Armas e sexo: dependência de condição em componentes do armamento de Hyalella bonariensis (Crustacea: Amphipoda)

• Autor(a) principal: Lopes, Fernando Benso
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Manancial - Repositório Digital da UFSM
• Texto Completo: http://repositorio.ufsm.br/handle/1/19550
• topic: Dependência de condição; Armamento; Hyalellidae; Morfometria geométrica; Condition dependence; Weapons; Hyalellidae; Geometric morphometry; CNPQ::CIENCIAS BIOLOGICAS::BIOQUIMICA

Condition dependence is when an individual's ability to develop a trait depends on the genes that will express the trait and depends on the resources the individual has accumulated. Then, higher quality individuals will develop the trait more than lower quality individuals. Examples of traits that are condition dependent are secondary sexual traits, such as animal weapons. Weapons are structures used in male-male fights to secure resources. However, studies have only looked at condition dependency on weapon size. We argue that weapons can be divided into size, shape and muscle components because the increase in weapon size does not increase the individual's reproductive success and access to resources. This increase will also depend on muscle and shape. This is because the musculature is responsible for the force that the weapon generates, and the shape ensures that the weapon will be able to apply that force. Increasing size and musculature requires the individual to have more resources, which means more costs, while shape is likely fine-tune adjustments which would not be as costly. Thus, because the different components have different production and maintenance costs, we investigated whether size, musculature and shape show the same condition dependence. For this, we collected males and females of Hyalella bonariensis and measured their body size using linear head measurements. We measured the shape and size of the weapons, represented by the posterior pair of gnathopods, using geometric morphometric methods. For the musculature, we measured the area of muscle mass present within the gnathopods. With these variables, we tested whether size, shape and muscle size of the gnathopods would differ regarding their relative size (i.e., slope and intercept - size relative to body size) and variation (i.e., residual values) of the relationship between the gnathopod and body size (our proxy of condition). Our results show that the size of the posterior gnathopod of males has a larger intercept and more variation than the anterior gnathopods and homologous female gnathopods. The muscle size of the male posterior gnathopod has a higher investment and intercept, and is more variable than the other gnathopods. For shape, the posterior gnathopods are different in investment from the others, but are not more variable. As we expected, size and muscle are condition dependent as they have larger intercepts and more variation than other gnathopods. Shape, however, is not condition dependent because it presents the same investment, intercept and variation among gnathopods. Also, if shape has any sort of biomechanical constraint, variation would need to be genetically inherited. This may be one mechanism to generate the large diversity of weapons we observe in nature.