Abstract
Taxonomic uncertainties in the Rattus genus persist due to among-species morphological conservatism coupled with within-species environmental variation in morphology. As a result, this genus contains a number of possible cryptic species. One important example can be found in R. praetor, where morphological studies indicate it is a possible species complex. Genetic studies of R. praetor (limited to analysis of mitochondrial DNA) have been inconclusive, but do indicate such subdivision. Here we use geometric morphometrics to explore this possible species complex by analysing the dental traits of 48 specimens from New Guinea and neighbouring regions. We find separate molar morphologies for Bougainsville Island, central New Guinea and west New Guinea which cannot be easily explained by different environmental factors (climate, precipitation and altitude), strongly suggesting the existence of a number of evolutionarily distinct taxa within what is currently called R. praetor thus supporting previous suggestions that R. praetor is a species complex. Our findings demonstrate the potential of advanced morphological analyses in identifying separate species, contrary to the claims of morphological conservatism. Future analyses should combine geometric morphometrics with genetic analyses over the species range and include sub-fossil specimens from the Bismarck archipelago and Solomon Islands to resolve the evolutionary history of R. praetor.
Highlights
Small mammal genera are often speciose (Michaux et al, 2001), despite a high degree of morphological uniformity
In assessing the dental morphology of R. praetor populations from across New Guinea and neighbouring islands, we demonstrate the power of this morphometric approach and highlight how it should be used in conjunction with genetic studies in the future
principal components analysis (PCA) of tooth shape indicated the possible presence of multiple geographical forms because the Bougainville Island population separated from the New Guinea mainland population (Fig. 1B), with the differences statistically significant based on the Procrustes ANOVA (Df = 1, Sum Sq. = 0.046, Mean Sq. = 0.046, F = 24.9, p < 0.001)
Summary
Small mammal genera are often speciose (Michaux et al, 2001), despite a high degree of morphological uniformity. The genus Rattus has one of the most complex taxonomies among mammals, which is regularly revised (Musser and Carleton, 2005; Pagès et al, 2010; Robins et al, 2014; Timm et al, 2016) Members of this genus are morphologically homogenous despite numerous radiations (Schenk et al, 2013) and, is an excellent test system for methods to detect cryptic diversity. More recent research has focused on genetic analyses for these species and the wider Rattus genus (Aplin et al, 2011; Pagès et al, 2010; Robins et al, 2008, 2014; Rowe et al, 2011) Some of these wider Sahulian Rattus genetic studies tentatively support earlier suggestions of the subdivision of R. praetor into a geographically distributed species complex (Robins et al, 2014), though without defining component species. In assessing the dental morphology of R. praetor populations from across New Guinea and neighbouring islands, we demonstrate the power of this morphometric approach and highlight how it should be used in conjunction with genetic studies in the future
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