Morphological variation in two sigmodontine rodents along the mainland and the Fuegian archipelago in Chilean southern Patagonia

Abstract

Background: Analysis of morphological variation in archipelagos has been essential to understand the evolution of terrestrial vertebrates. In particular, these natural scenarios allow to assess morphological changes experienced by insular fauna compared to their mainland counterparts. In mammals, morphological changes of insular forms have been observed in size and shape of body and cranial traits. The southern Patagonia of Chile represents a unique scenario to analyze morphological variation in two of the most widely distributed small rodents along western southern South America: Abrothrix olivacea and Oligoryzomys longicaudatus. Methods: We applied linear and three-dimensional geometric morphometric tools to analyze the variation in cranial morphology of A. olivacea (N = 80) and O. longicaudatus (N = 49). Sampled localities were distributed in the mainland and islands of the Fuegian archipelago in Chilean Patagonia. Standard multivariate methods, as Principal Components Analysis, and Logistic Regression models were carried out to evaluate differences in size and shape of crania. Results: We detected higher levels of morphological variation in the crania of A. olivacea if compared to O. longicaudatus. The variation was associated to cranial size instead of shape. We observed significant differences between insular and mainland individuals in A. olivacea, being the cranium size of this species significantly bigger on islands. Indeed, specimens of A. olivacea from "Isla Wellington", exhibited the higher increment in cranium size compared to any other mainland and insular site sampled for this species. In contrast, insular and mainland forms of O. longicaudatus did not show significant differences in cranial morphology. Conclusions: We suggest that the patterns of morphological variation observed in these two small rodents along Patagonia, could be explained in terms of the historical biogeography of the region, and the different ecological features of the studied species.

The skull variation of the olive field mouseAbrothrix olivacea(Cricetidae: Abrotrichini) is localized and correlated to the ecogeographic features of its geographic distribution

“…The second DFA performed (SM, Fig. S2 ) indicates that this population shows significant levels of cranial distinctiveness (see also Valladares-Gómez et al, 2020 ); as such, its subspecific status can be maintained. This status should be further evaluated by means of the analysis of nuclear genetic variation.…”

“…These have demonstrated that variation of the assessed traits is correlated with environmental characteristics, such as water availability and the latitudinal distribution of populations. A possible island effect (see van der Geer, 2018 ) on the skull morphology of the olive mouse has been suggested by Valladares-Gómez et al (2020) for a restricted area of Chilean Patagonia. In turn, those assessments centered on cranial and external variation, accounted for a wide variability that was the basis for the recognition of A .…”

“…The phenotypic variation of Abrothrix olivacea has been addressed by several studies, mainly focused on characterizing the anatomical variability of the digestive and excretory systems ( e.g ., Bozinovic et al, 2010 , 2011 ; Naya et al, 2014 ), as well as the shape and size of skull ( e.g ., Pine, 1973 ; Yáñez, Valencia & Jaksic, 1979 ; Patterson, Gallardo & Freas, 1984 ; Valladares-Gómez et al, 2020 ; Sánchez et al, 2022 ). These have demonstrated that variation of the assessed traits is correlated with environmental characteristics, such as water availability and the latitudinal distribution of populations.…”

Lista actualizada de los mamíferos vivientes de Chile

“…La distinción cariotípica que presenta O. yatesi (2n=54, NF=66) respecto a O. longicaudatus (2n=56, NF=66), anteriormente considerada para respaldar la distinción de O. magellanicus (e.g., Weksler y Bonvicino 2015), es mínima y del tenor del observado en otras especies de Oligoryzomys cromosómicamente variables (ver un resumen de la variación cromosómica de Oligoryzomys en Weksler y Bonvicino 2005). Por otro lado, individuos con morfotipo de O. longicaudatus se distribuyen en Puerto Hambre, la localidad típica de O. magellanicus (Valladares et al 2020); si bien no es posible descartar que dos especies, O. longicaudatus y O. magellanicus, se distribuyan en las inmediaciones de Puerto Hambre, hasta el momento no hay evidencia de la existencia de dos especies en dicha zona. Dado lo anterior, en esta lista se considera a O. yatesi, al igual que a O. magallenicus, como sinónimos de O. longicaudatus.…”

Unraveling the morphological patterns of a subantarctic eelpout: a geometric morphometric approach

“…This environmental variability as well as coastal geometry may impact on the body shape variability in terrestrial (i.e., rodents, Valladares‐Gómez et al. 2020) and marine species with shallow vertical distribution, such as some endemic eelpouts.…”