeomorphism needed to align them. We assess which features of the mandibular symphysis best discriminate the juvenile symphysis in these fossil species, relative to the intraspecific variation observed among modern humans. Our approach eliminates potential methodological inconsistencies with traditional approaches (i.e., the need for homologous anatomical landmarks, assumption of linearity). By enabling detailed comparisons of complex shapes in juvenile mandibles, our proposed approach offers new perspectives for more detailed comparisons among Australopithecus, Paranthropus and early Homo.
The UTSN grant was awarded to the Dutch natural history museum NCB Naturalis and the National Zoological Collection of Suriname to digitalize the Suriname collection at Naturalis and produce books to raise awareness of the diverse fauna of Suriname and stimulate eco-tourism to the country.
Abstract
Every day, wild animals suffer and die from myriad natural causes. For those committed to non-speciesism, what wild animal suffering entails for us morally is a question of the utmost importance, and yet there remains significant disagreement at the level of normative theory. In this paper I argue that in situations of moral urgency environmental managers and policy makers should refer to widely-agreeable moral principles for guidance. I claim that the principles of beneficence, non-maleficence, autonomy and justice do well to capture our widely-held values, and that the first three principles all support large-scale interventions in nature. I then argue that balancing these against non-maleficence will still allow for the careful consideration of interventions, although is unlikely to support lethal methods. This argument is intended to provide a reasonable starting point for theory-agnostic decision makers, and places the burden of proof on those who oppose intervention.