Comparative Cranial Geometric Morphometrics among Wistar Albino, Sprague Dawley, and WAG/Rij Rat Strains.

This research utilizes geometric morphometrics to investigate shape variation in the skull, mandible, and teeth among three rat strains: Wistar Albino (WA), Sprague Dawley (SD), and WAG/Rij (WR). Through the analysis of 48 rats using 2D geometric morphometric techniques, significant differences in their skull morphology were identified. This study indicates a shift from a rectangular to an oval cranial shape across strains, with notable size and morphological variances. Particularly, the WR strain's skull shape significantly differs from the SD and WA strains, suggesting distinct ecological or genetic pathways. Compared to the skull, mandible shape differences are less pronounced, but still significant. The WR strain exhibits a distinct mandible shape, potentially reflecting ecological adaptations like dietary habits. The teeth shape of WR rats is the most distinct. SD rats consistently exhibited larger sizes in both skull and mandible measurements, while WR rats were notably smaller. Interestingly, sexual dimorphism was not statistically significant in skull and teeth sizes, aligning with findings from previous studies. However, the mandible showed clear size differences between sexes, underscoring its potential for adaptive or behavioral studies. In summary, this study provides a comprehensive analysis of morphological variations in rat strains, highlighting the intricate interplay of size, shape, and ecological factors. These findings lay a foundation for deeper explorations into the adaptive, ecological, or genetic narratives influencing rat morphology.

Chewing asymmetry in dogs: Exploring the importance of the fossa masseterica and first molar teeth morphology.

Dogs are animals with strong bite force. This strong bite mechanism has led to significant changes in the skeletal system such as fossa masseterica. It can be thought that one side is used more than the other side in chewing and is related to the preference of using the same side's hand, eye and foot. In the study, directional asymmetry and fluctuating asymmetry, which occurs as a result of chewing asymmetry, were examined on the first molar teeth and the fossa masseterica in 85 dog mandibles including a wide diversity of morphotypes. The association of high PC1 values for directional asymmetry with a pronounced cranial index, as evident in breeds like Pekingese, Pomeranian and Bulldog, indicates a potential evolutionary or selective breeding trend favouring brachycephaly. On the contrary, guardian breeds like the German shepherd and Bernese mountain dog, which typically require strong jaws for their roles, showcased reduced PC1 values, which might be related to their functional morphology. Similarly, the PCA results for the first molar teeth shape variations also highlighted the influence of cranial shape, with boxer dogs displaying notably higher PC1 values. The fluctuating asymmetrical distributions provided valuable insights into individualistic variations. Interestingly, no specific breed distribution trend was observed for these asymmetries, indicating a more individual-based variation rather than breed-based. It is essential to note that while these results provide valuable insights, further studies are required to understand the underlying causes better. Factors like genetic variations, developmental processes, dietary habits and external environmental factors could play pivotal roles in these observed morphological differences.

A new species of Lethrinops (Cichliformes: Cichlidae) from a Lake Malawi satellite lake, believed to be extinct in the wild.

A new species of cichlid fish, Lethrinops chilingali is described from specimens collected from Lake Chilingali, near Nkhotakota, Malawi. It is assigned to the genus Lethrinops based on the form of the lower jaw dental arcade and by the absence of traits diagnostic of the phenotypically similar Ctenopharynx, Taeniolethrinops and Tramitichromis. It also lacks the enlarged cephalic lateral line canal pores found in species of Alticorpus and Aulonocara. The presence of a broken horizontal stripe on the flanks of females and immature/non-territorial males of Lethrinops chilingali distinguishes them from all congeners, including Lethrinops lethrinus, in which the stripe is typically continuous. Lethrinops chilingali also has a relatively shorter snout, shorter lachrymal bone and less ventrally positioned mouth than Lethrinops lethrinus. It appears likely that Lethrinops chilingali is now extinct in the wild, as this narrow endemic species has not been positively recorded in the natural environment since 2009. Breeding populations remain in captivity.