Ontogenetic allometry in the foot size of Oligoryzomys flavescens (Waterhouse, 1837) (Rodentia, Sigmodontinae)

Abstract

Ontogenetic allometry is the study of how the size or shape of certain structures changes over the course of an animal's development. In this study, using Huxley's formula of allometric growth (1932), we assessed the changes in the rate of growth of the feet size of the sigmodontine rodent Oligoryzomys flavescens during its ontogeny and compared differences between males and females. We find evidence of a change of polarity during the ontogenetic development of the species, with the presence of positive allometry during pregnancy and negative allometry in adulthood. Moreover, we note the presence of sexual dimorphism in the size of the feet, in which males of the species have a higher rate of growth than females. This growth pattern is positively related to escape from predators in childhood in both sexes and, in adulthood, provides a higher encounter rate of females by males, due to the larger displacement of the latter. We suggest that both the forces of natural selection and sexual selection have acted to shape the evolution of foot size in this species.Keywords: linear measures, ontogenetic trajectory, bipedal locomotion, sexual dimorphism. Alometria ontogenética no tamanho dos pés em Oligoryzomys flavescens(Waterhouse, 1837) (Rodentia, Sigmodontinae) ResumoA alometria ontogenética estuda como o tamanho ou forma de determinada estrutura muda ao longo do desenvolvimento. Neste estudo, através da fórmula do crescimento alométrico de Huxley (1932), acessamos as variações na taxa de crescimento do tamanho dos pés do roedor sigmodontineo Oligoryzomys flavescens, ao longo de sua ontogenia e entre machos e fêmeas. Nós encontramos evidência de uma mudança de polaridade ontogenética ao longo do desenvolvimento da espécie, com presença de alometria positiva na fase gestacional, e alometria negativa na fase adulta. Além disso, constatamos a presença de dimorfismo sexual no tamanho dos pés, onde machos da espécie apresentam uma maior taxa de crescimento nesta característica em comparação com as fêmeas. Esse padrão de crescimento deve estar positivamente relacionado com a fuga de predadores na infância em ambos os sexos, e na vida adulta propicia uma maior taxa de encontro de fêmeas pelos machos, devido ao maior deslocamento destes últimos. Sugerimos que tanto as forças da seleção natural quanto da seleção sexual tem atuado para moldar a evolução do tamanho dos pés nesta espécie.Palavras-chave: medidas lineares, trajetória ontogenética, locomoção bípede, dimorfismo sexual.

Evolutionary patterns of cranial ontogeny in Sigmodontines (Rodentia, Cricetidae)

“…Evaluating the processes of morphological change during ontogeny, it is possible to detect how selection has altered growth patterns, affecting adult morphology (Creighton & Strauss, 1986). The analysis of the ontogenetic trajectory of a single species (without a comparative context) is not enough to explain the direction of evolutionary change (Maestri et al, 2015). In addition, an evolutionary framing (phylogenetic approach) is crucial in comparative studies of ontogeny, as the behavior of a character during this process determines its evolutionary lability, or on the contrary, its constraint for change (Klingenberg, 1996).…”

“…Evaluating the processes of morphological change during ontogeny, it is possible to detect how selection has altered growth patterns, affecting adult morphology (Creighton & Strauss, 1986). The analysis of the ontogenetic trajectory of a single species (without a comparative context) is not enough to explain the direction of evolutionary change (Maestri et al, 2015).…”