Question

A species of rotifer, a small freshwater invertebrate, abandoned sexual reproduction millions of years ago. A remarkable feature of the rotifer's life cycle is its ability to withstand extreme drying. When the rotifer's watery environment dries out, so does the rotifer, and it can be blown in the wind to a new environment. Rotifers that are blown to water will rehydrate and resume an active life. A major pathogen of these rotifers is a species of fungus. Some scientists hypothesize that fungus-infected rotifers rid themselves of the pathogen when they dry. a. Design an experimental study to test this hypothesis. b. Why might the ability to withstand extreme drying reduce any potential advantage of sexual reproduction in this rotifer species?

Short answer

To test the hypothesis, first, create two groups of rotifers, one infected with fungus and another uninfected control group. Label, dry, and rehydrate both groups in controlled environments. Observe and compare the behavior and health of the rehydrated rotifers. The ability to withstand extreme drying might reduce the potential advantage of sexual reproduction because it allows rotifers to survive harsh conditions, defend against pathogens, and disperse without the need for genetic diversity provided by sexual reproduction.

Step-by-step solution

To design an experimental study to test the hypothesis, we need to follow these steps: 1. Create two groups of rotifers: One group infected with the fungus, and another group that is not infected (control group). 2. Label each group, allowing us to track the rotifers as they undergo the drying and rehydrating process. 3. Allow both groups to dry out completely in a controlled environment, simulating the natural conditions they experience in the wild. 4. After the rotifers have dried, place them in a new, watery environment for rehydration. 5. Observe and record the behavior and health of the rehydrated rotifers, comparing both the infected and control group. Specifically, look for evidence of whether the fungus-infected rotifers have rid themselves of the pathogen, in comparison to the control group. 6. Analyze the data collected and draw conclusions regarding the validity of the hypothesis in question. #b. Why might the ability to withstand extreme drying reduce any potential advantage of sexual reproduction in this rotifer species?#

The ability to withstand extreme drying might reduce the potential advantage of sexual reproduction in this rotifer species because: 1. In sexual reproduction, genetic diversity is created through the exchange of genetic material between two individuals. However, the rotifer's ability to withstand extreme drying might allow them to survive through harsh conditions without the need for genetic diversity to adapt to new environments. 2. Extreme drying effectively functions as a natural defense mechanism against pathogens for the rotifers. The process of drying might eliminate pathogens, such as fungus, which reduces the rotifer's dependence on sexual reproduction as a means of improving immunity to diseases. 3. The drying process offers another way of dispersal for the rotifers, further reducing the need for sexual reproduction to enhance survival. Sexual reproduction often allows for wider geographical distribution of offspring. However, if the dried rotifers can be blown by wind and rehydrate in new environments, it could provide them with ample opportunity for dispersal and population expansion without sexual reproduction.

Key concepts

Asexual Reproduction

In biology, asexual reproduction is a fascinating process where an organism can reproduce without the involvement of another individual contributing genetic material. This mode of reproduction allows the rotifers, a type of freshwater invertebrate, to reproduce without mating, which is significant given their unique lifestyle. One advantage is the simplicity and speed of population growth since a single individual can produce offspring genetically identical to itself. This can be beneficial when environmental conditions are stable and changes are minimal, allowing the species to thrive without the need for genetic variation.
This method contrasts with sexual reproduction, which mixes the genetic material of two parents to create diversity. However, for the rotifers, their ability to survive extreme desiccation and their mechanism of dispersal through drying and wind could reduce the reliance on genetic diversity traditionally gained from sexual reproduction.

Desiccation Tolerance

Desiccation tolerance is an extraordinary survival strategy by which organisms like rotifers can endure periods of extreme dryness. When their watery habitats dry out, these creatures effectively enter a dormant state by drying themselves out. This process does not kill them; instead, it essentially "pauses" their biological processes.
Once they are blown by the wind to a new location and reintroduced to water, they rehydrate and resume normal functions. Being able to survive in a dehydrated state allows rotifers to endure harsh environments and explore new habitats, which can often give them a survival edge even without the genetic variation provided by sexual reproduction.
The ability to dry and later revive reduces dependency on genetic diversity to handle changing conditions, acting as a natural survival tool that decreases the necessity for other adaptive methods.

Pathogen Defense

Rotifers are small yet resilient organisms, and their ability to dry out offers a unique form of defense against pathogens such as fungi. When a rotifer becomes infected, this drying capability comes in handy. As they dry out, many pathogens cannot survive the desiccation process, potentially leaving the rotifers pathogen-free upon rehydration.
This defense mechanism is potentially what makes asexual reproduction more viable for these creatures, as it minimizes the danger that pathogens generally pose to genetically identical populations. By naturally shedding pathogens during the drying phase, rotifers reduce their reliance on the genetic variability that sexual reproduction typically offers as a method of disease resistance.

Experimental Design

Designing experiments carefully enables scientists to draw valid conclusions that either support or refute hypotheses. To test if rotifers rid themselves of pathogens upon drying, a straightforward yet rigorous experimental approach can be followed. First, scientists can divide rotifers into two groups: one infected by fungi and a control group without the infection. Each group is monitored closely as they undergo the natural desiccation process.
After drying, rotifers are moved into water-rich environments to rehydrate. Researchers observe both groups for differences in health and presence of pathogens. This comparative analysis between the initially infected and control groups is crucial. Viewing changes can help establish if desiccation effectively clears pathogens, serving as a natural cleansing process for the rotifers. Through detailed observation and data analysis, researchers can understand whether the hypothesis holds true, shedding light on the unique survival capabilities of these fascinating creatures.