Localized versus generalist phenotypes in a broadly distributed tropical mammal: how is intraspecific variation distributed across disparate environments?

Abstract

BackgroundThe extent of phenotypic differentiation in response to local environmental conditions is a key component of species adaptation and persistence. Understanding the structuring of phenotypic diversity in response to local environmental pressures can provide important insights into species evolutionary dynamics and responses to environmental change. This work examines the influence of steep environmental gradients on intraspecific phenotypic variation and tests two hypotheses about how the tropical soft grass mouse, Akodon mollis (Cricetidae, Rodentia), contends with the disparate environmental conditions encompassed by its broad distribution. Specifically, we test if the species expresses a geographically unstructured, or generalist, phenotype throughout its range or if it shows geographically localized morphological differentiation across disparate environments.ResultsUsing geometric morphometric and ecomorphological analyses of skull shape variation we found that despite distinct environmental conditions, geographically structured morphological variation is limited, with the notable exception of a distinct morphological disjunction at the high-elevation forest-grassland transition in the southern portion of A. mollis distribution. Based on genetic analyses, geographic isolation alone does not explain this localized phenotype, given that similar levels of genetic differentiation were also observed among individuals inhabiting other ecosystems that are nonetheless not distinct morphologically.ConclusionsInstead of phenotypic specialization across environments in these tropical mountains, there was limited differentiation of skull shape and size across the broad range of A. mollis, with the exception of individuals from the puna, the highest-elevation ecosystem. The high morphological variance among individuals, together with a weak association with local environmental conditions, not only highlights the flexibility of A. mollis’ skull, but also highlights the need for further study to understand what maintains the observed morphological patterns. The work also indicates that mechanisms other than processes linked to local ecological specialization as a driver of diversification may contribute to the high diversity of this tropical region.

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

“…Recent cross‐species eco‐morphological comparisons demonstrated that temperature, precipitation and productivity affect the distribution of mammal body size and shape in tropical regions (Rodríguez et al ., ; Martínez & Cola, ; Cardini et al ., ). Yet, studies addressing this question at the intraspecific level are still rare (Cardini et al ., ; Marchán‐Rivadeneira et al ., ; Alvarado‐Serrano et al ., ; O'Keefe et al ., ), and, until now, non‐existent for the Atlantic forest fauna.…”

“…Random processes related to genetic drift and gene flow have been implied in human skull variation (Relethford, 1994), despite recent evidence of strong influence of non-random factors (Perez & Monteiro, 2008). Moreover, an intraspecific study of Akodon mollis demonstrated limited morphological differentiation related to ecological variables, yet found that genetic variables explained a small percentage of skull size and shape variation (Alvarado-Serrano et al, 2013).…”

“…Previous studies have partially addressed the causes of geographical patterns of morphological change by focusing on non-random causes of trait variation (Mullen et al, 2009;Wang et al, 2013). However, joint analyses of random and non-random evolutionary processes underlying patterns are rarely performed (Perez & Monteiro, 2008;Alvarado-Serrano et al, 2013). In particular, it remains unclear how and why phenotypic variation is geographically structured in widely distributed species, especially in tropical regions (Monteiro et al, 2003;Alvarado-Serrano et al, 2013).…”

“…However, joint analyses of random and non-random evolutionary processes underlying patterns are rarely performed (Perez & Monteiro, 2008;Alvarado-Serrano et al, 2013). In particular, it remains unclear how and why phenotypic variation is geographically structured in widely distributed species, especially in tropical regions (Monteiro et al, 2003;Alvarado-Serrano et al, 2013). Understanding the processes that underlie trait variation in these areas is important from a theoretical perspective, though not exclusively.…”

Geometric morphometrics meets metacommunity ecology: environment and lineage distribution affects spatial variation in shape

“…Variables were selected based on intraspecific and crossspecies studies that showed these variables are correlated with skull and mandible shape variation in mammals (temperature and temperature seasonality: Martínez and Cola 2011, Cáceres et al 2014, Martínez et al 2014, Meloro et al 2014elevation: Alvarado-Serrano et al 2013, primary productivity: Cardini et al 2007; land cover or vegetation type: Monteiro et al 2003, Alvarado-Serrano et al 2013). Variables were selected based on intraspecific and crossspecies studies that showed these variables are correlated with skull and mandible shape variation in mammals (temperature and temperature seasonality: Martínez and Cola 2011, Cáceres et al 2014, Martínez et al 2014, Meloro et al 2014elevation: Alvarado-Serrano et al 2013, primary productivity: Cardini et al 2007; land cover or vegetation type: Monteiro et al 2003, Alvarado-Serrano et al 2013).…”