Clinal and Allometric Variation in the Skull of Sexually Dimorphic Opossums

Abstract

We would like to thank Diego Astúa, Eliécer Gutiérrez, Geruza Melo, and Cristian Dambros for reviewing 17 this manuscript prior to submission. We are grateful to curators and staff of the MCNFZB (M.M. de A.

Mitogenomics of Didelphis (Mammalia; Didelphimorphia; Didelphidae) and insights into character evolution in the genus

“…Traitgrams also suggest a decrease in skull size along the history of the lineage leading to the MRCA of the white‐eared opossums, a pattern that is retained by the lineages leading to D. albiventris and D. imperfecta . It is congruent with an origin in savanna‐like environments, as predicted by (Cáceres et al, 2016) and is corroborated by the biogeographic implications of our results previously discussed, especially, if we consider that D. albiventris has been shown to conform to Bergman's rule (Bubadué et al., 2020). Differently from its closely related congeners, the history of D. pernigra exhibits a pattern similar to that displayed by D. virginiana, which suggests that they may share underlying adaptive processes leading to an increase in overall size and body mass (Amador & Giannini, 2016) beyond the historical component, since according to these authors' results, D. virginiana and D. pernigra exhibit the largest increase in body mass (in absolute values) of all Didelphidae.…”

“…In general, as the increase of these measurements along the history of Didelphis seems to be associated with larger taxa, or the decrease with smaller taxa, we suspect that these results may be explained mainly by allometric effect as pointed out by Astúa (2015a), Cáceres et al (2016), and Bubadué et al. (2020).…”

“…For this reason, we suggest that the white‐eared opossums might also illustrate a case of phenotypic variation influenced by environmental conditions in conformity with Bergmann's rule. Despite the size variation has been shown to follow an ecogeographic pattern in D. virginiana and D. albiventris (Bubadué et al., 2020; Nigenda‐Morales et al., 2018) and, conceivably, in D. albiventris species group, we cannot rule out, as pointed out by Nigenda‐Morales et al (2018), the possibility that the response to the environmental conditions is caused by phenotypic plasticity. Under this scenario, the larger size presented by D. pernigra would be associated to its more restricted distribution encompassing primarily colder environments, which would be consistent with the fact that D. albiventris occurring in colder and more seasonal environments presented larger skull size (Bubadué et al., 2020; Cáceres et al, 2016).…”

“…(2018) demonstrated that body size variation may be related to temperature seasonality, with larger individuals occurring in more seasonal habitats, implying that the species fits Bergmann's rule. Although no study of this kind concerning the whole D. albiventris group has been carried out so far, the fact that D. pernigra is the white‐eared opossum occurring in areas with higher altitudes and lower temperatures (Cerqueira, 1985b; Tocchio et al., 2015) and the only one exhibiting an average increase in body size and mass (Amador & Giannini, 2016), combined with the fact that D. albiventris follow a pattern of Bergman's rule for size (Bubadué et al., 2020), allow us to hypothesize that this pattern may be explained by adaptive evolution. For this reason, we suggest that the white‐eared opossums might also illustrate a case of phenotypic variation influenced by environmental conditions in conformity with Bergmann's rule.…”

“…We additionally took the same 17 measurements from 19 adult specimens of D. virginiana from throughout its range in Central and North America deposited in the Field Museum of Natural History (see Table for details). Since Didelphis species are known to be sexually dimorphic (Bubadué et al., 2020; Cerqueira & Lemos, 2000), all further analyses were carried out separately for females and males. The following analyses were carried out using R 3.6.1 (R Core Team, 2019).…”