Abstract
Studies of morphometric variation make it possible to delimit species and geographic intraspecific variation, mainly in species with wide distribution ranges. In the Neotropical otter, Lontra longicaudis, variation in the shape of the rhinarium of three potential subspecies has been described but it is not known whether there is a pattern to the morphometric variation in the skull throughout the distribution of this species. We analyzed morphological variation in the cranium (ventral view) and the mandible (lateral view) of the Neotropical otter, comparing male and female specimens and evaluating the differences between specified geographic units utilizing methods from geometric morphometrics. Specimens from the entire distribution of the species were analyzed. Between sexes, variability in the shape was determined by calculating the Procrustes distances and using Goodall's F test. Geographic variationwas analyzed using a discriminant analysis, an analysis of variance (ANOVA) on a matrix of partial warp scores, and a cluster analysis with Mahalanobis distances, allowing for similarities in shape to be identified between different geographic units. Variation in the size of the two structures was calculated based on the values for centroid size using a one-way ANOVA with a Bonferroni correction and a 95 % confidence interval. There was sexual dimorphism in shape for both views, with males the largest. In general, there was geographic variation in the shape and size of both the cranium and the mandible in the Neotropical otter, exhibiting a pattern that resembled Bergmann's rule. Variation in shape between geographic units could result from the presence of geographic barriers, the spatial configuration of hydrological regions, and/or the large distances between populations throughout this species' distribution. The Neotropical otter exhibits dimorphism in the size, but not in the shape of the skull. There is geographic variation between geographic units, and our results suggest that L.longicaudis could bea group of species. An integrative study using molecular and morphological data could elucidate its taxonomy.
Highlights
Studies of morphometric variation make it possible to delimit species and geographic intraspecific variation, mainly in species with wide distribution ranges
Sexual dimorphism in shape and size The principal component analysis (PCA) of the skull and the mandible indicate a small proportion of the variance was explained by the first two principal components, 63.6 and 42.9 %, respectively
The results of the analysis of variance (ANOVA) for centroid size indicated that males are significantly different from females in both skull size (F(1,54) = 6.2030, p = 0.0158) and mandible size (F(1,68) = 9.8040, p = 0.0025), with males larger than females for both views
Summary
Studies of morphometric variation make it possible to delimit species and geographic intraspecific variation, mainly in species with wide distribution ranges. The Neotropical otter (Lontra longicaudis) is an aquatic species with a wide distribution that is limited to the terrestrial-aquatic ecotone that corresponds to lagoon and riparian systems (Gallo-Reynoso et al 2008) This species is Neotropical in origin and has a continuous distribution from Argentina in South America to the Trans-Mexican Volcanic Belt (Fig. 1). Seasons, though different studies have shown its diet is largely made up of fish and crustaceans and to a lesser extent amphibians, mammals, birds, and turtles (GalloReynoso et al 2008; Carvalho-Junior et al 2010;Chemes et al 2010; Platt and Rainwater 2011) Owing to these factors and the variation in its habitat in terms of vegetation, climate, and food availability throughout its extensive distribution, potential changes in the cranial morphology of L. longicaudis may be interpreted as local adaptations to environmental variables such as different types of prey. The first hypothesis is that there should be a differentiation in the shape and size of the cranium and mandible between the sexes, and the second is that these variables differ between populations of the different geographic regions throughout its distribution
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