Environmental factors influence fish morphology and behavior

Experiments conducted in Brazil show that the positions of mouths and fins, among other variables, change according to foraging conditions during development.

By André Julião  |  Agência FAPESP – A study conducted at the University of São Paulo (USP) in Brazil shows that physical and behavioral traits of the large-spotted headstander, Megaleporinus macrocephalus, a species of ray-finned fish native to South America, change in accordance with the environmental conditions experienced by the animal during its development.

In the experiment, the researchers raised offspring from a single female in aquaria with and without plants and gravel. After eight months, the animals had developed different mouth and body shapes. The positions of their fins and their foraging methods also varied according to the environment.

A report on the study, which was supported by FAPESP, is published in the Journal of Experimental Zoology B.

According to the authors, the findings show that environmental factors influence the development of larvae in this species via a process known as phenotypic plasticity.

“We conclude that larval developmental processes involving the expression of genes that control the construction of specific tissues, such as muscles, tendons and bones, are influenced by environmental signals,” Tiana Kohlsdorf, principal investigator of the study, told Agência FAPESP.

According to Kohlsdorf, a professor at the University of São Paulo’s Ribeirão Preto School of Philosophy, Science and Letters (FFCLRP-USP), a great deal of research has pointed to a link between genetic information and phenotypes, but studies along these lines usually focus on how a single environmental factor correlates with a given phenotypic trait.

“Our study integrates foraging conditions with the complexity of the environment and evaluates the effect of the different combinations of these two factors on morphology, behavior and locomotor performance,” Kohlsdorf said.

The experiment was conducted as part of the master’s research of Bianca Bonini Campos, the first author of the article. The other authors are Renata Brandt, who received a scholarship from FAPESP during a postdoctoral internship, and Leandro Lofeu, a PhD candidate at the University of São Paulo’s Ribeirão Preto Medical School (FMRP-USP).

Four environments

The researchers placed 1,000 thirty-day-old fry in aquaria with different configurations and fed them in different ways. One aquarium had what they called a “surface” environment, with only surface vegetation and food available only at the surface. Another was a “generalist” environment, containing plants at the top and on the bottom of the aquarium and a layer of gravel. Food was available at the top and on the bottom.

The third type, “complex bottom”, was similar to the second but lacked surface plants and had food available only on the bottom. The fourth environment, “simple bottom”, contained only water, with food again available only on the bottom.

After eight months, the swimming performance, behavior and morphology, meaning the body shape and the relative positions of the mouths and fins, of the animals were analyzed.

“We observed alterations, mainly in the region of the head, compared with the averages for the species,” Campos said. “We noted different positions of the rostrum [snout-like projection], which, in some cases, was upturned, as well as relatively flat bodies and different fin positions, among other modifications.”

The individuals raised in the “generalist” and “surface” conditions developed more upturned rostra than those raised in the “complex bottom” and “simple bottom” environments, in which food was available only at the bottom of the aquarium.

Moreover, the “surface” fish developed stockier and more ventrally expanded bodies, whereas the “generalists” were longer and flatter. The bottom-raised fish (in both the “complex” and “simple” environments) developed ventrally flattened bodies and ventrally oriented rostra.

The fin position also differed in accordance with the environment in which the fry developed. The most extreme differences were found between the “complex bottom” and “generalist” fish: the former developed longer and taller caudal fins than the latter, with pectoral fins located closer to the rostrum and adipose fins more perpendicular to the body. The adipose fin is a small, fleshy fin located between the dorsal and caudal fins.

Old habits

When placed in a different environment from that in which they had been raised, the animals retained the behavioral traits acquired during the developmental phase. In an aquarium divided into four parts, with each quadrant representing one of the experimental environments, the fish preferred foraging in the position most similar to that of their developmental environment. Food was supplied through a tube to the bottom and surface of the aquarium.

The fish frequently continued to forage in their usual way. “If food was supplied at the surface but they had foraged on the bottom during development, they stayed at or near the bottom. If food was also available on the bottom but they were accustomed to feeding at the surface, they remained mainly near the surface,” Kohlsdorf said.

The plasticity of the animals’ morphological and behavioral traits, however, did not alter their ability to escape potential predators. The fish were placed singly in a water-only aquarium and filmed after manual stimulus simulating an attack by a predator. Swimming speed and acceleration were measured. There were no significant differences among the different groups.

“We found that the capacity to respond to the developmental environment was hereditary and specific to each group. This isn’t the case in every species. Until now, no one had managed to determine whether developmental programs for this species could integrate information from the developmental environment with genetic information. We have now provided an answer in the affirmative,” Kohlsdorf said.

The article “Different developmental environments reveal multitrait plastic responses in South American Anostomidae fish” (doi: 10.1002/jez.b.22905) by Bianca Bonini-Campos, Leandro Lofeu, Renata Brandt and Tiana Kohlsdorf can be retrieved from onlinelibrary.wiley.com/doi/full/10.1002/jez.b.22905.