Sexual size dimorphism in Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) from south Brazil / Dimorfismo sexual no tamanho do crânio de Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) no sul do Brasil

Among Vespertilionidae species, sexual size dimorphism is very well documented, in which females are larger than males. The differences are mainly in body weight, skull measurements and forearm length. Studies have discussed some hypothesis for this phenomenon. However, very little information is known about sexual size dimorphism in Myotis nigricans (Schinz, 1821) in Brazil. In this sense, the goal of this paper is to present a study of this phenomenon in the species. For this, we present a quantitative analysis of sexual size dimorphism assessed by traditional morphometrics. Ten skull measurements in addition to the forearm length of adult specimens were taken. Results of traditional morphometrics revealed sexual size dimorphism in five skull measurements and in the forearm length. Females were larger than males. These differences can be attributed to natural selection on large female size for increase fecundity. Bat females of the Vespertilionidae family are usually larger than males in order to perform parental care appropriately and to provide a successful reproductive process.

Entre as espécies de Vespertilionidae, o dimorfismo sexual, no qual as fêmeas são maiores que os machos, é bem documentado. As diferenças aparecem principalmente no peso do corpo, nas medidas cranianas e no comprimento do antebraço. Estudos têm discutido algumas hipóteses para este fenômeno. Contudo, poucas são as informações conhecidas sobre dimorfismo sexual de tamanho para a espécie Myotis nigricans (Schinz, 1821) no Brasil. O objetivo deste artigo é apresentar um estudo deste fenômeno na espécie. Para isso, apresentamos uma análise quantitativa do dimorfismo sexual através da morfometria tradicional, no qual 10 medidas cranianas e o comprimento do antebraço foram tomados. Resultados da morfometria tradicional revelaram dimorfismo sexual em cinco das dez medidas cranianas e no comprimento do antebraço. Em todas as medidas, as fêmeas foram maiores que os machos. As diferenças podem ser atribuídas à seleção natural, favorecendo tamanho maior para as fêmeas para aumentar a fecundidade. Fêmeas da família Vespertilionidae são geralmente maiores a fim de desempenhar adequadamente o cuidado parental e prover processo reprodutivo com sucesso.

Size and shape variability in the skull of Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) from two geographic areas in Brazil.

We present a quantitative analysis of sexual dimorphism and geographic variation in the skull of Myotis nigricans (Schinz, 1821) assessed by geometric morphometrics. Differences in size and shape of skulls were investigated using 30 landmarks plotted on two-dimensional images of lateral and ventral views. Results of geometric morphometrics revealed sexual dimorphism in the centroid size of the skull in both views. Females were larger than males. Nevertheless, there was no sexual dimorphism in skull shape of M. nigricans. Geographic variation was detected in size and shape of the skull. South Brazilian specimens were significantly larger than Ceará specimens only in the lateral view. Differences in skull shape were statistically significant in both views: specimens from South Brazil were brevirostri and presented a more expanded skull in the posterior region while Ceará specimens were longirostri and do not present any expansion in the brain case. Ecological factors for these phenomena are discussed in the text.

Size and shape variability in the skull of Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) from two geographic areas in Brazil / Variação de tamanho e forma no crânio de Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) de duas áreas geográficas no Brasil

We present a quantitative analysis of sexual dimorphism and geographic variation in the skull of Myotis nigricans (Schinz, 1821) assessed by geometric morphometrics. Differences in size and shape of skulls were investigated using 30 landmarks plotted on two-dimensional images of lateral and ventral views. Results of geometric morphometrics revealed sexual dimorphism in the centroid size of the skull in both views. Females were larger than males. Nevertheless, there was no sexual dimorphism in skull shape of M. nigricans. Geographic variation was detected in size and shape of the skull. South Brazilian specimens were significantly larger than Ceará specimens only in the lateral view. Differences in skull shape were statistically significant in both views: specimens from South Brazil were brevirostri and presented a more expanded skull in the posterior region while Ceará specimens were longirostri and do not present any expansion in the brain case. Ecological factors for these phenomena are discussed in the text.

Uma análise quantitativa do dimorfismo sexual e da variação geográfica do crânio de Myotis nigricans (Schinz, 1821) é apresentada através da morfometria geométrica. Diferenças no tamanho e na forma do crânio foram avaliadas através de imagens bidimensionais das vistas lateral e ventral do crânio, onde foram estabelecidos 30 marcos anatômicos. Os resultados indicaram a existência de dimorfismo sexual no tamanho do centróide do crânio para ambas as vistas estudadas. As fêmeas foram maiores que os machos. Contudo, não foi detectado dimorfismo sexual na forma do crânio de M. nigricans. A variação geográfica esteve presente no tamanho e na forma do crânio. Espécimes do Sul do Brasil tiveram tamanho do centróide maior que os espécimes do Ceará apenas na vista lateral. Diferenças na forma do crânio foram estatisticamente significativas em ambas as vistas: os espécimes do Sul do Brasil apresentaram-se brevirostri e com grande expansão na região posterior do crânio, enquanto os espécimes do Ceará apresentaram crânios longirostri e sem expansão posterior da caixa craniana. São discutidos fatores ecológicos para estes fenômenos.

Sexual size dimorphism in Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) from south Brazil.

Among Vespertilionidae species, sexual size dimorphism is very well documented, in which females are larger than males. The differences are mainly in body weight, skull measurements and forearm length. Studies have discussed some hypothesis for this phenomenon. However, very little information is known about sexual size dimorphism in Myotis nigricans (Schinz, 1821) in Brazil. In this sense, the goal of this paper is to present a study of this phenomenon in the species. For this, we present a quantitative analysis of sexual size dimorphism assessed by traditional morphometrics. Ten skull measurements in addition to the forearm length of adult specimens were taken. Results of traditional morphometrics revealed sexual size dimorphism in five skull measurements and in the forearm length. Females were larger than males. These differences can be attributed to natural selection on large female size for increase fecundity. Bat females of the Vespertilionidae family are usually larger than males in order to perform parental care appropriately and to provide a successful reproductive process.

Sexual size dimorphism in Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) from south Brazil

Among Vespertilionidae species, sexual size dimorphism is very well documented, in which females are larger than males. The differences are mainly in body weight, skull measurements and forearm length. Studies have discussed some hypothesis for this phenomenon. However, very little information is known about sexual size dimorphism in Myotis nigricans (Schinz, 1821) in Brazil. In this sense, the goal of this paper is to present a study of this phenomenon in the species. For this, we present a quantitative analysis of sexual size dimorphism assessed by traditional morphometrics. Ten skull measurements in addition to the forearm length of adult specimens were taken. Results of traditional morphometrics revealed sexual size dimorphism in five skull measurements and in the forearm length. Females were larger than males. These differences can be attributed to natural selection on large female size for increase fecundity. Bat females of the Vespertilionidae family are usually larger than males in order to perform parental care appropriately and to provide a successful reproductive process.

Entre as espécies de Vespertilionidae, o dimorfismo sexual, no qual as fêmeas são maiores que os machos, é bem documentado. As diferenças aparecem principalmente no peso do corpo, nas medidas cranianas e no comprimento do antebraço. Estudos têm discutido algumas hipóteses para este fenômeno. Contudo, poucas são as informações conhecidas sobre dimorfismo sexual de tamanho para a espécie Myotis nigricans (Schinz, 1821) no Brasil. O objetivo deste artigo é apresentar um estudo deste fenômeno na espécie. Para isso, apresentamos uma análise quantitativa do dimorfismo sexual através da morfometria tradicional, no qual 10 medidas cranianas e o comprimento do antebraço foram tomados. Resultados da morfometria tradicional revelaram dimorfismo sexual em cinco das dez medidas cranianas e no comprimento do antebraço. Em todas as medidas, as fêmeas foram maiores que os machos. As diferenças podem ser atribuídas à seleção natural, favorecendo tamanho maior para as fêmeas para aumentar a fecundidade. Fêmeas da família Vespertilionidae são geralmente maiores a fim de desempenhar adequadamente o cuidado parental e prover processo reprodutivo com sucesso.

Size and shape variability in the skull of Myotis nigricans (Schinz, 1821) (Chiroptera: Vespertilionidae) from two geographic areas in Brazil

We present a quantitative analysis of sexual dimorphism and geographic variation in the skull of Myotis nigricans (Schinz, 1821) assessed by geometric morphometrics. Differences in size and shape of skulls were investigated using 30 landmarks plotted on two-dimensional images of lateral and ventral views. Results of geometric morphometrics revealed sexual dimorphism in the centroid size of the skull in both views. Females were larger than males. Nevertheless, there was no sexual dimorphism in skull shape of M. nigricans. Geographic variation was detected in size and shape of the skull. South Brazilian specimens were significantly larger than Ceará specimens only in the lateral view. Differences in skull shape were statistically significant in both views: specimens from South Brazil were brevirostri and presented a more expanded skull in the posterior region while Ceará specimens were longirostri and do not present any expansion in the brain case. Ecological factors for these phenomena are discussed in the text.

Uma análise quantitativa do dimorfismo sexual e da variação geográfica do crânio de Myotis nigricans (Schinz, 1821) é apresentada através da morfometria geométrica. Diferenças no tamanho e na forma do crânio foram avaliadas através de imagens bidimensionais das vistas lateral e ventral do crânio, onde foram estabelecidos 30 marcos anatômicos. Os resultados indicaram a existência de dimorfismo sexual no tamanho do centróide do crânio para ambas as vistas estudadas. As fêmeas foram maiores que os machos. Contudo, não foi detectado dimorfismo sexual na forma do crânio de M. nigricans. A variação geográfica esteve presente no tamanho e na forma do crânio. Espécimes do Sul do Brasil tiveram tamanho do centróide maior que os espécimes do Ceará apenas na vista lateral. Diferenças na forma do crânio foram estatisticamente significativas em ambas as vistas: os espécimes do Sul do Brasil apresentaram-se brevirostri e com grande expansão na região posterior do crânio, enquanto os espécimes do Ceará apresentaram crânios longirostri e sem expansão posterior da caixa craniana. São discutidos fatores ecológicos para estes fenômenos.