Predictors of intraspecific morphological variability in a tropical hotspot: comparing the influence of random and non‐random factors

Abstract

Aim We describe patterns of skull size and shape variation in an Atlantic forest endemic rodent to test the influence of genetic structure, historical and environmental variables upon intraspecific morphological variability. Location South America, Brazil, Atlantic forest. Methods We analyse subtle differences in skull morphology of Akodon cursor through geometric morphometrics applied to 324 individuals from 12 localities distributed throughout the species range. Using cytochrome‐b gene (cyt‐b) sequences from 125 individuals (38 localities), we describe underlying patterns of genetic structure and transform them into distance measures that are included in our morphological analyses. We estimate the relative importance of genetic structure, historical variables and environmental variables on skull size and shape through mixed model selection and Akaike's information criterion. Results Geographical patterns in skull size are mainly explained by non‐random factors related to primary productivity and precipitation, whereas spatial shifts in shape correlate with mitochondrial divergence. Cytochrome‐b data revealed a phylogeographic break around the Jequitinhonha River, yet striking morphological shifts were observed further south. Differences in palaeostability between regions, and the configuration of rivers, appear as secondary sources of explanation for observed patterns. Main conclusions Multiple forces explain morphological variation within A. cursor. Teasing apart the effects of local adaptation and gene flow may be difficult, but is a key to improve our understanding of the drivers of intraspecific morphological variation. Our findings support the view that size is a more labile feature than shape, and that it may more easily break away from constraints imposed by gene flow. The combination of random and non‐random factors, together with documented breaks in the distribution of the Atlantic forest over the Late Quaternary, accounts for the majority of morphological differences observed in A. cursor.

Drivers of bromeliad leaf and floral bract variation across a latitudinal gradient in the Atlantic Forest

“…We test for trait variation in accordance with two hypotheses: (a) if shape is less labile than size (Cardini & Elton, 2009;Maestri et al, 2016) and is diagnostic for taxa (Neves et al, 2018), then we expect genetic structure to be a main predictor; (b) if vegetative characters are more labile than reproductive ones (Pélabon et al, 2011), then we expect variation in leaf traits to be better predicted by environmental shifts, while variation in floral bracts should be better predicted by genetic divergence.…”

“…In plants, the large variation of leaf shape and size reflects physiological demands imposed by environment (Givnish, 1979;Nicotra et al, 2011), and is observed both among and within species (Morello, Sassone, & López, 2018). Shape and size variability may have distinct patterns in distinct organisms, with size being considered more labile with variation mostly influenced by environment (phenotypic plasticity), while shape can be more conserved and variation usually genetically structured (Cardini & Elton, 2009;Chitwood et al, 2014;Maestri et al, 2016).…”

The role of soil features in shaping the bite force and related skull and mandible morphology in the subterranean rodents of genus Ctenomys (Hystricognathi: Ctenomyidae)

“…This suggests that, during the course of evolution, C. conoveri did not change the shape of its skull and mandible to adapt to the more‐compact soil, but might have changed its body size. Because variation in size is sometimes considered a more labile feature than shape, it is also more susceptible than shape to environmental changes (Thorpe, ; Patton & Brylski, ; Cardini & Elton, ; Maestri et al ., ). The cost of burrowing also increases with body size (Vleck, ) which generates a trade‐off between size increasing and metabolic economy in burrowing.…”

Pleistocene climatic oscillations in Neotropical open areas: Refuge isolation in the rodent Oxymycterus nasutus endemic to grasslands

“…nasutus populations were also depicted among the environments. Such skull differences might be related to genetic grouping or with environmental factors, exerting some form of local selection and/or guiding phenotypic plasticity in each physiognomy [ 8 ]. Similarly, studies on haplogroups of sympatric akodonts (e.g., Deltamys kempi [ 63 , 64 ] and Scapteromys spp.…”

“…In the recent years, some regions in the Neotropics have been systematically studied [ 6 ], as the high biological diversity provides an opportunity to test refuge hypotheses associated with climatic oscillations in the Quaternary Epoch, especially in complex ecoregions such as the Atlantic Forest [ 7 , 8 ]. A remarkable landscape in South America are the open areas, such as the Pampas biome, the largest temperate grasslands in the world [ 9 ], which are excellent environments to evaluate the influence of historical climatic fluctuations on the origin and evolutionary dynamics of species.…”