How do environmental determinants affect the development of certain vertebrate animals? This was the question that researcher Javier Díaz from the Marine Research Center of the University of Vigo tried to answer with his doctoral thesis, an in-depth study of how sex, early social environment and predation risk influence behavior, camouflage coloration and the expression of genes related to physiological stress. He focused his study on two very specific species: the black-backed gull (Larus michahellis) and the spiny fish (Gasterosteus aculeatus).
“Knowledge of the structure and origin of variation in phenotypic traits and the role of organismal development in evolutionary processes were considered key pieces to complete the neo-Darwinian theory of evolution, and its formal inclusion constituted a new expanded synthesis of the current evolutionary theory that also integrates the role of development,” explains the researcher, who frames this study in a new stream of research that emphasizes the importance of studying the genetic and environmental mechanisms that influence the diversity of characters based on alterations in the traits of organisms during their development.
Experiments were carried out on the island of Sálvora and also in the laboratory
Among other objectives, the study set out to study the plasticity during the juvenile phase of camouflage coloration and the behavior of selecting the background color -light or dark- in response to the risk of predation in the spiny fish, as well as to analyze how maternal effects, specifically, egg substances and birth order, influence the behavior during the first days of life of the yellow-legged gull chicks. On the other hand, the researcher also decided to try to determine if there was sexual dimorphism in the camouflage coloration in the juveniles of the spiny fish and the gull chicks, and to delve deeper into the relationship between the camouflage coloration, constituted by melanins, and the expression of genes associated with physiological stress in the gull chicks. To achieve this, he carried out two experiments: one with the gull chicks on the island of Sálvora and the other in the laboratory with juveniles of the spiny fish.
In the face of danger, the spiny fish does not change its coloration
The results obtained left no room for doubt: juvenile spiny fish do not modify their camouflage coloration in the face of a risk of predation, suggesting that the plasticity of this trait in response to a threat of predation is limited or too costly. On the contrary, the behavior of choosing the background color in the face of a risk of predation does occur: fish subjected to a risk of predation had a greater presence on a dark background. “These results suggest that plasticity in the behavior of choosing the background color represents a camouflage strategy in heterogeneous environments, in which light and dark patches are present”, explains the researcher.
In the case of the seagull, the birth hierarchy is decisive.
With respect to the yellow-legged gull, it is the birth hierarchy, and not the substances deposited by the mothers in the eggs, that determines the different behavioral strategies of the chicks during their first days of life. Specifically, the last chicks to be born in a nest emitted more calls for attention to the parents, were less likely to react to a parental alarm call and had a lower respiratory rate than those born first, regardless of the substances in the egg. “These results reject the general applicability of the assumption that the behavioral differences between first and third chicks in gulls are programmed by the maternal substances deposited in the eggs,” explains the researcher.
Sexual dimorphism is more widespread than previously thought
Although most work to date has focused on the study of sexual dimorphism in coloration in adult individuals, which usually display very colorful ornaments with important mating functions, the results of this thesis demonstrate that sexual dimorphism exists in camouflage coloration in juveniles of both species, “suggesting that dimorphism in juveniles may be more generalized in vertebrates than previously assumed.” In addition, different results found throughout the research suggest that darker poles suffer less stress during their development.
“There are hardly any job offers for our profile in Spain”
The author of the thesis, Javier Díaz (Plasencia, 1987) has a degree in Biology from the University of Salamanca, a Master’s degree in Biodiversity and Conservation Biology from the Pablo Olavide University of Seville and a doctorate in Biology from the University of Vigo. Author and co-author of seven scientific publications in international journals, with more than 50 citations to date, he is currently unemployed and looking for work in both the academic and business fields in Spain and abroad. “My case is another example of how in Spain the State trains doctors by spending a lot of public resources, but then there is no public or private labor market that can take advantage of this training, there is hardly any job offer for our profile in Spain”, emphasizes the researcher.
