Bdelloid rotifers are a group of microscopic, worm-like animal species that have caught the attention of biologists due to their adaptability to extreme environments as well as their unique system of reproduction. This article will explain the habitat, niche, and anatomy of bdelloid rotifers before exploring the adaptations that allow these fascinating organisms to not only survive, but thrive through asexual means of reproduction.

The typical habitats for Bdelloid rotifers are freshwater environments, but they can also be found on land in moist places such as moss and soil. Their bodies can range from around 150-700 µm in size, so they cannot be seen with the naked eye. Despite their microscopic size, bdelloid rotifers possess a complex body structure, which consists of a head, trunk, and foot. The corona, which is covered with tiny “hairs” called cilia, takes up much of the space on the head and is used for movement and feeding. The rhythmic beating movement of the cilia creates water currents that draw food into the mouth.

Bdelloid rotifers have an essential niche in their aquatic ecosystems. Since they mostly eat bacteria and microscopic fungi, they are considered micro-consumers. Micro-consumers are needed for the decomposition of organic matter and thus, the recycling of nutrients in ecosystems.

The anatomy of the bdelloid rotifers comprises a digestive system, a nervous system centered around a brain-like structure, and muscles. Due to their microscopic size, bdelloid rotifers do not need a respiratory and circulatory system like some animals do, instead depending on the diffusion of oxygen and carbon dioxide to fuel the process of cellular respiration. Additionally, bdelloid rotifers undergo anhydrobiosis, a suspended state in which an organism remains dry and dormant for an extended period of time – a state that is not quite alive, but also not quite dead. This phenomenon is similar to the way that the infamous tardigrade (also known as water bears or moss piglets), turn into a tun. Remaining in a tun-like form allows these microscopic animals to survive extreme conditions, rehydrating once water becomes available again. Bdelloid rotifers then continue on with typical life processes after spending years in the tun state.

Bdelloid rotifers reproduce through a process called parthenogenesis, in which an egg does not require fertilization to grow. Female bdelloid rotifers produce eggs with identical genomes as the mother without the need for male fertilization, meaning that there are no male bdelloid rotifers at all.

The bdelloid rotifer’s reproduction method has immense evolutionary implications. While reproduction with sexual means creates genetic diversity, leading organisms to adapt to changing environments, bdelloid rotifers have somehow been able to thrive for millions of years without sexual reproduction. This evidence suggests that alternative mechanisms of evolution exist that have allowed the bdelloid rotifer to maintain genetic adaptability.

There are many key adaptations that have contributed to the evolutionary success of bdelloid rotifers. First of all, the horizontal gene transfer process, commonly associated with bacteria rather than with multicellular organisms, allows bdelloid rotifers to assimilate DNA from foreign sources into their own genomes. DNA including that of bacteria, fungi, and plants, provide new functions to their biology. Through this unique and fascinating process, the bdelloid rotifer has been able to create genetic diversity without sexual reproduction. Additionally, bdelloid rotifers have highly efficient mechanisms for repairing DNA. During anhydrobiosis, DNA is easily fragmented due to the loss of water. After rehydrating, bdelloid rotifers are able to fix this damage, maintaining their genetic material. This powerful ability allows for the mitigation of the dangers of harmful mutations that would otherwise accumulate due to the lack of sexual reproduction.

Ultimately, the bdelloid rotifer raises questions on the necessity of sexual reproduction for the long-term survival of organisms. By studying bdelloid rotifers, scientists have new insights into mechanisms that allow organisms to maintain genetic diversity and adaptability without sexual reproduction.

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Works Cited 

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Eyres, Isobel, et al. “Horizontal Gene Transfer in Bdelloid Rotifers Is Ancient, Ongoing and More Frequent in Species from Desiccating Habitats.” BMC Biology, vol. 13, no. 1, 4 Nov. 2015, https://doi.org/10.1186/s12915-015-0202-9. Accessed 10 Mar. 2020.
Jennni, Bernard. “Bdelloid Rotifers: So Common yet so Weird!,” Youtube, 10 May 2016, www.youtube.com/watch?v=rIUxqKR-KrM.
Ricci, C., and D. Fontaneto. “The Importance of Being a Bdelloid: Ecological and Evolutionary Consequences of Dormancy.” Italian Journal of Zoology, vol. 76, no. 3, Sept. 2009, pp. 240–249, https://doi.org/10.1080/11250000902773484.