{"id":257,"date":"2021-10-20T04:06:54","date_gmt":"2021-10-20T04:06:54","guid":{"rendered":"http:\/\/depts.washington.edu\/scipos\/wordpress\/?p=257"},"modified":"2022-06-24T14:22:39","modified_gmt":"2022-06-24T21:22:39","slug":"grad-publication-yasmeen-hussain-and-making-spray-and-pray-pay","status":"publish","type":"post","link":"https:\/\/depts.washington.edu\/scipos\/wordpress\/2021\/10\/20\/grad-publication-yasmeen-hussain-and-making-spray-and-pray-pay\/","title":{"rendered":"Grad Publication: Yasmeen Hussain and Making Spray-and-Pray Pay"},"content":{"rendered":"\n

Have you ever wondered how sea urchins reproduce? Do you envision their spiny selves crawling over to other spiny friends, courting by poking each other, mysterious appendages emerging from their cryptic bodies?<\/p>\n\n\n\n

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Lytechinus pictus<\/em>, one sea urchin species I work with<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Unfortunately for your imagination, sea urchins don\u2019t look for mates. Instead, they broadcast spawn, releasing their sperm and eggs directly into the ocean environment. Sea urchins are not alone in broadcast spawning: jellyfish, sea cucumbers, most corals, sea stars, anemones, sponges, oysters, and many other marine organisms reproduce with this \u201cspray and pray\u201d strategy. Sea urchin sperm are small (~25 \u00b5m long) and sea urchin eggs are slightly less small (~100 \u00b5m in diameter, about the width of a human hair<\/a>). A tide pool with a volume of 1 cubic meter is gigantic<\/em> in comparison to these sexy little cells \u2013 if the sperm cell was now the size of an average-height person, the length of the tidepool would be nearly the length of Rhode Island. So we might wonder: how in the world do sea urchin sperm and eggs find each other?
One way that sea urchin eggs help sperm find them in the mystifyingly large, open, and dynamic ocean is by sending out chemical signals. Sea urchin eggs release species-specific attractant chemicals (chemoattractants) that diffuse through the water and help sperm sniff out eggs. Researchers have actually been studying how sperm use chemicals (chemo-) to orient towards eggs (-taxis,) a phenomenon called chemotaxis, for years. But what wasn\u2019t known is whether sperm from different males respond to these chemicals differently, or whether stronger sperm responses to chemoattractants really help males fertilize more eggs.
To investigate this problem, my coauthors and I conducted two studies. In the first study, we removed chemoattractants from some live eggs and compared how often these eggs were fertilized compared to eggs that still had chemoattractant. Eggs without chemoattractant were less likely to be fertilized, suggesting that sperm sniffing helps them find and fertilize eggs. Great! On to the even more exciting stuff.<\/p>\n\n\n\n

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Here\u2019s the microfluidic device we use in chemotaxis tests <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

In the second study, my collaborators designed a microfluidic device for chemotaxis tests. It\u2019s \u201cmicrofluidic\u201d because it\u2019s small (micro-) and allows us to flow liquid (-fluidic) through a channel.The device is designed to expose sperm to really specific, well-defined concentrations of chemoattractant. We put the device on a microscope and video-record sperm behavior so that we can see what direction the sperm swim. In our chemotaxis tests, sperm went in the middle channel and chemoattractant and clean seawater went on either side of the sperm. Using the recordings of sperm behavior combined with fertilization tests, we found that male urchins that have sperm that are more attracted to the chemoattractant side of the channel also fertilize more eggs. This tells us that urchin males that have sperm that are good at sniffing out eggs are also more likely to make babies. This is the first evidence that sperm chemotaxis could change the reproductive success of individual males! I hope you\u2019re as excited about this new discovery as I am.
So, how do sea urchin sperm find and fertilize eggs in the enormous and energetic ocean environment? In this paper, we\u2019ve shown that (in a lab) sea urchin eggs releasing attractant chemicals seems to really help sperm find eggs and fertilize them, and this likely also applies to urchins living outside the lab.<\/p>\n\n\n\n

FAQ: <\/strong>
Is sperm chemoattraction the same thing as pheromones?<\/p>\n\n\n\n