Comparative Morphometrics in Leptodactyline Frogs (Anura, Leptodactylidae, Leptodactylinae): Does Burrowing Behavior Relate to Sexual Dimorphism?
Fossorial habits occur in many animal lineages and usually involve both morphological and physiological adaptations that may evolve independently. Burrowing behavior in some species of the anuran subfamily Leptodactylinae involves the specialized use of the hind limbs and/or head. The aim of this study was to identify the morphometric characters associated with burrowing behavior in species of this subfamily. We then hypothesized that, as this habit is usually associated with males, we would find sexual dimorphism in head and hind-limb morphology in the burrowing species but not in the nonburrowing species. We compared 500 specimens from 24 species using phylogenetic statistical analyses and phylogenetic mapping of sexually dimorphic characters. The results demonstrated the following: 1) There was no correlation between the measurements of the limbs, head, or tarsal tubercle and burrowing behavior in the analyzed species; 2) there was no sexual dimorphism related to burrowing behavior reflected in measurements of the head or hind limbs; and 3) sexual dimorphism in the morphometric characters always was derived. Modifications of the ridged snout and increased ossification in the nasal region of the males of the fossorial species appear to be sufficient adaptations for burrowing. Los hábitos fosoriales ocurren en muchos linajes de animales y usualmente implican tanto adaptaciones morfológicas y fisiológicas que a menudo evolucionan independientemente. El comportamiento cavador en anuros de la subfamilia Leptodactylinae implica el uso especializado de miembros posteriores y/o cabeza. El objetivo de este trabajo fue identificar caracteres morfométricos asociados con hábitos cavadores en especies de este subfamilia. Hipotetizamos que, como este comportamiento usualmente está ligado a machos, existe dimorfismo sexual en la morfología de los miembros y cabeza en especies con hábitos fosoriales y no en las especies sin hábitos fosoriales. Comparamos 500 ejemplares de 24 especies a través de análisis estadísticos filogenéticos, y optimizamos en una filogenia los caracteres de dimorfismo sexual. Los resultados muestran que: (1) No hubo correlación entre medidas de cabeza, miembros posteriores, o tubérculo tarsal y comportamiento cavador en las especies analizadas; (2) No hubo dimorfismo sexual en medidas de la cabeza o miembro posterior relacionada a comportamiento cavador; y (3) El dimorfismo sexual en los caracteres estudiados fue siempre derivado. Las modificaciones en el hocico en forma de espátula, y una hiperosificación en la región nasal en los machos de las especies fosoriales serían suficientes adaptaciones para la excavación.Abstract
Resumen
Specimen of Leptodactylus bufonius (L440) showing the external analyzed measurements. (a) Ventral view. (b) Lateral view of the head. HH = head height; HL = head length; HW = head width; ITM = inner metatarsal tubercle; FL = feet length; SL = shank length; SVL = snout–vent length; TL = thigh length; TAL = tarsus portion length.
Phylogenetic framework provided in de Sá et al. (2014) reduced to include only the taxa of our study.
Phylogenetic PCA ordering of the sexual dimorphism index of the burrowing, nonburrowing, and nondata species. The PCA ordering of the sexual dimorphism index does not reflect cluster of burrowing or nonburrowing species.
Leptodactylus phylogeny by de Sá et al. (2014) in which relationships among the analyzed taxa are illustrated. The eight trees show the change of character states. Note that in this hypothesis, L. laticeps and L. syphax are transferred to the L. fuscus group; L. silvanimbus is relocated to the L. latrans group; and L. riveroi and L. discodactylus are included in the L. melanonotus group. Character 0 = head width; character 1 = head length; character 2 = head height; character 3 = thigh length; character 4 = shank length; character 5 = tarsus portion length; character 6 = foot length; character 7 = inner metatarsal tubercle.
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