Study reveals environmental factors that influence how organisms move

What makes you move? Although this is a philosophical question, science tells us that most organisms move throughout their lives due to many factors. They might move in search of food or a mate, or to new environments and habitats to live. Often their movement is influenced by the existing number of their own species and affects their distribution in an area. This phenomenon is called “density-dependent dispersion”. But what roles do the different environmental factors play in this dispersion? In a recent study, scientists from Indian Institutes of Science Education and Research (IISER), Puneidentified factors that affect the dispersal patterns of fruit flies (Drosophila melanogaster).

“One of the ways that species cope with environmental stress, such as a drought or climate change, is to move away to more suitable habitat. This process of movement is not only shaped by the various stresses to which the organisms face, but also by their physiology.”, explains Professor Sutirth Deyassociate professor at IISER Pune and author of the study.

The researchers of this study, published in the ecological journal, Oikosattempted to understand the consistency of species’ dispersal patterns in different environments, as well as how males and females respond differently to overcrowding or population increases in the area in which they reside. The study was supported by funding from Scientific and Technical Research Council (SERB).

Previous studies have shown that the pre-dispersal context, i.e. the environment an individual faces prior to dispersal, can affect their migration pattern. But its effects on density-dependent dispersal are poorly understood, and so an investigation was carried out to see how the pre-dispersal context could alter fruit fly dispersal. It is also known that the pre-dispersal context can generate a different impact on males and females, which prompted the researchers of this study to investigate whether the rate of dispersal was affected by the sex of the individual and the presence of the opposite sex.

The scientists conducted three experiments in their lab using around 34,000 fruit flies. They introduced the fruit flies into a conical vial and let them disperse for 4 hours in a clear plastic tube attached to a plastic bottle. The plastic bottle served as a destination for the flies, and it was replaced every 30 minutes to record the number and sex of fruit flies that were collected in the bottle.

The first and second experiments were performed to record the proportion of flies that left the source, also called the propensity to disperse, using two types of groups, one where the number of individuals before dispersal in a group varied , and the other where it was constant. . In the third experiment, they separated males and females to calculate dispersal propensity and observe dispersal behavior when the opposite sex was missing. Statistical analysis was performed to determine if the dispersion was biased by sex.

The results of the first two experiments showed that the dispersal of fruit flies decreased with increasing population size. The researchers observed this phenomenon for both sexes. Also, female fruit flies have been shown to be less likely to migrate than their male counterparts and are possibly more susceptible to overcrowding. Overall, the results showed that the sex of the fruit fly could affect its dispersal pattern.

The researchers also observed a unique phenomenon from the third experiment: there was no density-dependent dispersion! Because the sexes are separate, scientists have established that the presence of the other sex is necessary to allow density-dependent dispersal.

What do all these results mean for the field of ecology?

“Our results highlight that a detailed understanding of the local environment is needed before dispersal data from field studies are adopted for modeling or conservation applications. habitats is a common issue in conservation management, the response of species (including movement) to this issue requires careful attention,” says Dr Dey.

His team is currently trying to dig deeper into dispersal patterns and understand the evolution of traits that favor the movement of organisms.

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