Morphological variation in Bothrops jararaca and B. Insularis: sexual dimorphism and ontogeny
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Data
2021-09-17
Autores
Siqueira, Lucas Henrique Carvalho
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Universidade Estadual Paulista (Unesp)
Resumo
A morfologia é um dos traços mais variáveis nas serpentes. Ela é altamente correlacionada a vários traços biológicos e também a pressões ambientais. Usei duas técnicas complementares, morfometria linear e geométrica, para avaliar a variação morfológica em Bothrops jararaca e B. insularis dentro, e entre populações e espécies, para testar o efeito do dimorfismo sexual, distribuição geográfica e tendências microevolutivas. Medi entre 11 a 17 variáveis lineares de cada indivíduo. Além disso, 19 landmarks anatômicas foram posicionadas na cabeça, usando uma imagem fotográfica da vista dorsal. Em B. jararaca, fêmeas foram geralmente maiores para as medidas do corpo e da cabeça, ao passo que machos foram maiores para as variáveis da cauda. Encontrei efeito significativo da população, sendo que a população do planalto alcançou maiores tamanhos do que no litoral, e fêmeas apresentaram a cabeça com uma região pós-occipital em formato de flecha. Ambas as populações mostraram marcada alometria ontogenética, e a trajetória variou para cada traço medido. Um padrão de dimorfismo sexual similar ocorreu em B. insularis, mas não houve diferença no formato da cabeça, porém machos apresentaram olhos maiores. Os sexos tiveram trajetória ontogenética sobreposta para o formato do corpo, mas com inclinação diferente para o formato da cabeça. Comparações interespecíficas indicaram uma cabeça mais comprida e com focinho mais proeminente em B. insularis, mais similar à da população do planalto. A trajetória ontogenética também foi paralela com a do planalto e convergente com a população do litoral. A partição de nicho é uma explicação a para algumas das diferenças dos padrões aqui detectados. Da mesma forma, a disponibilidade de presas e ecologia comportamental podem produzir diferentes fenótipos em cada população ou espécie. Atribuo as diferenças na trajetória ontogenética principalmente à eventos de maturação heterocrônica e variação temporal nas mudanças ontogenéticas.
Morphology is one of the most variable traits in snakes. It is highly related to several biological traits and also environmental pressures. I used two complementary techniques, linear and geometric morphometrics, to evaluate morphological variation in Bothrops jararaca and B. insularis within and among populations and species, to test the effects of sexual dimorphism, geographic distribution and microevolutionary trends. I measured from 11 to 17 linear variables from each individual. Moreover, 19 anatomical landmarks were placed in the head using a photographed image of the dorsal view. In females were generally larger than males for body and head measures, while males were larger for tail variables. I found a significative effect of population, being that the highland population reached larger sizes than coastal population, and females presented a larger post-ocular region and a more arrow shaped head. Both populations showed a marked ontogenetic allometry and ontogenetic trajectory varied depending on each variable. A similar sexual dimorphism pattern occurred in B. insularis body, but with no difference in head shape, however males had larger eyes than females. Sexes had overlapped ontogenetic trajectory in body shape, but with different slopes in head shape. Interspecific comparisons indicated a longer head and prominent snout in B. insularis, closer to the highland population. Ontogenetic trajectory also was parallel with highland and convergent with coastal population. Niche partitioning is an explanation for the differences in the observed patterns. Accordingly, prey availability and behavioral ecology may produce different phenotypes on each population or species. I attribute differences in ontogenetic trajectories mainly due heterochronic maturation events and different onset on ontogenetic changes.
Morphology is one of the most variable traits in snakes. It is highly related to several biological traits and also environmental pressures. I used two complementary techniques, linear and geometric morphometrics, to evaluate morphological variation in Bothrops jararaca and B. insularis within and among populations and species, to test the effects of sexual dimorphism, geographic distribution and microevolutionary trends. I measured from 11 to 17 linear variables from each individual. Moreover, 19 anatomical landmarks were placed in the head using a photographed image of the dorsal view. In females were generally larger than males for body and head measures, while males were larger for tail variables. I found a significative effect of population, being that the highland population reached larger sizes than coastal population, and females presented a larger post-ocular region and a more arrow shaped head. Both populations showed a marked ontogenetic allometry and ontogenetic trajectory varied depending on each variable. A similar sexual dimorphism pattern occurred in B. insularis body, but with no difference in head shape, however males had larger eyes than females. Sexes had overlapped ontogenetic trajectory in body shape, but with different slopes in head shape. Interspecific comparisons indicated a longer head and prominent snout in B. insularis, closer to the highland population. Ontogenetic trajectory also was parallel with highland and convergent with coastal population. Niche partitioning is an explanation for the differences in the observed patterns. Accordingly, prey availability and behavioral ecology may produce different phenotypes on each population or species. I attribute differences in ontogenetic trajectories mainly due heterochronic maturation events and different onset on ontogenetic changes.
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Palavras-chave
Jararaca, Forma, Morfometria geométrica, Alometria, Jararaca-ilhoa, Pitviper, Shape, Geometrical morphometrics, Allometry, Golden lancehead