Como a sazonalidade e estratégias termorregulatórias influenciam a expressão de dimorfismo sexual em Squamata?
Data
2022-01-28
Autores
Battistini, Miguel Marson 
Orientadores
Palaoro, Alexandre Varaschin
Tipo
Trabalho de conclusão de curso
Título da Revista
ISSN da Revista
Título de Volume
Resumo
A seleção sexual pode ter como uma de suas consequências a expressão de dimorfismo sexual relacionado com características sexuais secundárias. Essas expressões de dimorfismo podem apresentar variações ao longo de diferentes ambientes. Especificamente, o clima pode se apresentar como um importante modulador evolutivo, principalmente para organismos ectotérmicos, pois estes dependem de fontes externas de calor para elevar e garantir a homeostase de seu metabolismo. Em lagartos, as estratégias de termorregulação e os níveis de sazonalidade do ambiente podem influenciar diversos fatores que estão sobre a ação da seleção sexual, como, por exemplo, ajustes nos ciclos reprodutivos e níveis metabólicos. Por sua vez, os ajustes fisiológicos determinados pela variação nos recursos ambientais podem influenciar as competições macho-macho por fêmeas, estabelecimento de territórios, dentre outras questões, o que levaria ao estabelecimento de características sexuais secundárias nas linhagens. Neste contexto, duas hipóteses contrastantes guiaram essa pesquisa. Por um lado, pode-se prever que lagartos que habitam ambientes mais sazonais são menos dimórficos, já que a restrição ambiental por recursos nestes ambientes não seria favorável à monopolização de parceiros sexuais, implicando na flexibilização temporal sobre o estabelecimento de características sexuais secundárias. Por outro lado, ambientes mais sazonais podem ser os ambientes mais propícios para a expressão de dimorfismo sexual, pois favoreceria um maior grau de interação agonística entre machos em busca do melhor território, em termos de recursos, tanto do ponto de vista termorregulatório, quanto alimentar. Para testar tais hipóteses, utilizei as dimensões da cabeça em diferentes linhagens como proxy para o dimorfismo sexual em lagartos, uma vez que este atributo está ligado diretamente à força de mordida e comunicação específica, fatores importantes na determinação de vencedores dos confrontos macho-macho. O dimorfismo sexual foi avaliado em função dos dados de temperatura corpórea das espécies e de sazonalidade do clima extraídos da literatura para um total de 25 linhagens. Os resultados mostraram que as variáveis termorregulatórias e de sazonalidade não têm efeito sobre o estabelecimento do dimorfismo sexual em lagartos.
One of the possible consequences of sexual selection is the sexual dimorphism related to secondary sexual characteristics. Those dimorphism expressions may show differences along the different environments. Specifically, climate might be an important evolutive modulator, mainly for ectothermic organisms, since those depend on external heat sources in order to raise and ensure their metabolism homeostasis. For lizards, the thermoregulation strategies and the environment seasonality can affect several different factors related to the action of sexual selection, as for instance, reproductive cycle adjustments and metabolic levels. In turn, physiological adjustments determined by the environment resources variation can affect the competition between males for female individuals, territory establishment, among other aspects, which would lead to the establishment of secondary sexual characteristics in their lineage. In this context, two contrasting hypothesis guide these research. On one hand, one can predict that lizard who habit mor seasonable environments are less dimorphic, since the environmental restriction due to lack of resources in this environments would not be favourable to the monopolization of sexual partners, resulting in a temporal flexibilization over the establishment of secondary sexual characteristics. On the other hand, the more seasonable the environment is, the more propitious it is for sexual dirmophism expression because it would cooperate for and higher degree of agonistic interaction between males looking for the best territory, in terms of resources, from both a termoregulatory and food perspective. In order to asses such hypothesis, I have used the head dimensions in different lineages as proxy to determine the sexual dimorphism in lizards, since this characteristics is directly related to the bite strength and specific communication, important factors in the determination of winners from male-male confrontations. Sexual dimorphism was assessed in terms of the species body temperature and environment seasonability data, both extracted from the literature for a total of 25 lineages. The results show that termoregulatories variables and seasonability have no effect over the stablishment of sexual dimophisms in lizards.
One of the possible consequences of sexual selection is the sexual dimorphism related to secondary sexual characteristics. Those dimorphism expressions may show differences along the different environments. Specifically, climate might be an important evolutive modulator, mainly for ectothermic organisms, since those depend on external heat sources in order to raise and ensure their metabolism homeostasis. For lizards, the thermoregulation strategies and the environment seasonality can affect several different factors related to the action of sexual selection, as for instance, reproductive cycle adjustments and metabolic levels. In turn, physiological adjustments determined by the environment resources variation can affect the competition between males for female individuals, territory establishment, among other aspects, which would lead to the establishment of secondary sexual characteristics in their lineage. In this context, two contrasting hypothesis guide these research. On one hand, one can predict that lizard who habit mor seasonable environments are less dimorphic, since the environmental restriction due to lack of resources in this environments would not be favourable to the monopolization of sexual partners, resulting in a temporal flexibilization over the establishment of secondary sexual characteristics. On the other hand, the more seasonable the environment is, the more propitious it is for sexual dirmophism expression because it would cooperate for and higher degree of agonistic interaction between males looking for the best territory, in terms of resources, from both a termoregulatory and food perspective. In order to asses such hypothesis, I have used the head dimensions in different lineages as proxy to determine the sexual dimorphism in lizards, since this characteristics is directly related to the bite strength and specific communication, important factors in the determination of winners from male-male confrontations. Sexual dimorphism was assessed in terms of the species body temperature and environment seasonability data, both extracted from the literature for a total of 25 lineages. The results show that termoregulatories variables and seasonability have no effect over the stablishment of sexual dimophisms in lizards.